On the Island of Samos (East Aegean region, Greece), two sedimentary basins are filled by thick continental series dated to the Late Miocene to Early Pliocene. A multidisciplinary study has been performed including (1) the definition of 21 sedimentary facies, (2) a review of the biological components and (3) carbon, oxygen and strontium stable isotope analyses. The succession is characterised by various depositional settings and hydrochemical compositions. Five main stages of basin evolution have been identified: (1) The Late Serravallian is marked by the development of alluvial fans and fan delta; (2) during the Lower Tortonian, isolated shallow lakes with variable salinity, from fresh to brackish, developed under warm and relatively humid conditions; (3) the Middle to Upper Tortonian is marked by the development of a large and deep lake with saline and alkaline waters, under colder and drier conditions; (4) the Latest Tortonian to Messinian period is represented by an ephemeral alluvial system, developed under a dry climate; (5) during the Zanclean, a palustrine and paludal wetland system, dominated by tufa carbonates, developed under moderately humid conditions. This succession is of particular interest for the reconstruction of the palaeoenvironmental evolution of the transition zone between the Mediterranean domain, and the Paratethys and circum-Paratethys areas. The geochemical data and the presence of flora (diatoms) and fauna (gastropods) of marine affinity suggest transient ingressions of marine-related water or groundwater inflows as early as the Lower Tortonian. The Samos succession records the complex interaction between the regional geodynamics and climate. The extensional regime of the Eastern Aegean zone generates subsidence, interrupted in the mid-Tortonian (9 Ma) by a brief compressive event and a major exposure of the basins. Furthermore, the Late Miocene progressive aridification, followed by a change to a more humid climate (Pliocene) is also a major driver of the sedimentation.
{"title":"Reconstruction of the Late Miocene to Pliocene continental succession of Samos Island: Palaeoenvironmental implications for the Eastern Aegean domain","authors":"Youri Hamon, Rémy Deschamps, Christian Gorini, Dimitris Sakellariou, Cédric Bailly, Tarik Kernif, Alina Bérénice Christ, Mathilde Adelinet, Jérôme Fortin","doi":"10.1002/dep2.249","DOIUrl":"10.1002/dep2.249","url":null,"abstract":"<p>On the Island of Samos (East Aegean region, Greece), two sedimentary basins are filled by thick continental series dated to the Late Miocene to Early Pliocene. A multidisciplinary study has been performed including (1) the definition of 21 sedimentary facies, (2) a review of the biological components and (3) carbon, oxygen and strontium stable isotope analyses. The succession is characterised by various depositional settings and hydrochemical compositions. Five main stages of basin evolution have been identified: (1) The Late Serravallian is marked by the development of alluvial fans and fan delta; (2) during the Lower Tortonian, isolated shallow lakes with variable salinity, from fresh to brackish, developed under warm and relatively humid conditions; (3) the Middle to Upper Tortonian is marked by the development of a large and deep lake with saline and alkaline waters, under colder and drier conditions; (4) the Latest Tortonian to Messinian period is represented by an ephemeral alluvial system, developed under a dry climate; (5) during the Zanclean, a palustrine and paludal wetland system, dominated by tufa carbonates, developed under moderately humid conditions. This succession is of particular interest for the reconstruction of the palaeoenvironmental evolution of the transition zone between the Mediterranean domain, and the Paratethys and circum-Paratethys areas. The geochemical data and the presence of flora (diatoms) and fauna (gastropods) of marine affinity suggest transient ingressions of marine-related water or groundwater inflows as early as the Lower Tortonian. The Samos succession records the complex interaction between the regional geodynamics and climate. The extensional regime of the Eastern Aegean zone generates subsidence, interrupted in the mid-Tortonian (9 Ma) by a brief compressive event and a major exposure of the basins. Furthermore, the Late Miocene progressive aridification, followed by a change to a more humid climate (Pliocene) is also a major driver of the sedimentation.</p>","PeriodicalId":54144,"journal":{"name":"Depositional Record","volume":null,"pages":null},"PeriodicalIF":2.4,"publicationDate":"2023-08-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1002/dep2.249","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"43386389","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
James Bishop, Steve Bachtel, Jesse Thompson, Cody Miller, Brooks Ryan, Morgan Sullivan, Zane Jobe
Deep-water carbonate deposition is relatively poorly understood but an area of vigorous research in academia and industry, where these deposits are a significant component of many unconventional petroleum reservoirs. Recent studies of modern deep-water carbonates have highlighted the wide variety of depositional processes, sediment types and resultant geomorphology; however, well-documented outcrops of ancient systems, their rock types and architecture are relatively sparse. The Mississippian Lake Valley Formation provides world-class exposures of slope-basinal carbonate deposits. The Tierra Blanca and Doña Ana members comprise submarine fans that are >14 to 20 km in length, >5 km wide, and exposed in strike and dip view, affording a unique opportunity to constrain the architecture, rock types and sedimentary processes. Tierra Blanca and Doña Ana sedimentation was dominated by crinoids shed from an up-dip platform and supplemented by sediments sourced locally from Waulsortian mounds. Depositional processes include turbidity flows, debris flows and hybrid sediment-gravity flows. The Tierra Blanca submarine fan thins towards its lateral flanks and distal fringe, where deposits become more mud-dominated, gravelly grain-supported flows are less common, and fewer beds have scoured bases. In proximal settings, bed tracing complemented by measured sections allow mapping of stratal surfaces and identification of stories, elements and complexes. The Tierra Blanca evolved from more unconfined to confined deposition. Point-sourced deposition of the Tierra Blanca fan required a funnelling mechanism, probably due to bathymetry created by Waulsortian mounds or possibly a platform margin re-entrant. Outcrop exposures illustrate that younger Doña Ana submarine fan deposits onlap onto, and compensationally stack with, the thickest portions of the antecedent Tierra Blanca fan. These outcrops illustrate both similarities and differences between carbonate and siliciclastic gravity flow deposits. Similarities include comparable deposit types, depositional processes and architecture; differences relate to hydrodynamics of carbonate grains, funnelling mechanisms for point-sourced deposits and sequence stratigraphic forcing.
{"title":"Carbonate submarine fan deposits of the Mississippian Lake Valley Formation, Sacramento Mountains, New Mexico","authors":"James Bishop, Steve Bachtel, Jesse Thompson, Cody Miller, Brooks Ryan, Morgan Sullivan, Zane Jobe","doi":"10.1002/dep2.246","DOIUrl":"10.1002/dep2.246","url":null,"abstract":"<p>Deep-water carbonate deposition is relatively poorly understood but an area of vigorous research in academia and industry, where these deposits are a significant component of many unconventional petroleum reservoirs. Recent studies of modern deep-water carbonates have highlighted the wide variety of depositional processes, sediment types and resultant geomorphology; however, well-documented outcrops of ancient systems, their rock types and architecture are relatively sparse. The Mississippian Lake Valley Formation provides world-class exposures of slope-basinal carbonate deposits. The Tierra Blanca and Doña Ana members comprise submarine fans that are >14 to 20 km in length, >5 km wide, and exposed in strike and dip view, affording a unique opportunity to constrain the architecture, rock types and sedimentary processes. Tierra Blanca and Doña Ana sedimentation was dominated by crinoids shed from an up-dip platform and supplemented by sediments sourced locally from Waulsortian mounds. Depositional processes include turbidity flows, debris flows and hybrid sediment-gravity flows. The Tierra Blanca submarine fan thins towards its lateral flanks and distal fringe, where deposits become more mud-dominated, gravelly grain-supported flows are less common, and fewer beds have scoured bases. In proximal settings, bed tracing complemented by measured sections allow mapping of stratal surfaces and identification of stories, elements and complexes. The Tierra Blanca evolved from more unconfined to confined deposition. Point-sourced deposition of the Tierra Blanca fan required a funnelling mechanism, probably due to bathymetry created by Waulsortian mounds or possibly a platform margin re-entrant. Outcrop exposures illustrate that younger Doña Ana submarine fan deposits onlap onto, and compensationally stack with, the thickest portions of the antecedent Tierra Blanca fan. These outcrops illustrate both similarities and differences between carbonate and siliciclastic gravity flow deposits. Similarities include comparable deposit types, depositional processes and architecture; differences relate to hydrodynamics of carbonate grains, funnelling mechanisms for point-sourced deposits and sequence stratigraphic forcing.</p>","PeriodicalId":54144,"journal":{"name":"Depositional Record","volume":null,"pages":null},"PeriodicalIF":2.4,"publicationDate":"2023-08-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1002/dep2.246","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"48706200","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Marcello Gugliotta, Daniel S. Collins, James A. MacEachern, Narjess El Euch-El Koundi
Rocks of coastal to shallow-marine origin are challenging to interpret owing to the complex interplay of various depositional processes. This study reevaluates the relative roles of fluvial, tidal and wave processes in the Upper Cretaceous Sego Sandstone (and subordinately in the underlying Buck Tongue) of the Book Cliffs, USA, a well-studied ancient coastal to shallow-marine succession. Detailed sedimentological and ichnological analyses were used to interpret a previously underemphasised riverine signature, consisting of centimetre- to decimetre-thick alternations of sandstone and heterolithic beds inferred to represent flood–interflood periods of variable river discharge. Recognition of a widespread fluvial-dominated signature across the studied units better agrees with other sedimentological and regional observations in the study area, such as high sandstone–mudstone ratios, largely unidirectional and seaward-oriented palaeocurrents, and modelled weak tidal conditions in the basin. When considering all of the sedimentological, ichnological and stratigraphic observations together with its regional depositional context, the Sego Sandstone/Buck Tongue system is better explained using a mixed-energy but fluvial-dominated deltaic model. This highlights an historical over-interpretation of tidal processes and subordinate wave processes in the Sego Sandstone and likely in similar units. The widely used approach that emphasises only certain sedimentary features in discerning the process regime from analysis of rocks of inferred coastal to shallow-marine origin is unrefined and may therefore underrepresent the actual complexity of these systems.
{"title":"Reevaluating the process regime in the Sego Sandstone: Sedimentological and ichnological evidence for an underemphasised fluvial signature","authors":"Marcello Gugliotta, Daniel S. Collins, James A. MacEachern, Narjess El Euch-El Koundi","doi":"10.1002/dep2.245","DOIUrl":"10.1002/dep2.245","url":null,"abstract":"<p>Rocks of coastal to shallow-marine origin are challenging to interpret owing to the complex interplay of various depositional processes. This study reevaluates the relative roles of fluvial, tidal and wave processes in the Upper Cretaceous Sego Sandstone (and subordinately in the underlying Buck Tongue) of the Book Cliffs, USA, a well-studied ancient coastal to shallow-marine succession. Detailed sedimentological and ichnological analyses were used to interpret a previously underemphasised riverine signature, consisting of centimetre- to decimetre-thick alternations of sandstone and heterolithic beds inferred to represent flood–interflood periods of variable river discharge. Recognition of a widespread fluvial-dominated signature across the studied units better agrees with other sedimentological and regional observations in the study area, such as high sandstone–mudstone ratios, largely unidirectional and seaward-oriented palaeocurrents, and modelled weak tidal conditions in the basin. When considering all of the sedimentological, ichnological and stratigraphic observations together with its regional depositional context, the Sego Sandstone/Buck Tongue system is better explained using a mixed-energy but fluvial-dominated deltaic model. This highlights an historical over-interpretation of tidal processes and subordinate wave processes in the Sego Sandstone and likely in similar units. The widely used approach that emphasises only certain sedimentary features in discerning the process regime from analysis of rocks of inferred coastal to shallow-marine origin is unrefined and may therefore underrepresent the actual complexity of these systems.</p>","PeriodicalId":54144,"journal":{"name":"Depositional Record","volume":null,"pages":null},"PeriodicalIF":2.4,"publicationDate":"2023-08-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1002/dep2.245","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"46441742","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Brady Z. Foreman, Grace M. Sutherland, Delaney J. Todd, Kristopher D. Phillips, Anthony Semeraro
The size and geometry of river channels play a central role in sediment transport and the character of deposition within alluvial basins across spatiotemporal scales spanning the initiation of grain movement to the filling of accommodation generated by subsidence. This study compares several different approaches to estimating palaeoflow depths from fluvial deposits in the early Palaeogene Willwood Formation of north-west Wyoming, USA. Fluvial story heights (n = 60) and mud plug thicknesses (n = 13) are statistically indistinguishable from one another and yield palaeoflow depth estimates of 4 to 6 m. The vertical relief on bar clinoforms (n = 112) yields smaller flow depths, by a factor of ca 0.3, with the exception that the largest bar clinoforms match story heights and mud plug estimates. This observation is consistent with modern river data sets that indicate unit bar clinoforms do not capture the reach-mean bank-full flow depths except in rare circumstances. Future studies should use story heights (i.e. compound bar deposits) and mud plugs to estimate bank-full flow depths in alluvial strata. Additionally, the thickness of multi-storied fluvial sandbodies (n = 102) and overbank cycles composed of paired crevasse splay and palaeosol deposits (n = 45) were compared. The two depositional units display statistically indistinguishable mean and median values. Building upon previous depositional models, these observations suggest basin rivers aggraded approximately one flow depth prior to major avulsion. This avulsion process generated widespread crevasse splay deposition across the floodplain. Once the main river channel stem was reestablished, overbank flooding and palaeosol development dominated floodplain settings. The depositional model implies river aggradation autogenically generated topography in the basin that was effectively filled during the subsequent avulsion. This constitutes a meso-timescale (103–104 years) compensational pattern driven by morphodynamics that may account for the high completeness of fossil and palaeoclimate records recovered from the basin.
{"title":"Flow depth estimates and avulsion behaviour in alluvial stratigraphy (Willwood Formation, Bighorn Basin, Wyoming, USA)","authors":"Brady Z. Foreman, Grace M. Sutherland, Delaney J. Todd, Kristopher D. Phillips, Anthony Semeraro","doi":"10.1002/dep2.243","DOIUrl":"10.1002/dep2.243","url":null,"abstract":"<p>The size and geometry of river channels play a central role in sediment transport and the character of deposition within alluvial basins across spatiotemporal scales spanning the initiation of grain movement to the filling of accommodation generated by subsidence. This study compares several different approaches to estimating palaeoflow depths from fluvial deposits in the early Palaeogene Willwood Formation of north-west Wyoming, USA. Fluvial story heights (<i>n</i> = 60) and mud plug thicknesses (<i>n</i> = 13) are statistically indistinguishable from one another and yield palaeoflow depth estimates of 4 to 6 m. The vertical relief on bar clinoforms (<i>n</i> = 112) yields smaller flow depths, by a factor of <i>ca</i> 0.3, with the exception that the largest bar clinoforms match story heights and mud plug estimates. This observation is consistent with modern river data sets that indicate unit bar clinoforms do not capture the reach-mean bank-full flow depths except in rare circumstances. Future studies should use story heights (i.e. compound bar deposits) and mud plugs to estimate bank-full flow depths in alluvial strata. Additionally, the thickness of multi-storied fluvial sandbodies (<i>n</i> = 102) and overbank cycles composed of paired crevasse splay and palaeosol deposits (<i>n</i> = 45) were compared. The two depositional units display statistically indistinguishable mean and median values. Building upon previous depositional models, these observations suggest basin rivers aggraded approximately one flow depth prior to major avulsion. This avulsion process generated widespread crevasse splay deposition across the floodplain. Once the main river channel stem was reestablished, overbank flooding and palaeosol development dominated floodplain settings. The depositional model implies river aggradation autogenically generated topography in the basin that was effectively filled during the subsequent avulsion. This constitutes a meso-timescale (10<sup>3</sup>–10<sup>4</sup> years) compensational pattern driven by morphodynamics that may account for the high completeness of fossil and palaeoclimate records recovered from the basin.</p>","PeriodicalId":54144,"journal":{"name":"Depositional Record","volume":null,"pages":null},"PeriodicalIF":2.4,"publicationDate":"2023-07-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1002/dep2.243","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"41606405","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Brooke E. Vitek, Erica P. Suosaari, Amanda M. Oehlert, Christophe Dupraz, Clément G. L. Pollier, R. Pamela Reid
Hamelin Pool, Shark Bay, Western Australia hosts the world's largest and most extensive assemblages of living marine microbialites, comparable in size and shape to ancient structures found throughout the fossil record. Documented here are the internal fabrics of modern microbialites collected throughout Hamelin Pool. Mesoscale and microscale observations of microbialite polished slabs and thin section scans, optical microscopy and scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy formed the basis for a fabric classification system that combines accretionary mat type with microfabric. Accretionary mat types included pustular, smooth, colloform, as well as ‘transitional’ mats that are a cross between pustular and smooth mats. Mapping of fabrics in 45 microbialite heads indicated bidirectional evolution. An upward progression of fabrics corresponded to changes in mat type as the head grew upward into shallower water. A downward evolution of microfabrics occurred as surface mats transitioned into the subsurface of the microbialite structure. Downward microfabric evolution occurred as a result of early taphonomic processes, and involved a progression from the original depositional architecture to subsequent stages of “Micritic Thickening”, and finally, “Cement Infilling”. The observed bidirectional evolution of microbialite microfabrics within Hamelin Pool offers a conceptual framework for the study of modern microbialites, not simply as the sole product of accretionary mat types but rather as the combined result of the activity of surface mats and their taphonomic evolution. Early taphonomic processes induce further lithification of the microbialites which may enhance preservation potential in the geological record.
{"title":"Bidirectional fabric evolution in Hamelin Pool microbialites, Shark Bay, Western Australia","authors":"Brooke E. Vitek, Erica P. Suosaari, Amanda M. Oehlert, Christophe Dupraz, Clément G. L. Pollier, R. Pamela Reid","doi":"10.1002/dep2.244","DOIUrl":"10.1002/dep2.244","url":null,"abstract":"<p>Hamelin Pool, Shark Bay, Western Australia hosts the world's largest and most extensive assemblages of living marine microbialites, comparable in size and shape to ancient structures found throughout the fossil record. Documented here are the internal fabrics of modern microbialites collected throughout Hamelin Pool. Mesoscale and microscale observations of microbialite polished slabs and thin section scans, optical microscopy and scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy formed the basis for a fabric classification system that combines accretionary mat type with microfabric. Accretionary mat types included pustular, smooth, colloform, as well as ‘transitional’ mats that are a cross between pustular and smooth mats. Mapping of fabrics in 45 microbialite heads indicated bidirectional evolution. An upward progression of fabrics corresponded to changes in mat type as the head grew upward into shallower water. A downward evolution of microfabrics occurred as surface mats transitioned into the subsurface of the microbialite structure. Downward microfabric evolution occurred as a result of early taphonomic processes, and involved a progression from the original depositional architecture to subsequent stages of “Micritic Thickening”, and finally, “Cement Infilling”. The observed bidirectional evolution of microbialite microfabrics within Hamelin Pool offers a conceptual framework for the study of modern microbialites, not simply as the sole product of accretionary mat types but rather as the combined result of the activity of surface mats and their taphonomic evolution. Early taphonomic processes induce further lithification of the microbialites which may enhance preservation potential in the geological record.</p>","PeriodicalId":54144,"journal":{"name":"Depositional Record","volume":null,"pages":null},"PeriodicalIF":2.4,"publicationDate":"2023-07-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1002/dep2.244","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"43051252","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Abhishek Kumar, Deepak M. Maurya, Binita Phartiyal, Mohammad Arif, Niteshkumar Khonde, Ravi Bhushan, Partha Sarathi Jena, Ankur Dabhi, L. S. Chamyal
Holocene evolutionary history of the Banni Plain in the Great Rann of the Kachchh Basin is reconstructed from a subsurface sediment core of ca 50 m. Detailed data on textural and lithofacies variations, grain-size analysis, environmental magnetism and accelerator mass spectrometry 14C dates on seven samples were generated on the sediment core retrieved from the Banni Plain near Berada. A high-resolution record extending back to 10 ka has been reconstructed from the top ca 40 m of the core section comprising shallow marine sediments. The core is divisible into five depositional units. The basal part is a fluvial depositional unit followed upward by estuarine, sub-tidal, intertidal and supra-tidal environments. The sediment accumulation rate is highest in the sub-tidal to intertidal facies (1.9 cm year−1) and decreases towards the supra-tidal facies to 0.09 cm year−1. Environmental magnetic analysis, χlf coupled with the S-ratio, indicates high magnetic mineral concentrations during the Early Holocene, suggesting a wet period accompanied by high monsoon precipitation. This is followed by the onset of semi-arid conditions in the Great Rann of the Kachchh Basin as indicated by the low values of the χlf and S-ratios. A westward and northward shift in the shoreline towards the deeper part of the basin is suggested during the Late Holocene, which is coupled with aridity and reduced monsoonal conditions. The change in depositional pattern from the retrogradational deposit of fluvial (Unit 1) to estuarine sediment (Unit 2), progressing to sub-tidal (Unit 3), is attributed to sea-level transgression followed by regressive intertidal (Unit 4) to supra-tidal deposition (Unit 5), culminating in complete withdrawal of the sea, aided by tectonic uplift, during the Late Holocene. The results reveal that the sediment accumulation rates and depositional environments changed over time in response to changes in sea level from minima to maxima and then eventually to the present level.
利用约50 m的地下沉积物岩心重建了Kachchh盆地大兰恩地区班尼平原的全新世演化历史。在贝拉达附近班尼平原的沉积物岩心上获得了7个样品的结构和岩相变化、粒度分析、环境磁性和加速器质谱14C测年的详细数据。在由浅海沉积物组成的岩心剖面顶部约40 m处重建了一个可追溯到10 ka的高分辨率记录。岩心可划分为五个沉积单元。基底部为河流沉积单元,向上依次为河口、潮下、潮间带和潮上环境。沉积速率在潮下-潮间相最大(1.9 cm /年),向潮上相减小(0.09 cm /年)。环境磁学分析χ f与s比的耦合表明,全新世早期具有较高的磁性矿物浓度,表明该区处于季风降水较多的湿润期。其次是Kachchh盆地大兰区半干旱条件的开始,这可以从χ f和s比的低值中看出。在晚全新世期间,岸线向盆地较深的部分西向北移动,并伴有干旱和季风条件的减少。沉积模式从河流沉积(第1单元)退积到河口沉积(第2单元),再到潮下沉积(第3单元)的变化,归因于海平面海侵、潮间带沉积(第4单元)退积到潮上沉积(第5单元),最终在构造隆升的帮助下完全退缩。结果表明,沉积物堆积速率和沉积环境随海平面从最小到最大再到现在的变化而随时间变化。
{"title":"Holocene evolution of the Banni Plain at the north-east margin of the Arabian Sea: Constraints from a ca 50 m long sediment core","authors":"Abhishek Kumar, Deepak M. Maurya, Binita Phartiyal, Mohammad Arif, Niteshkumar Khonde, Ravi Bhushan, Partha Sarathi Jena, Ankur Dabhi, L. S. Chamyal","doi":"10.1002/dep2.241","DOIUrl":"10.1002/dep2.241","url":null,"abstract":"<p>Holocene evolutionary history of the Banni Plain in the Great Rann of the Kachchh Basin is reconstructed from a subsurface sediment core of <i>ca</i> 50 m. Detailed data on textural and lithofacies variations, grain-size analysis, environmental magnetism and accelerator mass spectrometry <sup>14</sup>C dates on seven samples were generated on the sediment core retrieved from the Banni Plain near Berada. A high-resolution record extending back to 10 ka has been reconstructed from the top <i>ca</i> 40 m of the core section comprising shallow marine sediments. The core is divisible into five depositional units. The basal part is a fluvial depositional unit followed upward by estuarine, sub-tidal, intertidal and supra-tidal environments. The sediment accumulation rate is highest in the sub-tidal to intertidal facies (1.9 cm year<sup>−1</sup>) and decreases towards the supra-tidal facies to 0.09 cm year<sup>−1</sup>. Environmental magnetic analysis, χlf coupled with the S-ratio, indicates high magnetic mineral concentrations during the Early Holocene, suggesting a wet period accompanied by high monsoon precipitation. This is followed by the onset of semi-arid conditions in the Great Rann of the Kachchh Basin as indicated by the low values of the χlf and S-ratios. A westward and northward shift in the shoreline towards the deeper part of the basin is suggested during the Late Holocene, which is coupled with aridity and reduced monsoonal conditions. The change in depositional pattern from the retrogradational deposit of fluvial (Unit 1) to estuarine sediment (Unit 2), progressing to sub-tidal (Unit 3), is attributed to sea-level transgression followed by regressive intertidal (Unit 4) to supra-tidal deposition (Unit 5), culminating in complete withdrawal of the sea, aided by tectonic uplift, during the Late Holocene. The results reveal that the sediment accumulation rates and depositional environments changed over time in response to changes in sea level from minima to maxima and then eventually to the present level.</p>","PeriodicalId":54144,"journal":{"name":"Depositional Record","volume":null,"pages":null},"PeriodicalIF":2.4,"publicationDate":"2023-06-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1002/dep2.241","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"45686960","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Joshua L. Bonesso, Michael V. W. Cuttler, Nicola K. Browne, Caroline C. Mather, Victorien Paumard, William T. Hiscock, John N. Callow, Michael O'Leary
Coral reef islands are vulnerable landforms to environmental change. Constructed of largely unconsolidated reef-derived sediments, they are highly sensitive to variations in metocean boundary conditions, raising global concern about their future resilience and stability in the face of increased natural hazards, sea-level rise and anthropogenic climate change. This study examines the evolution of an inshore turbid reef island from the southern Pilbara region of Western Australia (Indo-Pacific) using detailed analyses of island chronostratigraphy (composition, texture) and geochronology (21 in-situ radiometric dates) from Eva Island. Downcore, composition of island-grade (reef-derived) sediments were homogenous, dominated by molluscan (37%–42%) and coral (32%–37%) constituents. The 14C radiometric dating of island sediments, beachrock and coral microatolls identified five stages of island formation across changing sea-level regimes over the mid to late Holocene: (1) limestone platform accretion at ca 6,000 cal yr BP, coinciding with reef decline or ‘give-up’ on neighbouring Exmouth Gulf reefs; (2) sand cay (i.e. core) initiation and vertical aggregation at ca 5,000 cal yr BP during the point of sea-level regression to current levels; (3) major accretion and lateral progradation of the island between 3,500 cal yr BP and 2,500 cal yr BP including the modification of island shorelines through alongshore reworking of sediment; (4) lateral accretion and minor expansion to the north and formation of beachrock pavement between 2,500 and 650 cal yr BP; and (5) planform adjustment (erosion of the north-west island) and backstepping under stabilised sea levels over the past 650 years. While this model is comparative to studies on island formation following incremental sea-level fall following the mid-Holocene highstand, it demonstrates active landform readjustment under stabilised sea levels over the past 2,000 years, probably the influence of local-scale metocean boundary conditions within climate windows across the mid to late Holocene period (i.e. independent of sea-level fluctuations). Importantly, while sediment production rates are predicted to be lower in turbid-water reef systems than clear water, Eva Island shows no change in carbonate producers (i.e. proportion of mollusc and coral) over the course of island building, indicating the carbonate factory has not experienced significant adjustments in reef ecology, but has remained stable despite low water quality.
珊瑚礁岛是易受环境变化影响的地貌。它们主要由未固结的珊瑚礁沉积物构成,对海洋边界条件的变化高度敏感,这引起了全球对它们在面对日益增加的自然灾害、海平面上升和人为气候变化时的未来复原力和稳定性的关注。本研究通过对伊瓦岛岛屿年代地层(组成、质地)和地质年代学(21个原位放射性测年)的详细分析,考察了西澳大利亚(印度太平洋)皮尔巴拉地区南部一个近海混浊礁岛的演化。岛级(礁源)沉积物组成均匀,以软体动物(37% ~ 42%)和珊瑚(32% ~ 37%)为主。对岛屿沉积物、滩岩和珊瑚微环礁的14C辐射定年确定了全新世中晚期海平面变化过程中岛屿形成的五个阶段:(1)大约6,000 cal - yr BP的石灰岩台地增生,与邻近的埃克斯茅斯湾珊瑚礁的珊瑚礁衰退或“放弃”相吻合;(2)海平面回归到当前水平时,约5000 calyr BP的沙岩(即岩心)形成和垂直聚集;(3)在3,500 cal - 2,500 cal - yr BP之间,岛屿发生了主要的增生和侧向进积,包括通过沿岸沉积物的改造而改变了岛屿海岸线;(4) 2500 ~ 650 cal yr BP期间,向北有少量的侧向增生和扩张,形成了滩岩铺装层;(5)在过去650年的稳定海平面下,台地调整(西北岛的侵蚀)和后退。虽然该模式可与全新世中期高点后海平面逐渐下降后岛屿形成的研究相比较,但它表明,在过去2000年里,在稳定的海平面下,地貌发生了积极的再调整,这可能是全新世中期至晚期气候窗内局地尺度的海洋边界条件的影响(即与海平面波动无关)。重要的是,虽然预测浊水珊瑚礁系统的产沙率低于清水,但伊娃岛在造岛过程中碳酸盐生产者(即软体动物和珊瑚的比例)没有变化,这表明碳酸盐工厂在珊瑚礁生态中没有经历重大调整,但在低水质下仍保持稳定。
{"title":"Reef island evolution in a turbid-water coral reef province of the Indo-Pacific","authors":"Joshua L. Bonesso, Michael V. W. Cuttler, Nicola K. Browne, Caroline C. Mather, Victorien Paumard, William T. Hiscock, John N. Callow, Michael O'Leary","doi":"10.1002/dep2.242","DOIUrl":"10.1002/dep2.242","url":null,"abstract":"<p>Coral reef islands are vulnerable landforms to environmental change. Constructed of largely unconsolidated reef-derived sediments, they are highly sensitive to variations in metocean boundary conditions, raising global concern about their future resilience and stability in the face of increased natural hazards, sea-level rise and anthropogenic climate change. This study examines the evolution of an inshore turbid reef island from the southern Pilbara region of Western Australia (Indo-Pacific) using detailed analyses of island chronostratigraphy (composition, texture) and geochronology (21 <i>in-situ</i> radiometric dates) from Eva Island. Downcore, composition of island-grade (reef-derived) sediments were homogenous, dominated by molluscan (37%–42%) and coral (32%–37%) constituents. The <sup>14</sup>C radiometric dating of island sediments, beachrock and coral microatolls identified five stages of island formation across changing sea-level regimes over the mid to late Holocene: (1) limestone platform accretion at <i>ca</i> 6,000 cal yr BP, coinciding with reef decline or ‘give-up’ on neighbouring Exmouth Gulf reefs; (2) sand cay (i.e. core) initiation and vertical aggregation at <i>ca</i> 5,000 cal yr BP during the point of sea-level regression to current levels; (3) major accretion and lateral progradation of the island between 3,500 cal yr BP and 2,500 cal yr BP including the modification of island shorelines through alongshore reworking of sediment; (4) lateral accretion and minor expansion to the north and formation of beachrock pavement between 2,500 and 650 cal yr BP; and (5) planform adjustment (erosion of the north-west island) and backstepping under stabilised sea levels over the past 650 years. While this model is comparative to studies on island formation following incremental sea-level fall following the mid-Holocene highstand, it demonstrates active landform readjustment under stabilised sea levels over the past 2,000 years, probably the influence of local-scale metocean boundary conditions within climate windows across the mid to late Holocene period (i.e. independent of sea-level fluctuations). Importantly, while sediment production rates are predicted to be lower in turbid-water reef systems than clear water, Eva Island shows no change in carbonate producers (i.e. proportion of mollusc and coral) over the course of island building, indicating the carbonate factory has not experienced significant adjustments in reef ecology, but has remained stable despite low water quality.</p>","PeriodicalId":54144,"journal":{"name":"Depositional Record","volume":null,"pages":null},"PeriodicalIF":2.4,"publicationDate":"2023-06-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1002/dep2.242","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"46121034","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
R. Weidlich, O. M. Bialik, A. Rüggeberg, B. Grobéty, T. Vennemann, A. Neuman, Y. Makovsky, A. Foubert
Methane-derived authigenic seep carbonates occur globally along continental margins. These carbonates are important archives to identify seep dynamics, the source of the ascending methane-enriched fluids together with their timing, and are an important carbon sequestration mechanism. Recently, seep carbonates were discovered in the Levant Basin in the south-eastern Mediterranean Sea. To elucidate past seepage activity and dynamics across the basin, different seep carbonate morphologies (chimneys, crusts and pavements) retrieved from the Levant Basin were mapped based on remotely operating vehicle data and analysed using standard sediment petrographic techniques, X-ray diffraction and stable carbon and oxygen isotope analyses. Carbonate chimneys consist of micrite (δ13CVPDB of −10‰ to +5‰) with dispersed baryte and dolomite crystals, fan-shaped aragonite (δ13CVPDB of −52‰ to −30‰) and high-magnesium calcite cements, with the latter often growing from low-magnesium calcite spherules. Botryoidal low-magnesium calcite cements are forming in small cavities. Carbonate crusts consist of micrite with low-magnesium calcite breccias, high-magnesium calcite nodules (δ13CVPDB of −35‰ to −20‰) and cements, and partially replaced fan-shaped aragonite cements. Carbonate pavements consist of low-magnesium calcite microsparite, micritic dolomite and high-magnesium calcite. Fan-shaped aragonite is locally present as pore-lining cement. Iron oxides are often seen coating the low-magnesium calcite, high-magnesium calcite and dolomite cements. Chimneys and crusts, characterised by high amounts of high-magnesium calcite and aragonite, are interpreted to have formed through advective methane fluxes. Pavements, with high quantities of dolomite, are explained as the product of diffusive methane flux. Sediment petrographic and geochemical analysis of the different carbonate morphologies and cement phases therein witness distinct modes of ascending fluid fluxes and their mixing with marine pore water and/or sea water during precipitation of the individual phases.
{"title":"Occurrence and Genesis of Cold-Seep Authigenic Carbonates from the South-Eastern Mediterranean Sea","authors":"R. Weidlich, O. M. Bialik, A. Rüggeberg, B. Grobéty, T. Vennemann, A. Neuman, Y. Makovsky, A. Foubert","doi":"10.1002/dep2.239","DOIUrl":"10.1002/dep2.239","url":null,"abstract":"<p>Methane-derived authigenic seep carbonates occur globally along continental margins. These carbonates are important archives to identify seep dynamics, the source of the ascending methane-enriched fluids together with their timing, and are an important carbon sequestration mechanism. Recently, seep carbonates were discovered in the Levant Basin in the south-eastern Mediterranean Sea. To elucidate past seepage activity and dynamics across the basin, different seep carbonate morphologies (chimneys, crusts and pavements) retrieved from the Levant Basin were mapped based on remotely operating vehicle data and analysed using standard sediment petrographic techniques, X-ray diffraction and stable carbon and oxygen isotope analyses. Carbonate chimneys consist of micrite (δ<sup>13</sup>C<sub>VPDB</sub> of −10‰ to +5‰) with dispersed baryte and dolomite crystals, fan-shaped aragonite (δ<sup>13</sup>C<sub>VPDB</sub> of −52‰ to −30‰) and high-magnesium calcite cements, with the latter often growing from low-magnesium calcite spherules. Botryoidal low-magnesium calcite cements are forming in small cavities. Carbonate crusts consist of micrite with low-magnesium calcite breccias, high-magnesium calcite nodules (δ<sup>13</sup>C<sub>VPDB</sub> of −35‰ to −20‰) and cements, and partially replaced fan-shaped aragonite cements. Carbonate pavements consist of low-magnesium calcite microsparite, micritic dolomite and high-magnesium calcite. Fan-shaped aragonite is locally present as pore-lining cement. Iron oxides are often seen coating the low-magnesium calcite, high-magnesium calcite and dolomite cements. Chimneys and crusts, characterised by high amounts of high-magnesium calcite and aragonite, are interpreted to have formed through advective methane fluxes. Pavements, with high quantities of dolomite, are explained as the product of diffusive methane flux. Sediment petrographic and geochemical analysis of the different carbonate morphologies and cement phases therein witness distinct modes of ascending fluid fluxes and their mixing with marine pore water and/or sea water during precipitation of the individual phases.</p>","PeriodicalId":54144,"journal":{"name":"Depositional Record","volume":null,"pages":null},"PeriodicalIF":2.4,"publicationDate":"2023-06-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1002/dep2.239","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"51503244","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Vladislav Rapprich, Pavel Čáp, Yulia V. Erban Kochergina, Eva Kadlecová, Zsolt Benkó, Jakub Sakala, Zuzana Rodovská, Jan Matějů, Daniel A. Petrash
Late Oligocene (ca 25 Ma) volcano-sedimentary successions exposed on the western periphery of the Doupovské Hory Volcanic Complex reveal a complex sedimentation history influenced in various ways by decay of the alkali basalt volcanic edifice. Weathering of the volcanic rocks supplied abundant reactants that promoted carbonate precipitation in the peripheral palaeolakes—as evidenced by strongly non-radiogenic 87Sr/86Sr values (0.7038–0.7041). On the other hand, the sediments of the initial shallow lake became deformed by the bulldozing effect of a debris avalanche. The debris flow and avalanche deposits filled up the original depression, modified the basin morphology and shifted the peripheral lacustrine setting further away from the volcano. At this stage, surface water influx from the surrounding granites conferred a more radiogenic character (87Sr/86Sr values 0.7046–0.7049) to the calcrete deposits. Fossil assemblages as well as limestone textures suggest significant seasonal water-level fluctuations, possibly reflecting the alternating rainy and dry-seasons of a prevalently humid Central-European Late Oligocene climate. The seasonal drying out of the ponds resulted in significant 18O enrichments. Although the ca 0‰ δ13C values might suggest mixing of atmospheric and volcanic CO2 during carbonate precipitation, no active volcanic conduits of relevant age are known in the close vicinity. The lower δ13C values are likely a result of mantle degassing through rift faults, a phenomenon observed in the magmatically extinct Ohře Rift until present. This paper demonstrates that limestones derived from weathered alkaline basalts are characterised by highly non-radiogenic Sr isotopic ratios (87Sr/86Sr ca 0.704), suggesting a magmatic origin for the Ca within these carbonates. Contrary to the notion of carbonatites being present when highly non-radiogenic Sr isotopes are found, these results show that Sr isotopes in carbonates formed in alkali basalt-sourced environments only reveal the source of the Sr (and Ca) ions, not necessarily the presence of carbonatite.
晚渐新世(约25 Ma)的火山-沉积序列暴露在doupovsk Hory火山杂岩的西边缘,揭示了一个复杂的沉积历史,在不同方面受到碱玄武岩火山建筑的衰变的影响。火山岩的风化作用提供了丰富的反应物,促进了外围古湖泊的碳酸盐沉积,87Sr/86Sr值(0.7038 ~ 0.7041)是非放射性成因的。另一方面,最初浅湖的沉积物由于碎片雪崩的推平作用而变形。泥石流和雪崩沉积充填了原有的凹陷,改变了盆地的形态,使周边的湖相环境向远离火山的方向移动。在这一阶段,来自周围花岗岩的地表水流入使钙砾岩矿床具有更强的放射性成因特征(87Sr/86Sr值为0.7046 ~ 0.7049)。化石组合和石灰石结构表明了显著的季节性水位波动,可能反映了普遍潮湿的中欧晚渐新世气候的雨季和旱季交替。池塘的季节性干涸导致18O显著富集。虽然约0‰的δ13C值可能表明碳酸盐降水过程中大气CO2和火山CO2的混合作用,但在邻近地区未发现相应年龄的活火山导管。较低的δ13C值可能是地幔通过裂谷断层脱气的结果,这种现象在岩浆灭绝的Ohře裂谷中一直存在。本文认为,风化碱性玄武岩灰岩具有高度非放射性成因的Sr同位素比值(87Sr/86Sr ca 0.704),表明这些碳酸盐岩中ca的岩浆成因。这些结果表明,在碱性玄武岩环境中形成的碳酸盐岩中的Sr同位素只能揭示Sr(和Ca)离子的来源,而不一定是碳酸盐岩的存在,与发现高度非放射性成因的Sr同位素时碳酸盐岩存在的概念相反。
{"title":"Interactions between distal epiclastic and bio-chemogenic sedimentation at the foothills of a mafic alkaline volcano: The case of the Oligocene Doupovské Hory Volcanic Complex (Czech Republic)","authors":"Vladislav Rapprich, Pavel Čáp, Yulia V. Erban Kochergina, Eva Kadlecová, Zsolt Benkó, Jakub Sakala, Zuzana Rodovská, Jan Matějů, Daniel A. Petrash","doi":"10.1002/dep2.240","DOIUrl":"10.1002/dep2.240","url":null,"abstract":"<p>Late Oligocene (<i>ca</i> 25 Ma) volcano-sedimentary successions exposed on the western periphery of the Doupovské Hory Volcanic Complex reveal a complex sedimentation history influenced in various ways by decay of the alkali basalt volcanic edifice. Weathering of the volcanic rocks supplied abundant reactants that promoted carbonate precipitation in the peripheral palaeolakes—as evidenced by strongly non-radiogenic <sup>87</sup>Sr/<sup>86</sup>Sr values (0.7038–0.7041). On the other hand, the sediments of the initial shallow lake became deformed by the bulldozing effect of a debris avalanche. The debris flow and avalanche deposits filled up the original depression, modified the basin morphology and shifted the peripheral lacustrine setting further away from the volcano. At this stage, surface water influx from the surrounding granites conferred a more radiogenic character (<sup>87</sup>Sr/<sup>86</sup>Sr values 0.7046–0.7049) to the calcrete deposits. Fossil assemblages as well as limestone textures suggest significant seasonal water-level fluctuations, possibly reflecting the alternating rainy and dry-seasons of a prevalently humid Central-European Late Oligocene climate. The seasonal drying out of the ponds resulted in significant <sup>18</sup>O enrichments. Although the <i>ca</i> 0‰ δ<sup>13</sup>C values might suggest mixing of atmospheric and volcanic CO<sub>2</sub> during carbonate precipitation, no active volcanic conduits of relevant age are known in the close vicinity. The lower δ<sup>13</sup>C values are likely a result of mantle degassing through rift faults, a phenomenon observed in the magmatically extinct Ohře Rift until present. This paper demonstrates that limestones derived from weathered alkaline basalts are characterised by highly non-radiogenic Sr isotopic ratios (<sup>87</sup>Sr/<sup>86</sup>Sr <i>ca</i> 0.704), suggesting a magmatic origin for the Ca within these carbonates. Contrary to the notion of carbonatites being present when highly non-radiogenic Sr isotopes are found, these results show that Sr isotopes in carbonates formed in alkali basalt-sourced environments only reveal the source of the Sr (and Ca) ions, not necessarily the presence of carbonatite.</p>","PeriodicalId":54144,"journal":{"name":"Depositional Record","volume":null,"pages":null},"PeriodicalIF":2.4,"publicationDate":"2023-06-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1002/dep2.240","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"41704883","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Romain Vaucher, Antoine Dillinger, Amy I. Hsieh, Wen-Rong Chi, Ludvig Löwemark, Shahin E. Dashtgard
Storm-flood-dominated deltas are sedimentary systems in which a complex interplay of hydrodynamic processes occurs during storms (e.g. tropical cyclones) due to the coeval action of continental and oceanic processes. This paper reports on a superbly exposed, 135.5 m thick stratigraphic succession of the Pleistocene Cholan Formation exposed along the Da'an River, Taiwan. The sedimentary succession comprises alternating mudstone and sandstone, is mostly fine-grained, and exhibits multiple event beds that record deposition during tropical cyclones and post-depositional deformation features produced during earthquakes. Detailed facies analyses reveal that deposition towards the base of the succession occurred in the palaeo-Taiwan Strait in storm-flood-dominated prodelta and delta-front environments passing upwards into delta-plain environments. Tropical cyclone beds are encountered throughout the subaqueous storm-flood delta successions, and are identified by (i) trough cross-stratified sandstone bedsets with erosive bases that contain both mud clasts and mudstone beds, (ii) sandstone with aggrading wave ripples and (iii) hummocky cross-stratified sandstone with rare gutter casts filled with coal fragments and shell remains. Tropical cyclone deposits are either top-down burrowed or capped by massive or laminated mudstone. Seismites are rare and are mainly recognised through soft-sediment deformation of beds; they do not show evidence of slope failure. Compared to storm-flood delta successions described elsewhere, the Cholan Formation shows significantly fewer oscillatory-generated sedimentary structures and gutter casts. This difference is attributed to the Cholan Formation being deposited in and along the margin of a strait characterised by strong shore-parallel currents and relatively small storm waves due to its position between Taiwan and mainland China. This study refines depositional process interpretations of the Cholan Formation, provides criteria for recognising storm-flood delta deposits in tectonically active straits with multiple sediment sources fed by steep drainages and short river catchments, and provides additional criteria for recognising tropical cyclone deposits in shallow-marine settings.
{"title":"Storm-flood-dominated delta succession in the Pleistocene Taiwan Strait","authors":"Romain Vaucher, Antoine Dillinger, Amy I. Hsieh, Wen-Rong Chi, Ludvig Löwemark, Shahin E. Dashtgard","doi":"10.1002/dep2.231","DOIUrl":"10.1002/dep2.231","url":null,"abstract":"<p>Storm-flood-dominated deltas are sedimentary systems in which a complex interplay of hydrodynamic processes occurs during storms (e.g. tropical cyclones) due to the coeval action of continental and oceanic processes. This paper reports on a superbly exposed, 135.5 m thick stratigraphic succession of the Pleistocene Cholan Formation exposed along the Da'an River, Taiwan. The sedimentary succession comprises alternating mudstone and sandstone, is mostly fine-grained, and exhibits multiple event beds that record deposition during tropical cyclones and post-depositional deformation features produced during earthquakes. Detailed facies analyses reveal that deposition towards the base of the succession occurred in the palaeo-Taiwan Strait in storm-flood-dominated prodelta and delta-front environments passing upwards into delta-plain environments. Tropical cyclone beds are encountered throughout the subaqueous storm-flood delta successions, and are identified by (i) trough cross-stratified sandstone bedsets with erosive bases that contain both mud clasts and mudstone beds, (ii) sandstone with aggrading wave ripples and (iii) hummocky cross-stratified sandstone with rare gutter casts filled with coal fragments and shell remains. Tropical cyclone deposits are either top-down burrowed or capped by massive or laminated mudstone. Seismites are rare and are mainly recognised through soft-sediment deformation of beds; they do not show evidence of slope failure. Compared to storm-flood delta successions described elsewhere, the Cholan Formation shows significantly fewer oscillatory-generated sedimentary structures and gutter casts. This difference is attributed to the Cholan Formation being deposited in and along the margin of a strait characterised by strong shore-parallel currents and relatively small storm waves due to its position between Taiwan and mainland China. This study refines depositional process interpretations of the Cholan Formation, provides criteria for recognising storm-flood delta deposits in tectonically active straits with multiple sediment sources fed by steep drainages and short river catchments, and provides additional criteria for recognising tropical cyclone deposits in shallow-marine settings.</p>","PeriodicalId":54144,"journal":{"name":"Depositional Record","volume":null,"pages":null},"PeriodicalIF":2.4,"publicationDate":"2023-05-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1002/dep2.231","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"43165545","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}