Article

Genesis and depositional model of subaqueous sediment gravity-flow deposits in a lacustrine rift basin as exemplified by the Eocene Shahejie Formation in the Jiyang Depression, Eastern China

Authors:
  • China University of Petroleum - East China
  • China University of Petroleum, Qingdao, China
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Abstract

Subaqueous sediment gravity-flow (SSGF) deposits have recently been recognized as a major reservoir plays in lacustrine basins. Research on their genesis and depositional models are crucial to understand gravity flow evolution and the distribution of their deposits. This study analysed SSGF deposits in the third member of the Shahejie Formation in the Jiyang Depression, Eastern China, based on 3-D seismic data, well-log data, and core observations. The types and origins of SSGF, the distribution patterns and depositional models of SSGF deposits have been investigated. The dominant types of SSGF include: muddy debris flows, sandy debris flows, high density turbidity currents, surge-like low density turbidity currents, and quasi-steady low density turbidity currents, which are mainly caused by river floods and sediment failures. The overall distribution of SSGF deposits is controlled by the sediment supplies, basin structure, and sequence stratigraphic framework. Paleotopography, flood energy, triggering mechanism, and the slope angle of the delta front are also important. SSGF deposits associated with river floods can be further subdivided into elongated and fan-shaped deposits. Elongated sandstones are composed predominantly of bedload-dominated and suspension load-dominated hyperpycnal flow deposits. The fan-shaped sandstones can be subdivided into an inner fan, a middle fan, and an outer fan. Inner fan deposits are dominated by gully-filling debrites. Middle fan deposits are composed predominantly of channel-fill deposits, while outer fan deposits consist of thin bedded and laterally extensive lobe intervals. SSGF deposits triggered by sediment failures can be further subdivided according to their proximity to slumping: proximal, intermediate and distal parts. The proximal deposits are composed predominantly of slide and slump deposits. The intermediate deposits are dominated by sandy debrite tongues, while the distal deposits are composed predominantly of thin-bedded, surge-like, low-density turbidites. This study offers some insight into the types, origin of gravity-flow, as well as the distribution of their deposits in a lacustrine rift basin.

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... Debris flows are one kind of sub-aqueous sediment gravity flows, which are caused by excessive sediment density (Yang et al., 2019). They are defined as a laminar plastic flow in which sediment is supported by the matrix strength, grain-to-grain interactions, excess pore fluid pressure, or buoyancy (Talling et al., 2012;Yang et al., 2019). ...
... Debris flows are one kind of sub-aqueous sediment gravity flows, which are caused by excessive sediment density (Yang et al., 2019). They are defined as a laminar plastic flow in which sediment is supported by the matrix strength, grain-to-grain interactions, excess pore fluid pressure, or buoyancy (Talling et al., 2012;Yang et al., 2019). ...
... Although more detailed classifications exist, debris flows can be typically subdivided into two types: sandy (or non-cohesive) debris flows, and muddy (or cohesive) debris flows (Shanmugam, 1996;Talling et al., 2012;Shanmugam, 2000;Yang et al., 2019). ...
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Analysis of ca. 1400 km of multi-channel seismic data indicate that the distal part of the Sakarya Canyon within the continental rise is an unstable region with sediment erosion. Fourteen buried debris flows (DB1-DB14), in the stacked form within Plio-Quaternary sediments between 1400 and 1950 m water depth, were observed in the surveyed area. 2 Their run-out distances range from 3.8 to 24.4 km. The largest debris flow DB10 affects ca. 225 km 2 surficial area transporting ca. 15 km 3 of sediment in S to N direction. The debris flows in the area are considered as gravity flows of unconsolidated sediments mobilized due to the excess pore pressures occurred in the unconsolidated shallow sediments arising from the high sedimentation rate. We also suggest that extensive seismic activity of North Anatolian Fault (NAF) located ca. 140 km south of the of the study area along with the possible local fault activity is also a significant triggering factor for the flows. The stacked form of the debrites indicates that the excess pore pressure conditions are formed periodically over the time in the continental rise, which makes the region a potentially unstable area for the installation of offshore engineering structures.
... A variety of subaqueous sediment gravity-driven flow types are recognized in deepwater environments, including: cohesive flows; non-cohesive flows such as hyper-concentrated, hyperconcentrated-grain-flows and concentratedsediment-gravity-flows/density-flows (sensu Lowe, 1982;Pierson & Costa, 1987;Mulder & Alexander, 2001); flows with some component of fluid turbulence, which can be sub-divided into high-density turbidity currents and lowdensity turbidity currents (Lowe, 1982); and flows that show mixed behaviour (sensu Haughton et al., 2009), or transitional flows (sensu Kane & Pont en, 2012;Kane et al., 2017). This broad range of flow types were defined using examples from deep-marine settings, and they also occur within deep-lacustrine environments (Baganz et al., 2012;Dodd et al., 2019;Yang et al., 2019). Subaqueous sediment gravity flows in deep-lacustrine basins can deposit clean, well-sorted sandstones with excellent reservoir potential (Horton & Schmitt, 1996;Baganz et al., 2012;Dodd et al., 2019;Zhang et al., 2019;Pan et al., 2020). ...
... These flow types have been modelled experimentally (Baas et al., 2009(Baas et al., , 2011Sumner et al., 2009Sumner et al., , 2012. Despite being welldocumented in marine environments Pierce et al., 2018), and HEB distribution and character widely explored (Hodgson et al., 2006;Davis et al., 2009;Kane et al., 2017;Spychala et al., 2017a,b;Bell et al., 2018;Pierce et al., 2018;Baas et al., 2021), their occurrence and variability in deep-lacustrine fan settings is less understood, with there being few published examples (Hovikoski, et al., 2016;Tan et al., 2017;Dodd et al., 2019;Yang et al., 2019;Shan et al., 2020;Zhang & Dong, 2020). ...
... Mud-clasts are often elongate, and can either define a bedding-parallel fabric, or more chaotic arrangements. Plant fragments or carbonaceous material are common in the H3 division, especially near to the top of the H3 unit Hodgson, 2009;Tan et al., 2017;Yang et al., 2019). A sub-division of the H3 unit was recognized in Terlaky & Arnott (2014), where matrix-rich sandstones (i.e. ...
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Hybrid event beds are texturally and compositionally-diverse deposits preserved within deepwater settings. They are deposited by flows exhibiting ‘mixed behaviour’, forming complex successions of sandstone and mudstone, which are often challenging to predict. Hybrid event beds are documented in deep-marine settings, where they have been thoroughly characterized, and are well-known as effective fluid transmissibility barriers and baffles in reservoirs. By comparison, there are far-fewer studies of hybrid event beds from deep-lacustrine settings, where their character and distribution remains relatively under-explored. In order to provide insights into these deposits, this study presents the detailed analysis of three-dimensional seismic data, wireline logs and core from a series of ancient deep-lacustrine fan systems in the North Falkland Basin. Results confirm that deep-lacustrine hybrid event beds comprise the same idealized sequence of the ‘H1–H5’ divisions. However, in this study H3 ‘debrite’ units can be sub-divided into ‘H3a–H3c’, based on: sharp or erosional intra-H3 contacts, bulk lithology, mud-content and discrete sedimentary textures. This study interprets the H3a–H3c sub-units as the products of multiple flow components formed through significant rearward longitudinal flow transformation processes, during the emplacement of a single hybrid event bed. Hybrid event beds are observed within lobe fringes, where flow types, energies, and transport mechanisms diversify as a result of flow transformation. The temporal context of hybrid event bed occurrences is considered in relation to stages of fan evolution, including: the Initiation; Growth (I); Growth (II); By-pass; Abandonment; and Termination phases. Hybrid event beds are mainly found in either the initiation phase where flow interaction and erosion of initial substrates promoted mixed flow behaviour, or in the abandonment phase as facies belt retreated landward. The results of this study have important implications in terms of flow processes of hybrid event bed emplacement, in particular sub-division of the H3 unit, as well as the prediction of hybrid event bed occurrence and character within ancient deep-lacustrine fan settings, in-general.
... In contrast to many well-documented sub-marine fan fringe deposits, there is much less information about the sub-lacustrine ones. Lacustrine sediment gravity flow deposits are probably different from marine ones, because marine environments are characterized by larger-scale depositional systems, deeper water, and a longer runout distance (Yang et al. 2019). Most sub-lacustrine fan deposits were interpreted mostly as debrites or/and turbidites, including the well-known Eocene Dongying depression and the Upper Triassic turbidites in the Ordos Basin (Zou et al. 2012;Liu et al. 2017;Yang et al. 2017Yang et al. , 2019. ...
... Lacustrine sediment gravity flow deposits are probably different from marine ones, because marine environments are characterized by larger-scale depositional systems, deeper water, and a longer runout distance (Yang et al. 2019). Most sub-lacustrine fan deposits were interpreted mostly as debrites or/and turbidites, including the well-known Eocene Dongying depression and the Upper Triassic turbidites in the Ordos Basin (Zou et al. 2012;Liu et al. 2017;Yang et al. 2017Yang et al. , 2019. This raises the following questions. ...
Article
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Submarine or sub-lacustrine lobe deposits are important reservoirs, but the fan fringe deposits form heterogeneities within deep water fan deposits. Fan fringe facies records the complex sediment gravity flow types. By understanding of the bed types and flow mechanisms, we can identify the fan fringe deposit, which aids in the reconstruction of deep water fan and reservoir evaluations. The Jiucaiyuanzi and Dalongkou sections in the West Bogda Mountains preserve well-exposed 536-m and 171-m thick successions, respectively, of a deep water lacustrine depositional system from the Middle Permian Lucaogou Formation. Bed types of the Lucaogou Formation include high-density turbidite, low-density turbidite, incomplete Bouma-type turbidite, hybrid event beds, and slump deposits. The Lucaogou Formation is interpreted here as a fan fringe facies due to the thin bed thickness that characterize turbidites and hybrid event beds, as well as the predominance of the isolated sheet architecture. Previous studies suggest that these deposits were considered as deposited in a deep water setting due to the absence of wave-related structures. The presence of abundant mud clasts in massive medium-coarse grained sandstone beds reflects the significant erosional capability and interactions between high-density turbidity currents and lake floor. The fan fringe facies here contains amalgamated and thick-bedded homolithic facies (~ 30%) and thin-bedded heterolithic facies (~ 70%). The examination of the bed type is of wider significance for facies prediction and reservoir heterogeneity in the sub-lacustrine fan fringe facies.
... The other feature of typical hyperpycnite deposits is a specific sequence comprising a basal upward-coarsening interval (UCI) and an upper upward-fining interval (UFI) with an intrasequence erosional contact, which forms during the flood peaks (Fig. 13d) (Soyinka and Slatt, 2008;Lamb and Mohrig, 2009;Yang et al., 2017b). The intense erosion induced by such flows increases the mud content of the bottom part of the flow and may cause transformation of the flow into a debris flow (Fig. 13b) (Mutti et al., 2003;Yang et al., 2017bYang et al., , 2019a. The flows travel toward the basin center as high-density turbidity currents, forming bedload deposits and suspended load deposits, and gradually evolve into low-density turbidity currents, forming suspended load deposits and lofting deposits (Fig. 13b) (Zavala et al., 2011;Zavala and Arcuri, 2016;Yang et al., 2017bYang et al., , 2019aYuan et al., 2019). ...
... The intense erosion induced by such flows increases the mud content of the bottom part of the flow and may cause transformation of the flow into a debris flow (Fig. 13b) (Mutti et al., 2003;Yang et al., 2017bYang et al., , 2019a. The flows travel toward the basin center as high-density turbidity currents, forming bedload deposits and suspended load deposits, and gradually evolve into low-density turbidity currents, forming suspended load deposits and lofting deposits (Fig. 13b) (Zavala et al., 2011;Zavala and Arcuri, 2016;Yang et al., 2017bYang et al., , 2019aYuan et al., 2019). ...
Article
Gravity flows have been well investigated in deep-marine settings but less so in deep-lacustrine environments. To further understand the sedimentary characteristics and processes of gravity flows in a lacustrine rift basin, sublacustrine fans in the Weixi'nan Depression in the South China Sea were identified and studied by integrating core, well logging and 3D seismic data. Several aspects of gravity flow deposits were discussed in this study: (1) classification: seven lithofacies types were further grouped into four lithofacies assemblages/associations associated with emplacement by slumps, gravel-rich debris flows, high-density turbidity currents (which may transform into muddy debris flows) and low-density turbidity currents. (2) Proximal vs. distal position: the quantitative analysis of the lithofacies associations indicated that the gravity flow deposits are dominated by gravel-rich debris flow deposits and high-density turbidites in the proximal parts of the sublacustrine fans, whereas low-density turbidites dominate in the basin center. (3) Major triggers (humid climate and/or slope failures): the presence of active structures and a humid climate favored the formation of gravity flows, which originated from delta collapses and/or floods. (4) Lateral and vertical lithofacies distributions: the coarse-grained deposits represent a spectrum of different categories of gravity flows. In proximity to the slope break zone, slumps transformed into gravel-rich debris flows through liquefaction and deformation. As the gravity flows advanced toward the basin, the gravel-rich debris flows gradually became diluted with the surrounding water and transformed into high-density turbidity currents. When the flows reached the deep basin plain, the high-density turbidity currents transformed into low-density turbidity currents because the coarse grains could no longer remain in suspension. (5) An alternative mechanism: when the flows eroded the muddy substrate/basement, an alternative mechanism involving reverse-flow transformation occurred. In some cases, high-density turbidity currents transformed into muddy debris flows because the eroded light material became segregated toward the rear of the turbidity current and inhibited turbulence. This sedimentary model of gravity flows can be used for oil exploration in the study area and similar lacustrine rift basins.
... The origins of massive sandstones that are devoid of primary sedimentary structures have provoked considerable debate (Shanmugam and Moiola, 1995;Lowe, 1997;Kneller, 1995;Stow and Johansson, 2000). The possible sediment transport regimes involved in the deposition of massive sandstones include high-density turbidity currents (Postma et al., 1988;Kneller, 1995;Kneller and Branney, 1995), sandy debris flows (Shanmugam, 1996;Xu et al., 2016;Liu et al., 2017;Yang et al., 2019), and hybrid gravity flows (Haughton et al., 2009;Hodgson, 2009). In this study, we interpret the massive, fine-grained sandstones with small mud clasts to be the products of high-density turbidity currents in which sediment grains are supported by buoyancy, grain collisions, and fluid turbulence (Lowe, 1982;Talling et al., 2012). ...
... Dispersed mud clasts in the core intervals of well A-12 and B-16 from lobe axis deposits could be analogous to the type B4 shale clasts described by Johansson and Stow (1995). Although sandy debris flows representing continuous processes between cohesive and cohesionless debris flows have been used to interpret massive sandstones with mud clasts (Shanmugam, 1996;Yang et al., 2019), the parallel-to-bedding rip-up clasts implying a full laminar-flow condition with shear strength in a debris flow (Shanmugam, 1996(Shanmugam, , 2000 are absent in the core intervals. Therefore, sandy debris flows are not suitable for interpreting the massive sandstones in the lobe axis of the study area. ...
... Faulted basin margins, which are generally characterized by episodic fault activities, steep faulted-slope geomorphology, large terrain altitude difference, proximity to source areas, strong weathering, short transport distance and complex depositional dynamics (Henstra et al., 2017;Zhu et al., 2018;Ge et al., 2019Ge et al., , 2020, probably represent one of the most promising regions for hyperpycnal flow generation Yuan et al., 2019;Yang et al., 2019), which would provide rare insight in helping establish complete hyperpycnite spectrum among different basin types. Moreover, deposits on faulted margins generally display Feng et al., 2013Feng et al., , 2016Cao et al., 2018). ...
... Interpretation. Previous studies suggest that ungraded and massive structure can be attributed to very rapidly freezing deposition of sandy debris flows (Shanmugam, 2012;Zou et al., 2012;Xian et al., 2017Xian et al., , 2018bYang et al., 2019) or collapse fall-out from the turbulent flow of an HDT (high density turbidity current) under suspended conditions (Middleton and Hampton, 1973;Lowe, 1982;Stow and Johansson, 2000) (Table 1). Similar deposits have been documented by outcrops and subsurface studies (Zavala et al., 2011;Zavala and Arcuri, 2016;Xian et al., 2018a;Dou et al., 2019), which can be attributed to suspended-load facies in gravel-rich hyperpycnites. ...
Article
There has been an increased attention on hyperpycnal flows due to its importance in delivering large volumes of sediments into deep-water. The process and products of hyperpycnal flow in tectonically-active margins are still poorly understood, and potentially constitute one of the most important deep-water mechanisms in rift basins. This study integrates core data, well-logging and 3D seismic data to investigate the hyperpycnal flow process and dispersal pattern on the Eocene Dongying rift margin. 17 facies, including 5 conglomerate facies, 9 sand facies and 3 mud facies are identified, interpreted as the product of debris flows, traction currents, turbidity currents, transitional flows and lofting plumes, and suggesting the complex blend in flood-triggered hyperpycnal flow on rift margin. Two different hyperpycnal flow types are identified and a related process model is proposed based on facies sequence, distribution, transport mechanism and flood discharge analysis, including seasonal-flood triggered hyperpycnal flow (SHF) and outburst-flood triggered hyperpycnal flow (OHF). The evolution of the hyperpycnal system suggests two dispersal styles, including proximal sublacustrine fan dominated by OHF and distal sublacustrine fan dominated by SHF, respectively. Climate and tectonic movements are suggested to be the main factors controlling hyperpycnal flow generation and deposition on rift margins. The relatively arid climate enhanced seasonal-flood activity and associated sustained and stable SHF, which further prompt distal sublacustrine fan development during a weak rifting period. On the other hand, the generation of outburst-floods can be attributed to the enhanced fault activity, which corresponds to the periodical tectonic movements in the basin. As a result, proximal sublacustrine fans tend to develop in near-shore topographic lows down-dip of syn-depositional faults due to increased tectonic activities, accommodation and enhanced OHF. A deep-water depositional model is proposed for hyperpycnal systems on rift margins by emphasizing the variety in sedimentary process and dispersal patterns controlled by climate and tectonics forces, which may provide new insights into hyperpycnal flow theories and deep-water exploration in world rift basins.
... In contrast to many well-documented sub-marine fan fringe deposits, there is much less information about the sub-lacustrine ones. Lacustrine sediment gravity flow deposits are probably different from marine ones, because marine environments are characterized by larger-scale depositional systems, deeper water, and a longer runout distance (Yang et al. 2019). Most sub-lacustrine fan deposits were interpreted mostly as debrites or/and turbidites, including the well-known Eocene Dongying depression and the Upper Triassic turbidites in the Ordos Basin (Zou et al. 2012;Liu et al. 2017;Yang et al. 2017Yang et al. , 2019. ...
... Lacustrine sediment gravity flow deposits are probably different from marine ones, because marine environments are characterized by larger-scale depositional systems, deeper water, and a longer runout distance (Yang et al. 2019). Most sub-lacustrine fan deposits were interpreted mostly as debrites or/and turbidites, including the well-known Eocene Dongying depression and the Upper Triassic turbidites in the Ordos Basin (Zou et al. 2012;Liu et al. 2017;Yang et al. 2017Yang et al. , 2019. This raises the following questions. ...
Article
Full-text available
Submarine or sub-lacustrine lobe deposits are important reservoirs, but the fan fringe deposits form heterogeneities within deep water fan deposits. The identification of fan fringe deposits can aid in the reconstruction of deep water fan and reservoir evaluations. Fan fringe facies records the complex sediment gravity flow types. By understanding of the bed types and flow mechanisms, we can identify the fan fringe deposit. The Jiucaiyuanzi and Dalonggou sections in the West Bogda Mountains preserve well-exposed 536-m and 171-m thick successions, respectively, of a deep water lacustrine depositional system from the Middle Permian Lucaogou Formation. Bed types of the Lucaogou Formation include high-density turbidite, low-density turbidite, incomplete Bouma-type turbidite, hybrid event beds, and slump deposits. The Lucaogou Formation is interpreted here as a fan fringe facies due to the thin bed thickness that characterize turbidites and hybrid event beds, as well as the predominance of the isolated sheet architecture. Previous studies suggest that these deposits were considered as deposited in a deep water setting due to the absence of wave-related structures. The presence of abundant mud clasts in massive medium-coarse grained sandstone beds reflects the significant erosional capability and interactions between high-density turbidity currents and lake floor. The fan fringe facies here contains amalgamated and thick-bedded homolithic facies (~30%) and thin-bedded heterolithic facies (~70%). The fan fringe facies forms heterogeneities. The examination of the bed type is of wider significance for facies prediction and reservoir heterogeneity in the sub-lacustrine fan fringe facies.
... Mansurbeg et al. (2008) also interpreted the circulation of the water as the result of hyperpycnal flow in the Shetland-Faroes Basin. Previous studies by Cao et al. (2018) and Yang et al. (2019) have demonstrated that hyperpycnal flow occurred in the Es4 interval. However, the impact of hyperpycnal flow on kaolinite was uncertain due to the periodic occurrence of this flow (Plink-Bjölrklund and Steel, 2004;Mansurbeg et al., 2008Mansurbeg et al., , 2020. ...
... Stratigraphy column presenting the sedimentary environments, major petroleum systems, and tectonic events of the Dongying depression (modified fromYang et al., 2019). ...
Article
A section of the northern Yanjia nearshore subaqueous fan sandy conglomerate was investigated to understand high-quality reservoirs' distribution and controlling factors in the retrogradation and progradation sequences. These conglomerates have been demonstrated to have strong heterogeneity, are tightly cemented, and feature low porosity and permeability. To provide an inclusive understanding of the formation mechanisms and factors governing the distribution of the high-quality reservoirs, we utilized integrated methods including seismic, cores description, wireline, petrography, scanning electron microscopy, cathodoluminescence, and mercury intrusion capillarity. The results showed that the retrogradation rock types are dominated by arkose and lithic arkose and the progradation by lithic arkose and feldspathic litharenite. The dominant diagenesis events are compaction, carbonate cementation, and dissolution. The mechanical compaction effect is similar in the progradation and retrogradation sequence. The average compaction index of 0.70 and 0.68 for the transgressive system tract and highstand system tract, respectively, revealed that compaction is the dominant mechanism in reducing reservoir quality in the nearshore subaqueous fan. The carbonate cementation is more extensive in the highstand system tract than the transgressive system tract. The braided channel sandy conglomerate from transgressive system tract and highstand system tract have the best reservoir quality and features type I and II mercury intrusion capillarity cures with large pore throat and good physical properties. However, the braided channel reservoir quality from the highstand system tract developed during the progradation phase is relatively better than the braided channel of the transgressive system tract in the retrogradation phase. These microfacies are characterized by a substantial dissolution of rock fragments and feldspar. The main channel and the interchannel deposited during the transgressive and highstand system tract, respectively, represented by type III mercury intrusion capillarity curves with small pore throats, are non-reservoirs. The formation mechanism of the high-quality reservoirs in the highstand system tract is guided by sedimentary facies, compaction resistant ability, dissolution of rock fragment, and feldspar. The genetic mechanism of the high quality in the transgressive system tract is governed by the sedimentary facies, compaction resistant ability, carbonate and feldspar dissolution. This study revealed that the progradation sequence retained the favorable high-quality in the nearshore subaqueous fan. This study proved that, for adequate assessment of reservoirs in the Yanjia area and similar reservoirs elsewhere, reservoir characterization must link sequence stratigraphy, sedimentary facies, and diagenesis to comprehend the high-quality reservoir distribution to help the predrill evaluation of reservoirs.
... During the deposition of Es3m, the Jishan delta in the northern margin prograded into the basin quickly as the Linnan Sag subsided rapidly and provided sufficient sediments (Li et al., 2014). The progradation front of the Jishan delta was interrupted by the fault activities and frequent magmatic extrusions, which resulted in a vast amounts of fine-grained massive sandstones and graded sandstones gravity-flow deposits in the Linnan Sag (Li et al., 2014;Yang et al., 2019). The thickness of gravity-flow event beds ranges from 0.1 to 5 m, characterized by normal grading and massive beds (Yang et al., 2019). ...
... The progradation front of the Jishan delta was interrupted by the fault activities and frequent magmatic extrusions, which resulted in a vast amounts of fine-grained massive sandstones and graded sandstones gravity-flow deposits in the Linnan Sag (Li et al., 2014;Yang et al., 2019). The thickness of gravity-flow event beds ranges from 0.1 to 5 m, characterized by normal grading and massive beds (Yang et al., 2019). The vertical stacking of different event beds made the total thickness of the gravity-flow successions reaching approximately 160 m. ...
Article
It has been shown that ankerite in clastic reservoirs can preserve an extended record of diagenesis and thus the fluid flow history in sedimentary basins. Ankerite cements with distinct zoning textures are well developed in gravity-flow sandstones associated with magmatic intrusions in the Linnan Sag, Eastern China. This example offering a rare opportunity to investigate the history of complex diagenetic fluid flow events in a lacustrine rift basin. An integrated study including thin section petrography, fluid inclusion micro-thermometry, carbon and oxygen isotope, SEM-EDS, XRD, CL, BSE-EPMA, LA-ICP-MS analyses was undertaken. The aim is to resolve the mineralogical, geochemical and isotopic composition of the sandstone and constitutional minerals. The sandstones are mainly of lithic arkoses (Q43F34L23), with an average carbonate cements of approximately 8.2 wt %. The carbonate cements are dominated by zoned ankerite appearing as rhombohedral and poikilotopic blocky crystals. Calcite, ferroan calcite, dolomite and siderite cements are also present. Non-carbonate cements including barite, authigenic clay minerals, and quartz overgrowth are common in the sandstone. The δ¹³ C values of ferroan calcite range from −4.2‰ to +1.2‰ PDB. Ferroan calcite was re-precipitated at a temperature of 93.1 °C at the expense of the dissolution of eodiagenesis carbonate cement in the sandstone. Ankerite was precipitated at temperature ranges from 107.8 to 140.9 °C, accompanied with the formation of pore-filling barite. The δ¹³C values of ankerite range from −1.8‰ to +1.1‰, and δ¹⁸O values range from −14.8‰ to −10.5‰, indicating an involvement of hydrothermal fluids in the formation of the zoned ankerite. The hydrothermal fluids were probably related to the mafic magmatic activities and migrated into the sandstones along faults. These fluids are rich in iron and magnesium, and also contains abundant inorganic carbon dioxide and sulphate, episodic charging into the reservoir. The abundances of most of the elements, including magnesium, iron, REEs and trace elements in the zoned ankerite consistently decrease away from the magma intrusion centres. We therefore conclude that multiple magmatic activities were primarily responsible for the zoned ankerite precipitation in the research area. The intimate relationship between magmatic activity and carbonate cementation in sandstone reservoirs documented in this paper may have significant implications for studying fluid flow in lacustrine rift basins.
... Sub-aqueous sediment gravity flows transport large volumes of sediment, commonly characterised by high proportions of sand, into generally mud-prone deep-marine settings (e.g. Bouma, 2000;Heller & Dickinson, 1985;Mutti & Normark, 1987Talling, 2013), and have been shown to have the potential to deposit excellent reservoir-quality sandstones in deep-lacustrine settings (Dodd et al., 2019;Yang et al., 2019Yang et al., , 2020. The scale geometry and internal character of deepwater fans can also be used to infer structural information, with different fan systems developing in response to a particular set of characteristics, such as recent fault activity or changes in regional hinterland drainage patterns (Bowman, 1985;. ...
Article
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Fault relay ramps are important sediment delivery points along rift margins and often provide persistent flow pathways in deepwater sedimentary basins. They form as tilted rock volumes between en-echelon fault segments, which become modified through progressive deformation, and may develop through-going faults that ‘breach’ the relay ramp. It is well established that hinterland drainage (fluvial/alluvial systems) is greatly affected by the presence of relay ramps at basin margins. However, the impact on deepwater (deep-marine/lacustrine) subaqueous sediment gravity flow processes, particularly by breached relay ramps, is less well documented. To better evaluate the complex geology of breached relay settings, this study examines a suite of high-quality subsurface data from the Early Cretaceous deep-lacustrine North Falkland Basin (NFB). The Isobel Embayment breached relay-ramp, an ideal example, formed during the syn-rift and was later covered by a thick transitional and early post-rift succession. Major transitional and early post-rift fan systems are observed to have consistently entered the basin at the breached relay location, directed through a significant palaeo-bathymetric low associated with the lower, abandoned ramp of the structure. More minor systems also entered the basin across the structure-bounding fault to the north. Reactivation of basin-bounding faults is shown by the introduction of new point sources along its extent. This study shows the prolonged influence of margin-located relay ramps on sedimentary systems from syn-rift, transitional and into the early post-rift phase. It suggests that these structures can become reactivated during post-rift times, providing continued control on deposition and sourcing of overlying sedimentary systems. Importantly, breached relays exert control on fan distribution, characterised by laterally extensive lobes sourced by widespread feeder systems, and hanging walls settings by small scale lobes, with small, often line-sourced feeders. Further characterising the likely sandstone distribution in these structurally-complex settings is important as these systems often form attractive hydrocarbon reservoirs.
... Subaqueous sediment gravity flows (SSGF) represent one of the most important sediment transport mechanisms on a global scale (e.g., Mulder and Alexander, 2001;Talling et al., 2007Talling et al., , 2015Meiburg and Kneller, 2010;Postma et al., 2021) and can result in extensive, thick bodies of coarse-grained clastic and associated fine-grained sediments on submarine slopes, on abyssal plains, and in deep lakes (e.g., Stow and Mayall, 2000;Talling et al., 2013;Yang et al., 2019;Dodd et al., 2019;McArthur et al., 2020). Considerable advances have been made in research related to subaqueous sediment gravity flows deposits (SSGFD), such as the classification of flow types (e.g., Postma, 1986;Mutti, 1992;Mulder and Alexander, 2001;Gani, 2004;Haughton et al., 2009;Talling et al., 2012;, transport mechanisms of SSGFs (Kuenen and Migliorini, 1950;Hampton, 1973, 1976;Lowe, 1982;Hage et al., 2018), the genesis of SSGFDs (Mutti et al., 2003(Mutti et al., , 2009Piper and Normark, 2009;Talling et al., 2013;Zavala and Arcuri, 2016;Yang et al., 2020), and the depositional elements and distribution patterns of SSGFD (Mutti andNormark, 1987, 1991;Reading and Richards, 1994;Shanmugam, 2000;Stow and Mayall, 2000;. ...
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Understanding how subaqueous sediment gravity flows (SSGF) evolve in time and space, and how their deposits vary spatially, is a key research focus for gravity flow sedimentology. This study investigates depositional facies, depositional elements, and sediment transport processes of supercritical flows and hybrid event beds (HEBs) of the Lingshandao Formation in Lingshan Island, Eastern China. Three kinds of depositional elements were recognized: mass transport deposits (MTDs), channel-lobe transition zone (CLTZs), and lobe complexes. MTDs can be sub-divided into proximal and distal deposits. CLTZs are characterized by facies changes from massive coarse-grained pebbly sandstone to backset bedding sandstone in a down-slope direction, which are the deposits of supercritical turbidity currents. HEBs are common in both proximal and distal lobe settings. Tripartite structure in HEBs, which may be caused by up-slope substrate erosion, implies a relatively proximal origin compared with bipartite HEBs, perhaps caused by fluid fractionation in the research area. The succession is formed by a prograding lobe unit, followed by MTDs which are themselves overlain by deposits from a CLTZ. This vertical stacking pattern implies the potential longitudinal facies tract from CLTZ; to lobe complex deposits, is accompanied by emplacement of MTDs at the slope break. The flow types accompanied by sediment transport processes imply that erosion by supercritical turbidity currents associated with a hydraulic jump in the channel-lobe transition zone may be the main reason for mud-clasts and matrix addition to the flow. The large-scale addition of mud-clasts and suspended mud may dampen turbulence in proximal to medial lobe settings, and result in medium-to thick-bedded HEBs with common erosional features and tripartite structures. The remaining suspension flow (with abundant mud) may further transport down-dip and form medium-to thin-bedded HEBs with bipartite structures and rare mud-clasts. These findings may be applicable to other SSGF systems with supercritical flow deposits and hybrid event beds, emphasizing the downdip and lateral variation in depositional elements associated with gravity flow evolution.
... The thickness of individual sandy gravity-flow reservoir beds ranges from 0.1 to 10 m (~0.3-33 ft), with a total thickness ranging from 10 to 158 m (~33-518 ft) ( Figure 2). Turbidites with Bouma sequences and debrites with massive bedding are the most common gravity-flow deposits in these reservoirs (Bouma, 1962;Yang et al., 2015Yang et al., , 2019. Because the compositional and structural differences of these sandstones are minor, they provide a good case study to evaluate the effect of diagenesis on the reservoir quality of gravity-flow sandstones. ...
... The use of high-resolution seafloor images and high-resolution threedimensional (3D) seismic datasets to investigate submarine sediment gravity-flow systems has led to substantial progress in understanding the morphology, stratigraphy, and architecture of such systems and in predicting the presence of hydrocarbon reservoirs within such systems (Alpak et al., 2011;Olariu et al., 2011;Sylvester et al., 2011;Wiles et al., 2013;Zhang et al., 2015;Chen et al., 2019). Petroleum exploration in continental basins has shown that deep-lacustrine gravity-flow systems have formed important hydrocarbon reservoirs in a number of basins and lake sequences worldwide (Feng et al., 1991;Feng et al., 2010a;Zou et al., 2012;Liu et al., 2015Liu et al., , 2016Meng et al., 2016;Pan et al., 2017Pan et al., , 2019Pan et al., , 2020Liu, L. et al., 2017;Liu, X et al., 2017;Yang et al., 2017a, b;Fongngern et al., 2018;Fan et al., 2018;Xian et al., 2018;Dodd et al., 2019;Yang et al., 2019;Liu et al., 2020). At present, research on gravity-flow deposits in lacustrine basins is mainly focused on genetic and depositional models, especially deposits related to slope failures; however, few studies have discussed deep-lake channel-levee-lobe systems associated with river floods, with the exceptions of Yang et al. (2017b), Fan et al. (2018) and Xian et al. (2018), who studied these systems in the Upper Triassic Ordos Basin, and Feng et al. (2010a), who described such systems in the first member of the Nenjiang Formation (K 2 n 1 ) within the Upper Cretaceous Songliao Basin, China. ...
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The Songliao Basin is a large Cretaceous nonmarine petroliferous postrift downwarped basin in northeastern China. Deep lake channel-levee-lobe and slope fan deposits are identified within six depositional sequences that span from the Turonian Qingshankou Formation to the second member of the Campanian Nenjiang Formation. Research on the sediment gravity-flow systems in the Songliao Basin has broad application for understanding the sedimentary processes and pattern of sediment gravity-flow systems, and predicting the presence of good sandstone reservoirs within postrift downwarped lacustrine basins. Research results show that the channel-levee-lobe deposits are present within sequences in the first member of the Qinshankou Formation and the first member of the Nenjiang Formation. The straight channel levees and slope fans were on high-gradient slopes, whereas the sinuous channel levees were on low-gradient slopes. The straight-to-sinuous channel levees, fed by northeastern deltaic subaqueous distributary channels, extend for 15–70 km, predominantly within transgressive-to early highstand system tracts, which terminated in bifurcated or small lobes. The channel-levee-lobe and slope fan deposits sourced from western deltas were deposited basinward of the syndepositional flexural slope-break zones controlled by deep-seated faults. The falling trajectories of the paleoshorelines during the highstand and lowstand systems tracts and large sediment fluxes during the transgressive systems tracts resulted in the development of the slope fans and channel-levee-lobes. Lakebed paleorelief influenced the channel forms. Sand bodies within the channel-levee-lobes and slope fans, encased within organic-rich source rocks, represent new significant targets for hydrocarbon exploration.
... Understanding the origin of fine-grained sediments based on the sedimentary characteristics and distribution patterns is vital for unconventional oil and gas exploration and development in fine-grained sediment formations, and for the reconstruction of paleoclimate and paleoenvironment (Macquaker et al., 2010;Schieber, 2016;Schieber et al., 2007;Piper, 1984a, 1984b;Zavala and Arcuri, 2016;Yang et al., 2019). Origins of fine-grained sediments of the lower Cretaceous Lingshandao Formation indicated that vertical suspension fallout and downslope transport by gravity flows are the dominant mechanisms for fine-grained sediments deposition (Figs. 10 and 13). ...
... rocesses of sediment gravity flows, and the distribution patterns of gravity-flow deposits (e.g., Reading and Richards, 1994;Mulder and Alexander, 2001;Piper and Normark, 2009;Talling et al., 2012Talling et al., , 2013bTalling et al., , 2015Zavala and Arcuri, 2016;Southern et al., 2017;Pierce et al., 2018;B. Xian et al., 2018a;T. Yang et al., 2018aT. Yang et al., , 2019. The comprehensive process referred to as "triggering-transportation-deposition" of deep-water sediment gravity flows to form gravity-flow deposits, which is also referred to as a deep-water sediment gravity-flow event (Talling et al., 2012). Therefore, a gravityflow event may be commonly composed of different types of gravity flows and ...
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"Gravity flows may be triggered by different initiation processes in both marine and lacustrine basins. Recognizing the different initiation processes of gravity flow based on their deposits is vital to accurately establish gravity-flow sandstone distribution, which is important for defining paleogeography and for efficient oil and gas exploration. Gravity-flow deposits in the Dongying sag were analyzed using three-dimensional seismic, well-log, grain size, and porosity and permeability data, along with core descriptions. Eleven lithofacies, nine bed types, and six bed-type associations were recognized in the gravity-flow deposits in the Dongying sag. Gravity-flow deposits around well Niu-110 were caused by delta-fed sediment failure. These deposits are characterized by medium to very fine-grained sandstone, abundant liquefaction and soft-sediment deformation structures, and thick laminae rich in plant debris. They formed massive sandstones accompanied by normally graded sandstone and lenticular- shaped sandbodies and are composed of chaotic deposits and tongue lobes. The above features collectively are indicative of typical collapsed-sediment transport to deep water by slumping and poorly cohesive debris flow to low-density turbidity current. Gravity-flow deposits around well Shi-100 are interpreted to have been caused by flooding river-fed hyperpycnal flows. These deposits are characterized by gravel to very fine-grained sand, abundant erosional structures and climbing ripples, and thin laminae rich in plant debris. They formed massive sandstone with some space stratification accompanied by inverse- then-normal grading sandstone and elongate or fan-shaped sand- bodies and are composed of channel-levee systems and lobes. Stratified hyperpycnal flow is prone to form a hydraulic jump at "the slope break. After the hydraulic jump, coarse-grained sediments were transported to the basin under the drag and shear of the upper part of the suspension flow. Gravity-flow deposits caused by flooding river-fed hyperpycnal flow are better reservoirs than those caused by delta-fed sediment failure under the same conditions. This study offers insight into the recognition criteria and flow processes of gravity flows caused by the different initiation processes in a lacustrine basin."
... Deep-water deposits in the lacustrine system have been of great interest for the identification, classification and prediction of gravity flows in recent years (Fugelli and Olsen, 2007;Jobe et al., 2017;Porten et al., 2016;Southern et al., 2015;Stevenson et al., 2014;Talling et al., 2007;Talling, 2014;Talling et al., 2015;Tinterri et al., 2016;Zavala and Arcuri, 2016). According to different grain sizes and sedimentary structures, the sublacustrine turbidite sediments were classified as flood turbidites (quasi-steady turbidites) resulting from flooding and slump turbidites (surge-like turbidites) resulting from sediment slumping Yang et al., 2019). FA 3 is distributed in the central sag of the TST ahead of the delta front deposit (FA 2), and we defined this unit as the turbidite deposit of the sublacustrine fan on the basis of its diverse grain sizes, sedimentary structures and seismic reflections. ...
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The influence exerted by the linkage and growth of fault segments on the sedimentation pattern in a lacustrine rift subbasin, the northern Bonan Sag in the Jiyang Depression in the Bohai Bay Basin, is studied by integrating drilling cores, wireline logs and 3D seismic data. The NW-trending Guxi Fault formed through the linkage of three fault segments, which display a roughly en echelon arrangement in map view and are probably related to early-stage regional transtensional and slip-strike stress. Between the vertical displacement troughs of normal faults, two narrow relay ramps, attributed to the coherent fault linkage-and-growth model, formed through the linkage of the three fault segments. A relatively wide relay ramp, attributed to the isolated fault linkage-and-growth model, developed due to the linkage of the NW-trending Guxi Fault and E-W-oriented segmented Chengnan Fault. The sedimentation pattern was strongly controlled by the geometry and evolution of the relay ramps. The sediment routing system was dominated by the relay zone, and fan-delta and sublacustrine fan depositional systems developed in the early stage of relay ramp formation. Lateral breaching of the relay ramps through extensive faulting and rifting probably caused an increase in the vertical throw and resulted in deposition of a coarse-grained nearshore subaqueous fan in front of the normal faults. The relay zone that formed from the linkage of independent faults (the Chengnan and Guxi faults) is associated with a broad drainage area and fan-delta and sublacustrine fan deposits, which contain the most effective hydrocarbon reservoirs in this deeply buried setting.
... A debris flow is a gravity-driven mass flow with plastic rheology and laminar state, it is predominantly supported by the matrix strength, grain-to-grain interactions, excess pore fluid pressure, or buoyancy, and accumulated by en masse settling (Coussot & Meunier, 1996;Locat & Lee, 2005;Naylor, 1980;Qian & Das, 2019;Shanmugam, 2016;Talling, Masson, Sumner, & Malgesini, 2012;Yang, Cao, et al., 2019). Deposits formed by debris flows are termed debrites, which can also be sandy and muddy in composition (Coussot & Meunier, 1996;Locat & Lee, 2005). ...
Article
The Songliao Basin in NE China is a large rift basin filled with Cretaceous terrestrial sediments. Lacustrine mudstones of the Nenjiang Formation form an important source rock in the Cretaceous Songliao Basin. These shales are commonly thought to have been deposited in deep, quiet, and anoxic environments. Samples obtained from the core of the SK‐2 scientific borehole provide critical insights to understand the hydrodynamic and hydroclimatic environments, which are, however, different from the traditional views regarding the deposition of these rocks. By following a mudstone description guide, five different mudstone lithofacies (LF) transported and deposited by muddy hyperpycnal flows and muddy debris flows were recognized. They are laminated fine mudstone (LF1), laminated medium mudstone (LF2), and laminated coarse mudstone (LF3) showing pairs of inverse grading (Ha) and normal grading (Hb) under the microscope, graded coarse mudstone (LF4) and massive coarse mudstone (LF5). We found that mudstones of the First Member of the Nenjiang Formation are dominated by siliciclastic detritus and argillaceous components and show frequent variations in grain size. Because large‐scale sub‐lacustrine channels travelling long distance (>80 km) were widely distributed in the Songliao palaeolake during the deposition of the Nenjiang Formation, fluctuations in mudstone grain size might have been caused by velocity fluctuations in flows. Sedimentary structures and textures preserved in mudstones of the First Member of the Nenjiang Formation indicate that the majority of these lithofacies were accumulated by muddy hyperpycnal flows and muddy debris flows. Therefore, a depositional model dominantly influenced by muddy hyperpycnal flows and debris flows is proposed. This work not only provides a new view for the depositional process of mudstones of the Songliao Basin, NE China, but also give insights to understand lacustrine palaeoenvironment and terrestrial palaeoclimate.
... Vast amounts of detrital materials were transported into the basin forming amounts of source rocks and turbidites (Wang et al., 2013;Yang et al., 2015) (Fig. 1). The target stratum of this study is the 3-4 sand formation in the middle of the third member of Shahejie Formation (Es3z), which a large number of turbidite deposits developed in Yang et al. (2015Yang et al. ( , 2019. Reservoir depth is 2800-3200 m, porosity is 16.9-22.3%, ...
... The rip-up clasts, aligned parallel to bedding plane, indicate laminar conditions with shear strength in the debris flows (Hampton, 1975;Enos, 1977;Sohn et al., 1999). Although sustained liquefied high-density turbidity currents may generate massive sandstones (Lowe, 1982;Kneller and Branney, 1995;Cartigny et al., 2013), pebbly sandstones and conglomerates with spaced stratification and basal erosion structures are considered to be the common features of high-density turbidites (Lowe, 1982;Cartigny et al., 2013;Yang et al., 2019). Neither the sedimentary structures nor the vertical sequence of the fine-grained sandstones in well B-2 resembles a typical sequence of sandstones deposited by high-density turbidity currents (Lowe, 1982;Kneller and Branney, 1995;Talling et al., 2012;Cartigny et al., 2013;Zavala and Arcuri, 2016); hence, they cannot be regarded simply as an analogue to high-density turbidites, which show grading and grain sorting (Talling et al., 2012). ...
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In recent years, shallow-marine fans have attracted considerable attention because they may serve as valuable targets in hydrocarbon exploration. By integrating 3-D seismic, well log, core, and other measured data, this study analyzed the sedimentary characteristics and factors controlling the deposition of shallow-marine fans in Member #1 of the Huangliu Formation in the Yinggehai Basin. Four depositional elements were recognized in the channel-lobe complexes (CLCs), channel-fill sandy debrites, channel-fill turbidites, sand-rich lobe deposits and mud-rich lobe deposits. The channel-fill sandy debrites, which are characterized by low root-mean-square (RMS) amplitude in plan view and deep V-shaped reflections in seismic profile, are commonly located in the internal regions of CLCs. They have widths ranging from 1 to 2 km and single sandbody thicknesses exceeding 25 m. A cored interval from a channel-fill sandy debrite comprising several ungraded sand units revealed massive fine-grained sandstones with floating mud clasts and muddy rip-up clasts. In contrast, the channel-fill turbidites are characterized by low or high RMS amplitude in plan view and shallow V-shaped or vermiform-shaped reflections in profile. They have a small-size frontal splay at the terminus, thus forming a lobe-channel-lobe depositional style. The width of a channel-fill turbidite is usually less than 0.5 km, and the single sandbody thickness is no more than 20 m. A cored interval of channel-fill turbidite consisted of very fine-grained sandstones containing incomplete Bouma subdivisions Ta–Tb. The sand-rich and mud-rich lobe deposits are characterized by high RMS amplitude and low RMS amplitude with continuous sheet reflection patterns, respectively. The deposition of the shallow-marine fans was significantly influenced by sea-level fluctuations and paleogeomorphology. When sea level fell rapidly, gravity flows with higher erosive energy and velocity tended to form widely developed large-scale channel-fill sandy debrites and sand-rich lobe deposits. When sea level rose, small-scale channel-fill turbidites were dominant because of relatively decreased gravity flow energy. Distinct variations of reservoir characteristics, including mean grain size, mud content, and pore-throat radius, were controlled by sea-level fluctuations. From the period of rapid sea-level fall to the period of rising sea level, the gravity flows may have been increasingly diluted due to sufficient mixing with ambient seawater, resulting in a gradual transformation from sandy debris flows into turbidity currents. In addition, changes in gradient caused by irregular paleogeomorphology may have significantly triggered different depositional styles. With a steeper gradient, the CLC is dominated by a channelized-lobe depositional style; however, a lobe-channel-lobe depositional style prevails under a gentler gradient condition. Taking the reservoir characteristics and depositional styles into consideration, it is suggested that the sandy debrites, with better physical properties, constitute favorable hydrocarbon reservoir intervals. The shallow-marine fans in this study may serve as a distinctive analogue to similar gravity flow deposits in other basins worldwide.
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The tight sandstone reservoirs have become the focus of today's oil and gas exploration. To clarify the microscopic characteristics of the tight sandstone reservoirs of the Chang 63 deep water gravity flow origin in the Huaqing area, the Chang 63 gravity flow origin reservoirs in the study area are divided into three categories. They are the formation reservoir of sandy clastic flow (FROSF), formation reservoir of muddy debris flow deposits and turbidites (FROMT) and formation reservoir of slides and slumps (FROSS). In this study, core and logging data, thin sections, field emission scanning electron microscopy (FE‐SEM), and mercury intrusion capillary pressure (MICP) were combined to investigate the rock composition and pore‐throat characteristics of tight sandstone reservoirs with different types of gravity flow origins. The reservoir micro‐heterogeneity is also investigated in this paper. The results show that the reservoirs with different gravity flow origins are similar in lithology and are mainly composed of feldspar lithic sandstone and lithic feldspar sandstone. The pore types are mainly intergranular pores and feldspar‐dissolved pores. There are significant differences in the porosity, permeability, microscopic pore‐throat characteristics and microscopic heterogeneity of the reservoirs. From FROSF to FROMT and FROSS, the porosity, permeability, mercury inlet saturation, discharge pressure, median pressure and mercury removal efficiency gradually decrease. The tightness of the reservoir gradually increases. The storage capacity is gradually reduced. The disparity between the throat radius and pore radius gradually increases. The pore‐throat structure becomes more complex, and the microscopic heterogeneity of the reservoir gradually increases. The distribution of different types of gravity flows in Chang 63 reservoir in Huaqing area, Ordos Basin, China. Different types of gravity flow reservoirs have different microscopic characteristics.
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Tight sandstone in the Upper Triassic Yanchang Formation, Ordos Basin, contains large accumulations of hydrocarbon resources. This study presents an investigation of the deep-lacustrine sandy-debris-flow tight sandstones in the Yanchang Formation, based on petrographic, geochemical and petrophysical analysis. It reveals that reservoir heterogeneity and hydrocarbon accumulation of tight sandstones were affected by diagenetic alteration. These tight sandstones are dominantly lithic arkoses and feldspathic litharenites which are characterized by moderate to good sorting, fine to medium grain, subangular to subrounded and poor reservoir properties (average porosity and permeability are 10.5% and 1.23 mD, respectively). Significant diagenesis including compaction, feldspar dissolution and cementation by carbonate, quartz and authigenic clay have altered the studied tight sandstones. Compaction and carbonate cementation are the dominant destructive diagenetic processes. Carbonate cements are mainly developed at the edge of sandstone (distance to the sandstone-mudstone boundary mostly < 1 m) due to the limited transportation distance from adjacent mudstone. The relative high-quality reservoir intervals will preferentially develop in the middle of sandstone (distance to the sandstone-mudstone boundary mostly > 1 m). Feldspar dissolution has no significant impact on reservoir quality, as it results in pore space redistribution. There is little variation due to the primary intergranular pores being converted to dissolution pores and intercrystal micropores of authigenic clay. The lower level of compaction in the middle sandstone is due to cemented marginal sandstone. Moreover the preservation and redistribution of the pore space of the middle sandstones is generally due to carbonate cementation and feldspar dissolution. Different petrophysical properties between marginal and central sandstones lead to reservoir heterogeneity. Reservoir petrophysical properties display a positive correlation with oil-bearing capacity, which reveals that hydrocarbon accumulation can also be affected by reservoir property. Ultimately, tight sandstones with porosity > 6%, permeability > 0.1mD and thickness > 2 m can be regarded as effective reservoirs in the Yanchang Formation. The results will contribute to the understanding of the origin of deep-lacustrine sandy-debris-flow tight sandstones reservoirs, which will enable further exploration for effective reservoirs in lacustrine sandy debrites across the globe, predominantly in those sharing the same geological features.
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Coarse‐grained subaqueous fans are vital oil and gas exploration targets in the Bohai Bay basin, China. Researchers still lack understanding of their sedimentary processes, depositional patterns and controlling factors, which restricts the efficient exploration and development. Coarse‐grained subaqueous fans in the Yongan area, Dongying Depression, are investigated. These fans include nearshore subaqueous fans, and sublacustrine fans, and their sedimentary processes, depositional patterns and distribution characteristics are mainly controlled by tectonic activity and paleogeomorphology. Nearshore subaqueous fans developed near the boundary fault during the early‐middle deposition stage due to strong tectonic activity and large topographic subsidence. In the area where the topography changed from gentle to steep along the source direction, early sublacustrine fans developed at the front of the nearshore subaqueous fans. While the topography was gentle, sublacustrine fans did not develop. During the late weak tectonic activity stage, late sublacustrine fans developed with multiple stages superimposed. Frequent fault activity and related earthquakes steepened the basin margin, and the boundary fault slopes were 25.9° ‐ 34°. During the early‐middle deposition stage, hyperpycnal flows triggered by outburst floods developed. During the late deposition stage, with weak tectonic activity, seasonal floods triggered hyperpycnal flows, and hybrid event beds developed distally.
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The shallow-marine turbidite fans in the Upper Miocene Huangliu Formation of the Yinggehai Basin in the northwestern South China Sea (SCS) provide an excellent opportunity to understand their sedimentary processes in a shelf depositional environment. The down-slope gravity flow processes and along-slope bottom-current reworking processes of shallow-marine turbidite fans were interpreted by using seismic, well logging, core, petrographic, geochemical, and petrophysical data. Several depositional elements were identified in the shallow-marine turbidite fans, namely, channel-fill high-density turbidites (HDTs), channel-fill low-density turbidites (LDTs) and associated frontal splays, sand-rich/mud-rich lobe deposits, and bottom-current reworked channel-fill/lobe deposits. Deep U-shaped (or V-shaped) seismic reflections and low root-mean-square (RMS) amplitudes characterize the channel-fill HDTs that consist of massive fine-grained sandstones with mud clasts. The channel-fill LDTs, characterized by V-shaped or worm-shaped reflections, mostly consist of normally graded, laminated and rippled, very fine-grained sandstones. Frontal splays are generally associated with channel-fill LDTs. The sand-rich lobe deposits show continuous high-amplitude sheet-like reflections and consist of HDTs and LDTs, whereas the mud-rich lobe deposits show continuous moderate-amplitude reflections and consist of muddy debrites. The bottom-current reworked sandstones (BCRSs), which comprise well-sorted, fine-grained sandstones with traction-current structures, are usually located in the upper parts of thick sandbodies. The variability of depositional elements from large-scale channel-fill HDTs with strong basal erosion in fan-1 to small-scale channel-fill LDTs in fan-2 is closely linked with sea-level fluctuations that result in variable gravity-flow energy and sediment input. However, the reoccurrence of large-scale channel-fill HDTs in fan-3 at sea-level highstands may possibly be attributed to enhanced sediment input from the source areas. Down-slope flow transformation from turbidity flows into muddy debris flows within an individual channel-lobe complex (CLC) resulted in a dramatic increase in clay content and resultant decreasing reservoir quality from the channel-fill HDTs to the mud-rich lobe deposits, because muddy sediments are incorporated into the precursor turbidity flows and turbulence is suppressed. Additionally, it is suggested that the widely developed traction-current structures and tidal signatures (double mud layers, mud-draped ripples, discrete wavy bedding, internal truncation surface, and convex-up laminae) are the products of reworking by internal waves and -tides. During periods of sea-level highstands, the upper parts of gravity-flow sandstones would undergo bottom-current reworking, thus resulting in the retransportation of muddy fines and the formation of reworked sandstones with traction-current structures and tidal signatures. In this study, a combination of traction-current structures, tidal signatures, vertical sequences showing sharp upper contacts and non-gradational upper contacts, and trace elements is considered to be convincing diagnostic criteria in distinguishing reworked sandstones from gravity-flow sandstones. The representative bottom-current reworked sandstones should be preferable hydrocarbon targets in further exploration because of their better reservoir properties compared with gravity-flow sandstones. This research offers some insight into gravity-flow processes and bottom-current reworking processes in a shallow marine environment.
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Approximate 500 m deltaic-lacustrine successions were formed within 2 Ma in the Liangjialou area of the Dongying Depression in the Bohai Bay Basin (eastern China). However, few studies on sequence stratigraphy were previously conducted in the east of Liangjialou. In the present study, we integrate high-resolution three-dimensional (3D) seismic data with well-logging data to study the sequence stratigraphy and the depositional system. Our study shows that: (1) Four systems tracts have been identified in the study interval, they are HST, FSST, LST and TST. The HST has an ascending shelf-edge trajectory and aggradation to progradation stacking pattern. FSST has a descending shelf-edge trajectory and progradation to degradation stacking pattern. LST has a low-angle ascending shelf-edge trajectory and progradation to aggradation stacking pattern. TST has a backstepping shelf-edge trajectory and retrogradation stacking pattern. (2) Five high-resolution sequences (equal to 4th-order sequence), HRS1∼HRS5, are further subdivided within the 3rd-order LST. In addition, the depositional systems of HRS1∼HRS5 are significantly variable in 3D space. The delta and deep-water deposits in the north are larger than those in the south. (3) The formation of the sequence is controlled by both tectonics and dry-wet climatic cycles. The tectonic subsidence, and high sediment supply in overall wet climate play a major role in the formation of the 3rd-order sequence. The higher frequency dry-wet climatic cycles control the formation of internal systems tracts. We further divide the climate of study interval into three stages that are excellent correlated to the specific systems tracts: Stage 1 (evaporation < precipitation) corresponds to HST; Stage 2 (evaporation > precipitation) corresponds to FSST; Stage 3 (evaporation < precipitation) corresponds to LST. (4) The basin morphology and source location mainly control the lateral variability of the depositional system of LST. Low paleotopography, narrow shelf width and steep slope dip in the north cause a large accommodation, and promote the development of the deltaic and deep-water deposits. In contrast, a high relief, wide shelf width and gentle slope cause only minor accommodation in the south, and limit the development of the deltaic and deep-water deposits.
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Understanding the flow processes that form gravity flow deposits is vital for modelling and prediction of sandstone bodies in the subsurface, which is of great significance for conventional and unconventional oil and gas exploration and development. This study analyses gravity flow deposits in the Late Triassic Chang 7 member of Yanchang Formation in the Ordos Basin, using a combination of well-log analysis, core observations, thin section analysis, and laboratory measurements. Through this, the sedimentary facies, formational mechanisms, distribution patterns, and depositional models of gravity flow deposits are investigated. Thirteen facies and eight-bed types are recognized in the gravity flow. Bed types represent deposits of sandy slides, sandy slumps, muddy debrites, sandy debrites, hybrid event beds, transitional flow deposits, surge-like low-density turbidites, and quasi-steady-state low-density turbidites. Gravity flow deposits, particularly those caused by sediment failure, are composed of slides, slumps, sandy debrites, hybrid event beds/transitional flow deposits, and surge-like low-density turbidites. These deposits form as lenticular sand bodies, with retrogradational internal stacking patterns. Gravity flow deposits caused by hyperpycnal flow are composed of sandy debrites, hybrid event beds/transitional flow deposits, and quasi-steady-state low-density turbidites. These deposits exhibit elongate morphologies in the southern part of the basin, with progradation internal stacking patterns. The collision between the North China Block and South China Block, which occured during the closing of Qinling Ocean, lead to frequent volcanic eruptions and earthquakes. This likely promoted the development of gravity flow deposits associated with sediment failure from delta fronts in both the northeastern and southwestern parts of the basin. Concurrently, extremely humid climatic conditions promoted increased run-off in the hinterland and heightened fluvial drainage, which ultimately lead to enhanced hyperpycnal flows into the deep-lacustrine basin depocenters. Keywords: Gravity flow deposits, depositional model, deep-lacustrine, Yangchang Formation, Ordos Basin
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The Jiyang Depression is an important oil and gas production zone in the Bohai Bay Basin. Through a systematic investigation of the gas components and stable carbon isotopes, the genetic types of natural gas found in the Jiyang Depression were determined, that is, biogas, oil-associated gas, coal-derived gas, high-mature oil-related gas, and mantle-derived carbon dioxide (CO2). From the results, natural gas in the Jiyang Depression can be divided into four groups. Group I, which is distributed in the northwest area, is the only typical oil-associated gas. Group II, distributed in the northeast area, is dominated by oil-associated gas, and involves biogas, coal-derived gas, and high-mature oil-related gas. Group III, distributed in the southeast area, has all genetic types of gas that are dominated by oil-associated gas and have mantle-derived CO2. Group IV, distributed in the southwest area, is dominated by biogas and involves coal-derived gas and oil-associated gas. The differences in each group illustrate the lateral distribution of the natural gas types is characterized by the eastern and southern areas being more complex than the western and northern areas, the vertical distribution of gas reservoirs has no obvious evolutionary law. The main controlling factor analysis of the spatiotemporal changes of the gas reservoirs revealed that the synergy of geochemical characteristics, thermal evolution of the Shahejie Formation and Carboniferous-Permian source rocks, and sealing properties of various faults are jointly responsible for determining the gas reservoir spatiotemporal changes.
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The commercial exploitation of unconventional petroleum resources (e.g., shale oil/gas and tight oil/gas) has drastically changed the global energy structure within the past two decades. Sweet-spot intervals (areas), the most prolific unconventional hydrocarbon resources, generally consist of extraordinarily high organic matter (EHOM) deposits or closely associated sandstones/carbonate rocks. The formation of sweet-spot intervals (areas) is fundamentally controlled by their depositional and subsequent diagenetic settings, which result from the coupled sedimentation of global or regional geological events, such as tectonic activity, sea level (lake level) fluctuations, climate change, bottom water anoxia, volcanic activity, biotic mass extinction or radiation, and gravity flows during a certain geological period. Black shales with EHOM content and their associated high-quality reservoir rocks deposited by the coupling of major geological events provide not only a prerequisite for massive hydrocarbon generation but also abundant hydrocarbon storage space. The Ordovician–Silurian Wufeng–Longmaxi Shale of the Sichuan Basin, Devonian Marcellus Shale of the Appalachian Basin, Devonian–Carboniferous Bakken Formation of the Williston Basin, and Triassic Yanchang Formation of the Ordos Basin are four typical unconventional hydrocarbon systems selected as case studies herein. In each case, the formation of sweet-spot intervals for unconventional hydrocarbon resources was controlled by the coupled sedimentation of different global or regional geological events, collectively resulting in a favorable environment for the production, preservation, and accumulation of organic matter, as well as for the generation, migration, accumulation, and exploitation of hydrocarbons. Unconventional petroleum sedimentology, which focuses on coupled sedimentation during dramatic environmental changes driven by major geological events, is key to improve the understanding of the formation and distribution of sweet-spot intervals (areas) in unconventional petroleum systems.
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On the basis of detailed sedimentological investigation, three types of hybrid event beds (HEBs) together with debrites and turbidites were distinguished in the Lower Cretaceous sedimentary sequence on the Lingshan Island in the Yellow Sea, China. HEB 1, with a total thickness of 63–80 cm and internal bipartite structures, is characterised by a basal massive sandstone sharply overlain by a muddy sandstone interval. It is interpreted to have been formed by particle rearrangement at the base of cohesive debris flows. HEB 2, with a total thickness of 10–71 cm and an internal tripartite structure, is characterised by a normal grading sandstone base, followed by muddy siltstone middle unit and capped with siltstones; the top unit of HEB 2 may in places be partly or completely eroded. The boundary between the lowest unit and the middle unit is gradual, whereas that between the middle unit and the top unit is sharp. HEB 2 may be developed by up-dip muddy substrate erosion. HEB 3, with a total thickness up to 10 cm and an internal bipartite structure, is characterised by a basal massive sandstone sharply overlain by a muddy siltstone interval. The upper unit was probably deposited by cohesive debris flow with some plant fragments and rare mud clasts. HEB 3 may be formed by the deceleration of low-density turbidity currents. The distribution of HEBs together with debrites and turbidites implies a continuous evolution process of sediment gravity flows: debris flow → hybrid flow caused by particle rearrangement → high-density turbidity current → hybrid flow caused by muddy substrate erosion → low-density turbidity current → hybrid flow caused by deceleration.
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Subaquatic channels are known as active conduits for the delivery of terrigenous sediments into related marine and lacustrine basins, as well as important targets for hydrocarbon exploration. Compared to submarine channels, lacustrine subaqueous channels created by hyperpycnal flows are understudied. Using well-exposed outcrops collected from three different locations in the southern Ordos Basin, central China, morphologies and architecture of a channelized hyperpycnal system were studied and classified. Six facies associations represent sedimentary processes from strong erosion by bedload dominated hyperpycnal flows, to transitional deposition jointly controlled by bedload and suspended-load dominated hyperpycnal flows, finally to deposition from suspended-load dominated hyperpycnal flows. On the basis of channel morphologies, infilling sediments and sedimentary processes, the documented channels can be classified into four main categories, which are erosional, bedload dominated, suspended-load dominated, and depositional channels. In very proximal and very distal locations, erosional channels and depositional channels serve as two end-members, while in middle areas, bedload-dominated channels and suspended-load dominated channels are transitional types. Erosional channels, as a response to strong erosion from bedload dominated hyperpycnal flows on upper slope, were mainly filled by mud interbedded with thin sand beds. As flow energy decreases, bedload dominated channels develop on middle slopes, which are characterized mainly by under- to balanced sediment infillings with cross-bedded sandstones and/or minor massive sandstones. Compared to bedload dominated channels, suspended-load dominated channels mainly develop in deeper water, and were filled mainly by massive or planar-laminated sandstones. Depositional channels, as a response to suspended-load dominated hyperpycnal flows in deep-water areas, are characterized by thin-medium bed classical turbidites with Bouma sequences and thin- to thick massive sandstones. Such evolution patterns of hyperpycnal channel systems are ascribed to the progressive decrease in flow capacity of hyperpycnal flows, and provide an adequate explanation for the basinward channelization behavior of hyperpycnal systems.
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Based on the integrated analysis of seismic, drilling and core data, a large channel-fan system of hyperpycnal flow origin was found in the Qijia-Gulong area of the Nen 1 Member of the Cretaceous Nenjiang Formation in the Songliao Basin. The hyperpycnal flow in this area, which originated from the edge of the basin and then passed the northern delta, formed a complete channel-fan system in the deepwater area. The channel-fan system comprises straight channels and meandering channels extending from north to south over a straight distance of more than 80 km with a width of 100900 m, and distal fan lobes at the channel tip cover a maximum area of 20 km 2. This system, which is dominated by fine-grained deposits, contains massive sandstone, sedimentary structures of flow-water origin, and internal erosion surfaces; it also contains abundant continental organic clasts and exhibits evidence of bed-load and suspended-load transportation mechanisms. The hyperpycnite sequence contains pairs of coarsening-upward lower sequences and fining-upward upper sequences, reflecting the dynamic features of cycles in which floods first strengthen and then weaken. A new sedimentary model has been built for hyperpycnites in the Songliao Basin.
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Subaerial rivers and turbidity currents are the two most voluminous sediment transport processes on our planet, and it is important to understand how they are linked offshore from river mouths. Previously it was thought that slope failures or direct plunging of river flood water (hyperpycnal flow) dominated the triggering of turbidity currents on delta-fronts. Here we re-analyse the most detailed time-lapse monitoring yet of a submerged delta; comprising 93 surveys of the Squamish Delta in British Columbia, Canada. We show that most turbidity currents are triggered by settling of sediment from dilute surface river plumes, rather than landslides or hyperpycnal flows. Turbidity currents triggered by settling plumes occur frequently, run out as far as landslide-triggered events, and cause the greatest changes to delta and lobe morphology. For the first time, we show that settling from surface plumes can dominate the triggering of hazardous submarine flows and offshore sediment fluxes.
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Growing evidence suggests that land generated sediment gravity flows are the most important source of clastic sediments into marine and lacustrine sedimentary basins. These sediments are mostly transferred from source areas during exceptional river discharges (river floods). During floods rivers discharge a sediment-water mixture having a bulk density that often exceeds that of the water in the receiving water body. Consequently, when these flows enter a marine or lacustrine basin they plunge and move basinward as a land-derived underflow or hyperpycnal flow. Depending on the grain-size of suspended materials, hyperpycnal flows can be muddy or sandy. Sandy hyperpycnal flows also can carry bedload resulting in sandy to gravel composite beds with sharp to gradual internal facies changes laterally associated with lofting rhythmites. Lofting occurs because flow density reversal due to the buoyant effect of freshwater when a waning turbulent flow loses part of the sandy load. On the contrary, muddy hyperpycnal flows are loaded by a turbulent suspension of silt and clay. Since the concentration of silt and clay don’t decrease with flow velocity, muddy hyperpycnal flows will be not affected by lofting and the flow will remain attached to the sea bottom until its final deposition. The last characteristics commonly result in cm-thick graded shales disposed over an erosive base with dispersed plant debris and displaced marine microfossils. Deposits related to hyperpycnal flows are hyperpycnites. Although hyperpycnites display typical and diagnostic characteristics that allow a clear recognition, these deposits are often misinterpreted in the literature as Sandy debrites, shoreface, estuarine of fluvial deposits. The correct identification and interpretation of hyperpycnites provides a new frontier for the understanding and prediction of conventional and unconventional reservoirs.
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Sediment avalanche from delta ramp is one of the significant development mechanisms for a turbidite system in a lacustrine basin. To advance our understanding of deep-water sedimentary processes in a lacustrine delta ramp, delta-fed turbidites in the Eocene Dongying depression of the Bohai Bay Basin were studied using core data, 3-D seismic data and well log data. Sandy debris flows, muddy debris flows, mud flows, turbidity currents, slides, sandy slumps and muddy slumps were interpreted based on the identification of lithofacies. Data indicates that deep-water sedimentary processes in the study area were dominated by debris flows and slumps, which accounted for ∼68% and 25% (in thickness) of total gravity flow deposits, respectively; turbidity-current deposits only accounted for ∼5%. Mapping of turbidites showed that most were deposited after short-distance transportation (<20 km), restricted by the scale of deep-water areas and local topography. Channels, depositional lobes, debris flow tongues, muddy turbiditic sheets, slides and slumps were identified in a delta-fed ramp system. Slides and slumps were dominant at the base of slopes or at the hanging walls of growth faults with strong tectonic activity. Channels and depositional lobes developed in gentle, low-lying areas, where sediments were transported longer distances. Sand-rich sediment supply, short-distance transportation and local topography were crucial factors that controlled sedimentation of this ramp system. Channels generally lacked levees and only produced scattered sandstones because of possible hydroplaning of debris flow and unstable waterways. In addition to lobes, debris flow tongues could also be developed in front of channels. These findings have significant implications for hydrocarbon exploration of deep-water sandstone fed by deltas in a lacustrine basin.
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The sedimentary architectures of submarine/sublacustrine fans are controlled by sedimentary processes, geomorphology and sediment composition in sediment gravity flows. To advance understanding of sedimentary architecture of debris fans formed predominantly by debris flows in deep-water environments, a sub-lacustrine fan (Y11 fan) within a lacustrine succession has been identified and studied through the integration of core data, well logging data and 3D seismic data in the Eocene Dongying Depression, Bohai Bay Basin, east China. Six types of resedimented lithofacies can be recognized, which are further grouped into five broad lithofacies associations. Quantification of gravity flow processes on the Y11 fan is suggested by quantitative lithofacies analysis, which demonstrates that the fan is dominated by debris flows, while turbidity currents and sandy slumps are less important. The distribution, geometry and sedimentary architecture are documented using well data and 3D seismic data. A well-developed depositional lobe with a high aspect ratio is identified based on a sandstone isopach map. Canyons and/or channels are absent, which is probably due to the unsteady sediment supply from delta-front collapse. Distributary tongue-shaped debris flow deposits can be observed at different stages of fan growth, suggesting a lobe constructed by debrite tongue complexes. Within each stage of the tongue complexes, architectural elements are interpreted by wireline log motifs showing amalgamated debrite tongues, which constitute the primary fan elements. Based on lateral lithofacies distribution and vertical sequence analysis, it is proposed that lakefloor erosion, entrainment and dilution in the flow direction lead to an organized distribution of sandy debrites, muddy debrites and turbidites on individual debrite tongues. Plastic rheology of debris flows combined with fault-related topography are considered the major factors that control sediment distribution and fan architecture. An important implication of this study is that a deep-water depositional model for debrite–dominated systems was proposed, which may be applicable to other similar deep-water environments.
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Lacustrine organic-rich shalesare well-developed within the Eocene Dongying Depression (DD) in the Bohai Bay Basin (BBB) in eastern China and across southeast Asia. Understanding the sedimentation of these shales is essential to the study of depositional processes, paleoenvironment and paleoclimate reconstruction. This study investigates the sedimentary characteristics and formation mechanisms of lacustrine shales in the upper fourth member of the Eocene Shahejie Formation (Es4s) within the DD based on thin sections and field emission scanning electron microscope (FESEM) observations of well cores combined with X-ray diffraction and geochemical indicators. Six lithofacies were identified: (1) laminated calcareous mudstone (LCM-1), (2) laminated dolomitic mudstone (LDM), (3) laminated clay mudstone (LCM-2), (4) laminated gypsum mudstone (LGM), (5) massive mudstone (MM), and (6) siltstone. The organic matter (OM) in the Es4s shale mainly comprises type I and type II kerogens, as well as a small proportion of type III kerogen. On the basis of lithofacies associations, paleosalinity values, redox properties, and terrigenous inputs, the Lower Es4s shale can be divided into six intervals from bottom to top, numbered I, II, III, IV, V, and VI. The thickness of each interval ranges from several meters to more than ten meters, reflecting high-frequency oscillations in the environment of the lake basin, markedly different from a relatively stable marine environment. The laminated mudstones are characterized by fine grain sizes, scarce large terrigenous debris (quartz and feldspar), and compositions that are rich in pyrite and sapropelic OM. These features indicate that these lithofacies were deposited out of suspension in a quiet waterbody characterized by a relatively low rate of deposition. The characteristics laminae of these lithofacies indicate the subtle differences of Manuscript Click here to download Manuscript Manuscript (Revision 3).docx 2 depositional process. The LGM was likely deposited in an evaporation environment as its formation would have consumed Ca2+ and SO4 2-, promoting the deposition of a LDM. In contrast, LCM-2 was deposited in a manner that increased the volumes of small terrigenous materials. Deposition of these lithofacies was comprehensively controlled by the nature of the water body, paleoclimate, and terrigenous inputs. Laminated mudstones are dominant in the Lower Es4s shale, suggesting that suspension was the main depositional process leading to formation of the Lower Es4s shale. In contrast, the MMs were likely rapidly deposited associated with siltstone as the result of fine-grained turbidites. The Lower Es4s shale was formed in a comprehensive depositional environment that comprised a saline, medium-depth lake, under anoxic conditions, and with limited terrigenous inputs. The depositional process included suspension and turbidity currents. The high salinity is suggested to be related to a marine transgression, which may be promoted by a rise in sea level caused by global warming in the early Eocene, together with the large-scale tectonic activity of East Asia. Seawater input affect the lithofacies, lake waterbody conditions, triggered turbidity currents, and the accumulation of OM. The deposition of Es4s shale in DD may help to understand the deposition of lacustine shale, paleoclimate reconstruction of Eocene and tectonic activity of East Asia.
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The Triassic Yanchang Formation contains the main oil-bearing strata in the Ordos Basin, central China. But the sedimentology of the Upper Triassic is still under debate, and flood-generated, hyperpycnal-flow deposits and their implications for unconventional petroleum development have long been overlooked. Our study indicates that hyperpycnites are well developed in the seventh oil member of the Yanchang Formation. They are characterized by couplets of upward-coarsening intervals and upward-fining intervals , separated by microscale erosion surfaces. The origination of hyperpycnal flows was controlled mainly by episodic tectonic movements and the humid climate. The deposits extend from distributary estuaries into the deep lake, have intercalations of dark shales and tuffs, and coexist with debrites and turbidites as a result of the progradation of subaqueous fans. The hyperpycnites have implications for unconventional petroleum reservoirs, because the flows supplied not only large amounts of coarse grains and organic material to the deep-water, fine-grained central lake sediments but also affected the ecosystems, resulting in a higher total organic carbon content in the sediments.
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Although recent work has shown that changing interstitial fluid density within turbidity currents is a frequently overlooked factor affecting the texture and internal architecture of turbidites, little is known about its influence on submarine fan morphology. Here we present the results of three-dimensional flume experiments of turbidity currents that clearly demonstrate the role of low-density interstitial fluid, in combination with sediment concentration and basin gradient, on submarine fan geometry. The experiments show that turbidity currents with reversing buoyancy, and their resulting deposits, are narrower than those that remain ground hugging. Furthermore, wider deposits result from increases in sediment concentration and/or basin-floor gradient. We also propose that Taylor-Gortler vortices associated with currents traveling over a break in slope may lead to the deposition of wider lobes compared with those traveling over a constant gradient.
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Rivers and turbidity currents are the two most important sediment transport processes by volume on Earth. Various hypotheses have been proposed for triggering of turbidity currents offshore from river mouths, including direct plunging of river discharge, delta mouth bar flushing or slope failure caused by low tides and gas expansion, earthquakes and rapid sedimentation. During 2011, 106 turbidity currents were monitored at Squamish Delta, British Columbia. This enables statistical analysis of timing, frequency and triggers. The largest peaks in river discharge did not create hyperpycnal flows. Instead, delayed delta-lip failures occurred 8–11 h after flood peaks, due to cumulative delta top sedimentation and tidally-induced pore pressure changes. Elevated river discharge is thus a significant control on the timing and rate of turbidity currents but not directly due to plunging river water. Elevated river discharge and focusing of river discharge at low tides cause increased sediment transport across the delta-lip, which is the most significant of all controls on flow timing in this setting.
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The Wollaston Forland Basin, NE Greenland, is a half-graben with a Middle Jurassic to Lower Cretaceous basin-fill. In this outcrop study we investigate the facies, architectural elements, depositional environments and sediment delivery systems of the deep marine syn-rift succession. Coarse-grained sand and gravel, as well as large boulders, were emplaced by rock-falls, debris flows and turbulent flows sourced from the immediate footwall. The bulk of these sediments were point-sourced and accumulated in a system of coalescing fans that formed a clastic wedge along the boundary fault system. In addition, this clastic wedge was supplied by a sand-rich turbidite system that is interpreted to have entered the basin axially, possibly via a prominent relay ramp within the main fault system. The proximal part of the clastic wedge consists of a steeply dipping, conformable succession of thick-bedded deposits from gravity flows that transformed down-slope from laminar to turbulent flow behaviour. Pervasive scour-and-fill features are observed at the base of the depositional slope of the clastic wedge, c. 5 km into the basin. These scour-fills are interpreted to have formed from high-density turbulent flows that were forced to decelerate and likely became subject to a hydraulic jump, forming plunge pools at the base of slope. The distal part of the wedge represents a basin plain environment and is characterised by a series of crude fining upward successions that are interpreted to reflect changes in the rate of accommodation generation and sediment supply, following from periodic increases in fault activity. This study demonstrates how rift basin physiography directly influences the behaviour of gravity flows. Conceptual models for the stratigraphic response to periodic fault activity, and the transformation and deposition of coarse-grained gravity flows in a deep water basin with strong contrasts in slope gradients, are presented and discussed.
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Liquefaction-induced soft-sediment deformation structures (SSDS) formed by earthquakes in southern Siberia, that were historically mentioned or monitored by instruments, are described and analyzed. Clastic dikes are the most common among all SSDS in the epicentral areas of the investigated seismic events. They are also the most reliable paleoseismic indicators in regions where cryogenic processes are intense. We suggest seven criteria that may be useful to distinguish the seismogenic clastic dikes from non-seismogenic SSDS in a single outcrop: (1) pushed up sedimentary blocks within the dike body; (2) regular distorted contacts of a dike with host sediments, reflecting cyclic loading during propagation of seismic waves; (3) turned up layers of host deposits on contacts with a dike; (4) displacement along dike contacts usually in the form of a normal fault caused by subsidence that compensates for the removed sediment; (5) a dike structure similar to a diapir; (6) filling of a clasic dike with coarser materials than the host sediments; and (7) a sediment layer extruded on the surface or between strata, similar in composition to the dike. In the extruded sandy-gravel-pebble layer, rock fragments show normal grading (from large to small clasts). In addition to these indicators, fractures may indirectly indicate the seismogenic genesis of liquefaction-induced SSDS. Due to the close spatial relationship of dikes with the fault structures of the investigated areas, they can be used to identify seismogenic fault, and the characteristics of dikes (lateral gradual changes in the frequency, size, and type of the deformations) can help to determine the epicenter, magnitude and the local intensity of the associated earthquakes.
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Turbidites in lacustrine sediments are commonly used to assess the frequencies of flood events and/or earthquakes. Understanding the origin of those deposits is key to adequately assess the sources and triggers of such events in large lacustrine systems. Ca/Ti X-ray fluorescence core scanner and magnetic susceptibility values on sediment cores of the deep basin of Lake Geneva are used as a provenance indicator of the turbidites either from the Dranse or Rhone deltas or from the slopes not influenced by deltaic input. This tool is validated by mineralogical analyses (X-ray diffraction), major-, and trace-element geochemistry (X-ray fluorescence). Based on this discrimination method, the turbidites deposited in the central part of the deep basin can be classified regarding their origin. From all identified turbidites, four turbidites are chosen based on their large depositional area and volumes and are studied in more detail in order to better understand the processes leading to turbidite deposition in the deep basin. The age intervals of these turbidites were compared to the historical records of extreme events in the region of Lake Geneva. These turbidites can be related to extreme floods, earthquakes, and “spontaneous” delta collapses. The cause of two turbidites could not be identified precisely due to large dating intervals that did not allow attributing a specific historical event to the turbidite layer. Overall, this study provides a tool in classifying the turbidites in deep Lake Geneva and exemplifies that defining the cause of turbidites is complex although it remains a prerequisite for paleohydrology and paleoseismology studies.
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Turbidite systems or submarine fans are considered the most important clastic accumulations in the deep sea and represent the sediment-transfer system between the hinterland source area and the deep-sea depositional sink. Their deposits contain information about global factors and local factors. Different scales and varying observational methods have contributed to the lack of a unifying terminology. In order to solve this problem several authors have proposed an “elemental approach”. The main architectural elements defining a turbidite system are: large-scale erosive features (mass-movements and canyons), channels and channel-fill deposits, overbank deposits and lobes. The sediment making up these elements is principally from gravity flow deposits, the most widely recognised being the turbidite, and other submarine mass movements. The genesis and character of these elements, as well as the overall geometry of the systems, indicate they are formed by a complex interaction between global and local factors. Various turbidite-system classifications are found in the literature, the most widely-used being based on grain size and feeder systems. Besides the scientific importance of turbiditic systems, they are predominantly studied because of the economic interest in them, as turbidite sandstones constitute important gas and oil reservoirs. Turbidite systems shape the seafloor of the Iberian continental margins and contribute in a large part to their outbuilding and basin infilling. They are hugely variable in size, location within the physiographic domains, style and overall geometry of the architectural elements, as well as sediment composition. The most studied Iberian turbidite fans are in the Mediterranean Sea whereas those of the Atlantic Ocean remain poorly known. © 2015, Instituto Geologico y Minero de Espana. All rights reserved.
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Rift basin tectono-stratigraphic models indicate that normal fault growth controls the sedimentology and stratigraphic architecture of syn-rift deposits. However, such models have rarely been tested by observations from natural examples and thus remain largely conceptual. In this study we integrate 3D seismic reflection data and biostratigraphically constrained core and wireline-log data from the Vingleia Fault Complex, Halten Terrace, offshore Mid-Norway to test rift basin tectono-stratigraphic models. The geometry of the basin-bounding fault and its hangingwall, and the syn-rift stratal architecture, vary along strike. The fault is planar along a large part of its length, bounding a half-graben containing a faultward-thickening syn-rift wedge. Locally, however, the fault has a ramp-flat-ramp geometry with the hangingwall defined by a fault-parallel anticline-syncline pair. Here, an unusual bipartite syn-rift architecture is observed, comprising a lower faultward-expanding and an upper faultward-thinning wedge. Fine-grained basinfloor deposits dominate the syn-rift succession, although isolated coarse-clastics occur. The spatial and temporal distribution of these coarse clastics is complex due to syn-depositional movement on the Vingleia Fault Complex. High rates of accommodation generation in the fault hangingwall led to aggradational stacking of fan deltas that rapidly (<5 km) pinch out basinward into offshore mudstone. In the south of the basin, rapid strain localisation meant that relay ramps were short-lived and did not represent major, long-lived sediment entry points. In contrast, in the north, strain localisation occurred later, thus progradational shorefaces developed and persisted for a relatively long time in relay ramps developed between unlinked fault segments. The footwall of the Vingleia Fault Complex was characterised by relatively low rates of accommodation generation, with relatively thin, progradational hangingwall shorelines developed downdip of the fault block apex, some time after the onset of sediment supply to the hangingwall. We show that rift basin tectono-stratigraphic models need modifying to take into account along-strike variability in fault structure and basin physiography, and the timing and style of syn-rift sediment dispersal and facies types in both hangingwall and footwall locations.This article is protected by copyright. All rights reserved.
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Magallanes-Austral Basin (MAB) fill is preserved along a >1000 km north-south trending outcrop belt in the southern Patagonia region of Argentina and Chile. Although the stratigraphic evolution of the MAB has been well documented in the Chilean sector (referred to as the Magallanes Basin), its northern terminus in southern Argentina (Austral Basin) is poorly constrained. We present new stratigraphic and geochronologic analyses of the early basin fill (Aptian-Turonian) from the Argentine sector (49-51°S) of the MAB to document spatial variability in stratigraphy and timing of deposition during the initial stages of basin evolution. The initiation of the retroarc foreland basin fill is marked by the transition from mudstone to coarse-clastic deposition, which is characterised by the consistent presence of sandstone beds > ca. 20 cm thick interpreted to represent sediment gravity flows deposited in a submarine fan system. Depositional environments within the early fill of the basin range from lower to upper deep-water fan settings as well as previously undocumented slope deposits. These facies are present as far north as El Chalten, Argentina (ca. 49°S), indicating that facies-equivalent rocks can be traced along-strike for at least 5 degrees of latitude, based on correlation with strata as far south as the Cordillera Darwin (ca. 54°S). Eight new U-Pb zircon ages from ash beds reveal an overall southward younging trend in the initiation of coarse clastic deposition. Inferred depositional ages range from ca. 115 ± 1.9 Ma in the northernmost study area to not older than 92 ± 1 Ma and 89 ± 1.5 Ma in the central and southern sectors respectively. The apparent diachronous delivery of coarse detritus into the basin may reflect (1) gradual southward progradation of a deep-water fan system from a northerly point source and/or (2) orogen-parallel variations in the timing and magnitude of thrust-belt deformation and erosion that provided more local sources for sediment delivery.
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The origin of massive sands in turbidite successions has commonly been attributed to the rapid dumping of sand due to flow unsteadiness in collapsing, single surge-type, high-density turbidity currents. The general applicability of this model is questioned, and it is proposed that rapid deposition of massive sands also occurrs due to non-uniformity in prolonged, quasi-steady high-density turbidity currents. -from Authors
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Recent studies of marine continental shelves show that hyperpycnal flows are responsible for offshore transport of large volumes of sediment. Detailed facies analysis and petrography of the lower Genesee Group in the Northern Appalachian Basin (NAB) shows a wealth of sedimentary textures and fabrics that indicate mud deposition by lateral transport across and along the shelf under energetic conditions. Intervals of silt-rich mudstones and muddy siltstones with internal scours, diffuse stratification, soft-sediment deformation, normal and inverse lamina-set grading, and a reduced intensity and diversity of bioturbation occur in multiple facies types and "interrupt" what appears to be the overall background sedimentation. These intervals and their sedimentary features are interpreted as products of high-density fluvial discharge events, which generated turbulent flows that carried fine-grained clastics several tens of kilometers offshore from the paleoshoreline. Recognizing these sediments as products of river-flood- and storm-wave-generated offshore-directed underflows challenges previous depositional models for organic-rich mudstones in the lower Genesee succession, which call for clastic starvation and suspension settling of clay and silt in a deep stratified basin. Rapid deposition of fine-grained intervals from hyperpycnal plumes in a setting favoring preservation of organic-rich mudstones calls for a reappraisal of the depositional setting of not only the Genesee Group, but also of comparable mudstone successions in the Appalachian Basin and elsewhere.
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Deep-water gravity flows are one of the most important sediment transport mechanisms on Earth. After 60 years of study, significant achievements have been made in terms of classification schemes, genetic mechanisms, and depositional models of deep-water gravity flows. The research history of deep-water gravity flows can be divided into five stages: incipience of turbidity current theory; formation of turbidity current theory; development of deep-water gravity flow theory; improvement and perfection of deep-water gravity flow theory; and comprehensive development of deep-water gravity flow theory. Currently, three primary classification schemes based on the sediment support mechanism, the rheology and transportation process, and the integration of sediment support mechanisms, rheology, sedimentary characteristics, and flow state are commonly used. Different types of deep-water gravity flow events form different types of gravity flow deposits. Sediment slump retransportation mainly forms muddy debris flows, sandy debris flows, and surge-like turbidity currents. Resuspension of deposits by storms leads to quasi-steady hyperpycnal turbidity currents (hyperpycnal flows). Sustainable sediment supplies mainly generate muddy debris flows, sandy debris flows, and hyperpycnal flows. Deep-water fans, which are commonly controlled by debris flows and hyperpycnal flows, are triggered by sustainable sediment supply; in contrast, deep-water slope sedimentary deposits consist mainly of debris flows that are triggered by the retransportation of sediment slumps and deep-water fine-grained sedimentary deposits are derived primarily from fine-grained hyperpycnal flows that are triggered by the resuspension of storm deposits. Harmonization of classification schemes, transformation between different types of gravity flow deposit, and monitoring and reproduction of the sedimentary processes of deep-water gravity flows as well as a source-to-sink approach to document the evolution and deposition of deep-water gravity flows are the most important research aspects for future studies of deep-water gravity flows study in the future.
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Subaqueous sandy mass-transport deposits (SMTDs), which are a type of sedimentary deposit formed in deep water environments, have attracted increased attention in recent years. Based on the analysis of outcrops, cores and thin sections using X-ray diffraction and scanning electron microscopy, numerous sandy mass-transport deposits or sandy debrites have been identified in the delta-front and deep lake environments recorded by the Chang 6-7 Member of the Yanchang Formation in the Ordos Basin; thus, a mass-transport model has been established in this paper. These sandy mass-transport deposits are characterized by two distinct features: first, sandstones are characterized by a low matrix content and are defined as massive clean sands; second, massive sandstones are characterized by the widespread development of a rimed chlorite cement with a two-layer structure, which is identical to that present in distributary channel sands of the delta-front environment of the Yanchang Formation. The occurrence of and components of clay minerals indicates that the isopachous rimed cements in the inner layer are related to the original sedimentary environment. Rimed chlorite cements are formed from isopachous clay films that originally adhered to the surfaces of the detrital particles and represent syn-depositional products. Further studies suggest that during the process of retransporting delta-front sediments and forming the sandy debris flows, this material, which was adhered to the surfaces of clastic particles as isopachous clay coatings, together with the small amount of clay-water matrix present in the flow, acted as an “adhesive agent” between particles during the subsequent remobilization of the deposits and the formation of sandy debris flows. The adhesion strength and local matrix support strength created by the clay-water matrix (gels), together with the frictional strength of the sediments, provided support strength for the subaqueous mass transport of the Yanchang Formation. The adhesion formed by the isopachous clay rim or the clay-water matrix is especially dominant and is considered to be the root cause holding the sandy debris flows together during their mass transport. This research may have global implications for better understanding analogous subaqueous mass-transport processes and the distribution of sandstone reservoirs in other locations.
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Hierarchical classifications are used in the field of clastic deep-marine sedimentary geology to assign spatial and temporal order to the sedimentary architecture of preserved deep-marine deposits and to genetically related modern landforms. Although such classifications aim to simplify the description of complex systems, the wide range of developed approaches limits the ease with which deep-marine architectural data derived from different sources can be reconciled and compared. This work systematically reviews and compares a selection of the most significant published hierarchical schemes for the description of deep-marine sedimentary architecture. A detailed account of each scheme is provided, outlining its aims, environmental contexts and methods of data collection, together with the diagnostic criteria used to discern each hierarchical order from observational standpoints (e.g., via facies associations, geometry, scale and bounding-surface relationships) and also on interpretational grounds (e.g., processes and sub-environments of deposition). The inconsistencies and pitfalls in the application of each scheme are also considered. The immediate goal of this review is to assist sedimentologists in their attempts to apply hierarchical classifications, both in the contexts in which the classifications were originally developed and in alternative settings. An additional goal is to assess the causes of similarities and differences between schemes, which may arise, for example, in relation to their different aims, scales of interest or environmental focus (e.g., channelized or lobate units, or both). Similarities are found between the approaches that commonly underlie the hierarchical classifications. Hierarchies are largely erected on the basis of common types of observations, in particular relating to the lithology and geometries of deposits, in association with analysis of bounding-surface characteristics and relationships. These factors are commonly considered in parallel with their associated genetic interpretations in terms of processes or (sub-) environments of deposition. A final goal of the review is to assess whether a universal standard for the description of deep-marine sedimentary architecture can be devised. Despite the commonalities that exist between classification approaches, a confident reconciliation of the different hierarchical classification schemes does not appear to be achievable in the current state of knowledge.
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The origin of the fourth member of the Eocene Shahejie Formation in the northern steep slopes of the Minfeng Sub-sag, Dongying Sag, China, was investigated by integrating core studies and flume tank depositional simulations. A non-channelized depositional model is proposed in this paper for nearshore subaqueous fans in steep fault-controlled slopes of lacustrine rift basins. The deposits of nearshore subaqueous fans along the base of steep border-fault slopes of rift basins are typically composed of deep-water coarse-grained sediment gravity-flow deposits directly sourced from adjacent footwalls. Sedimentation processes of nearshore subaqueous fans respond to tectonic activities of boundary faults and to seasonal rainfall. During tectonically active stages, subaqueous debris flows triggered by episodic movements of border-faults dominate the sedimentation. During tectonically quiescent stages, hyperpycnal flows generated by seasonal rainfall-generated floods, normal discharges of mountain-derived rivers and deep-lacustrine suspension sedimentation are commonly present. The results of a series of flume tank depositional simulations show that the sediments deposited by subaqueous debris flows are wedge-shaped and non-channelized, whereas the sediments deposited by hyperpycnal flows generated by sporadic floods from seasonal rainfalls are characterized by non-channelized, coarse-grained lobate depositional bodies which switch laterally because of compensation sedimentation of hyperpycanal flows. The hyperpycnal-flow-deposited non-channelized lobate depositional bodies can be divided into a main body and lateral edges. The main body can be further subdivided into proximal part, middle part and frontal part. Normal mountain-derived river-discharge-deposited sediments are characterized by thin-bedded, fine-grained sandstones and siltstones with a limited distribution range. Normal mountain-derived river-discharge-deposited sediments and deep-lacustrine mudstones are commonly eroded in the area close to boundary faults. A nearshore subaqueous fan can be divided into three segments: inner fan, middle fan and outer fan. The inner fan is composed of debrites and the proximal part of main body. The middle fan consists of the middle part of main body and lateral edges, normal mountain-derived river-discharge-deposited fine-grained sediments and deep-lacustrine mudstones. The outer fan comprises the frontal part of main body, lateral edges, and deep-lacustrine mudstones. Based on the non-channelized depositional model for nearshore subaqueous fans, criteria for stratigraphic subdivision and correlation are discussed and applied. This article is protected by copyright. All rights reserved.
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The lacustrine deep-water gravity-flow sandstone reservoirs in the third member of the Shahejie Formation are the main exploration target for hydrocarbons in the Dongying Sag, Eastern China. Carbonate cementation is responsible for much of the porosity and permeability reduction in the lacustrine deep-water gravity-flow sandstone reservoirs. The sandstones are mainly lithic arkose with an average framework composition of Q43F33L24. The carbonate cements are dominated by calcite, ferroan calcite, ankerite and a small amount of dolomite. The calcite and ferroan calcite are mainly poikilotopic blocky crystals, while the dolomite and ankerite are mainly euhedral rhombohedra crystals filling intergranular and intragranular pores. The relatively positive δ¹³C values (−2‰ to +3.9‰) of the carbonate cements in the sandstone reflect a mainly inorganically sourced carbon. From 32 Ma to 25 Ma, the pore water was rich in bicarbonate and Ca²⁺ due to carbonate dissolution in mudstone, and which were transported with the pore water from mudstone to sandstone via advection and precipitated calcite cementation in thinly bedded sandstones and some high permeability zones in the middle of medium-to-thick sandstone beds. From 12 Ma to present, abundant Ca²⁺, Fe³⁺, Fe²⁺, Mg²⁺ and bicarbonate had been transported from mudstone to sandstone via diffusion to form tight ferroan calcite cementation in the upper and lower parts of the medium-to-thick bedded sandstones. Ankerite is mainly distributed in the reservoirs associated with oil migration or charge, because change of Fe³⁺ to Fe²⁺ from oil charge may supply sufficient Fe²⁺ for ankerite precipitation. The center of sandstone beds (>0.6 m) is with potential of high-quality reservoirs in the research area. Carbonate cementation appears to be an important factor that controls the accumulation of oil in deep-water gravity-flow sandstone reservoirs in the study area.
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Deep lacustrine deposits provide records of palaeoclimate and tectonics, and often host major hydrocarbon reservoirs, but their facies description and long-term stratigraphic architecture are not sufficiently reported. A combined outcrop and three-dimensional seismic dataset in the western Dacian Basin of Romania is used to decipher depositional systems, basin fill architecture and clastic sediment dispersal across a narrow shelf. The lake clinoforms are about 400 m high in seismic images and all of their aggradational bottomsets total up to 350 m in thickness. Depositional elements and morphology of fluvial channels, delta lobe complexes, sublacustrine channel forms, sublacustrine canyons and deep-lacustrine lobes are interpreted on the seismic attribute maps. Outcrops show that sharp-based deltaic units contain thin delta front deposits. The slope succession is dominated by channel-levée thin-bedded turbidites with terrestrial debris. Thicker and coarser turbidites are founded in sublacustrine channels. The channelized sandstones on the slope are 10 to 25 m thick and often overlie tens of metre thick mass-transport deposits. Tabular turbidite beds, sandy-conglomeratic debrites with shallow-water fossils, mud-rich mass-transport deposits and hybrid event beds within fan lobes are found on the basin floor. The integrated seismic-outcrop analysis suggests that low accommodation on the narrow (10 to 30 km) morphological shelf and high sediment supply resulted in the prograding lacustrine shelf-margin clinoforms with fluvial-dominated topsets and significant sediment bypass to the deep-lacustrine. The late Miocene–Pliocene Dacian Basin provides a typical example of a supply (river) dominated basin margin and possible recognition criteria of deep-lacustrine clinothems including: fluvial dominated topset deposits with abrupt vertical facies changes, bottomset-dominated sediment partitioning, and frequent sediment gravity flow activities denoted by closely-spaced and aggradational channel-levée systems, thick bottomsets and rare indication of sediment starvation in the deep-lacustrine deposits.
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Sediment gravity flow deposits are common, particularly in sandy formations, but their origin has been a matter of debate and there is no consensus about the classification of such deposits. However, sediment gravity flow sandstones are economically important and have the potential to meet a growing demand in oil and gas exploration, so there is a drive to better understand them. This study focuses on sediment gravity flow deposits identified from well cores in Palaeogene deposits from the Liaodong Bay Depression in Bohai Bay Basin, China. We classify the sediment gravity flow deposits into eight lithofacies using lithological characteristics, grain size, and sedimentary structures, and interpret the associated depositional processes. Based on the scale, spatial distribution, and contact relationships of sediment gravity flow deposits, we defined six types of lithofacies associations (LAs) that reflect transformation processes and depositional morphology: LA1 (unconfined proximal breccia deposits), LA2 (confined channel deposits), LA3 (braided-channel lobe deposits), LA4 (unconfined lobe deposits), LA5 (distal sheet deposits), and LA6 (non-channelized sheet deposits). Finally, we established three depositional models that reflect the sedimentological characteristics and depositional processes of sediment gravity flow deposits: (1) slope-apron gravel-rich depositional model, which involves cohesive debris flows deposited as LA1 and dilute turbidity currents deposited as LA5; (2) non-channelized surge-like turbidity current depositional model, which mainly comprises sandy slumping, suspended load dominated turbidity currents, and dilute turbidity currents deposited as LA5 and LA6; and (3) channelized subaqueous-fan depositional model, which consists of non-cohesive bedload dominated turbidity currents, suspended load dominated turbidity currents, and dilute turbidity currents deposited as LA2–LA5, originating from sustained extrabasinal turbidity currents (hyperpycnal flow). The depositional models may be applicable to oil and gas exploration and production from sediment gravity flow systems in similar lacustrine depositional environments elsewhere.
Article
Erosion and deposition by supercritical density flows can strongly impact the facies distribution and architecture of submarine fans. Field examples from coarse-grained channel-levée complexes from the Sandino Forearc Basin (southern Central America) show that cyclic-step and antidune deposits represent common sedimentary facies of these depositional systems and relate to the different stages of avulsion, bypass, levée construction and channel backfilling. During channel avulsion, large-scale scours (18 to 29 m deep, 18 to 25 m wide, 60 to > 120 m long) were incised by supercritical density flows. The multi-storey infill of the large-scale scours comprises amalgamated massive, normally coarse-tail graded or widely spaced subhorizontally stratified conglomerates and pebbly sandstones, interpreted as deposits of the hydraulic-jump zone of cyclic steps. The large-scale scour fills can be distinguished from small-scale channel fills based on the preservation of a steep upper margin and a coarse-grained infill comprising mainly amalgamated hydraulic-jump zone deposits. Channel fills include repeated successions deposited by cyclic steps with superimposed antidunes. The deposits of the hydraulic-jump zone of cyclic steps comprise regularly spaced scours (0.2 to 2.6 m deep, 0.8 to 23 m long) infilled by intraclast-rich conglomerates or pebbly sandstones, displaying normal coarse-tail grading or backsets. These deposits are laterally and vertically associated with subhorizontally stratified, low-angle cross-stratified or sinusoidally stratified sandstones and pebbly sandstones, which were deposited by antidunes on the stoss side of the cyclic steps during flow re-acceleration. The field examples indicate that so-called spaced stratified deposits may commonly represent antidune deposits with varying stratification styles controlled by the aggradation rate, grain-size distribution and amalgamation. The deposits of small-scale cyclic steps with superimposed antidunes form fining-upwards successions with decreasing antidune wavelengths, indicating waning flows. Such cyclic step-antidune successions form the characteristic basal infill of mid-fan channels, and are inferred to be related to successive supercritical high-density turbidity flows triggered by retrogressive slope failures.
Article
Submarine lobe fringe deposits form heterolithic successions that may include a high proportion of hybrid beds. The identification of lobe fringe successions aids interpretation of paleogeographic setting and the degree of basin confinement. Here, for the first time, the sedimentological and architectural differences between frontal and lateral lobe fringe deposits are investigated. Extensive outcrop and core data from Fan 4, Skoorsteenberg Formation, Karoo Basin, South Africa, allow the rates and style of facies changes from axis to fringe settings of lobes and lobe complexes in both down-dip (frontal) and across-strike (lateral) directions to be tightly constrained over a 800 km2 study area. Fan 4 comprises three sand-prone divisions that form compensationally stacked lobe complexes, separated by thick packages of thin-bedded siltstone and sandstone intercalated with (muddy) siltstone, interpreted as the fringes of lobe complexes. Lobe-fringe facies associations comprise: i) thick-bedded structureless or planar laminated sandstones that pinch and swell, and are associated with underlying debrites; ii) argillaceous and mudclast-rich hybrid beds; and iii) current ripple-laminated sandstones and siltstones. Typically, frontal fringes contain high proportions of hybrid beds and transition from thick-bedded sandstones over length-scales of 1 to 2 km. In contrast, lateral fringe deposits tend to comprise current ripple-laminated sandstones that transition to thick-bedded sandstones in the lobe axis over several kilometers. Variability of primary flow processes are interpreted to control the documented differences in facies association. Preferential deposition of hybrid beds in frontal fringe positions is related to the dominantly downstream momentum of the high-density core of the flow. In contrast, the ripple-laminated thin beds in lateral fringe positions are interpreted to be deposited by more dilute low-density (parts of the) flows. The development of recognition criteria to distinguish between frontal and lateral lobe fringe successions is critical to improving paleogeographic reconstructions of submarine fans at outcrop and in the subsurface, and will help to reduce uncertainty during hydrocarbon field appraisal and development.
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Hybrid event beds, comprising clay-poor and clay-rich sandstone, are abundant in Maastrichtian-aged sandstones of the Springar Formation in the north-west Vøring Basin, Norwegian Sea. This study focuses on an interval, informally referred to as the Lower Sandstone, which has been penetrated in five wells that are distributed along a 140 km downstream transect. Systematic variations in bed style within this stratigraphic interval are used to infer variation in flow behaviour in relatively proximal and distal settings, although individual beds were not correlated. The Lower Sandstone shows an overall reduction of total thickness, bed amalgamation, sand to mud ratio and grain size in distal wells. Turbidites dominated by clay-poor sandstone are at their most common in relatively proximal wells, whereas hybrid event beds are at their most common in distal wells. Hybrid event beds typically comprise a basal clay-poor sandstone (non-stratified or stratified) overlain by banded sandstone, with clay-rich non-stratified sandstone at the bed top. The dominant type of clay-poor sandstone at the base of these beds varies spatially; non-stratified sandstone is thickest and most common proximally, whereas stratified sandstones become dominant in distal wells. Stratified and banded sandstone record progressive deposition of the hybrid event bed. Thus, the facies succession within hybrid event beds records the longitudinal heterogeneity of flow behaviour within the depositional boundary layer; this layer changed from non-cohesive at the front, through a region of transitional behaviour (fluctuating non- cohesive and cohesive flow), to cohesive behaviour at the rear. Further, spatial variation in the dominant type of clay-poor sandstone at the bed base suggests that the front of the flow remained non-cohesive, and evolved from high-concentration and turbulence-suppressed to increasingly turbulent flow; this is thought to occur in response to deposition and declining sediment fall out. This research may be applicable to other hybrid event bed prone systems, and emphasises the dynamic nature of hybrid flows.
Article
The aim of this study is to describe density-flow facies variability and interpret their flow evolution in a fresh-water rift-lake system. The data were collected from the 500-m- Thick Paleogene lacustrine oil-prone sourcerock succession penetrated by the Enreca-3 core-hole at the intersection of the Song Hong and the Beibuwan basins, Vietnam. The sedimentological data collected are supplemented with source-rock screening data to get an insight into the origin of mud in the density flows. A wide range of density-flow facies are recognized and can be assigned to turbulent, transitional, and laminar flow processes. The beds range from centimeter-scale, mudstone-rich beds to meter-scale cohesive debrites and hybrid beds. Similarly to the "classic" hybrid beds, the centimeter-scale beds are interpreted to record flow transformation and concentration. The hybrid bed motifs include essentially similar bed divisions (H1-H5; Haughton et al. 2009) to those described from marine basins. Moreover, transitional-flow facies are particularly common and include transitional current ripples and variously developed cyclic banding and lamination. These facies occupy a fixed position below and/or at plug-flow units in the bed motifs, suggesting that flow dynamics related to plug-flow development governed their development. Source-rock screening data show that most of the mudstone in hybrid beds represents lake-bottom and lake-margin mud, which was likely assimilated into the density flows along their path. Similarly, sedimentological data show common evidence for interaction between flow and the muddy lake floor such as sheared flame structures, deformed mud intrusions, and interbeds in turbidite facies. The assimilation of the lake-bottom mud into the density flows probably played a key role in modulating flow turbulence and explains the common occurrence of transitional-flow facies and indications of late-stage flow concentration in these strata.
Article
The deep lacustrine gravity-flow deposits are widely developed in the lower Triassic Yanchang Formation, southeast Ordos Basin, central China. Three lithofacies include massive fine-grained sandstone, banded sandstone, and massive oil shale and mudstone. The massive fine-grained sandstones have sharp upper contacts, mud clasts, boxed-shaped Gamma Ray (GR) log, but no grading and Bouma sequences. In contrast, the banded sandstones display different bedding characteristics, gradational upper contacts, and fine-upward. The massive, fine-grained sandstones recognized in this study are sandy debrites deposited by sandy debris flows, while the banded sandstones are turbidites deposited by turbidity currents not bottom currents. The sediment source for these deep gravity-flow sediments is a sand-rich delta system prograding at the basin margin. Fabric of the debrites in the sandy debris fields indicates initial formation from slope failure caused by the tectonic movement. As the sandy debris flows became diluted by water and clay, they became turbidity currents. The deep lacustrine depositional model is different from the traditional marine fan or turbidite fan models. There are no channels or wide lobate sand bodies. In the lower Triassic Yanchang Formation, layers within the sandy debrites have higher porosity (8–14%) and permeability (0.1–4 mD) than the turbidites with lower porosity (3–8%) and permeability (0.04–1 mD). Consequently, only the sandy debrites constitute potential petroleum reservoir intervals. Results of this study may serve as a model for hydrocarbon exploration and production for deep-lacustrine reservoirs from gravity-flow systems in similar lacustrine depositional environments.
Article
Subaquatic canyons are an important pathway for sediment transport into oceanic and lacustrine basins. Understanding the mechanisms governing their geomorphological evolution is a key to predict the sediment distribution patterns through these sediment conduits as well as to implement geo-hazard assessments. Submerged channels developed in large lacustrine basins offer a small-scale natural laboratory to understand the sedimentological processes operating in submarine channels. For this reason, a multidisciplinary research initiative -including time-lapse, high-resolution bathymetric surveys, innovative coring using submersibles, in situ geotechnical tests, and geophysical and sedimentological analyses-was applied to unravel the factors controlling the geomorphological evolution of the Rhone delta channels in Lake Geneva during the last decades. The morphology of the lacustrine Rhone Delta consists of a freshwater delta system deeply incised by nine canyons (C1single bondC9). Geotechnical measurements in proximal areas and sediment cores retrieved in the distal fans at the end of each canyon revealed complex sediment dynamics. No turbidity current events have occurred in the easternmost canyons (C1single bondC4) during the last decades while the western canyons sediment record (C5single bondC9) indicated repeated flushing events during the 20th century. The main “active” canyon C8 has been dominated by turbidite activity on the canyon floor with frequent overspill events along the levees. A large 6.2 × 106 m3 Mass-Transport Deposit (MTD) that resembles a debrite in its upper section was found in the distal area of the active channel. The MTD was dated at 1998–2000 CE and most likely originated from proximal delta areas affected by frequent slope failures of the steep channel walls. In situ geotechnical tests on the modern proximal channel floor showed an unconsolidated soft top-layer that might have served as a low-friction surface favouring the MTD long run-out distance to the distal part of the channel. The MTD has had a major effect morphological evolution of the distal channel by filling the existing conduit, indirectly promoting the formation of a new channel. The role of MTD emplacement in subaquatic channels has important implications for hydrocarbon exploration as they control channel avulsion processes and the location of sand-prone deposits. This study gives a detailed insight on poorly investigated short-term sedimentological dynamics that affect the long-term evolution of turbidite systems and channel migration processes. This detailed model of a river-dominated deep-lacustrine depositional system can be used as an analog for similar modern and ancient deep-water systems.
Article
This paper discusses the composition and distribution of soft-sediment deformation structures induced by lique-faction in Late Pleistocene lacustrine terrace deposits on the southern shore of Issyk-Kul Lake in the northern Tien Shan mountains of Kyrgyzstan. The section contains seven deformed beds grouped in two intervals. Five deformed beds in the upper interval contain load structures (load casts and flame structures), convolute lamination, ball-and-pillow structures, folds and slumps. Deformation patterns indicate that a seismic trigger generated a multiple slump on a gentle slope. The dating of overlying subaerial deposits suggests correlation between the deformation features and strong earthquakes in the Late Pleistocene.
Article
This study investigates Ionian Sea seismo-turbidite (ST) deposits that we interpret to be triggered by major historic earthquakes and tsunamis in the Calabrian Arc. ST beds can be correlated with the 1908 CE Mw 7.24 Messina, 1693 CE Mw 7.41 Catania, and 1169 CE Mw 6.6 Eastern Sicily earthquakes while two previously unknown turbidites might have been generated by the 1818 CE Mw 6.23 Catania and 1542 CE Mw 6.77 Siracusa earthquakes.
Article
The discovery of turbidites represents perhaps themajor genuine advance of sedimentology during the twentieth century. Turbidites are the deposits of turbidity currents and were originally related to the gravitational instability and re-sedimentation of previously accumulated shallow water sediments into deep waters. As these flows originate and entirely evolve within a marine or lacustrine basin, their associated deposits are here termed intrabasinal turbidites. Controversially, increasing evidences support that turbidity currents can also be originated by the direct discharge of sediment–water mixtures by rivers in flood (hyperpycnal flows). Since these flows are originated in the continent, their associated deposits are here termed extrabasinal turbidites. Deposits related to these two different turbidity currents are often confused in the literature although they display diagnostic features that allow a clear differentiation between them. Intrabasinal turbidites are mostly related to surge-like (unsteady) flows that initiate from a cohesive debris flow that accelerates along the slope and evolves into a granular and finally a turbulent flow. Its flow behavior results on the accumulation of normally graded beds and bedsets that lacks terrestrial phytodetritus and lofting rhythmites. Extrabasinal turbidites, on the contrary, are deposits related to fully turbulent flows having interstitial freshwater and sustained by a relatively dense and long-lived river discharge. According to the grain size of suspended materials, hyperpycnal flows can be muddy or sandy. Sandy hyperpycnal flows (with or without associated bedload) often accumulate sandy to gravelly composite beds in prodelta to inner basin areas. Their typical deposits show sharp to gradual internal facies changes and recurrence, with abundant plant remains. In marine waters, the density reversal induced by freshwater results in the accumulation of lofting rhythmites at flow margin areas. Muddy hyperpycnal flows are loaded by a turbulent suspension dominantly composed of a mixture of silt and clay-sized particles (b62.5 μm) of varying compositions. Since the suspended sediment concentration does not substantially decrease in waning flows, muddy hyperpycnal flows will be not affected by lofting, and the flow will remain attached to the sea bottom until its final accumulation. Typical deposits compose cm to dm-thick graded shale beds disposed over an erosive base with displaced marine microfossils and dispersed plant remains.
Article
Deep-water gravity-flow sandstones are important hydrocarbon exploration and production targets in the Bohai Bay Basin, a Paleogene intra-continental rift basin in eastern China. In this paper, the seismic-sedimentology techniques are used to characterize, in plan view, the temporal and spatial evolution of a gravity-flow-channel complex of the Paleogene Shahejie Formation (Es) on the Qinan faulted-monoslope (Qinan Slope), Bohai Bay Basin. The results show that two or three gravity-flow channels, 9–12 km long and 0.5–2 km wide, were successively developed in later Es (Es1z–Es1s). The channels initially experienced westward migration and then shifted eastward. The corresponding wireline logs of the channel-fill sequences mainly present blocky-shaped or bell-like configurations, whereas their seismic profile features are characterized by strong amplitude reflections, such as U-shaped, plate-like, spindle-shaped and lenticular configurations. The syndepositional activity of three normal faults, i.e., the Nandagang Fault to the northwest, the Zhangbei Fault to the northeast and the Zhaobei Fault to the east led to gradient changes of the Qinan Slope, which have controlled the plan morphology (width, curvature, and bifurcation) of the gravity-flow channels. In the medium-late period of Es1z, triggered by intensive faulting on the three faults, the gradient of the Qinan Slope was steepened abruptly, resulting in an increase of flow velocity and erosion amplitude to underlying deposits. As a result, channels exhibiting narrow and straight configurations in plan view were formed. During the stage of early Es1z and Es1s, tectonic activity intensity was relatively low and the gradient of the Qinan Slope was gentle, so channels with great width and curvature were bifurcated and merged downstream. Comparison of the faulting amplitude of the three syndepositional faults suggests that the Nandagang and Zhaobei faults were inversely strengthened in the Es1z and Es1s. The Nandagang Fault to the west was found to be more active than the Zhaobei Fault to the east in the Es1z stage. This condition was reversed in Es1s. For that reason, the channels migrated to the west in the Es1z stage and then went back to the east during Es1s. Core analysis shows that the channel fills are mainly composed of sandy-debrites, slumps and turbidites. Among them, sandy debrites dominate deposition in terms of reservoir volume and hydrocarbon potential. These units primarily consist of sandstones and gravel-bearing sandstones, with bed thicknesses ranging from 10 to 40 m, an average porosity of 11% and a permeability of 25 mD. Being mostly encased in organic-rich dark mudstones, these sandy debrites are significant hydrocarbon exploration targets. The results of this study are not only useful to the hydrocarbon exploration and development planning for the Qinan Slope, but also helpful when considering other faulted-depressions in the Bohai Bay Basin and other intra-continent rifted basins around the world, particularly in terms of gravity-flow hydrocarbon exploration and research.
Article
In this paper, we review the work presented at the AAPG-Shengli Petroleum Administration Research Symposium dealing with lacustrine basin exploration in China and southeast Asia. This meeting, held in the fall of 1995, revealed that there has been an expansion of the available knowledge base associated with these basins. This increase in information has resulted in a better understanding of lacustrine basin-fill properties and characteristics, even though many of the causal mechanisms for these properties have not yet been established. The many papers presented suggest that there are two primary causes for economic failure within many of these basins: 1) communication between source and reservoir and 2) the limited reservoir potential within the lacustrine sequence of these basins. More effective petroleum systems are found in basins where marine sandstones are in communication with lacustrine sources. The discussions also clearly demonstrated that lacustrine basins are sensitive to environmental changes, causing complex sedimentary facies successions. Each facies, however, displays unique characteristics that can be mapped. Several presenters also suggested that within extensional lacustrine settings the stratigraphic succession follows a distinct pattern. Although most of these basins are predominantly oil prone, several lacustrine basins within the region contain significant volumes of gas. Included within these gas reserves are biogenic accumulations that appear to have formed nearly penecontemporaneously with deposition. Recent work on several of the Chinese basins suggests the possibility for immature hydrocarbon generation and expulsion in a manner different than that associated with marine type II-S kerogens. Even with the progress that this symposium revealed there are several key questions that remain, including questions associated with how technology might be used to improve the economics of many of these systems that display limited reservoir potential.
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Huge landslides, mobilizing hundreds to thousands of km3 of sediment and rock are ubiquitous in submarine settings ranging from the steepest volcanic island slopes to the gentlest muddy slopes of submarine deltas. Here, we summarize current knowledge of such landslides and the problems of assessing their hazard potential. The major hazards related to submarine landslides include destruction of seabed infrastructure, collapse of coastal areas into the sea and landslide-generated tsunamis. Most submarine slopes are inherently stable. Elevated pore pressures (leading to decreased frictional resistance to sliding) and specific weak layers within stratified sequences appear to be the key factors influencing landslide occurrence. Elevated pore pressures can result from normal depositional processes or from transient processes such as earthquake shaking; historical evidence suggests that the majority of large submarine landslides are triggered by earthquakes. Because of their tsunamigenic potential, ocean-island flank collapses and rockslides in fjords have been identified as the most dangerous of all landslide related hazards. Published models of ocean-island landslides mainly examine ‘worst-case scenarios’ that have a low probability of occurrence. Areas prone to submarine landsliding are relatively easy to identify, but we are still some way from being able to forecast individual events with precision. Monitoring of critical areas where landslides might be imminent and modelling landslide consequences so that appropriate mitigation strategies can be developed would appear to be areas where advances on current practice are possible.
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Based on cores and logging data, and gravity flow theory, the sedimentary characteristics and facies model of gravity flow deposits in the Longdong area in southwestern Ordos Basin were analyzed. Five types of gravity flow deposits are recognized: slides, slumps, sandy debris flows, muddy debris flows and turbidity currents. Affected by multiple provenances, paleogeomorphology and triggering mechanisms jointly, the gravity flows resulted in sublacustrine fans and slump olistoliths in the basin center. Containing channels, the sublacustrine fans can be divided into three subfacies, inner fan, middle fan and outer fan and subdivided into six microfacies, main channel, main channel lateral margin, distributary channel, distributary channel lateral margin, inter-channel and sheeted turbidite sand. It is inferred that they are caused by seasonal floods. The slump olistoliths, with no channels, consist four parts: slide rock, slump rock, debris flow lobe and sheeted turbidite sand, and are inferred to be the product of collapse of break belts triggered by events like earthquakes. Combining facies models with types of gravity flow deposits can reveal the sedimentary characteristics and genetic models of gravity flow deposits in deep water more directly and provide theoretical basis for deep water oil and gas exploration.
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Common facies models of turbidite deposits are based on idealized sequences of turbidite units, which are assumed to reflect the depositional processes of a decelerating turbidity current. We show how suites of turbidite units, i.e., distinct turbidite facies associations that are easily described from core and outcrop, may characterize the entire range of large-scale dynamics of turbidity currents, enabling estimates of their densimetric Froude number (Fr; subcritical versus supercritical) and suspension fall-out rate (stratified versus nonstratified flows). The linking of facies associations with large-scale flow dynamics resolves process-facies links that were hitherto unresolved by the common turbidite facies models.
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The channel-lobe transition zone (CLTZ) is an important, but commonly overlooked, element of many deep-water turbidite systems. Recognizing this zone is difficult in both modern and ancient environments and depends largely on the quality and resolution of the data obtained. In this article, three case studies of modern CLTZs are presented, largely based on high-resolution side-scan sonar imagery. These data are then compared to other well-defined CLTZs; both modern and ancient, and the common characteristics identified. CLTZs occur at canyon/channel mouths and are commonly associated with a break of slope. Most sediment bypasses this zone, and consequently only coarse sands and gravels are deposited, although these are commonly patchily distributed and extensively reworked. The CLTZ is characterized by abundant erosional features, including isolated spoon- and chevron-shaped scours up to 20 m deep, 2 km wide, and 2.5 km long. In areas of more widespread erosion, these merge to form amalgamated scours several kilometers across. Depositional bed forms include sediment waves with wavelengths of 1-2 km and wave heights up to 4 m. The presence or absence of a CLTZ has important implications for hydrocarbon exploration and development, especially in terms of the connectivity between sandy channel-fill and lobe facies.
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The Holocene turbidite systems of Lake Kivu and the Pliocene turbidite systems of Lake Albert in the East African Rift were examined using high-resolution 2-D and 3-D seismic reflection data and sediment core information. Based on investigations of seismic facies and lithofacies, several key turbidity-flow depositional elements were observed, including channels, overbank levees with sediment waves, and depositional lobes. Analyses of the sources of the recent and ancient turbidite systems in these two extensional basins suggest that flood-induced hyperpycnal flows are important triggers of turbidity currents in these lacustrine rift basins. From source to sink, sediment dispersal, facies distribution, and depositional thickness of the turbidite systems are strongly influenced by rift topography. The Lake Kivu and Lake Albert rifts serve as excellent analogues for understanding the sedimentary patterns of lacustrine turbidites in extensional basins.
Article
Investigations on turbidite sandstones are mostly confined to marine deep-water systems with only limited information available on those developed in lacustrine environments. In this paper, we document the characteristics and distribution of a previously unrecognized sequence of lacustrine turbidite sandstones from the Dongying Sag in the Bohai Bay Basin, North China Craton. The Eocene Shahejie Formation in the Dongying Sag has been previously interpreted as a shallow lacustrine deposit, such as a deltaic system, with delta-front to sag and back-barrier environments. However, the numerous sandstone layers associated with the third member (Es3) of the Shahejie Formation define an integrated deep-water turbidite system. Analysis of the characteristics of lithofacies, seismic facies and wire-line logs of the sandstone layers has been undertaken, as well as investigation of the distribution characteristics and the factors governing the development of these sandstones. The results from our study show that the development of this turbidite sequence was controlled by a number of parameters including sediment supply, accommodation of the sag, palaeo-topography, hydrodynamics, scale and formation of the delta, subsidence rate of the sedimentary basin, and tectonic activity associated with the Jiyang Movement during the Cenozoic destruction of the North China Craton. Copyright © 2013 John Wiley & Sons, Ltd.