S.W. Fietz, J.A. MacEachern, M.K. Gingras, M. Ranger, S.E. Dashtgard
Sedimentological and ichnological descriptions of fluvio-tidal translating point bars are rare, and complex physico-chemical processes make highly detailed but concise facies descriptions challenging. Herein, mesofacies are defined to describe and interpret three ancient translating point bars from the Lower Cretaceous McMurray Formation, Alberta, Canada. Twenty-three mesofacies are defined, based on their recurring sedimentological and ichnological characteristics. These mesofacies form the building blocks of beds and bedsets that make up three depositional facies. Facies 1 reflects sand dune migration at the channel base, which grades into inclined heterolithic stratification of facies 2 and 3. Facies 2 occurs in the centre and seaward portions of the translating point bars and records tide-dominated deposition of sand and muddy sand during periods of reduced river discharge. Ichnological suites and bioturbation intensities in these beds reflect persistent but variable brackish-water conditions, fluctuating deposition rates and the deposition of mud. Mud beds are derived from flows with high suspended-sediment concentrations. Tidally derived mud beds are typically bioturbated with trace fossil suites indicative of slow deposition rates and brackish-water conditions. Mud deposited during elevated river discharge is burrowed after the dewatering of the bed. Facies 3 occurs at the landward apex of the translating point bar and is marked by sand-rich and mud-rich dune deposits with abundant soft-sediment deformation, indicative of elevated flow velocities and deposition rates. Bioturbation is rare and sporadically distributed owing to unstable substrates. The distribution of the facies reflect the hydrodynamic variations that occurred vertically and laterally across the bar in response to temporal variations in fluvial and tidal flow interaction, as recorded by their mesofacies. The detailed facies analysis strongly suggest that deposition of the three McMurray Formation translating point bars occurred in proximity to the turbidity maximum zone of a fluvio-tidal channel system.
{"title":"Sedimentological and ichnological variations in fluvio-tidal translating point bars, McMurray Formation, Alberta, Canada","authors":"S.W. Fietz, J.A. MacEachern, M.K. Gingras, M. Ranger, S.E. Dashtgard","doi":"10.1111/sed.13164","DOIUrl":"https://doi.org/10.1111/sed.13164","url":null,"abstract":"Sedimentological and ichnological descriptions of fluvio-tidal translating point bars are rare, and complex physico-chemical processes make highly detailed but concise facies descriptions challenging. Herein, mesofacies are defined to describe and interpret three ancient translating point bars from the Lower Cretaceous McMurray Formation, Alberta, Canada. Twenty-three mesofacies are defined, based on their recurring sedimentological and ichnological characteristics. These mesofacies form the building blocks of beds and bedsets that make up three depositional facies. <i>Facies 1</i> reflects sand dune migration at the channel base, which grades into inclined heterolithic stratification of facies 2 and 3. <i>Facies 2</i> occurs in the centre and seaward portions of the translating point bars and records tide-dominated deposition of sand and muddy sand during periods of reduced river discharge. Ichnological suites and bioturbation intensities in these beds reflect persistent but variable brackish-water conditions, fluctuating deposition rates and the deposition of mud. Mud beds are derived from flows with high suspended-sediment concentrations. Tidally derived mud beds are typically bioturbated with trace fossil suites indicative of slow deposition rates and brackish-water conditions. Mud deposited during elevated river discharge is burrowed after the dewatering of the bed. <i>Facies 3</i> occurs at the landward apex of the translating point bar and is marked by sand-rich and mud-rich dune deposits with abundant soft-sediment deformation, indicative of elevated flow velocities and deposition rates. Bioturbation is rare and sporadically distributed owing to unstable substrates. The distribution of the facies reflect the hydrodynamic variations that occurred vertically and laterally across the bar in response to temporal variations in fluvial and tidal flow interaction, as recorded by their mesofacies. The detailed facies analysis strongly suggest that deposition of the three McMurray Formation translating point bars occurred in proximity to the turbidity maximum zone of a fluvio-tidal channel system.","PeriodicalId":21838,"journal":{"name":"Sedimentology","volume":null,"pages":null},"PeriodicalIF":3.5,"publicationDate":"2023-11-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"138509476","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Selma Sarı, Ali Mohammadi, Georg Schwamborn, Negar Haghipour, Byung Yong Yu, Kürşad Kadir Eriş, Razyeh Lak
A 25 m long sediment core from hypersaline Urmia Lake (north-west Iran) was studied for the Late Quaternary depositional history and palaeoclimate variations using the abundance and compositional characteristics of Artemia faecal pellets. Sediment analysis is supported by scanning electron microscopy – energy dispersive X-ray spectroscopy, organic and inorganic carbon content measurements, and stable isotopes (δ13C and δ18O) from faecal pellet carbonates. The imprecise chronology of the core back to 50 kyr bp is supported by ten radiocarbon ages from faecal pellets and bulk sediments. The palaeoenvironmental record is subdivided into four periods: (i) During much of Marine Isotope Stage 3, a period of lake level lowering is characterized by a decreasing amount of faecal pellets, and an increasing amount of coated grains, sulphate minerals and reworked shell fragments. (ii) During late Marine Isotope Stage 3 and early Marine Isotope Stage 2 a lake level lowstand and a lake floor exposure is interpreted based on the relatively low abundance of pellets, which are multicoloured and appear together with volcanic lithics and rounded sulphate minerals. (iii) During late Marine Isotope Stage 2 the record is devoid of pellets but dominated by large sulphate crystals suggesting a prolonged low lake level. (iv) During Marine Isotope Stage 1 a relative lake level highstand is rapidly established with sediments that are highly abundant in fresh pellets. The modern lake level lowstand is represented by a salt crust. The δ13C and δ18O records measured from faecal pellet carbonates suggest a link with the precipitation versus evaporation balance in the lake over time. From bottom to top the linear trend towards more negative delta values illustrates the increasing amount of precipitation arriving at the lake from the Late Pleistocene to the Holocene. Two prominent isotope minima during the Late Pleistocene and one prominent minimum in the early Holocene mark relative high lake levels, which can also be linked to Lake Van in Turkey.
{"title":"Sedimentary evolution and lake level fluctuations of Urmia Lake (north-west Iran) over the past 50 000 years; insights from Artemia faecal pellet records","authors":"Selma Sarı, Ali Mohammadi, Georg Schwamborn, Negar Haghipour, Byung Yong Yu, Kürşad Kadir Eriş, Razyeh Lak","doi":"10.1111/sed.13159","DOIUrl":"https://doi.org/10.1111/sed.13159","url":null,"abstract":"A 25 m long sediment core from hypersaline Urmia Lake (north-west Iran) was studied for the Late Quaternary depositional history and palaeoclimate variations using the abundance and compositional characteristics of <i>Artemia</i> faecal pellets. Sediment analysis is supported by scanning electron microscopy – energy dispersive X-ray spectroscopy, organic and inorganic carbon content measurements, and stable isotopes (δ<sup>13</sup>C and δ<sup>18</sup>O) from faecal pellet carbonates. The imprecise chronology of the core back to 50 kyr <span>bp</span> is supported by ten radiocarbon ages from faecal pellets and bulk sediments. The palaeoenvironmental record is subdivided into four periods: (i) During much of Marine Isotope Stage 3, a period of lake level lowering is characterized by a decreasing amount of faecal pellets, and an increasing amount of coated grains, sulphate minerals and reworked shell fragments. (ii) During late Marine Isotope Stage 3 and early Marine Isotope Stage 2 a lake level lowstand and a lake floor exposure is interpreted based on the relatively low abundance of pellets, which are multicoloured and appear together with volcanic lithics and rounded sulphate minerals. (iii) During late Marine Isotope Stage 2 the record is devoid of pellets but dominated by large sulphate crystals suggesting a prolonged low lake level. (iv) During Marine Isotope Stage 1 a relative lake level highstand is rapidly established with sediments that are highly abundant in fresh pellets. The modern lake level lowstand is represented by a salt crust. The δ<sup>13</sup>C and δ<sup>18</sup>O records measured from faecal pellet carbonates suggest a link with the precipitation versus evaporation balance in the lake over time. From bottom to top the linear trend towards more negative delta values illustrates the increasing amount of precipitation arriving at the lake from the Late Pleistocene to the Holocene. Two prominent isotope minima during the Late Pleistocene and one prominent minimum in the early Holocene mark relative high lake levels, which can also be linked to Lake Van in Turkey.","PeriodicalId":21838,"journal":{"name":"Sedimentology","volume":null,"pages":null},"PeriodicalIF":3.5,"publicationDate":"2023-11-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"138509473","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
C. Pellegrini, I. Sammartino, J. Schieber, T. Tesi, F. Paladini de Mendoza, V. Rossi, J. Chiggiato, K. Schroeder, A. Gallerani, L. Langone, F. Trincardi, A. Amorosi
Depositional processes recorded by shelf deposits may vary widely along-strike, depending largely on the mode of delivery and deposition of sediments to the basin. In fine-grained systems in particular, depositional processes are difficult to reconstruct with standard facies analysis of sediment cores due to the ostensibly featureless and homogenous appearance of muds. In this study, sedimentological, palaeontological, geochemical and oceanographic data were combined in a detailed characterization of depositional conditions via sedimentary structures, type of organic matter, trace-metal geochemistry and benthic fauna assemblages (foraminifera and ostracods) along the 600 km long shelf delta clinothems of the West Adriatic shelf (Italy). Processes inferred from sedimentary facies and micro-structures were then considered in the context of the modern Adriatic oceanographic regime. Specific attention was given to the Little Ice Age stratigraphic unit (1500–1850 CE), which contains a continuum of genetically related fine-grained strata. The Little Ice Age deposit offers the opportunity to examine a source-to-sink system with the high resolution typical of modernanalogues, at a time interval when Apennine rivers were not yet hydraulically engineered with man-made sediment traps along their trunks. Individual beds within the Little Ice Age muddy prodelta form hectometre to kilometre-wide bedsets that reflect the interplay between energetic meteo-ocean conditions (storm-dominated beds), flood supply (river-dominated beds or hyperpycnites) and along-shelf bottom-current dispersion (drift-dominated beds). The multidisciplinary approach applied at different scales of observations helped in understanding sediment provenance and the relative timing of sediment transport before final burial that strongly promoted organic matter oxygen exposure and the loss of carbon by microbial degradation. Overall, the distinctive depositional processes that acted in concert along the prodelta slope produced a subtle lateral heterogeneity of preserved sedimentary structures, faunal associations and organic matter composition in a laterally-continuous lithostratigraphic unit deposited at centennial scale. These findings have implications on the forcing conditions that ultimately control the location and nature of fine-grained beds in both modern and ancient, mud-dominated depositional systems.
{"title":"On depositional processes governing along-strike facies variations of fine-grained deposits: Unlocking the Little Ice Age subaqueous clinothems on the Adriatic shelf","authors":"C. Pellegrini, I. Sammartino, J. Schieber, T. Tesi, F. Paladini de Mendoza, V. Rossi, J. Chiggiato, K. Schroeder, A. Gallerani, L. Langone, F. Trincardi, A. Amorosi","doi":"10.1111/sed.13162","DOIUrl":"https://doi.org/10.1111/sed.13162","url":null,"abstract":"Depositional processes recorded by shelf deposits may vary widely along-strike, depending largely on the mode of delivery and deposition of sediments to the basin. In fine-grained systems in particular, depositional processes are difficult to reconstruct with standard facies analysis of sediment cores due to the ostensibly featureless and homogenous appearance of muds. In this study, sedimentological, palaeontological, geochemical and oceanographic data were combined in a detailed characterization of depositional conditions via sedimentary structures, type of organic matter, trace-metal geochemistry and benthic fauna assemblages (foraminifera and ostracods) along the 600 km long shelf delta clinothems of the West Adriatic shelf (Italy). Processes inferred from sedimentary facies and micro-structures were then considered in the context of the modern Adriatic oceanographic regime. Specific attention was given to the Little Ice Age stratigraphic unit (1500–1850 CE), which contains a continuum of genetically related fine-grained strata. The Little Ice Age deposit offers the opportunity to examine a source-to-sink system with the high resolution typical of modernanalogues, at a time interval when Apennine rivers were not yet hydraulically engineered with man-made sediment traps along their trunks. Individual beds within the Little Ice Age muddy prodelta form hectometre to kilometre-wide bedsets that reflect the interplay between energetic meteo-ocean conditions (storm-dominated beds), flood supply (river-dominated beds or hyperpycnites) and along-shelf bottom-current dispersion (drift-dominated beds). The multidisciplinary approach applied at different scales of observations helped in understanding sediment provenance and the relative timing of sediment transport before final burial that strongly promoted organic matter oxygen exposure and the loss of carbon by microbial degradation. Overall, the distinctive depositional processes that acted in concert along the prodelta slope produced a subtle lateral heterogeneity of preserved sedimentary structures, faunal associations and organic matter composition in a laterally-continuous lithostratigraphic unit deposited at centennial scale. These findings have implications on the forcing conditions that ultimately control the location and nature of fine-grained beds in both modern and ancient, mud-dominated depositional systems.","PeriodicalId":21838,"journal":{"name":"Sedimentology","volume":null,"pages":null},"PeriodicalIF":3.5,"publicationDate":"2023-11-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"138509475","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Sophie Decrée, Etienne Deloule, Renata Barros, Julien Mercadier, Stefan Höhn, Chantal Peiffert, Jean-Marc Baele
In phosphorites, the content and distribution of rare earth elements are linked to the environment of phosphogenesis. This paper focuses on the question of sources and processes controlling the rare earth element content of apatite from Belgian phosphorites formed during three major phosphogenic events in the Lower Palaeozoic, Late Cretaceous and Cenozoic. To constrain sources and processes, new data include petrological, mineralogical (including cathodoluminescence and Raman spectroscopy) and in situ trace element and Sr and O isotope analyses of apatite. Fluorapatite from Lower Palaeozoic P-rich conglomerates has the greatest rare earth element enrichment. It is affected by metamorphism that led to deformation of apatite nodules and formation of garnet porphyroblast inclusions. The role of Fe-oxyhydroxides in element scavenging is highlighted by some apatite nodules that maintain their primary middle rare earth element enrichment, while others are characterized by altered rare earth element patterns resulting from competition for these elements between co-crystallizing minerals during deformation. A systematic shift towards lower δ18O and radiogenic Sr isotopic composition compared to contemporaneous seawater indicate interaction with 18O-depleted meteoric fluids and a crustal component. By contrast, carbonate-rich fluorapatite from the Late Cretaceous phosphatic chalk mostly keeps its primary trace element and isotopic signatures (close to seawater), although an external rare earth element addition is noted as well as rare earth element redistribution induced by diagenetic alteration. Cenozoic carbonate fluorapatite nodules mostly present flat rare earth element patterns that are indicative of a detrital influence. Slight changes in rare earth element distribution are assigned to post-depositional alteration, which also led to an increase in radiogenic Sr, with unchanged δ18O compared to seawater. The methodology followed here efficiently helps in deciphering the processes that modified the chemistry of apatite in the frame of major phosphogenic events.
{"title":"Processes controlling Rare Earth Element distribution in sedimentary apatite: Insights from spectroscopy, in-situ geochemistry and O and Sr isotope composition","authors":"Sophie Decrée, Etienne Deloule, Renata Barros, Julien Mercadier, Stefan Höhn, Chantal Peiffert, Jean-Marc Baele","doi":"10.1111/sed.13160","DOIUrl":"https://doi.org/10.1111/sed.13160","url":null,"abstract":"In phosphorites, the content and distribution of rare earth elements are linked to the environment of phosphogenesis. This paper focuses on the question of sources and processes controlling the rare earth element content of apatite from Belgian phosphorites formed during three major phosphogenic events in the Lower Palaeozoic, Late Cretaceous and Cenozoic. To constrain sources and processes, new data include petrological, mineralogical (including cathodoluminescence and Raman spectroscopy) and <i>in situ</i> trace element and Sr and O isotope analyses of apatite. Fluorapatite from Lower Palaeozoic P-rich conglomerates has the greatest rare earth element enrichment. It is affected by metamorphism that led to deformation of apatite nodules and formation of garnet porphyroblast inclusions. The role of Fe-oxyhydroxides in element scavenging is highlighted by some apatite nodules that maintain their primary middle rare earth element enrichment, while others are characterized by altered rare earth element patterns resulting from competition for these elements between co-crystallizing minerals during deformation. A systematic shift towards lower δ<sup>18</sup>O and radiogenic Sr isotopic composition compared to contemporaneous seawater indicate interaction with <sup>18</sup>O-depleted meteoric fluids and a crustal component. By contrast, carbonate-rich fluorapatite from the Late Cretaceous phosphatic chalk mostly keeps its primary trace element and isotopic signatures (close to seawater), although an external rare earth element addition is noted as well as rare earth element redistribution induced by diagenetic alteration. Cenozoic carbonate fluorapatite nodules mostly present flat rare earth element patterns that are indicative of a detrital influence. Slight changes in rare earth element distribution are assigned to post-depositional alteration, which also led to an increase in radiogenic Sr, with unchanged δ<sup>18</sup>O compared to seawater. The methodology followed here efficiently helps in deciphering the processes that modified the chemistry of apatite in the frame of major phosphogenic events.","PeriodicalId":21838,"journal":{"name":"Sedimentology","volume":null,"pages":null},"PeriodicalIF":3.5,"publicationDate":"2023-11-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"138509474","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Hangyu Liu, Kaibo Shi, Bo Liu, Yong Li, Yang Li, Haofu Zheng, Yuting Peng, Yingxiao Fu
ABSTRACT The source and pumping mechanism of magnesium play crucial roles in dolomitization. The preferential dolomitization of burrows has been extensively documented in geological archives. Although burrows are abundantly preserved in Cretaceous carbonates, burrow‐selective dolomitization is uncommon in normal salinity marine environments due to the low Mg/Ca ratio of seawater. However, burrow‐selective dolomitization occurred in the Cenomanian Rumaila Formation carbonates of the Arabian Platform providing an excellent example to further clarify the mechanism and explore other potential Mg sources of burrow‐elective dolomitization. Integrated studies of petrography, stable isotope geochemistry and laser ablation–inductively coupled plasma–mass spectrometry‐based in situ element geochemistry were conducted. It was found that the burrow‐selective dolomitization exclusively occurred in echinoderm fragment‐filled Thalassinoides networks which occurred as Glossifungites ichnofacies. Burrow dolomites showed fine to medium crystalline and planar subhedral to euhedral textures with cloudy centres and clear rims. They exhibited relatively greater Mn, lower Sr and Fe concentrations, no or very weak negative Ce anomaly and middle rare earth element‐bulge patterns, and are slightly enriched with occasionally depleted δ 13 C and comparable δ 18 O relative to the surrounding calcite matrix. The initial high‐Mg calcite echinoderm fragments in burrows have been stabilized to low‐Mg calcite, and echinoderm syntaxial overgrowth calcite cement was practically nonexistent. Echinoderm fragments were frequently replaced by dolomite in part or whole. Undolomitized echinoderms have negative Ce anomaly and seawater‐like rare earth element patterns, as well as very low Mn, Fe and relatively greater Sr concentrations. These suggest that echinoderm stabilization occurred in fluid unsaturated with respect to high‐Mg calcite driven by aerobic decomposition of organic matter in oxic seawater near the sediment–water interface, meanwhile, Mg ions were liberated into pore water. This process pre‐dated the dolomitization allowing the Mg derived from echinoderm to raise the Mg/Ca ratio of burrow interstitial water. The dolomites in burrows were generated by initial replacement and subsequent overgrowth cementation associated with bacterial sulphate reduction and methanogenesis in low‐temperature and suboxic to anoxic fluids in the near‐surface realm, and faintly recrystallized as burial depth increased. This study sheds light on the echinoderm stabilization process, links the early diagenesis of skeletons to burrow dolomitization, and proposes a conceptual model illustrating that high‐Mg calcite skeletons could act as a major Mg source for burrow‐selective dolomitization, which compensates for the deficiency of Mg in normal low Mg/Ca ratio Cretaceous seawater. This study implies the interaction effect and element cycle among components in early diagenetic systems, and verifies th
{"title":"High‐magnesium calcite skeletons provide magnesium for burrow‐selective dolomitization in Cretaceous carbonates","authors":"Hangyu Liu, Kaibo Shi, Bo Liu, Yong Li, Yang Li, Haofu Zheng, Yuting Peng, Yingxiao Fu","doi":"10.1111/sed.13139","DOIUrl":"https://doi.org/10.1111/sed.13139","url":null,"abstract":"ABSTRACT The source and pumping mechanism of magnesium play crucial roles in dolomitization. The preferential dolomitization of burrows has been extensively documented in geological archives. Although burrows are abundantly preserved in Cretaceous carbonates, burrow‐selective dolomitization is uncommon in normal salinity marine environments due to the low Mg/Ca ratio of seawater. However, burrow‐selective dolomitization occurred in the Cenomanian Rumaila Formation carbonates of the Arabian Platform providing an excellent example to further clarify the mechanism and explore other potential Mg sources of burrow‐elective dolomitization. Integrated studies of petrography, stable isotope geochemistry and laser ablation–inductively coupled plasma–mass spectrometry‐based in situ element geochemistry were conducted. It was found that the burrow‐selective dolomitization exclusively occurred in echinoderm fragment‐filled Thalassinoides networks which occurred as Glossifungites ichnofacies. Burrow dolomites showed fine to medium crystalline and planar subhedral to euhedral textures with cloudy centres and clear rims. They exhibited relatively greater Mn, lower Sr and Fe concentrations, no or very weak negative Ce anomaly and middle rare earth element‐bulge patterns, and are slightly enriched with occasionally depleted δ 13 C and comparable δ 18 O relative to the surrounding calcite matrix. The initial high‐Mg calcite echinoderm fragments in burrows have been stabilized to low‐Mg calcite, and echinoderm syntaxial overgrowth calcite cement was practically nonexistent. Echinoderm fragments were frequently replaced by dolomite in part or whole. Undolomitized echinoderms have negative Ce anomaly and seawater‐like rare earth element patterns, as well as very low Mn, Fe and relatively greater Sr concentrations. These suggest that echinoderm stabilization occurred in fluid unsaturated with respect to high‐Mg calcite driven by aerobic decomposition of organic matter in oxic seawater near the sediment–water interface, meanwhile, Mg ions were liberated into pore water. This process pre‐dated the dolomitization allowing the Mg derived from echinoderm to raise the Mg/Ca ratio of burrow interstitial water. The dolomites in burrows were generated by initial replacement and subsequent overgrowth cementation associated with bacterial sulphate reduction and methanogenesis in low‐temperature and suboxic to anoxic fluids in the near‐surface realm, and faintly recrystallized as burial depth increased. This study sheds light on the echinoderm stabilization process, links the early diagenesis of skeletons to burrow dolomitization, and proposes a conceptual model illustrating that high‐Mg calcite skeletons could act as a major Mg source for burrow‐selective dolomitization, which compensates for the deficiency of Mg in normal low Mg/Ca ratio Cretaceous seawater. This study implies the interaction effect and element cycle among components in early diagenetic systems, and verifies th","PeriodicalId":21838,"journal":{"name":"Sedimentology","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2023-11-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"134992697","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Jeremy McCormack, Andre Baldermann, Tomaso R. R. Bontognali, Annabel Wolf, Ola Kwiecien
ABSTRACT Dolomite is globally present in past geological records, but rare in modern environments. The mechanisms favouring its precipitation under ambient conditions remain highly debated. This study investigates sediments, containing high concentrations of early diagenetic calcian dolomite, from alkaline Lake Van (Republic of Türkiye, formally Turkey) dating back to 252 ka BP. Powder X‐ray diffraction and scanning electron microscopy evidence suggests that dolomite formation is associated with prior dissolution of aragonite and low‐Mg calcite and a subsequent co‐precipitation with, and/or partial transformation of, high‐Mg calcite into dolomite. The infrequent presence of diatom frustules encapsulated by dolomite suggests, for Lake Van, unusually low pore‐water pH at the time of dolomite formation. Conditions facilitating the preservation of silica, as well as dissolution and subsequent reprecipitation of carbonate phases, could result from periodic reventilations of Lake Van's deep water and an advection of pore fluids with contrasting redox potential and chemical concentration gradients. This continental analogue of the coastal ‘mixing‐zone’ dolomitization model argues that not overcoming a single specific hydrochemical threshold, but highly dynamic and fluctuating conditions trigger dolomite formation in Lake Van.
{"title":"Hydrochemical mixing‐zones trigger dolomite formation in an alkaline lake","authors":"Jeremy McCormack, Andre Baldermann, Tomaso R. R. Bontognali, Annabel Wolf, Ola Kwiecien","doi":"10.1111/sed.13155","DOIUrl":"https://doi.org/10.1111/sed.13155","url":null,"abstract":"ABSTRACT Dolomite is globally present in past geological records, but rare in modern environments. The mechanisms favouring its precipitation under ambient conditions remain highly debated. This study investigates sediments, containing high concentrations of early diagenetic calcian dolomite, from alkaline Lake Van (Republic of Türkiye, formally Turkey) dating back to 252 ka BP. Powder X‐ray diffraction and scanning electron microscopy evidence suggests that dolomite formation is associated with prior dissolution of aragonite and low‐Mg calcite and a subsequent co‐precipitation with, and/or partial transformation of, high‐Mg calcite into dolomite. The infrequent presence of diatom frustules encapsulated by dolomite suggests, for Lake Van, unusually low pore‐water pH at the time of dolomite formation. Conditions facilitating the preservation of silica, as well as dissolution and subsequent reprecipitation of carbonate phases, could result from periodic reventilations of Lake Van's deep water and an advection of pore fluids with contrasting redox potential and chemical concentration gradients. This continental analogue of the coastal ‘mixing‐zone’ dolomitization model argues that not overcoming a single specific hydrochemical threshold, but highly dynamic and fluctuating conditions trigger dolomite formation in Lake Van.","PeriodicalId":21838,"journal":{"name":"Sedimentology","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2023-11-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135291194","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
ABSTRACT Identification of the processes producing soft‐sediment deformation structures, common in siliciclastic deposits and less abundant in carbonate successions, is complex, because different processes may produce similar structures. Thus, interpreting the origin of these structures may be challenging: it requires both a detailed sedimentological study and the knowledge of the depositional environment and stratigraphic evolution, in order to provide hints to identify the processes affecting sediments after deposition. Among the potential causes of the formation of soft‐sediment deformation structures, seismic shock is one of the possibilities, but their origin could be also related to other triggering mechanisms, such as volcanic activity, sediment loading, salt tectonics, fluid expulsion, meteorite impacts and mass movements. Although it is a plausible option, the interpretation of these structures as ‘seismites’ is not obvious: it must be supported by different lines of evidence, considering that the correct interpretation of soft‐sediment deformation structures as a consequence of seismic shocks acquires important implications in palaeoseismology studies. The occurrence of diverse soft‐sediment deformation structures in a fault‐controlled basin (i.e. in a geological setting characterized by syndepositional tectonics) preserved in different subenvironments of a Norian carbonate system in the Southern Alps of Italy provides the chance to characterize different types of soft‐sediment deformation structures along a platform‐to‐basin depositional profile. Presence of pseudonodules in basinal resedimented limestone, sedimentary dykes and clinostratified breccias with unlithified clasts in slope settings and liquefaction of inner platform facies at the platform top testify to an origin compatible with multiple seismic shocks, repetitively affecting the same stratigraphic intervals. The diverse types of soft‐sediment deformation structures in the studied carbonate system provide a rich catalogue of structures related to seismic shocks, representing a possible reference for other similar settings.
{"title":"Soft‐sediment deformation structures and Neptunian dykes across a carbonate system: Evidence for an earthquake‐related origin (Norian, Dolomia Principale, Southern Alps, Italy)","authors":"Fabrizio Berra","doi":"10.1111/sed.13154","DOIUrl":"https://doi.org/10.1111/sed.13154","url":null,"abstract":"ABSTRACT Identification of the processes producing soft‐sediment deformation structures, common in siliciclastic deposits and less abundant in carbonate successions, is complex, because different processes may produce similar structures. Thus, interpreting the origin of these structures may be challenging: it requires both a detailed sedimentological study and the knowledge of the depositional environment and stratigraphic evolution, in order to provide hints to identify the processes affecting sediments after deposition. Among the potential causes of the formation of soft‐sediment deformation structures, seismic shock is one of the possibilities, but their origin could be also related to other triggering mechanisms, such as volcanic activity, sediment loading, salt tectonics, fluid expulsion, meteorite impacts and mass movements. Although it is a plausible option, the interpretation of these structures as ‘seismites’ is not obvious: it must be supported by different lines of evidence, considering that the correct interpretation of soft‐sediment deformation structures as a consequence of seismic shocks acquires important implications in palaeoseismology studies. The occurrence of diverse soft‐sediment deformation structures in a fault‐controlled basin (i.e. in a geological setting characterized by syndepositional tectonics) preserved in different subenvironments of a Norian carbonate system in the Southern Alps of Italy provides the chance to characterize different types of soft‐sediment deformation structures along a platform‐to‐basin depositional profile. Presence of pseudonodules in basinal resedimented limestone, sedimentary dykes and clinostratified breccias with unlithified clasts in slope settings and liquefaction of inner platform facies at the platform top testify to an origin compatible with multiple seismic shocks, repetitively affecting the same stratigraphic intervals. The diverse types of soft‐sediment deformation structures in the studied carbonate system provide a rich catalogue of structures related to seismic shocks, representing a possible reference for other similar settings.","PeriodicalId":21838,"journal":{"name":"Sedimentology","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2023-11-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135291450","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Abstract Upper Palaeozoic lacustrine basin deposits not only record local tectonism but are also an archive to evaluate global palaeoclimate changes linked to the Late Palaeozoic Gondwanan ice age. The Tournaisian Horton Group of Nova Scotia, south‐east Canada, accumulated in rift basins following the final accretion of peri‐Gondwanan terranes to the Appalachians. Sedimentology, mineralogy and geochemistry of the well‐exposed sandstones and shales at the classic Blue Beach section ( ca 353.5 to 352 Ma) reveal the interplay of local tectonism and global climatic controls on lacustrine sedimentation. The lacustrine depositional environment gradually transitioned from deep water offshore at the base of the section to wave‐dominated and fluvial‐dominated nearshore at the top. Multiple small transgressive–regressive sedimentation cycles have an average 21 ka duration, likely related to Milankovitch cyclicity. Unusually abundant soft‐sediment deformation structures and landslides are the sedimentary responses to frequent earthquakes during the most active phase of rift subsidence. The overall succession shows changes from a shallowing‐up balanced‐filled to an overfilled lacustrine basin. The chemical weathering intensity index and the Th/K ratio show a longer‐term trend from dry and cool conditions low in the section to humid and warm conditions near the top, with rapid change in the transition period. The section records the peak of the global mid‐Tournaisian carbon isotope excursion and the corresponding cooling event (354 Ma to approximately 351 Ma). The sedimentary succession is a response to long‐term and short‐term climatic cycles influencing lake level and sediment supply during the time of maximum rift basin subsidence recorded by the soft‐sediment deformation structures.
{"title":"Architecture of lacustrine deposits in response to early Carboniferous rifting and Gondwanan glaciation, Nova Scotia, south‐east Canada","authors":"Wenbin Tang, Georgia Pe‐Piper, David J.W. Piper, Anqing Chen, Mingcai Hou, Zhaojie Guo, Yuanyuan Zhang","doi":"10.1111/sed.13140","DOIUrl":"https://doi.org/10.1111/sed.13140","url":null,"abstract":"Abstract Upper Palaeozoic lacustrine basin deposits not only record local tectonism but are also an archive to evaluate global palaeoclimate changes linked to the Late Palaeozoic Gondwanan ice age. The Tournaisian Horton Group of Nova Scotia, south‐east Canada, accumulated in rift basins following the final accretion of peri‐Gondwanan terranes to the Appalachians. Sedimentology, mineralogy and geochemistry of the well‐exposed sandstones and shales at the classic Blue Beach section ( ca 353.5 to 352 Ma) reveal the interplay of local tectonism and global climatic controls on lacustrine sedimentation. The lacustrine depositional environment gradually transitioned from deep water offshore at the base of the section to wave‐dominated and fluvial‐dominated nearshore at the top. Multiple small transgressive–regressive sedimentation cycles have an average 21 ka duration, likely related to Milankovitch cyclicity. Unusually abundant soft‐sediment deformation structures and landslides are the sedimentary responses to frequent earthquakes during the most active phase of rift subsidence. The overall succession shows changes from a shallowing‐up balanced‐filled to an overfilled lacustrine basin. The chemical weathering intensity index and the Th/K ratio show a longer‐term trend from dry and cool conditions low in the section to humid and warm conditions near the top, with rapid change in the transition period. The section records the peak of the global mid‐Tournaisian carbon isotope excursion and the corresponding cooling event (354 Ma to approximately 351 Ma). The sedimentary succession is a response to long‐term and short‐term climatic cycles influencing lake level and sediment supply during the time of maximum rift basin subsidence recorded by the soft‐sediment deformation structures.","PeriodicalId":21838,"journal":{"name":"Sedimentology","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2023-11-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135191253","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Romain Grime, Philippe Sorrel, Kevin Boulesteix, Sebastien Landru, Alexandre Bouche, Tim Rice, Benjamin Kyle Bowlin, Bernard Pittet
ABSTRACT The mechanisms controlling the stacking patterns of deep‐water turbidite lobes are currently open to a wide range of interpretations. A study of Turonian to Coniacian turbidite lobe complexes in the greater Marulk area (Dønna Terrace, Norwegian Sea) was undertaken to examine the balance and respective influences of various controlling factors using a large sediment core, well‐log and seismic dataset. A four‐tiered lobe hierarchy is described based on a detailed sedimentological study of three Cretaceous turbidite lobe systems, involving a variety of sedimentary processes and flow regimes. The inferred depositional stacking patterns were then used to identify autogenic and allogenic forcings on the large‐scale depositional architecture of turbidite lobes. Autogenic processes (best observed in core data) control the self‐regulation of sediment dispersal and the broad evolution of lobe sub‐environments. Conversely, allogenic forcings (best observed in well‐log data) regulate axial migration within the turbidite lobe succession, and control sediment pulses and ultimately the general evolutionary trend of the turbidite lobe complex. Beyond this, an updated approach is proposed here aiming at deciphering autogenic‐dominant and allogenic‐dominant processes at different hierarchical levels in both confined and unconfined turbidite lobe deposits, which may help with assigning appropriate inputs for geomodels for an improved understanding of the internal and external controls on lobe depositional architecture. It is advocated that this approach may eventually be used in other depositional systems, such as in deltaic complexes from coastal settings, both in actual and ancient sediments.
{"title":"Autogenic and allogenic controls on turbidite lobe stacking pattern and architecture: The case of the Turonian to Coniacian deep‐water turbidite lobe complexes (Dønna Terrace, offshore <scp>Mid‐Norway</scp>)","authors":"Romain Grime, Philippe Sorrel, Kevin Boulesteix, Sebastien Landru, Alexandre Bouche, Tim Rice, Benjamin Kyle Bowlin, Bernard Pittet","doi":"10.1111/sed.13141","DOIUrl":"https://doi.org/10.1111/sed.13141","url":null,"abstract":"ABSTRACT The mechanisms controlling the stacking patterns of deep‐water turbidite lobes are currently open to a wide range of interpretations. A study of Turonian to Coniacian turbidite lobe complexes in the greater Marulk area (Dønna Terrace, Norwegian Sea) was undertaken to examine the balance and respective influences of various controlling factors using a large sediment core, well‐log and seismic dataset. A four‐tiered lobe hierarchy is described based on a detailed sedimentological study of three Cretaceous turbidite lobe systems, involving a variety of sedimentary processes and flow regimes. The inferred depositional stacking patterns were then used to identify autogenic and allogenic forcings on the large‐scale depositional architecture of turbidite lobes. Autogenic processes (best observed in core data) control the self‐regulation of sediment dispersal and the broad evolution of lobe sub‐environments. Conversely, allogenic forcings (best observed in well‐log data) regulate axial migration within the turbidite lobe succession, and control sediment pulses and ultimately the general evolutionary trend of the turbidite lobe complex. Beyond this, an updated approach is proposed here aiming at deciphering autogenic‐dominant and allogenic‐dominant processes at different hierarchical levels in both confined and unconfined turbidite lobe deposits, which may help with assigning appropriate inputs for geomodels for an improved understanding of the internal and external controls on lobe depositional architecture. It is advocated that this approach may eventually be used in other depositional systems, such as in deltaic complexes from coastal settings, both in actual and ancient sediments.","PeriodicalId":21838,"journal":{"name":"Sedimentology","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2023-10-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"136133496","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
M. Namik Çağatay, Emre Damci, Germain Bayon, Mustafa Sari
ABSTRACT Lake Van, the world's largest alkaline lake, hosts some of the largest microbialite towers worldwide, which are considered as modern analogues of ancient stromatolites. This study investigates the links between microbialite evolution, geology, climate and hydrology, and the role of biotic and abiotic processes in microbialite growth and morphology. For these objectives, the northern shelf of Lake Van was surveyed by subbottom seismic profiling and diving, and two 9 m and 15 m high microbialite chimneys were sampled at 25 m water depth. Samples were analysed for stable oxygen and carbon isotopes, X‐ray diffractometry, scanning electron microscopy and U/Th age dating. Lake Van microbialites precipitate wherever focused Ca‐rich groundwater flows to the lake floor to mix with alkaline lake water. Variable columnar, conical and branching morphologies of the microbialites indicate various processes of formation by groundwater channelling within the chimneys. Collectively, our data suggest that the microbialite chimneys have formed within the last millennium, most likely during the warm and humid Medieval Climate Anomaly ( ca AD 800–1300), when lake level rose approximately to the present level due to enhanced Inputs of riverine Ca‐rich freshwater and groundwater. Our new scanning electron microscopy observations indicate that the internal structure of the microbialites below the outer cyanobacteria‐covered crust is constructed by calcified filaments, globular aggregates and nanocrystals of algal, cyanobacterial and heterobacterial origins and inorganically precipitated prismatic calcite crystals. These textural features, together with dive observations, clearly demonstrate the important role of inorganic carbonate precipitation at sites of groundwater discharge, followed by cyanobacteria and algal mucilage deposition and microbially meditated calcification in the photic zone in the rapid growth of the microbialite chimneys. Considering the close similarities of some textures with those of ancient stromatolites and meteorites, the results of this study provide new insights into the environmental conditions associated with stromatolite formation and extra‐terrestrial life evolution.
{"title":"Microbialites on the northern shelf of Lake Van, eastern Türkiye: Morphology, texture, stable isotope geochemistry and age","authors":"M. Namik Çağatay, Emre Damci, Germain Bayon, Mustafa Sari","doi":"10.1111/sed.13153","DOIUrl":"https://doi.org/10.1111/sed.13153","url":null,"abstract":"ABSTRACT Lake Van, the world's largest alkaline lake, hosts some of the largest microbialite towers worldwide, which are considered as modern analogues of ancient stromatolites. This study investigates the links between microbialite evolution, geology, climate and hydrology, and the role of biotic and abiotic processes in microbialite growth and morphology. For these objectives, the northern shelf of Lake Van was surveyed by subbottom seismic profiling and diving, and two 9 m and 15 m high microbialite chimneys were sampled at 25 m water depth. Samples were analysed for stable oxygen and carbon isotopes, X‐ray diffractometry, scanning electron microscopy and U/Th age dating. Lake Van microbialites precipitate wherever focused Ca‐rich groundwater flows to the lake floor to mix with alkaline lake water. Variable columnar, conical and branching morphologies of the microbialites indicate various processes of formation by groundwater channelling within the chimneys. Collectively, our data suggest that the microbialite chimneys have formed within the last millennium, most likely during the warm and humid Medieval Climate Anomaly ( ca AD 800–1300), when lake level rose approximately to the present level due to enhanced Inputs of riverine Ca‐rich freshwater and groundwater. Our new scanning electron microscopy observations indicate that the internal structure of the microbialites below the outer cyanobacteria‐covered crust is constructed by calcified filaments, globular aggregates and nanocrystals of algal, cyanobacterial and heterobacterial origins and inorganically precipitated prismatic calcite crystals. These textural features, together with dive observations, clearly demonstrate the important role of inorganic carbonate precipitation at sites of groundwater discharge, followed by cyanobacteria and algal mucilage deposition and microbially meditated calcification in the photic zone in the rapid growth of the microbialite chimneys. Considering the close similarities of some textures with those of ancient stromatolites and meteorites, the results of this study provide new insights into the environmental conditions associated with stromatolite formation and extra‐terrestrial life evolution.","PeriodicalId":21838,"journal":{"name":"Sedimentology","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2023-10-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"136135220","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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