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Abstract
The Shulu subbasin lying in the southwestern part of the Jizhong depression is a typical single-downfaulted subbasin in an extensional system. Its structure is simple with a NE extensional fault system and a NW-trending transverse accommodation zone. Based on the evolutionary history and drilling well data of the subbasin, this paper discusses the mechanism and time of formation of this transverse accommodation zone and proposes that the first-order accommodation zone formed in a stage of strong extension of the subbasin, while the second-order accommodation zone formed in a stage of weak extension of the subbasin. The formation of the first-order transverse accommodation zone is controlled by inhomogeneous extension of the boundary fault and basement uplift, the deference in lithologie association is the trigger mechanism of the second-order transverse accommodation zone, and the alternating development of en-echelon faults that control the subbasin is the dynamic mechanism of formation of the second-order transverse accommodation zone.
... Multiple seismites were identified based on the cores in the lake basin (Zheng et al., 2015) and the adjacent basin (Jinxian Sag) (see Fig. 2A for location) (Yang et al., 2014). The activity of the Taijiazhuang Fault and Jinqiu Fault may have caused these paleo-seismic events, and their growth indices range from 1.1 to 1.8, and from1.3 to 1.9, respectively (Kong et al., 2005;Zheng et al., 2015). ...
... It is difficult to track the extended field of deformation phenomena because the research in the Shulu Sag is based on cores. However, abundant soft-sediment deformation phenomena in Shulu Sag are related to seismic shaking: (1) nearly all the wells contain seismite-like structures (Zheng et al., 2015), (2) the adjacent basin (Jinxian Sag) (see Fig. 2A for location) has similar sedimentary structures (Yang et al., 2014), (3) the deformed sedimentary layers are positioned between undisturbed layers (Fig. 11), (4) the deformation phenomena include brittle and plastic deformations, which can be considered as a common feature that developed during earthquakes (Rossetti and Góes, 2000), and (5) the activities of the boundary fault and intrabasinal faults control the evolution of the basin and influence the distribution and deformation of the sediments (Kong et al., 2005). Therefore, strong seismic activity was considered to exist in the Shulu Sag, as confirmed by the activity curve of Es 3 L , which was proposed by Zheng et al., (2015). ...
... Many studies have been done on the sequences, sedimentary characteristics, structural disturbances, reservoir characteristics and the formation of rudstone in the Shulu sag, and a series of important results have been obtained Zhao et al., 2014a, b;Jin et al., 2008;Jiang et al., 2007;Liang et al., 2007;Qiu et al., 2006;Kong et al., 2005;Cui et al., 2003;Wu et al., 2001). Different opinions exist in terms of the depositional environments or formation processes of the conglomerates; the possibilities include fan delta, debris flows and landslides. ...
... Fan delta systems can develop on the gentle slopes that develop in the expansion stages of basins (Wang, 1993). During the early stage of deposition of the Es3, the Shulu sag rifted strongly, and the eastern portion of the Ningjin uplift (that is, the western slope of the Shulu sag) dipped (Kong et al., 2005). This area contains the geomorphological features of a large slope and a narrow ramp (Cui et al., 2003). ...
Based on observations made on cores and cuttings from several wells in the lowermost part of the third member of the Shahejie Formation, several rock types, specifically clast-supported rudstone, matrix-supported rudstone, mixed-source rudstone, calcisiltite/calcarenite, massive calcilutite and laminated calcilutite, have been identified in the Shulu sag. According to the sedimentary structures and distribution characteristics of these rocks, the carbonate breccias fall into two categories, based on their origins: one formed by fan-delta channel sedimentation, whereas the other formed by earthquake-induced slump fan deposition. Clast-supported rudstone and matrixsupported rudstone are the main lithologies deposited by braided rivers in the fan delta plain and front, of which the pore space is mainly dissolution pores within gravels and tectonic fissures. Clastsupported rudstone, matrix-supported rudstone and mixed-source rudstone are the main lithologies of the earthquake-induced slump fans. These carbonate breccias developed along with soft-sediment deformation structures, which are interpreted as seismites and are widely distributed in the sag, in which intercrystalline pores, intergranular pores and fissures created from diagenetic shrinkage are developed. The two kinds of rudstones have different reservoir characteristics and oil/gas testing results. The rudstones generated in the fan delta have higher porosity and permeability, as well as better oil/gas testing results. Thus, they are key targets for petroleum exploration.
... During deposition of the Shahejie 3 member, the NW-trending Taijiazhuang fault growth index was from 1.1 to 1.8 and the NNE-trending Xinhe fault growth index was 1.3-1.9 (Kong et al., 2005). Some synsedimentary faults developed along the western slope of the depression, showing consequent normal faulting along a NE trending zone (Fig. 2B). ...
... (v) Similar SSDSs have been reproduced in the laboratory through the modeling of earthquake effects in water-saturated soft sediments (Owen, 1996;Moretti et al., 1999). (vi) Growth indices of the nearby NW-trending Taijiazhuang fault and the NNE-trending Xinhe fault during the third member of the Shahejie Formation (Kong et al., 2005) indicate that these faults could have controlled the topographic relief within the basin and exerted a great influence on the distribution of sediment and its deformation. ...
The Shulu Sag, located in the southwestern corner of the Jizhong Depression, Bohai Bay Basin of east China, is a NE-SW trending, elongate Cenozoic half-graben basin. The lowermost part of the third member of the Shahejie Formation in this basin is characterized by continental rudstone and calcilutite to calcisiltite facies. Based on core observation and regional geologic analysis, seismites are recognized in these lacustrine deposits, which include soft-sediment deformation structures (sedimentary dikes, hydraulic shattering, diapir structures, convolute lamination, load-flame structures, ball-and-pillow structures, loop bedding, and subsidence structures), synsedimentary faults, and seismoturbidites. In addition, mixed-source rudstones, consisting of the Paleozoic carbonate clasts and in situ calcilutite clasts in the lowermost submember of Shahejie 3, appear in the seismites, suggesting an earthquake origin. A complete representative vertical sequence in the lowermost part of the third member found in well ST1H located in the central part of the Shulu Sag shows, from the base to the top: underlying undeformed layers, synsedimentary faults, liquefied carbonate rocks, allogenetic seismoturbidites, and overlying undeformed layers. Seismites are widely distributed around this well and there are multiple sets of stacked seismites separated by undeformed sediment. The nearby NW-trending Taijiazhuang fault whose fault growth index is from 1.1 to 1.8 and the NNE-trending Xinhe fault with a fault growth index of 1.3-1.9 may be the source of the instability to create the seismites. These deformed sedimentary layers are favorable for the accumulation of oil and gas; for example, sedimentary dikes can cut through many layers and serve as conduits for fluid migration. Sedimentary faults and fractures induced by earthquakes can act as oil and gas migration channels or store petroleum products as well. Seismoturbidites and mixed-source rudstones are excellent reservoirs due to their abundant primary or dissolved pores.
... The Shulu Sag is located in the southern Jizhong Depression of the Bohaiwan Basin ( Figure 1). It is a fault basin formed during the Eocene and has a pre-Paleozoic to Paleozoic basement [21]. The Eocene-Oligocene sediments of the Kongdian Fm and Shahejie Fm in the Shulu Sag mainly consist of mud, marl, mud-bearing gypsum, and halite ( Table 1). ...
The centimeter-scale halite rhythmites in the first member of the Shahejie Formation in the Shulu Sag of the Bohai Bay Basin are investigated, and the Eocene to early Oligocene paleoenvironmental characteristics of a typical saline lake basin are restored by reconstructing the temperature and compositional information of ancient brines. The obtained homogenization temperatures (Th) of fluid inclusions range from 6.5 to 49.2 °C, with a relative lower Th from transparent halite samples than from gray halite samples. This suggests different temperature conditions and a probable association with seasonal changes. The ion contents of halite fluid inclusions reveal the lake brine is a Na-Mg-K-Ca-Cl type and reached the initial stage of halite deposition. The transparent halite samples plotted within different phase regions than the gray halite samples on plots of ion contents and showed significant change within phase regions. Combined with the observed cm-scale rhythm in the evaporite sequences of the Shulu Sag, these results suggest a shallow water environment and frequent dilution by inflows of fresher water caused by seasonal climate change. The gray halite formed under higher temperatures and increased inflow conditions, and the transparent halite formed under lower temperatures and decreased inflow conditions. Compared with the Jiangling Sag in Hubei Province in southern China, the Shulu Sag may have been less affected by igneous rocks in the Es1 Formation due to the material source, and the concentration of trace elements such as lithium, strontium and boron in the ancient salt lake brine was lower.
... Numerous studies have been carried out to understand the formation of accommodation zones (Bosworth, 1985;Colletta et al., 1988;Langhi and Borel, 2008;Tesfaye et al., 2008). Fault systems that form accommodation zones in rifts are genetically related faults formed at approximately the same time (Coffield, 1987;Ebinger, 1989;Farhoud, 2009;Faulds et al., 1990;Kong et al., 2005). In the study area, the northern fault system (Zone 1) created multiple E-dipping faults that dip in an opposite direction to faults in Zone 3, with an E-trending accommodation zone separating these two zones (Fig. 3). ...
A high-quality 3D seismic volume from offshore Espírito Santo Basin (SE Brazil) is used to assess the importance of gravitational collapse to the formation of crestal faults above salt structures. A crestal fault system is imaged in detail using seismic attributes such as curvature and variance, which are later complemented by analyses of throw vs. distance (T-D) and throw vs. depth (T-Z). In the study area, crestal faults comprise closely spaced arrays and are bounded by large listric faults, herein called border faults. Two episodes of growth are identified in two opposite-dipping fault families separated by a transverse accommodation zone. Statistical analyses for eighty-four (84) faults show that fault spacing is < 250 m, with border faults showing the larger throw values. Fault throw varies between 8 ms and 80 ms two-way time for crestal faults, and 60–80 ms two-way time for border faults. Fault length varies between ∼410 m and 1750 m, with border faults ranging from 1250 m to 1750 m. This work shows that border faults accommodated most of the strain associated with salt growth and collapse. The growth history of crestal faults favours an isolated fault propagation model with fault segment linkage being associated with the lateral propagation of discrete fault segments. Importantly, two episodes of fault growth are identified as synchronous to two phases of seafloor erosion, rendering local unconformities as competent markers of fault reactivation at a local scale. This paper has crucial implications for the understanding of fault growth as a means to assess drilling risk and oil and gas migration on continental margins. As a corollary, this work demonstrates that: 1) a certain degree of spatial organisation occurs in crestal fault systems; 2) transverse accommodation zones can form regions in which fault propagation is enhanced and regional dips of faults change in 4D.
... Li et al., 2010b;Suo et al., 2015), and the aforementioned NNE-to NE-trending faults were inverted to normal faults, accompanied by the development of numerous new normal faults and extensive magmatism, further facilitating the development of a series of sags in the Bohai Bay Basin, such as the Beijing, the Wuqing, the Shijiangzhuang, the Jinxian, the Shulu, the Linqing and the Huanghua sags. Coevally, a series of WNW-trending faults transverse structures such as the Niutuozhen-Baodi (Fig. 2, I 1 ), the Xushui-Wen'an ( Fig. 2, I 2 ), and the Hengshui (Fig. 2, I 3 ) transverse structures (Fig. 2, I 3 ), gradually formed, which progressively divided the NNCP into four areas (Kong et al., 2005). Since then, the NNCP experienced spacevariable uplifting or subsiding. ...
Following the collecting and analyzing of field data on the geometry and kinematics characteristics of ground fissures in the northern North China Plain (NNCP), this paper shows that en échelon ground fissures or tectonic ground fissures with a length of several meters to tens of kilometers extending along active faults are possibly controlled by underlying active faults. There are two groups of tectonic ground fissures developed in the NNCP. One group consists of ENE-trending “right-stepping” ground fissures, some of which have a component of sinistral motion. The other group is NNE-trending “left-stepping” ground fissures with dextral motion. A large amount of data from trenches, boreholes and seismic exploration reflect that they are active-faulting-related. The NNW-trending regional extensional stress field and the reactivation of pre-existing faults are the major factors controlling ground fissures. Data from the Quaternary sedimentary records, deep incised valleys, the distribution of earthquakes and ground fissures, and our field work show that the Holocene intracontinental deformation of the NNCP is characterized by intense faulting and northwestward tilting, which may be related to a NNW-SSE-oriented tensional stress field in the shallow crust and asthenospheric upwelling in the mantle.
... The Shulu Sag is located on the southern edge of the Jizhong Depression of the Bohai Bay Basin (North China), and surrounded by the Hengshui and Xinhe Faults on its northern and eastern margins, and the Ningjin and Xiaoniuchun uplifts along its western and southern margins (Fig. 1). It is a typical half graben-like fault basin 26,27 formed during the Eocene. Halite samples were collected from drill core in the southern Shulu Sag (Fig. 1) and preserved well since there were few volcanic thermal fluid events during the Paleogene to Neogene 28 . ...
Climate changes within Cenozoic extreme climate events such as the Paleocene-Eocene Thermal Maximum and the First Oligocene Glacial provide good opportunities to estimate the global climate trends in our present and future life. However, quantitative paleotemperatures data for Cenozoic climatic reconstruction are still lacking, hindering a better understanding of the past and future climate conditions. In this contribution, quantitative paleotemperatures were determined by fluid inclusion homogenization temperature (Th) data from continental halite of the first member of the Shahejie Formation (SF1; probably late Eocene to early Oligocene) in Bohai Bay Basin, North China. The primary textures of the SF1 halite typified by cumulate and chevron halite suggest halite deposited in a shallow saline water and halite Th can serve as an temperature proxy. In total, one-hundred-twenty-one Th data from primary and single-phase aqueous fluid inclusions with different depths were acquired by the cooling nucleation method. The results show that all Th range from 17.7°C to 50.7°C,with the maximum homogenization temperatures (ThMAX) of 50.5°C at the depth of 3028.04 m and 50.7°C at 3188.61 m, respectively. Both the ThMAX presented here are significantly higher than the highest temperature recorded in this region since 1954and agree with global temperature models for the year 2100 predicted by the Intergovernmental Panel on Climate Change.
The Shulu Sag which is a rifted sag with NNE trend is located in the south of Jizhong Depression, Bohai Bay Basin, northern China. The gentle slope and three troughs are situated in the west and east of the sag, respectively. Both of the lower part of Shasan Member (Es3x) and the lower part of Shayi Member (Es1x) act as source rocks in this sag. Researches on the type, quantity, quality and thermal maturity of the respective organic matter have been conducted using Rock-Eval pyrolysis data. Type II is the dominant kerogen in Es1x of all troughs. However, Type II1 and III is the dominant kerogen in Es3x of Middle-Southern and Northern trough, respectively. TOC (total organic carbon) and pyrolysis S2 (hydrocarbon) values suggest that the Es1x source rocks in Middle-Southern and Northern trough are fair to good and poor to fair generative potential of hydrocarbon, separately. The Es3x source rocks in Middle-Southern and Northern trough possess fair to excellent and poor to fair generative potential of hydrocarbon, individually. Tmax (pyrolysis temperature at maximum S2) values indicate that most of Es3x samples are thermally mature, but all Es1x samples are thermally immature. Under large scale condition, the hydrocarbon secondary migration in the upper part of Shasan Member (Es3s), Shaer Member (Es2) and the upper part of Shayi Member (Es1s) have been simulated using fluid potential model with Arcgis 9.3 software. The simulation results reveal the direction of hydrocarbon secondary migration and the distribution of hydrocarbon migration-accumulation units (HMAUS), and also suggest that the hydrocarbon migration direction is obviously controlled by nose-like structure belts where most of hydrocarbons accumulate. That shows high reliability because they are consistent with the hydrocarbon exploration result in this area. On the basis of integrated analyses of source rocks and hydrocarbon migration direction, the following five areas in the gentle slope are identified to be the preferred hydrocarbon accumulation area: Taijiazhuang area, northern and southern Xicaogu area, as well as northern and southern Leijiazhuang area. It is considerably helpful to reduce the risk in hydrocarbon exploration of Shulu Sag.
The Shulu Sag is located in the southwestern corner of the Jizhong Depression, Bohai Bay Basin of East China. The lower part of the Shahejie Formation developed massive conglomerate characterized by low porosity and low permeability with carbonate fragment as its main constituent. According to the sedimentary structure and distribution characteristics, etc., the carbonate breccia may fall into two genetics: one formed by fan-delta channel sedimentation, whereas the other is formed by earthquake-induced slump fan deposition. The braided river is the main sedimentary body of the fan delta and the typical characteristics are imbricate structures with normal graded bed sequence. The latter appears along with typical seismites widely distributed in the sag, which include soft sediment deformation structures (sedimentary dikes, hydraulic shattering, etc.), and brittle deformation (synsedimentary faults).
A large amount of primary single-phase aqueous fluid inclusions and secondary petroleum inclusions are discovered in the halite in the first member of Palaeogene Shahejie Formation in Shulu depression, which facilitates the determination of the origin of evaporite and the migration and preservation conditions of oil and gas. In this paper, the formation time and the trapping paleopressure of fluid inclusions and the burial history of oil and gas are analyzed by linking the homogenization temperature of both the primary single-phase aqueous fluid inclusions and secondary petroleum inclusions with the petrography of halite. As the results, the homogenization temperature of the aqueous inclusion, which is symbiosis with the petroleum inclusions, ranges from 66.5 to 91.5℃ and 103.7 to 108.9℃, respectively. The trapping time of the former is about 10.56 to 10.11 Ma and the trapping time of the latter is about 1.10 Ma. It is concluded that the time of oil and gas fluid entering into the salt rock is about the middle-late Guantao Formation and Pleistocene, which is also evidenced by the investigation of the oil and gas generation history. The paleopressure coefficient of the middle part of the salt rock modeled by fluid inclusions is up to 1.64, suggesting that there existed a hyperpressure system under the salt rock which probably facilitated the migration and preservation of oil and gas.
On the basis of the previous classification research, the features of transfer structure in Bohai Bay Basin were analyzed. The transfer structures in Bohai Bay Basin can be divided into two styles of transfer zone and transfer fault according to the connection or non-connection status. The transfer structure in Bohai Bay Basin is mainly exhibited in the style of transfer zone, especially in basin or depression, while the transfer fault only militates in the sag-control level. With the occasional development of transfer fault, most of high-level transfer zones are horizontally connected with different relay ramps. These strike transfer structures in NWW-NW direction are the most important structure styles to control the ″north-south segmentation″ tectonic framework in Bohai Bay Basin. The difference of oil and gas reserves in Bohai Bay Basin is related to the distribution of prolific hydrocarbon depressions and sags controlled by transfer structure. The paleotopography and rich-sand drainage channels controlled by transfer structure are favorable to the formation of lithologic reservoirs. The adjacent zones of the transfer structure are the important regions for finding the buried-hill structure reservoirs.
The Shulu Sag is a typical rift valley basin in Eastern China, where the formation mechanism of Cenozoic salt-bearing series has been poorly understood. In this paper, petrologic analysis, X-ray powder Diffraction (XRD) analysis and the analysis of halite ion concentrations of the first member of the Shahejie Formation from two drilling cores were conducted to interpret the formation mechanism of these salt-bearing series in Shulu Sag. The results indicated that the salt-bearing series is mainly composed of calcilutite or mudstone at top and bottom, and anhydrite-bearing halite and thin interbeds of salt-bearing calcilutite and dark grey shale in the middle part. These thin interbeds with porphyritic or petalshaped glauberite crystals or some thinner dark grey shale interbeds separated halites into several members with the average thickness of only 9~12 cm in the two drilling holes. This typical rhythmic pattern due to frequent alternation of concentration was evidenced by the variation of chemical composition and hydrogen isotopes of halite fluid inclusions. The presence of large number of primary fluid inclusions within chevron crystals and vertically oriented bottom-growth crystals showed that the halite were precipitated in shallow water (