Daniel F. Cupertino, Camila Wense Ramnani, Michael D. Vanden Berg, Stanley M. Awramik
ABSTRACT Authigenic magnesium‐clays have been observed and documented in the Green River Formation, specifically as ooidal stevensite grains. Magnesian clays are a valuable proxy for reconstructing shallow‐water, saline‐alkaline lake palaeoenvironments due to their responses to chemical changes. Magnesium‐rich clay minerals are relatively common components in modern and ancient lake systems. A rare interaction of lacustrine magnesian clays, microbialites, carbonates and volcanoclastic deposits of the Eocene Green River Formation crop out in Sanpete Valley, Utah, USA. The characterization of this interaction, Mg‐rich clay and carbonate minerals genesis, the environmental controls on Mg‐rich clay minerals distribution and accumulation is still poorly understood. This study has identified various species of Mg‐clay minerals (stevensite, mixed‐layer kerolite‐stevensite, and sepiolite), along with calcite and dolomite, found in four Mg‐clay‐bearing lithofacies: (i) Mg‐clay stromatolites; (ii) Mg‐clay arenites; (iii) Mg‐claystone; and (iv) intraclastic Mg‐clay hybrid arenites and conglomerates. Magnesium‐clay bearing rocks from the Sanpete Valley area were deposited in a south‐western, shallow embayment of Eocene Lake Uinta along the margin of the Sevier fold and thrust belt. Sanpete Valley´s Mg‐clay‐bearing section shows syngenetic mineralogical paragenesis with neoformation of magnesian clays accompanied by calcite and silica. Regional chronostratigraphic correlation of Sanpete Valley´s Mg‐clay‐bearing section with the Uinta Basin was made by zircon U–Pb dating (laser ablation – inductively coupled plasma – mass spectrometry) of two tuff beds. Stevensite and kerolite are precipitated under very specific conditions. This study presents a depositional model, considering evidence from the authigenic mineralogy, facies, fossil evidence, and basin context. All these findings allow a comprehensive analysis of the lithostratigraphic and chemostratigraphic evolution of this isolated bay system, as well as texture classification. This study provides analogue for detailed correlation and comparison to other basins containing similar Mg‐clay and microbialite‐bearing deposits.
{"title":"Formation of magnesium‐clay in a lacustrine microbialite‐bearing carbonate deposit, Eocene Green River Formation, Sanpete County, Utah","authors":"Daniel F. Cupertino, Camila Wense Ramnani, Michael D. Vanden Berg, Stanley M. Awramik","doi":"10.1111/sed.13136","DOIUrl":"https://doi.org/10.1111/sed.13136","url":null,"abstract":"ABSTRACT Authigenic magnesium‐clays have been observed and documented in the Green River Formation, specifically as ooidal stevensite grains. Magnesian clays are a valuable proxy for reconstructing shallow‐water, saline‐alkaline lake palaeoenvironments due to their responses to chemical changes. Magnesium‐rich clay minerals are relatively common components in modern and ancient lake systems. A rare interaction of lacustrine magnesian clays, microbialites, carbonates and volcanoclastic deposits of the Eocene Green River Formation crop out in Sanpete Valley, Utah, USA. The characterization of this interaction, Mg‐rich clay and carbonate minerals genesis, the environmental controls on Mg‐rich clay minerals distribution and accumulation is still poorly understood. This study has identified various species of Mg‐clay minerals (stevensite, mixed‐layer kerolite‐stevensite, and sepiolite), along with calcite and dolomite, found in four Mg‐clay‐bearing lithofacies: (i) Mg‐clay stromatolites; (ii) Mg‐clay arenites; (iii) Mg‐claystone; and (iv) intraclastic Mg‐clay hybrid arenites and conglomerates. Magnesium‐clay bearing rocks from the Sanpete Valley area were deposited in a south‐western, shallow embayment of Eocene Lake Uinta along the margin of the Sevier fold and thrust belt. Sanpete Valley´s Mg‐clay‐bearing section shows syngenetic mineralogical paragenesis with neoformation of magnesian clays accompanied by calcite and silica. Regional chronostratigraphic correlation of Sanpete Valley´s Mg‐clay‐bearing section with the Uinta Basin was made by zircon U–Pb dating (laser ablation – inductively coupled plasma – mass spectrometry) of two tuff beds. Stevensite and kerolite are precipitated under very specific conditions. This study presents a depositional model, considering evidence from the authigenic mineralogy, facies, fossil evidence, and basin context. All these findings allow a comprehensive analysis of the lithostratigraphic and chemostratigraphic evolution of this isolated bay system, as well as texture classification. This study provides analogue for detailed correlation and comparison to other basins containing similar Mg‐clay and microbialite‐bearing deposits.","PeriodicalId":21838,"journal":{"name":"Sedimentology","volume":"08 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-09-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135878007","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}
A. Nolting, C. Kerans, F. Fernandez-ibanez, S. Fullmer, P. Moore, C. Breithaupt, Stephanie LeBlanc, M. Dafov, Eric Bunge, J. Gulley
The Bahamian Archipelago has been the subject of extensive studies of stratigraphy, carbonate island morphology and diagenetic overprinting for many decades. A recently‐acquired dataset comprised of high‐resolution light detection and ranging, tightly spaced cored boreholes with image logs, thin sections, porosity and permeability measurements, and isotopic geochemical analyses provides a unique opportunity to perform detailed sequence stratigraphic analysis. This multi‐faceted study first establishes a new high‐resolution sequence stratigraphic framework for the Sandy Point area of San Salvador Island, encompassing six unconformity bound sequences (exposure surfaces) representing varying lengths of missing time. The stratigraphically lowest sequence is Late Pliocene in age and is dominated by reef facies capped by an extensive laminar caliche that represents 1.5 million years of exposure. The overlying Early Pleistocene is split into two sequences, EP1 and EP2, which are both dominated by low‐energy subtidal facies. The upper three sequences are tied to the Marine Isotope Stage 11, 9 and 5e interglacials, and are distinctly different in facies composition and architecture, being dominated by higher energy facies distributed in a more complex mosaic. The new stratigraphic framework highlights significant changes in depositional style and facies architecture that can be linked to increasing sea‐level amplitude oscillations and greater climate gradient at the Mid Pleistocene Transition. The well‐constrained framework is then used to provide key context for observed complex diagenetic evolution through repeated sea‐level inundation and subaerial exposure. These results suggest that well‐developed subaerial exposure surfaces drive increases in non‐matrix features in the subsequent stratigraphic package following exposure as the well‐cemented exposure surface acts to concentrate fluid flow and dissolution. Integration of non‐matrix features within this framework highlights the importance of dissolution/cementation patterns on formation of these modified unconformity surfaces for focusing later meteoric diagenesis and creating enhanced fluid flow pathways for continued multicyclic diagenetic events.
{"title":"Three‐dimensional stratigraphic architecture, secondary pore system development and the Middle Pleistocene transition, Sandy Point area, San Salvador Island, Bahamas","authors":"A. Nolting, C. Kerans, F. Fernandez-ibanez, S. Fullmer, P. Moore, C. Breithaupt, Stephanie LeBlanc, M. Dafov, Eric Bunge, J. Gulley","doi":"10.1111/sed.13134","DOIUrl":"https://doi.org/10.1111/sed.13134","url":null,"abstract":"The Bahamian Archipelago has been the subject of extensive studies of stratigraphy, carbonate island morphology and diagenetic overprinting for many decades. A recently‐acquired dataset comprised of high‐resolution light detection and ranging, tightly spaced cored boreholes with image logs, thin sections, porosity and permeability measurements, and isotopic geochemical analyses provides a unique opportunity to perform detailed sequence stratigraphic analysis. This multi‐faceted study first establishes a new high‐resolution sequence stratigraphic framework for the Sandy Point area of San Salvador Island, encompassing six unconformity bound sequences (exposure surfaces) representing varying lengths of missing time. The stratigraphically lowest sequence is Late Pliocene in age and is dominated by reef facies capped by an extensive laminar caliche that represents 1.5 million years of exposure. The overlying Early Pleistocene is split into two sequences, EP1 and EP2, which are both dominated by low‐energy subtidal facies. The upper three sequences are tied to the Marine Isotope Stage 11, 9 and 5e interglacials, and are distinctly different in facies composition and architecture, being dominated by higher energy facies distributed in a more complex mosaic. The new stratigraphic framework highlights significant changes in depositional style and facies architecture that can be linked to increasing sea‐level amplitude oscillations and greater climate gradient at the Mid Pleistocene Transition. The well‐constrained framework is then used to provide key context for observed complex diagenetic evolution through repeated sea‐level inundation and subaerial exposure. These results suggest that well‐developed subaerial exposure surfaces drive increases in non‐matrix features in the subsequent stratigraphic package following exposure as the well‐cemented exposure surface acts to concentrate fluid flow and dissolution. Integration of non‐matrix features within this framework highlights the importance of dissolution/cementation patterns on formation of these modified unconformity surfaces for focusing later meteoric diagenesis and creating enhanced fluid flow pathways for continued multicyclic diagenetic events.","PeriodicalId":21838,"journal":{"name":"Sedimentology","volume":"25 1","pages":""},"PeriodicalIF":3.5,"publicationDate":"2023-08-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"81109218","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}
Wenchao Shen, L. Shao, Qianyu Zhou, Jinshui Liu, K. Eriksson, Shilong Kang, R. Steel
The Eocene Pinghu Formation in the Xihu Depression of the East China Sea Shelf preserves mixed‐process deltaic deposits and contains a large number of thin coal seams. This study improves the prediction of coal seam occurrences based on facies distribution and stratigraphic architecture models of deltaic deposits, using core and wireline log datasets. Sedimentological analysis reveals four facies associations, which represent delta plain (including distributary channels and interdistributary bays), delta front, prodelta and tidal flat. These facies associations reflect and preserve the interaction of fluvial and marine processes. Delta‐plain and delta‐front deposits record progressively greater tidal influences when traced southwards. Well‐log correlations show that coal‐forming mires on the tide‐influenced lower delta plain were relatively favourable for peat accumulation because the stability of the tidal channels lead to a stable platform for peat accumulation on the lower delta plain. The temporal and spatial distribution of coal seams is a function of both autogenic and allogenic responses to forcing. Increased probability of frequent changes in subsidence rates and sea‐level in an active tectonic setting and erosion by channels resulted in thin single‐layer coal seams (mostly 0.5 to 1.0 m). Autogenic processes (for example, delta growth and delta lobe switching) played a significant role in the areal distribution, lateral variation in thickness (ranging from 3 to 71 m) and large cumulative thicknesses (up to 71 m) of coal seams. A general vertical decrease in coal seam thickness likely records a cooling palaeoclimate during deposition of the Pinghu Formation. By comparing delta plain processes to favourable environments of peat accumulation in modern systems with favourable mineralogical, chemical and physical conditions, it can be concluded that: (i) relatively few and discontinuous coal seams developed on the tide‐dominated delta plain generated; (ii) laterally discontinuous and ribbon‐shaped coal seams developed in tide‐influenced deltas; whereas (iii) coal seams formed in river‐dominated deltaic environments have better lateral continuity.
{"title":"The role of fluvial and tidal currents on coal accumulation in a mixed‐energy deltaic setting: Pinghu Formation, Xihu Depression, East China Sea Shelf Basin","authors":"Wenchao Shen, L. Shao, Qianyu Zhou, Jinshui Liu, K. Eriksson, Shilong Kang, R. Steel","doi":"10.1111/sed.13133","DOIUrl":"https://doi.org/10.1111/sed.13133","url":null,"abstract":"The Eocene Pinghu Formation in the Xihu Depression of the East China Sea Shelf preserves mixed‐process deltaic deposits and contains a large number of thin coal seams. This study improves the prediction of coal seam occurrences based on facies distribution and stratigraphic architecture models of deltaic deposits, using core and wireline log datasets. Sedimentological analysis reveals four facies associations, which represent delta plain (including distributary channels and interdistributary bays), delta front, prodelta and tidal flat. These facies associations reflect and preserve the interaction of fluvial and marine processes. Delta‐plain and delta‐front deposits record progressively greater tidal influences when traced southwards. Well‐log correlations show that coal‐forming mires on the tide‐influenced lower delta plain were relatively favourable for peat accumulation because the stability of the tidal channels lead to a stable platform for peat accumulation on the lower delta plain. The temporal and spatial distribution of coal seams is a function of both autogenic and allogenic responses to forcing. Increased probability of frequent changes in subsidence rates and sea‐level in an active tectonic setting and erosion by channels resulted in thin single‐layer coal seams (mostly 0.5 to 1.0 m). Autogenic processes (for example, delta growth and delta lobe switching) played a significant role in the areal distribution, lateral variation in thickness (ranging from 3 to 71 m) and large cumulative thicknesses (up to 71 m) of coal seams. A general vertical decrease in coal seam thickness likely records a cooling palaeoclimate during deposition of the Pinghu Formation. By comparing delta plain processes to favourable environments of peat accumulation in modern systems with favourable mineralogical, chemical and physical conditions, it can be concluded that: (i) relatively few and discontinuous coal seams developed on the tide‐dominated delta plain generated; (ii) laterally discontinuous and ribbon‐shaped coal seams developed in tide‐influenced deltas; whereas (iii) coal seams formed in river‐dominated deltaic environments have better lateral continuity.","PeriodicalId":21838,"journal":{"name":"Sedimentology","volume":"46 1","pages":""},"PeriodicalIF":3.5,"publicationDate":"2023-08-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"74567325","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}
Fine sediment stored in the gravel bed is an important component of river systems. Current field protocols usually allow evaluation of the silt–clay fraction of fine sediment stocks only and neglect the sand fraction. This study proposes a new protocol to quantify fine sediment stocks, including the sand fraction inside the gravel bed matrix. Fine sediment stocks were sampled within patches of 0.30 m × 0.30 m on the dry gravel bed surface, separating the surface layer and the subsurface layer. The grain‐size distribution of the samples was obtained by field sieving (10 mm, 2 mm, 500 μm and 100 μm) over a bucket, using a known volume of water. The mass of the fraction below 100 μm was measured based on the concentration within the bucket. The local stocks were then integrated over the whole river reach by assigning local stocks to facies, in which fine sediment stocks were assumed to be homogeneously distributed. The methodology was applied to a 1 km long reach of the River Galabre (Southern French Alps), characterized by significant fine sediment stocks and upstream sediment input. Results from local measurements show a large amount of sand in both surface and subsurface layers. The quantity of sand can reach up to three times the quantity of silt–clay. An estimation of porosity showed that fine material may play an important role in structuring the bed, since porosity increases with increasing fine sediment content. The potential fine sediment stock that can be re‐suspended due to channel migration is found to be of the same order of magnitude as the sediment budget estimated from the measured flux in the upstream hydrometric station of the studied reach.
储存在砾石层中的细泥沙是水系的重要组成部分。目前的现场方案通常只允许评估细沉积物的粉砂粘土部分，而忽略了砂部分。本研究提出了一种新的方案来量化细粒沉积物储量，包括砾石床基质内的砂分数。在干砾石床表面0.30 m × 0.30 m的斑块内取样细粒沉积物，将表层与次表层分开。样品的粒度分布通过使用已知体积的水在桶上进行现场筛分(10 mm, 2 mm, 500 μm和100 μm)获得。根据桶内浓度测定100 μm以下馏分的质量。然后，通过将局部种群划分为相，将整个河段的局部种群进行整合，并假设细粒沉积物种群均匀分布。该方法应用于Galabre河(法国南部阿尔卑斯山脉)1公里长的河段，其特征是大量的细沉积物和上游沉积物输入。局部测量结果显示，表层和次表层都有大量的沙子。沙子的数量可以达到粉质粘土数量的三倍。孔隙度的估算表明，细粒物质可能在床的构造中起重要作用，因为孔隙度随着细粒沉积物含量的增加而增加。研究发现，由于河道迁移而可能重新悬浮的潜在细沙存量与研究河段上游水文站测量通量估算的泥沙收支具有相同的数量级。
{"title":"Estimation of fine sediment stocks in gravel bed rivers including the sand fraction","authors":"J. Deng, B. Camenen, C. Legoût, G. Nord","doi":"10.1111/sed.13132","DOIUrl":"https://doi.org/10.1111/sed.13132","url":null,"abstract":"Fine sediment stored in the gravel bed is an important component of river systems. Current field protocols usually allow evaluation of the silt–clay fraction of fine sediment stocks only and neglect the sand fraction. This study proposes a new protocol to quantify fine sediment stocks, including the sand fraction inside the gravel bed matrix. Fine sediment stocks were sampled within patches of 0.30 m × 0.30 m on the dry gravel bed surface, separating the surface layer and the subsurface layer. The grain‐size distribution of the samples was obtained by field sieving (10 mm, 2 mm, 500 μm and 100 μm) over a bucket, using a known volume of water. The mass of the fraction below 100 μm was measured based on the concentration within the bucket. The local stocks were then integrated over the whole river reach by assigning local stocks to facies, in which fine sediment stocks were assumed to be homogeneously distributed. The methodology was applied to a 1 km long reach of the River Galabre (Southern French Alps), characterized by significant fine sediment stocks and upstream sediment input. Results from local measurements show a large amount of sand in both surface and subsurface layers. The quantity of sand can reach up to three times the quantity of silt–clay. An estimation of porosity showed that fine material may play an important role in structuring the bed, since porosity increases with increasing fine sediment content. The potential fine sediment stock that can be re‐suspended due to channel migration is found to be of the same order of magnitude as the sediment budget estimated from the measured flux in the upstream hydrometric station of the studied reach.","PeriodicalId":21838,"journal":{"name":"Sedimentology","volume":"19 1","pages":""},"PeriodicalIF":3.5,"publicationDate":"2023-08-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"74011770","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}
{"title":"Erratum to Marine carbonate factories: Review and update","authors":"","doi":"10.1111/sed.13130","DOIUrl":"https://doi.org/10.1111/sed.13130","url":null,"abstract":"","PeriodicalId":21838,"journal":{"name":"Sedimentology","volume":"453 1","pages":""},"PeriodicalIF":3.5,"publicationDate":"2023-08-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"77027317","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}
B. Bellwald, V. Nigg, S. Fabbri, L. Becker, A. Gilli, F. Anselmetti
High‐Alpine regions are prone to a large variety of geohazards, among which earthquakes have the strongest impact on landscape and local population. Historic records indicate a moderate to high seismic activity in the northern, south‐western and central parts of Switzerland. In contrast, south‐eastern Switzerland has less historic earthquake chronicles due to the low population density, resulting in a poorly constrained seismic event catalogue. The aim of this study is to evaluate the palaeoseismic activity for south‐eastern Switzerland by using the sedimentary record of Lake Silvaplana in the Engadine Valley. A dense grid of high‐resolution two‐dimensional seismic profiles, high‐resolution bathymetry and a 10 m long sediment core from the deepest basin were used to investigate the stratigraphy of the lake sediments. The bathymetry reveals a flat basin, flanked by steep slopes to the north‐west and south‐east. The acoustic basement consists of four ridges, and gently‐dipping fans to the south‐west and north‐east. Expressions of slope failure can be identified in all domains of the lake floor and the subsurface data. Multiple coevally‐triggered chaotic mass‐flow deposits, overlain by megaturbidites with a coarse‐sand base, have been detected along ten horizons in the seismic data. The four most recent of these deposits are cored and radiocarbon dated to approximately 230, 310, 960 and 1330 cal yr BP, indicating four over‐regional seismic events that triggered large slope failures in Lake Silvaplana in the last 1400 years. Correlation with sediments of Lake Sils, Lake Como, Lake Iseo and Lake Ledro indicate within radiocarbon uncertainties a large earthquake around 1330 cal yr BP. Within their age ranges, the postulated earthquake at 310 cal yr BP (1640 CE) further correlates with a moment magnitude Mw ca 5.4 event in Ftan in 1622 CE, and the 960 cal yr BP (990 CE) earthquake correlates with a Mw ca 5.2 earthquake in Brescia in 1065 CE. Six mass‐movement deposits, also suggested to be caused by earthquakes, were not reached by the sediment core and have suggested ages between 7800 and 11300 cal yr BP. Thus, Lake Silvaplana sediments provide the first reliable record of seismic activity for the mid and Late Holocene in this region, likely related to the neotectonic activity of the Engadine Line, a major fault zone running along the main valley.
高高山地区容易发生各种地质灾害，其中地震对景观和当地人口的影响最大。历史记录表明，瑞士北部、西南部和中部地区的地震活动中度到高度。相比之下，由于人口密度低，瑞士东南部的历史地震编年史较少，导致地震事件目录约束较差。本研究的目的是利用恩加丁山谷Silvaplana湖的沉积记录来评价瑞士东南部的古地震活动。利用高分辨率二维地震剖面的密集网格、高分辨率测深和来自最深盆地的10米长的沉积物岩心来研究湖泊沉积物的地层学。水深测量显示了一个平坦的盆地，两侧是西北和东南的陡峭斜坡。声学基底由四个山脊组成，西南和东北有缓慢倾斜的扇。斜坡破坏的表达式可以在湖底和地下数据的所有域中识别出来。在地震资料中，在10个层位上发现了多个共凹触发的混沌质量流沉积，其上覆盖着粗砂基的超缓积岩。这些沉积物中最近的四个已被取心，放射性碳测年约为230、310、960和1330 calyr BP，表明在过去1400年里，四次跨区域地震事件引发了西尔瓦普拉纳湖的大规模斜坡破坏。与锡尔斯湖、科莫湖、伊塞奥湖和莱德罗湖沉积物的对比表明，在放射性碳不确定度范围内，约1330 calyr BP发生了一次大地震。在他们的年龄范围内，310 cal yr BP(公元1640年)的假定地震与1622年发生在Ftan的矩震级为Mw - 5.4级的地震进一步相关，960 cal yr BP(公元990年)的地震与1065年发生在布雷西亚的Mw - 5.2级地震相关。6个质量运动沉积物，也被认为是由地震引起的，没有被沉积物岩心到达，并且年龄在7800到11300 cal yr BP之间。因此，西尔瓦普兰湖沉积物为该地区全新世中晚期的地震活动提供了第一个可靠的记录，可能与恩加丁线的新构造活动有关，恩加丁线是沿主山谷运行的主要断裂带。
{"title":"Holocene seismic activity in south‐eastern Switzerland: Evidence from the sedimentary record of Lake Silvaplana","authors":"B. Bellwald, V. Nigg, S. Fabbri, L. Becker, A. Gilli, F. Anselmetti","doi":"10.1111/sed.13131","DOIUrl":"https://doi.org/10.1111/sed.13131","url":null,"abstract":"High‐Alpine regions are prone to a large variety of geohazards, among which earthquakes have the strongest impact on landscape and local population. Historic records indicate a moderate to high seismic activity in the northern, south‐western and central parts of Switzerland. In contrast, south‐eastern Switzerland has less historic earthquake chronicles due to the low population density, resulting in a poorly constrained seismic event catalogue. The aim of this study is to evaluate the palaeoseismic activity for south‐eastern Switzerland by using the sedimentary record of Lake Silvaplana in the Engadine Valley. A dense grid of high‐resolution two‐dimensional seismic profiles, high‐resolution bathymetry and a 10 m long sediment core from the deepest basin were used to investigate the stratigraphy of the lake sediments. The bathymetry reveals a flat basin, flanked by steep slopes to the north‐west and south‐east. The acoustic basement consists of four ridges, and gently‐dipping fans to the south‐west and north‐east. Expressions of slope failure can be identified in all domains of the lake floor and the subsurface data. Multiple coevally‐triggered chaotic mass‐flow deposits, overlain by megaturbidites with a coarse‐sand base, have been detected along ten horizons in the seismic data. The four most recent of these deposits are cored and radiocarbon dated to approximately 230, 310, 960 and 1330 cal yr BP, indicating four over‐regional seismic events that triggered large slope failures in Lake Silvaplana in the last 1400 years. Correlation with sediments of Lake Sils, Lake Como, Lake Iseo and Lake Ledro indicate within radiocarbon uncertainties a large earthquake around 1330 cal yr BP. Within their age ranges, the postulated earthquake at 310 cal yr BP (1640 CE) further correlates with a moment magnitude Mw ca 5.4 event in Ftan in 1622 CE, and the 960 cal yr BP (990 CE) earthquake correlates with a Mw ca 5.2 earthquake in Brescia in 1065 CE. Six mass‐movement deposits, also suggested to be caused by earthquakes, were not reached by the sediment core and have suggested ages between 7800 and 11300 cal yr BP. Thus, Lake Silvaplana sediments provide the first reliable record of seismic activity for the mid and Late Holocene in this region, likely related to the neotectonic activity of the Engadine Line, a major fault zone running along the main valley.","PeriodicalId":21838,"journal":{"name":"Sedimentology","volume":"1 1","pages":""},"PeriodicalIF":3.5,"publicationDate":"2023-08-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"90061797","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}
N. Nieminski, T. McHargue, J. Gooley, A. Fildani, D. Lowe
The deposits of the upper Neoproterozoic Zerrissene Group of central‐western Namibia represent a large siliciclastic deep‐water depositional system that showcases the intricacies of facies and architectural relationships from bed‐scale to fan‐system‐scale. The lack of vegetation in the Namib Desert and regular east–west repetition of folded stratigraphy (reflecting ca 50% tectonic shortening) provides quasi‐three‐dimensional exposure over a current area of approximately 2700 square kilometres. The Brak River Formation, the middle sand‐rich unit of the Zerrissene Group, consists of nearly 600 m of strata exposed in multiple parallel continuous outcrops up to ca 10 km in length and oriented obliquely to depositional dip. Ten stratigraphic sections are correlated ca 32 km (ca 64 km restored) across the basin and offer exposure comparable in scale to modern submarine fans. Six sedimentary facies are identified and grouped into four facies associations that represent axial‐to‐marginal portions of deep‐water lobes in an unconfined submarine fan system. Spatial facies patterns, regional thickness variations, and palaeocurrents indicate that Brak River Formation sediments were transported primarily from the north to south–south‐west through a trough‐like basin and deposited within an unconfined basin plain at the junction of the Adamastor and Khomas oceans. The unique outcrop exposure and extent permits the documentation of system‐scale architecture and basin configuration of the Brak River submarine fan system. A transition from the sand‐rich lower Brak River Formation to more intercalated mudstone‐dominated intervals in the middle and upper Brak River Formation is interpreted to record a change from aggradational to compensational stacking of lobe deposits. This records the evolution of a large submarine fan as it filled the subtle seafloor topography and became less confined at the system‐scale. The documentation of these deep‐water deposits from centimetre‐scale to basin‐scale provides a new model for a system with extensive long‐distance transport of sand‐rich sediment gravity flows to submarine lobes without apparent channelization.
{"title":"Spatial distribution and variability of lobe facies in a large sand‐rich submarine fan system: Neoproterozoic Zerrissene Group, Namibia","authors":"N. Nieminski, T. McHargue, J. Gooley, A. Fildani, D. Lowe","doi":"10.1111/sed.13129","DOIUrl":"https://doi.org/10.1111/sed.13129","url":null,"abstract":"The deposits of the upper Neoproterozoic Zerrissene Group of central‐western Namibia represent a large siliciclastic deep‐water depositional system that showcases the intricacies of facies and architectural relationships from bed‐scale to fan‐system‐scale. The lack of vegetation in the Namib Desert and regular east–west repetition of folded stratigraphy (reflecting ca 50% tectonic shortening) provides quasi‐three‐dimensional exposure over a current area of approximately 2700 square kilometres. The Brak River Formation, the middle sand‐rich unit of the Zerrissene Group, consists of nearly 600 m of strata exposed in multiple parallel continuous outcrops up to ca 10 km in length and oriented obliquely to depositional dip. Ten stratigraphic sections are correlated ca 32 km (ca 64 km restored) across the basin and offer exposure comparable in scale to modern submarine fans. Six sedimentary facies are identified and grouped into four facies associations that represent axial‐to‐marginal portions of deep‐water lobes in an unconfined submarine fan system. Spatial facies patterns, regional thickness variations, and palaeocurrents indicate that Brak River Formation sediments were transported primarily from the north to south–south‐west through a trough‐like basin and deposited within an unconfined basin plain at the junction of the Adamastor and Khomas oceans. The unique outcrop exposure and extent permits the documentation of system‐scale architecture and basin configuration of the Brak River submarine fan system. A transition from the sand‐rich lower Brak River Formation to more intercalated mudstone‐dominated intervals in the middle and upper Brak River Formation is interpreted to record a change from aggradational to compensational stacking of lobe deposits. This records the evolution of a large submarine fan as it filled the subtle seafloor topography and became less confined at the system‐scale. The documentation of these deep‐water deposits from centimetre‐scale to basin‐scale provides a new model for a system with extensive long‐distance transport of sand‐rich sediment gravity flows to submarine lobes without apparent channelization.","PeriodicalId":21838,"journal":{"name":"Sedimentology","volume":"11 1","pages":""},"PeriodicalIF":3.5,"publicationDate":"2023-08-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"85747279","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}
{"title":"Geochemical evidence of provenance diversity in Holocene sandy land of Qinghai Lake Basin in north‐eastern margin of Qinghai–Tibet Plateau and its implications for climate change","authors":"Zhiyong Ding, Ruijie Lu, Xiaokang Liu, Yongqiu Wu, Dongxue Chen","doi":"10.1111/sed.13128","DOIUrl":"https://doi.org/10.1111/sed.13128","url":null,"abstract":"","PeriodicalId":21838,"journal":{"name":"Sedimentology","volume":"28 1","pages":""},"PeriodicalIF":3.5,"publicationDate":"2023-07-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"72838185","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}
J. Ponce, N. Carmona, Damián Jait, Martín F. Cevallos, Christian Rojas
{"title":"Sedimentological and ichnological characterization of delta front mouth bars in a river‐dominated delta (Upper Cretaceous) from the La Anita Formation, Austral Basin, Argentina","authors":"J. Ponce, N. Carmona, Damián Jait, Martín F. Cevallos, Christian Rojas","doi":"10.1111/sed.13127","DOIUrl":"https://doi.org/10.1111/sed.13127","url":null,"abstract":"","PeriodicalId":21838,"journal":{"name":"Sedimentology","volume":"33 1","pages":""},"PeriodicalIF":3.5,"publicationDate":"2023-07-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"87010558","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}
J. Hippertt, I. D. Rudnitzki, L. Morais, B. Freitas, G. R. Romero, H. A. Fernandes, M. G. P. Leite, J. Leme, P. Boggiani, R. Trindade
Extensive phosphorite deposition is observed in the Neoproterozoic after a prolonged hiatus during most of the Mesoproterozoic era. This event is thought to represent an important record of major palaeoenvironmental, palaeoceanographic and biotic changes that shaped Neoproterozoic ecosystems, suggesting close relationships between phosphogenesis and the preservation of key Ediacaran biotas. However, high‐grade Ediacaran phosphorite deposits are relatively uncommon, diminishing the opportunity to test current phosphate mineralization–deposition models and their implications for Neoproterozoic research. In this scenario, widespread Ediacaran phosphorite–dolomite–shale successions of the Bocaina Formation (Corumbá Group – Central Brazil) are poorly explored in international literature. Nevertheless, recent advances in phosphate exploration gave access to continuous drill core sections and freshly opened mine pits, revealing an unprecedented record of complex phosphatic successions featuring the occurrence of Ediacaran microfossils assigned to the Doushantuo–Pertatataka assemblages. This work seeks to constrain main lithofacies, sequence stratigraphy and depositional settings from these phosphatic successions in order to analyse the sedimentary evolution of the unit under the current Neoproterozoic phosphorite research framework. These results indicate that the Bocaina Formation records secular sustained phosphate deposition. These deposits are related to unprecedented, microbialite reef rim phosphorites deposited during a lower accretionary rimmed platform stage, followed by the deposition of Doushantuo‐like, whole platform phosphorites associated with a later, drowned platform stage, therefore, reinforcing the evidence for the operation of strong allogeneic controls on phosphate mineralization–concentration. In addition, this study concludes that fossiliferous Ediacaran phosphatic deposits such as the Bocaina Formation are important to understanding Neoproterozoic phosphogenic events, because they may record the transition from a Precambrian to Phanerozoic‐like phosphogenesis associated with the instauration of the Ediacaran–Cambrian phosphatic taphonomic window. This evidence hints that the growing dataset from the Bocaina Formation may bring new, exciting perspectives for Neoproterozoic research as a whole.
{"title":"Sedimentary evolution and sequence stratigraphy of Ediacaran high‐grade phosphorite–dolomite‐shale successions of Bocaina Formation (Corumbá Group), Central Brazil: Implications for the Neoproterozoic phosphogenic event","authors":"J. Hippertt, I. D. Rudnitzki, L. Morais, B. Freitas, G. R. Romero, H. A. Fernandes, M. G. P. Leite, J. Leme, P. Boggiani, R. Trindade","doi":"10.1111/sed.13125","DOIUrl":"https://doi.org/10.1111/sed.13125","url":null,"abstract":"Extensive phosphorite deposition is observed in the Neoproterozoic after a prolonged hiatus during most of the Mesoproterozoic era. This event is thought to represent an important record of major palaeoenvironmental, palaeoceanographic and biotic changes that shaped Neoproterozoic ecosystems, suggesting close relationships between phosphogenesis and the preservation of key Ediacaran biotas. However, high‐grade Ediacaran phosphorite deposits are relatively uncommon, diminishing the opportunity to test current phosphate mineralization–deposition models and their implications for Neoproterozoic research. In this scenario, widespread Ediacaran phosphorite–dolomite–shale successions of the Bocaina Formation (Corumbá Group – Central Brazil) are poorly explored in international literature. Nevertheless, recent advances in phosphate exploration gave access to continuous drill core sections and freshly opened mine pits, revealing an unprecedented record of complex phosphatic successions featuring the occurrence of Ediacaran microfossils assigned to the Doushantuo–Pertatataka assemblages. This work seeks to constrain main lithofacies, sequence stratigraphy and depositional settings from these phosphatic successions in order to analyse the sedimentary evolution of the unit under the current Neoproterozoic phosphorite research framework. These results indicate that the Bocaina Formation records secular sustained phosphate deposition. These deposits are related to unprecedented, microbialite reef rim phosphorites deposited during a lower accretionary rimmed platform stage, followed by the deposition of Doushantuo‐like, whole platform phosphorites associated with a later, drowned platform stage, therefore, reinforcing the evidence for the operation of strong allogeneic controls on phosphate mineralization–concentration. In addition, this study concludes that fossiliferous Ediacaran phosphatic deposits such as the Bocaina Formation are important to understanding Neoproterozoic phosphogenic events, because they may record the transition from a Precambrian to Phanerozoic‐like phosphogenesis associated with the instauration of the Ediacaran–Cambrian phosphatic taphonomic window. This evidence hints that the growing dataset from the Bocaina Formation may bring new, exciting perspectives for Neoproterozoic research as a whole.","PeriodicalId":21838,"journal":{"name":"Sedimentology","volume":"308 1","pages":""},"PeriodicalIF":3.5,"publicationDate":"2023-07-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"74386207","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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