High Bioproductivity Research Articles

Oil source rock characteristics of the pelagic carbonates in the Shabwah depression, southeastern Sabatayn Basin, Yemen

Bituminous lime mudstone from the Late Tithonian--Early Barremian Naifa Formation was collected from five wells in the Shabwah depression of the southeastern Sabatayn Basin for basic organic geochemical analyses. The collected samples’ nannofossil contents were also studied. The current study preliminarily evaluated the nature of the organic matter regarding the richness and type of organic facies and their relation to oil generation potential. Most of the lime mudstone samples are organically rich and include favorable source rocks, as indicated by the high TOC content of up to 1 wt%. The presence of the warm-water index nannofossil taxa Watznaueria barnesae suggests warm climate conditions, thereby contributing to high bioproductivity that consequently enhanced organic richness. The samples are also hydrogen rich, with HI values between 302 and 740 mg HC/g TOC, resulting in two dominant organic facies of kerogen Types I and II, and are consistent with high bioproductivity of phytoplankton algae in warm-water conditions during deposition. Both geochemical maturity values Tmax and PI indicate that the bituminous lime mudstones are at different thermal maturity levels and range from immature to early mature stages of the oil generation window. This implies that the bituminous lime mudstones were not buried to a sufficient depth for commercial oil generation. Therefore, further exploration efforts in deeper parts of the Shabwah depression, particularly in the area around well Misah-01, are recommended.

The characteristics of a relic steppe of Northeast Asia: refuges of the Pleistocene Mammoth steppe (an example from the Lower Kolyma area)

An ecosystem of a relic petrophytic steppe was studied in the Lower Kolyma River region. The soils of the steppe area significantly differed from those of the surrounding open larch forests in the following features: the presence of humus-accumulative horizons with a high content of roots; low moisture content; high heat supply; an extremely contrasting temperature regime; neutral reaction; decreased potential acidity; higher humification of organic matter; accumulation of exchangeable bases, soluble salts and organic nitrogen; and the presence of carbonate neoformations in the form of cutans on pebbly units. They also had a high microorganism saturation of the soil profile, a high share of actinomycetes in the microbial community, as is typical for arid soils, and a shift in the ratio of potential enzyme activities toward oxidoreductases, which reflects a deeper destruction of plant residues and more intensive humus formation. The petrophytic steppe had high bioproductivity. The growth rate of the aboveground phytomass (ANP) was closer to the true steppes of Central Asia than to the zonal tundras of the Arctic and Subarctic; such communities can serve as models for paleoreconstructions and study of the Late Pleistocene cold steppes - mammoth fauna large grazing mammals habitats.

Composition of recent bottom sediments of the Chukchi Sea. Results of an integrated sedimentological research

Results of high-resolution research of recent bottom sediments from south, central and north Chukchi Sea reveal striking data on environmental changes during the last decades. The composition of surface sediments from the Arctic Sea gives evidence of the decrease of ice cover and an increase of biogenic elements, caused by higher bioproductivity.

Paleo-sedimentary environment in relation to enrichment of organic matter of Early Cambrian black rocks of Niutitang Formation from Xiangxi area China

Abstract Early Cambrian organic-rich black rocks are extensively distributed in the southern China. In this study, we have discussed the relation of paleo-sedimentary environments with enrichment of organic matter. Based on TOC data, we divided the Niutitang Formation into three parts (Upper, Middle, and Lower). The amount of total organic carbon in the Lower (1.55 wt %) and the Upper part (1.35 wt %) of Niutitang Formation is significantly smaller than the Middle part (8.0 wt %) which suggest initial transgression, and regression stages of the sea level respectively. The Middle part from both sections (Longbizui and Sancha) contains higher TOC content, which is a clue of intense transgression stage of sea level with high bio-productivity. Kerogen type index (KTI) using different macerals specify the organic matter in these black rock series is mainly type-I with a minor amount of type-II1. Moreover, these black rocks were deposited in weak to moderately restricted hydrographic conditions. The heterogenic mineral composition was also observed in these black rocks, including quartz, clay, gypsum, pyrite, barite, dolomite, and plagioclase. Quartz content in the Middle part is relatively higher than the Upper, and the Lower part displays a strong positive relation with TOC which suggests the main source of quartz during deposition of the Middle part was biogenic quartz. During Early Cambrian period due to extension between the Yangtze and the Cathaysian plate, the hydrothermal fluids rich in uranium, vanadium, molybdenum, zinc, barium, etc. from the deeper part of the earth crust and entered the ocean basin through extensional remnant fissures and cracks, and due to upwelling phenomena entered to the shelf area. These nutrient-rich deep crustal fluids at the surface of the sea enhanced the evolution and breeding of planktons and other marine life; meanwhile, it upsurges the bio-productivity. Additionally, it creates bottom water hypoxia, which is favourable for the preservation of organic matter in the sedimentary rocks. The main factors responsible for the enrichment of organic matter in these Early Cambrian black rock series of Niutitang Formation were a hydrographic restriction, hydrothermal activities, and paleo-redox conditions, respectively.

The fate of a Neoproterozoic intracratonic marine basin: Trace elements, TOC and IRON speciation geochemistry of the Bambuí Basin, Brazil

Neoproterozoic marine systems are associated with major paleoecological changes that took place in the Ediacaran and during the Ediacaran-Cambrian transition. During this timespan, the Bambuí basin located on east Brazil held a peculiar paleoenvironmental scenario. Due to its intracratonic evolution, the basin was partially disconnected from neighboring open marine systems. This setting raises a very interesting opportunity to understand how an isolated Neoproterozoic marine system evolved in contrast with typical (globally connected) open marine systems. To understand the paleoenvironmental changes that took place in the Bambuí basin, we investigate the pre-glaciogenic deposits of the Carrancas Fm and the post-glaciogenic mixed (shale-carbonate) successions of the Bambuí Group. Through the analysis of iron speciation, TOC, trace element and C-O isotope systematics, our study suggests a very complex environmental evolution. Firstly, our samples are marked by strong contamination of detrital continental material that can be related to an increased bioproductivity on both the Carrancas Fm. and lower Bambuí group stratigraphic units, and provenance data show that all studied sediments probably shared common source areas. Iron speciation data, Ce anomalies and RSE enrichments shows that lower Bambuí Group stratigraphic units were likely deposited in an open marine scenario featuring high bioproductivity in shallow waters and euxinic incursions in predominant anoxic/ferruginous bottom waters. On the other hand, upper Bambuí stratigraphic units register a marine evolution in a restricted scenario, where anoxic ferruginous conditions probably reached surface waters. Finally, our data show that the lack of oceanic connection prevented the re-supply of marine sulfate, RSE, bionutrients and ultimately of dissolved oxygen which may have decreased biological activity and probably hindered biological evolution, preventing the rise of a typical modern-like Cambrian ecosystem. In this sense, our data suggest that oceanic connectivity and proper re-supply of inorganic marine input were important features in the development of complex life in the Ediacaran-Cambrian environment.

Organic geochemical characteristics and depositional setting of Paleogene oil shale, mudstone and sandstone from onshore Penyu Basin, Chenor, Pahang, Malaysia

The eastern Chenor Pahang area of the Penyu Basin contains an untapped potential, in part due to poor knowledge of its organic facies characteristics The sedimentary succession of eastern Chenor Pahang area is dominated by fine to coarse grained sandstone occurring in association with oil shale and mudstone in a predominantly fining upward sequence. Detailed geochemical and petrographic characterization was carried out on oil shale and mudstone samples to evaluate the origin and type of organic matter (OM), as well as the paleoenvironmental conditions and organic richness of the Paleogene sedimentary succession. The facies are only enriched in total organic carbon (TOC), potential hydrocarbon yield (S2) and extractible organic matter (EOM) the types of organic matter are important index reflecting the potential of the source rock(s). Based on elemental ratios, the analyzed samples are shown to contain Types I and II kerogens. This finding is supported by the high hydrogen index (HI) of >300 mg HC/g TOC and the presence of abundant liptinitic materials. Biomarker signatures [n-alkanes >n-C25, high C29/C30 17α (H) hopane ratios (0.8–3.3) and high C29 steranes (49–78%)]. Low total sulfur and V/(V + Ni) ratio] suggest a predominantly terrestrial source input with some contribution from aquatic microorganisms as indicated by the common occurrence of amorphous organic matter. Combining this results with n-alkane patterns, kerogen types and organic petrography, predominance of C29 sterane probably indicates a contribution of aquatic organisms such as green and brown algae (consistent with Botrycoccus braunii race A and Pediastrum contribution) and some influence of higher plants OM. Integration of biomarker studies with bulk geochemical and petrographic analysis suggests that the analyzed samples were deposited under suboxic conditions in a fresh water lacustrine environment. This finding is corroborated by the ratios of pristane/phytane, V/Ni and Sr/Br. High bioproductivity and a stratified fresh water column with suboxic bottom water condition enhanced OM preservation in the analyzed mudstone and shale facies. The high OM content in these samples maybe related to the fine-grained matrix of the mud rocks and the paleoclimate in the area.

Исследование химического состава надземных органов брусники

Data on the elemental composition of plant materials is important for establishing their therapeutic value in medical practice and ensuring the safety of drugs produced therefrom. This article presents the results of a study aimed at determining the elemental composition of the above-ground organs of Vaccinium vitis-idaea L. (lingberry) collected across the Slyudyansky district of the Irkutsk Oblast. Growing under favourable environmental conditions, this species is characterised by a high bioproductivity. The method of X-ray fluorescence analysis (XRF) was used to estimate the content of the following elements in leaf samples: Na, Mg, Al, Si, P, S, Cl, K, Ca, Fe, Cr, Mn, Ni, Ti, Cu, Zn, Ba, Rb, Sr and Pb. According to the obtained data, the plant under study features such essential elements as calcium, potassium, magnesium and phosphorus, as well as such microelements as manganese and barium. The content of potentially toxic metals (Ti, Cr, Ni, Cu, Zn, Sr, Ba and Pb) does not exceed the threshold levels established for land plants. A high content of vital elements and the absence of toxic effects make Vaccinium vitis-idaea L. a promising medicinal material for the prevention and treatment of microelementoses. Due to their broad-spectrum therapeutic properties, lingberry leaves are widely used in traditional medicine.

Warm-humid paleoclimate control of salinized lacustrine organic-rich shale deposition in the Oligocene Hetaoyuan Formation of the Biyang Depression, East China

Lacustrine organic-rich shales are widely developed within the Oligocene Biyang Depression in the Nanxiang Basin in east China and across Southeast Asia. These shales have been proven as hydrocarbon source rocks of crude oil, as well as sources and reservoirs of shale oil. Understanding the deposition of these shales is essential to reconstruct the paleoenvironment and paleoclimate during the Oligocene in east China, as well as target the potential shale oil resources. Based on X-ray diffraction, organic and inorganic petrologic, organic and inorganic geochemical, and stable isotopic analyses, paleoenvironment, paleoclimate and hydrocarbon potential of the lacustrine organic-rich shales in the Oligocene Hetaoyuan Formation were investigated. The mineral composition of Hetaoyuan Formation organic-rich shales is dominated by clay minerals, followed by quartz, plagioclase, calcite, dolomite, pyrite and gypsum. Six lithotypes are identified, including siltstone, silty shale, clay shale, calcareous shale, dolomite shale and massive mudstone. The organic matter (OM) of the organic-rich shales is dominated by type I kerogen (lamalginite). Maturity parameters (Tmax, biomarker ratios and calculated vitrinite reflectance) suggest that the OM enters the oil window maturity. High TOC and generative potential, together with high contents of brittle minerals (including quartz, plagioclase and carbonates) reveal the Oligocene Hetaoyuan Formation hold good to very good potential of shale oil exploitation. Six organic-rich shale layers have been identified in the Hetaoyuan Formation (shale layer 1 to 6, from top to bottom). Among them shale layers 5 and 3 hold the best shale oil potential and therefore be investigated in the present paper. Shale layer 5 was deposited in a semi-deep lacustrine environment under the moderately warm-humid paleoclimate, further dividing into lower, middle and upper units. Relatively low TOC contents (av. 2.6 wt%) in the lower unit are probably caused by high sedimentation rate. High bioproductivity under favorable preservation conditions led to relatively high TOC contents (av. 3.6 wt%) in the middle unit. Less reducing conditions together with moderate-low bioproductivity resulted in relatively low TOC contents (av. 2.6 wt%) in the upper unit. Warm-humid paleoclimate prevailed during deposition of shale layer 3, deepened water depth and formed a deep lacustrine environment. The stratified water column led to stable anoxic condition and photic zone euxinia in the saline, deep lacustrine environment, which enabled the accumulation of high amounts of OM (av. 4.9 wt% TOC) under excellent preservation (av. HI: 710 mg HC/g TOC). The results of core scanning analysis indicate that formation of the laminated shales probably controlled by seasonal fluctuations of paleoclimate.

Postglacial Deposits of the Dal’nyaya Taiga Group: Early Vendian in the Ura Uplift, Siberia. Communication 2. Ura and Kalancha Formations and History of the Basin

The paper presents the facies characteristics and sequence-stratigraphic reconstructions of the Lower Vendian postglacial deposits of the Dal’nyaya Taiga Group (Ura Uplift, Patom basin, Siberia). The section is divided into two sequences: the first sequence corresponds to the Barakun Formation; the second sequence, to the Ura and Kalancha formations. Together, they make up a continuous transgressive-regressive succession, with its significant part formed in a deep-water zone of the low-angle (about 1°) homoclinal carbonate–terrigenous and clayey–carbonate ramps. The upper sequence boundary passing along the top of deposits in the Kalancha carbonate platform corresponds to the stratigraphic hiatus at the Zhuya Group base. The fine-grained siliciclastic material, which makes up as much as 50 vol % of the Ura sediments, has an eolian origin. Probably, high activity of eolian processes promoted by a moderately cold arid or semiarid climate at that time was one of the reasons for high bioproductivity in the paleobasin. The consequent large-scale burial of organic matter could foster the reactivation of methanogenic processes. The lithological features of sediments were responsible for their thixotropic state that provoked the slumping of sedimentary masses during high seismic activity.

Organic matter accumulation in the Upper Devonian Duvernay Formation, Western Canada Sedimentary Basin, from sequence stratigraphic analysis and geochemical proxies

We present a model for organic carbon accumulation in the Upper Devonian Duvernay Formation of the Western Canada Sedimentary Basin, relating total organic carbon (TOC) concentrations to a high resolution geochemical and organic petrologic database and comparing these to a core-based sequence stratigraphic interpretation. Many previous source rock studies have suggested that organic matter is enriched in transgressive systems tracts or at maximum flooding surfaces, an observation that is commonly attributed to an assumed relationship between water depth and oxygen levels. Our data set enables us to associate total organic matter content and organic assemblages with particular systems tracts and to examine how the organic assemblages change across the basin, tested against proxies for redox conditions and bioproductivity to relate relative sea level to specific mechanisms for organic accumulation.The Duvernay Formation comprises three third-order depositional sequences, superimposed on a second-order late transgressive systems tract and early highstand systems tract. Sequences are composed almost entirely of transgressive systems tracts and highstand systems tracts, with a lowstand systems tract only at the base of the upper cycle that marks the second-order sea level turnaround. Depositional facies generally vary from bioturbated carbonate-rich siltstones to siliceous mudstones from the platform margins to basin center. Organic petrologic analysis records predominantly amorphous organic matter and solid bitumen, with much less abundant vitrinite and inertinite. Organic matter type indicated by Rock-Eval analysis shows that in most cases, high total organic carbon (TOC) content is associated with better quality organic matter (high hydrogen index) and vice versa, indicating more reducing conditions or higher bioproductivity were responsibility for organic enrichment. However, near carbonate reefs, hydrogen index is uncorrelated with TOC, indicating that here, dilution by carbonate minerals was the primary control on organic enrichment. Across most of the basin, highest TOCs are recorded just above the second-order maximum flooding surface. Secondary peaks in TOC are recorded above the maximum flooding surface in the upper third-order cycle and in the transgressive systems tract of lower third-order cycle. Low TOC values are recorded in the lowstand systems tract and in the middle and upper third-order transgressive systems tracts almost up to the maximum flooding surfaces.Throughout much of the basin, proxies for relative sea level, restriction of water masses (Mo/TOC), redox conditions (Mo/Al and S/Fe) and bioproductivity (biogenic silica) coincide. These relationships demonstrate that organic carbon accumulation resulted from influxes of nutrient-rich upwelled water during high sea level; thus, TOC values are highest in the upper part of transgressive systems tracts and lower highstand systems tracts. Anoxia typically developed as a result of bioproductivity and enhanced organic matter accumulation but was not itself a trigger for organic sedimentation. Near carbonate reefs, however, varying sea level regulated carbonate sedimentation rate and organic matter dilution, and bioproductivity had less impact on organic matter concentrations; thus, TOC was high when carbonate deposition was low during transgressions, which forced carbonate reefs to backstep, limiting carbonate sedimentation in deeper water area.

Lithological and Geochemical Characteristics of the Paleocene/Eocene Sediments corresponding to the PETM Biospheric Event in the Eastern Crimea (Nasypnoe Section)

The paper reports lithological and geochemical data on the stratigraphic interval corresponding to the Paleocene/Eocene Thermal Maximum (PETM) event in the Paleogene section of Eastern Crimea (Nasypnoe section). The section is located on the western continuation of the sublatitudinal profile consisting of 15 PETM sections spanning the area from Crimea to Tajikistan (over 2500 km). It is shown that PETM sediments have the negative δ13C and δ18O isotope excursions and are enriched in kaolinite, which is typical of most sections of this interval around the world. At the same time, the extremely low content of organic matter (OM) in sediments of the Nasypnoe section makes them sharply different from the highly carbonaceous rocks of the PETM interval in Central and Eastern Caucasus, and Central Asian regions. This is correlated with the low contents of many chemical elements in the studied rocks, and their extremely high contents in the highly carbonaceous rocks of the easterly sections. Thus, Eastern Crimea in the end of the Paleocene‒beginning of the Eocene was occupied by the low-bioproductive marine paleobasin, whereas the coeval paleobasin in Central Asia was characterized by extremely high bioproductivity owing to the presence of significant amount of phosphorus.

Transient marine euxinia at the end of the terminal Cryogenian glaciation

Termination of the terminal Cryogenian Marinoan snowball Earth glaciation (~650–635 Ma) is associated with the worldwide deposition of a cap carbonate. Modeling studies suggest that, during and immediately following deglaciation, the ocean may have experienced a rapid rise in pH and physical stratification followed by oceanic overturn. Testing these predictions requires the establishment of a high-resolution sequence of events within sedimentary records. Here we report the conspicuous occurrence of pyrite concretions in the topmost Nantuo Formation (South China) that was deposited in the Marinoan glacial deposits. Sedimentary facies and sulfur isotope data indicate pyrite precipitation in the sediments with H2S diffusing from the overlying sulfidic/euxinic seawater and Fe (II) from diamictite sediments. These observations suggest a transient but widespread presence of marine euxinia in an ocean characterized by redox stratification, high bioproductivity, and high-fluxes of sulfate from chemical weathering before the deposition of the cap carbonate.

Sr chemostratigrphy, δ13C, and δ18O of rocks in the Crimean carbonate platform (Late Jurassic, northern Peri-Tethys)

The paper presents the results of study of the Sr, C, and O isotope compositions in Upper Jurassic carbonate rocks of the Baidar Valley and Demerdzhi Plateau in the Crimean Mountains represented by different facies of the carbonate platform at the northern active margin of the Tethys. The 87Sr/86Sr value in them varies from 0.70699 to 0.70728. Based on the Sr chemostratigraphic correlation, the age of massive and layered limestones in the western part of the Ai-Petri and Baidar yailas (pastures) is estimated as late Kimmeridgian–early Tithonian, whereas the age of flyschoids of the Baidar Valley are estimated as late Tithonian–early Berriasian. The nearly synchronous formation of carbonate breccias of the Baidar Valley and Demerdzhi Plateau in late Tithonian–early Berriasian is substantiated. A summary section of Upper Jurassic rocks is compiled based on the Sr chemostratigraphic data. It has been established that δ18O values in the studied carbonate sediments vary from–2.9 to 1.3‰ (V-PDB). At the same time, shallow-water sediments in the internal part and the edge of the Crimean carbonate platform are depleted in 18O (–2.9 to +0.1‰) relative to sediments on the slope and foothill (–0.5 to +1.3‰). It is demonstrated that δ13C values do not depend on the facies properties and decrease in younger carbonate sediments from 3–3.5‰ to 1–1.5‰ in line with the Late Jurassic general trend. The δ13C values obtained for the Crimean carbonate platform turned out to be 0.5–1‰ higher than the values typical of the deep-water marine setting at the western margin of the Tethys. These discrepancies are likely related to peculiarities of water circulation and high bioproductivity in marine waters of the northern Peri-Tethys.

Diverse Sedimentary Conditions During Deposition Of Coal And Oil Shale From The Meihe Basin (Eocene, Ne China)

The Meihe Basin in northeastern China is a normal-fault-controlled basin filled with Eocene nonmarine deposits, the sediments assigned to the Meihe Formation. Sediment grain-sizes, core study, well-log analysis and micropetrographic study combined with sedimentary facies analysis indicate that the main sedimentary facies of the Meihe Basin represent fan-delta, lake, and turbidite deposits. Thick coal seams that are mainly distributed in the eastern part of the studied area were deposited in the swamp facies of the Lower Coal-Bearing Member. Oil shale was mainly deposited in the deep lake represented by the Mudstone Member, and is mainly distributed in the southern part of the studied area. In the Lower Coal-Bearing Member, organic-rich sediments are characterized by TOC content between 0.6 wt.% and 43.1 wt.%and contain Type II and III kerogen. The thick coal seams are the result of high landplant productivity and good preservation conditions. Thin coal seams in the fan-delta plain resulted from the migration and erosion of the fan-delta channel. In the shallow lake and fan-delta front, limited productivity coupled with dilution by inorganic matter resulted in lower organic-matter content in theMudstoneMember. Oil shale and mudstone rich in organic matter were deposited in a deep lake with an average TOC content of 3.4 wt.%. The origin of the organic matter was mainly algae and aquatic plants mixed with land plants. The improved preservation conditions and high bioproductivity in this environment resulted in three oil-shale layers in the lower part of this sedimentary succession. Three coal-bearing and oil-shale-bearing fault basins lie adjacent to the Dunhua-Mishan Fault zone, among which the Fushun Basin is located in the southwest, the Meihe Basin is in themiddle, and theHuadian Basin is in the southeast. From the Fushun Basin to the Huadian Basin, the oil shale and coal seams have distinct sedimentation characters laterally. Vertically in each basin, the organic-matter sources all have the same variation trend from land plants to land plants mixed with algae to algae then to algae mixed with land plants, and the TOC content also shows a similar trend from high to medium-high then to low in each basin.

Controls on organic matter accumulation in the Triassic Chang 7 lacustrine shale of the Ordos Basin, central China

The Triassic Chang 7 Formation is a rich lacustrine source rock in the Ordos Basin, central China. Petrographic and geochemical analyses were performed in order to research the mechanism of organic matter (OM) enrichment in the Chang 7 shales. Bulk geochemical data indicate that the OM-rich shales were formed in a fresh and brackish water, which is not usually the case for high TOC (Total Organic Carbon Content) sediments. Therefore, there must be some special conditions favorable for OM enrichment in Chang 7 shales.Petrography and element geochemistry show that the Chang 7 OM-rich shales are abundant in OM-enriched laminae, framboidal pyrites, collophanes, and some elements including iron (Fe), diphosphorus pentoxide (P2O5), copper (Cu), vanadium (V), molybdenum (Mo), and uranium (U). High bio-productivity (algae blooming) and anoxic depositional environments are critical for OM enrichment. As the organic carbon contents increase, the Fe, P2O5, Cu, V, Mo, and U element contents increase as well and the ratios of U/Th and V/(V+Ni) are growing. Many geochemical data demonstrate that the water was oxic, while the environment under the sediment-water interface was anoxic as a result of a high organic supply that sufficiently consumed oxygen.Taking into account the geological settings and our previous studies, we propose that the frequent volcanic events and hydrothermal activity caused by the collision of the North China landmass with the Yangtze landmass and consequential formation of the Qingling Mountains had a significant role in the OM enrichment in the fresh and brackish lacustrine shales. Deposition of volcanic ash into aqueous environments might lead to the increase of some key nutrients, such as Fe and P2O5, which might enhance primary bio-productivity. New evidence for hydrothermal activity, the reddingite, was demonstrated in this study. Not only can the hydrothermal activity provide elements necessary for life, but is also favorable for formation of anoxic settings.The deposition of the Chang 7 lacustrine OM-rich shales can be explained using the High-Bio-Productivity-Driven Model, which is related to volcanic events and hydrothermal activity as a consequence of regional tectonic movements. An anoxic depositional setting is beneficial for OM preservation and slow sedimentation rates in the deep lacustrine environments are favorable for OM enrichment.

Anomalous mercury enrichment in Early Cambrian black shales of South China: Mercury isotopes indicate a seawater source

Extremely elevated Hg levels up to the μgg−1 range were found in sulfide-rich black shale and phosphorite in the lowermost part of the Early Cambrian black shale sequences on the Yangtze Platform in South China. In this study, mercury isotopes were used to help resolve the origin of this anomalous Hg enrichment. Mass independent fractionation signatures of Hg isotopes with positive Δ199Hg values of 0.13 to 0.24‰ and positive Δ200Hg values of 0.05 to 0.10‰ were observed, indicating seawater is an important source of Hg. We hypothesize that upwelling of nutrient-rich waters from the open ocean resulted in high bioproductivity in the photic zone with concomitant scavenging of Hg from seawater. Advanced decay of biomass and remineralization under anoxic to euxinic conditions combined with very low clastic input led to enrichment of Hg and a broad spectrum of other redox-sensitive and biogenic metals up to 107 compared to modern seawater. Such spectacular hydrogenous metal enrichment has previously been observed in the oxic deep-sea environment only, i.e. manganese crusts/nodules.

Depositional environment of oil shale within the second member of Permian Lucaogou Formation in the Santanghu Basin, Northwest China

The non-marine Santanghu Basin in northwest China hosts one of the richest and thickest Permian lacustrine source rock intervals in the world. Conventional oil in Jurassic sandstone reservoirs and tight oil in the tuffaceous Permian Tiaohu Formation were sourced from mudrocks in the underlying second member of Lucaogou Formation, which also have tight oil potential proved by recent commercial discoveries. Based on inorganic and organic geochemistry, organic petrography, and stable isotope geochemistry, the depositional environment and the tight oil potential of the second member of Permian Lucaogou Formation were investigated. The data imply a gradual evolution of the depositional environment from a stratified, saline to a freshwater lake. The succession can be subdivided into a lower, middle, and an upper unit, each characterized by decreasing water salinity. High bioproductivity has been caused by the bloom of algae and photosynthetic cyanobacteria. Water column stratification accelerated the activity of methanothrophs, as indicated by low δ13C values of hopanes. Biomarker composition provides evidence for decreasing contributions of cyanobacteria to the biomass and increasing abundance of Prasinophytae compared to other algae with decreasing salinity. Enhanced terrigenous organic matter input appeared during periods of high freshwater inflow. Low total organic carbon (TOC) contents in the lower unit are most likely caused by rapid sedimentation rate. High bioproductivity and excellent preservation conditions resulted in high TOC contents in the middle unit. Terrigenous organic matter input increased together with fresh water inflow in the upper unit, resulting in high TOC values during periods of possibly low sedimentation rates in a deep water column. The samples of the second member exhibit a good to very good potential to generate conventional oil. High TOC and extractable organic matter yields, together with the thickness of the fine-grained sediments, show that the middle and upper units of the second member of Lucaogou Formation hold significant tight oil potential. Mineralogical composition of this dolomite-rich shale with respect to abundance of brittle minerals (including quartz and carbonates) and rare clay testifies a good tight oil potential.

Calcareous sediments of the Muwaqqar Chalk Marl Formation, Jordan: Mineralogical and geochemical evidences for Zn and Cd enrichment

Immature organic-rich siliceous chalk (‘oil shale’) and organic-poor limestones of the Maastrichtian-Paleocene Muwaqqar Chalk Marl Formation (MCM) (central Jordan) deposited on the southern Neo-Tethys epicontinental shelf provide a perfect example of carbonate sedimentation in a bioproductive upwelling environment. The MCM sediments have been studied by XRD, SEM, EMPA, sequential extraction, ICP-MS, GC–MS, and FTIR to gain insights into causes of their unusual composition. The sediments are remarkable by exceptionally high enrichment in phosphorus and redox sensitive elements (RSE), mainly Cd (up to 225ppm), Zn (1500ppm), and Mo (up to 180ppm), as well as in Ni, V, Cr, and U, with a total RSE budget reaching 3200ppm, coupled with up to 23wt% organic matter and 4.3wt% sulphur. The bulk organic matter consists of type I/II kerogens sulphurised during sulphate reduction. Redox sensitive metals were brought to sediments mainly by biogenic shuttle, while the terrestrial input was minor, and hydrothermal fluids apparently did not contribute to total RSE. The metals can reside in sulphide (Zn-Cd-(Cu)) in sphalerite or/and würtzite; Fe-Ni-V-Cu-(Mo) in pyrite, carbonate (Zn-Cd-(Mo-Ni-V)), and organic (Ni-V-Cu) phases. Authigenic Cd-rich sphalerite and würtzite are much more abundant than pyrite in immature ‘oil shales’, for three main reasons: (i) S-bearing ligands coordinating Cd and Zn in primary organic matter; (ii) high sulphur in organic matter; and (iii) low concentrations of reactive iron in bottom sediments. Limestones redeposited under oxic environments lose all sulphides, but high Zn (up to 337ppm) and Cd (up to 29ppm) become redistributed into the newly formed carbonates. Thus, shelf carbonates of different ages deposited under anoxic/sulfidic conditions in zones of high bioproductivity, as well as their derivative limestones and dolomites, can be the primary Zn and Cd storage for Mississippi Valley-type deposits with high Zn/Pb and Cd/Zn ratios.

The type section of the Maikop Group (Oligocene–lower Miocene) at the Belaya River (North Caucasus): Depositional environment and hydrocarbon potential

The type section of the Oligocene to lower Miocene Maikop Group, considered the main source rock in the eastern Paratethys, has been studied using geochemical proxies to gain insights into depositional setting and hydrocarbon potential. The Maikop Group at the type section is approximately 600 m (2000 ft) thick. Deposition commenced after a major late Eocene sea level drop and a subsequent early Oligocene sea level rise. The Maikop Group is composed mainly of carbonate-free pelitic rocks. Calcareous rocks are limited to the lower Oligocene succession, including the Polbian Bed that forms a basin-wide marker horizon deposited during a time with significantly decreased salinity (Solenovian event). Anoxic conditions prevailed and were only interrupted for longer periods during deposition of the lower part of the lower Oligocene Pshekha Formation, the Polbian Bed, and the lower Miocene Olginskaya Formation. Total organic carbon (TOC) contents range up to 3.5 wt. %. Hydrogen index values are typically less than 300 mg hydrocarbons (HC)/g TOC but reach 420 mg HC/g TOC in black shales overlying the Polbian Bed (lower Morozkina Balka Formation). Organic richness of this level, approximately 10 m (33 ft) thick, is controlled by low salinity and high bioproductivity. The Maikop Group could generate approximately 2.0 t HC/m2 surface area. A significant part (0.45 t/m2) comes from the lower Morozkina Balka Formation, which generates a high-wax paraffinic–naphthenic–aromatic mixed oil. The Pshekha, upper Morozkina Balka, and Batalpashinsk Formations would generate low-wax oil or condensate. The hydrocarbon generation potential of the overlying formations is minor. Overall, the generation potential of the Maikop Group is surprisingly low.

Past sedimentation rates and environments of the Mendeleev Rise inferred from Sr isotope and δ18O chemostratigraphy of its Late Cenozoic sediments

Multiproxy investigation of sediment core AF-0731 from the Mendeleev Rise revealed several epochs of high bioproductivity corresponding to climate amelioration and surface water mass warming in the Arctic. During these periods, sediments became enriched in carbonate microfossils as well as in coarsegrained ice- and iceberg-rafted debris (IRD) that precipitated from melting sea ice and icebergs. Variability in the δ18О composition of planktic foraminifers also reflects glacial-interglacial periodicity. Low δ18О values correspond to glacial epochs and, especially, glacial terminations with strong meltwater inputs. Increased δ18О values characterize interglacial epochs of sea-level rise and growing salinity due to enhanced water exchange with neighboring oceans. The 87Sr/86Sr ratio was measured in foraminifers from basal core layers, and their SIS-age was estimated at 670 + 50 ka. Sedimentation rates at AF-0731 core site on the Mendeleev Rise varied between 0.4 and 0.6 cm/kyr.