The non-marine strata of the Ypresian Naredi Formation have been deposited and intermittently pedogenized after the culmination of the Early Eocene Climatic Optimum(EECO).This continental interval comprises intercalat...The non-marine strata of the Ypresian Naredi Formation have been deposited and intermittently pedogenized after the culmination of the Early Eocene Climatic Optimum(EECO).This continental interval comprises intercalation of laterite and palaeosol horizons developed by cyclic episodes of erosion,subaerial exposure,and deposition.The palaeopedological analyses investigate the morphological and micromorphological features evidencing repeated subaerial exposure and consequently moderate to well-developed palaeosol horizons.The topmost laterite bed records an intensely bioturbated ichnofabric(consisting of the root traces and the composite ichnotaxa of lungfish aestivation burrows,Macanopsis(possible arachnid burrows),and Skolithos.The pedogenized shale horizons contain the paucispecific Camborygma-root trace ichnofabric with highly localized patchy preservation of Camborygma symplokonomos,Camborygma eumekenomos,and rhizoturbation.The ichnospecies variation of Camborygma along with the ichnofabric analyses led to the demarcation of stratigraphic horizons and evaluation of the palaeowater-table fluctuations vis-a-vis the low-order allocyclicity,the ethology of producers,and the depositional setting.The paucispecific suite of trace fossils refers to the Camborygma Ichnofacies,where the substrate is intermittently pedogenized and lateritized with upward increasing thickness of beds and intensity of pedogenesis,lateritization,ichnodiversity,and ichnoabundance.Hence,as an expression of high-frequency(interpreted as 5th-order)stratigraphic fluctuations within an early Falling Stage Systems Tract(FSST),a hot palaeoclimate with seasonality varying between humid inundated to dry desiccated conditions is interpreted with the palaeowater table being the base-level control.It culminates with the driest condition at the top with the thickest laterite development associated with the RAeMaS ichnofabric.With the onset of early transgression as documented in the overlying marine deposits of the Bartonian Harudi Formation,the top of the studied interval marks an induced subaerial unconformity.展开更多
Integrating the ichnologic,taphonomic,and sedimentologic data enhances the accuracy of palaeoenvironmental interpretations.The integrated analysis of the Chattian-age Coral Limestone Member within the Maniyara Fort Fo...Integrating the ichnologic,taphonomic,and sedimentologic data enhances the accuracy of palaeoenvironmental interpretations.The integrated analysis of the Chattian-age Coral Limestone Member within the Maniyara Fort Formation in Kutch Basin focuses on understanding the palaeogeographic architecture of microfacies association and the influencing factors determining the same on a typical Late Oligocene carbonate ramp.Through distinct petrographic examination,six distinct microfacies representing outer ramp(MF1 and MF2),middle ramp(MF3,MF4,and MF5),and inner ramp(MF6)depositional settings were identified.The Member,characterised primarily by multiple carbonate coquina intervals,was further classified based on taphonomical and ichnological characteristics.Four taphofacies(TF1,TF2,TF3,and TF4)and five ichnofabrics were identified.The outer ramp exhibits massive-appearing intensely to completely bioturbated(BI 5-6)marly mudstone-wackestone lithofacies with erosional contacts.The middle ramp displays oligotrophic conditions characterised by swaley cross-stratified bioclastic packstone-rudstone beds showing an upward intensifying moderate to intense bioturbation(BI 3-5).The storm-influenced inner ramp features the crudely swaley cross-stratified rudstone shell beds and patchy coral reefs with intense bioturbation(BI 5).Intermittent non-depositional and bioerosional short-duration episodes were observed at the top of skeletal concentrations.The integrated findings mentioned above exhibit coherence and offer valuable insights into the development of carbonate ramps.Our study offers insight into the aggrading and prograding shoal deposits within the carbonate ramp settings of a Chattian tropical sea.It highlights the complex interaction of environmental factors during this period within a high-resolution sequence-stratigraphic framework,extending up to the 5th-order,reported for the first time.This study deepens our comprehension of Oligocene carbonate buildups on a global scale—a research that has received lesser recognition compared to Eocene or Miocene carbonates.展开更多
Unconsolidated siliciclastic sediments can undergo post-burial deformation, which leads to the formation of distinctive sedimentary structures, known as soft-sediment deformation structures(SSDS). The presence of a se...Unconsolidated siliciclastic sediments can undergo post-burial deformation, which leads to the formation of distinctive sedimentary structures, known as soft-sediment deformation structures(SSDS). The presence of a series of sand volcanoes confined to a particular lithostratigraphic horizon can represent a paleoseismic activity and, thereby, exemplifies the concept of “seismite”. The Kutch Basin has been a tectonically active region since the initiation of eastern Gondwana rifting followed by a tectonic inversion during the Cenozoic due to the collision of the Indian and Eurasian plates. A stratum-bound series of sand volcanoes belonging to the Khari Nadi Formation(KNF) is exposed along the banks of Khari River. They separate the shallow marine deposits below and non-marine deposits above with their characteristic marine and paleosol trace fossil suites, respectively. Although a seismogenic origin has been much debated for the SSDS,the ichnofabric analysis of the sand-volcano-bearing stratum unequivocally points toward such an origin under a shallow seafloor condition. In addition to the sedimentary regime change from an open shallow-marine setting to a continental depositional environment concomitant with basinal uplift, the behavior of the burrowing crustaceans testifies to a syn-depositional development of a fault network associated with the fluidization, sand volcanism, and the resilience of the trace-producers in surviving those processes until the sedimentary regime change in the overlying strata. Although the ichno-sedimentological evidence apparently differs from the previous works that proposed a continuous base-level rise from the beginning of deposition of the Khari Nadi Formation up to the middle part of the overlying Chhasra Formation, the paleoseismic activity,its ichnologic signature, and the depositional regime change refer to a higher-resolution(i.e., lower-order)sequence-stratigraphic change causing a short-duration regression within a longer-duration cycle of base-level rise.展开更多
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:th...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.展开更多
The present work analyzes the monotypic Taenidium barretti ichnofabric developed in abandoned channels and floodplains to understand its paleoecological significance in highly seasonal fluvial systems.The data come fr...The present work analyzes the monotypic Taenidium barretti ichnofabric developed in abandoned channels and floodplains to understand its paleoecological significance in highly seasonal fluvial systems.The data come from the Cretaceous paleosols of the Marília Formation(Bauru Basin,SE Brazil),in which the T.barretti ichnofabric and rhizoliths represent the biotic record.Beetle larvae are considered to be the most likely T.barretti tracemakers in these paleosols.The intensity and recurrence of bioturbation suggest that the windows of opportunity for beetle population growth were very short and controlled by the progressive substrate desiccation after flood cessation.The characteristics of the trace fossil assemblage suggest soil colonization by r-strategic organisms triggered by flooding events that provided the resource inputs necessary for their living during rainy seasons.The results also show that in fluvial systems with high discharge variations,the boundaries between a“pre-desiccation suite”and a“desiccation suite”in the Scoyenia ichnofacies can be diffuse due to the short duration of colonization windows and progressive terrestrialization of floodplains and channels.Therefore,the frequency of flooding events,the lowered water table,and the rapidity of substrate desiccation constrained colonization by other burrowers and may be considered as firstorder factors controlling the generation of a monotypic T.barretti ichnofabric.Thus,the monotypic Taenidium ichnofabric in the Scoyenia ichnofacies context is an ichnomarker of brief windows for colonization in highly seasonal environments.展开更多
基金Science and Engineering Research Board(SERB),Government of India(grant#CRG/2018/000259 to SDG)Industrial Research and Consultancy Centre(IRCC),IIT Bombay(seed grant#RD/0517-IRCCSH0-035 to SDG and final-year scholarship to MD)+1 种基金IITB and Ministry of Education,Government of India(doctoral scholarship for MD)Council of Scientific&Industrial Research(CSIR)(doctoral scholarship for RD.
文摘The non-marine strata of the Ypresian Naredi Formation have been deposited and intermittently pedogenized after the culmination of the Early Eocene Climatic Optimum(EECO).This continental interval comprises intercalation of laterite and palaeosol horizons developed by cyclic episodes of erosion,subaerial exposure,and deposition.The palaeopedological analyses investigate the morphological and micromorphological features evidencing repeated subaerial exposure and consequently moderate to well-developed palaeosol horizons.The topmost laterite bed records an intensely bioturbated ichnofabric(consisting of the root traces and the composite ichnotaxa of lungfish aestivation burrows,Macanopsis(possible arachnid burrows),and Skolithos.The pedogenized shale horizons contain the paucispecific Camborygma-root trace ichnofabric with highly localized patchy preservation of Camborygma symplokonomos,Camborygma eumekenomos,and rhizoturbation.The ichnospecies variation of Camborygma along with the ichnofabric analyses led to the demarcation of stratigraphic horizons and evaluation of the palaeowater-table fluctuations vis-a-vis the low-order allocyclicity,the ethology of producers,and the depositional setting.The paucispecific suite of trace fossils refers to the Camborygma Ichnofacies,where the substrate is intermittently pedogenized and lateritized with upward increasing thickness of beds and intensity of pedogenesis,lateritization,ichnodiversity,and ichnoabundance.Hence,as an expression of high-frequency(interpreted as 5th-order)stratigraphic fluctuations within an early Falling Stage Systems Tract(FSST),a hot palaeoclimate with seasonality varying between humid inundated to dry desiccated conditions is interpreted with the palaeowater table being the base-level control.It culminates with the driest condition at the top with the thickest laterite development associated with the RAeMaS ichnofabric.With the onset of early transgression as documented in the overlying marine deposits of the Bartonian Harudi Formation,the top of the studied interval marks an induced subaerial unconformity.
基金supported by the Science and Engineering Research Board(SERB)Government of India(Grant No.CRG/2018/000259 to SDG)+3 种基金Industrial Research and Consultancy Centre(IRCC)IIT Bombay(Seed Grant No.RD/0517-IRCCSH0-035 to SDG)Council of Scientific and Industrial Research(CSIR)(Dr.SP Mukherjee Fellowship No.SPM09/0087(13946)/2022-EMR-I to KPDoctoral Fellowship No.09/0087(0993)/2019-EMR-I to RD)。
文摘Integrating the ichnologic,taphonomic,and sedimentologic data enhances the accuracy of palaeoenvironmental interpretations.The integrated analysis of the Chattian-age Coral Limestone Member within the Maniyara Fort Formation in Kutch Basin focuses on understanding the palaeogeographic architecture of microfacies association and the influencing factors determining the same on a typical Late Oligocene carbonate ramp.Through distinct petrographic examination,six distinct microfacies representing outer ramp(MF1 and MF2),middle ramp(MF3,MF4,and MF5),and inner ramp(MF6)depositional settings were identified.The Member,characterised primarily by multiple carbonate coquina intervals,was further classified based on taphonomical and ichnological characteristics.Four taphofacies(TF1,TF2,TF3,and TF4)and five ichnofabrics were identified.The outer ramp exhibits massive-appearing intensely to completely bioturbated(BI 5-6)marly mudstone-wackestone lithofacies with erosional contacts.The middle ramp displays oligotrophic conditions characterised by swaley cross-stratified bioclastic packstone-rudstone beds showing an upward intensifying moderate to intense bioturbation(BI 3-5).The storm-influenced inner ramp features the crudely swaley cross-stratified rudstone shell beds and patchy coral reefs with intense bioturbation(BI 5).Intermittent non-depositional and bioerosional short-duration episodes were observed at the top of skeletal concentrations.The integrated findings mentioned above exhibit coherence and offer valuable insights into the development of carbonate ramps.Our study offers insight into the aggrading and prograding shoal deposits within the carbonate ramp settings of a Chattian tropical sea.It highlights the complex interaction of environmental factors during this period within a high-resolution sequence-stratigraphic framework,extending up to the 5th-order,reported for the first time.This study deepens our comprehension of Oligocene carbonate buildups on a global scale—a research that has received lesser recognition compared to Eocene or Miocene carbonates.
基金Science and Engineering Research Board (SERB), Government of India (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 and Industrial Research (CSIR) (doctoral scholarship for AS),University Grants Commission (doctoral scholarship for KC),IIT Bombay and Ministry of Education of India (doctoral scholarship for MD)。
文摘Unconsolidated siliciclastic sediments can undergo post-burial deformation, which leads to the formation of distinctive sedimentary structures, known as soft-sediment deformation structures(SSDS). The presence of a series of sand volcanoes confined to a particular lithostratigraphic horizon can represent a paleoseismic activity and, thereby, exemplifies the concept of “seismite”. The Kutch Basin has been a tectonically active region since the initiation of eastern Gondwana rifting followed by a tectonic inversion during the Cenozoic due to the collision of the Indian and Eurasian plates. A stratum-bound series of sand volcanoes belonging to the Khari Nadi Formation(KNF) is exposed along the banks of Khari River. They separate the shallow marine deposits below and non-marine deposits above with their characteristic marine and paleosol trace fossil suites, respectively. Although a seismogenic origin has been much debated for the SSDS,the ichnofabric analysis of the sand-volcano-bearing stratum unequivocally points toward such an origin under a shallow seafloor condition. In addition to the sedimentary regime change from an open shallow-marine setting to a continental depositional environment concomitant with basinal uplift, the behavior of the burrowing crustaceans testifies to a syn-depositional development of a fault network associated with the fluidization, sand volcanism, and the resilience of the trace-producers in surviving those processes until the sedimentary regime change in the overlying strata. Although the ichno-sedimentological evidence apparently differs from the previous works that proposed a continuous base-level rise from the beginning of deposition of the Khari Nadi Formation up to the middle part of the overlying Chhasra Formation, the paleoseismic activity,its ichnologic signature, and the depositional regime change refer to a higher-resolution(i.e., lower-order)sequence-stratigraphic change causing a short-duration regression within a longer-duration cycle of base-level rise.
基金the following funding agencies for the research grants:Science and Engineering Research Board (SERB)Government ofIndia (grant#CRG/2018/000259 to SDG)+2 种基金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)。
文摘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.
基金the Sao Paulo Research Foundation(FAPESP)for supporting and funding this work(grant 2015/17632-5)The Brazilian National Council for Scientific and Technological Development(CNPq)is also thanked for the Ph.D.grant provided to DLN(140807/2017-9)+3 种基金the post-doctoral fellowship grant to DS(159548/2018-7)the research grants to AB(310734/2020-7)RGN(310377/2019-6)FSBL(307951/2018-9,303977/2021-3).
文摘The present work analyzes the monotypic Taenidium barretti ichnofabric developed in abandoned channels and floodplains to understand its paleoecological significance in highly seasonal fluvial systems.The data come from the Cretaceous paleosols of the Marília Formation(Bauru Basin,SE Brazil),in which the T.barretti ichnofabric and rhizoliths represent the biotic record.Beetle larvae are considered to be the most likely T.barretti tracemakers in these paleosols.The intensity and recurrence of bioturbation suggest that the windows of opportunity for beetle population growth were very short and controlled by the progressive substrate desiccation after flood cessation.The characteristics of the trace fossil assemblage suggest soil colonization by r-strategic organisms triggered by flooding events that provided the resource inputs necessary for their living during rainy seasons.The results also show that in fluvial systems with high discharge variations,the boundaries between a“pre-desiccation suite”and a“desiccation suite”in the Scoyenia ichnofacies can be diffuse due to the short duration of colonization windows and progressive terrestrialization of floodplains and channels.Therefore,the frequency of flooding events,the lowered water table,and the rapidity of substrate desiccation constrained colonization by other burrowers and may be considered as firstorder factors controlling the generation of a monotypic T.barretti ichnofabric.Thus,the monotypic Taenidium ichnofabric in the Scoyenia ichnofacies context is an ichnomarker of brief windows for colonization in highly seasonal environments.
