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28741. 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.

28742. 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.

28743. 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.

28744. 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.

28745. 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.

28746. 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.

28747. 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.

28748. 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.

28749. 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.

28750. 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.

28751. 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.

28752. 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.

28753. 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.

28754. 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.

28755. 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.

28756. 题目: Organic contamination as a driver of structural changes of hydroid's assemblages of the coral reefs near to Havana Harbour, Cuba
文章编号: N180625A4
期刊: Marine Pollution Bulletin
作者: Susel Castellanos-Iglesias, Ana Caroline Cabral, César C. Martins, Maikon Di Domenico, R.M. Rocha, Maria Angélica Haddad
更新时间: 2018-06-25
摘要: Hydroid assemblage's responses to organic contamination were evaluated using sedimentary sterols as explanatory variables. At seven coral reef sites in the Havana west coast, hydroids were collected along three 10 m × 1 m, 10 m deep transects. Five sterols were analysed, i.e., coprostanol, an indicator of faecal contamination, and cholestanol, cholesterol, stigmasterol and brassicasterol, indicators of biogenic organic matter inputs. The sampling sites were classified by level of contamination. A total of 65 species comprised the hydroid assemblages. Hydroids community abundance and richness decreased in the contaminated sites. Coprostanol had the highest relative importance for these variables and also for Plumularia floridana and Clytia gracilis abundances. Obelia dichotoma and Halecium bermudense were relatively abundant in the contaminated sites. The results indicate that faecal contamination negatively affected the hydroid assemblages, highlighting the importance of integrated biological and chemical indicators to evaluate the environmental conditions of the Havana coral reef.

28757. 题目: Ants alter molecular characteristics of soil organic carbon determined by pyrolysis-chromatography/mass spectrometry
文章编号: N180625A3
期刊: Applied Soil Ecology
作者: Zhongsheng Zhang, Zhuo Wei, Jim Jian Wang, Ran Xiao, Yili Meng, Haitao Wu, Xianguo Lyu
更新时间: 2018-06-25
摘要: Colonization by ecosystem engineers, such as ants, have important but occasionally unnoticed roles in regulating soil carbon cycles. However, little information is available pertaining to ant effects on changing molecular features of soil organic matter. In this study, we characterized total soil organic carbon (SOC), total nitrogen, water extractable organic carbon (WEOC) as well as molecular characteristics of humic acids (HAs) of ant mound soils (SoilAnt) and the surrounding soils (SoilCon) using pyrolysis-chromatography/mass (py-GC/MS). SOC, total nitrogen and WEOC contents of SoilAnt were significantly lower than those of SoilCon. SoilAnt samples had significant higher nitrogen containing compounds proportions in pyrolysis products of HAs as opposed to SoilCon samples. Another remarkablecharacteristic was that no polysaccharides, lignin, and phenols were identified in HAs of SoilAnt samples. It indicated that ant colonization significantly changed the molecular composition of soil organic matter.

28758. 题目: Comprehensive analysis of grazing intensity impacts soil organic carbon: A case study in typical steppe of Inner Mongolia, China
文章编号: N180625A2
期刊: Applied Soil Ecology
作者: Meng Zhang, Xiaobing Li, Hong Wang, Qi Huang
更新时间: 2018-06-25
摘要: Overgrazing is a primary cause of grassland degradation, including the loss of soil carbon, but comprehensive analysis of the mechanism by which grazing affects soil organic carbon (SOC) is limited. To investigate this mechanism, we measured the contents of total soil organic carbon (TSOC) and active SOC fractions in grazed and ungrazed soil, and we examined the influence of grazing on soil microenvironments, soil carbon input, transformation and utilization, and soil respiration. The experiment was conducted in typical steppe in Inner Mongolia, China, under light, moderate, and heavy grazing plus a no-grazing control. Grazing changed the contents and stocks of the TSOC and active SOC fractions as well as the composition of the SOC. After three years, light and moderate grazing increased TSOC content by 3.44% and 5.43%, respectively, while heavy grazing decreased it by 4.30%. The changes in active SOC fractions were not uniform under different grazing intensities. All grazing intensities increased the stocks of microbial biomass carbon (MBC) and dissolved organic carbon (DOC) compared with the control, but their magnitudes did not rise with increased grazing intensity. Moderate grazing increased the stocks of potentially mineralizable carbon (PMC) and particulate organic carbon (POC), whereas light and heavy grazing decreased them; this may indicate likely long-term changes in SOC following changes in grazing intensity. Light grazing resulted in a larger C input to soil and faster transformation, more emission, and less accumulation of SOC. Moderate grazing led to a smaller C input to soil, and its transformation, utilization and emission rates were between those associated with light grazing and heavy grazing, and there was more accumulation. Heavy grazing resulted in the smallest C input, faster transformation and utilization, less change in emission, and less accumulation. Based on these results, moderate grazing is likely the most practical grazing intensity for the sustainable utilization of this grassland ecosystem to feed livestock. However, because this was a short-term study, the results did not reach significance, and long-term studies are needed.

28759. 题目: Distribution of prokaryotic communities throughout the Chernozem profiles under different land uses for over a century
文章编号: N180625A1
期刊: Applied Soil Ecology
作者: Mikhail V. Semenov, Timofey I. Chernov, Azida K. Tkhakakhova, Alena D. Zhelezova, Ekaterina A. Ivanova, Tatyana V. Kolganova, Olga V. Kutovaya
更新时间: 2018-06-25
摘要: Land use affects physical, chemical and biological properties and processes in soil. Long-term field experiments were employed to reveal changes of soil characteristics induced by land use. Using high-throughput 16S rRNA gene amplicon sequencing and quantitative PCR, comparative analyses were conducted on prokaryotic community structure in different soil diagnostic horizons of Chernozems under forest, fallow and arable land within a long-term field experiment established by V.V. Dokuchaev in 1892. Soil organic carbon (SOC) was a more sensitive and reliable indicator of changes than microbial diversity indexes. Verrucomicrobia changed most among different prokaryotic phyla. Long-term tillage did not result in detectable changes in α-diversity of Chernozem prokaryotic communities, except for that plow pan horizon that showed a pronounced decrease in microbial diversity. The differences in prokaryotic community structure between soil horizons were more contrasting than between land uses. Analysis of β-diversity indicated that soil microbial communities at different depths formed non-overlapping clusters of A and B horizons, while microbiomes of transitional AB horizons fall in between these two clusters. The sharp decline in α-diversity in the plow pan horizon, as well as significant differences between the communities of A and B horizons indicate that the soil microbiomes are horizon-specific.

28760. 题目: DNA occurrence in organic matter fractions isolated from amended, agricultural soils
文章编号: N180625A0
期刊: Applied Soil Ecology
作者: Claudio Zaccone, Luciano Beneduce, Concetta Lotti, Giulia Martino, César Plaza
更新时间: 2018-06-25
摘要: The persistence of soil organic matter (SOM) constituents as a function of their recalcitrance has been recently questioned, with several papers showing the influence of the combined action of physical protection and chemical stabilization mechanisms as the main factors affecting SOM mean residence time. Using a physical fractionation method, SOM located between aggregates (FR), occluded within macro- (MA) and micro-aggregates (MI), and associated with the mineral fractions (MIN) were isolated from an agricultural soil differently amended (using compost, sewage sludge and biochar), and the occurrence of (total, bacterial and plant) DNA in these SOM pools was investigated. Following physical fractionation, total DNA (tDNA) was recovered from all SOM pools and from all treatments. Independently from the amendment, most tDNA accumulates in the FR fraction (30–70%), followed by the MIN pool (25–55%). The positive correlation between tDNA contents and C/N ratios (both tending to decrease following the order FR, MA and MI) observed for the light SOM fractions, together with the opposite pattern characterizing the heavy, MIN fraction (characterized by relatively high tDNA contents and low C/N ratios), suggests a different origin of the latter SOM pool, i.e., new molecules resulting from microbial transformations rather than highly degraded litter inputs. Therefore, tDNA may represent a promising proxy of organic matter dynamics in mineral soils. Finally, the MI fraction shows the highest number of microbial taxa and diversity, and seems to constitute a separate microbial niche in which different bacterial communities carry out their activity.