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28781. 题目: On the petrographic distinction of bituminite from solid bitumen in immature to early mature source rocks
文章编号: N180625C4
期刊: International Journal of Coal Geology
作者: Paul C. Hackley, Brett J. Valentine, Javin J. Hatcherian
更新时间: 2018-06-25
摘要: The oil-prone maceral bituminite (and its equivalents: ‘amorphous organic matter’, ‘sapropelinite’, ‘amorphinite’, etc.) converts to petroleum during thermal maturation of source rocks, resulting in formation of a mobile saturate-rich hydrocarbon and a polar-rich residue of solid bitumen. Evidence of this transition is preserved in immature to early mature source rocks (e.g., Alum, Bakken, Kimmeridge, New Albany, Ohio shales, among many others), where organic petrography reveals a continuum of textures, reflectance, and fluorescence intensity occurring between bituminite and solid bitumen. Bituminite generally is characterized by high(er) intensity fluorescence, low contrast to the inorganic matrix, lower reflectance (compared to solid bitumen), and heterogeneous wispy or ‘schlieren’ textures. In comparison, solid bitumen generally shows lower intensity or no fluorescence compared to bituminite, a distinct contrast to the mineral matrix which usually includes a gray homogeneous surface of low to moderate reflectance, and may possess void-filling, embayment or groundmass textures suggesting evidence of migration or its in situ exsolution. However, these properties may manifest across a continuous spectrum in a sample or in a single microscope field, often making identification inconclusive. Unambiguous identification is further hampered by sample preparation, e.g., mechanical polish may improve homogeneity of larger accumulations, whereas smaller accumulations, or those sheltered by hard minerals, may appear more heterogeneous, leading to identification of the same organic matter as solid bitumen or bituminite, respectively. The disruptive innovation of ion milling in shale sample preparation leads to increased organic reflectance and surface homogeneity, causing bituminite and other oil-prone macerals, e.g., alginite, to develop a gray reflecting surface which is easy to confuse with solid bitumen, especially when obvious void-filling or embayment textures of the latter are absent. Herein we review distinction of solid bitumen from bituminite and alginite in immature to early mature source rocks, providing examples from nine samples illustrated by typical organic petrography images, including samples from hydrous pyrolysis experiments. Based on a review of the literature, we observe an arbitrary reflectance limit of 0.30% in mechanically polished samples seems to differentiate bituminite (<0.30%) from confident identifications of homogeneous solid bitumen (which otherwise lacks obvious void-filling or identifying embayment textures) as individual macerals on a continuous spectrum in immature and early mature source rocks. Future work conducted by governing bodies such as the International Committee for Coal and Organic Petrology (ICCP) should consider interlaboratory studies conducted on multiple immature source rock samples to develop consensus guidelines for bituminite and solid bitumen discrimination.

28782. 题目: Origin, properties, and implications of solid bitumen in source-rock reservoirs: A review
文章编号: N180625C3
期刊: International Journal of Coal Geology
作者: Maria Mastalerz, Agnieszka Drobniak, Artur B. Stankiewicz
更新时间: 2018-06-25
摘要: This paper reviews the significance of solid bitumen with emphasis on source-rock reservoirs. We discuss difficulties and discrepancies with terminology, especially those terms related to the origin of solid bitumen and its physical and chemical properties. Various definitions of solid bitumen have their own justifications and can be used provided there is clarity about which defining criteria are being considered. Difficulties in conforming to chemical-, solubility-, or origin-related definitions lead us to suggest adapting the reflectance of solid hydrocarbon as a practical choice for placing the boundary between solid bitumen and pyrobitumen, and 1.50% is proposed as the boundary value. It has to be noted that this boundary may be shifted down to 1.3% for sulfur-rich kerogen. Recently, much progress has been made by combining imaging and physical adsorption techniques in porosity studies, and so the porosity of solid bitumen is given special emphasis. Comparing pore characteristics obtained from SEM versus those generated by gas adsorption, mercury intrusion, or neutron scattering techniques indicates that the SEM pore inventory fails to account for the smallest pores (<5 nm in size) present in organic matter. Therefore, low-pressure CO2 adsorption is still the most effective technique to assess microporosity (pores <2 nm in diameter) in shales. We conclude that combining observational in situ techniques with techniques based on physical principles is necessary to make progress toward a better understanding of porosity systems in organic matter, including solid bitumen. We review the implications of the abundance of solid bitumen on reservoir quality, porosity, permeability, and producibility, based on examples of selected sequences. One of the difficulties in predicting the influence of solid-bitumen-bearing horizons on reservoir quality arises from the problems with detecting organic phases using various logging techniques. The use of specialized techniques such as NMR logging that allows two-dimensional T1 and T2 measurements should be expanded, and other potential techniques need to be further researched and tested. Certain aspects of the properties of solid bitumen that are not as well understood, such as its hydrocarbon generation potential or its role in hydrocarbon migration are also discussed with the aim of identifying further research that could lead to a better understanding of the role that solid bitumen plays in unconventional reservoirs.

28783. 题目: Paleoenvironmental reconstruction and hydrocarbon potentials of Upper Cretaceous sediments in the Anambra Basin, southeastern Nigeria
文章编号: N180625C2
期刊: International Journal of Coal Geology
作者: Olajide Femi Adebayo, Adebanji Kayode Adegoke, Khairul Azlan Mustapha, Mutiu Adesina Adeleye, Amos Okechukwu Agbaji, Nor Syazwani Zainal Abidin
更新时间: 2018-06-25
摘要: Palynological, organic petrographic, and organic geochemical analyses of the Campanian-Maastrichtian sediments in Akukwa-2 well were carried out to infer their paleoenvironments, origin of the organic matter, and hydrocarbon generation potentials. The TOC values of the analysed sediments range from 0.27–3.02 wt%, while the S2 pyrolysis yield range from 0.55 to 3.35 mg HC/g rock. This indicates that the Nkporo and Mamu sediments possess fair source generative potential. The samples contain Type III-II and Type III kerogen as shown by the present-day HI values between 58 and 292 mg HC/g TOC and pyrolysis-GC data. The organic matter within the sediments is also likely to generate mainly gas. This is in agreement with the petrographic observations, which revealed that the analysed shale samples contain abundant vitrinite macerals, apart from bituminite, alginite, cutinite, and resinite. Also, the sediments are immature to early mature in terms of hydrocarbon generation as indicated by vitrinite reflectance, biomarker maturity, and pyrolysis Tmax data. Biomarker distribution ratios, palynomorphs assemblage, and organic petrographic observations further point out that the organic materials within the sediments were of mixed aquatic and terrigenous origin and were deposited under suboxic paleodepositional conditions. Based on sedimentological, palynological, and biomarker characteristics, the environment of deposition of the analysed sediments was inferred to be a relatively quiet, shallow marine with fluvial incursion, most especially at the upper part of the intervals studied and consequently, it is a delta associated depositional environment with a fluviatile influence. The sediments are therefore suggested to be deposited in a paleogeographic setting close to vegetation source.

28784. 题目: Permeability anisotropy and gas slippage of shales from the Sichuan Basin in South China
文章编号: N180625C1
期刊: International Journal of Coal Geology
作者: Wen Zhang, Qin Wang
更新时间: 2018-06-25
摘要: Permeability anisotropy (A p ) and gas slippage of shales are critical for shale gas exploration, but laboratory measurements are still limited. We investigated composition, pore structure, permeability anisotropy and gas slippage of the Longmaxi and Wufeng shales from the Sichuan Basin in South China. The total organic carbon (TOC) content is positively related with the effective porosity and volume fraction of micropores, suggesting enhanced pore connectivity by organic matter. Dependence of permeability on the effective pressure (i.e., the confining pressure minus the pore pressure of N2) follows an exponential equation for five shale samples. At effective pressure of 6.9 MPa, our samples show very large A p variation from 1.2 to 1864.4. Compared with pore structure, clay content and the TOC content, microfractures significantly increase both permeability and A p of shales and play a predominant role in shale gas production. For shales with A p > 4, A p generally decreases with the increasing effective pressure due to the closure of oriented microcracks and slit-shaped macropores. At effective pressure of 6.9 MPa, the gas slippage is observed in four cores, with deviation from the Klinkenberg plot in three cores at high pore pressure. A new equation is proposed to describe the log trend of measured permeability with pore pressure. It allows us to quantify the deviation amount from the Klinkenberg plot and to constrain the pore pressure range where the effective stress law breaks down. In addition, the deviation from the Klinkenberg plot is more significant in shales with relatively high permeability and large pore width. The dominant transport regime in shales can change from the slip flow to the Darcy flow in fracture-bearing samples. The results indicate the important influence of permeability anisotropy and gas slippage of shales on final gas production and reservoir management.

28785. 题目: Petrographical and organic geochemical study of the lignite from the Smederevsko Pomoravlje field (Kostolac Basin, Serbia)
文章编号: N180625C0
期刊: International Journal of Coal Geology
作者: Nata?a ?okovi?, Danica Mitrovi?, Dragana ?ivoti?, Achim Bechtel, Reinhard F. Sachsenhofer, Vesna Mati?, Lidija Glamo?anin, Ksenija Stojanovi?
更新时间: 2018-06-25
摘要: Three Upper Miocene (Pontian) lignite seams are present in the Smederevsko Pomoravlje field (Kostolac Basin, Serbia). The origin of their organic matter (OM), the characteristics of the depositional environment and certain utilisation properties have been evaluated based on petrographic data, bulk organic geochemical parameters, biomarker patterns and their isotope signatures. Moreover, results of isotopic analysis were used for the investigation of the influence of diagenetic aromatisation on δ13C signatures of biomarkers. The studied lignites are typical humic coals. The OM of lignites is derived from woody vegetation and herbaceous peat-forming plants, with a strong prevalence of the former. The peat-forming vegetation is dominated by decay resistant conifers, including gymnosperm families Cupressaceae, Taxodiaceae, and Pinaceae. Angiosperms occurred in lower amounts. Minor contribution of ferns, fungi and emergent aquatic macrophyta to the biomass is also evident. Chemoautotrophic- and heterotrophic bacteria played an import role during diagenesis. Diagenetic alterations, associated with change in the number of carbon atoms, influence δ13C ratios. Diagenetic aromatisation of di- and non-hopanoid triterpenoids is accompanied with 13C depletion, whereas aromatisation of hopanoids displays the opposite trend. Peatification proceeded in a fresh water environment under variable, anoxic to slightly oxic redox conditions. The lowermost coal seam III accumulated in a topogenous fresh water peat mire with open water areas, which changed occasionally into a wet forest swamp. This resulted in the deposition of mineral-rich coal. The characteristics of lignite in coal seam II are similar to those of coal seam III. This is supported also by generally similar δ13C values of individual biomarkers. Coal seam I is dominated by xylite-rich coal, formed under mesotrophic to ombrotrophic conditions. Rapid flooding of the bogs stopped peat growth in all three coal seams. The ratios of ring-A-degraded and non-degraded aromatic diterpenoids and non-hopanoid triterpenoids, proposed in this study, as well as degree of aromatisation of these biomarkers, reflect changes in the water table. Calorific values of the samples indicate that they meet basic requirements for utilisation in the thermal power plants. None of the lignite samples is suitable for coal briquetting, whereas, based on petrographic data, lignite from coal seam I possesses certain potential for fluidized bed gasification.

28786. 题目: Revelation of organic matter sources and sedimentary environment characteristics for shale gas formation by petrographic analysis of middle Jurassic Dameigou formation, northern Qaidam Basin, China
文章编号: N180625B9
期刊: International Journal of Coal Geology
作者: Jing Qin, Shuangqing Wang, Hamed Sanei, Chunqing Jiang, Zhuoheng Chen, Shoumai Ren, Xuemin Xu, Jiajia Yang, Xiaotao Zhang
更新时间: 2018-06-25
摘要: The 7th member of Middle Jurassic Dameigou Formation (J2d7) in northern Qaidam Basin, China was proposed to have good hydrocarbon generating potential in previous studies. Here we apply an integrated petrographic and geochemical analysis to investigate the depositional environment, real thermal maturity and shale gas potential of organic-matter (OM)-rich assemblage. The relatively high content of C29 regular sterane (56.8%–62.8%) and vitrinite predominance in maceral composition suggesting plenty of higher-plant input, combined with the high pristane/phytane ratio (Pr/Ph)(2.8–8.2) and low gammacerane index (0.2–0.4) reveals oxic water column with in-situ depositional condition of carbonaceous-mudstone when the lower J2d7 was deposited. The maceral composition of oil shale at the upper part of J2d7 is mainly amorphous OM with small proportion of reworked vitrinite and inertinite, consistent with a mainly algea and small amount of exogenous OM input. When associated with low Pr/Ph (0.8) and high gammacerane index (4.3), the oil shale was deposited in an anoxic saline water column with mainly zooplankton OM source. The geochemical and petrographic result implies a transitional environment ranging from suboxic semi-saline to oxic fresh water environment with varying proportion of higher-plant and algae input by in-situ deposition and distant transportation for the mudstone at the middle part of J2d7. By use of random reflectance (Ro) distribution, two sedimentary environment microcycles which are confirmed by maceral composition, from the depth of 1983 m to 1962 m and 1954 m to 1931.9 m, are differentiated within the homogenous mudstone section. The variation of OM input condition and alternation of depositional environment led to accumulation and deposition of various kinds of abundant OM when J2d7 was deposited. Although the OM has actually low maturity at oil window with vitrinite reflectance around 0.6% according to the petrographic results, the liptinite inherited from higher-plants especially suberinite is the main maceral to generate gaseous hydrocarbons at the low maturity, which implies that the Dameigou formation (J2d7) of Qaidam Basin is of gas potential.

28787. 题目: Role of organo-clay composites in hydrocarbon generation of shale
文章编号: N180625B8
期刊: International Journal of Coal Geology
作者: Xiaojun Zhu, Jingong Cai, Guoli Wang, Mingshui Song
更新时间: 2018-06-25
摘要: Organic-mineral interactions are universal in natural environments. They cause the majority of the total organic carbon (TOC) in sediments and sedimentary rocks to combine with clay minerals to form organo-clay composites. However, the role of organo-clay composites in hydrocarbon generation is not clear. In this study, we select a suite of successively deposited shales to examine the association between organic matter (OM) and minerals, and to analyze the correlations of TOC with different mineral surface areas (MSAs) and the Rock-Eval pyrolysis in both bulk shales and their organo-clay composites. We find that OM in shale is dominantly incorporated with clay minerals by the main way of adsorbing on internal mineral surfaces rather than external mineral surfaces, which forms organo-clay composites. Further analyses on TOC-MSA correlations demonstrate the great heterogeneity of OM occurrence within shale. Also, the OM quality of organo-clay composites is poorer for hydrocarbon generation than that of bulk shales. We conclude that the variations in organic geochemistry between bulk shales and organo-clay composites are caused by hydrocarbon generation, which reduces the OM quality for further generation. Taken together, organo-clay composites dominate OM occurrence and have been generating hydrocarbons, which highlight the main control of organo-clay composites on hydrocarbon generation in natural samples. In comparison with the long-standing theory of hydrocarbon generated from kerogen, we propose the organo-clay composites to be the in situ and main source for hydrocarbon generation. This new hypothesis improves the existing knowledge of the organic origin of hydrocarbons in natural systems.

28788. 题目: The origin of pale and dark layers in Pliocene lignite deposits from Yunnan Province, Southwest China, based on coal petrological and organic geochemical analyses
文章编号: N180625B7
期刊: International Journal of Coal Geology
作者: Bangjun Liu, Cunliang Zhao, Jialiang Ma, Yuzhuang Sun, Wilhelm Püttmann
更新时间: 2018-06-25
摘要: A set of 39 pale lignite and dark lignite samples, obtained from a profile of the Pliocene Jinsuo lignite basin, Yunnan Province, China, were analyzed using coal petrology and biomarkers to determine whether changes in the depositional environment and/or vegetation caused the color changes ultimately observed in the lignites. A comprehensive analysis of all the data obtained revealed significant differences in the petrological and geochemical composition of the two lignite types. The pale lignites are characterized by a higher abundance of the liptinite group compared with the dark lignites. The composition of liptinites is dominated by bituminite (mineral-bituminous groundmass) and sporinite, along with a relatively low abundance of the huminite group. This indicates a higher degree of oxidation in the drier, more elevated peatland environments during deposition of the pale lignites. The low values of the tissue preservation index (TPI), vegetation index (VI), and gelification index (GI) in the pale lignites suggest a relatively high decomposition rate of plant materials under dry/aerobic conditions. In contrast, the dark lignites have a very high proportion of huminite dominated by ulminite, along with a low content of liptinite and inertinite macerals, which suggests the prevalence of wet/anaerobic conditions in the peat-forming mire. The high values of TPI, VI, and GI in the dark layers suggest better preservation of organic matter during deposition under anaerobic conditions, and more wet/humid climatic conditions, when compared with the pale lignites. With respect to the biomarker composition, the high concentrations of long-chain (C27-C31) n-alkanes in both pale and dark lignites are typical characteristics for the predominance of higher terrestrial plants. Significant concentrations of mid-chain n-alkanes (n-C21-C25) were detected preferentially in the dark lignites, suggesting that aquatic plants might also have contributed to the plant community during the formation of the dark layers. The content of diterpenoids, and the average ratio of diterpenoids to the sum of diterpenoids and triterpenoids (Di-/(Di- + Tri-terpenoids)) are higher in the pale lignites than in the dark lignites. This indicates that gymnosperms made a crucial contribution to the plant community during the formation of the pale lignites. In the dark lignites, triterpenoids are generally far more abundant than diterpenoids, which suggests that the dark layers were overwhelmingly formed by angiosperm plants. This is consistent with lower C/N ratios in the dark lignite layers (av. 40.8) compared with the pale lignite layers (av. 60.6). Higher microbial activities in the pale lignites than in the dark lignites are reflected by the higher concentration of hopanoids and 17α,21β-homohopane (22R) in the pale lignites.

28789. 题目: A 1500?year record of river discharge inferred from fluvial-marine sediments in the Australian subtropics
文章编号: N180625B6
期刊: Palaeogeography, Palaeoclimatology, Palaeoecology
作者: J. Coates-Marnane, J. Olley, J. Tibby, J. Burton, D. Haynes, J. Kemp
更新时间: 2018-06-25
摘要: In Australia, there is a scarcity of high resolution hyrdoclimate reconstructions for the last several millennia. Fluvial-marine sediments offer a potential avenue for examining trends in freshwater input to coastal settings and, by inference, past hydroclimates. Here, major elemental geochemistry, δ13C and C:N ratios of organic matter, grain size and diatom species abundance, measured in a 4.4 m long sediment core collected from Moreton Bay, in east coast Australia, are used to infer the relative freshwater discharge of the adjacent catchment over the last ~1500 years. Reduced freshwater discharge into the Bay occurred from 630 to 1200 CE, especially between 1100 and 1200 CE. A broad increase in discharge is indicated after 1300 CE, extending to the present. The initial shift to the prolonged wet period coincides with both a decrease in the frequency of ‘dry’ El Ni o events based on regional records from the austral Pacific, and a broad hemispheric-scale cooling trend. This record provides further insight into low amplitude climate variability in the Australian subtropics over the last 1000 years, supporting efforts in both forecasting current and future climates, and managing regional water resources. Importantly, instrumental records do not cover the full range of natural climate variability experienced in the region over the last 1000 years.

28790. 题目: Black carbon and charcoal records of fire and human land use over the past 1300?years at the Tongguan Kiln archaeological site, China
文章编号: N180625B5
期刊: Palaeogeography, Palaeoclimatology, Palaeoecology
作者: Zhihai Tan, Longjiang Mao, Yongming Han, Duowen Mo, Haibin Gu, Zhao Liu, Yanxia Long, Zhisheng An
更新时间: 2018-06-25
摘要: To examine fire patterns and landscape evolution in the Xiangjiang River Basin over the past 1300 years, high-resolution charcoal and black carbon (BC, char and soot) records from the Tongguan Kiln archaeological site of historical ceramic production have been analyzed in combination with robust Optically Stimulated Luminescence (OSL) and accelerator mass spectrometry radiocarbon (AMS14C) dating, archaeological documents, and paleo-environmental proxies (i.e., magnetic susceptibility, total organic carbon, XRF-derived elemental data, etc.). Throughout history, charcoal and BC have recorded changes in regional land use at the Tongguan Kiln site. Peaks in char and macro-charcoal contents indicate that local smoldering fire occurrences were typical with large amount of fuel used for kilns between 1300 and 1100 years B.P. under wet climate conditions. These peaks coincided with the size of the Tongguan Kiln archaeological site, which led to reduction of forest cover from nearby mountains and activated soil erosion. Subsequently, the frequency of fire activity declined to a very low level between 1100 and 600 years B.P., coupling with the decline of the Tongguan Kiln, and with a warm period in the study region. Over the past 600 years, with sharp growth in population, regional fires increased to an unprecedented scale for land reclamation for dry crop cultivation during a cold period, which in turn resulted in further environmental deterioration. In summary, shifts of fire patterns in the study site over the past 1300 years have been closely related to (1) climate variation; (2) the mode of human land use; and (3) vegetation type and fuel combustion efficiency. There was an interactive, complex relationship between these factors in the Xiangjiang River Basin, and these results suggest that the intensity and pattern of human land use could have further impacts on fire patterns and landscape evolution in response to climatic change of the East Asian Monsoon, in the past as well as in the future.

28791. 题目: Carbon isotopic composition of branched tetraether membrane lipids in a loess-paleosol sequence and its geochemical significance
文章编号: N180625B4
期刊: Palaeogeography, Palaeoclimatology, Palaeoecology
作者: Hongxuan Lu, Weiguo Liu, Weijuan Sheng
更新时间: 2018-06-25
摘要: Carbon isotopes of organic matter have been widely used in quantitative reconstruction of paleovegetation and paleoclimate since they are sensitive to vegetation and environmental changes. However, the effect of transformation of soil organic matter after burial remains unclear. The carbon isotopes of brGDGTs, which were likely produced by heterotrophic bacteria in soil or peat, provide an opportunity to fill this gap. In this study, we investigated the stable carbon isotopic composition of brGDGT-derived alkane spanning the last 60 kyr in the Lantian loess-paleosol sequence from the southern Chinese Loess Plateau, as well as its relationship with δ13C values of total organic carbon (TOC) and other established climatic proxies. The results show that the δ13C values of brGDGTs were slightly depleted (ca. 1–2‰) relative to TOC, and a good linear relationship between them was observed. These support a heterotrophic lifestyle of brGDGT-producing bacteria and suggest that δ13C values of brGDGTs may have potential use in paleovegetation reconstruction. The similar variations between δ13C values of brGDGTs and TOC in the soil core also suggest that the effect of soil organic matter transformation after burial may have limited impact on the environmental significance of δ13C values of TOC. In comparison with δ13C values of the TOC, the widely used proxy for past vegetation changes, the δ13C values of brGDGTs seem more specific and sensitive in the Lantian profile due to its specific origin and stable chemical structure.

28792. 题目: Climate and anthropogenic controls on the carbon cycle of Xingyun Lake, China
文章编号: N180625B3
期刊: Palaeogeography, Palaeoclimatology, Palaeoecology
作者: Aubrey L. Hillman, Mark B. Abbott, JunQing Yu
更新时间: 2018-06-25
摘要: The organic and inorganic carbon cycles in lakes are responsive to both natural climate variability and human-induced environmental changes. Here we present an 8600-year sediment record from Xingyun Lake in Yunnan, China that provides insight into carbon cycling and lake primary productivity using stable isotope measurements of organic carbon and nitrogen, carbon to nitrogen ratio, inorganic carbon isotopes, and mass accumulation rates of carbon, nitrogen, and calcite. The early to middle Holocene is characterized by relative stability in most proxies although some variation in organic carbon isotopes reflects fluctuating terrestrial organic matter inputs. The middle to late Holocene, from 5300 to 3300 years BP, is marked by amplified variability in nearly all proxies and suggests either increased C4 vegetation or increased primary productivity. These changes are coincident with declining lake levels and increased aridity throughout the Indian Summer Monsoon region. After 3300 years BP, the greatest variability is in nitrogen isotopes and coincides closely with human settlement in the region. These changes are accompanied by further indications of increased primary productivity, suggesting eutrophic lake conditions. While we cannot definitively link human activity to these changes, the balance of evidence suggests that other mechanisms are unlikely. This study supports previous work that anthropogenic activities began measurably impacting the landscape in southwestern China within the last few millennia.

28793. 题目: Direct and indirect effects of Holocene climate variations on catchment and lake processes of a treeline lake, SW China
文章编号: N180625B2
期刊: Palaeogeography, Palaeoclimatology, Palaeoecology
作者: Xu Chen, Suzanne McGowan, Xiayun Xiao, Mark A. Stevenson, Xiangdong Yang, Yanling Li, Enlou Zhang
更新时间: 2018-06-25
摘要: Sedimentary records of inorganic elements and pigments over the last 12,000 years are used to assess major changes in limnological conditions of Tiancai Lake (a small treeline lake, SW China), in response to Holocene climate variations. Algal communities shifted from the dominance of cyanobacteria and cryptophytes in the early Holocene, towards siliceous algae in the mid-Holocene and chlorophytes in the late Holocene. Algae responded to a combination of climate-mediated vegetation and soil development associated with allochthonous inputs of dissolved nutrients and organic matter, and sediment infilling. Decreases in Al, Pb, Cu and Zn from the early Holocene probably resulted from soil podsolization and the sequestration of these elements within soils. Changes in Mn and Fe were likely linked to redox condition in catchment soils and water column. Synchronous peaks in Ti, Ba, Ca, Sr, Na, K and Mg, median grain size and magnetic susceptibility coincided with the troughs in the chemical index of alteration, indicating that episodic cold events enhanced upland bedrock erosion and transported unleached and coarse detritus into the lake. These cold events broadly correlate with Holocene ice-rafting events in the North Atlantic. Although the cold events altered the influx of minerogenic elements by regulating upland bedrock erosion, climate-mediated vegetation and soil development led to a muted impact on primary producers. Holocene algal community shifts were subtle, reflecting the relative abundance of P (derived from weathering) and N (derived from soils) throughout the record, with the most pronounced effects on the lake biota being benthic expansion which occurred in response to sediment infilling.

28794. 题目: Distribution and constraining factors of planktonic and benthic foraminifers in bottom sediments of the southern South China Sea
文章编号: N180625B1
期刊: Palaeogeography, Palaeoclimatology, Palaeoecology
作者: Jian Yin, Chunlian Liu, Jinpeng Zhang, Xiaoqiang Yang, Jie Wu, Wolfgang Oschmann, Franz T. Fürsich, Benduo Zhu, Huodai Zhang
更新时间: 2018-06-25
摘要: A total of 93 surface sediment samples were collected to analyze the environmental factors constraining the foraminiferal distribution pattern in the southern South China Sea (SCS). Species distributions and stable isotopic compositions were combined to reveal the controlling factors, such as depth, salinity, substrate, runoff, currents, and cold seep activities. Water depth is the dominant factor controlling both assemblage composition and δ18O of benthic foraminiferal tests. The 1000 m isobath separates the sites into two clusters (Cluster A and B), which are dominated by deep-water species and shallow-water species, respectively. The sites in the deep-water zone (Cluster A) are characterized by lower absolute abundances, species richness and Shannon Index values (a measure of diversity), and higher proportions of planktonic foraminifers compared with the sites in the shallow-water zone (Cluster B). Increasing proportions of agglutinated tests with depth and rapidly decreasing proportions of planktonic foraminifera in the Nansha Trough Basin provide evidence of calcium dissolution occurring at a depth corresponding with previous reports. Oxygen stable isotopes (δ18OB) of benthic foraminifera become more positive with depth only up to 1000 m and remain constant beyond. Differences in the proportion of agglutinated and porcelaneous tests in the shallow-water zone suggest that terrestrial runoff from nearby river systems (Mekong River and northern Borneo rivers) and seasonal surface currents (SCS Southern Cyclonic Gyre and SCS Southern Anticyclonic Gyre) jointly influence the distribution patterns of foraminifera in the study area. Enrichment of planktonic δ18O is a response to cold waters brought by the SCS southern cyclonic gyre during winter. An upwelling current (Winter Natuna Off-Shelf Current) containing higher amounts of organic matter/nutrients contributes to the depleted δ13C of planktonic foraminifera and to the abnormal abundance of foraminifera at the sites within its area of influence. The dominance of the foraminifer Melonis barleeanus at sites belonging to Subcluster A1 and the stable isotope compositions of benthic foraminifera (δ18O > 0, δ13C < 0) across the sites suggest the influence of active cold seeps in the southern SCS. This research highlights the complexity of environmental variables that interact to influence the foraminiferal assemblages and geochemistry in the southern South China Sea, which could serve as a model for paleoenvironmental and palaeoceanographic reconstructions.

28795. 题目: Eocene (Bartonian) benthic foraminifera and paleoenvironmental changes in the Western Tethys
文章编号: N180625B0
期刊: Palaeogeography, Palaeoclimatology, Palaeoecology
作者: L. Rivero-Cuesta, E. Molina, L. Alegret
更新时间: 2018-06-25
摘要: The Eocene was a period of intense climate variability and the response of deep-sea biota is still poorly understood, especially across certain understudied intervals from the middle Eocene. We present new benthic foraminiferal data from a Bartonian marine sequence deposited in the western Tethys Ocean (Torre Cardela section, Spain), and determine the biotic and paleoenvironmental turnover. The assemblages indicate a middle to lower bathyal depth of deposition, and they contain allochthonous taxa (e.g. asterigerinids) that were transported from shallower settings. A Detrended Correspondence Analysis (DCA) performed on the total assemblage differentiates the autochthonous and allochthonous taxa, supporting the idea of different provenience. We suggest that the latter were likely transported downslope by currents. Quantitative analyses of the autochthonous assemblages show a strong dominance of calcareous infaunal taxa, mainly bolivinids, which point to a high flux of organic matter to the seafloor. Bolivinoides crenulata, the most common species, is associated with inputs of refractory organic matter and high-energy environments. Five intervals were differentiated based on changes in the relative abundance of taxa. Two intervals (B and D) show the highest percentages of allochthonous taxa and B. crenulata. We suggest that enhanced current activity not only transported allochthonous taxa, but also brought in refractory organic matter to the seafloor, which was consumed by opportunistic taxa during these two intervals. We conclude that benthic foraminiferal assemblages at Torre Cardela were strongly controlled by the amount and type of organic matter reaching the seafloor, which were in turn affected by sedimentary and, ultimately, by climatic factors.

28796. 题目: Nitrogen isotope and trace element composition characteristics of the Lower Cambrian Niutitang Formation shale in the upper -middle Yangtze region, South China
文章编号: N180625A9
期刊: Palaeogeography, Palaeoclimatology, Palaeoecology
作者: Min Li, Jianfa Chen, Tieguan Wang, Ningning Zhong, Shengbao Shi
更新时间: 2018-06-25
摘要: The Early Cambrian is a key interval in the global development of biological evolution, in which occurred many important environmental events and organic-rich sedimentary layers were deposited, which formed important hydrocarbon source rocks. The Lower Cambrian Niutitang Formation is one of the most important marine sedimentary layers in the Yangtze region, South China, and it records abundant important geological information that can be used for the reconstruction of the Lower Cambrian paleo-climates and paleo-environments. Nitrogen isotope compositions record and reflect variations in the original sedimentary environment and the redox conditions of marine ecosystems. Trace elements are also reliable indicators of sedimentary environments. In this study, we collected samples from the Lower Cambrian Niutitang Formation shale in the upper-middle Yangtze region of South China and measured the nitrogen isotope values of bulk sediments (δ15Nbulk), as well as their organic carbon isotope values (δ13Corg), total organic carbon (TOC) contents, total nitrogen (TN) contents and trace element concentrations. The δ15Nbulk values of the Niutitang shale range from 0.6‰ to 2.8‰, they show a certain positive excursion from bottom to top in the longitudinal direction, and they exhibit a significant correlation with the longitudinal variations in trace elements. These trace element characteristics suggest that the lower section of the Niutitang Formation existed in a strongly reduced sedimentary environment and was located in a hydrothermally active layer. During the deposition of the lower section of black shale, the nitrogen cycle was dominated by anaerobic nitrogen fixation; thus, its nitrogen isotope values are relatively lighter. In contrast, during the deposition of the upper section of the Niutitang Formation, the redox conditions of water column were unstable, the oxygen contents increased, and oxygenated reactions were intermittent or localized; thus producing relatively strong isotopic fractionation and causing the δ15Nbulk values in the upper section of black shale to exhibit a positive excursion. We conclude that the sedimentary environment is the key factor affecting nitrogen isotopes and that the redox conditions of the water column exhibit a significant correlation with the nitrogen isotope values.

28797. 题目: Oligo-Miocene lacustrine microbial and metazoan buildups from the Limagne Basin (French Massif Central)
文章编号: N180625A8
期刊: Palaeogeography, Palaeoclimatology, Palaeoecology
作者: Adeline Roche, Emmanuelle Vennin, Anthony Bouton, Nicolas Olivier, Aurélia Wattinne, Irina Bundeleva, Jean-Fran?ois Deconinck, Aurélien Virgone, Eric C. Gaucher, Pieter T. Visscher
更新时间: 2018-06-25
摘要: The Limagne Basin (French Massif Central) is an extensive continental lacustrine system accommodating microbial and metazoan buildups from Chattian to Aquitanian age. A description of these buildups and their associated biotic components in Grand Gandaillat and Crechy quarries provides insights into their spatio-temporal distribution patterns. Flats, cauliflowers, domes, cones and coalescent columnar morphologies have been identified with a main laminated mesofabric and laminated, columnar, filamentous and caddisfly-coated microfabrics. Two low-gradient margin models emerged based on the changes in the distribution, morphology and size of the microbial and metazoan-rich deposits through time: the first model applies to the Chattian deposits in the Grand Gandaillat quarry and the second to the Aquitanian deposits in the Crechy quarry. This study emphasizes the heterogeneity of marginal lacustrine carbonate-siliciclastic cycles. The lacustrine/palustrine cycles of the Limagne Basin record (i) lacustrine deposits composed of microbial and metazoan buildups and organic matter-rich marls indicating periods of high accommodation, and (ii) palustrine deposits composed of mudstone and clayey paleosoils, indicative of periods of low accommodation. The cycles differ with thin and symmetrical deposits that dominate the Chattian cycles whereas thicker and asymmetrical deposits mark the Aquitanian cycles. In addition, the Chattian buildups are exclusively microbial and only a few centimeters thick whereas the Aquitanian ones are multiple meters in height and are composed of both microbes and metazoans. Climatic, tectonism, volcanic and local parameters are involved in the deposition of buildups and their organization in each different cycle. Climate may control the long-term arid/humid sedimentary succession, tectonic may explain the difference in the deposit thickness between two cycles of different ages and localizations as well as the specific distribution of the buildups throughout the basin, volcanism may control the chemical lacustrine conditions and local physiography may impact the soil removal ability of the lake margin.

28798. 题目: Post-caldera evolution of Deception Island (Bransfield Strait, Antarctica) over Holocene timescales
文章编号: N180625A7
期刊: Palaeogeography, Palaeoclimatology, Palaeoecology
作者: M.C. Muniz, R.M. Anjos, R.P. Cardoso, L.H. Rosa, R. Vieira, H. Marotta, K. Macario, A. Ayres Neto, J.P. Felizardo, C.D.N. Barboza, L.F. Rodrigues, E.Q. Alves
更新时间: 2018-06-25
摘要: The study of palaeoclimatic changes in fast warming regions can contribute to the understanding of the forcing mechanisms responsible for the global changes that are presently happening. Deception is an active volcanic island in the Bransfield basin that has a complex history strongly influenced by both magmatic and tectonic processes. However, without accurate information on the distribution of melt, depth of sediments and Holocene timescales of its volcanic eruptions, the models for the post-caldera evolution of Deception Island are poorly constrained. Although this region has undergone severe environmental changes due to recent eruptions, hindering the location of potential study areas of paleo-volcanic eruptions, it is still possible to reconstruct post-caldera evolution at a local scale. Employing analyses such as radiocarbon dating, stable carbon and nitrogen isotopic compositions and particle-size distributions in subsoil horizons, we have studied the coastal areas of Whalers Bay and between Wensleydale Beacon and Cross Hill to identify the major periods of alluvial sedimentation on Deception Island. Whalers Bay was influenced by a large amount of moving water generated by ice melting. The coastal location of both sampling sites contributes to preserve the sedimentation history in their soil profiles, despite the severe environmental changes due to recent eruptions. Our findings indicate that from approximately 13 to 5 cal kyr BP, the accumulation of organic matter was stable and the landforms were not altered. After that time, post-caldera eruptions occurred, melting the glacier and, consequently, flooding surficial soil layers with mud. These changes are consistent with old 14C ages for subsoil organic matter and, therefore, with the occurrence of intense cryogenic disturbance processes.

28799. 题目: Refining the Jurassic-Cretaceous boundary: Re-Os geochronology and depositional environment of Upper Jurassic shales from the Norwegian Sea
文章编号: N180625A6
期刊: Palaeogeography, Palaeoclimatology, Palaeoecology
作者: Gyana Ranjan Tripathy, Judith L. Hannah, Holly J. Stein
更新时间: 2018-06-25
摘要: Limited chronological information for Upper Jurassic rocks hampers precise age assignment of the Jurassic-Cretaceous (J/K) boundary. This study presents Re-Os geochronology, Rock-Eval pyrolysis and geochemical data for Upper Jurassic rocks in the Nordland VII area, offshore northern Norway. Four intervals of organic-rich shale were investigated, two from the Krill and one from the Alge Member of the Hekkingen Formation and one from the underlying M snykan Formation (drilled cores 6814/04/U-01 and 6814/04/U-02). Rock-Eval pyrolysis data indicate immature organic matter with mixed (Type II/III) oil-gas potential in these units. Among the four intervals, Re-Os isochroneity prevails only for the Hekkingen Formation samples; data from the shale interval in the otherwise sand-rich M snykan Formation, deposited in a shoreface-to-foreshore marine environment, are not isochronous. Non-isochroneity of the samples from relatively proximal setting is attributable to non-conservative elemental (desorption of Os from sediments to dissolved phase) and isotopic exchange of Os at this depositional site. The Re-Os isochron age for the Alge Member (153.2 ± 7.3 Ma (Model 3); MSWD = 29; n = 9) is consistent with its biostratigraphic Kimmeridgian age (152.1–157.3 Ma). A Re-Os isochron for the lower part of the Krill Member yields an age of 144.5 ± 1.4 Ma (Model 3; MSWD = 3.7; n = 10) with an initial 187Os/188Os ratio of 0.552 ± 0.007. Given the interval's lower Tithonian biostratigraphic age, the Re-Os age suggests that the J/K boundary must be a few Myr younger than its currently assigned age of ~145.0 Ma (2017/02 time scale; www.stratigraphy.org). A Re-Os model age for shales from the upper part of the Krill Member places an upper age limit for the J/K boundary at 142 (±2) Ma. Hence, the J/K boundary is between 142 Ma and 144.5 Ma. Fe and S concentrations for the Hekkingen Formation show strong correlation and the S/Fe slope (~1.19) mimics the stoichiometric S/Fe ratio for pyrite (~1.15). A Fe-S-TOC ternary diagram for these samples points to an iron-limiting, sulphidic depositional environment. Anoxic to sulphidic depositional conditions for the Hekkingen shales are also evident from relatively higher authigenic enrichment of Mo compared to U. Unlike the Hekkingen Formation, shales from the more sandy M snykan Formation have lower S/Fe ratios and lower enrichment factors for redox-sensitive elements, indicating relatively oxygenated marine conditions during deposition.

28800. 题目: Stepwise oxygenation of early Cambrian ocean controls early metazoan diversification
文章编号: N180625A5
期刊: Palaeogeography, Palaeoclimatology, Palaeoecology
作者: Xiangkuan Zhao, Xinqiang Wang, Xiaoying Shi, Dongjie Tang, Qing Shi
更新时间: 2018-06-25
摘要: The Ediacaran–Cambrian transition is a critical period in Earth history, during which both marine environment and life experienced drastic changes. It was suggested that pervasive oxygenation and associated chemical changes in the ocean have potentially triggered the rapid diversification of early Cambrian metazoans. The timing and process of ocean oxygenation, however, have not been well constrained. In this paper, an integrated study was conducted on the lower Cambrian Niutitang (NTT) Formation in Siduping area, western Hunan, which was paleogeographically located at shelf margin–upper slope setting of the Yangtze Platform. Using ICP-MS, Element Analyzer, FESEM, EDS and XRD techniques, the abundance of RSEs (redox sensitive elements), patterns of RSEs distribution, pyrite morphology, TOC (total organic carbon), TS (total sulfur), SPY (pyrite sulfur) as well as N and P contents were investigated systematically. The results show that during the NTT deposition, bottom seawater in the study area experienced a complicated evolution, with a dynamic alternation of three ferruginous and three euxinic intervals, and suboxic–oxic conditions occurring only in the latest Cambrian Stage 3. Comparison with relevant sections reported previously from other facies belts within the Yangtze Platform shows that the seawater oxygenation was a progressive process expanding from shallow to deep-water areas in time. Shallow-water platform area became oxygenated in the late Cambrian Stage 2, shelf margin area in the late Cambrian Stage 3, and the deep-water basin remained ferruginous until the latest Cambrian Stage 3, when it became euxinic. Sediment Mo/TOC, U/TOC ratios increased from bottom to top in the section, coupled with elevated Mn, N and P secular trends, likely indicating an overall enhancement of seawater oxygenation. The spatial-temporal distribution and increased paleoecologic complexity of major fossil groups on the Yangtze Platform over time coincide with the seawater oxygenation process, likely implying that increased ocean oxygenation and declining euxinic seawaters have driven the rapid diversification of early Cambrian metazoans.