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古地理学报(英文版)
古地理学报(英文版)

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古地理学报(英文版)/Journal Journal of PalaeogeographyCSCDSCI
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    High-frequency lacustrine sequence stratigraphy of clastic lakes:lessons from ancient successions

    Carlos ZavalaHua-Qing LiuXiang-Bo LiValentin Trobbiani...
    621-645页
    查看更多>>摘要:Sequence stratigraphic concepts and methods provide novel tools for performing stratigraphic analysis,allowing us to improve our understanding of depositional models and basin evolution.Main controls and depositional elements(e.g.,surfaces,systems tracts,parasequences,etc.)recognized in conventional sequence stratigraphy are designed for marine-related systems.In contrast,the sequence stratigraphy of lacustrine successions is much more complex and poorly understood,because it is not driven by sea-level changes,but by a complex interaction between tectonics and high-frequency climatic cycles.The compre-hensive analysis of the water balance of lacustrine systems allows the recognition of three types of lake conditions:Underfilled,balanced-fill and overfilled lakes.Understanding the lake conditions in ancient suc-cessions is fundamental for unraveling lacustrine sequence stratigraphy,since these conditions effectively control water salinity,internal stacking pattern and the characteristics of systems tracts.Underfilled lakes are hydrologically closed lakes,and consequently,the lake-level can highly fluctuate,driven by high-frequency wet-dry climatic cycles.During wet periods,rivers supply water and sediments,resulting in fining-and thin-ning-upward elementary depositional sequences(EDS's)accumulated during the transgressive systems tract(TST).In contrast,dry periods are characterized by a relative lake-level fall with the subaerial exposure of lake margin areas during the regressive systems tract(RST).Lake water salinity can fluctuate from brackish to hypersaline.Balanced-fill lakes are partially closed lakes,and consequently,they have characteristics of both underfilled and overfilled lakes.During the TST,the lake is in underfilled condition,and consequently,the introduction of water and sediment will accumulate a fining-upward interval until reaching the spill point during the maximum flooding.The RST is accumulated under an overfilled lake condition,with coarsening-upward progradational littoral deltas and related subaqueous delta deposits.Lake water salinity fluctuates from brackish to freshwater.Overfilled lakes are hydrologically open lakes.Most deposits accumulate during the RST,forming coarsening-upward progradational littoral deposits,with associated subaqueous deltas.All overfilled lakes are freshwater lakes.Subsidence is crucial for allowing the long-term preservation of lacus-trine deposits.Lakes can temporarily store water and sediments in areas that lack subsidence,but these deposits will not be preserved in the stratigraphic record.Consequently,two types of lakes are recognized:1)subsiding lakes,which have permanent accommodation space and 2)hanging lakes,having temporary ac-commodation space.Although they cannot permanently store sediments,hanging lakes are fundamental for lacustrine sequence stratigraphy,since they can flood subsiding lakes with the near-instantaneous release of a substantial volume of water,creating favorable conditions for the accumulation of organic-rich shales.This rapid flooding from hanging lakes induced a forced transgression(FT),which is a large-scale rapid trans-gression(xenoconformity)not related to the normal sediment and water supply from local source areas.

    Spatio-temporal variability in microfossil and geochemical records of Cenomanian-Turonian oceanic anoxic event-2:a review

    C.P.SoorajShweta GuptaJahnavi Punekar
    646-674页
    查看更多>>摘要:The Cenomanian-Turonian boundary oceanic anoxic event(OAE-2;Bonarelli event;-94 Ma)is associated with a species turnover in the marine calcareous microfossil record,widespread marine anoxia,black shale deposition and positive δ13C excursions.This study reviews 141 CTBE sites globally,aiming to understand micropaleontological,geochemical,and sedimentological expressions of OAE-2.There is a clear palaeogeographic and palaeobathymetric heterogeneity in the development of OAE-2 marine anoxia.A ma-jority of the documented OAE-2 sites are from deep marine environments.The calcareous nannoplankton and benthic foraminifera record a diversity decline,while planktic foraminifera shows community level shifts and no major mass extinction.The variability of total organic carbon in OAE-2 sediments across sites(<1 to>10 wt.%)and the δ13C profiles(diachronous)have been attributed to different mechanisms of anoxia development.The increased primary"productivity model"gains support from productivity proxies(e.g.,Ba,P,Cu,Ni),redox-sensitive elements(e.g.,Mn,Mo,U,V,As),and eutrophic genera(e.g.,benthic foraminifera Gabonita spp.,calcareous nannofossils Biscutum spp.and Zeugrhabdotus erectus).The enhanced organic carbon"preservation model"in stratified(semi)restricted basins gains support from sites with lower enrichment of redox-sensitive elements and oligotrophic flora and fauna in the OAE-2 records.Geochronology of the Caribbean and the High Atlantic Large Igneous Province events(CLIP and HALIP)mark them as likely triggers of the OAE-2 related global perturbation of marine biogeochemistry.Volcanic triggers may have caused climate warming,altered hydrological cycles,enhanced continental weathering,shifts in ocean circulation,and nutrient flows.Addressing knowledge gaps,further research is urged,utilizing innovative proxies,and exploring underrepresented depositional systems to comprehensively understand OAE-2 onset and biotic crisis.

    The"underfilled trinity model"of foreland basins revisited:reality or myth?

    Xiu-Mian HuEduardo GarzantiJuan LiMarcelle BouDagher-Fadel...
    675-705页
    查看更多>>摘要:The"underfilled trinity"model of foreland-basin stratigraphy was proposed based on the observation that the initial sedimentary stages along the western and northern front of the western and central Alps were represented by shallow-water carbonates(Calcaires à Nummulites)overlain by hemipelagic marls(Marnes Bleues)and capped by siliciclastic turbidites(Grès d'Annot).Subsequently,this model has been widely accepted and applied in foreland basins worldwide.We here re-investigated the Eocene-Oligocene sedimentary succession of the Western Alps to check its validity.Major geological features of this region include:i)the existence of a Cretaceous-Eocene unconformity spanning more than 25 Myr in the studied sections;ii)a virtually synchronous age of the Calcaires à Nummulites,Marnes Bleues,and Grès d'Annot formations across the Western Alps;iii)a long-term deepening-upward trend,from inner to outer ramp,documented by the Calcaires à Nummulites,followed by the pelagic Marnes Bleues and by the Grès d'Annot turbidites;iv)the provenance of the Grès d'Annot Formation from the Maures-Estérel Massif and/or Corsica-Sardinia block in the south,rather than from the Alpine orogen in the east.By integrating field observations,sedimentological,biostratigraphic,and provenance analyses,we found the Eocene"underfilled foreland"model too simplistic and inadequate to explain the basin evolution in the western Alpine region.Based on the alternative scenario proposed herein,the Annot and Barrême basins formed in the late Eocene(40-35 Ma)in an extensional/transtensional setting during a period of major change in tectonic stress fields across western Europe on the upper plate of the Apennine subduction.

    Evolution of Neoproterozoic siliciclastic Kerur Formation in the light of sequence stratigraphic framework:Badami Basin,Karnataka,India

    Soumik MukhopadhyayNipun GhoshPradip SamantaArunava Sen...
    706-737页
    查看更多>>摘要:Field-based sedimentology,state of the art facies analysis and sequence stratigraphic framework analysis have revealed the controls of local and global tectonics,basin-marginal slope,climate and changes in relative sea level(RSL)over the sedimentation pattern and evolution of a Neoproterozoic Kerur Formation within the Badami Group of Kaladgi Supergroup in India.The entire succession shows three major cycles of deposition.Facies study and fluvial architectural elemental analysis suggest considerable variations in depositional environments as well as palaeogeography.A transition from basin-margin alluvial cone deposits to braided system,initially with fluctuating ephemeral flows then to a steadier semi-perennial nature,is discernible within the 1st cycle,in response to decreasing depositional slope with rising water table.The initial alluvial cone and braided ephemeral streams of high slope areas is designated as a product of low accommodation systems tract(LAST),while the semi-perennial system with steadier flows,representing the axial river of the initial rift valley,appears to be a product of high-accommodation systems tract(HAST).The 2nd cycle begins with a perennial and steady braided river system and grades upward to a shallow marine succession,comprising wave-dominated,well-sorted sandstone,with a granular transgressive lag at the base.Thus,the bottommost fluvial interval of the 2nd cycle constitutes the lowstand systems tract(LST).The marine succession represents deposits of outer shelf offshore to foreshore-beach settings and is composed of an initially deepening and fining upward transgressive systems tract(TST),followed by a coarsening and shal-lowing upward highstand systems tract(HST)with a maximum marine flooding surface(MFS)in between,demarcated by a shale-rich condensed zone.The 3rd cycle,with its prograding alluvial fan and aggrading braided fluvial deposits and restricted occurrence,represents only the low accommodation systems tract(LAST)with a subaerial unconformity at the base.The basin evidently initiated in the western sector,followed by its eastward expansion during the first major rejuvenation of the basin margin faults,after the deposition of the 1st cycle.After the basin-wide deposition of the 2nd cycle,restricted development of the 3rd cycle took place in the western sector only,following the second major rejuvenation of the fault system.The proposed sedimentological model,supported by established geochronological constraints,suggests that the sedimen-tation in the 1st cycle begins with scree cones,alluvial fans and braided ephemeral channel networks,orig-inated from faulted basin margins within a riftogenic setting possibly related to the global-scale extensional tectonics of Rodinia breakup.After the expansion of the basin,the marine inundation has been correlated to the transgression that possibly took place during the post-rift maturation stages.

    A combined tectono-climatic control on Holocene sedimentation in Ladakh Himalaya,India:Clues from Anisotropy of Magnetic Susceptibility(AMS)of lake sediments

    B.V.LakshmiK.DeenadayalanMujahed BabaSaumitra Misra...
    738-753页
    查看更多>>摘要:Anisotropy of Magnetic Susceptibility(AMS)data from a~27.8 m thick soft sedimentary mud sequence(~10.5-3.25 k yrs)from the Spituk Palaeolake Sequence(SPSS)of Holocene age,located in the northern bank of the Indus River in the Leh-Ladakh Himalaya,show effects of tectonic versus climate dynamics responsible for the Himalayan sedimentation.The sedimentary sequence,consisting of alternating of aeolian sand and glacio-fluvial mud flow deposits,has been subdivided into an older Last Glacier Phase I(LGP 1)and a younger Last Glacier Phase Ⅱ(LGP 2),where the termination of each phase is marked by the occurrence of gravel beds of thickness ≤1 m,which were deposited due to glacial melting.The present AMS data along with previously published information on sedimentology confirm that the mudflow deposits of the LGP 1 and LGP 2 phases were deposited in a lacustrine environment under glacio-fluvial conditions.However,a weak fluvial flow towards NW and NE could have existed for the LGP 1 and LGP 2,respectively.The glacial beds terminating LGP 1 and LGP 2 appear to have formed by climatic warming and tectonic activity,respectively.Hence,the Holocene Himalayan sedimentation was influenced by both climatic and tectonic activities.However,the thickness of the gravel bed(~0.8 m)terminating LGP 2 occupies only~2.8 vol%of the total studied thickness~28 m,of the SPSS in the present study,which indicated a lesser control of tectonism in the growth of the Himalaya in and around the study area.

    Evolution of a confined gravelly river to a braided-meandering river in the Late Cretaceous Khasi group,southern Shillong plateau,NE India

    Adrita ChoudhuriPrem Raj UddandamDebarati Nag
    754-774页
    查看更多>>摘要:This paper intends to unravel the depositional condition of the Basal Conglomerate/Jadukata Formation and the Lower Mahadek Formation in southern Shillong Plateau,NE India deposited during the Late Cretaceous period.The studied succession is entirely siliciclastics in composition and was built up on the Precambrian basement rocks.State-of-art facies analysis and palaeocurrent evidence helped us to reconstruct the palaeogeography and palaeoenvironment.The facies tracts reveal that frequent hyperconcentrated mass flow deposits dominated the proximal part of the river channels.Gradually,the river evolved to a sandy braided and finally mud-dominated,meandering system.The river channel changed its pattern through onlapping and progressive elimination of the accommodation space created by the tectonic subsidence/upliftment.Major shifts in palaeocurrent direction at different stages of the river evolution confirm the role of tectonics on the river channel evolution.QFL detrital modes of the sandstones reflecting lithic wacke composition and the recycled orogeny corroborate the interpretation.Rapid lateral and vertical facies transition suggests a pull-apart type basin due to ongoing rifting.Geochemical analyses also show signatures of the overlapping tectonic conditions supporting the pull-apart basin model.

    Sedimentary dynamics and depositional model for mud accumulation in deep lake basins:A case study in the Upper Triassic Chang-7 Member,Ordos Basin,northern China

    Wei YuFeng WangJing-Chun TianJiao Wang...
    775-792页
    查看更多>>摘要:Shales in deep lake basins have become the main focus of continental shale oil and gas explo-ration.In order to highlight the sedimentary dynamics of mud deposition in deep lake basins,a combination of core observation,thin section examination,X-ray diffraction,and QEMSCAN(quantitative evaluation of minerals by scanning electron microscopy)was used to analyze the depositional characteristics of mudrocks in the Chang-7 Member from the Yanchang Formation(Upper Triassic)in Ordos Basin,and to establish a depo-sitional model for mud accumulation in deep lake basins.This study recognizes four mudrock lithofacies in the Chang-7 Member:(1)the laminated silt-bearing mudstone,which generally develops a binary composition of"silt-clay"or a ternary composition of"silt-clay-organic matter";(2)the graded mudstone,mainly composed of dark gray and gray-black mudstone sandwiched by silt-bearing mudstone;(3)the massive mudstone,internally showing a uniform distribution of quartz,clay,and carbonate minerals,with also a small amount of organic detritus;and(4)the laminated shale,which is generally composed of clay laminae,and organic laminae of the former two.Sediment supply,topographic slope,and flood intensity combine to control the evolution of gravity flows and the transport and deposition of the mudrock in the Chang-7 Member.The influence of orogeny provides terrain gradient,water depth,abundant sediments at source areas,and trig-gering mechanism for the formation of gravity flows.Floods triggered by wetting events provide the impetus for sediment transport.Mud deposition in the Chang-7 Member was mainly related to the transport and sedimentation of mud by hyperpycnal flows and rapid sedimentation by buoyant plume flocculation.A comprehensive evolutionary model for shale accumulation in the deep lake basin is established by integrating various triggering mechanisms and mud transport sedimentary processes.

    Sedimentary environment shift and organic matter enrichment mechanism in response to volcanic ash influence:A case study of the Permian Lucaogou Formation,Santanghu Basin,NW China

    Miao YuGang GaoMiao LiuHui Liang...
    793-822页
    查看更多>>摘要:The second member of the Lucaogou Formation(P2l2)in the Tiaohu and Malang Sags of the Santanghu Basin(study area)underwent periodic volcanic activity and frequent lithological changes.This study comprehensively analyzed the organic geochemistry,mineral composition,organic matter(OM)types,volcanic cycle,and palaeoenvironment of shale in the study area.Techniques such as total organic carbon(TOC),rock pyrolysis(Rock-Eval),organic petrology,scanning electron microscopy(SEM)with energy-dispersive spectrum(EDS)analysis,X-ray diffraction(XRD),trace elements,and saturated hydrocarbon gas chromatography and mass spectrometry(GC-MS)were employed.The findings suggest that limited terrige-nous input during the sedimentary period of the P2l2 led to the deposition of a distinctive mixture of volcanic ash(felsic)and carbonate(dolomite and calcite),with a low average clay mineral content of 6%.The P2l2 shale emerged as a high-quality source rock,predominantly composed of type I and Ⅱ kerogens,with moderate OM maturity.The deposition environment was characterized by hot and arid conditions,high salinity,and intensive reducibility,which was favorable for algae development and conducive to OM preservation.Notably,two lamalginite types,labeled as lamalginite"A"and lamalginite"B,"were identified.Lamalginite"B"-rich shales were deposited in a hotter and drier climate compared to lamalginite"A"-rich shales.Lamalginite"B"-rich shale inexhibited high levels of C28 regular sterane and β-carotenes,distinguishing it from lamalginite"A"-rich shale.A comprehensive analysis involving organic petrology,SEM,sedimentary environment,and biomarker characteristics suggests that lamalginite"B"may be a salt-tolerant green alga,while lamalginite"A"may be a cyanobacterium.Finally,an OM enrichment model for the P2l2 shale was established.

    Geochemistry of cherts from the northern Jiangxi region,South China:Implication for paleoenvironment

    Guo-Liang XieGao-Jie ZhouYu-Yong SunYan-Ran Hu...
    823-838页
    查看更多>>摘要:The extensive bedded cherts deposited during the Ediacaran-Cambrian(E-C)transition period play a crucial role in understanding the geological evolution of this period,yet the origin of these cherts remains disputed.Here,we present new geochemical data for cherts of the Piyuancun(PYC)Formation deposited during the Late Ediacaran and the Hetang(HT)Formation deposited during the Early Cambrian in northern Jiangxi region,Lower Yangtze region,South China.The PYC cherts contain a small amount of monaxons sponge spicules and radiolarian fragments,while the HT cherts lack siliceous organism evidence.Major and trace element analysis,coupled with discriminant diagrams,indicate a possible shift in redox conditions of seawater during the E-C transition in the northern Jiangxi region.The shift suggests a change from weakly-moderately restricted euxinic conditions to strongly restricted euxinic conditions.Furthermore,the location of both cherts are distant from the source area of siliceous organisms.Fossil evidence,as well as the values of Fe/Ti and Fe/(Mn+Ti),Eu anomalies,Post-Archean Australian Shale(PAAS)normalized REE+Y patterns,and various discriminant diagrams,support the conclusion that the PYC and HT cherts originated primarily from direct seawater precipitation,with the PYC cherts exhibiting weak hydrothermal evidence.Upwelling contributes to the formation of HT cherts and organic matter(OM)accumulation.Ocean acidification,triggered by OM degradation and biodegradation pro-cesses during the E-C transition period,leads to the extensive silica precipitation and preservation.These re-sults enhance our understanding of the geological processes during the E-C transition.

    Provenance and tectonic setting of sandstones of the Lomas Coloradas Formation,Cabullona Group,Sonora,México:Constraints on petrography and geochemistry

    J.MadhavarajuD.G.Noriega-MontoyaE.Ramirez-MontoyaC.M.González-León...
    839-861页
    查看更多>>摘要:The sedimentary rocks of the Cabullona Group are well exposed in the Cabullona Basin of northeastern Sonora,México,which represent syntectonic sedimentation associated with Laramide-style deformation during the Campanian-early Maastrichtian.The sandstones of the Lomas Coloradas Formation deposited at the upper part of the Cabullona Group.Petrography and geochemical(major,trace,and rare earth elements)studies were carried out on the sandstones to interpret the palaeoweathering,provenance,and tectonic setting of the Lomas Coloradas Formation sandstones.Most of the sandstone modal analysis data plotted in the QFL and QmFLt ternary diagrams fall into the fields of dissected arcs and recycled orogens,respectively.Geochemically the sandstones are classified as litharenites while few samples plot into the arkosic field.The chondrite-normalized REE diagrams for sandstones have LREE-enriched,relatively flat HREE patterns with negative Eu anomalies.CIA values and the A-CN-K diagram indicate a low intensity of chemical weathering in the source area.The tectonic setting diagram suggests both arc and rift settings for the studied sandstones.The bivariate and ternary diagrams and elemental ratios suggest a felsic source for the Lomas Coloradas Formation.The average REE patterns of the studied sandstones are comparable with REE patterns of the granite from the Caborca block,the rhyolite and granite of the Tarahumara Formation,and the Mesozoic felsic volcanic rocks.The modeled mixture of 40%Proterozoic granite,30%Triassic arc,10%Jurassic arc,and 20%Laramide arc represents the probable source rocks for the Lomas Coloradas Formation.