Ariana Osman, Ronald J. Steel, Ryan Ramsook, And Cornel Olariu
Compound clinoforms are well-recognized in modern large muddy deltas and in some ancient deltas, but there is still a lack of understanding regarding their lithology variations and the process by which sand from the shoreline clinothem reaches the subaqueous clinothem foresets that are sometimes 100 km away. Net-to-gross, thickness and facies association evaluation show overall coarsening-upward through a 191 m thick exposure of the late Pliocene Orinoco, Lower Morne L'Enfer Formation, with a distinct tripartite lithology distribution. The subaqueous clinothem records a lower, relatively muddy coarsening-upward interval, 112 m thick, with net-to-gross increasing from zero to 60%. On the lower delta front, zero net sand units show graded beds of silt and mud with occasional spring–neap rhythmites, strongly suggesting gravity flows influenced by tidal currents. These foreset beds are overlain by structureless very fine sand, interbedded with deformed wavy to lenticular, grey fluid mud layers that rapidly accumulated near the subaqueous clinoform rollover point. The tidally dominated subaqueous platform (subaqueous delta topset), 1 to 4 m thick, shows zero net sand units with anomalously high mud content, >70%, due to the high near-bed suspended sediment concentration of externally derived fluid mud that migrated littorally alongshore from the Amazon Delta. The interaction of freshwater river flood discharge with fluid-mud banks gave rise to density stratification with fine sand hypopycnally dispersing as a turbulent layer above the denser fluid-mud carpet. The shoreline clinothem (<8 m thick) has high net-to-gross, >85%, attributed to winnowing of sediment by waves and tides. Utilizing net-to-gross trends and facies changes provide useful criteria to identify compound clinoforms in the rock record. The Orinoco Delta deposits, however, are unusual, since fluid mud hinders sand deposition on the platform, allowing for easy identification of platform facies and a clear distinction between the subaqueous and shoreline clinothem in outcrop.
{"title":"Impact of wave, tides, and fluid mud on fluvial discharge across a compound clinoform (Pliocene Orinoco Delta)","authors":"Ariana Osman, Ronald J. Steel, Ryan Ramsook, And Cornel Olariu","doi":"10.1111/sed.13167","DOIUrl":"https://doi.org/10.1111/sed.13167","url":null,"abstract":"Compound clinoforms are well-recognized in modern large muddy deltas and in some ancient deltas, but there is still a lack of understanding regarding their lithology variations and the process by which sand from the shoreline clinothem reaches the subaqueous clinothem foresets that are sometimes 100 km away. Net-to-gross, thickness and facies association evaluation show overall coarsening-upward through a 191 m thick exposure of the late Pliocene Orinoco, Lower Morne L'Enfer Formation, with a distinct tripartite lithology distribution. The <i>subaqueous clinothem</i> records a lower, relatively muddy coarsening-upward interval, 112 m thick, with net-to-gross increasing from zero to 60%. On the lower delta front, zero net sand units show graded beds of silt and mud with occasional spring–neap rhythmites, strongly suggesting gravity flows influenced by tidal currents. These foreset beds are overlain by structureless very fine sand, interbedded with deformed wavy to lenticular, grey fluid mud layers that rapidly accumulated near the subaqueous clinoform rollover point. The tidally dominated <i>subaqueous platform</i> (subaqueous delta topset), 1 to 4 m thick, shows zero net sand units with anomalously high mud content, >70%, due to the high near-bed suspended sediment concentration of externally derived fluid mud that migrated littorally alongshore from the Amazon Delta. The interaction of freshwater river flood discharge with fluid-mud banks gave rise to density stratification with fine sand hypopycnally dispersing as a turbulent layer above the denser fluid-mud carpet. The <i>shoreline clinothem</i> (<8 m thick) has high net-to-gross, >85%, attributed to winnowing of sediment by waves and tides. Utilizing net-to-gross trends and facies changes provide useful criteria to identify compound clinoforms in the rock record. The Orinoco Delta deposits, however, are unusual, since fluid mud hinders sand deposition on the platform, allowing for easy identification of platform facies and a clear distinction between the subaqueous and shoreline clinothem in outcrop.","PeriodicalId":21838,"journal":{"name":"Sedimentology","volume":"10 1","pages":""},"PeriodicalIF":3.5,"publicationDate":"2023-11-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"138529987","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}
Alexandre Normandeau, Lynn T. Dafoe, Michael Z. Li, D. Calvin Campbell, Kimberley A. Jenner
The evolution of submarine canyons is primarily controlled by turbidity currents, which erode and fill them over time; however, many other hydrodynamic currents operate within canyons. Bottom currents from these other hydrodynamic processes, including internal tides can be dominant processes, but their deposits are seldom recognized in sediment cores or the rock record. This study combines autonomous underwater vehicle swath bathymetry imagery and sub-bottom profiles, high-resolution sediment core analyses (X-ray imagery and thin sections), and previously collected seabed video and flow measurements within Logan Canyon head (eastern Canada) to provide a detailed, modern record of facies associated with hydrodynamic processes in a canyon head. These results suggest that bottom currents are responsible for maintaining gullies on canyon sidewalls and an axial channel on the canyon floor. Thin sections of sediment cores reveal that muddy sand in the canyon head consists of mud aggregates and silt and fine-grained sand, both behaving similarly in terms of flow dynamics. Three facies are present at macro-scale and micro-scale: laminated, partially laminated and bioturbated sandy mud. Sedimentary structures include rhythmic sand and mud aggregate couplets, planar to wavy laminations, current ripple cross-laminations and fining-upward successions, which is attributed to bottom currents induced by internal tides. Bioturbated facies, characterized by discrete biogenic structures and cross-cutting relationships, predominate and overprint a mottled background. A mottled bioturbation fabric also alternates with or locally disrupts layering within the partially laminated facies. Internal tide currents, capable of bedload transport and forming ripples, were measured during a monitoring period in the canyon head, followed by rapid re-establishment of benthos and associated biogenic structures, confirming the core interpretations. Preservation of sedimentary facies associated with these internal tides occurs when the sedimentation rate outpaces the rate of bioturbation, likely during stormier conditions on the shelf. These results represent observations of sedimentary facies associated with modern bottom currents and internal tides, and can be used to interpret similar occurrences within the rock record.
{"title":"Sedimentary record of bottom currents and internal tides in a modern highstand submarine canyon head","authors":"Alexandre Normandeau, Lynn T. Dafoe, Michael Z. Li, D. Calvin Campbell, Kimberley A. Jenner","doi":"10.1111/sed.13165","DOIUrl":"https://doi.org/10.1111/sed.13165","url":null,"abstract":"The evolution of submarine canyons is primarily controlled by turbidity currents, which erode and fill them over time; however, many other hydrodynamic currents operate within canyons. Bottom currents from these other hydrodynamic processes, including internal tides can be dominant processes, but their deposits are seldom recognized in sediment cores or the rock record. This study combines autonomous underwater vehicle swath bathymetry imagery and sub-bottom profiles, high-resolution sediment core analyses (X-ray imagery and thin sections), and previously collected seabed video and flow measurements within Logan Canyon head (eastern Canada) to provide a detailed, modern record of facies associated with hydrodynamic processes in a canyon head. These results suggest that bottom currents are responsible for maintaining gullies on canyon sidewalls and an axial channel on the canyon floor. Thin sections of sediment cores reveal that muddy sand in the canyon head consists of mud aggregates and silt and fine-grained sand, both behaving similarly in terms of flow dynamics. Three facies are present at macro-scale and micro-scale: laminated, partially laminated and bioturbated sandy mud. Sedimentary structures include rhythmic sand and mud aggregate couplets, planar to wavy laminations, current ripple cross-laminations and fining-upward successions, which is attributed to bottom currents induced by internal tides. Bioturbated facies, characterized by discrete biogenic structures and cross-cutting relationships, predominate and overprint a mottled background. A mottled bioturbation fabric also alternates with or locally disrupts layering within the partially laminated facies. Internal tide currents, capable of bedload transport and forming ripples, were measured during a monitoring period in the canyon head, followed by rapid re-establishment of benthos and associated biogenic structures, confirming the core interpretations. Preservation of sedimentary facies associated with these internal tides occurs when the sedimentation rate outpaces the rate of bioturbation, likely during stormier conditions on the shelf. These results represent observations of sedimentary facies associated with modern bottom currents and internal tides, and can be used to interpret similar occurrences within the rock record.","PeriodicalId":21838,"journal":{"name":"Sedimentology","volume":"24 1","pages":""},"PeriodicalIF":3.5,"publicationDate":"2023-11-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"138529988","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}
Distinguishing between shallow-water delta and fluvial fan deposits in the subsurface of lacustrine basins is challenging due to their similar depositional characteristics and distribution patterns. This study focuses on the Middle Jurassic Shaximiao Formation in the central Sichuan Basin using core observations, seismic analyses, petrology analyses, zircon analyses, palaeoclimate indicators and palaeocurrent analyses to address this issue. Fifteen sedimentary lithofacies and eight lithofacies associations were established, corresponding to channelized fluvial deposits, non-channelized fluvial deposits and shallow-water delta deposits. Shallow-water deltas are dominated by channels and mouth-bar complexes with grey, red and green interbedded mudstone. Shingled seismic reflection, green mud clasts, small burrows and wave ripples are common with occasional palaeosols. Fluvial fans are dominated by channels and crevasse-splays with pink colour and accompanied by red coloured floodplain deposits. Bright spot seismic reflection, red mud clasts, big burrows, current ripples and palaeosols are common. The increased uplift of the Dabashan Mountains controls the palaeocurrent direction, promoting the evolution from a shallow-water delta in relatively humid environments to a fluvial fan in relatively arid environments. The channel widths in shallow-water deltas are wider than those in fluvial fans, whereas the opposite applies for the channel amalgamation rate. Highly frequent channel-width variations are controlled by short-cycle climate fluctuation, corresponding to chemical index of alteration value fluctuations in different sandstone groups. The channel width in the relatively humid environments is wider than those in arid environments for both shallow-water deltas and fluvial fans. It is likely that the sedimentary evolution from shallow-water deltas to fluvial fans is relatively common in lacustrine basins in relatively arid environments with wide and gentle slope landforms.
{"title":"Evolution from shallow-water deltas to fluvial fans in lacustrine basins: A case study from the Middle Jurassic Shaximiao Formation in the central Sichuan Basin, China","authors":"Tian Yang, Xiaofang Li, Yu Yang, Long Wen, Zhenglin Cao, Xiaojun Wang, Shaomin Zhang, Qiangshao Liang","doi":"10.1111/sed.13163","DOIUrl":"https://doi.org/10.1111/sed.13163","url":null,"abstract":"Distinguishing between shallow-water delta and fluvial fan deposits in the subsurface of lacustrine basins is challenging due to their similar depositional characteristics and distribution patterns. This study focuses on the Middle Jurassic Shaximiao Formation in the central Sichuan Basin using core observations, seismic analyses, petrology analyses, zircon analyses, palaeoclimate indicators and palaeocurrent analyses to address this issue. Fifteen sedimentary lithofacies and eight lithofacies associations were established, corresponding to channelized fluvial deposits, non-channelized fluvial deposits and shallow-water delta deposits. Shallow-water deltas are dominated by channels and mouth-bar complexes with grey, red and green interbedded mudstone. Shingled seismic reflection, green mud clasts, small burrows and wave ripples are common with occasional palaeosols. Fluvial fans are dominated by channels and crevasse-splays with pink colour and accompanied by red coloured floodplain deposits. Bright spot seismic reflection, red mud clasts, big burrows, current ripples and palaeosols are common. The increased uplift of the Dabashan Mountains controls the palaeocurrent direction, promoting the evolution from a shallow-water delta in relatively humid environments to a fluvial fan in relatively arid environments. The channel widths in shallow-water deltas are wider than those in fluvial fans, whereas the opposite applies for the channel amalgamation rate. Highly frequent channel-width variations are controlled by short-cycle climate fluctuation, corresponding to chemical index of alteration value fluctuations in different sandstone groups. The channel width in the relatively humid environments is wider than those in arid environments for both shallow-water deltas and fluvial fans. It is likely that the sedimentary evolution from shallow-water deltas to fluvial fans is relatively common in lacustrine basins in relatively arid environments with wide and gentle slope landforms.","PeriodicalId":21838,"journal":{"name":"Sedimentology","volume":"4 1","pages":""},"PeriodicalIF":3.5,"publicationDate":"2023-11-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"138509496","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}
Stephanie Neuhuber, Susanne Gier, Erich Draganits, Peter Steier, Monika Bolka, Franz Ottner, Christoph Spötl, Dorothee Hippler, Patrick Meister
Authigenic Mg-calcite and dolomite are frequently observed in restricted, evaporative environments, such as lagoon or lake systems, but their formation is difficult to capture due to slow growth rates. Lake Neusiedl, an alkaline and subhaline lake with a mean water depth of 0.7 m in Austria, offers a natural system to study the precipitation of Ca-Mg-carbonate phases, which occur as fine-grained, unconsolidated and largely homogenized mud. To elucidate the timing and formation mechanisms of these authigenic carbonate phases, the mineralogical and isotopic composition and radiocarbon age of different sediment grain-size fractions from <0.2 to >3.0 μm were analysed. X-ray diffraction analyses show two broad peaks of Mg-calcite and protodolomite (lacking ordering peaks), suggesting that the carbonates are authigenic rather than detrital in origin. Calibrated carbon-14 ages range between 200 cal yr BP and 3700 cal yr BP. The linear correlation of age and grain size suggests a very slow growth rate of single crystals of 0.23 to 0.60 μm/ka. These rates suggest an extremely slow sedimentation rate in a shallow lake that existed during most of the Holocene. The higher abundance of protodolomite in older grain fractions, in contrast to the presence of high-Mg calcite in the youngest fractions, suggests a growth succession where high-Mg calcite develops first and subsequently transforms into protodolomite. Much higher ages of 6 cal ka BP to 15 cal ka BP are measured in carbonates of lake deposits exposed on land, in a section northwest of the recent lake, suggesting a growth rate of those carbonate minerals of 0.13 μm/ka. These time constraints further suggest that some carbonate grains could already have nucleated from lake water before or during the last glacial maximum, although under slightly different hydrochemical conditions.
自生镁方解石和白云石经常在有限的蒸发环境中观察到，如泻湖或湖泊系统，但由于生长速度缓慢，它们的形成很难捕捉。Neusiedl湖位于奥地利境内，平均水深0.7 m，为研究ca - mg -碳酸盐岩相的沉淀提供了一个自然系统，ca - mg -碳酸盐岩相以细粒、松散、均质化的泥浆形式存在。为了阐明这些自生碳酸盐相的形成时间和形成机制，分析了<0.2 ~ >3.0 μm不同沉积物粒度组分的矿物学、同位素组成和放射性碳年龄。x射线衍射分析显示镁方解石和原白云岩有两个宽峰(无序峰)，表明碳酸盐为自生而非碎屑成因。校正后的碳14年龄范围在200至3700 cal - year BP之间。年龄与晶粒尺寸的线性关系表明单晶生长速率非常缓慢，为0.23 ~ 0.60 μm/ka。这些速率表明，在全新世的大部分时间里，一个浅湖的沉积速率极其缓慢。在较老的颗粒组分中原白云石的丰度较高，而在较年轻的颗粒组分中则存在高镁方解石，这表明了一个生长演替过程，即高镁方解石首先发育，随后转化为原白云石。在新近形成的湖泊西北剖面上，裸露在陆地上的湖泊沉积物碳酸盐的年龄在6 ~ 15 cal ka BP之间，表明这些碳酸盐矿物的生长速率为0.13 μm/ka。这些时间限制进一步表明，在末次极大期之前或期间，一些碳酸盐颗粒可能已经从湖水中成核，尽管水化学条件略有不同。
{"title":"Radiocarbon ages of microcrystalline authigenic carbonate in Lake Neusiedl (Austria) suggest millennial-scale growth of Mg-calcite and protodolomite","authors":"Stephanie Neuhuber, Susanne Gier, Erich Draganits, Peter Steier, Monika Bolka, Franz Ottner, Christoph Spötl, Dorothee Hippler, Patrick Meister","doi":"10.1111/sed.13161","DOIUrl":"https://doi.org/10.1111/sed.13161","url":null,"abstract":"Authigenic Mg-calcite and dolomite are frequently observed in restricted, evaporative environments, such as lagoon or lake systems, but their formation is difficult to capture due to slow growth rates. Lake Neusiedl, an alkaline and subhaline lake with a mean water depth of 0.7 m in Austria, offers a natural system to study the precipitation of Ca-Mg-carbonate phases, which occur as fine-grained, unconsolidated and largely homogenized mud. To elucidate the timing and formation mechanisms of these authigenic carbonate phases, the mineralogical and isotopic composition and radiocarbon age of different sediment grain-size fractions from <0.2 to >3.0 μm were analysed. X-ray diffraction analyses show two broad peaks of Mg-calcite and protodolomite (lacking ordering peaks), suggesting that the carbonates are authigenic rather than detrital in origin. Calibrated carbon-14 ages range between 200 cal yr BP and 3700 cal yr BP. The linear correlation of age and grain size suggests a very slow growth rate of single crystals of 0.23 to 0.60 μm/ka. These rates suggest an extremely slow sedimentation rate in a shallow lake that existed during most of the Holocene. The higher abundance of protodolomite in older grain fractions, in contrast to the presence of high-Mg calcite in the youngest fractions, suggests a growth succession where high-Mg calcite develops first and subsequently transforms into protodolomite. Much higher ages of 6 cal ka BP to 15 cal ka BP are measured in carbonates of lake deposits exposed on land, in a section northwest of the recent lake, suggesting a growth rate of those carbonate minerals of 0.13 μm/ka. These time constraints further suggest that some carbonate grains could already have nucleated from lake water before or during the last glacial maximum, although under slightly different hydrochemical conditions.","PeriodicalId":21838,"journal":{"name":"Sedimentology","volume":"71 1","pages":""},"PeriodicalIF":3.5,"publicationDate":"2023-11-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"138530004","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}
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":"5 2","pages":""},"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":"6 3","pages":""},"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":"5 9","pages":""},"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":"4 6","pages":""},"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":"2 6","pages":"0"},"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}
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