查看更多>>摘要:Anomalously positive δ13C values in ancient dolomites are very rare.Dark gray argillaceous rocks of the lacustrine sediments of the Permian Lucaogou Formation are important source rocks in the Junggar Basin,and dolomites of varying thicknesses from 10 cm to 150 cm are often interspersed in argillaceous rocks.Based on the study of petrographic sections,this paper systematically analyzes the carbon and oxygen isotopes of dolomite and discusses the causes of abnormally high carbon isotope values and their significance in reconstructing paleoenvironment and paleoclimate.The results show that carbon isotope values are abnor-mally high in the dolomite of Lucaogou Formation,and the δ13C value is between+3.2 ‰ PDB and+19.6‰ PDB,with an average of+9.7‰ PDB.The δ18O values range from-17.4‰ PDB to-1.7‰ PDB,with an average of-8.1‰PDB.From the lower part to the upper part of the Lucaogou Formation,the carbon isotope value gradually increases and becomes increasingly positive,and the carbon isotope of the dolomite deposited near the shore is more positive than that of the dolomite deposited far from the shore.The anomalously positive δ13C of the dolomite is mainly caused by microbial methanogenesis,with some contribution from evaporation.Microor-ganisms are mainly distributed at the redox interface.Evaporation controls the salinity and fluctuation of the redox interface in sedimentary water.The positive deviation difference in carbon isotopes between nearshore and offshore sedimentary dolomites may be related to the location of the redox interface during deposition.Together,the petrographic features and carbon and oxygen isotope signatures of the sections reflect the gradual evolution of the paleolake from a hydrologically open environment to a hydrologically closed one and the possible transition of the paleoclimate from a relatively warm to an arid condition,which is possibly a geochemical response to global climate change in the Permian period.
查看更多>>摘要:One of the largest Ordovician sea-level rises is the Evae transgression,which occurs in the lower part of the Oepikodus evae Biozone,indicative of a late Floian age.Specifically,the characteristics associated with the highstand of this event included:a higher proportion of specimens of the index species O.evae than other species,a diversity acme in the evae Biozone,and a reduction of biogeographic barriers that resulted in a high proportion of species with cosmopolitan distribution.In the present contribution,the pattern of species similarity among Laurentia,Argentine Precordillera,Baltica,Kazakhstania,South China,and Australia is evaluated with a multiple coefficient analysis including only the sections that recorded the highstand of the Evae transgression.Moreover,the effect of possible terrestrial,latitudinal,physicochemical barriers and palaeogeographic distance on the species distribution is statistically analysed.Our results show a global pattern of conodont species distribution that is highly constrained by the tested palaeoenvironmental factors.This suggests that contrary to what was expected for a prominent transgression,faunal barriers did not decrease significantly during the Evae drowning peak.
查看更多>>摘要:The Chhasra Formation(CF)of Kutch Basin exemplifies a typical mixed siliciclastic-carbonate system with alternations of biostromal carbonate and fine-grained siliciclastic beds.The CF is subdivided into two members:the lower Claystone(CM)and the upper Siltstone(SM)member.Three CM outcrops(P1-P3)comprising buried palaeosols that formed under a specific environmental set-up involving imperfectly to poorly drained conditions,are exposed along the Berwali River.The biostromal carbonate beds,alternating with the palaeosols,contain invertebrate bioclasts(bivalves,gastropods,echinoids,etc.)and are charac-terized by a paucispecific firmground Thalassinoides ichnofabric.At section P1,below the contact between the underlying palaeosol and overlying carbonate,Thalassinoides transforms into firmground Gyrolithes inside the palaeosol forming a compound ichnotaxon.The palaeosol intervals of sections P1 and P2 consist of a Vondrichnus-Termitichnus-root trace ichnofabric defining the Termitichnus ichnofacies.At section P3,lenses of fully bioturbated siltstones with a monospecific firmground Thalassinoides ichnofabric can be observed within an overall silty palaeosol horizon,thereby,locally cross-cutting the pedogenic features.The ichnofa-brics of section P3 indicate polyphase pedogenesis with three stages:(1)initial stage:pedogenesis in siltstone of undefined depositional affinity which was obscured by pedogenic processes,(2)transient stage:recurring marine incursions and colonization by crustaceans within the lens-shaped palaeotopographic depressions overprinting the palaeosol,and(3)final stage:subaerial exposure and another preserved phase of pedogen-esis.The CM shows an apparent low-order T-R(transgressive-regressive)cyclicity within a 3rd-order TST(transgressive systems tract)that is supported by pedogenic intensity,ichnofabrics,and reciprocal sedimen-tation near the Miocene basin margin,though the cyclicity can be the result of both autogenic and/or lower-order allogenic changes.
查看更多>>摘要:Girvanella is one of the common genera of cyanobacteria that plays a monumental role in the evolution of life on Earth and the formation of microbialites.Based on a detailed search in the literature of Girvanella fossils,we have compiled a global database of Girvanella fossils and revealed the evolution of Gir-vanella fossils throughout the Phanerozoic.Four species,Girvanella kasakiensis,Girvanella problematica,Girvanella wetheredii,and Girvanella staminea,are recognized and described.These data show that Girvanella fossils have well-defined temporal distribution during the Paleozoic Era,have a significant temporal gap in the Mesozoic Era,and have only been recorded sporadically in the Cenozoic Era.They were relatively abundant during the Cambrian Epoch 2-Early Ordovician,Late Ordovician,Late Devonian-Mississippian,and tended to lesser degrees during the Silurian-Early Devonian,Lopingian Epoch-Middle Jurassic,and Cretaceous-Present day.Furthermore,the evolution of the abundance and diversity of Girvanella fossils was fundamentally consistent and showed episodical declining during the Phanerozoic.To further explore these relationships,we thoroughly compared them with environmental factors such as seawater carbonate saturation state,Ca2+con-centration,pH values,and atmospheric partial pressure of carbon dioxide(pCO2).This study indicates that seawater carbonate saturation state and Ca2+concentration are major controls on secular patterns of the abundance and diversity of Girvanella fossils,together with the secondary factors of pH values and pCO2.Considering the long history of Girvanella fossils,their abundance and diversity offer the potential to assist the interpretation of the long-term evolution of marine and atmosphere components during the Phanerozoic.
Olev VinnJorge ColmenarSamuel ZamoraSofia Pereira...
939-953页
查看更多>>摘要:Seven Cornulites species,including a new one-Cornulites leonei n.sp.,are described from the Upper Ordovician Portixeddu Formation(Katian,stage slices Ka2-3)of Sardinia and the Cavá(lower Katian,stage slice Ka2)and Estana(upper Katian,stage slices Ka3-4)formations of the Pyrenees.The Sardinian and Pyrenean cornulitids represent an adaptation to live in environments with high sedimentation rates and limited hard substrates availability.Their prominent annuli could have had a stabilizing function in the soft sediment that helped cornulitids to keep a favourable position in the sediment to enable suspension feeding.The known Late Ordovician cornulitid diversity in different Gondwana areas is low,usually ranging from one to three taxa,being higher(seven)in Sardinia.Like other benthic groups during the Late Ordovician,the cornulitid tubeworm faunas within the high-latitude peri-Gondwana Province indicate a certain endemism and share morphological and ecological affinities,such as a small body size and tubes with a strikingly small apical angle.Although essentially endemic,some links with cornulitids from the Late Ordovician of Scotland are revealed.
查看更多>>摘要:Abundant plant fossils were found in the Upper Miocene Shengxian Formation,eastern Zhejiang Province,China,among which Trapa belongs to a dominant population.The fossil fruits of Trapa were well preserved with abundant details.However,due to compaction during fossilization,Trapa fruits were often flattened,leading to the loss of some characteristic features.Thereby,a bias in taxonomic and phylogenetic studies would occur when such studies were based on these fruit fossils.In this study,we present the first quantitative three-dimensional reconstruction of compressed Trapa fruit fossils to restore their original morphology prior to burial.This approach provides a novel perspective for the identification and classification of compressed fruit fossils.The three-dimensional reconstruction of Trapa fruit fossils enabled accurate comparisons with extant species.We subsequently identified it as a new species,named Trapa radiatiformis L.Xiao sp.nov.,revealing differences from previously known taxa of Trapa.Importantly,our comparison suggests that the long lower horns and residual stalk may represent inherent characteristics of early Trapa fruits.However,these traits gradually degenerated during fruit evolution,resulting in morphological simplification during geological time.T.radiatiformis with primitive features exhibits good resemblance to Trapa natans fruit characteristics,which means it may be an ancestor of T.natans.We summarize the palaeogeographic distribution of fossil Trapa using previously published literature and demonstrate that the genus was most prosperous in the Miocene and exhibited the same distribution as that at present.Additionally,through detailed morphological comparisons between Trapa and Hemitrapa fruits,along with phylogenetic analysis within the Primotrapa genus itself,we propose a homology between Trapa and Hemitrapa,suggesting that they could have a common ancestor.
查看更多>>摘要:The Taiyuan Basin is of importance for intraplate tectonic deformation in North China and con-tains Cenozoic strata with a maximum thickness of 3800 m.A-853.5-m-deep borehole(ZK01)with an overall core recovery rate of 85.09%was drilled at Yuci(37°35′37″N,112°39′47″E)in the central Taiyuan Basin,to obtain high-resolution records of paleomagnetism,paleoclimatic and paleoenvironmental conditions,and depositional environment of the sediments.The obtained magnetic polarity sequence consists of 13 normal and 12 reverse zones,which correspond to C1n-C4An.2n of the geomagnetic polarity time scale.Magneto-stratigraphic data show that the evolution of ZK01 core covers the interval from 8.1 Ma to the present,and the bottoms of Pliocene,Quaternary,and Middle Pleistocene were identified in Taiyuan Basin,with a sedimentary accumulation rate ranging from 62.5 m/Ma to 175.9 m/Ma.Geochemical data reveal that the source rocks in the study area underwent intense weathering and the sediments mainly formed in a semi-arid and oxygen-rich conditions.In addition,paleoclimatic changes occurred at~7 Ma,3.8 Ma,and 1.7 Ma,which can be closely related to the tectonic uplift of the Loess Plateau and Tibetan Plateau,as well as the variations in the Asian monsoon and associated regional and global climatic change.
查看更多>>摘要:Upwelling currents play a crucial role in the enrichment of organic matter,yet the mechanisms driving this process remain incompletely understood due to methodological and data resolution limitations.In this paper,we employ a combination of biostratigraphic classification,qualitative methods,and quantitative methods to systematically analyze the sedimentological and geochemical characteristics of the Lower Silurian Longmaxi Formation in the northern Chongqing-western Hubei area,southern China.The relationship be-tween the upwelling currents and organic matter enrichment in the shale of the Longmaxi Formation is investigated.Results indicate that the upwelling currents in the study area were primarily influenced by the foreland flexure process.From the Rhuddanian(flexure-sedimentation stage)to the Aeronian(flexure-mi-gration stage),the more intense tectonic activity led to gradual opening of the barrier between the South Qinling Ocean and the Yangtze Platform,resulting in an increase in the influx of the oceanic current.The upwelling currents significantly contributed to the organic matter production,albeit without substantially affecting the preservation conditions.Throughout the succession of the Longmaxi Formation,the organic matter content decreased gradually from the passive continental margin to the foreland flexural stagnant basin,which was mainly due to deterioration of the preservation conditions as a result of sea level fall and increased terrigenous input.Despite the increase in the upwelling currents,they did not decisively control the organic matter enrichment.Spatially,during the Rhuddanian to Aeronian period,the organic matter content decreased similarly from the passive continental margin to the foreland flexural stagnant basin,influenced by reduced organic matter production caused by weakening of the upwelling currents and the worsening pres-ervation conditions caused by sea-level fall.The terrigenous input had a relatively minor impact.The results of this study provide new insights into the role of upwelling currents in the organic matter enrichment within the Longmaxi Formation,overcoming previous methodological and resolution barriers.
查看更多>>摘要:Peatlands have obvious carbon storage capacity and are crucial in mitigating global climate change.As the end-product of peatlands,coals have preserved a large amount of palaeoenvironmental in-formation.The carbon accumulation rate and the net primary productivity(NPP)of coal-forming peatlands can be used as proxies for recovering palaeoenvironments.A super-thick coal seam(42°35′N,91°25′E)was developed in the Middle Jurassic Xishanyao Formation in the Shaerhu coalfield in the southern margin of the Tuha(Turpan-Hami)Basin,northwestern China.In this study,we use the time series analysis to identify the periods of Milankovitch orbital cycles in the Gamma-ray curve of this super-thick(124.85 m)coal and then use the obtained cycle periods of 405 ka,173 ka,44 ka,37.6 ka,22.5 ka to calculate the timeframe of the coal-forming peatlands which ranges from 2703.44 to 2975.11 ka.Considering that the carbon content of the coal seam is 78.32%and the carbon loss during the coalification is about 25.80%,the carbon accumulation rate of the targeted coal seam is estimated to be 58.47-64.34 g C/m2.a,and the NPP is estimated to be 252.28-277.63 g C/m2·a.The main palaeoenvironmental factors controlling the NPP of peatlands are CO2 content,palaeolatitude and palaeotemperature.The reduced NPP values of the palaeo-peatlands in the Shaerhu coalfield can be attributed to the mid-palaeolatitude and/or too low atmospheric CO2 contents.To a certain extent,the NPP of palaeo-peatlands reflects the changes in atmospheric CO2,which can further reveal the dynamic response of the global carbon cycle to climate change.Therefore,predicting the level of NPP in the Middle Jurassic and studying the final destination of carbon in the ecosystem are beneficial to under-standing the coal-forming process and palaeoenvironment.
查看更多>>摘要:In this editorial,an Associate Editor-in-Chief of the Journal of Palaeogeography(JoP)reminisces his publication experience in JoP during the period 2014-2024.1)During a period of nine years,he contributed eight review articles,three discussions,two replies,one book review,one glossary,and one tribute to the first Editor-in-Chief Prof.Zeng-Zhao Feng.His contributions totaled 534 printed pages.2)His contributions examined 19 different domains,such as landslides,submarine fans,seismites,SSDS,hyperpycnites,rivers,etc.3)His contributions coincided with the formative years of JoP.4)The impact of his articles is evident from the Stats published by ResearchGate.For example,his review article"The Landslide Problem"has reached 11,611 Reads and 186 Citations after nine years of publication in 2015.5)In 2023,the CNKI(China National Knowledge Infrastructure)recognized his article"Submarine fans:a critical retrospective(1950-2015)"as the Top-1%most-highly cited publications in the Journal of Palaeogeography published during a 10-year survey period:2012-2022.6)He was inducted as a Founding Member of the International Society of Palaeogeography(ISP)at Changping District of China University of Petroleum(Beijing),Beijing on July 16,2022.7)His JoP editorship during the past 10 years has been the most challenging,inspiring,and rewarding experience of his global scientific journey spanning over six decades(1962-2024).