Organic Geochemical Studies Research Articles

Uranium enrichment driven by paleomarine condition and event deposition: Insights from the lower Cambrian Niutitang Formation organic-rich shales in northeastern Guizhou, South China

Organic-rich shale related uranium (U) mineralization has attracted widespread attention as a strategic and clean alternative to fossil energy and a paleoceanic redox proxy. A comprehensive study of mineralogy, organic geochemistry and elemental geochemistry of the lower Cambrian Niutitang Formation organic-rich shales in northeastern Guizhou, South China was conducted to address this issue. SEM-EDS results showed that the U occurrence state in the Niutitang Formation shales is dominated by nanoscale U minerals, mainly including coffinite, brannerite, U-bearing apatite and U-bearing xenotime. Various states of U are closely associated with organic matter, apatite, pyrite and clay minerals. Based on geochemical indexes, paleomarine condition and event deposition jointly drove the U enrichment in the Niutitang shales, in which hydrothermal activities and/or volcanic eruptions increased U fluxes in seawater and euxinic environment with high primary productivity provided a favorable condition for U reduction. The adsorption, complexation and reduction of UO22+ by organic matter and the formation of uranyl phosphate complexes by the combination of phosphate and UO22+ accelerated U immobilization and enrichment from bottom water to sediments. The microbial activities (e.g., BSR) in this process created favorable euxinic conditions and released inorganic-phase P to provide available ligands for UO22+. The U enrichment models of the lower Cambrian Niutitang shales in northeastern Guizhou were established. This paper provides a new insight into the U enrichment mechanism in organic-rich shales, and may also have implications for the applicability of U as redox proxy and the exploration of organic-rich shale related U deposits.

Organic geochemical study of Aleksinac oil shale

Organic geochemical study of Aleksinac oil shale

Aliphatic Biomarker Signatures of Crude Oil from Tarakan Subbasin, Tarakan Basin, North Kalimantan, Indonesia

Organic geochemical studies of crude oil from Pamusian Field, Tarakan Subbasin, Tarakan Basin, North Kalimantan, have been done. Biomarker aliphatic hydrocarbon fractions were identified using a combined gas chromatography-mass spectrometer (GC - MS). Identified biomarkers consist of n-alkane groups, isoprenoids, bicyclic sesquiterpenoids, and pentacyclic triterpenoids. The most abundant aliphatic hydrocarbon biomarker is pristane followed by n-C19. The existence of n-alkanes shows a homologous (n-C16- n-C30) with a unimodal distribution type. The abundance of n-C19 is higher than other n-alkanes, supported by LHCPI value of 2.03, as an indicator of organic matter derived from microbial organisms. The amount of long chain n-alkanes (n-C25- n-C30) is almost the same as medium chain n-alkanes (n-C19 - n-C24) indicating the source of organic compounds is not only from microbial organisms, but also from terrestrial higher plants. The presence of 8β (H)-drimane compounds together with homodrimane shows the presence of bacterial input on the formation of oil from organic compounds. Ratio of Pr/Ph is 3.76, ratio of drimane/homodrimane is 1.058, ratio of Pr/n-C17 is 34.41, and ratio of Ph/n-C18 is 16.02 indicating the source of organic compounds came from terrestrial higher plants deposited in the oxic environment, and disposed to increase biodegradation. The CPI value is 0.95, and the highest amount of 17α (H), 21β (H)-hopane compounds suggest that Tarakan Subbasin oil was mature, and the source of organic compounds was derived from bacteria Keywords: Tarakan Basin, organic geochemistry, aliphatic hydrocarbon fraction, CPI

Microbially mediated fossil concretions and their characterization by the latest methodologies: a review.

The study of well-preserved organic matter (OM) within mineral concretions has provided key insights into depositional and environmental conditions in deep time. Concretions of varied compositions, including carbonate, phosphate, and iron-based minerals, have been found to host exceptionally preserved fossils. Organic geochemical characterization of concretion-encapsulated OM promises valuable new information of fossil preservation, paleoenvironments, and even direct taxonomic information to further illuminate the evolutionary dynamics of our planet and its biota. Full exploitation of this largely untapped geochemical archive, however, requires a sophisticated understanding of the prevalence, formation controls and OM sequestration properties of mineral concretions. Past research has led to the proposal of different models of concretion formation and OM preservation. Nevertheless, the formation mechanisms and controls on OM preservation in concretions remain poorly understood. Here we provide a detailed review of the main types of concretions and formation pathways with a focus on the role of microbes and their metabolic activities. In addition, we provide a comprehensive account of organic geochemical, and complimentary inorganic geochemical, morphological, microbial and paleontological, analytical methods, including recent advancements, relevant to the characterization of concretions and sequestered OM. The application and outcome of several early organic geochemical studies of concretion-impregnated OM are included to demonstrate how this underexploited geo-biological record can provide new insights into the Earth's evolutionary record. This paper also attempts to shed light on the current status of this research and major challenges that lie ahead in the further application of geo-paleo-microbial and organic geochemical research of concretions and their host fossils. Recent efforts to bridge the knowledge and communication gaps in this multidisciplinary research area are also discussed, with particular emphasis on research with significance for interpreting the molecular record in extraordinarily preserved fossils.

Fly ashes generated from coal-fired thermoelectric power plants on the Balkan Peninsula – Organic geochemical study

Organic matter (OM) presence in fly ashes (FA) might be a serious obstacle towards their utilization or beneficial use. Though, it is imperative to enhance the knowledge of FA geochemical composition and environmental impact. Feed coals and FA from thermoelectric power plants (TPP) in Bulgaria (Maritza East 2 TPP), Greece (Megalopolis TPP and Agios Dimitrios TPP) and Serbia (TENT A, Nikola Tesla A TPP and TENT B, Nikola Tesla B TPP) were comparatively studied by geochemical proxies. Extractable organic matter, 0.45–6.10% for the feed coals and 0.013–0.025% for the FA, was subjected to extensive chromatographic separation and species in different chemical series were GC–MS identified and quantified. Changes in the biomarker assemblages triggered by combustion in the pairs feed coal/FA were picked up, series of chemical classes quantified and subsequently alterations in chemical series were expressed in rel. %.Combustion has affected the biomarkers separation mode though the signatures for FA keep some features of the parent coals. Feed coal biomarker were rich in functionalities as were composed by a broad range of series, i.e., n-alkanes, regular isoprenoids, terpenoids, hopanoids and their aromatized counterparts. Polycyclic aromatic hydrocarbons (PAH) are of especial environmental concern. After combustion, FA biomarkers pattern of distribution was simplified as only two main series remained at appreciable amounts, n-alkanes and diterpenoids. Aromatic triterpenoids were also recognizable. Combustion has altered the n-alkanes separation mode as in the distribution curves for FA samples was visualized well-expressed shift to the shorter-chain n-alkanes, nC15-nC19.There were some similarities in PAH assemblages for FA from the studied thermoelectric power plants (TPP) as the combination of fluoranthene, pyrene, benzo[a]anthracene, chrysene and benzo[k]fluoranthene was rather frequent. Also, in all samples (except Maritza East 2 TPP) there was a preponderance of the four rings (4R) PAH and considerable presence of 5R PAH, i.e., benzo[k]fluoranthene. Ranges for ΣPAH (16 USEPA) and ΣCPAH for FA were: ΣPAH (16 USEPA), 1.5–33.0 μg/kg, and ΣCPAH, 0–12.0 μg/kg. Respectively, values for FA Benzo[a]pyrene equivalent (B[a]Peq) up to 0.80 μg/kg and toxic equivalency quantities (TEQ) up to 1.22 μg/kg values were calculated. The range of 4–12 μg/kg for ƩCPAH was considerably lower than 300 μg/kg designated by the Swedish Environmental Protection Agency (Swedish EPA) for FA used in soil remediation. Enrichment ratios, ER < 1, for all TPP located on the Balkan Peninsula implied that PAH were mostly emitted into the atmosphere by the flue gases.

Organic geochemical studies and origin of black hydrocarbon material (heavy oil) produced from Risha gas field (Jordon): insights into produced contaminated organic-inorganic materials during production

After several years of gas production, a black solid hydrocarbon material began to be produced along with the gas stream from the Risha gas field, in the northeastern part of Jordan. The main reason for the formation of this material is still unknown until this time, so knowing the source of this material is this study’s main goal. Organic geochemical studies for black solid material and effective source rocks (Lower Silurian shales) are used to determine the physical and organic components of the produced black solid material (heavy oil) and attempt to identify its source. The black solid material demonstrates high organic carbon (TOC = 12% by leco instrument) and a high calorific value, like those of oils, asphalts, and shale oils with moderate sulfur content. The gross composition of the black solid material sample is dominated by saturates and asphaltene but contains very low aromatic hydrocarbons reflecting the naphthenic oil type. Meanwhile, the Silurian extracts range between paraffinic and paraffinic-naphthenic organic matters. The biomarker indicators related depositional environment and carbon isotopic composition for the black solid material sample and Silurian extracts, show that they were relatively deposited in a reducing marine environment. The black material reveals lower maturity level than the Silurian extracts. Oil/source rock correlation study for the studied samples suggests strong affinity between the black material and Lower Silurian source rock in their source characteristics, suggesting that the black hydrocarbon material was expelled from the Silurian source rocks at low maturity stage as normal oil. This normal oil is subjected to secondary alteration process (evaporative fractionation) and was stored in the reservoir. It contaminated with some inorganic material that was introduced into the well as a component of a drilling mud additive or drill string lubricant or, potentially, in part, a corrosion product of wellbore tubulars, since significant iron was present in the sample.

The organic geochemistry of Permian high latitude sediments in two boreholes in the southern Sydney Basin, New South Wales, Australia

Twenty six samples of Permian high latitude sedimentary rocks from the southern Sydney Basin were analysed using organic geochemical methods for their thermal maturity, organic matter inputs, and depositional environment. Fourteen samples are from the Elecom Clyde River (ECR) DDH01 borehole (inland; Southern Highlands), and 12 are from the ECR-DDH07 borehole (coastal; near Nowra). The analysed formations are the Berry Siltstone, the Nowra Sandstone, the Wandrawandian Siltstone, the Snapper Point Formation and the Pebbley Beach Formation. This study is the first organic geochemical study of samples from the Berry Siltstone and Nowra Sandstone. The formations mostly have total organic carbon varying from 1 to 2 wt%, but the Snapper Point Formation is leaner in TOC (0.2–0.7 wt%). The samples vary from low to very high thermal maturity. The samples from the ECR-DDH01 borehole are in the early to middle of the oil window (vitrinite reflectance equivalent = 0.60–0.80%), based on hopane, sterane, alkylnaphthalene, alkylphenanthrene, alkylbiphenyl, and alkyldibenzothiophene thermal maturity parameters. The samples from the ECR-DDH07 borehole are much more thermally mature, in the late part of the oil window to the early gas window (vitrinite reflectance equivalent = 1.2–1.7%). This high thermal maturity has led to the loss of nearly all polycyclic biomarkers, and the thermal rearrangement of many groups of compounds, including monomethylalkanes. The ECR-DDH01 borehole location and time-equivalent outcrop samples south-west of Ulladulla have similar thermal maturities and are close to the margins of the Sydney Basin, and it is estimated to have previously been covered by about 3 km of overburden. In contrast, the samples in the ECR-DDH07 borehole were buried much deeper, with about 4–5 km of overburden, which means that only limited information about their source inputs and depositional environment could be recovered. Aliphatic biomarker, n-alkane and aromatic data are consistent with an overall strong terrigenous organic matter input for the samples from the ECR-DDH01 borehole. Sterane/hopane ratios are mostly low, but only a few compounds diagnostic of specific source inputs were identified. There is a microbially-dominated sample near the base of the Snapper Point Formation (high C29 αβ hopane/C30 αβ hopane ratio and 2α-methylhopanes), and high amounts of parent polycyclic aromatic hydrocarbons in some samples from the Berry Siltstone, likely reflecting an occasional pyrogenic signature from palaeo-forest fires. Several parameters, including sterane carbon number distributions, terpane ratios and the relative abundance of dibenzofuran compared to phenanthrene show that the samples from the ECR-DDH01 borehole have a more strongly terrigenous signal than the previously analysed outcrop samples. This is inferred to be because the ECR-DDH01 location was closer to the palaeo-shoreline than the likely more distal outcrop samples. Based on the pristane/phytane ratio and hopane distributions, deposition of the sediments was under varying oxicity conditions, from highly oxic to suboxic. The inferred environments are marine shale/lacustrine and fluvial/deltaic, so the organic geochemical data agrees with the Permian depositional history of the southmost part of the Sydney Basin previously inferred from sedimentological and palaeogeographic studies.

Organic Geochemistry of Carbonate Rocks, Silicites and Black Shales of the Vendian (Ediacaran) Khatyspyt Formation, Northeastern Siberia

Abstract —The paper presents the results of the study of organic geochemistry of carbonate rocks, silicites, and calcareous mudstones of the Vendian (Ediacaran) Khatyspyt Formation in the northeast of the Siberian Platform. The distribution of dispersed organic matter (OM) is shown to be uneven. The formation comprises carbonate-dominated intervals depleted in OM, with total organic carbon content (TOC) &amp;lt; 0.1%, or weakly enriched in OM (TOC up to 0.4%), interstratified with carbonate-shale, carbonate-shale-siliceous, carbonate-siliceous and siliceous intervals enriched in OM (TOC up to 1–4%). There is also a thin-layered calcareous mudstones anomalously enriched in OM (black shales with TOC at 10%) cropping out in the Khorbusuonka River valley (unit thickness 10 cm). The redox conditions in the water column varied during deposition of the Khatyspyt Formation. Certain intervals characterize a stratified water column and euxinic bottom water conditions. During the study, the assessment was conducted of the OM catagenesis and the generative potential of the Khatyspyt Formation. Based on the results of geochemical study and the synthesis of information on the geological structure of sedimentary succession in the northeastern Siberian Platform, the Khatyspyt Formation has been evaluated as one of the hydrocarbon sources for the territory.

Millimetre-scale biomarker heterogeneity in lacustrine shale identifies the nature of signal-averaging and demonstrates anaerobic respiration control on organic matter preservation and dolomitization

Mm-scale and/or µm-scale in situ inorganic geochemical analyses of organic-rich, laminated fine-grained sediments increasingly offer decadal or even seasonal perspectives of ecological or environmental dynamics. Organic geochemical studies, in contrast, seldom explicitly consider mm-scale variability, so that it remains unclear to what extent organic geochemical proxy-based reconstructions are a product of signal-averaging of higher-resolution variability. Here we assess the 2–8 mm-scale variability in organic geochemical proxies for depositional environment and organic source, utilising an organic-rich, low maturity and well-laminated shale from the Eocene Shahejie Formation, Dongying Depression, Bohai Bay Basin. We identify mm-scale (approximately decadal-scale) compositional variability that is comparable in magnitude to vertical variability at the m-scale (approximately millennial-scale), test multiple relationships between key biomarker and mineral proxies at the mm-scale, and assess likely implications for palaeowater conditions, anaerobic heterotrophic microbial activity, early diagenetic dolomitization, and organic matter preservation. Our results suggest that the decadal-scale oscillation of organic carbon content is a result of varying degrees of anaerobic heterotrophic microbial reworking with periodic euxinia in the deep photic zone. In contrast to previous models based on analysis of bulk samples, our results suggest that anaerobic respiration during intervals of more intense/persistent euxinia is likely accompanied by more organic matter loss. Variable low-light euxinia seems to be a modifier to the net OM content. The analysis of bulk samples may hide important relationships at shorter temporal scales which are key to reconstructing palaeoenvironments and the operation of key controls on, for example, the carbon cycle.

Petrographic and organic geochemical studies of the Oligocene-Pliocene mud-rich formations, East Mediterranean concession, Egypt

Petrographic and organic geochemical studies of the Oligocene-Pliocene mud-rich formations, East Mediterranean concession, Egypt

Occurrence and preservation of primary organic matter in a hybrid unconventional reservoir: Montney Formation, Western Canada Sedimentary Basin

The Lower Triassic Montney Formation of the Western Canada Sedimentary Basin (WCSB) is a world-class unconventional hydrocarbon resource in North America. It was deposited on the northwestern margin of Pangaea at mid-latitudes in an arid climate and after major mass extinction at the Late Permian-Triassic boundary. Despite decades of exploration and economic importance, the origin of organic matter and source of accumulated hydrocarbons is not well understood. The Montney Formation is primarily composed of dolomitic siltstone with a mean total organic carbon (TOC) content of ≤1 wt%. In this study, we re-examined samples from an Alberta Geological Survey (AGS) data release in 2010 on Montney Formation organic petrography and expand the sampling and analysis to further investigate organic matter type, thermal maturity, and possible internal hydrocarbon source intervals within the Montney Formation as well as organic matter preservation and depositional environment by integrating programmed pyrolysis, organic petrography, and molecular geochemistry.Organic petrography and molecular geochemistry show that millimeter to centimeter thick mudstone intervals with TOC ≤ 1 wt%, are dominantly comprised of Type II marine kerogen (Prasinophyte and Tasmanites) with minimal terrigenous organic matter. The presence of these organic-rich mudstone beds in central and western Alberta reveals intra-formational sources of hydrocarbons within the Montney Formation, in addition to hydrocarbons sourced from overlying organic-rich source rocks (i.e., Triassic Doig and Jurassic Gordondale). These results confirm that the Montney Formation can be considered as a hybrid unconventional hydrocarbon reservoir with an interbedded source and reservoir.Molecular geochemistry data suggest that photic zone euxinia (PZE) was favorable for the preservation of organic matter during deposition of the Montney Formation. However, in many instances, this only happened during very short periods similar to depositional conditions on the offshore present day Namibian shelf. Traces of terrigenous organic matter were able to reach the basin, likely in the form of inertinite and combustion-derived polycyclic aromatic hydrocarbons (PAHs). Although the results of this study show there are source rock intervals within the Montney Formation, a comprehensive organic petrography and geochemistry study on a series of full-length Montney cores throughout the basin will help to ascertain the major paleo depositional variation and their effect on organic matter preservation as well as hydrocarbon source intervals and their contribution to WCSB petroleum systems.

Poleward mangrove expansion in South America coincides with MCA and CWP: A diatom, pollen, and organic geochemistry study

The projected warming trend in the 21st century is likely to alter the global distribution of mangroves. However, the migratory pattern of different mangrove species is still unclear, especially in the subtropical Brazilian littoral. This study utilizes pollen, diatom, and organic geochemistry to document the late Holocene morphological and ecological transformation in São Francisco do Sul Bay, the mangrove sub-range limit in south Brazil. This multi-proxy dataset indicates the establishment of saltmarshes and mangroves on muddy tidal flats at ∼1720 and ∼870 cal yr BP, and Laguncularia, Avicennia, and Rhizophora colonized the study area at ∼870, ∼390, and ∼70 cal yr BP, respectively. This stepwise succession of three mangrove species in São Francisco do Sul Bay, and poleward mangrove expansion toward the austral mangrove range limit, indicate that the migratory histories of different mangrove species were not synchronized during the late Holocene, and temperature is the primary climatic factor regulating the mangrove distribution in south Brazil. More importantly, the Medieval Climate Anomaly and the Current Warm Period were clearly registered in the pollen record, suggesting that the two climate anomalies likely facilitated the mangroves colonization into higher latitudes in south Brazil. Overall, our dataset indicates that mangrove expansion into more temperate zones will likely accelerate in South America.

Organic geochemical study of Permian series from the Jeffara and Dahar areas (Southern Tunisia): Identification and characterization of a Tunisian Permian source rock

Permian rock samples from four wells drilled in the Jeffara (J1 and J2) and Dahar (D1 and D2) areas of southern Tunisia were evaluated using the Rock-Eval® Shale Play™ method. Quantification of most liquid hydrocarbon compound families released at specific temperature range for the Sh0 and Sh1 as well as Sh2 and S3 parameters was achieved with subsequent calculations of appropriate indices. In addition, stable carbon isotopes evaluation of Permian samples was carried out in order to estimate the origin of their fossilized organic matter. Biomarker analyses were also undertaken on Permian samples and other proven Paleozoic source rocks samples of the study area (Ordovician Azzel and Upper Silurian Fegaguira formations) for comparison purposes.The results show that the Permian series encompass highly-rich organic matter intervals which may exceed 5%. The organic matter is of type II2-III, proven either by the Rock-Eval®, carbon isotopes and biomarker data. Permian samples from three wells (D1, D2, and J2) are found mostly at an early mature stage. Contrary, Permian samples from the J1 Well show abnormal Tmax temperatures testifying an overmature stage which could be related to abnormal heat flow around the Jeffara area. The depositional environment of the organic matter-rich Permian intervals is mainly suboxic of normal salinity, similar to the other Paleozoic investigated source rocks in the study area. Overall, this research comes to validate the occurrence within the Dahar and Jeffara areas of an active Permian oil/gas prone source rock, competitive to the other proven Paleozoic source rocks.

Geochemical Evidence for the Origin of the Daranna Manganese Deposit, Kebbi State, Nigeria

Inorganic and organic geochemical and geostatistical studies of manganese ore deposits exposed at Daranna, near Kaoje have been carried out with the aim of characterizing and delineating the origin of the manganese ore deposits. Data were obtained from field observations and chemical analyses of 12 ore samples. Major and trace elements and organic geochemical analyses were conducted with Energy Dispersion X-ray Fluorescence Spectrometer and Rock-Eval pyrolysis method at Geo-data GmbH Garbsen, Germany. Results of the Major and trace elements, total organic carbon content abundances and the correlation among them imply that Daranna mineralizations are mainly of hydrothermal origin with little contribution from contemporaneous volcanic materials and this is confirmed by high Fe/Mn (8.274 to 24.066 wt%) and low Co/Zn ratios and trace element patterns. The significant geochemical characteristics such as high Mn content (22.660 to 62.330 wt%; average 45.919 wt%), low concentration of Fe (2.590 to 3.310 wt%; average 3.008 wt%) reveal a primary distal hydrothermal source for mineralization. The position of samples on Ni–Zn–Co and (Co/Zn)–(Co + Ni + Cu) diagrams and evaluation of these data reveals that hydrothermal activity was the main process with sedimentary influence responsible for mineralization in the Daranna manganese deposit.

Palynological and organic geochemical studies of the middle Eocene Siju Formation of Garo Hills, Meghalaya, India

Palynological and organic geochemical studies of the middle Eocene Siju Formation of Garo Hills, Meghalaya, India

Variations in microbial ecology during the Toarcian Oceanic Anoxic Event (Early Jurassic) in the Qiangtang Basin, Tibet: Evidence from biomarker and carbon isotopes

Reduced animal diversity during mass extinctions is commonly associated with resurgence of microbial abundances. The Toarcian Oceanic Anoxic Event (T-OAE) was a critical interval characterized by dramatic perturbations to the environment and life in the oceans and on land. A comprehensive organic geochemical study was performed on 19 samples from the upper Pliensbachian-lower Toarcian interval of the Quse Formation across the T-OAE at the Bilong Co outcrop section (also known as Biluo Co) in the Qiangtang Basin. Bulk geochemical analysis [total organic carbon contents (TOC): 2.0–8.0% wt., S2: 11–37 mg hydrocarbon/g bulk rock, Tmax: 435–441 °C] consistently suggests a narrow thermal maturity range of the Quse shale samples. The δ13C of maltene (δ13Cmaltene) and kerogen (δ13Ckerogen) fractions generally agree with the previously published δ13Corg curves, demonstrating the global T-OAE negative carbon isotope excursion (N-CIE). The elemental composition suggests a predominance of Type II kerogen, indicating the kerogen composition casts minimal effect on carbon isotopic signals. Petrographic examination demonstrated that the kerogens are mainly composed of alginate and amorphous organic matter, suggesting that a dominant source of kerogen originated from primary producers such as marine photosynthetic species that recorded the carbon fixation isotopic signature, whereas the bulk maltene represents a mixture of diversified organisms. By comparing the offset between δ13Corg, δ13Cmaltene and δ13Ckerogen in the T-OAE interval, two phases separated by the nadir of δ13C were recognized: early N-CIE and late N-CIE. In general, Phanerozoic δ13C values for preserved maltene and bulk organic matter in sediments are equal to or more negative than syngenetic kerogen; in the early N-CIE, however, δ13Ckerogen is more negative than δ13Cmaltene. Such isotopic inversions were previously attributed to the proliferation of 13C-enriched cyanobacteria and heterotrophic bacteria, which have been reported in Precambrian and Permo-Triassic transitional records. Moreover, the corresponding low sterane/hopane values in early N-CIE indicate an ecological shift reflecting microbial response to catastrophic environmental change that caused the extinction and initiated ecosystem changes during the early stage of T-OAE.

Geochemical characteristics and geological significance of humid climate events in the Middle-Late Triassic (Ladinian-Carnian) of the Ordos Basin, central China

Many Middle-Late Triassic (Ladinian-Carnian) global and local humid climate events that impacted on global palaeontological evolution and mineral distribution have been recorded in the rocks. The lacustrine sedimentary sequence of the Yanchang Formation in the Ordos Basin in the northeastern Tethys region may be an important example of control by global humid climate events. As revealed by an established chronostratigraphic framework and the study of organic carbon isotopes, elemental geochemistry and clay minerals, the Chang 7 Member of the Yanchang Formation was deposited in the Ladinian-Carnian, and the high total organic carbon (TOC) and total nitrogen (TN) contents indicate the high productivity of the ancient lake. The observed elemental ratios (Sr/Cu, Rb/Sr and Al2O3/MgO) and high contents of mixed-layer smectite indicate humid climate events in the Chang 73 and Chang 71 members. The increases in weathering degree, surface temperature and terrigenous clastic material input indicate enhancement of the hydrological cycle driven by a warm-humid climate. The arid-wet transitions, the negative excursions of the studied organic carbon isotope and the temperature fluctuations during the deposition of the Chang 73 and Chang 71 members of the Yanchang Formation are consistent with the Carnian humid event (CHE) and Ladinian-Carnian humid interval (L-CHI). The palaeontological diversity and the development of organic shales, turbidity currents and sandy debris flows in the Chang 7 Member may represent the continental sedimentary responses to coeval global humid climate events. The isochronous eruptions of volcanoes around the Ordos Basin may have intensified the global greenhouse effect and become an important factor driving the multi-stage humid climate events in the Ordos Basin.

Uranium Deposits of Erlian Basin (China): Role of Carbonaceous Debris Organic Matter and Hydrocarbon Fluids on Uranium Mineralization

The relationship of sedimentary organic matter, oil-gas and sandstone-type uranium (U) deposits is the key problem of U-mineralization. Whether migrate hydrocarbons participate in U-mineralization is still a controversy. Typical U deposits of the Erlian Basin in northeast China have been investigated through detailed petrography, mineralogical, micro spectroscopic, organic geochemical and C-isotope studies. Petrographic observations, Microscopic Laser Raman Spectroscopic, Infrared Spectroscopic and Scanning Electron Microscope analyses indicated there are three types of organic matter (including carbonaceous debris and migrated hydrocarbons). A significant amount of uranium was associated with pyrites, clay minerals and carbonaceous debris organic matter, either coexisted with hydrocarbon fluids. There are at least two stages mineralization events, stage I is related to sedimentary organic matter (syngenetic pre-enrichment stage), and stage II is related to mobile hydrocarbon fluids (main mineralization stage). Therefore, our results support that migrated hydrocarbons were involved as a reducing agent for the main uranium mineralization after synsedimentary mineralization.

Hydrothermal Organic Geochemistry (HOG) sampler for deployment on deep-sea submersibles

The fate of carbon while passing through the rocky subseafloor of the ocean has direct implications on the global carbon cycle now and over geologic time, as well as the abundance and distribution of subseafloor life. Many organic geochemical studies require larger volumes of fluids than traditional hydrothermal samplers can provide, and also require rigorous steps to be taken to prevent contamination. The Hydrothermal Organic Geochemistry (HOG) sampler is designed to collect large volume (2–9 L) fluid samples with minimal introduction of organic or microbial contamination, and to be powered and deployed in real time from a submersible. Additional design constraints include utilizing materials appropriate for sampling fluids with elevated temperatures, fitting the sampler into the space available on the submersible, and minimizing the time needed to remove samples and prepare the sampler for re-deployment between dives. It utilizes two inlets, one devoted to natural abundance geochemistry and one that can be used for samples pre-dosed with isotopic labels or preservatives. Temperature probes providing real-time data are incorporated into each inlet to facilitate positioning the intake in areas of the hottest fluid flow, thereby minimizing entrainment of ambient bottom seawater while sampling. Fluids are shunted through two main conduits by a large volume pump. Smaller ports stemming off the main conduit connect to positive displacement fluid sample chambers and in situ filters. The outlets of these chambers and filter holders are connected to a 24-port valve, which in turn is connected to a small volume pump. The HOG sampler has successfully collected over 100 high purity fluid samples and 50 in situ filters during two expeditions to deep sea hydrothermal fields.

Terrestrial ecosystem collapse and soil erosion before the end-Permian marine extinction: Organic geochemical evidence from marine and non-marine records

A terrestrial ecosystem collapse event accompanied by extensive soil erosion has been widely recorded in marine sedimentary rocks at the vicinity of the end-Permian mass extinction. However, the precise timing of this event and its impact on the marine extinction have not yet been ascertained. Here we present an organic geochemical study of non-marine and marine sections from the South China Craton, which shows that terrestrial ecosystem collapse was accompanied by a soil erosion event, and was followed by the end-Permian marine extinction. Two separate events devastated the terrestrial ecosystem prior to the marine extinction event, over a timespan of dozens of kyr. Bacteria flourished in the non-marine section coeval with a decline in terrestrial plants and in the marine section during the end-Permian marine extinction. A proto-recovery of herbaceous plants (not woody plants) occurred dozens of kyr after the end-Permian marine extinction and coincided with a global warming maximum and oceanic anoxia/euxinia. • Plant extinction was followed by soil erosion and the end-Permian marine extinction. • Bacteria flourished during the plant extinction in the non-marine section. • Bacteria flourished during the end-Permian marine extinction in the marine section. • Proto-recovery of vegetation coincided with global warming and oceanic euxinia.