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The boundary between the Devonian and the Carboniferous has been drawn using ammonoids, conodonts and miospores, while geochemical data have only rarely been used. The sampling of eight sections (Aprath, Apricke, Effenberg, Wocklum, Stockum, Drewer WJ, Drewer WA, Marsberg) at the northern margin of the Rhenish Mountains demonstrates the potential of the isotope ratio of organic carbon to regionally correlate sections in different facies areas. With the help of the carbon isotopes, a distinct stratigraphic succession is documented, which is characterised by several positive and negative excursions; this succession was recorded in all examined sections. The carbon isotopes can therefore make a significant contribution to the stratigraphic subdivision of sections and complement the biostratigraphic methods. [ABSTRACT FROM AUTHOR]

The recently discovered Yangchang deposit in Zhenxiong County, Zhaotong City, Yunnan Province is an ultra-large-scaled buried phosphate deposit. Previous research on this deposit mainly focused on the metallogeny, while the study of sedimentary geochemistry and the paleoenvironment is lacked. More importantly, the inorganic (δ13Ccarb) and organic (δ13Corg) carbon isotopes as well as their relationships in the early Cambrian were rarely reported. In this study, three drill cores (ZK001, ZK0701, ZK1512) in Yangchang phosphate deposit were selected for high-resolution investigations of δ13Ccarb and δ13Corg. Both δ13Ccalb and δ13Corg show negative shifts in the top Pre-cambrian Dengying Formation and the bottom of its overlying Zhujiaqing Formation, which is consistent with the global Basal Cambrian Carbon Isotopic Excursion (BACE), likely due to the oxidation of organic carbon reservoir. However, we did not find significant positive shifts in the overlying strata (i. e., Zhujiaqing Carbon Isotopic Excursion, ZHUCE), which may be caused by sedimentary hiatus given that the Yangchang phosphate deposit is mostly intra-clastic phosphorus-rich deposits. Nevertheless, we propose that this phosphate deposit was mainly formed during the Fortunian according to the comparison between the δ13Ccarb in the three drill cores and the composite profile of δ13Ccarb in South China. The comparisons for the δ13Ccarb and δ13Corg values in the drill cores ZK001 and ZK0701, show that the average value of the ΔCcarb.org(difference between δ13Ccalb and δ13Corg) is 28.%‰ and 22.2‰ in the Dengying Formation, and these values change to 31.7‰ and 31.7‰ at the bottom of the Zhujiaqing Formation, and 29.6‰ and 29.8‰, in the middle and upper of the Zhujiaqing Formation, respectively. We propose that the decoupled δ13Ccarb and δ13Corg occurring in the middle of the Zhujiaqing Formation may be caused by the increased primary productivity or buried organic carbon. In summary, the high-resolution paired inorganic and organic carbon isotopes in this work indicate the formation time of Yangchang phosphate deposit and shed light on associated paleo-environmental changes, which also support the regional stratigraphic correlation. [ABSTRACT FROM AUTHOR]

[Display omitted] • Black shales with basin-wide distribution were deposited during the Snowball Earth. • Petrographic and geochemical evidence indicates intensified chemical weathering. • Biodiversification might have been bolstered by cyclic ice waxing and waning. The Marinoan glaciation is the younger of the two extraordinary glaciations during the Cryogenian Period. It has been debated whether the glacial world was featured by a complete ice cover or if parts of the oceans remained ice free. Here, we present petrographic and geochemical data of two black shale units found within diamictites of the Marinoan-aged Nantuo Formation in South China. The lower black shales exhibit low values of the chemical index of alteration (CIA) and muted enrichments of uranium, while the upper black shales show elevated CIA and uranium concentrations. These distinct geochemical signals are best explained by intensified chemical weathering and terrestrial runoff, which might be linked to global/local temperature changes. Our study is consistent with the notion that significant climate variations occurred during the Marinoan glaciation. The cyclic isolation and expansion of habitable areas might have acted as a biodiversity pump, contributing to the rapid radiation of eukaryotic life in the aftermath of the glaciation. [ABSTRACT FROM AUTHOR]

The Ediacaran – Cambrian transition witnessed dramatic changes in the marine environment that are thought to have strongly influenced biological evolution. Previous studies have linked biological innovations to palaeo‐redox changes and suggested that increased productivity is the primary driver of the marine environment. However, the primary productivity and redox control mechanism still need to be clarified. Here, we present new organic carbon isotopes, total organic carbon contents, major elements, and trace and rare earth elements in drill‐core ZK107 from South China to reveal the continental chemical weathering, primary productivity, and redox control mechanism during the Earliest Cambrian (E‐C). Our studies have shown intense continental weathering, and primary productivity fluctuations that were supported by weathering (CIA, Rb/Al) and productivity (Babio, P) indicators. Additionally, the quantitative reconstructed productivity proxies (PP18, PP21, PP23) indicate a high primary productivity level in the E‐C ocean, surpassing that of the modern oceans. The strengthening of continental weathering mainly causes high primary productivity because it can alter the nutrient supply to the oceans. We suggest that changes in primary productivity closely associated with continental weathering are the leading cause of marine anoxia during the E‐C. This study establish a linkage between the land and marine system during the E‐C, confirming the terrestrial controls on the marine chemical changes and providing new insights into understanding the evolution of the Earth's surface changes during the Ediacaran – Cambrian transition. [ABSTRACT FROM AUTHOR]

Recently, methane seepage related to the dissociation of natural gas hydrates has attracted much attention, which has a significant impact on the study of the global carbon and nitrogen cycles. Based on the detailed geochemical analyses of sediments (core Q6) from the Qiongdongnan Basin, South China Sea, three methane seepage activities were identified and the exact horizons of anaerobic oxidation of methane (AOM) were defined. Furthermore, organic carbon isotopic (δ13CTOC) levels ranged from −23.696‰−−20.696‰ PDB; nitrogen isotopes (δ15NTN) of the same sedimentary samples ranged from 1.899‰–5.399‰. We also found obvious simultaneous negative excursions of organic carbon isotopes (δ13CTOC) and nitrogen isotopes (δ15NTN) in the horizons of methane seepages. Compared with the normal sediments, their maximum negative excursions were 2.699‰ and 2.599‰, respectively. We discuss in detail the various characteristics of δ15NTN and δ13CTOC levels in sediments and their coupling responses to methane seepage activities. We believe that the methane seepage events changed the evolution trajectory of δ15NTN and δ13CTOC levels in sediment records, which resulted in the simultaneous negative excursions. This phenomenon is of great significance to reveal the historical dissociation of natural gas hydrates and their influence on the deep-sea carbon and nitrogen pool. [ABSTRACT FROM AUTHOR]

The Tarim Basin is the only petroliferous basin enriched with marine oil and gas in China. It is presently also the deepest basin for petroleum exploration and development in the world. There are two main sets of marine Source Rocks (SRs) in the Tarim Basin, namely the high over‐mature Cambrian–Lower Ordovician (∊ –O1) and the moderately mature Middle–Upper Ordovician (O2–3). The characteristic biomarkers of SRs and oils indicate that the main origin of the marine petroleum is a mixed source of ∊ –O1 and O2–3 SRs. With increasing burial, the hydrocarbon contribution of the ∊ –O1 SRs gradually increases. Accompanied by the superposition of multi‐stage hydrocarbon‐generation of the SRs and various secondary alteration processes, the emergence and abnormal enrichment of terpenoids, thiophene and trimethylaryl isoprenoid in deep reservoirs indicate a complex genesis of various deep oils and gases. Through the analysis of the biofacies and sedimentary environments of the ∊ –O1 and O2–3 SRs, it is shown that the lower Paleozoic high‐quality SRs in the Tarim Basin were mainly deposited in a passive continental margin and the gentle slope of the platform, deep‐water shelf and slope facies, which has exhibited a good response to the local tectonic‐sedimentary environment. The slope of the paleo‐uplift is the mutual area for the development of carbonate reservoirs and the deposition of marine SRs, which would be favorable for the accumulation of petroleum. Due to the characteristics of low ground temperature, the latest rapid and deep burial does not cause massive oil‐cracking in the paleo‐uplift and slope area. Therefore, it is speculated that the marine reservoirs in the slope of the Tabei Uplift are likely to be a favorable area for deep petroleum exploration, while the oil‐cracking gas would be a potential reserve around the west margin of the Manjiaer Depression. Hydrocarbons were generated from various unit SRs, mainly migrating along the lateral unconformities or reservoirs and the vertical faults. They eventually brought up three major types of exploration fields: middle and lower Cambrian salt‐related assemblages, dolomite inner reservoirs and Middle and Lower Ordovician oil‐bearing karst, which would become the most favorable target of marine ultra‐deep exploration in the Tarim Basin. [ABSTRACT FROM AUTHOR]

Organic carbon isotopic composition (δ13Corg) in loess deposits is an important indicator of terrestrial paleovegetation, and it has been widely used for paleoenvironmental reconstruction in aeolian sediments around the world. However, little research has been done on the variation and paleoenvironmental implication of δ13Corg from loess deposits on Shengshan Island, East China Sea, during the last glacial period (LG). In this research, we present optically stimulated luminescence (OSL) ages, total organic carbon (TOC) data and δ13Corg records of the loess section at Chenqianshan (CQS) on Shengshan Island. Additionally, to study the effectiveness of δ13Corg in documenting paleoenvironmental changes, magnetic susceptibilities and diffuse reflectance spectra were surveyed. TOC concentration for the CQS loess section ranged from 0.11% to 0.47%, and the δ13Corg composition of the CQS loess section varied between −20.80‰ and −24.56‰ during the LG. The average value of C4 abundance was 21.31%. TOC, δ13Corg, χfd, and Hm/(Hm + Gt) curves for the CQS loess section showed similar patterns. The results of our study indicated that the vegetation of the CQS loess deposit was mainly C3/C4 mixed vegetation, and C3 vegetation was the most important vegetation. The comparison between the δ13Corg curve for the CQS section and other existing δ13Corg records of the loess sections from central and northern China showed similar trends and their vegetation succession exhibited synchronous change during the LG. Based on a comparison of the δ13Corg record, C4 abundance and χfd of the CQS section and other global geological records, it was concluded that the mutual effects of precipitation and temperature caused the change of paleovegetation in loess deposits on islands in the East China Sea during the LG. [ABSTRACT FROM AUTHOR]

Organic carbon isotopic composition (δ13Corg) in loess deposits is an important indicator of terrestrial paleovegetation, and it has been widely used for paleoenvironmental reconstruction in aeolian sediments around the world. However, little research has been done on the variation and paleoenvironmental implication of δ13Corg from loess deposits on Shengshan Island, East China Sea, during the last glacial period (LG). In this research, we present optically stimulated luminescence (OSL) ages, total organic carbon (TOC) data and δ13Corg records of the loess section at Chenqianshan (CQS) on Shengshan Island. Additionally, to study the effectiveness of δ13Corg in documenting paleoenvironmental changes, magnetic susceptibilities and diffuse reflectance spectra were surveyed. TOC concentration for the CQS loess section ranged from 0.11% to 0.47%, and the δ13Corg composition of the CQS loess section varied between −20.80‰ and −24.56‰ during the LG. The average value of C4 abundance was 21.31%. TOC, δ13Corg, χfd, and Hm/(Hm + Gt) curves for the CQS loess section showed similar patterns. The results of our study indicated that the vegetation of the CQS loess deposit was mainly C3/C4 mixed vegetation, and C3 vegetation was the most important vegetation. The comparison between the δ13Corg curve for the CQS section and other existing δ13Corg records of the loess sections from central and northern China showed similar trends and their vegetation succession exhibited synchronous change during the LG. Based on a comparison of the δ13Corg record, C4 abundance and χfd of the CQS section and other global geological records, it was concluded that the mutual effects of precipitation and temperature caused the change of paleovegetation in loess deposits on islands in the East China Sea during the LG.

The geologic history of Wyoming's Hanna Basin is still being written. Surprisingly, here appeared an opportunity to share insights from previously accomplished work with that conducted anew by other scholars. The area of study was in the southeastern quadrant of Wyoming, which exhibits the state's most complex history with respect to the Laramide orogeny. Especially important for present purposes were the tectonic conditions of the late Paleocene and earliest Eocene, recorded within the Hanna Formation. Of central focus is the 2020 publication by Dechesne and her six co-authors. Geographically, the landscape they covered was a thin, synclinal slice of the northeastern margin of the Hanna Basin. Key goals for the present publication have been to illustrate positive linkages and to highlight discrepancies between Dechesne et al. (2020) and relevant prior geological work. A concern that permeates all facets of this approach is the ability to verify viability of brand-new geologic descriptions, data, and resulting conclusions. Essential graphical elements were introduced first into this present publication. Once that package of background information was available, more focused analyses were rigorously pursued on diverse issues within the Dechesne et al. (2020) publication. Dechesne's team presented a significantly modified but adequately defended approximation of the Paleocene-Eocene boundary. Data from fossil plants (macro-and palynofloras), continental mollusks, and bulk organic-carbon isotopes all agree within one measured section (of five sections studied) with an approximated Paleocene-Eocene boundary along with a 'carbon isotope excursion' (CIE). Strength of available evidence seems questionable, however, in that the inordinately high variability in bulk organic carbon (characteristic of a CIE) has been demonstrated only in the Hanna Draw Section. Although fluvial, paludal, and lacustrine facies are considered in several contexts, in no sense does the publication's organizational form provide a 'detailed stratigraphic framework.' One zircon-based U-Pb depositional date (54.42 ±0.27 Ma) came from this study that matched early Wasatchian time. Participants in the Dechesne et al. (2020) project are to be commended in that their resulting paper ranged broadly across the geologic setting, stratigraphy, paleocurrents, paleobotany, continental mollusks, zircon geochronology, associated lithofacies, and paleogeography. Despite that breadth, there exists a plethora of unexpected and wholly avoidable inconsistencies, strong contradictions within what should be homogeneous datasets, and seemingly inexplicable omissions of obviously necessary and sometimes clearly existing but unutilized data, one must question the reliability of much of the information presented in their paper. [ABSTRACT FROM AUTHOR]

Black shales in the Ediacaran Doushantuo Formation (predominantly from Member II, IV and equivalent strata) and the Lower Cambrian Niutitang Formation (or equivalents) occur widely in the Yangtze Platform, South China. These black shales could provide sufficient hydrocarbons for the petroleum system in this region. However, biomarker parameters have proven invalid in the assessment of petroleum resources because of the high thermal maturity. Therefore, it is necessary to study the characteristics and formation mechanisms of these two black shales. This study analyzed redox-sensitive elements, total organic carbon (TOC) contents, and carbon isotopic compositions of organic matter in four continuous sedimentary successions including the two investigated shales in the Yangtze Platform (namely Jiulongwan on the inner shelf, Songlin in an intra-shelf lagoon, Dongkanshang on the upper slope, and Fengtan in the basin). Combined with other previously reported five sections, the redox conditions of sedimentary waters and marine paleoproductivity of the Ediacaran to Lower Cambrian black shales in the Yangtze Platform were discussed and compared. The results showed that the redox conditions of the Early Cambrian in the study area were similar to those of the Ediacaran Doushantuo period, which were oxic-suboxic at surface water, and anoxic in the deep with the occurrence of euxinic conditions. However, the euxinic conditions in the deep waters were distributed more widely in the Early Cambrian than in the Ediacaran period. The source of organic matter in the Doushantuo Formation was dominated by algae in the shallow-water platform and the shelf-margin areas, while chemoautotrophic/methanotrophic biomass may also have contributed in the intra-shelf lagoon and deep-water basin areas. In contrast, the organic matter of the Niutitang Formation was mainly contributed by the chemoautotrophic/methanotrophic biomass, with a minor contribution by photosynthetic algae and cyanobacteria. During the Doushantuo period, the input of terrigenous clastic materials was low, resulting in the enrichment of organic matter and formation of organic-rich black shale in the Yangtze Platform over a long geological time period. Compared to the Doushantuo period, the shorter sedimentation time and the higher deposition rate during the Early Cambrian produced a thicker and higher-quality Niutitang Formation source rock widely distributed in the Yangtze Platform. • Ediacaran and lower Cambrian source rocks in the Yangtze Platform were studied. • Geochemical characteristics of the two source rocks have been analyzed and compared. • Formation mechanisms for the two source rocks have been proposed. • Conclusions about the source rocks give theoretical basis for petroleum exploration. • Validity of δ13C org values as a method for hydrocarbon-source correlation is proved. [ABSTRACT FROM AUTHOR]

Abstract Shallow water carbonate rocks are especially prone to diagenetic alteration. As such they are sometimes problematic archives of past carbon cycle perturbations, casting doubt on the reliability of shallow-water carbonates carbon isotopes analyses for chemostratigraphic purposes. In this paper, bulk organic carbon isotopes (δ13C org) is used as a robust replacement of the more sensitive carbonate carbon isotope systems for the establishment of a refined chronostatigraphic framework for the evolution of Sinemurian-Pliensbachian neritic carbonate systems in the Central High Atlas Basin of Morocco. These data show very similar patterns and characteristics in the organic carbon isotope curves of basinal and platform sections and thus illustrate the reliability of these archives. Simultaneously, we explore the expression of the global carbon isotope excursion at the Sinemurian-Pliensbachian boundary (S P event) in the study area in Morocco. This event has been previously described as a negative carbon isotope excursion of ∼2‰ associated with a large transgression in numerous basins. In Morocco and other neritic carbonate records, the S P event is better described as a return to previous values after a positive carbon isotope excursion coinciding with a major latest Sinemurian regression recognised on a global scale. Similar patterns are also found in other sections, although sometimes poorly expressed. However, it shows, that the S P event has ambiguous characteristics and questions the conventional hypothesis of it being linked to the massive injection of 13C-depleted carbon into the atmosphere-ocean system. Highlights • Carbon isotope chemostratigraphic constrain on Sinemurian-Pliensbachian sections. • A positive C-isotope excursion characterizes the latest Sinemurian. • The S P event is a return to background C-isotopes values. [ABSTRACT FROM AUTHOR]

Highlights • Three high resolution and complete profiles of δ13C org record have been built for the late Cryogenian (non-glacial) interval. • The built δ13C org records are from organic carbon-rich black shale. • There was an organic carbon isotope gradient in the late Cryogenian (non-glacial) interval ocean. • There was a large organic carbon reservoir in the late Cryogenian (non-glacial) interval ocean. • Late Cryogenian (non-glacial) interval interglacial ocean was gradually oxygenated and redox stratified. Abstract The late-Cryogenian warm (non-glacial) interval (c.660 − c.650 Ma) is potentially of great significance to the co-evolution between life and the surface environment during the emergence of animal life on Earth. In this study, three high-resolution organic carbon isotopic (δ13C org) records for the Datangpo/Xiangmeng Formation on the Yangtze Craton are presented. The data derive from drill cores representing different depositional settings at Daotuo (slope setting), Minle (shallow-water basin), and Xiangtan (basin), respectively. The Daotuo and Minle samples exhibit an overall increase of 6–8‰ as well as significant isotopic fluctuations following the Tiesi'ao/Sturtian glaciation, while samples from the deeper Xiangtan section show relatively muted fluctuations (±1‰) and no overall trend over the same interval. These findings can be plausibly explained by a much longer residence time for marine organic matter, which may have acted as a redox buffer against oxygenation and climate change. The build-up and eventual oxidation of a sub-pycnocline organic carbon reservoir in the redox stratified non-glacial ocean could help to explain the extreme positive and negative carbon isotope perturbations, respectively, in time-equivalent shallow-marine carbonate Platform successions from Mongolia, Australia and Namibia. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Rhaetian to Hettangian shales interbedded in chert in the Katsuyama, SW Japan. • δ 13 C org and major, trace, and rare earth elements data obtained from the shales. • Three negative δ 13 C org excursions (NCIEs) are recognized in the mid-Panthalassa. • Multiple episodes of volcanic outgassing is a plausible cause for three NCIEs. • Deep Panthalassa remained under oxic conditions. Abstract To examine environmental changes in the biosphere during the Triassic–Jurassic transition, with a particular focus on the global carbon cycle related to Central Atlantic Magmatic Provinces (CAMP) volcanism in the mid-Panthalassa, we established stratigraphic δ 13 C org variations using Rhaetian (Late Triassic) to Hettangian (Early Jurassic) shales interbedded within deep-sea cherts in the Katsuyama section in the Mino-Tanba belt, SW Japan. High-resolution record of Rhaetian to Hettangian δ 13 C org values in the mid-Panthalassa contain three distinct negative carbon isotopic excursions (NCIEs) before and across the Triassic–Jurassic boundary (TJB): the Rhaetian NCIE1 and NCIE2 show a deviation of 5.0‰ from ca. −24.0‰ to ca. −29.0‰, whereas NCIE3 across the TJB shows a 3.5‰ deviation from ca. −23.5‰ to ca. −27.0‰. Our newly obtained NCIEs in the deep mid-Panthalassa can be correlated with the δ 13 C org records in the shallow-marine Tethyan regions (i.e., precursor, initial, and main CIEs), suggesting that three NCIEs in the Tethys and mid-Panthalassa likely reflected the global perturbations of the carbon cycle. Three NCIEs before and across the TJB can be interpreted as the consequence of the multiple CAMP volcanic episodes; i.e., the release of thermogenic methane from organic-rich sediments by CAMP intrusive rocks for NCIE1 and large-scale volcanically derived carbon species for NCIE2 and NCIE3. In addition, progressive increase of atmospheric p CO 2 throughout three NCIEs was possibly attributed to accumulation of volcanically derived CO 2 from multiple CAMP eruptions, which resulted in the development of ocean acidification across the TJB. On the other hand, in view of the oxic conditions in the deep mid-Panthalassa during three NCIEs, the development of coeval oceanic anoxic–euxinic conditions was restricted solely to shallow-marine regions. Therefore, ocean acidification together with localized shallow-marine anoxia acted as environmental stresses on the biosphere, which eventually resulted in the severe biotic crisis at the end of the Triassic. [ABSTRACT FROM AUTHOR]

The Kungurian (late Cisuralian) is associated with elevated atmospheric p CO 2 levels and numerous substantial changes in the ocean and terrestrial systems, but carbon cycle perturbations through this time interval are poorly understood. Here, three well-dated organic carbon isotope (δ 13 C org ) curves from South China, paired with their respective carbonate carbon isotope (δ 13 C carb ) data published before, are presented for the first time. Their comparison demonstrates that a prominent, rapid, and synchronous negative excursion in δ 13 C org and δ 13 C carb occurred in the early Kungurian (the herein proposed KCIE event dated to ca. 277.9–277.4 Ma). A comparable shift is observed in other deeper-water marine sections in South China and two terrestrial sections in North China and eastern Australia. Based on carbon mass-balance calculations and a review of concurrent geological records, we propose that the KCIE event was driven by an intensive volcanism of a large igneous province in northern Gondwana, dissociation of voluminous methane hydrates induced by this volcanism, and the ensuing worldwide conflagrations. Predicted elevated production of greenhouse gases involved would have warmed the Earth and further resulted in ocean stagnation, anoxia, and acidification, all of which are in conformity with the documented sedimentological, geochemical, and palaeontological data. This major anomaly in the carbon cycle in the late Cisuralian is considered here to play a key role to promote the transition of the Earth to a greenhouse mode. [ABSTRACT FROM AUTHOR]

Ediacaran stratigraphic correlation depends on the integration of paleontological and δ 13 C carb data. However, these data often come from different lithologies (e.g., shales vs. carbonates), making it difficult to directly link biostratigraphic and chemostratigraphic markers. Ediacaran successions in South China consist of mixed carbonates and shales, offering an opportunity for integrated biostratigraphic and chemostratigraphic investigations. Black shales of the Ediacaran Miaohe Member in the Yangtze Gorges area contain macroalgae and Ediacara-type macrofossils, both preserved as carbonaceous compressions. The Miaohe Member has been traditionally regarded as an equivalent to Member IV of the uppermost Doushantuo Formation that records part of the Shuram negative δ 13 C carb excursion in South China. Thus, the Miaohe Member may have the potential to clarify the stratigraphic relationship between Ediacara-type fossils and the Shuram excursion. Recently, however, the Miaohe Member has been partially correlated with the Shibantan Member of the Dengying Formation (the “A” correlation) or partially with Member IV (the “Z” correlation). These correlations have different implications for the relationship between the Miaohe Member and the Shuram excursion. Here we test these two correlations using δ 13 C data of sedimentary kerogen or total organic carbon (δ 13 C org TOC ), taking advantage of the distinct δ 13 C org TOC values between the Shibantan Member and Member IV. Our data show that δ 13 C org TOC of the Miaohe Member is more similar to that of Member IV than to Shibantan Member, providing tentative support for the “Z” correlation. In addition, we also analyzed δ 13 C org of individual carbonaceous compression fossils (δ 13 C org taxon ), which have lower carbon isotope values than TOC. The data suggest that oxygenic photosynthesizers (e.g., macroalgae, cyanobacteria, and eukaryotic phytoplankton) were not the only contributors to sedimentary TOC. Methylotrophs, photoautotrophs, and chemoautotrophs living in anoxic waters or at the oxycline may have fixed recycled CO 2 derived from organic carbon remineralization, thus contributing a significant amount of 13 C-depleted organic carbon to sedimentary kerogen in the Miaohe Member. [ABSTRACT FROM AUTHOR]

This study has reconstructed the Holocene environmental history of central Tibetan Plateau, a transitional area between monsoon-dominated Asia and Westerlies-dominated Asia, to examine the interplay between the two circulation systems and effects of other potential mechanisms on the temporal variability of Holocene climatic conditions in the study area. Specifically, this study has produced a twin record of palaeo-hydrology and palaeotemperature from an alpine wetland sediment sequence using two sets of lipid-based biomarker indices: n-alkanes and branched glycerol dialkyl glycerol tetraethers (bGDGTs). The results show that (1) the Asian summer monsoon has supplied moisture that helped initiate the wetland habitat around 8000 cal. yr BP, about 2000 years later than locations along the southeastern edge of the plateau; (2) a significant decline in moisture supply is evident since the Medieval Warm period; (3) the Westerlies have transmitted variability of the North Atlantic climate to the study area, resulting in periodic increases in evaporation and causing short-term expansion or contraction of the wetland and (4) the palaeo-air temperature change follows closely that of global sea level and sea surface temperature, implying a link to global ice volume change throughout the Holocene. This study concludes that the Holocene climate history of central Tibetan Plateau is a result of monsoonal moisture supply interacted with the Westerlies variability, while the palaeo-temperature has followed changes in global ice volume during the present warm interglacial. [ABSTRACT FROM AUTHOR]

In order to reconstruct the Holocene environmental history of a coastal site in the northern South China Sea, this study analysed the organic carbon isotope ratios (δ 13 C org ) and alkenone unsaturation ratios (U K′ 37 ) from a 36.5 m-long sediment core drilled at seabed in the mouth region of the Pearl River estuary and generated a coupled hydrological and temperature record. This record reveals changes of monsoon-induced sediment discharge and sea surface temperature of the Holocene in four stages. In Stage I, the site was under fluvial conditions prior to postglacial marine transgression. Stage II saw an increase of sea surface temperature from c. 23.0 °C to 27.0 °C, associated with a strengthened summer monsoon from c. 10,350 to 8900 cal. years BP. This was also a period of rapid sea-level rise and marine transgression, during which the sea inundated the palaeo-incised channel, i.e. the lower part of the T-shape accommodation space created by the rising sea. In these 1500 years, fluvial discharge was strong and concentrated within the channel, and the high sedimentation rate (11.8 mm/year) was very close to the rate of sea-level rise. In the subsequent 2000 years (Stage III) sea level continued to rise and the sea flooded the broad seabed above the palaeo-incised channel, resulted in fluvial discharge spreading thinly across the wide accommodation space and a much reduced sedimentation rate (1.8 mm/year). Sea surface temperature in this stage reached 27.3 °C initially, but dropped sharply to 26.1 °C towards c. 8200 cal. years BP. The final stage covers the last 7000 years, and the site was under a stable sea level. Sedimentation in this stage varied a little, but averaged at 1.8 mm/year. Whilst fluvial discharge and sea surface temperature didn’t change much, two short periods of hydrological and temperature change were observed, which are related to the climatic cooling events of c. 4200 cal. years ago and the Little Ice Age. [ABSTRACT FROM AUTHOR]

Analysis of the stable carbon isotopes (δ 13 C) in organic material in various geological archives has been widely used for paleoclimatic reconstruction. Consequently, it is important to characterize the δ 13 C values of modern plants and surface soils to provide analogues for strengthening paleoclimatic reconstructions. In this paper, > 10.000 previously reported δ 13 C values from modern plants and surface soils at globally distributed sites, together with newly obtained surface soil δ 13 C data from 107 sites in inland China, are used to establish relationships with corresponding mean annual temperature (MAT) and precipitation amount (MAP). Using a δ 13 C value of − 24‰ of surface soil as the discriminator between pure C 3 vegetation and C 3 /C 4 mixed vegetation, our results demonstrate a close relationship between MAT and C 4 relative abundance, implying that temperature is the primary climatic factor determining the C 3 /C 4 relative abundance. Both the δ 13 C values of modern C 3 plants and surface soils under pure C 3 vegetation are significantly negatively correlated with MAP, confirming that the δ 13 C of material sourced from pure C 3 vegetation can be used for paleoprecipitation reconstruction. However, unlike C 3 plants, the δ 13 C values of modern C 4 plants are significantly positively correlated with MAP. Thus our results can serve as a reference for the paleoclimatic interpretation of sedimentary δ 13 C data. [ABSTRACT FROM AUTHOR]

Carbon isotopic compositions of organic matter (δ13C org) provide critical information about changes in the global carbon cycle through Earth's history. However, several biotic and abiotic processes occurring after sediment deposition may overprint the original geochemical signals, complicating their paleoenvironmental interpretation. Here, we report multiple large and rapid δ13C org swings (ranging from −30.8‰ to −23.3‰) from three Paleozoic drill cores in the Ordos Basin, Northwest China, which may reflect different organic contributions related to lithology. As a potentially important organic matter source, migrated hydrocarbons may substantially alter the original δ13C org and total organic carbon contents (TOC), and their oxidation may contribute to forming 13C- and 18O-depelted carbonate cements in siliciclastic-dominated strata at depth. Cross-plots of δ13C org and TOC from samples of the three drill cores all show similar hyperbolic trends that are well simulated using Rayleigh fractionation and a two-component mixing model, thus providing potential criteria for identifying the reservoir and the related hydrocarbon source in oil exploration. Our data call for a critical reassessment of the δ13C org records of sedimentary rocks if hydrocarbon redistribution or mixing of organic sources is suspected to have occurred during the burial history. • Large δ13C org swings are revealed in Paleozoic drill cores from the Ordos Basin. • Cross-plots of δ13C org and TOC show hydrocarbon redistribution and mixing. • A critical reassessment of the δ13C org records of sedimentary rocks is needed. [ABSTRACT FROM AUTHOR]

Oil shales from the Yamalikeshan (YML), Shuimogou (SMG) and Sangonghe (SGH) sections of the Lucaogou Formation in the southeastern Junggar Basin, Northwest China are rich in organic matter and have high hydro­carbon generation potential, as shown by bulk Rock-Eval and chloro­form extract analyses. The contrast in organic composition between the oil shales implies that Sangonghe is the richest hydrocarbon source rock section in the studied area in the Junggar Basin. The distribution of biomarkers and organic carbon isotope parameters indicate that oil shales of the Lucaogou Formation were deposited in a cool and humid paleoclimate and that some layers were partly subjected to microbial modification. In addition, the Sangonghe oil shale suggested a strongly reducing depositional environment, deeper and higher-salinity lake waters and a higher input of lower aquatic organisms compared with oil shales of the other two sections. Therefore we conclude that brackish reducing deep lakes were favourable for the develop­ment of petroleum source rocks. Ketones and aldehydes were identified in two Yamalikeshan oil shale samples, while ketones and fatty acid methyl esters (FAMEs) were found in the other two samples from the same section. In none of the samples the co-existence of all three compounds was established. The unique occurrence of aldehydes and fatty acid methyl esters may imply the varying depositional environment of the Yamalikeshan section. [ABSTRACT FROM AUTHOR]

Characteristics of redox-sensitive elements and organic carbon isotopes of a drilling section covering the Ediacaran-Cambrian (E-C) boundary at Anhui Province, South China were studied. Total organic carbon (TOC), organic carbon isotope values of organic compounds, abundances of Mo, V, U, and Ni, and ratios of V/(V + Ni) and Th/U co-vary across the section, suggesting that the redox condition is the main factor controlling carbon isotope values of organic matter, and sequestration of trace elements. The E-C boundary is characterized by the lowest organic carbon isotope and the highest ratios of Mo/TOC, V/TOC, and U/TOC in the section, which are correlated with reported carbon isotope excursions in other regions. This is the first time that signatures of Mo, V, and U in the Hetang Formation at the Lower Yangtze Platform are used for stratigraphic correlations. The results highlight abnormally high ratios of Mo/TOC, V/TOC, and U/TOC near the E-C boundary. Petrological and geochemical characteristics in this section suggests that intense upwelling activities during the E-C transition may be the main contributor to 13 C-depleted CO 2 and enrichment of trace metals. The co-existing pervasive transgression led to ocean anoxia and facilitated the preservation of 13 C-depleted organic matter and trace metal sequestration. Furthermore, oxidation of the bottom ocean water may have completed during the early Cambrian. A combination of these factors may be among the reasons for significant evolutionary changes during the E-C transition. [ABSTRACT FROM AUTHOR]

The Lower Yangtze Region of southeastern China is an important area for the study of Permian–Triassic Boundary (PTB). In this region many well-known PTB sections (e.g., Meishan) have been investigated widely and extensively; however, these sections are dominantly in shallow-water settings and data from deep-water areas are lacking. To fill the gap, we conducted a field survey recently and found a deep-water PTB section with relatively continuous deposition using integrated organic carbon isotopic and U–Pb geochronological studies. This well-exposed and fresh section is located at Niushan, Xuancheng city, Anhui Province, ~ 90 km west of the well-known Meishan section, which is the PTB Global Boundary Stratotype Section and Point. The organic carbon isotope curve of the section contains three positive excursions (PCIEs) and two negative excursions (NCIEs), which can be well correlated with other PTB sections as well as with Wuchiapingian–Changhsingian Boundary (WCB) sections worldwide. They archive the original PTB and WCB signatures. Further U–Pb dating of magmatic zircons in volcanic ashes validates this new finding, i.e., the PTB interval between 252.49 ± 0.76 Ma and 251.74 ± 0.77 Ma. Carbon isotopes of PTB sections in South China reflect the regional paleogeography. The two NCIEs (NCIE-2 and NCIE-3) across the PTB transition are most likely caused by widespread large-scale volcanic activity. In contrast, the NCIE-1 near the WCB is possibly related to an increase in the productivity of organic matter as a result of transgression and a change in the organic matter type from terrigenous to marine. [ABSTRACT FROM AUTHOR]

In order to understand redox variations and organic matter accumulation on the Yangtze carbonate platform during the Late Ediacaran–Early Cambrian, petrological and geochemical studies of several wells were carried out in this work. Our data suggest that depositional environments were dominated by oxidizing bottom water conditions during the late Ediacaran, and evolved to anoxic conditions, triggered by blooms of microbial organisms in surface waters during the earliest Cambrian. Subsequently, massive release of H 2 S derived from both anaerobic recycling of organic matter and, probably, hydrothermal venting promoted a sulfidic ocean. The discovery of a Ni-Mo sulfide ore layer in the basal Cambrian implies that such a sulfidic condition spread onto the Yangtze carbonate platform interior during the late Cambrian Stage 2. Further, transgressive flooding led to widespread black shale deposition and persistently anoxic conditions, as indicated by geochemical proxies. During the late Ediacaran to earliest Cambrian, local and widespread phosphogenesis indicates that organic matter accumulation was intimately associated with microbial (especially cyanobacterial) blooms driven by phosphorus cycling. The organic matter accumulations in early Cambrian black shales, however, were in connection with anoxic bottom water conditions and intermittent replenishment of recycled organic phosphorus to surface waters. [ABSTRACT FROM AUTHOR]

The mechanisms and controls of the Middle-Late Miocene paleoenvironmental evolution of the northeastern Tibetan Plateau remain elusive. Here, we present an integrated multiproxy study of total organic carbon isotopes, lipid biomarkers, petrographic components and micropaleontological records in the well-dated Xigou section of the Xunhua Basin. Our data reveal a large decrease (−1.1 ‰) in bulk organic carbon isotopes (δ13C org) at ∼12.7 Ma, a broad minimum at ∼12.7–8.0 Ma, and a large increase (+1.3 ‰) at ∼8.0 Ma. The decline in δ13C org at 12.7 Ma was accompanied by pronounced changes in n -alkane indices, clay minerals, palynology, and ostracods, recording a major rise of lake level of paleo-Lake Xunhua due to increased precipitation in the regional catchment. Our inference of sustained elevated humidity in the Xunhua Basin at 12.7–8.0 Ma is contrary to previously reported cooling and drying trends on the NE Tibetan Plateau for the Middle-Late Miocene (∼14–8 Ma), thus precluding the role of global climate change as the dominant driver. Rather, we attribute the paleoenvironmental evolution of the Xunhua Basin to changes in regional rainfall patterns related to orogenic uplift. The Jishi Shan mountain range reached a critical threshold elevation at ∼12.7 Ma, becoming an orographic barrier to Westerlies-transported moisture and thus enhancing intensified precipitation within the Xunhua Basin. By ∼8 Ma, further uplift caused this orogen to become a barrier to the East Asian monsoon, resulting in aridification of the Xunhua Basin. • The Xunhua Basin sensitively recorded environmental changes on NE Tibetan Plateau. • Uplift of Jishi Shan since ∼13 Ma caused moister Xunhua Basin and drier Lixia Basin. • Regional humidity changes due to trapping of Westerlies moisture to west, rain shadow effect to east. • This environmental change recorded by d13C org , n -alkanes, ostracods, and palynology. • Two key environmental transition periods—at ∼12.7 Ma and ∼8.0 Ma. [ABSTRACT FROM AUTHOR]

This study has examined bulk and compound specific organic carbon isotopes (δ 13 C org ) and lipid n -alkanes of modern plants and a wetland sediment sequence from the central Tibetan Plateau and explores the usefulness of these two methods for palaeoenvironmental reconstructions. Results show that a combination of δ 13 C org values and n -alkane indices can help differentiate organic matter from C3 terrestrial plant, C4 terrestrial plant and submerged macrophytes, the three main sources of organic matter in the study area. The analyses of total organic carbon, δ 13 C org values and n -alkane indices for the sediment sequence imply that a wetland habitat was established about 8000 years ago, and the wetland conditions were largely stable with dominantly C3 wetland herbs covering the wetland. However, small fluctuations in the dominant organic matter supply between vascular and aquatic plants are revealed, suggesting short duration changes in the extent of open water area within the wetland or variations in the productivity of submerged macrophytes and aquatic plants within the wetland ecosystem, which reflects variations in the strength of precipitation and evaporation. [ABSTRACT FROM AUTHOR]

Integration of new data in sedimentology, mieropalaeontology and organic carbon isotope analysis of upper Ypresian strata in central Belgium (Zemst hole) enables differentiation of a series of biotic events and carbon isotope trends, which are believed to be associated with the 1.5-million-year-long period of global warming, known as the Early Eocene Climatic Optimum (EECO). The relatively low values in S13Corg (-26.5%o to -27. l%o) in the interval from the Panisel Sand to the Merelbeke Clay Members (upper NP12-lowerNP13) are shown to be coinciding with a fairly high frequency in Apectodinium (>3%, up to 14%) and a DiscoasterAAoom (16%-50%, essentially D. kuepperi). This is quite analogous, although less prominent, to what has been observed during the Paleocene- Eocene Thermal Maximum (PETM: Apectodinium abundance of 75% at middle and high latitudes and Discoaster blooms in tropical areas). The abrupt positive shift of up to l%o in S13Corg values at the base of the overlying Pittem Clay Member (mid-NP13, mid-chron C22r), which is coincident with the virtual disappearances of Apectodinium (<0.1 %) and Discoaster (<0.5%) seems to mark the end of the EECO in the southern North Sea Basin. The Zemst data allow the identification of the NP12/NP13 boundary, virtually coinciding with chron C23n/C22r boundary, at the depositional break between the Panisel Sand Member and the overlying Kwatrecht Member. The new data also allow to substantially refine the calcareous nannofossil stratigraphy during Biochron NP15 (mid-Lutetian) at middle latitudes. This is corroborated by additional data from Belgium, which furthermore reveal that the primary criterion for identifying the base of the Lutetian (LO of Blackites inflatus), as adopted in the Gorrondatxe GSSP (Spain), cannot be applied in the North Sea Basin s.s. (excluding the Paris Basin) and that there is an urgent need for defining appropriate substitutes for this boundary at these latitudes. [ABSTRACT FROM AUTHOR]

The organic matter (OM)-rich, relatively monotonous sequence of upper Barremian–Albian deposits in the western part of the Silesian Nappe in the Polish Outer Carpathians, was investigated, using geochemical proxies to show environmental changes. The amounts of organic carbon (0.4–4.32 wt.% of TOC) co-vary with the concentration of S and/or redox sensitive trace elements (RSTE: Mo, U, Co, V, As). Kerogen is present as Type III and mixed Type II/III. Maceral assemblages consist of vitrinite, inertinite and liptinite. The carbon isotopic composition of the organic matter (δ 13 C org ) varies between − 25.38 and − 21.31‰ with an outlier at − 15.14‰. During the Early Cretaceous the Proto-Silesian Basin was the site of OM accumulation in a detrital oceanic anoxic event as a result of increased sedimentation rates of terrestrial organic matter. Runoff of terrestrial organic matter was accompanied by the production of plankton on an occasional basis. The marine matter contribution is inferred from occurrence of siliceous microfauna, the domination of short-chain n -alkanes, the distribution of sterane and prevalence of cholestane, and enrichment in nutrient elements (P 2 O 5, Ba, Ag, Cd). The bottom waters could have been dysoxic to anoxic, with a mid-water oxygen minimum zone (OMZ) developed owing to the oxidation of organic matter. Anoxia is inferred from the lamination, pyritization patterns, RSTE concentration and low Pr/Ph and C 23 t/C 30 H ratios. Intervals enriched in TOC and RSTE in the Veřovice Formation record pulses of marine productivity, preceded by volcanic (teshenite) and hydrothermal activity. They are referable to the following episodes: the Taxy (Barremian–Aptian), early Aptian Selli, Fallot and Paquier during the late Aptian and at the Aptian–Albian boundary. The initiation of turbidite deposition during the Albian led to bottom ventilation. The Lhoty Formation records the late Albian Toolebuc Episode, marked by a TOC peak, which resulted from the detrital flux. Acidic solution was responsible for reducing conditions in the sediment. [ABSTRACT FROM AUTHOR]

In this paper, we present organic carbon isotope records from continental sediments spanning the late Paleocene-middle Miocene (57.9–15.0 Ma) in the Lanzhou Basin, northeastern Tibetan Plateau to investigate terrestrial ecosystem-response to global climate change. The continuous sediment δ13C TOC values that we obtained range from −27.83‰ to −20.05‰. Combining these data with the sediment C/N ratios and n-alkane distribution, we infer that the major source of sediment organic matter was terrestrial C 3 plants. Furthermore, we note that both sediment δ13C TOC and δ13C n-alkanes values gradually become more positive from 57.9 to 26 Ma and then become relatively more negative from 26 to 15 Ma. These δ13C values vary closely with global temperature changes. We propose that global temperature controlled δ13C values with cooler conditions resulting in less rainfall in inland Asia, and vice versa. Therefore, mainly driven by the global temperature, the regional climate in the Lanzhou Basin gradually changed from warm-wet to cold-dry conditions during 57.9–26 Ma, and the climatic conditions became warmer and wetter again after 26 Ma. This long-sequence terrestrial ecologic environment study obtained from the northeast Tibetan Plateau powerfully demonstrates the first-order role of global climate in regulating the long-term evolution of regional environment. • We obtained continuous organic carbon isotope records on the NE Tibetan Plateau at 57.9–15 Ma. • δ13C TOC and δ13C n-alkanes values vary negatively with global temperature. • Rainfall dominated by global temperature affects plant δ13C change within terrestrial ecosystem. [ABSTRACT FROM AUTHOR]

Total organic carbon (TOC) content of marine sediments represents residual carbon, originally derived from terrestrial and marine sources, which has survived seafloor and shallow subseafloor diagenesis. Ultimately, its preservation below the sulfate reduction zone in marine sediments drives methanogenesis. Within the gas hydrate stability zone (GHSZ), methane production along continental margins can supersaturate pore fluids and lead to the formation of gas hydrate. In this paper we examine the inventory and sources of TOC in sediments collected from four regions within the GHSZ along the Indian continental margins. The recovered sediments vary in age from Oligocene to recent. Mean TOC abundance is greatest in the Krishna–Godavari (K–G) Basin and decreases progressively to the Mahanadi basin, Andaman wedge, and Kerala–Konkan (K–K) Basin. This decrease in TOC is matched by a progressive increase in biogenic CaCO 3 and increasing distance from terrestrial sources of organic matter and lithogenic materials. Organic carbon sources inferred from C/N and δ 13 C TOC range from terrestrial (K–G Basin) to mixed marine and terrestrial (Mahanadi Basin), to marine dominant (Andaman wedge and K–K Basin). In the K–G Basin, variation in the bulk δ 13 C TOC is consistent with changes in C 3 and C 4 vegetation driven by monsoon variability on glacial-interglacial timescales, whereas in the Mahanadi Basin a shift in the δ 13 C TOC likely reflects the onset of C 4 plant deposition in the Late Miocene. A large shift the δ 13 C TOC in the K–K basin is consistent with a change from C 3 to C 4 dominated plants during the middle Miocene. We observe a close relationship between TOC content and gas hydrate saturation, but consider the role of sedimentation rates on the preservation of TOC in the zone of methanogenesis and advective flow of methane from depth. Although TOC contents are sufficient for in situ methanogenesis at all the sites where gas hydrates were observed or inferred from proxy data, seismic, borehole log, pressure core, and gas composition data coupled with relatively high observed gas hydrate saturations suggest that advective gas transport may also play a role in the saturation of methane and the formation of gas hydrates in these regions. Although TOC content may be a first order indicator for gas hydrate potential, the structural and stratigraphic geologic environment along a margin will most likely dictate where the greatest gas hydrate saturations will occur. [ABSTRACT FROM AUTHOR]

The climate in the eastern margin of the Tibetan Plateau (TP) is mainly controlled by the Indian Ocean summer monsoon and the TP monsoon. Widely distributed aeolian deposits in this region are one of the best terrestrial materials for studies on the evolutionary history of the Indian summer monsoon and the climatic response to uplift of the TP. In this study, two loess-palaeosol sequences from the western Sichuan Province in southwest China were studied in detail using geochemical and sedimentological methods. Carbon isotope compositions of organic matter, major element geochemistry and grain-size records of these two loess-palaeosol sequences indicate that the extent of aridity in the eastern margin of the TP increased rapidly between 300 and 150 ka BP and stabilized at a relatively higher level after 150 ka BP. Marine records from the Indian Ocean indicate that the Indian summer monsoon did not experience obvious weakening since 300 ka BP. The deep-sea δ 18 O record, which reflects changes in global ice volume, also lacks any obvious changes during this period. Therefore, we interpret this palaeoclimate event to reflect the decreased influence of the Indian Ocean summer monsoon on this region, which is related to the uplift of the TP since 300 ka BP. This process of increasing aridity is a local palaeoclimate event, which is not recorded in the loess-palaeosol sequences in the Chinese Loess Plateau in northern China where the climate is mainly controlled by the East Asian monsoon. This indicates that the climate response to the uplift of the TP differs in different monsoon regions. [ABSTRACT FROM AUTHOR]

Organic carbon isotope ( δC) data from two well-preserved sections across a shallow-to-deep water transect of the late Ediacaran-Early Cambrian Yangtze Platform in South China show significant temporal and spatial variations. In the shallow-water Jiulongwan-Jijiapo section, δC values of the late Ediacaran Dengying Formation range from −29‰ to −24‰. In the deep-water Longbizui section, δC values from time-equivalent strata of the Dengying Formation are mostly between −35 and −32‰. These new data, in combination with δC data reported from other sections in South China, reveal a 6‰-8 shallow-to-deep water δC gradient. High δC values (>−30‰) occur mostly in shallow-water carbonate rocks, whereas low δC values (<−32‰) dominate the deep-water black shale and chert. The large temporal and spatial δC variations imply limited buffering effect from a large dissolved organic carbon (DOC) reservoir that was inferred to have existed in Ediacaran-Early Cambrian oceans. Instead, δC variations between platform and basin sections are more likely caused by differential microbial biomass contribution to total organic matter. High δC values (>−30‰) documented from shallow-water carbonates are within the range of typical Phanerozoic δC data and may record the isotope signature of organic matter from primary (photosynthetic) production. In contrast, low δC values (<−32‰) from deep-water sections may have resulted from higher chemoautotrophic or methanotrophic biomass contribution to bulk organic matter in anoxic environments. The δC data provide indirect evidence for ocean stratification and episodic chemocline fluctuations in the Ediacaran-Early Cambrian Yangtze Platform. [ABSTRACT FROM AUTHOR]

Abstract: N and Corg isotope results are presented from six sections along a West–East transect in the South China Basin (SCB) covering both shallow and deeper domains, in order to investigate biogeochemical cycling, stratigraphic correlation and isotope systematics over the crucial Ediacaran–Cambrian transition. δ15N bulk values range between −3‰ and +7‰, while δ13Corg values range between −21‰ and −39‰. Similar isotopic trends have been identified for both these proxies across the basin, although hiatuses, differences in depositional setting and syn-depositional bacterial fermentation may have caused some inconsistencies. A trend towards negative N isotope values can be recognized above the Pc–C boundary in both shallow and deeper basin realms across the Yangtze platform. This negative δ15N excursion is probably a response to photic zone anoxia and intense nitrogen fixation/assimilation by diazotrophic cyanobacteria and green/purple sulfur bacteria (GSB and PSB). The Xiaotan section and a composite section from the Yangtze Gorges area show meaningful similarities in their nitrogen isotope trends, interpreted as chemocline fluctuations in the water column that testify to rapid mixing of water overlying the shallow platform. Using carbon isotope stratigraphy, we correlate boundary strata across the platform to test the wider significance of nitrogen isotopic variations. Increased bioturbation and food-chain complexity across the Ediacaran–Cambrian transition probably led to more frequent variations in nitrate isotope composition and related pool dimension during the early Cambrian, reflecting the beginning of a new more biologically controlled era. [Copyright &y& Elsevier]

The Permian-Triassic Mass Extinction (PTME) is the greatest biodiversity crisis in Earth history and while the marine crisis is increasingly well constrained, the timing and cause(s) of terrestrial losses remain poorly understood. There have been suggestions that the End-Permian Terrestrial Collapse (EPTC) pre-dated, was synchronous with or post-dated the marine crisis, or even occurred asynchronously in different regions. We address these conflicting interpretations through a detailed geochemical study of a terrestrial sequence in the Liujiang Coalfield on the North China Plate (NCP) in which we apply zircon U-Pb dating of tuffaceous claystone, kerogen identification, and analysis of organic carbon isotopic composition (δ13C org), total organic carbon (TOC), continental weathering (via the chemical index of alteration; CIA) and Ni concentrations. Our study constrains the Permian-Triassic boundary (PTB) near the base of bed 20 in our sequence at approximately 251.9 ± 1.1 Ma, immediately above a Ni anomaly also known from other terrestrial sequences and the marine PTME. Organic carbon isotope chemostratigraphy together with evidence for algal blooms and the presence of mudstone clasts suggests that the onset of the EPTC in the NCP was synchronous with the crisis in low latitudes (e.g., South China), but was about 310 kyr later than the EPTC in higher southerly latitudes (e.g., Australia). The EPTC predates the marine PTME. Kerogen macerals suggest that a phase of increased wildfire was sustained from the onset of the EPTC in the NCP until the marine PTME interval, implicating wildfire as a major driver of the EPTC (at least in low latitudes) that, in turn, had devastating consequences for the marine realm. • The PT boundary is radioisotopically constrained on the North China Plate. • Catastrophic soil erosion marks the onset of terrestrial losses prior to the PTB. • Extinctions in North China began in terrestrial settings before the marine crisis. • Humid/arid conditions promoted frequent wildfires that were responsible for losses. • End Permian Terrestrial Collapse led to marine crisis through a cascade of effects. [ABSTRACT FROM AUTHOR]

Abstract: Organic carbon isotope data from two slope to basinal sections across the Ediacaran–Cambrian transition on the Yangtze Platform, South China record secular variations in δ13C. Data supplement highly comparable organic carbon isotope profiles from time equivalent shallow shelf and slope settings. No environmentally determined carbon isotope gradient across the Yangtze Platform is discernible, suggesting that a transgressive anoxic event provided an isotopically homogenous carbon source for primary productivity that originated from the deeper part of an anoxic and/or sulfidic basin. [Copyright &y& Elsevier]

Abstract: The early Cambrian (ca. 542–520Ma) strata in South China record two prominent negative carbonate carbon isotope (δ13Ccarb) excursions of early Nemakit–Daldynian (N–D) and early Tommotian ages. Across each of these excursions, carbonate and organic carbon isotopes (δ13Ccarb and δ13Corg) are strongly decoupled. Regional correlation across a shelf-to-basin transect shows lateral heterogeneity of δ13Corg during the early-middle N–D but more homogenized δ13Corg values across the basin during the late N–D and Tommotian. The temporal and lateral variations in δ13Corg suggest that decoupled δ13Ccarb and δ13Corg across the N–D δ13Ccarb excursion were possibly caused by diagenetic alteration of organic matter and/or amplification of detrital organic carbon isotope signature in low-TOC carbonates. In contrast, decoupled δ13Ccarb and δ13Corg of the upper N–D and Tommotian were likely resulted from chemoautotrophic–methanotrophic biomass contribution to TOC in organic-rich black shale and carbonates. The decoupled δ13Ccarb–δ13Corg pattern from the lower N–D strata (ca. 542Ma) shows striking similarities with those from the basal (ca. 635Ma) and upper (ca. 551Ma) Doushantuo Formation. In all three cases, decoupled δ13Ccarb–δ13Corg are seen in organic-poor carbonates (TOC≤0.1‰) and coupled δ13Ccarb–δ13Corg occur in organic-rich black shale and carbonates at the end of the negative δ13Ccarb excursion. These similarities suggest that the shift from decoupled to coupled δ13Ccarb–δ13Corg has no causal link with the terminal oxidation of a large oceanic DOC reservoir. Given the pervasive anoxia/euxinia in Ediacaran–early Cambrian oceans, local DOC-rich environments may have been common, but a large oceanic DOC reservoir capable of buffering the δ13C of marine organic matter requires independent evidence. [Copyright &y& Elsevier]

We firstly present the description of the river terrace at Tangjia (唐家) Village in Lhasa, Tibet, collect soil samples, and select the climate indicators including δC, total organic carbon (TOC), and the Rb/Sr ratios to study its paleoclimate in this area. Ancient climate changes have been reconstructed since the last glacier period. The results show that the δC, TOC, and the Rb/Sr ratio are good indicators of ancient climate fluctuations. Paleoclimatic evolution in the Lhasa Tangjia region could be divided into seven stages. In stages II (11.7-10.2 kaB.P.) and IV (8.1-6.1 kaB.P.), δC was positive and TOC was high, indicating that the climates in these two stages were relatively warm and humid. In stages III (10.2-8.1 kaB.P.) and V (6.1-4.9 kaB.P.), δC showed cyclical fluctuations, but TOC exhibited less change, suggesting that the climates displayed variation on the millennial scale. Moreover, the climatic variations were on a century-long scale during the later Middle Holocene. Compared with δC from Sumxi Co (松木希错) and δO from the Guliya (古里雅) ice core, the study confirmed that four cold events occurred during the Holocene (9.4, 8.2, 5.4, and 4.2 kaB.P.). The climate indicators were limited to the river terrace based on the geological characteristics of the Lhasa region. Unexpectedly, δC was a sensitive indicator of climate change. [ABSTRACT FROM AUTHOR]

Abstract: High-resolution carbon isotope records of organic carbon (δ13Corg) across the Permian–Triassic boundary (PTB) from the expanded sections of the Trøndelag and Finnmark platforms in Norway demonstrate that the negative carbon isotope excursion around the PTB begins with a stepwise 8‰ negative decline to a first minimum. After a subsequent positive excursion, a second minimum follows in the basal Griesbachian. Particulate organic matter (POM) is dominated by terrestrial particles with changing marine contributions. Intervals with minor C-isotope fluctuations coincide with homogeneous terrestrial POM assemblages, whereas intervals with pronounced C-isotope fluctuations correspond to heterogeneous marine–terrestrial POM assemblages, suggesting that the C-isotope curve represents a global signal with superimposed local variations of carbon sources. The δ13Corg of the contributing organic carbon ranges from −32‰ (marine organic carbon) to −22‰ (terrestrial organic carbon). Comparison of the new record, divided into 10 chemostratigraphic intervals with other, globally distributed sections suggests the presence of gaps in several classical PTB sections. Detailed chemostratigraphic correlation reveals that the extinction of marine organisms occurred during the stepwise negative shift and the end-Permian floral turnover occurred prior to the first C-isotope minimum. The correlation also shows that the marker of the recently defined Global Stratotype Section and Point PTB occurs within a broad interval ranging from most negative δ13C values up to the subsequent isotopic increase. [ABSTRACT FROM AUTHOR]

Abstract: Prominent negative carbonate carbon isotope (δ13Ccarb) anomalies from some Ediacaran successions are accompanied by invariant or decoupled organic carbon isotope (δ13Corg) values and have been interpreted as resulting from the remineralization of a large dissolved organic carbon (DOC) reservoir capable of buffering carbon isotopes of organic matter. This inferred oceanic DOC reservoir was thought to have initiated with the onset of Cryogenian glaciations (ca. 720Ma) and lasted for millions of years until the late Ediacaran Period (<560Ma). Carbon isotope analyses of the basal Doushantuo Formation (ca. 635Ma) in south China reveal that (1) the cap carbonate has δ13Corg around −26‰ (VPDB) and relatively low Δδ13C (22±2‰) and (2) the overlying organic-rich black shale and shaly dolostone have more negative δ13Corg (−28‰ to −35‰) and higher Δδ13C (28‰–30‰). Both δ13Ccarb and δ13Corg show a +6‰ shift within a 4-m-thick interval overlying the Doushantuo cap carbonate. The δ13Corg values of the cap carbonate are associated with low TOC (mostly<0.1%); their paleoceanographic significance requires further tests in other Ediacaran basins. The co-varying positive shift in δ13Ccarb and δ13Corg following cap carbonate deposition is best interpreted as resulting from a rapid increase in organic carbon burial, which may have resulted in the rise of oxygen and heralded the first appearance of animals a few meters above the Doushantuo cap carbonate. The data suggest that a large oceanic DOC reservoir did not exist in the early Ediacaran ocean. Excess oceanic DOC required to explain the Ediacaran Shuram and upper Doushantuo δ13C excursions, if it existed, had to be developed during the Ediacaran Period after cap carbonate deposition. [Copyright &y& Elsevier]

The article presents a study on the sedimentary evidence of human activities in Pearl River Delta, China 4,000 years ago. The study uses the analysis of modern sediment and plant samples, particle size and diatom analysis, and surface sediment samples gathered by a grab sampler. The study shows that the organic carbon isotope ratios presented melt smelting for about 2,000 years ago, while the increased bulk organic isotopic value identified copper, iron, and lead in the sedimentary sequence.

Using -24‰ and -14‰ as the endpoints of stable carbon isotopic composition of total organic carbon (δ13 CTOC) of surface soil under pure C3 and C4 vegetation, and surface soil δ13 CTOC data from eastern China, Australia and the Great Plains of North America, we estimate the relative abundance of C3/C4 plants (i.e., the ratio of C3 or C4 biomass to local primary production) in modern vegetation for each region. The relative abundance of modern C3/C4 vegetation from each region is compared to the corresponding climatic parameters (mean annual temperature and precipitation) to explore the relationship between relative C4 abundance and climate. The results indicate that temperature controls the growth of C4 plants. However, even where temperature is high enough for the growth of C4 plants, they will only dominate the landscape when precipitation declines as temperatures increase. Our results are consistent with those of other investigations of the geographic distribution of modern C4 plant species. Therefore, our results provide an important reference for interpretation of past C3/C4 relative abundance records in these three regions. [ABSTRACT FROM AUTHOR]

Abstract: Large carbon isotope fluctuations have been systematically reported for Ediacaran carbonate rocks, the meaning of which remains controversial. In order to better understand the mechanisms behind such variations, we present new paired δ 13C data on carbonates (δ 13Ccarb) and their associated organic matter (δ 13Corg) from a shelf-margin section (Yangjiaping) of the Doushantuo Formation. In this section, the Doushantuo Formation starts with cap dolostones presenting δ 13Ccarb values around −5‰ and δ 13Corg values between −30.3 and −27.6‰. Up-section, phased variations in δ 13Ccarb and δ 13Corg describe positive and negative excursions, while their difference (Δ13Cdol–org = δ 13Ccarb − δ 13Corg) remains around +29.2‰. These new data allow the first reconstruction of lateral variations of δ 13Ccarb, δ 13Corg and Δ13Ccarb–org for a shelf-to-basin cross-section of the Yangtze platform (South China) after integration with results reported previously for two other sections. Across the Yangtze platform, the isotope signals reveal strong lateral heterogeneities, with complex variations of δ 13Ccarb and Δ13Cdol–org in the inner-shelf section, phased variations in the shelf-margin section with positive δ 13Ccarb and Δ13Cdol–org close to 29‰, and dominantly negative δ 13Ccarb with δ 13Corg as low as −35‰ in the basin. These variations are incompatible with the idea that the δ 13Ccarb can systematically be used as a proxy of ocean surface waters. Assuming that δ 13Ccarb are acquired in bottom waters and/or upper sediments, we show that the heterogeneous δ 13Ccarb and Δ13Cdol–org are compatible with a stratified water column composed of up to three layers: (i) an oxic surface layer, where dissolved inorganic carbon (DIC) is probably in isotope equilibrium with the atmosphere; (ii) an intermediate euxinic layer with a lower δ 13CDIC due to organic matter oxidation by ongoing sulphate reduction; (iii) a bottom euxinic layer that seems to be restricted to the inner-shelf lagoonal facies, lacking sulphate, containing methane and with a higher δ 13CDIC due to DIC production by methanogenesis. If our model holds true, it suggests that not only negative but also positive Ediacaran carbon isotope excursions may reflect ocean stratification, the positive excursion possibly recording a sulphate-free methanogenic layer at the bottom of restricted basins. [Copyright &y& Elsevier]

A massive emission of light carbon about 56 Ma, recorded in marine and terrestrial sediments by a negative carbon isotope excursion (CIE), caused a short-lived (~170 kyr) global warming event known as the Paleocene–Eocene Thermal Maximum (PETM). The onset and core of this event is represented in the south Pyrenean Tremp-Graus Basin by two successive alluvial units, the Claret Conglomerate (CC) and the Yellowish Soils, which represent laterally juxtaposed depositional environments. It is generally agreed that these units record a dramatic increase in seasonal rain and an increased intra-annual humidity gradient during the PETM, but the timing of the sedimentary response to this hydrological change is a matter of debate. Some authors maintain that the CC was developed during the early, most intense phase of the carbon emission, others that its formation lagged by 16.5 ± 7.5 kyr behind the onset of the PETM. The latter claim was mainly based on the assumption that in two sections of this basin, Claret and Tendrui, the onset of the CIE occurs 3 and 8 m below the base of the CC, respectively. Here we show that in some zones between these two sections the CC was not deposited and the Yellowish Soil unit rests directly and conformably on the underlying Esplugafreda Formation. New δ13C org data from this intervening zone provide evidence that the onset of the CIE is situated just ~1 m below the Yellowish Soils. In adjacent sections the CC erosional base cuts down deeper than 5 m, thus removing or obscuring the chemostratigraphically-defined base of the PETM. A tentative estimate based on averaged sedimentation rates indicates that ~3.8 kyr, or less, may have elapsed from the onset of the CIE to the arrival of PETM alluvium into the Claret-Tendrui study area, less than half of the lowest estimate of previous authors. Since the study area was situated about 15 km from the source area, our new estimate supports a rapid response of the sedimentary system to the hydrological change at the onset of the PETM. • The PETM hydrological change is recorded in the Pyrenees by two alluvial units. • Between the PETM onset and the alluvial accumulation a lag of ~3.8 kyr is estimated. • The new data entail a rapid sedimentary response to the PETM hydrological change. [ABSTRACT FROM AUTHOR]

Abstract: In situ analytical techniques – Fourier transform infrared microspectroscopy (μFTIR) and ion microprobe – have been used to unravel the origin of solid bitumen associated with the uranium deposits of Athabasca (Saskatchewan, Canada). Both aliphaticity and carbon isotopic compositions within the samples are heterogeneous but spatially organized in concentric zonations at the micrometer scale. Finally, the δ 13C values are positively correlated to the aliphatic contents over an extremely large isotopic range from ∼−49‰ to ∼−31‰. We infer that this positive correlation may be related to the carbon isotopic fractionations associated with the synthesis of bitumen through the catalytic hydrogenation of CO2, rather than the result of pre-existing petroleum product precipitation and/or alteration (such as radiolysis). This explanation is consistent with (i) published results of abiogenic synthesis experiments, in which the differences in δ 13C values between saturated and unsaturated hydrocarbons range from +2 and +19‰, in contrast to the differences systematically observed in conventional bitumen and petroleum ranging from 0‰ to −4‰; (ii) the absence of a similar positive correlation between aliphatic contents and δ 13C values in the other bitumen analyzed in the present study, for which a biogenic origin has been unequivocally established (samples from Oklo, Gabon, and Lodève, France, uranium deposits); (iii) the presence of CO2 and H2 in the gas-phase of fluid inclusions in the Athabasca uranium deposits, H2 resulting from water radiolysis. The present results suggest that the δ 13C vs. aliphaticity correlation could be used as a criterion to discriminate between abiogenic vs. biogenic origin of macromolecular organic matter. [Copyright &y& Elsevier]

A high-resolution loess section in the western Chinese Loess Plateau, Yuanbao Section, was sampled for organic carbon isotopic analyses. The soil organic carbon isotope (δ Corg) varied between -22.6‰ and -27.5‰ during the last glacial at the section. During the last interstadial, the δ Corg values were more negative than those in both early and late periods of the last glacial by 4‰. The isotopic composition indicates a coupled response of the pure C3 plants to the temperature, precipitation and the concentration of atmospheric CO2. Decrease in temperature and the atmospheric CO2 concentration from the last interstadial to Last Glaicial Maximum (LGM) caused the organic carbon isotopes to become positive by 1.5‰ 2.0‰. The amplitude of 4‰ in the δ Corg variation during the last glacial should be mainly caused by the precipitation change. Therefore, the δ Corg variations of the Yuanbao Section during the last glacial period documented the large-amplitude fluctuation of the monsoon precipitation, which is estimated to be 250-310 mm more during the last interstadial than that in the LGM, and 100 mm more than that during early last glacial. The rapid changes of the monsoon precipitation on millennial scale during the last glacial have also been recorded in the isotopic variations in Yuanbao loess section. As the isotopic composition varies complicatedly as shown in the loess-paleosol sequence, it cannot be simply attributed to the abundances of C3 and C4 plants or be used as an indicator of the summer monsoon variations. [ABSTRACT FROM AUTHOR]