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The influence of hyperpycnal flows on the salinity of deep-marine environments, and implications for the interpretation of marine facies
Abstract
Interpretation of the continental or marine character of sediments on the basis of the paleosalinity is increasingly based on the concentration of some trace elements. The paleosalinity can be affected, however, also in deep-marine environments, by discharge peaks of major sediment-laden rivers. These induce hyperpycnal flows that run down the basin slope. The huge volume of fresh water gradually mixes with the ambient saline seawater, diminishing the paleosalinity. The temporary lowered paleosalinity may be preserved in the sedimentary record in the form of ‘diverging’ concentrations of trace elements and trace-element ratios. This is exemplified for the Early Cretaceous Lingshandao Formation on Lingshan Island (western Yellow Sea). It was found during field work and geochemical analysis that hyperpycnal currents may not only lower the salinity of a deep-marine environmental setting, but may also carry along continental plant fragments and other biological remains, which may obscure the marine character of the sediments. It is deduced that detailed facies analysis in the field is consequently required to reveal the true character of a marine environment.
... Deep lacustrine facies were deposited in the centre of the basin, while shallow lake sediments were deposited in the southern part, and sub-lacustrine fan deposits were deposited in the northern part (Feng et al., 2006;Feng, Jia, et al., 2010;. Based on the analysis of high-resolution three-dimensional seismic data, Feng et al. (2006) and identified large-scale sub-lacustrine channels (Lamb & Mohrig, 2009;Mulder et al., 2001Mulder et al., , 2003Mulder & Chapron, 2011;Yang et al., 2017Yang et al., , 2018Zavala et al., 2012;Zavala & Arcuri, 2016). Different from hyperpycnal flows, the chaotically distributed floating mudstone clasts are the very distinct sedimentary features present in the deposits of muddy debris flows (Locat & Lee, 2005;Pierson, 2005;Qian & Das, 2019;Shanmugam, 2016). ...
... If the energy of the hyperpycnal flow is relatively high but not high enough to fully erode the lower inversely graded unit, an erosional surface would be present between the inverse grading and normal grading, then form the laminated medium mudstones (LF2). If the energy during the peak period of hyperpycnal flows is strong enough to fully erode the sediment on the bottom, then the inversely graded unit would be missing and a clear erosional surface would be present at the base (Chang & Chun, 2012;Lamb & Mohrig, 2009;Luan et al., 2018;Mulder et al., 2003;Yang et al., 2018), thus form the laminated coarse mudstone (LF3) and graded coarse mudstone (LF4) with basal scour surfaces and normal grading. ...
... Detrital quartz is angular to sub-rounded.4.1.2 | InterpretationEven though some laminated mudstones might be deposited in a quiet environment, as traditional view considers, evidences of detrital quartz silt(Figure 3), tiny plant debris(Figure 2), pairs of inverse and normal grading, IES, and ITC (Figure 3)suggest an alternative origin.These mudstones are similar to the hyperpycnites from the Lower Cretaceous Lingshandao Formation, Laiyang Group, Qingdao, China(Yang, Fan, Van Loon, Han, & Zavala, 2018). According to these evidences, it is interpreted that the laminated mudstones showing pairs of inverse and normal grading of the Nenjiang Formation were transported and deposited by hyperpycnal flows. ...
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.
... In a serious scientific discussion, one expects meaningful nomenclature and verifiable empirical data in documenting a specific process. Let's rigorously evaluate their claim of a modern "hyperpycnal flow" based on an article by Yang et al. (2018). ...
... However, the concept of hyperpycnal is meant for natural river-mouth processes (Bates 1953), not for artificial flows associated with an anthropogenic dam. 2) In their Fig. 1 caption, Van Loon et al. claim that their Fig. 1 is from an article by Yang et al. (2018) published in Marine and Petroleum Geology (MPG) and from a website "www.quanjing.com". But this figure is absent in the MPG article by Yang et al. (2018). ...
... 2) In their Fig. 1 caption, Van Loon et al. claim that their Fig. 1 is from an article by Yang et al. (2018) published in Marine and Petroleum Geology (MPG) and from a website "www.quanjing.com". But this figure is absent in the MPG article by Yang et al. (2018). Quanjing is a Chinese language website that also does not display their Fig. 1. ...
In this reply, I respond to 18 issues associated with comments made by Zavala (e.g., inverse-to normally-graded sequence, origin of massive sands, experimental sandy debris flows, tidal rhythmites, facies models, etc.), and 10 issues associated with comments made by Van Loon et al. (e.g., 16 types of hyperpycnal flows, anthropogenic hyperpycnal flow, etc.).
... serious scientific discussion, one expects meaningful nomenclature and verifiable empirical data in 424 documenting a specific process. Let's rigorously evaluate their claim of a modern "hyperpycnal flow" 425 based on an article by Yang et al. (2018). 426 1) Yang et al. (2018) claimed that hyperpycnal flows were associated with a dam built by human activity 427 (i.e., anthropogenic). ...
... Let's rigorously evaluate their claim of a modern "hyperpycnal flow" 425 based on an article by Yang et al. (2018). 426 1) Yang et al. (2018) claimed that hyperpycnal flows were associated with a dam built by human activity 427 (i.e., anthropogenic). However, the concept of hyperpycnal is meant for natural river-mouth processes 428 (Bates, 1953), not for artificial flows associated with an anthropogenic dam. ...
... 2) In their Fig. 1 caption, Van Loon et al. claim that their Fig. 1 is from an article by Yang et al. (2018) 430 published in Marine and Petroleum Geology (MPG) and from a website "www.quanjing.com". But this 431 figure is absent in the MPG article by Yang et al. (2018). Quanjing is a Chinese language website that also 432 does not display their Fig. 1. ...
In this reply, I respond to 18 issues associated with comments made by Zavala (e.g., inverse-to 16 normally-graded sequence, origin of massive sands, experimental sandy debris flows, tidal rhythmites, 17 facies models, etc.), and 11 issues associated with comments made by Van Loon et al. (e.g., 16 types of 18 hyperpycnal flows, anthropogenic hyperpycnal flow, etc.). 19 20
... In a 356 serious scientific discussion, one expects meaningful nomenclature and verifiable empirical data in 357 documenting a specific process. Let's rigorously evaluate their claim of a modern "hyperpycnal flow" 358 based on an article by Yang et al. (2018). 359 1) Yang et al. (2018) claimed that hyperpycnal flows were associated with a dam built by human activity 360 (i.e., anthropogenic). ...
... Let's rigorously evaluate their claim of a modern "hyperpycnal flow" 358 based on an article by Yang et al. (2018). 359 1) Yang et al. (2018) claimed that hyperpycnal flows were associated with a dam built by human activity 360 (i.e., anthropogenic). However, the concept of hyperpycnal is meant for natural river-mouth processes 361 (Bates, 1953), not for artificial flows associated with an anthropogenic dam. ...
... figure is absent in the MPG article by Yang et al. (2018). Quanjing is a Chinese language website that also 365 does not display their Fig. 1. ...
... SSGFDs are present in the Lower Cretaceous Lingshandao Formation, Laiyang Group, on Lingshan Island, Jiaonan, Qingdao (Fig. 1). Previous research has focused on the stratigraphic features (Zhang et al., 2013), depositional environment (Wang et al., 2014;Yang et al., 2018b;Zhang et al., 2018), origin and characteristics of soft-sediment deformation structures (Yang and Van Loon, 2016), distribution of slump layers (Ge and Zhong, 2018), and types of SSGF (Yang et al., 2018a, b). ...
... Yang and Van Loon (2016), Ge and Zhong (2018) interpreted the overall deposits in the research area as slumps and sandy debrites. Using geochemical data, Yang et al. (2018b) inferred that turbidites of the Lingshandao Formation were caused by hyperpycnal flows. Yang et al. (2017aYang et al. ( , b, 2018a recognized deposits of both coarse-grained supercritical turbidity currents and relatively fine-grained HEBs. ...
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.
... Recent sedimentological research, in particular the depositional mechanisms, indicates that sediments were not continental (as suggested on the basis of plant fossils present within sediment) but rather deep marine. Hyperpycnal flows carried the remains of continental and shallow-marine flora and fauna to a deep-sea environment (Yang, Fan, et al., 2017a;Yang, Fan, Van Loon, Han, & Zavala, 2018). ...
... The stratigraphy of the nearby Jiaolai Basin (Figure 1; Peng et al., 2015) and on the basis of rare fossils in the sediments of the lower part of the Laiyang Group , these sediments should be attributed to the Laiyang Group. However, the rhythmic alternation of sandstone and mudstone beds in this succession suggests deposition as distal turbidites and other deep-marine mass-flow deposits such as hyperpycnites Yang et al., , 2017aYang et al., , 2018Yang, Jin, Van Loon, Han, & Fan, 2017b;Zhao, Zhou, & Van Loon, 2018) do not fit in the context of the Laiyang Group, so a new stratigraphic unit, the Lingshandao Formation, was introduced by Zhang et al. (2013). ...
Longstanding debates on the tectonic setting and provenance of the Lower Cretaceous Lingshandao Formation have hindered basin analysis and tectonic studies of the collision of the Yangtze Craton and the North China Craton, and thus the evolution of the Sulu Orogen. Thin-section analysis, identification of rock particles, cathodoluminescence, heavy minerals and trace-element analysis have, in addition to field investigations, been applied to reconstruct the source area and transport pathways of the sediments that build the Lower Cretaceous Laiyang Group on the Lingshan Island, western Yellow Sea. These analyses indicate that the Laiyang Group consists mainly of material derived from a recycled orogen and from transitional continental sediments. The Laiyang Group on Lingshan Island has been sourced from igneous and metamorphic rocks. Comparing analyses of detrital minerals with rocks from surrounding areas leads to the conclusion that the main source area is the Sulu Orogen that supplied sediment to rift basin rather than a residual basin between the Yangtze Craton and the North China Craton.
• A recycled orogenic belt is the source area for the Laiyang Group on Linshan Island.
• Felsic metamorphic and igneous rocks form the most probable sources.
• The rift basin was filled by sediments supplied from the Sulu Orogen on both sides.
... It is known that echinoids are mostly stenohaline animals that poorly tolerate salinity fluctuations (e.g., Russell 2013). It is possible that less saline waters could be introduced by hyperpycnal flows (Yang et al. 2018), but again the animal should then burrow more deeply where the pore water should be more saline. Inflow of hypersaline waters may be considered as well, but the expected reaction of the animal should be the same as in the former case. ...
The first recognition of a tracemaker responding to a temporary shift in the redox boundary is recognized. This is recorded by a new trace fossil, Sursumichnus orbicularis igen. et isp. nov., which is established for mound-like structures on the upper surfaces of sandstone beds from the Borjomi Flysch (upper Paleocene–lower Eocene) in the Lesser Caucasus (Georgia). It is connected with the spatangoid echinoid burrow Scolicia de Quatrefages, 1849 and interpreted as a resting trace of the same tracemaker produced after moving up from a deeper position within the sediment. The resting is caused by an episode of unfavorable conditions related to shallowing of the redox boundary. The trace fossil is a component of the Nereites ichnofacies.
... Marine turbidites have been put in a classification scheme that has been used widely (Talling et al., 2012) and this holds also for lacustrine hyperpycnites (Zavala et al., 2006), but these classification systems focus almost exclusively on medium-and coarse-grained sediments. The growing interest in unconventional hydrocarbons, particularly shale oil and gas, has made research of fine-grained sediments increasingly important, being now a hot topic in sedimentology (Hovikoski et al., 2008;Aplin and Macquaker, 2011;Kostic, 2014;Plint, 2014;Terlaky et al., 2016;Yang et al., 2017aYang et al., , 2018Van Loon et al., 2019). ...
Research into transport and deposition mechanisms of fine-grained mass-flow deposits is hampered by the absence of an easily applicable classification scheme. We propose here such a scheme on the basis of the mud content in combination with the presumed transport mechanism. The scheme comprises 12 types of gravity-flow deposits. The practical applicability of this classification is shown for the Triassic lacustrine Yanchang Formation in the Southern Ordos Basin (China). This formation contains abundant slump deposits, debrites, turbidites, and hyperpycnites.
The analysis of the fine-grained gravity-flow deposits indicates that (1) mud can be deposited under active hydrodynamic conditions; (2) lacustrine mudstones and shales consist in a large part of gravity-flow deposits; (3) fine-grained gravity flows contribute much to the transport and deposition of organic matter, and thus are important mechanisms involved in the generation of hydrocarbons; (4) the mechanisms of transport and deposition, and consequently the resulting sorting, largely determine the reservoir capability of fine-grained gravity-flow deposits.
... The effectiveness of each proxy needs to be discussed because of the different chemical behaviors of elements. The Sr/Ba ratio for salinity estimation has been questioned in recent cases because of its inconsistency with paleosalinity and the B/Ga ratio (Zhang et al., 2017a;Wei et al., 2018;Yang et al., 2018). Sr/Ba ratio did not exhibit a simple correlation with paleosalinity in the present study (Fig.6a). ...
Paleosalinity is vital for the paleoenvironmental reconstruction and affects the formation of source rock. The lower-middle sections of the third member of Eocene Shahejie formation (Es3M-L) constitute the most important source rock layer in Laizhou Bay Sag. However, the paleosalinity of the depositional water in which Es3M-L submembers are deposited remains unclear. A series of integrated experiments, including major and trace elements, X-ray diffraction, total organic carbon, and Rock-Eval, was performed to reveal the paleosalinity and its relationship with organic matter (OM). Various inorganic proxies (Sr/Ba, Rb/K, B/Ga, Walker’s paleosalimeter, Adam’s paleosalimeter, and Couch’s paleosalimeter) were employed to determine the paleosalinity of samples. Prominent differences existed in the proxies. Couch’s paleosalimeter is the most reliable and qualitative approach for Laizhou Bay Sag. Samples from the lake center (depocenter) and margin showed paleosalinities from 4.92 wt‰ to 9.73 wt‰, suggesting a ubiquitous brackish (oligohaline-mesohaline) water body in the paleolake. Molybdenum enrichment in samples indicates an oxygen-depleted (suboxic or anoxic) condition. The increase in salinity has a certain but non-significant positive correlation with oxygen reduction. This condition may be attributed to the weak stratification of the water column in brackish water bodies. Moreover, paleosalinity has a weak and indirect relationship with OM accumulation during the deposition of Es3M-L submembers in Laizhou Bay Sag.
... The brackish-water nature of the embayment may have facilitated the formation of hyperpycnal flows (Felix et al., 2006). In addition, recurrent episodes of fluvial discharge may have further reduced the salinity of the receiving embayment, increasing the likelihood of further generation of hyperpycnal flows (Felix et al., 2006;Buatois et al., 2006;Yang et al., 2018). ...
The Upper Cretaceous M2 and U Sandstone members of the Napo Formation are prolific hydrocarbon producers in the Oriente Basin of eastern Ecuador. To understand the depositional origin of these reservoirs, an integrated sedimentologic, sequence-stratigraphic, and ichnologic study, using 490 ft (∼149 m) of conventional core from six wells of oil fields located in the eastern part of the basin, was performed. Sedimentary facies, stratal stacking pattern, discontinuity surfaces, and trace fossils were documented. Nine lithofacies and two depositional sequences in each member were identified. Three main broad environments, fluvial, estuarine and deltaic, have been interpreted. Trace fossils are very rare in the fluvial deposits and comprise facies-crossing ichnotaxa. The trace-fossil association of estuarine deposits is of low diversity containing ichnotaxa indicative of marine influence (e.g. Asterosoma, Teichichnus). In comparison, deltaic deposits display higher ichnodiversity, and are more intensely bioturbated, locally including some ichnotaxa (e.g. Zoophycos) that suggest the system may have experienced fully marine conditions sporadically. Controlling factors are typically expressed differently in the various subenvironments as a result of the interplay of tides and river discharge. The most important stress factors were substrate type and consistency, episodic sedimentation, high energy, water turbidity, and changes in salinity. Our integrated approach may prompt similar studies in other hydrocarbon-bearing units in Ecuador.
... However, Lake Pannon generally preserved its brackish water environment up to its final state during the Pliocene (Uhrin, 2011;Magyar et al., 2013). Another explanation of these possibly apparent changes in salinity could be a gradual increase of deposition from hyperpycnal flows, which would preserve the properties of riverine water (Yang et al., 2018). ...
Deep wells penetrated Cenozoic sedimentary record of two different basins: 1) Oligocene retro-arc basin which is buried under the 2) Miocene back-arc Danube Basin. This study is focused on biotic and abiotic proxies discussed in terms of existing biostratigraphical, paleoenvironmental and sedimentological data. Biotic proxies are represented by palynofacies and biomarkers (palynomorphs, AOM, phytoclasts, TOC, Pr/Ph ratio, steranes). Abiotic proxies are represented by inorganic geochemistry (e.g., CIA, Sr/Ba, Ga/Rb, Th/U, SiO2/Al2O3, Corg/P and enrichment factors). The biotic and abiotic proxies helped to refine the knowledge about the changes in redox conditions, salinity, depositional system, and paleoclimate. In the study area five temporally different environments are observed: 1) Sedimentation in the Oligocene fragment of the retro-arc Hungarian Paleogene Basin that took place on a highly proximal part of the shelf. A major dysoxic event connected with humid marsh environment is documented within (last Rupelian transgression; Ru4/Ch1–Ch2). 2) After a hiatus the Danube Basin initiated with early Badenian (Langhian) stable oxic to slightly dysoxic shelf with minor salinity changes (Lan2/Ser1-Ser2 transgression). 3) Late Badenian (early Serravallian) dysoxic deposition, similar in all basins of the Central Paratethys, was influenced by upwelling connected with the Ser2-Ser3 transgression. 4) Sarmatian (late Serravallian) dysoxic event associated with subsequent flooding (Ser3-Ser4/Tor1), which created shallow marginal marine environment. 5) Pannonian (Tortonian-Messinian) sedimentationtook place on an oxic shelf of the Lake Pannon near a fluvio-deltaic source, most likely represented by the paleo-Danube delta system.
... Journal of Asian Earth Sciences 186 (2019) 104065 floccules that are transported as bed load under low-density turbidity current can result in part of the horizontal bedding mudstones such as the top interval of LA 1 (Fig. 7b) (Schieber et al., 2007). In addition, previous work by Yang et al. (2018b) indicated the fine-grained sediments in the research area are caused by low-density hyperpycnal flow with an obvious inverse-then-normal grading. However, the same features were not observed in this work, which may be due to the selection of samples. ...
... Moreover, Shanmugam himself mentions repeatedly that turbidity currents and hyperpycnal flows behave in very comparable ways. It is therefore only understandable that numerous studies indicate that hyperpycnites, like turbidites, occur far away from the shore in deep-water environments Yang et al. , 2017bYang et al. , 2018Zhao et al. 2018). If turbidites can run over a hundred kilometers or more, and if-like Shanmugam states repeatedly-turbidity currents and hyperpycnal flows flow in the same way, why would hyperpycnal flows not run that far? ...
Abstract A recent review article (“The hyperpycnite problem”) by Shanmugam (Journal of Palaeogeography 7(3):197–238, 2018) in this journal has some shortcomings, comes to scientifically incorrect conclusions, and calls for student education in a way that would significantly diminish the students’ changes for a geological career. Having studied--and still studying--hyperpycnites in the field, it seems only appropriate to inform the readers of this journal about our concerns regarding the review article mentioned above. Actually, the article by Shanmugam (Journal of Palaeogeography 7(3):197–238, 2018) is not a review paper but rather a comment, criticizing all researchers who have come to the conclusion, on the basis of both field research and theory, that hyperpycnal flows result in sediments (hyperpycnites) with characteristics that make it possible to distinguish them from deposits formed in another way. This is also the essence of Shanmugam’s comment: as he states himself, he is “an ardent critic of all genetic facies models”.
The Qaidam Basin is located in the northeastern part of the Tibetan Plateau, which is a natural place to study climate change. Here, new data on Eocene sediments in the Qaidam Basin are reported. The Qaidam Basin is divided into the early Eocene Lulehe Formation and late Eocene Xiaganchaigou Formation. Based on the petrological characteristics and element geochemistry of core samples, the results show that the clay mineral assemblage of the Lulehe Formation consists of smectite, chlorite, and illite, while the clay mineral assemblage of the Xiaganchaigou Formation consists of an illite/smectite mixed layer, chlorite, and illite. The palaeosalinity calculated using the B content and Sr/Ba and Rb/Sr ratios indicates that the Lulehe Formation was formed in a freshwater environment, and the Xiaganchaigou Formation was formed in alternating brackish water and freshwater environments. The chemical weathering index, La/Th ratio, and Eu anomaly index indicate that the overall chemical weathering in the Pingtai area was weak, the provenance was relatively stable, and the influence of diagenesis on the clay minerals and the trace element contents was negligible. From the Lulehe Formation to the Xiaganchaigou Formation, the palaeoclimate gradually changed from warm and humid to cold with humid–dry seasonal changes, which is consistent with the global decrease in temperature in the Eocene. Moreover, because of the uplift of the Altun Mountains and global cooling, the rainfall decreased, resulting in the Xiaganchaigou Formation being formed in a higher-salinity environment. These studies provide some guidance for sedimentary evolution and palaeoclimate change.
The deep-marine environment is a complex setting in which numerous processes —settling of pelagic and hemipelagic particles in the water column, sediment gravity flows (downslope density currents; turbid flows), and bottom currents— determine sediment deposition, hence a variety of facies including pelagites/hemipelagites, contourites, turbidites and hyperpycnites. Characterization and differentiation among deep-sea facies is a challenge, and numerous features may be highlighted to this end: sedimentary structures, geochemical data, micropaleontological information, etc. Ichnological information has become a valuable, yet in some cases controversial, proxy, being in most of cases understudied. This paper gathers the existing ichnological information regarding the most frequent deep-sea facies —from those in which ichnological analyses are numerous and detailed (e.g. pelagites/hemipelagites and turbidites), to those for which ichnological information is lacking or imprecise (hyperpycnites and contourites). This review analyses palaeoenvironmental (i.e., ecological and depositional) conditions associated with deep-sea sedimentary processes, influence of these changes on the tracemaker community, and associated ichnological properties. A detailed characterization of trace fossil assemblages, ichnofabrics and ichnofacies is presented. Special attention is paid to variations in trace fossil features, approached through sedimentary facies models and the outcrop/core scale. Similarities and differences among deep-sea facies are underlined to facilitate differentiation. Pelagic/hemipelagic sediments are completely bioturbated, showing biodeformational structures and trace fossils, being characterized by composite ichnofabrics. The trace fossil assemblage of muddy pelagites and hemipelagites is mainly assigned to the Zoophycos ichnofacies, and locally to the distal expression of the Cruziana ichnofacies. Turbidites are colonized mostly from the top, determining an uppermost part that is entirely bioturbated, the spotty layer; below it lies the elite layer, characterized by deep-tier trace fossils. Turbidite beds pertain to two different groups of burrows, either “pre-depositional”, mainly graphogliptids, or “post-depositional” traces. Turbidite deposits are mostly characterized by the Nereites ichnofacies, with differentiation of three ichnosubfacies according to the different parts of the turbiditic systems and the associated palaeoenvironmental conditions. There are no major differences in the trace fossil content of the hyperpycnite facies and the classical post-depositional turbidite, nor in the pelagic/hemipelagic sediments, except for a lower ichnodiversity in the hyperpycnites. Trace fossil assemblages of distal hyperpycnites are mainly assigned to the Nereites ichnofacies, while graphogliptids are scarce or absent. Ichnological features vary within contourites, largely related to palaeoenvironmental conditions, depositional setting, and type of contourite. Ichnodiversity and abundance can be high, especially for mud-silty contourites. The ichnological features of mud-silty contourites are similar to those of the pelagic/hemipelagic sediments (the tiering structure probably being more complex in pelagic/hemipelagic) or to the upper part of the muddy turbidites (contourites probably being more continuously bioturbated). No single archetypal ichnofacies would characterize contourites, mainly assigned to the Zoophycos and Cruziana ichnofacies.
Lower Cretaceous sedimentary rocks of Lingshan Island, located along the continental margin of East Asia, have received increased attention. The Lingke-1 core mainly belongs to the Lower Cretaceous Laiyang Group. We investigate provenance, tectonic setting, palaeoclimate and palaeoredox conditions in the study area using elemental geochemistry, thereby elucidating the depositional history of the Lower Cretaceous sediments and reconstructing the palaeo-environment. To achieve this, 90 siltstones and 76 mudstones were sampled from this core and other outcrops on Lingshan Island. The chemical index of alternation (CIA) values for the majority of the samples and the bivariate diagrams indicate that the sedimentary rocks were subjected to minor weathering processes. Geochemical results suggest that source rocks for the region are felsic igneous and metamorphic rocks, along with minor proportions of intermediate igneous rocks. Major- and trace-element discrimination diagrams, deciphering the tectonic history, indicate that source rocks mainly originated from the continental island-arc and active continental margin. Several representative geochemical indices and the bivariate plots based on elemental contents show that the Laiyang Group was predominantly deposited in arid conditions. Sr/Ba values suggest a palaeosalinity transition from brackish to saline, demonstrating a depositional transformation from lacustrine facies for the lower Laiyang Group to marine facies in the upper Laiyang Group. U/Th and V/(V+Ni) ratios and Ce anomalies in the rocks indicate anoxic conditions. We conclude that the conspicuous decline in the trends of the above three geochemical indices, ranging between 400 and 800 m, may be related to the latest Hauterivian oceanic anoxic event.
This study focuses on the organic-rich rocks in the Central Uplift of the South Yellow Sea Basin using the CSDP-2 borehole, which was drilled through the integrated Lower Triassic–Silurian sediments and yielded approximately 2736 m of cores. Geochemical analyses of core samples, including Rock-Eval pyrolysis, elemental analysis, maceral analysis, and gas chromatography–mass spectrometry, revealed multiple sets of effective source rocks developed from the Lower Triassic Qinglong Formation to the Lower Silurian Gaojiabian Formation. The organic matter is dominated by types II–III kerogen, most of which are mature to post-mature. Comprehensive geochemical analysis shows that Permian and Lower Carboniferous mudstones are the most important source rocks and have strong hydrocarbon generation capacity. Most of the source rocks are dominated by planktonic/bacterial sources and deposited mainly in a low-salinity marine environment, and influenced by the input of terrigenous detrital materials. Basin modeling results show that most of the Paleozoic–Mesozoic source rocks in the Central Uplift generally entered the oil-generation window during the Triassic to Late Jurassic. The timing of hydrocarbon generation and expulsion was simultaneous or earlier than the collisional orogenic movement between the Sino-Korean Platform and the Lower Yangtze Craton, which may have some destructive impact on the oil and gas preservation. Therefore, it is preservation condition rather than source rocks that may be one of the most important elements for hydrocarbon accumulation in the Central Uplift of the SYSB.
The Bayan Har Group in Quanshuigou area of the northern Tibetan Plateau is regionally subdivided into three litho‐stratigraphic units, namely, the upper, middle, and lower formations. In this study, we report geochemical data for the fine‐grained sandstones from the upper formation aiming to constrain their source area weathering, provenance, palaeoenvironment, and tectonic setting. The fine‐grained sandstones exhibit similar contents of SiO2 and Al2O3 relative to upper continental crust (UCC) and Post‐Archean Australian Shale and classified as wacke on log (SiO2/Al2O3)–log (Fe2O3/K2O) diagram. The trace elements are characterized by the depletion of the transition elements compared with the UCC. The chondrite‐normalized rare earth element (REE) patterns demonstrate enrichment of light REE (LREE) and depletion of heavy REE (HREE) with LREE/HREE varying from 7.99 to 10.28, as well as distinctive negative Eu anomalies (δEu = 0.63–0.73). The high index of compositional variability values indicates the fine‐grained sandstones are compositionally immature and first cycled. The low chemical index of alteration and plagioclase index of alteration values of the samples indicate the weak source weathering condition. Additionally, the characteristics of A–CN–K plot reveal that K‐metasomatism occurred after burial. A series of palaeoenvironment indexes imply that the Bayan Har Group was deposited in a oxic/suboxic marine–terrestrial transitional environment. On the basis of the newly established DF1–DF2 discrimination functions as well as other tectonic setting discrimination plots, we speculate that the Bayan Har Basin was a back‐arc basin during the Late Triassic.
The significance of Cretaceous hothouse climate in terrestrial systems is currently unclear, and its records in terrestrial strata are rarely reported. This study investigated the sedimentary environment of the Fajiaying Formation, characterised by abundant black shale and soft-sediment deformation structures. Five lithofacies have been identified for the Fajiaying Formation, e.g. Facies A: black shale with siltstone inter-bedding, Facies B: black and gray-black shale and siltstone alternations with minor sandstone, Facies C: black and gray-black shale interbedded with gray-black sandstone, Facies D: pebbly sandstone and Facies E: gray-black shale and siltstone. The average TOC content of the shales decreases from facies A (av. 1.32%) to facies E (av. 0.46%) through facies B (av. 0.57%) and facies C (av. 0.40%). The paleosalinity gradually decreases from lithofacies A to lithofacies E, corresponding to the change of paleoclimate. In addition, Bivariate Scatter Plot of SiO2 and Al2O3 + K2O + Na2O and the clay mineral assemblages suggest an arid climate. Combined with distribution characteristics and paleontology of saliferous strata in eastern China, we determine that hothouse climate influenced the salification of lakes located in eastern China during the Early Cretaceous. Furthermore, the Fajiaying Formation in Lingshan Island was deposited in a terrestrial salified lake. Salinization of the sedimentary water bodies of the Fajiaying Formation might be related to an oceanic anoxic event. The black shale developed extensively in the Fajiaying Formation and represents the terrestrial record of hothouse climate.
To better understand the sedimentary environment of the rift basin under the influence of a warm global climate, Lingshan Island in eastern Shandong Province (China) was studied. Inorganic geochemical indexes (B, equivalent B, B/Ga, Ga, V, Couch’s palaeosalinity, Adams’s palaeosalinity, Sr/Ba, Sr/Cu, Rb/Sr, Al2O3/MgO, and CaO/MgO·Al2O3) were analyzed and a quantitative calculation of palaeosalinity was carried out based on the Adams and Couch methods. The sedimentary environment of the rift basin at Lingshan Island was determined according to the morphology and distribution of its palaeobiota as well as inorganic geochemical indexes. We demonstrate that eastern China had high-temperature drought-like conditions during the Early Cretaceous, which may have been influenced by the Faraoni event. The dry-hot climate transformed the rift basin at Lingshan Island into saline lacustrine basin. Therefore, the salinization of water was not influenced by seawater but was the response of terrestrial strata to the warm, dry climate. This study helps to understand the sedimentary background of Cretaceous rift basins in eastern China and the influence of a warm climate on China’s terrestrial strata.
The sedimentary background and sedimentary environment of the Lower Cretaceous of Lingshan Island, Shandong, remain unclear. There is considerable controversy as to whether the sedimentary environment was marine or continental. In this study, analyses were conducted with respect to indicators of paleosalinity, the chemical composition of clay, paleobiota, the characteristics of strata exhibiting salinization in eastern China during the Early Cretaceous, and the relationship between paleosalinity and paleoclimate. The results indicate that the sedimentary environment of the Lower Cretaceous Laiyang Group of Lingshan Island was that of a salified lake rather than a marine environment. This study not only provides a reference for determining the sedimentary environment of the Lower Cretaceous Laiyang Group of Lingshan Island but also offers a new perspective for the study of Cretaceous strata with salinization characteristics in eastern China.
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.
Fine-grained sediments from the Late Triassic Yanchang Fm. in the Ordos Basin (central China) were studied by core analysis and geophysical logging. Part of the mudstones in this formation are stratified, part of them are unstratified; the various mudstones can be subdivided into eight types on the basis of their structures and textures. They represent a variety of environments, ranging from delta fronts and subaqueous fans to deep-water environments. Part of the sediments were reworked and became eventually deposited from subaqueous gravity flows, such as mud flows, turbidity currents and hyperpycnal flows that easily developed on the clay-rich deltaic slopes. The sediments deposited by such gravity flows show abundant soft-sediment deformation structures. Understanding of such structures and recognition of fine-grained sediments as gravity-flow deposits is significant for the exploration of potential hydrocarbon occurrences. Because fine-grained deposits become increasingly important for hydrocarbon exploration, and because the sediments in the lacustrine Yanchang Formation were deposited by exactly the same processes that play a role in the accumulation of deltaic and prodeltaic fine-grained sediments, the sedimentological analysis provided here is not only important for the understanding of deep lacustrine sediments like the Yanchang Formation, but also for a better insight into the accumulation of fine-grained prodeltaic deep-marine sediments and their potential as hydrocarbon source rocks and reservoir rocks.
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.
No abstract is available for this article.
Detailed facies characterization of the Middle Devonian Geneseo Formation in the Northern Appalachian Basin (NAB) shows a rich assembly of sedimentary features and textures that suggest shelfal mud deposition in a stormdominated, shallow epeiric sea. At the time of deposition, Acadian uplift supplied fine-grained detritus from the east and stimulated delta growth. As sediment was shed from the hinterland, distribution of mudstone facies was controlled by a combination of autogenic processes and a general rise in sea level. The vertical and lateral distribution of nine mudstone facies observed in this succession indicates an overall shallowingupwards trend (westward progradation of Catskill delta) with multiple modes of sediment transport and deposition. The water column became more oxygenated upsection as indicated by an increase in benthic fauna diversity (e.g., Leiorhynchus and Orbiculoidea), increasing bioturbation diversity (e.g., Chondrites, Palaeophycus, Planolites, Teichichnus, Thalassinoides, and Zoophycos), and a decline of organic-carbon content (via oxidation and consumption). Physical and biological attributes of this mudstone-dominated succession are used to reconstruct sedimentary processes and depositional conditions. Although a stratified-basin model has previously been proposed for the Geneseo Formation, observations made in this study do not support that interpretation. Collectively, our observations indicate shelfal mud deposition above storm-wave base, in a relatively energetic environment with persistent lateral transport and advection by oscillatory flow, waveinduced currents, river-flood, and storm-wave generated offshore-directed underflows, as well as storm setup-relaxation flows.
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.
The documented presence of the pesticide DDT (1,1,1-trichloro-2,2-bis(p-chlorophenyl)ethane) and its metabolites DDE (1,1-dichloro-2,2-bis(p-chlorophenyl)ethylene), and DDD (1,1-dichloro-2,2-bis(p-chlorophenyl)ethane), collectively referred to as ΣDDT, in sediments from the Monterey Submarine Canyon, Monterey Fan Channel and Monterey Fan indicates that during the present sea-level highstand the Monterey Fan has been an active depositional system. The presence of ΣDDT in marine sediment is an indication of the recent arrival of terrigenous fine-grained sediment because DDT was only applied on land in California between 1944 and 1972, and is being transported to the ocean in the fine-grained sediment fraction of rivers. ΣDDT was found in 81 out of 82 cores collected in water depths deeper than 3,000 m in the Monterey Fan Channel and in the Monterey Fan, within a geographical extent of 250 km to the south and 210 km to the west of the Monterey Canyon head, with surface concentrations averaging 6 and 3 ng g- 1, in the upper and lower Monterey Fan, respectively. This is the first documentation of ΣDDT presence in ocean sediments below 3,000 meters water depth worldwide. The estimated total amount of ΣDDT in the fan is consistent with the amount of ΣDDT discharged by the Salinas and Pajaro Rivers since DDT started being used in California, suggesting that current fine-grained sediment discharge from these rivers has been accumulating in the fan. The ratio DDE/ΣDDT, an indication of the extent of DDT degradation, provides a first-order proxy for the relative age of the sediments. DDT is found along the thalweg of the Monterey Fan channel as far as 215 km from the canyon head, indicating recent fine-grained sediment transport along the channel. In contrast, only DDE was detected in sediments on the fan, which suggests that the fan does not accumulate fine-grained sediments at a constant rate.
Based on the analysis of numerous drill cores and drilling data, lacustrine gravity flow depositional systems were analyzed comprehensively in the Chang6 and Chang7 oil members (Triassic Yanchang Formation) in the southern part of the Ordos Basin. The gravity flow depositional systems in these members are made up of slides, slumps, sandy debris flows, liquefied flows, turbidity current etc, forming well developed units in the study area. Successive beds characterized by, from bottom to top, massive bedding (MB), graded bedding (GB) and horizontal bedding (HB) form well developed sequences; parallel bedding (GB) and ripple bedding (RB) are rare. It turns out that the depositional sequences are quite different from turbidites with a Bouma sequence: (1) MB represents a sandy debris flow, (2) GB deposits in a turbidity current, (3) PB and RB are deposits that were reworked by bottom currents (traction flow), and (4) HB represents a deep-water environment rather than gravity flows. Deposits in the proximal part of the subaqueous lacustrine fan consist mainly of slides, slumps and massive sandy debris flows. Deposits at the middle part of the fan are characterized by an MB-GB-HB sequence of massive sandy debris flows, graded turbidites and horizontally bedded lacustrine mudstones. Deposits at the end of the subaqueous lacustrine fan were mainly graded turbidites and horizontally bedded lacustrine mudstones (GB-HB sequence). Sandy gravity flow deposits mainly developed on the delta front and in the basin plain, extending for dozens of kilometers. They directly cover the source rock in the Chang7 oil members, which has the advantage of near-source oil accumulation. The sandstones at the bottom of each sedimentary cycle are worth further exploration because of their good reservoir properties and high oil content.
According to its original conception, turbidites have been related to slope instability of previously accumulated shallow water deposits. These are intrabasinal (I) turbidites, since the parent flow derived from a subaqueous sediment failure originated within the basin, and are characterized by an interstitial fluid having a similar density compared to that of the ambient water. In recent years, growing evidences support that turbidites can also be originated by direct discharges of rivers in flood. These fluvial discharges (via hyperpycnal
flows) accumulate extrabasinal (E) turbidites, since the parent flow is originated on land, and is composed of interstitial freshwater. This paper provides for the first time a sedimentological criterion to differentiate between intrabasinal and extrabasinal turbidites (here called I and E turbidites respectively). Intrabasinal turbidites, related to slope instability, are affected by several hydraulic jumps and flow transformations during their travel basinward. They are characterized by a fast moving head and high flow entrainment. On the contrary, pure extrabasinal turbidites are fully turbulent flows, characterized by a slow moving head and limited flow entrainment. The last result in the common occurrence of extrabasinal light components (as plant debris and charcoal) in the deposit, which are derived from the fluvial parent flow. The occurrence of plant remains is here considered a diagnostic criterion for the recognition of extrabasinal (hyperpycnal) turbidites. Main plant bearing hyperpycnal facies are medium to fine grained sandstone beds showing low angle asymptotic cross stratification, massive and laminated bedding, climbing ripples and lofting rhythmites.
Lingshan Island, the highest island in norther n China, is situated in the nearshore w ater to the
southeast of Jiaonan City, Q ingdao, Shandong Province, China. T he island is amo ng the Sulu Or ogenic
Belt betw een the South China Block and North China Block. Although the island is very important o n the
regional tectonics, its major geolog ic fact s are seldom show n so far in the geolo gical literatures. The
authors of this paper inv est ig ated the island and fo und the distal turbidites and interbedded slump deposits
in the Mesozoic clastic rocks. T he horizon has been t reated, in the geolog ic map, as the Laiyang
Formatio n, the low ermo st format io n in the Cr etaceous. However, the deposits might be formed in Jurassic
acco rding to po llen analy sis. The slump st ructures are mainly sy nsedimentary slump folds, containing
other synsedimentary deformatio n st ructures, such as synsedimentary boudinages, synsedimentary
st retching lineat ions and sy nsedimentary duplexes. The slump st ructures indicate that the slump sediments
w ere transported f rom southeast to northw est . The graded interv als of the rhythmites ar e mainly f ine
sands to silt s and the mud intervals ar e black shales, show ing the characterist ics of distal turbidites in a
remnant ocean basin betw een South China Block and the North China Blo ck. T he X-type shear joint ing,
no rmal to the sedimentary beds, indicates that the hor izon w as compressed in SE ) NW direct ion before
they w ere folded tectonically. T he asymmet ric fo lding st ructur es o f the ho rizon suggest that the So uth
China Plate w as subduct ing tow ar d northw est under the N orth China Plate after the slump beds set t led
dow n in the Mesozo ic t ime. Although the ex act ag e of the slump beds is st ill unav ailable, the distal
turbidites and the synsedimentary slump st ructures found in Ling shan Island are valuable data for tectonic
resear ch on the evo lut ion history in the Sulu Oro genic Belt betw een South China Block and North China
Blo ck.
We present results from analyses of the redox-sensitive metals Mo, V, Mn, and Fe in sediment recovered from the Cariaco Basin (Ocean Drilling Program Leg 165, site 1002). Results are interpreted in the context of previous studies of delta15N, export production (percent total organic carbon), colian input, and hemipelagic deposition in the basin. Variations in redox metal ratios over the past ~578,000 years were compared to variations in delta18O at Milankovitch frequencies and show a strong relationship between glacial-interglacial cycles in sea level, governed by the shallow sills encircling Cariaco Basin, and bottom water oxygen content. During 100 kyr and 41 kyr cyclicity, enrichments of Mo and V occur during highly productive interglacials, indicating bottom water anoxia. During glacials, sediments are less depleted or enriched in Mn and Fe relative to the interglacials, reflecting oxic conditions. During 23 kyr and 19 kyr cyclicity, however, these redox metal patterns are not observed, indicating that the Cariaco Basin responds differently to the higher-frequency climate changes.
Oxygen isotope data from planktonic and benthic foraminifera, on a high-resolution age model (44 14C dates spanning 17,400 years), document deglacial environmental change on the southeast Alaska margin (5933.32N, 1449.21W, 682 m water depth). Surface freshening (i.e., δ18O reduction of 0.8‰) began at 16,650 170 cal years B.P. during an interval of ice proximal sedimentation, likely due to freshwater input from melting glaciers. A sharp transition to laminated hemipelagic sediments constrains retreat of regional outlet glaciers onto land circa 14,790 380 cal years B.P. Abrupt warming and/or freshening of the surface ocean (i.e., additional δ18O reduction of 0.9‰) coincides with the Blling Interstade of northern Europe and Greenland. Cooling and/or higher salinities returned during the Allerd interval, coincident with the Antarctic Cold Reversal, and continue until 11,740 200 cal years B.P., when onset of warming coincides with the end of the Younger Dryas. An abrupt 1‰ reduction in benthic δ18O at 14,250 290 cal years B.P. likely reflects a decrease in bottom water salinity driven by deep mixing of glacial meltwater, a regional megaflood event, or brine formation associated with sea ice. Two laminated opal-rich intervals record discrete episodes of high productivity during the last deglaciation. These events, precisely dated here at 14,790 380 to 12,990 190 cal years B.P. and 11,160 130 to 10,750 220 cal years B.P., likely correlate to similar features observed elsewhere on the margins of the North Pacific and are coeval with episodes of rapid sea level rise. Remobilization of iron from newly inundated continental shelves may have helped to fuel these episodes of elevated primary productivity and sedimentary anoxia.
On November 8, 1980, a major earthquake (magnitude 6.5 to 7.2) occurred
60 km off the coast of northern California. A survey of the area using
high-resolution seismic-reflection and side-scan sonar equipment
revealed the presence of extensive sediment failure and flows in a zone
about 1 km wide and 20 km long that trends parallel to the shelf on the
very gently sloping (< 0.25°) Klamath River delta. The failure
zone is marked by a well-defined terrace that slopes seaward at about
0.02c and a prominent 1- to 2-m high, seaward-facing toe
scarp on the outer margin of the terrace. This toe scarp is sinuous,
appears to be nearly continuous for a distance of 20 km, and closely
parallels the 60-m isobath. Evidence indicates that the toe scarp is the
terminus of lateral spreads and lobes of sediment flows. Side-scan sonar
records show evidence of gas vents and small (10 × 3 × 0.5 m
high) pressure ridges formed seaward of and parallel to the sediment
flow scarp. Indicators of liquefaction (sand boils and collapse craters)
are present on the sediment flow terrace. Extensive sediment failure
occurred on a sea-floor slope of less than 0.25°, and we can
unequivocally pinpoint the cause as an earthquake of known location,
magnitude, and time.
Sediments on the continental shelf, atop the accretionary prism of the eastern North Island, are dominated by mud. This situation reflects a highly erodible provenance of soft Tertiary sediments, active tectonism, meteorological extremes, and, in historical times, changing land use.
Off Poverty Bay, mud is supplied by the Waipaoa River, New Zealand's fourth largest river in terms of sediment supply. Under normal conditions, suspended sediment is dispersed as surface or hypopycnal plumes that have a net northeastward or southward dispersal along the shelf, mainly in response to the prevailing wind‐driven circulation. During extreme floods with return periods of 10 years or more, fluvial suspended sediment concentrations are probably high enough to form subsurface or hyperpycnal plumes that move and disperse under gravity and shelf currents. After the 100 year Cyclone Bola event of 1988, reef communities of the inner shelf were temporarily inundated by a fluid mud layer.
Surficial sediments and 3.5 kHz seismic reflection profiles reveal that mud accumulates in a subsiding synclinal basin occupying the middle shelf. Offshelf dispersal is hindered by the growing Lachlan and Ariel Anticlines along the outer shelf. As a result, 20 km³ of mud has been deposited since c. 18 ka, of which 8 km³ accumulated since c. 8 ka. This late Holocene rate is nearly five times lower than the modern rate of mud supply, which equates with the marked increase in terrestrial erosion following European deforestation in the late nineteenth century.
Analysis of data from 280 rivers discharging to the ocean indicates that sediment loads/yields are a log-linear function of basin area and maximum elevation of the river basin. Other factors controlling sediment discharge (e.g., climate, runoff) appear to have secondary importance. A notable exception is the influence of human activity, climate, and geology on the rivers draining southern Asia and Oceania. Sediment fluxes from small mountainous rivers, many of which discharge directly onto active margins (e.g., western South and North America and most high-standing oceanic islands), have been greatly underestimated in previous global sediment budgets, perhaps by as much as a factor of three. In contrast, sediment fluxes to the ocean from large rivers (nearly all of which discharge onto passive margins or marginal seas) have been overestimated, as some of the sediment load is subaerially sequestered in subsiding deltas. Before the proliferation of dam construction in the latter half of this century, riv
Few hyperpycnal flows have ever been observed in marine environments although they are believed to play a critical role in sediment dispersal within estuarine and deltaic depositional systems. The paper describes hyperpycnal flows observed in situ off the Huanghe (Yellow River) mouth, their relationship to tidal cycles, and the mechanisms that drive them. Simultaneous observations at six mooring stations during a cruise off the Huanghe mouth in the flood season of 1995 suggest that hyperpycnal flows observed at the river mouth are initiated by high concentrations of sediment input from river and modulated by tides. Hyperpycnal flows started near the end of ebb tides, when near-bottom suspended sediment concentration (SSC) increased rapidly and salinity decreased drastically (an inverse salt wedge). The median grain size of suspended particles within the hyperpycnal layer increased, causing strong stratification of the suspended sediments in the water column. Towards the end of flood tides, the hyperpycnal flow attenuated due to frictions at the upper and lower boundaries of the flow and tidal mixing, which collapsed the stratification of the water column. Both sediment concentration and median grain size of suspended particles within the bottom layer significantly decreased. The coarser sediment particles were deposited and the hyperpycnal flows stopped. The intra-tidal behaviors of hyperpycnal flows are closely associated with the variations of SSC, salinity, and stratification of the water column. As nearly 90% of riverine sediment is delivered to the sea during the flood seasons when hyperpycnal flows are active, hyperpycnal flows at the Huanghe mouth and the river's high sediment loads have caused rapid accretion of the Huanghe delta. Copyright © 2010 John Wiley & Sons, Ltd.
The Lingshan Island is located approximately 16km in the south of Jiaodong Peninsula. It is known as the eastern part of the Dabie-Sulu orongenic belt conjuncting the North China Craton (NCC) and the Yangtze Block (YB). In Late Early Cretaceous, magmatic activities strongly occurred in this place, developing numerous rhyolites and volcanic breccias in the upper part of the island that unconformably overlies the clastic sedimentary rocks in the lower part. What ' s more, mafic dyke swarms (diabase porphyrite) widely intrude into the clastic sedimentary rocks along the NE-SW trend. In this study, petrogeochemical and chronological analyses were conducted on the rhyolite and diabase porphyrite. The results show that the rhyolite samples have high K2O contents (4. 10% ∼ 4.42%) and are alkali-rich (Na2O + K2O = 8. 83%-9.06%), with low contents of CaO (0.10% ∼ 0.46%), TiO2 (0.08%-0. 09%), MgO (0. 12% ∼ 0. 15%) and Fe2O3TO (0. 79% ∼ 0. 83%). All the samples are slightly peraluminous and belong to calcic-alkaline rock series. Their chondrite-normalized REE patterns are characterized by slightly enrichment of LREEs ((La/Yb) N = 6. 42 ∼ 8. 09), relatively low REE contents (∑ REE = 109. 0 × 10 ⁻⁶ ∼ 128. 8 × 10 ⁻⁶) and negative Eu anomalies (δEu = 0. 27 ∼ 0. 28). The diabase porphyrite samples have low SiO2 contents (51. 17% ∼ 51. 97%), high alkali contents (Na2O + K2O =5. 01% ∼ 6. 07%) and Mg# values (67.6 ∼ 69.4), belonging to shoshonitic rock series. Their chondrite-normalized REE patterns show relatively enrichment of LREEs ((La/Yb) N =11. 1 ∼ 11.6) and relatively high REE contents (∑ REE = 160. 6 × 10⁻⁶ ∼ 173. 5 × 10⁻⁶), with slightly positive Eu anomalies (δEu =1. 12-1. 18). In the primitive mantle-normalized trace element patterns and chondrite-normalized REE patterns, these diabase porphyrite samples display OIB affinity. All these geochemical features reveal that the rhyolite and diabase porphyrite were generated in an extentional setting with low pressure. Futhermore, LA-ICP-MS zircon U-Pb dating results show that the rhyolite and diabase porphyrite were produced by Early Cretaceous magmatism, with formation age of 118 ± 2Ma and 109 ± 3Ma, respectively. Zircon Lu-Hf isotopic analyses indicate that the rhyolite was derived from an ancient crustal origin with negative ϵHf (t) values of-31. 0 ∼-24. 5, while the diabase porphyrite was derived from the enriched mantle source with negative ϵHf (t) values of-31. 2 ∼-28. 8 which mingled by deep depleted mantle components with positive ϵHf (t) values of + 7. 1 ∼ + 8. 1. All these signatures, together with regional contemporary tectonic events suggest that, affected by the direction-changed of subduction of Izanagi plate and paleo-Pacific plate, tectonic regime in eastern China was transformed during Mesozoic. In Late Early Cretaceous, the eastern NCC was under extensional regime, producing a series of rhyolites and diabase porphyrite dykes, which represent geological response to the Yanshan Movement in Jiaodong Peninsula. © 2018 Yanshi Xuebao/Acta Petrologica Sinica. All rights reserved.
The roof, floor and gangue samples of coal seams were collected from a borehole in the Gujiao mining area. The vertical distribution of major elements, trace elements and rare earth elements (REEs) was tested through X-ray fluorescence spectrometry and inductively coupled plasma-mass spectrometry (ICP-MS). The formation environment and material source of the strata were analysed. The results showed that the major elements of the coal seam roof, floor and gangue are Si and Al, followed by Fe, K, and Ti. In the Shanxi Formation, Sn, B, Ta, Bi, Th, U, Li, Be, Nb, In, Cs and Hf are enriched. In the Taiyuan Formation, B, Bi, U, Li, Sr, Mo and Sb are enriched. Sn, B, Th, U, and Be of the Shanxi Formation and B, U, Mo, and Sb of Taiyuan Formation are enriched hazardous elements. The ratios of Sr/Ba, U/Th, Ni/Co and V/Cr could indicate the paleosalinity and redox conditions. The Shanxi Formation was mainly formed in an oxic environment. The roof and floor of the No. 7 coal and the roof of the No. 8 coal are limestone, indicating anoxic and suboxic to dysoxic environments. The lithology of the Shanxi Formation and Taiyuan Formation material source is complex, including sedimentary rocks, granite and alkaline basalt. Most samples are distributed at the intersection of the granite and alkaline basalt, indicating dual sourcing from the granite and alkaline basalt.
Soft-sediment deformation structures (SSDS) are reported from the turbidite deposits of Lower Cretaceous in the sea cliffs of Lingshan Island, East China. The depositional sequence including the deformations consists of turbidite sequences, each made up of a sandstone part anda fine-grained sediments part. They are related to the deposition of turbidity currents in outer fan-basin plain setting characterized by low energy and fine-grained sedimentation. The axial plane of slump folds dip to NW, consist with the palaeocurrent direction measured from sole marks. Two types of deformational structures: flame structures and rhythmite rip-up clasts are recognized. These structures usually involve the sandstone part of an overlying turbidite sequence and the rhythmite of the underlying sequence. The paper assess facies, possible triggers and available criteria to recognizing rapid sedimentation as the trigger. Rapid sedimentation of the turbidity currents offered overloading exerted directly on the underlying beds, making their pore fluid pressure increase dramatically to bring about liquefaction/fluidization. The flow of turbidity currents or downslope component of the overlying turbidite gravitation induce shear stress. During liquefaction, the reverse density gradient initiated the flame structures, and the lateral shear stress induced the rhythmite rip-up clasts and the preferred orientation of some flame structures. It is convinced that liquefaction/fluidization induced by rapid sedimentation is common processes in turbidite deposits.
The Es3L (lower sub-member of the third member of the Eocene Shahejie Formation) shale in the Jiyang Depression is a set of relatively thick and widely deposited lacustrine sediments with elevated organic carbon, and is considered to be one of the most important source rocks in East China. We can determine the mineralogy, organic and inorganic geochemistry of the Es3L shale and calculate paleoclimate indexes by using multiple geochemical proxies based on organic chemistry (total organic carbon [TOC] and Rock-Eval pyrolysis), major and trace elements, X-Ray diffraction, and carbon and oxygen isotope data from key wells alongside ECS (Elemental Capture Spectroscopy) well log data. These indicators can be used to analyze the evolution of the paleoenvironment and provide a mechanism of organic matter (OM) accumulation. The Es3L oil shale has high TOC abundance (most samples >3.0%) and is dominated by Type I kerogens. Additionally, the organic-rich shale is rich in CaO and enrichment in some trace metals is present, such as Sr, Ba and U. The positive δ¹³C and negative δ¹⁸O values, high Sr/Ba, B/Ga and Ca/Ca + Fe ratios and low C/S ratios indicate that the Es3L shales were mainly deposited in a semi-closed freshwater-brackish water lacustrine environment. The consistently low Ti/Al and Si/Al ratios reflect a restricted but rather homogeneous nature for the detrital supply. Many redox indicators, including the Th/U, V/(V + Ni), and δU ratios, pyrite morphology and TOC-TS-Fe diagrams suggest deposition under dysoxic to suboxic conditions. Subsequently, the brackish saline bottom water evolved into an anoxic water body under a relatively arid environment, during which organic-lean marls were deposited in the early stage. Later, an enhanced warm-humid climate provided an abundant mineral nutrient supply and promoted the accumulation of algal material. OM input from algal blooms reached a maximum during the deposition of the organic-rich calcareous shale with seasonal laminations. High P/Ti ratios and a strongly positive relationship between the P and TOC contents indicate that OM accumulation in the oil shale was mainly controlled by the high primary productivity of surface waters with help from a less stratified water column. Factors such as the physical protection of clay minerals and the dilution of detrital influx show less influence on OM enrichment.
The influence of paleoclimate on the depositional process of lacustrine mudstone and organic matter accumulation is important to both paleoclimate reconstruction and hydrocarbon exploration. Here we study the lower third Member (Es3L) of the Eocene Shahejie Formation in the Zhanhua Depression, Bohai Bay Basin, eastern China in order to understand how paleoclimate influenced depositional processes and organic matter accumulation of lacustrine organic-rich mudstone. By combining detailed core descriptions and microscopic observations, and high-resolution mineralogical and geochemical analyses, we identified two major lithofacies, including massive calcareous mudstone and laminated calcareous mudstone, from the Luo 69 drilling core. The sedimentologic observations and changes of geochemical proxies, including detritus index, Ln(Al2O3/Na2O), B/Ga, and V/(V + Ni), suggest that the massive calcareous mudstone was deposited in a small, shallow, salt lake that was dysoxic-anoxic, and the paleoclimate in the lake catchment was cool and arid, and the laminated calcareous mudstone was deposited in a large and deep stratified lake, which has anoxic, highly saline bottom and oxic, less saline surface water, and the lake catchment was more humid and warm. The dominant lithofacies changed from laminated calcareous mudstone to massive calcareous mudstone in the studied core, suggesting that the lake became shallower and smaller when the paleoclimate became cooler and drier through time. Such a climate trend may be a response to global cooling during the middle Eocene. The average total organic content (TOC) in both lacustrine highstand and lowstand are comparable even though the lake water chemistry and amount of terrigenous input are different. We infer that the accumulation of organic matter within the lacustrine highstand was controlled by the combination of primary productivity, carbonate production, and preservation in anoxic bottom water, while accumulation within lacustrine lowstand was only controlled by primary productivity.
The validity of boron as a salinity index has been established by numerous studies over the past 2 decades. It is known that all the major clay minerals may contain boron which can be correlated with paleosalinity. However, under given conditions, illites will contain the most boron and kaolinites the least. Montmorillonites and probably chlorites are intermediate. Published data indicate that a detrital clay will adsorb boron from solution, fix it at the surface, and later incorporate it within the structure. For seawater systems, this boron uptake can be expressed as a Freundlich adsorption isotherm, as log B = C1 log S + C2, where B = boron uptake (ppm), S = salinity of the water (^pmil), and C1, C2 = constants, dependent on the particular clay. Factors other than salinity that affect boron content are inherited boron, clay mineralogy, grain size, and crystallinity of the clay minerals. Sufficient independent data were available to use an adsorption isotherm to calculate paleosalinities for a kaolinitic Tertiary shale in Nigeria. The constants necessary for calibration of the isotherm were evaluated as: Inherited "kaolinite boron," O; "Kaolinite boron" uptake at 1 ^pmil salinity 1.3 ppm (C2 = 0.11); and "Kaolinite boron" uptake at 35 ^pmil salinity 65 ppm (C1 = 1.28). Boron concentrations, related to kaolinite, were converted graphically to paleosalinities from a log-log calibration curve with the use of these values. Paleosalinities determined in this manner are in good agreement with independent faunal interpretations.
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.
Professional and Scholarly Publishing by the Association of American Publishers (AAP) Best Reference 2005, by the Library Journal Rivers of North America is an important reference for scientists, ecologists, and students studying rivers and their ecosystems. It brings together information from several regional specialists on the major river basins of North America, presented in a large-format, full-color book. The introduction covers general aspects of geology, hydrology, ecology and human impacts on rivers. This is followed by 22 chapters on the major river basins. Each chapter begins with a full-page color photograph and includes several additional photographs within the text. These chapters feature three to five rivers of the basin/region, and cover several other rivers with one-page summaries. Rivers selected for coverage include the largest, the most natural, and the most affected by human impact. This one-of-a-kind resource is professionally illustrated with maps and color photographs of the key river basins. Readers can compare one river system to another in terms of its physiography, hydrology, ecology, biodiversity, and human impacts. * Extensive treatment provides a single source of information for North America's major rivers * Regional specialists provide authoritative information on more than 200 rivers * Full-color photographs and topographical maps demonstrate the beauty, major features, and uniqueness of each river system * One-page summaries help readers quickly find key statistics and make comparisons among rivers.
Large Rivers: Geomorphology and Management explores an important topic in geomorphology and sedimentology: the form and function of major rivers. Our knowledge of the big rivers of the world is limited. It is currently difficult to recognise large rivers of the past from relict sedimentary deposits or to structure management policies for long international rivers. This exciting book brings together a set of papers on large rivers of the world, as a unique introduction to a demanding subject. The book includes thirty chapters and is organised into three sections. The first part is on the environmental requirements for creating and maintaining a major river system. The second is a collection of case studies on 14 large rivers from different continents, covering a range of physical environments. The third section includes chapters on the measurement and management of large rivers. First book to offer in a single volume state-of-the-art knowledge on management and geomorphology of large rivers of the world. A pioneering study, pushing the boundaries of our knowledge related to big rivers. Includes comprehensive case studies covering the major large rivers of the world including Amazon, Mississippi, Nile, Congo, Indus, and Mekong. Written by a leading team of distinguished, international contributors.
Hueneme and Dume submarine fans in Santa Monica Basin consist of sandy channel and muddy levee facies on the upper fan, lenticular sand sheets on the middle fan, and thinly bedded turbidite and hemipelagic facies elsewhere. Fifteen widely correlatable key seismic reflections in high-resolution airgun and deep-towed boomer profiles subdivide the fan and basin deposits into time-slices that show different thickness and seismic-facies distributions, inferred to result from changes in Quaternary sea level and sediment supply. At times of low sea level, highly efficient turbidity currents generated by hyperpycnal flows or sediment failures at river deltas carry sand well out onto the middle-fan area. Thick, muddy flows formed rapidly prograding high levees mainly on the western (right-hand) side of three valleys that fed Hueneme fan at different times; the most recently active of the lowstand fan valleys, Hueneme fan valley, now heads in Hueneme Canyon. At times of high sea level, fans receive sand from submarine canyons that intercept littoral-drift cells and mixed sediment from earthquake-triggered slumps. Turbidity currents are confined to 'underfit' talweg channels in fan valleys and to steep, small, basin-margin fans like Dume fan. Mud is effectively separated from sand at high sea level and moves basinward across the shelf in plumes and in storm-generated lutite flows, contributing to a basin-floor blanket that is locally thicker than contemporary fan deposits and that onlaps older fans at the basin margin. The infilling of Santa Monica Basin has involved both fan and basin-floor aggradation accompanied by landward and basinward facies shifts. Progradation was restricted to the downslope growth of high muddy levees and the periodic basinward advance of the toe of the steeper and sandier Dume fan. Although the region is tectonically active, major sedimentation changes can be related to eustatic sea-level changes. The primary controls on facies shifts and fan growth appear to be an interplay of texture of source sediment, the efficiency with which turbidity currents transport sand, and the effects of delta distributary switching, all of which reflect sea-level changes.
A set of sedimentary strata represented by terrigenous clastic rocks, volcaniclastic rocks and volcanic lava are developed among the metamorphic rocks and Yanshan granites in Eastern Shandong, which leave fierce debates on their ages, sedimentary characteristics and significance of the regional tectonics. This paper presents the characteristics of the strata around the outcrops of Lingshandao, Tangdaowan, Dashangzhuang in Wulian, Shandongtou in Zhucheng, Yakou in Mountain Laoshan. Samples from the Yakou of Laoshan Mountain and Laohuizui of Lingshan Island were dated using zircon LA-ICP-MS method, yielding two weighted mean 206Pb/238U ages of 118.9±3.3 Ma and 119.2±2.2 Ma which are coincident with the beginning of the volcanism of the Qingshan stage in the Jiaolai Basin. There was a large-scale rift basin extending in NE direction developed in the offshore areas of Eastern Shandong Province during the Late Mesozoic, inferred by the sedimentary structures. This basin is characterized by alternating uplifts and depressions. Late Mesozoic tectono-magmatic activities and the evolution of regional tectonic stress field were systematically summarized, and it shows a fine comparability between the rift basin and Jiaolai Basin. These two basins may be a whole in the Laiyang stage and were separated by the volcanic arc exposing along the Wulian-Qingdao fault zone and Mouji fault zone in the Qingshan stage. Finally, this offshore prototype basin of the Late Mesozoic was restored based on the above analysis. ©, 2014, The Editorial Office of Earth Science Frontiers. All right reserved.
Four periods of extreme turbidity were measured in Monterey Submarine Canyon over the past 12 yr. These turbid events occurred simultaneously with the four largest flood events of the nearby Salinas River. They filled the canyon with fresher, warmer, and, apparently, buoyant water that extended to depths below 1 km. The low-salinity signature must reflect underflow of the Salinas River plume that was driven to depth by negative buoyancy contributed from the suspended sediment. A flux estimate for the 1995 event suggests that one-half, or more, of the river's suspended sediment load was carried down the canyon in the underflow. Underflows may contribute significantly to the carbon budget of the continental slope.
Greenland ice-core records indicate that the last deglaciation (~7-21 ka) was punctuated by numerous abrupt climate reversals, involving temperature changes of up to 5-10oC within decades. However the cause behind many of these events is uncertain. A likely candidate may have been the input of deglacial meltwater, from the Laurentide ice sheet (LIS), to the high latitude North Atlantic, which disrupted ocean circulation and triggered cooling. Yet the direct evidence of meltwater input for many of these events has so far remained undetected. In this study, we use the geochemistry (paired Mg/Ca-delta18O) of planktonic foraminifera from a sediment core south of Iceland to reconstruct the input of meltwater to the northern North Atlantic during abrupt deglacial climate change. Our record can be placed on the same timescale as ice-cores and therefore provides a direct comparison between the timing of meltwater input and climate variability. Meltwater events coincide with the onset of numerous cold intervals, including the Older Dryas (14.0 ka), two events during the Allerød (at ~13.1 and 13.6 ka), the Younger Dryas (12.9 ka), and the 8.2 ka event, supporting a causal link between these abrupt climate changes and meltwater input. During the Bølling-Allerød warm interval, we find that periods of warming are associated with an increased meltwater flux to the northern North Atlantic, which in turn induces abrupt cooling, a cessation in meltwater input, and eventual climate recovery. This implies that feedback between climate and meltwater input produced a highly variable climate during the deglaciation. A comparison to published data sets suggests that this feedback likely included fluctuations in the southern margin of the LIS causing rerouting of LIS meltwater between southern and eastern drainage outlets, as proposed by Clark et al. [Science, 2001, v293, 283-287].
Patterns of uranium–molybdenum covariation in marine sediments have the potential to provide insights regarding depositional conditions and processes in paleoceanographic systems. Specifically, such patterns can be used to assess bottom water redox conditions, the operation of metal-oxyhydroxide particulate shuttles in the water column, and the degree of water mass restriction. The utility of this paleoenvironmental proxy is due to the differential geochemical behavior of U and Mo: (1) uptake of authigenic U by marine sediments begins at the Fe(II)–Fe(III) redox boundary (i.e., suboxic conditions), whereas authigenic Mo enrichment requires the presence of H2S (i.e., euxinic conditions), and (2) transfer of aqueous Mo to the sediment may be enhanced through particulate shuttles, whereas aqueous U is unaffected by this process. In the present study, we examine U–Mo covariation in organic-rich sediments deposited mostly in the western Tethyan region during oceanic anoxic events (OAEs) of Early Jurassic to Late Cretaceous age. Our analysis generally confirms existing interpretations of redox conditions in these formations but provides significant new insights regarding water mass restriction and the operation of particulate shuttles in depositional systems. These insights will help to address contentious issues pertaining to the character and origin of Mesozoic OAEs, such as the degree to which regional paleoceanographic factors controlled the development of the OAEs.
The validity of boron in illite as a salinity indicator has been questioned recently. Using analytical data from whole rocks, some workers argue that illite is predominantly detrital and inherits much of its boron from the parent rocks. They also believe that additional boron, absorbed at the time of deposition, is a function of soluble organic matter associated with clay minerals as well as with paleosalinity. Therefore, it has been proposed that equivalent boron variations in cyclothems, previously reported by the writer, could be related to source and organic carbon rather than to paleosalinity. Further studies of illitic clay fractions, reported in this paper, failed to reveal a significant correlation between organic carbon and boron in illite (observed boron) or the boron-K2O ratio (adjusted boron). However, equivalent boron, computed from clay-fraction analyses, may be influenced by organic carbon. Equivalent boron, as defined in earlier publications, depends on the boron-K2O ratio and the K2O concentration in pure illite. Assuming that all the K2O in a clay fraction is held in illite, the dilutent effect of organic matter must lead to inverse correlation between organic carbon and K2O. Consequently, equivalent boron which depends on the K2O concentration must be related similarly to organic carbon. Correct on for this dilutent effect leads to equivalent-boron values which correlate more closely with other geological information. Cyclothems in the lower Yoredale Formation of the upper Visean (Upper Mississippian in part) of England have been interpreted as accretion cycles related to repeated advances of deltas in a slowly subsiding basin. In Recent analogues of these cyclothems a marked reduction in salinity characterizes the initial phases of accretion, but salinity becomes extremely variable toward the end of each cycle. Near the base of Yoredale cyclothems, where paleosalinity is most predictable, equivalent boron precisely parallels the inferred salinity changes. Poor correlation between equivalent boron and inferred paleosalinity in the upper part of many cyclothems is attributed to difficulties in predicting paleosalinity from geological information, rather than to an undetected relation between equival nt boron and some other environmental parameter. Results from earlier paleosalinity investigations emphasize the exploration potential of this technique. For example, supposedly nonmarine rocks have been recognized correctly as marine; the primary depositional origin of reeflike structures has been confirmed; reef and off-reef facies have been correlated; finally, periods of maximum reef growth have been shown to coincide with periods of widespread marine transgression. Although the additional costs associated with geochemical exploration may not be justified in shallow prospects where abundant control is available, geochemical methods could increase significantly the wildcat success ratio in newly discovered oil provinces where drilling costs are high. Many offshore basins, as for example the newly discovered basins in the North Se area, are in this category.
Late Pleistocene Heinrich ice-rafting events produced layers rich in ice-rafted debris in major parts of the North Atlantic north of 40°N. A high detrital carbonate content points to the Hudson Strait outlet of the Laurentide ice sheet as a dominant source of the icebergs. Heinrich events were coupled with short-term climate fluctuations during the last and penultimate glaciations and provide evidence for cryosphere-hydrosphere-atmosphere interaction in Pleistocene climate change. An unsolved problem with Heinrich layers has been their high concentration of fine-grained detrital carbonate (>80% of the total detrital carbonate), which cannot have been delivered by icebergs alone. We propose combinations of different processes that deposited four sedimentologically different types of Heinrich layers: ice rafting alone for the coarser, sand- to gravel-sized fractions and the fine fractions in distal regions (type IV Heinrich layers), whereas nepheloid flows deposited the bulk of the fine sediment in regions proximal to the Hudson Strait (type I Heinrich layers). On the Labrador slope, turbidity currents spilling over from canyons were also involved in transporting the fine-grained carbonate-rich material, causing an alternation of mud-turbidites and thin laminae of ice-rafted debris in type II Heinrich layers. On the levees of the Northwest Atlantic Mid-Ocean Channel, the thickness relationship is reversed: mud-turbidites deposited by occasional spillover of currents from the channel are thin and alternate with thicker laminae of ice-rafted debris (type III Heinrich layers).
Meteoric-water flux and formation of kaolinite owing to the dissolution of detrital silicates are common features of continental and paralic sandstones. In deep-water marine sandstones, meteoric-water flux is commonly considered unlikely to occur. However, the study of deep-water, marine sandstones of the Shetland–Faroes Basin on the British continental shelf revealed widespread and extensive dissolution and kaolinitization of mica and feldspar grains, which are attributed to meteoric-water flux during a sea-level lowstand. We suggest that this apparently enigmatic meteoric-water flux mechanism is likely to have occurred by hyperpycnal flow. Hyperpycnal flow occurs when river effluent directly transfers into sediment gravity flow, and enters seawater as a mixture of sediment and fresh water. The likelihood for hyperpycnal flows increases at times when rivers and distributary channels reach the shelf edge, and their flows are delivered directly onto the deepwater slope.
Eight geochemical indices used for the interpretation of bottom water palaeo-oxygen concentrations for argillaceous sedimentary rocks have been calculated for a suite of Upper Jurassic mudstones drawn from the Draupne and Heather Formations of the Norwegian North Sea, and the Kimmeridge Clay Formation from onshore England.The eight indices: DOP, C/S, U/Th, authigenic uranium, V/Cr, Ni/Co, Ni/V and have been examined by means of factor analysis, to identify the most reliable. DOP, U/Th, authigenic uranium, V/Cr and Ni/Co form an internally consistent set and are recommended as the most reliable of the indices. Ni/V, C/S and convey little palaeo-oxygenation information and are not regarded as reliable.The parameters identified as reliable (DOP, Ni/Co, V/Cr, U/Th and authigenic uranium), have been calibrated against DOP, for inter-comparison purposes, and to allow their interpretation against DOP-derived depositional conditions.
Speed and direction of bottom currents induced by density underflow of two sediment-laden rivers were measured by oceanographic current meters in the Walensee (= Lake of Walenstadt), Switzerland. The apparently shooting flow of currents (up to 30 cm/s in this study) is suggested as an explanation for laminations in turbidite sequences. The current speed apparently stabilizes on slopes around 2°; this angle seems to correspond to the critical slope where the flow of the measured currents becomes steady. Current direction is controlled by bottom topography and direction of river inflow. Reversal of current direction observed at two sites is probably due to the underflow-induced backward motion of the overlying lake water. Underflow activity in Walensee is correlative with density peaks of the river water input. The currents are compared to Lake Mead (Southwestern U.S.) underflows and sporadic currents in some submarine canyons.
River floods influence sedimentary environments and ecosystems from the terrestrial to the deep-marine. This study documents the occurrence conditions of hyperpycnal flows generated by river floods and related organic-matter sedimentation for Holocene sediments of the Niigata Plain, Central Japan, based on detailed sedimentary facies, total sulfur and total organic carbon content, diatom assemblages and organic-matter composition. Holocene sediments of the Niigata Plain consist of sand, mud and gravel that were deposited in estuarine and fluvial systems during a sea-level rise (15 000–6800 years BP) and stillstand (after 6800 years BP) following the Last Glacial Maximum. Hyperpycnites are present in the upper part of the estuarine lagoon sediments. The depositional age is considered to be about 5000 years BP. The hyperpycnites comprise two successions of a top fining-up unit and a basal coarsening-up unit, and include abundant terrigenous organic matter and freshwater diatoms. A large volume of freshwater is inferred to have flowed into the lagoon during deposition of the upper part of the lagoon sediments. In consequence, hyperpycnal flows may have readily formed in the lagoon, because the halocline was weak. The hyperpycnal flows also produced a layer of concentrated terrigenous organic matter in the uppermost part of the hyperpycnites. The abundant organic matter on the estuarine floor is inferred to have produced anoxic bottom conditions owing to oxidative decomposition by benthic bacteria.
Results from modern and ancient sediments suggest that a boron-illite equilibrium, reflecting salinity, is established at the time of deposition. This condition is not appreciably changed by subsequent processes of diagenesis and lithification. Equivalent boron in thirteen samples, from two augerholes through Dovey Estuary sediments, ranges between 260 p.p.m. and 370 p.p.m. and averages 336 ± 29 p.p.m. (95% confidence limits).
Salinity conditions in the present estuary vary greatly. A very significant direct correlation exists between equivalent boron and inferred depositional salinity of Dovey Estuary sediments.
Sandy hyperpycnal flows and their deposits, hyperpycnites, have been documented in modern environments and, more recently, in Cretaceous and Tertiary strata; they may be more common in the rock record, and within petroleum reservoirs, than has been previously thought. Muddy hyperpycnites also occur within the rock record, but these are more difficult to document because of their finer-grained nature and lack of common sedimentary structures. This paper documents the presence of submarine slope mudstone and siltstone hyperpycnites (and muddy turbidites) in the delta-fed, Upper Cretaceous Lewis Shale of Wyoming; based on field measurements, analyses of rock slabs and thin sections, and laser grain-size distributions. Four lithofacies comprise laminated and thin-bedded mudstones that are associated with levéed channel sandstones: (L1) grey, laminated, graded mudstone with thin siltstone and sandstone interbeds; (L2) dark grey to tan, laminated mudstone with very thin siltstone and sandstone stringers; (L3) light grey, laminated siltstones; and (L4) laminated mudstones and siltstones with thin sandstone interbeds. Two styles of mudstone grain-size grading have been documented. The first type is an upward-fining interval that typically ranges in thickness from 2·5 to 5 cm. The second type is a couplet of a lower, upward-coarsening interval and an upper, upward-fining interval (sometimes separated by a micro-erosion surface) which, combined, are about 3·8 cm thick. Both individual laminae and groups of laminae spaced millimetres apart exhibit these two grain-size trends. Although sedimentary structures indicative of traction-plus-fallout sedimentary processes associated with sandier hyperpycnites are generally absent in these muddy sediments, the size grading patterns are similar to those postulated in the literature for sandy hyperpycnites. Thus, the combined upward-coarsening, then upward-fining couplets are interpreted to be the result of a progressive increase in river discharge during waxing and peak flood stage (upward increase in grain-size), followed by waning flow after the flood begins to abate (upward decrease in grain-size). The micro-erosion surface that sometimes divides the two parts of the size-graded couplet resulted from waxing flows of sufficiently high velocity to erode the sediment previously deposited by the same flow. Individual laminae sets which only exhibit upward-fining trends could be either the result of waning flow deposition from either dilute turbidity currents or from hyperpycnal flows. The occurrence of these sets with the size-graded couplets suggests that they are associated with hyperpycnal processes.