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Shu Jiang - One of the best experts on this subject based on the ideXlab platform.
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difference analysis of organic matter enrichment mechanisms in upper ordovician lower silurian shale from the yangtze region of southern china and its geological significance in shale gas exploration
2019Co-Authors: Zhenxue Jiang, Shu Jiang, Kun Zhang, Yan Song, Yizhou Huang, Chuanxun ZhouAbstract:The upper Ordovician-lower Silurian shale has always been the main target of marine shale gas exploration in southern China. However, the shale gas content varies greatly across different regions. The organic matter content is one of the most important factors in determining gas content; therefore, determining the enrichment mechanisms of organic matter is an important problem that needs to be solved urgently. In this paper, upper Ordovician-lower Silurian shale samples from the X-1 and Y-1 wells that are located in the southern Sichuan area of the upper Yangtze region and the northwestern Jiangxi area of the lower Yangtze region, respectively, are selected for analysis. Based on the core sample description, well logging data analysis, mineral and elemental composition analysis, silicon isotope analysis, and TOC (total organic carbon) content analysis, the upper Ordovician-lower Silurian shale is studied to quantitatively calculate its content of excess silicon. Subsequently, the results of elemental analysis and silicon isotope analysis are used to determine the origin of excess silicon. Finally, we used U/Th to determine the characteristics of the redox environment and the relationship between excess barium and TOC content to judge Paleoproductivity and further studied the mechanism underlying sedimentary organic matter enrichment in the study area. The results show that the excess silicon from the upper Ordovician-lower Silurian shale in the upper Yangtze area is derived from biogenesis. The sedimentary water body is divided into an oxygen-rich upper water layer that has higher Paleoproductivity and a strongly reducing lower water that is conducive to the preservation of sedimentary organic matter. Thus, for the upper Ordovician-lower Silurian shale in the upper Yangtze region, exploration should be conducted in the center of the blocks with high TOC contents and strongly reducing water body. However, the excess silicon in the upper Ordovician-lower Silurian shale of the lower Yangtze area originates from hydrothermal activity that can enhance the reducibility of the bottom water and carry nutrients from the crust to improve Paleoproductivity and enrich sedimentary organic matter. Therefore, for the upper Ordovician-lower Silurian shale in the lower Yangtze region, exploration should be conducted in the blocks near the junction of the two plates where hydrothermal activity was active.
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effect of sedimentary environment on the formation of organic rich marine shale insights from major trace elements and shale composition
2019Co-Authors: Luchuan Zhang, Dianshi Xiao, Shu JiangAbstract:Abstract Sedimentary environment and redox conditions play a significant role in the formation of organic-rich shale. The vertical variations of major/trace elements, TOC (total organic carbon) and mineral compositions were investigated for the Lower Silurian Longmaxi typical marine shale in the Upper Yangtze Platform, South China, to decipher sedimentary environment (redox conditions, detrital input, sedimentation rate (SR), Paleoproductivity and watermass restriction). This gives insight to the effects of variations in sedimentary environment on the formation of organic-rich shale. The results show that the Lower Longmaxi Formation is composed of three systems tracts: TST (transgressive systems tract), EHST (early highstand systems tract) and LHST (late highstand systems tract). From TST to LHST, the contents of TOC, quartz and pyrite decline steadily, whereas clay minerals and carbonate show an increasing trend. Thus, organic-rich siliceous (ORSS), organic-moderate mixed (OMMS) and organic-lean argillaceous (OLAS) shales are dominant for TST, EHST and LHST, respectively. Due to a continues fall of the relative sea-level, a deep-water shelf environment with anoxic condition, high Paleoproductivity and low detrital input in TST gradually evolves into a semi-deep-water environment with dysoxic-oxic conditions, moderate Paleoproductivity, and moderate detrital influx in EHST, further to an environment of oxic condition, low Paleoproductivity, and high detrital flux in LHST. As evidenced by Mo-TOC and Mo U patterns, ORSS was deposited in a moderately restricted watermass, weaker than Black Sea, which progressively evolved into an enhanced restriction degree during the deposition of OMMS and OLAS due to a fall of relative sea-level. Major/trace elements and excess silica (EX-SiO2) concentrations illustrate that origins of quartz in the Lower Longmaxi shale are primarily terrigenous, biogenic and authigenic (smectite illitization). The average proportions of EX-SiO2 (biogenic and authigenic quartz) are 52.34%, 24.86% and 6.57% for ORSS, OMMS and OLAS, respectively. Biogenic quartz is the dominant contributor to EX-SiO2, while the contribution of authigenic quartz is limited, and the formation of the former is earlier than the latter according to the diagenetic transformation temperature. As both biogenic quartz and organic matter are firmly related to the abundance and preservation of paleoorganisms, anoxic condition, high Paleoproductivity, low detrital flux and moderate restriction collectively control the high enrichment and preservation of organic matter and biogenic quartz, while oxic condition, low Paleoproductivity, high detrital flux and stronger watermass restriction are unfavorable for the enrichment of biogenic quartz and organic matter.
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effects of volcanic activities in ordovician wufeng silurian longmaxi period on organic rich shale in the upper yangtze area south china
2018Co-Authors: W U Lanyu, Shu Jiang, L U Yongchao, H E GuisongAbstract:Abstract Based on the corresponding relationship between the Paleoproductivity, redox conditions and volcanism within a chronostratigraphic framework, the effects of volcanic events in the Wufeng–Longmaxi period on organic abundance of shale were examined. Bentonite layers were mostly developed in the transgressive systems tract 1 (TST1, Wufeng Formation) and transgressive systems tract 2 (TST2, Longmaxi Formation), and the two systems tracts corresponded to favorite shale lithofacies with high silica and total organic carbon (TOC) contents. According to the stratigraphic characteristics of bentonite rich interval, TST1 is classified as the interval with dense bentonite layers with the frequency of bentonite layer (bentonite layers/time) of more than 1.5 layers/Ma and the cumulative thickness ratio of bentonite layers (thickness of bentonite layers/thickness of shale) of more than 1%; TST2 is classified as the interval with sparse bentonite layers (frequency
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Effect of Hydrothermal Activity on Organic Matter Enrichment of Shale: A Case Study of the Upper Ordovician and the Lower Silurian in the Lower Yangtze, South China
2018Co-Authors: Yizhou Huang, Shu Jiang, Kun Zhang, Zhenxue Jiang, Yan Song, Weiwei Liu, Ming Wen, Xuelian Xie, Tianlin LiuAbstract:The effect of organic matter on hydrocarbon potential, storage space, and gas content of shale is well-known. Additionally, present-day content of sedimentary organic matter in shale is controlled by depositional and preservation processes. Therefore, a study of the enrichment mechanisms of sedimentary organic matter provides a scientific basis for the determination of favorable areas of shale gas. In this study the Upper Ordovician Xinkailing Fm. and the first member of the Lower Silurian Lishuwo Fm. were examined. Stratigraphic sequences were identified through conventional logs and elemental capture spectrum data. Oxygen isotope analysis was applied to recover paleotemperature of seawater in the study area. The excess silicon content was calculated and the origin of the silica was determined by the Fe-Al-Mn ternary plot. The enrichment mechanism of organic matter was analyzed by two aspects: redox conditions and Paleoproductivity. As a result, the stratigraphic interval was divided into two 3rd-order sequences. Through oxygen isotope, the paleotemperature of seawater was 62.7⁻79.2 °C, providing evidence of the development of hydrothermal activity. Analysis of excess siliceous minerals identified two siliceous mineral origins: terrigenous and hydrothermal. It also revealed an upwards decreasing tendency in hydrothermal activity intensity. Strong hydrothermal activity during the Late Ordovician, recognized as TST1, formed a weak-oxidizing to poor-oxygen environment with high Paleoproductivity, which promoted organic matter enrichment. During the Late Ordovician to the Early Silurian, identified as RST1, TST2, and RST2, weakening hydrothermal activity caused the decline of Paleoproductivity and increased oxidation of bottom waters, leading to a relative decrease of organic matter content in the shale. Therefore, favorable areas of shale gas accumulation in the Upper Ordovician and Lower Silurian are determined stratigraphically as the TST1, with a high total organic carbonate content. Geographically, the hydrothermally-active area near the plate connection of the Yangtze and the Cathaysian is most favorable
Dierk Hebbeln - One of the best experts on this subject based on the ideXlab platform.
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high interglacial diatom Paleoproductivity in the westernmost indo pacific warm pool during the past 130 000 years
2012Co-Authors: Oscar E Romero, Mahyar Mohtadi, Peer Helmke, Dierk HebbelnAbstract:[1] A wealth of sedimentary records aimed at reconstructing late Quaternary changes in productivity and temperature have been devoted to understanding linkages between the Indo-Pacific Warm Pool (IPWP) and other distant oceanic areas. Most of these reconstructions are based, however, on biogeochemical and sedimentological proxies, with comparatively less attention devoted to microfossils. A high-resolution (<1 ka) study of diatom concentrations and the community at site GeoB10038-4, recovered off southern Sumatra (ca. 6°S, 103°E), closely tracks the variations of diatom concentrations in the westernmost IPWP during the last glacial-interglacial cycle. The diatom record provides evidence that diatom Paleoproductivity was highest during interglacials, primarily due to the input of lithogenics and nutrients following the rise in sea level after full glacials. In addition, the co-variation of total diatom concentration and Northern Hemisphere forcing for Marine Isotope Stage 5 suggests a direct response of diatom productivity and upwelling intensity to boreal summer insolation. Temporal shifts of the diverse diatom community at site GeoB10038-4 correspond well with the present-day seasonal monsoon pattern and the strengthening and weakening phases of upwelling along the southern coast of Sumatra. Resting spores ofChaetoceros, typical of nutrient-rich waters, were dominant during periods of highest diatom Paleoproductivity and responded to the strengthening of the SE monsoon, while diatoms of oligotrophic to mesotrophic waters characterized intermonsoon periods. The close correspondence between the dominance of upwelling diatoms and the boreal summer insolation resembles the present-day dynamics of diatom production. The observed interglacial highs and glacial lows of diatom productivity at site GeoB10038-4 is a unique pattern in the late Quaternary tropics.
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Paleoproductivity evolution off central chile from the last glacial maximum to the early holocene
2006Co-Authors: Oscar E Romero, Junghyun Kim, Dierk HebbelnAbstract:A geochemical and paleontological reconstruction of Paleoproductivity, upwelling intensity and sea surface temperature (SST) off central Chile at 35°S (GeoB3359-3) reveals marked changes from the Last Glacial Maximum (LGM) through the Early Holocene. Surface-water productivity was determined by the interaction between the atmospheric (the Southern Westerlies) and oceanographic (the Antarctic Circumpolar Current, ACC) systems from the LGM through early Termination I (TI). The northward shift of the climate zones during the LGM brought the ACC, as the main macronutrient source, closer to the GeoB3359-3, SST lowered, and surface water productivity and accumulation rates of biogenic components enhanced. With the poleward return of the Southern Westerlies and the ACC, the subtropical high-pressure system became the dominant atmospheric component southward till 35°S during the late TI and Early Holocene and caused surface water productivity to increase through enhanced upwelling.
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mechanisms and variations of the Paleoproductivity off northern chile 24 s 33 s during the last 40 000 years
2004Co-Authors: Mahyar Mohtadi, Dierk HebbelnAbstract:[1] A multiparameter investigation including organic carbon, carbonate, opal, and planktic foraminifera was carried out on five sediment cores from the coastal upwelling area between 24°S and 33°S along the Peru-Chile Current to reconstruct the history of the Paleoproductivity and its driving mechanisms during the last 40,000 years. Inferred from our data, we conclude that the Antarctic Circumpolar Current as the main nutrient source in this region mainly drives the productivity by its latitudinal shifts associated with climate change. Simplified, its northerly position during the last glacial led to enhanced productivities, and its southerly position during the Holocene caused lower productivities. At 33°S the Paleoproductivity was additionally affected by the southern westerlies and records highest levels during the Last Glacial Maximum (LGM). North of 33°S, several factors (e.g., position and strength of the South Pacific anticyclone, wind stress, continental runoff, and El Nino Southern Oscillation events) supplementary influenced upwelling and Paleoproductivity, where maximum values occurred prior to the LGM and during the deglaciation.
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Paleoproductivity in the southern peru chile current through the last 33 000 yr
2002Co-Authors: Dierk Hebbeln, Margarita Marchant, Gerold WeferAbstract:Abstract Based on a multiparameter approach including organic carbon, biogenic opal, carbonate and the species composition of planktic foraminifera, this paper provides the first qualitative assessment of the history of Paleoproductivity on glacial–interglacial time scales in the southern Peru–Chile Current (PCC) off Chile, which belongs to the least studied parts of the world ocean. During the Last Glacial Maximum (LGM) highest relative Paleoproductivity of the last 33 kyr, indicated by high accumulation rates of organic carbon, biogenic opal and carbonate, has been found, contrasted by lowest values during the early and Middle Holocene. This shift from high to low productivity is accompanied by a major change in the species composition of planktic foraminifera from a dominance of Neogloboquadrina pachyderma (sin.) to the dominance of N. pachyderma (dex.). The temporal pattern of Paleoproductivity off Chile is very similar to the history of the continental paleoclimate in the region, which is supposed to be driven by the position of the Southern Westerlies. This observation points to a functional relationship between the position of the Southern Westerlies and the history of Paleoproductivity off Chile. Assuming that atmospheric and oceanographic circulation are closely linked, a northward displacement of the Antarctic Circumpolar Current during the LGM, in line with the northward movement of the Southern Westerlies, would bring the main nutrient source closer to our core sites resulting in increased productivity. However, based on the available data, it is not clear if the higher productivity in the southern PCC during the LGM reflects generally higher productivity during this time or only a regional displacement of the main productivity centers.
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high concentrations of biogenic barium in pacific sediments after termination i a signal of changes in productivity and deep water chemistry
2001Co-Authors: Jens Klump, Dierk Hebbeln, Gerold WeferAbstract:Abstract High concentrations of barium have been found in sediments deposited on the Chilean continental slope after glacial Termination I. When compared to independent proxies of Paleoproductivity, the pattern of biogenic barium accumulation does not match the changes in Paleoproductivity in this region and cannot be explained by changes in the terrigenous supply of barium alone. This leaves an increased concentration of dissolved barium in sea water as the most likely cause of the observed barium anomalies. Based upon the accumulation rate of biogenic barium and the Paleoproductivity index, which was calculated from the accumulation rates of organic carbon, biogenic opal and carbonate, the changes in the concentration of dissolved barium in the Pacific Ocean in the course of the last glacial and through the Holocene could be modelled. This model shows that barium concentrations in the Pacific during the last glacial were comparable to today (150 nmol kg1). The highest dissolved barium concentrations were calculated for the Early and Middle Holocene (190 nmol kg1). The resulting pattern of variations in the barium concentration in the seawater agrees well with Ba/Ca ratios in benthic foraminifera published in the literature. The observed changes are probably driven by the Holocene shoaling of the Pacific carbonate compensation depth, which is assumed to have caused an increased flux of previously carbonate-bound barium from the sediment to the deep ocean waters, leading to the observed longstanding maximum of dissolved barium in the Pacific during the Holocene.
Gerold Wefer - One of the best experts on this subject based on the ideXlab platform.
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Paleoproductivity in the southern peru chile current through the last 33 000 yr
2002Co-Authors: Dierk Hebbeln, Margarita Marchant, Gerold WeferAbstract:Abstract Based on a multiparameter approach including organic carbon, biogenic opal, carbonate and the species composition of planktic foraminifera, this paper provides the first qualitative assessment of the history of Paleoproductivity on glacial–interglacial time scales in the southern Peru–Chile Current (PCC) off Chile, which belongs to the least studied parts of the world ocean. During the Last Glacial Maximum (LGM) highest relative Paleoproductivity of the last 33 kyr, indicated by high accumulation rates of organic carbon, biogenic opal and carbonate, has been found, contrasted by lowest values during the early and Middle Holocene. This shift from high to low productivity is accompanied by a major change in the species composition of planktic foraminifera from a dominance of Neogloboquadrina pachyderma (sin.) to the dominance of N. pachyderma (dex.). The temporal pattern of Paleoproductivity off Chile is very similar to the history of the continental paleoclimate in the region, which is supposed to be driven by the position of the Southern Westerlies. This observation points to a functional relationship between the position of the Southern Westerlies and the history of Paleoproductivity off Chile. Assuming that atmospheric and oceanographic circulation are closely linked, a northward displacement of the Antarctic Circumpolar Current during the LGM, in line with the northward movement of the Southern Westerlies, would bring the main nutrient source closer to our core sites resulting in increased productivity. However, based on the available data, it is not clear if the higher productivity in the southern PCC during the LGM reflects generally higher productivity during this time or only a regional displacement of the main productivity centers.
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high concentrations of biogenic barium in pacific sediments after termination i a signal of changes in productivity and deep water chemistry
2001Co-Authors: Jens Klump, Dierk Hebbeln, Gerold WeferAbstract:Abstract High concentrations of barium have been found in sediments deposited on the Chilean continental slope after glacial Termination I. When compared to independent proxies of Paleoproductivity, the pattern of biogenic barium accumulation does not match the changes in Paleoproductivity in this region and cannot be explained by changes in the terrigenous supply of barium alone. This leaves an increased concentration of dissolved barium in sea water as the most likely cause of the observed barium anomalies. Based upon the accumulation rate of biogenic barium and the Paleoproductivity index, which was calculated from the accumulation rates of organic carbon, biogenic opal and carbonate, the changes in the concentration of dissolved barium in the Pacific Ocean in the course of the last glacial and through the Holocene could be modelled. This model shows that barium concentrations in the Pacific during the last glacial were comparable to today (150 nmol kg1). The highest dissolved barium concentrations were calculated for the Early and Middle Holocene (190 nmol kg1). The resulting pattern of variations in the barium concentration in the seawater agrees well with Ba/Ca ratios in benthic foraminifera published in the literature. The observed changes are probably driven by the Holocene shoaling of the Pacific carbonate compensation depth, which is assumed to have caused an increased flux of previously carbonate-bound barium from the sediment to the deep ocean waters, leading to the observed longstanding maximum of dissolved barium in the Pacific during the Holocene.
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use of proxies in paleoceanography examples from the south atlantic
1999Co-Authors: Gerhard Fischer, Gerold WeferAbstract:Clues to Ocean History: a Brief Overview of Proxies.- Surface Water Circulation.- Sea-Surface Temperature Estimations Using a Modern Analog Technique with Foraminiferal Assemblages from Western Atlantic Quaternary Sediments.- The Distribution of Living Planktic Foraminifera in Relation to Southeast Atlantic Oceanography.- Coccolithophores as Indicators of Ocean Water Masses, Surface-Water Temperature, and Paleoproductivity - Examples from the South Atlantic.- Calcareous Dinoflagellate Cysts as Paleo-Environmental Tools.- Oxygen Isotope Values of Planktic Foraminifera: A Tool for the Reconstruction of Surface Water Stratification.- Stable Isotopes of Pteropod Shells as Recorders of Sub-Surface Water Conditions: Comparison to the Record of G. ruber and to Measured Values.- On the Reconstruction of Paleosalinities.- Bottom- and Deep Water Circulation.- Stable Carbon Isotopes in Benthic Foraminifera: Proxies for Deep and Bottom Water Circulation and New Production.- Carbonate Dissolution in the Deep-Sea: Methods, Quantification and Paleoceanographic Application.- Kaolinite and Chlorite as Tracers of Modern and Late Quaternary Deep Water Circulation in the South Atlantic and the Adjoining Southern Ocean.- Paleoproductivity and Nutrients.- Organic Carbon and Carbonate as Paleoproductivity Proxies: Examples from High and Low Productivity Areas of the Tropical Atlantic.- Biogenic Barium as a Proxy for Paleoproductivity: Methods and Limitations of Application.- Variability in Export Production Documented by Downward Fluxes and Species Composition of Marine Planktic Diatoms: Observations from the Tropical and Equatorial Atlantic.- Reliability of the 231Pa/230 Th Activity Ratio as a Tracer for Bioproductivity of the Ocean.- Sediment Redistribution, 230Thex - Normalization and Implications for the Reconstruction of Particle Flux and Export Paleoproductivity.- The South Atlantic Carbon Isotope Record of Planktic Foraminifera.- Reconstruction of Surface Ocean Nitrate Utilization Using Stable Nitrogen Isotopes in Sinking Particles and Sediments.- CO2 in Oceans and Atmosphere.- Alkenone ?13C as a Proxy for Past PCO2 in Surface Waters: Results from the Late Quaternary Angola Current.- Reassessing Foraminiferal Stable Isotope Geochemistry: Impact of the Oceanic Carbonate System (Experimental Results).- Implications of a Carbonate Ion Effect on Shell Carbon and Oxygen Isotopes for Glacial Ocean Conditions.- Atmospherical Circulation.- Pollen and Spores in Marine Sediments from the East Atlantic - A View from the Ocean into the African Continent.- Terrestrial Organic Matter in Marine Sediments: Analytical Approaches and Eolian-Marine Records in the Central Equatorial Atlantic.- Environmental Magnetism.- The Magnetic View on the Marine Paleoenvironment: Parameters, Techniques, and Potentials of Rock Magnetic Studies as a Key to Paleoclimatic and Paleoceanographic Changes.- Using Rock Magnetic Proxy Records for Orbital Tuning and Extended Time Series Analyses into the Super- and Sub-Milankovitch Bands.- Geomagnetic Events and Relative Paleointensity Records - Clues to High-Resolution Paleomagnetic Chronostratigraphies of Late Quaternary Marine Sediments?.- Modelling.- Simulation of Oxygen Isotopes in a Global Ocean Model.- Reconstructing and Modelling the Last Glacial Maximum: Beyond CLIMAP.- Data Management.- Data Management of Proxy Parameters with PANGAEA.
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late quaternary surface temperatures and productivity in the east equatorial south atlantic response to changes in trade monsoon wind forcing and surface water advection
1996Co-Authors: Ralph R Schneider, Peter J Muller, Gotz Ruhland, Gerrit Meinecke, Heike Schmidt, Gerold WeferAbstract:In order to reconstruct Late Quaternary variations of surface oceanography in the east- equatorial South Atlantic, time series of sea-surface temperatures (SST) and Paleoproductivity were established from cores recovered in the Guinea and Angola Basins, and at the Walvis Ridge. These records, based on sedimentary alkenone and organic carbon concentrations, reveal that during the last 350,000 years surface circulation and productivity changes in the east-equatorial South Atlantic were highly sensitive to climate forcing at 23- and 100-kyr periodicities. Covarying SST and Paleoproductivity changes at the equator and at the Walvis Ridge appear to be driven by variations in zonal trade-wind intensity, which forces intensification or reduction of coastal and equatorial upwelling, as well as enhanced Benguela cold water advection from the South. Phase relationships of precessional variations in the Paleoproductivity and SST records from the distinct sites were evaluated with respect to boreal summer insolation over Africa, movements of southern ocean thermal fronts, and changes in global ice volume. The 23-kyr phasing implies a sensitivity of eastern South Atlantic surface water advection and upwelling to West African monsoon intensity and to changes in the position of the subtropical high pressure cell over the South Atlantic, both phenomena which modulate zonal strength of southeasterly trades. SST and productivity changes north of 20°S lack significant variance at the 41-kyr periodicity; and at the Walvis Ridge and the equator lead changes in ice volume. This may indicate that obliquity-driven climate change, characteristic for northern high latitudes, e.g fluctuations in continental ice masses, did not substantially influence subtropical and tropical surface circulation in the South Atlantic. At the 23-kyr cycle SST and productivity changes in the eastern Angola Basin lag those in the equatorial Atlantic and at the Walvis Ridge by about 3500 years. This lag is explained by variations in cross-equatorial surface water transport and west-east countercurrent return flow modifying precessional variations of SST and productivity in the eastern Angola Basin relative to those in the mid South Atlantic area under the central field of zonal trade winds. Sea level-related shifts of upwelling cells in phase with global climate change may be also recorded in SST and productivity variability along the continental margin off Southwest Africa. They may account for the delay of the paleoceanogreaphic signal from continental margin sites with respect to that from the pelagic sites at the equator and the Walvis Ridge.
Caina Yan - One of the best experts on this subject based on the ideXlab platform.
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influence of sedimentary environment on organic matter enrichment in shale a case study of the wufeng and longmaxi formations of the sichuan basin china
2018Co-Authors: Jianhua Zhao, Zhijun Jin, Caina Yan, Quanyou LiuAbstract:Abstract As two essential controls on the formation of organic matter (OM)-enriched shales, both Paleoproductivity and preservation models remain controversial for the Wufeng and Longmaxi shales in the Sichuan Basin, southwest China. This study provides geochemical parameters as proxies for the Paleoproductivity characteristics (Ba, P/Al, and (Ni+Cu)/Al), bottom water redox status (U/Th, V/(V+Ni), V/Cr, and Mo), and terrigenous clastic flux (Th and Al) of the Wufeng–Longmaxi Formations in the Sichuan Basin, a back-deep basin in a foreland basin system in southwest China. Combining these data with total organic carbon (TOC) content and sedimentation rate data obtained from graptolite zones allowed us to discuss the validity of these popular indices and to identify the main factors that controlled OM enrichment in the formations. TOC contents exceed 4 wt% in the upper Wufeng Formation to the bottom part of the Longmaxi Formation (LM1-3), which are the most OM-rich intervals. The average P/Al ratio for well JY2 in the Jiaoshiba area is 0.009, which is lower than those for well YY1 (0.028) in the Yongchuan area and well DY1 (0.02) in the Dingshan area, indicating the lowest productivity levels were in the Jiaoshiba area. Based on the redox proxies, the samples from well DY1 reflect less reducing bottom water conditions than those from wells JY2 and YY1. The Th and Al indices increase upwards, indicating that the terrigenous clastic input increased, and that those in the Yongchuan area were lower than those in the Jiaoshiba and Dingshan areas. The sedimentation rate was too low to dilute the OM in the Sichuan Basin, especially during the depositional time of the OM-rich intervals, such that the redox status of the water became more critical. Given the more strongly reducing conditions of the sedimentary environment and the high thermal maturity of the OM in this formation, the Ba concentrations appeared anomalously low and became inaccurate as a Paleoproductivity index, as well as the validity of V, V/Cr, and V/(V+Ni) anomalously decreased as redox indices.
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applying sedimentary geochemical proxies for paleoenvironment interpretation of organic rich shale deposition in the sichuan basin china
2016Co-Authors: Jianhua Zhao, Zhijun Jin, Zhenkui Jin, Yikai Geng, Xin Wen, Caina YanAbstract:Abstract Depositional environment highly affects the geochemical feature of sediments recording the information of paleoenvironment and its evolution. Geochemical data for Ordovician Wufeng Formation and Silurian Longmaxi Formation black shale deposition in the Sichuan Basin are presented and applied as proxies for deciphering paleoenvironment (detrital influx, redox conditions, Paleoproductivity) and providing insight to paleoenvironmental conditions responsible for organic carbon accumulation. These data suggest that siliceous shale in the Wufeng and Longmaxi Formations reveals high TOC content, whereas silty, argillaceous, and limey shale display relatively low TOC contents. Major element and petrological evidences indicate that most of quartz in siliceous shales is biogenic origin (as shown by excess silica concentrations); therefore, Si is an unreliable indicator of detrital influx. The similar distribution of detrital influx proxies (Ti/Al, Ce, Hf, La, Nb Th and Zr) suggests a rather homogeneous coarse-grained detrital fraction supply. Redox proxies (Mo, Th/U, Ni/Co, V/Cr, and V/(V + Ni)) indicate that siliceous shales were deposited in a relatively dysoxic/anoxic environment, whereas the argillaceous, silty, and limey shales were deposited in a relatively oxic environment. Barium was solubilized under reducing conditions and cannot be applied confidently as a Paleoproductivity indicator in high-TOC siliceous shales. Productivity proxies (Cu/Al, Ni/Al, excess Si) suggest that Paleoproductivity was high during siliceous shales deposition, and weak during argillaceous and limey shales deposition. Our data suggests that high Paleoproductivity and dysoxic/anoxic conditions controlled organic matter accumulation in Wufeng and Longmaxi shales.
Sean Crowe - One of the best experts on this subject based on the ideXlab platform.
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Empowering conventional Rock-Eval pyrolysis for organic matter characterization of the siderite-rich sediments of Lake Towuti (Indonesia) using End-Member Analysis
2019Co-Authors: Luis Ordoñez, Hendrik Vogel, David Sebag, Daniel Ariztegui, Thierry Adatte, James Russell, Jens Kallmeyer, Aurèle Vuillemin, André Friese, Sean CroweAbstract:Qualitative and quantitative changes of organic and carbonate carbon in sedimentary records are frequently used to reconstruct past environments, Paleoproductivity and sediment provenance. Amongst the most commonly used proxies are Total organic carbon (TOC), Mineral carbon (MinC), as well as Hydrogen (HI) and Oxygen Indices (OI) of organic matter (OM). Rock Eval pyrolysis enables the assessment of these quantitative and qualitative parameters with a single analysis. This is achieved through transient pyrolysis of the samples up to 650°C followed by combustion up to 850°C, with hydrocarbons, CO and CO2 measured during the thermal decomposition of both OM and carbonate minerals. Carbonate minerals with low thermal cracking temperatures such as siderite (