Lower-order transgressive-regressive cycles within a higher-order transgression at the basin margin:an aberrant intercalation of palaeosol and biostromal ichnofabrics from the early Miocene Kutch Basin,India  

作　　者：Ayush Srivastava Sudipta Dasgupta Seema Singh 

机构地区：[1]Bombay Ichnos Research Group,Department of Earth Sciences,Indian Institute of Technology Bombay(IIT Bombay),Powai,Mumbai,Maharashtra 400076,India [2]Department of Geology,Panjab University,Chandigarh 160014,India

出　　处：《Journal of Palaeogeography》2024年第4期906-923,共18页古地理学报（英文版）

基　　金：the following funding agencies for the research grants:Science and Engineering Research Board (SERB);Government ofIndia (grant#CRG/2018/000259 to SDG);Industrial Research and Consultancy Centre (IRCC);IIT Bombay (seed grant#RD/0517-IRCCSH0-035 to SDG);Council of Scientific&Industrial Research (CSIR) (doctoral scholarship for AS)。

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 characterized 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 ichnofabrics 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 pedogenesis.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 sedimentation near the Miocene basin margin,though the cyclicity can be the result of both autogenic and/or lowerorder allogenic changes.

关 键 词：PALAEOSOL Biostrome Ichnofabrics Chhasra Formation Transgressive-regressive cycles TST Kutch(Kachchh)Basin 

分 类 号：P534.621[天文地球—古生物学与地层学] P512.2[天文地球—地质学] Q911[生物学—古生物学]