Phyllis Mono, René Hoffmann, Max Wisshak, Stephen W. Lokier, Chelsea L. Pederson, Dominik Hennhoefer, Mara R. Diaz, Peter Swart, Gernot Nehrke, Adrian Immenhauser
ABSTRACT Ooids are abundant carbonate grains throughout much of Earth's history, but their formation is not well understood. Here, an in‐depth study of microbial bioerosion features of Holocene ooids from the Schooner Cays ooid shoals (Great Bahama Bank, Eleuthera, Bahamas) and the Shalil al Ud ooid shoals in the Gulf (Abu Dhabi, United Arab Emirates) is presented. No obvious differences were found in ooid size distribution, cortex layer thickness, the composition of nuclei or euendolithic community when comparing ooids from both locations. Microendolithic borings are present in most studied ooid surfaces, but the intensity of (micro‐)bioerosion varies significantly. Applying an epoxy vacuum cast‐embedding technique allowed the identification of ichnotaxa and their inferred producers (various genera of diatoms, cyanobacteria, coccolithophores and unspecified bacteria). Euendolithic taxa have specific low‐light tolerances and light optima. This implies that information about the relative bathymetry (seafloor versus burial within an ooid shoal) and ecology for ooid cortex formation can be obtained via the presence or absence of their respective ichnotaxa. The history of a statistically significant number of ooid cortices can be translated into dune dynamics and the temporal variations thereof by allocating the inferred index producer to a defined burial or light penetration zone. In this context, ooid formation can be divided into four stages: (i) an agitation stage in the water column, characterized by the colonization of grains by photoautotrophs; (ii) a resting stage, characterized by temporary burial of the ooid, leading to immobilization and a shift towards heterotrophs; (iii) a sleeping stage, characterized by prolonged burial and colonialization by organotrophs; and (iv) a reactivation stage, characterized by a resurfacing of the ooid and a subsequent shift towards photoautotrophs. The sleeping stage is presumably a stage of ooid degradation where bioerosion, mainly by heterotrophic fungi and bacteria is particularly active.
在地球的大部分历史中，卵状体是丰富的碳酸盐颗粒，但它们的形成尚不清楚。本文对Schooner Cays鲕滩(巴哈马群岛伊鲁塞拉岛大巴哈马滩)和Shalil al Ud鲕滩(阿拉伯联合酋长国阿布扎比)全新世鲕滩的微生物侵蚀特征进行了深入研究。两个地点的卵体在卵体大小分布、皮层厚度、核组成和中石器群落等方面均无明显差异。微内石器时代的钻孔存在于大多数研究的流体表面，但(微)生物侵蚀的强度差异很大。应用环氧树脂真空铸造包埋技术，可以鉴定出鱼分类群及其推断的生产者(硅藻、蓝藻、球石藻和未指明的细菌的各种属)。中石器类群具有特定的弱光耐受性和最佳光照条件。这意味着关于相对水深的信息(海底与埋藏在一个卵状浅滩内)和卵状皮质形成的生态学可以通过它们各自的鱼分类群的存在或不存在来获得。通过将推断的指数生产者分配到确定的埋藏区或光穿透区，统计上显著数量的球状皮质的历史可以转化为沙丘动力学及其时间变化。在这种情况下，流体的形成可分为四个阶段:(i)水柱中的搅动阶段，以光自养生物定植颗粒为特征;(ii)休养期，特征是卵体暂时埋藏，导致固定和向异养转变;(iii)睡眠阶段，特征是长时间埋葬和有机营养物的殖民化;(iv)再激活阶段，其特征是水体表面重新形成，随后向光自养生物转变。睡眠阶段可能是液体降解的一个阶段，主要是由异养真菌和细菌引起的生物侵蚀特别活跃。
{"title":"Microborings reveal alternating agitation, resting and sleeping stages of modern marine ooids","authors":"Phyllis Mono, René Hoffmann, Max Wisshak, Stephen W. Lokier, Chelsea L. Pederson, Dominik Hennhoefer, Mara R. Diaz, Peter Swart, Gernot Nehrke, Adrian Immenhauser","doi":"10.1111/sed.13149","DOIUrl":"https://doi.org/10.1111/sed.13149","url":null,"abstract":"ABSTRACT Ooids are abundant carbonate grains throughout much of Earth's history, but their formation is not well understood. Here, an in‐depth study of microbial bioerosion features of Holocene ooids from the Schooner Cays ooid shoals (Great Bahama Bank, Eleuthera, Bahamas) and the Shalil al Ud ooid shoals in the Gulf (Abu Dhabi, United Arab Emirates) is presented. No obvious differences were found in ooid size distribution, cortex layer thickness, the composition of nuclei or euendolithic community when comparing ooids from both locations. Microendolithic borings are present in most studied ooid surfaces, but the intensity of (micro‐)bioerosion varies significantly. Applying an epoxy vacuum cast‐embedding technique allowed the identification of ichnotaxa and their inferred producers (various genera of diatoms, cyanobacteria, coccolithophores and unspecified bacteria). Euendolithic taxa have specific low‐light tolerances and light optima. This implies that information about the relative bathymetry (seafloor versus burial within an ooid shoal) and ecology for ooid cortex formation can be obtained via the presence or absence of their respective ichnotaxa. The history of a statistically significant number of ooid cortices can be translated into dune dynamics and the temporal variations thereof by allocating the inferred index producer to a defined burial or light penetration zone. In this context, ooid formation can be divided into four stages: (i) an agitation stage in the water column, characterized by the colonization of grains by photoautotrophs; (ii) a resting stage, characterized by temporary burial of the ooid, leading to immobilization and a shift towards heterotrophs; (iii) a sleeping stage, characterized by prolonged burial and colonialization by organotrophs; and (iv) a reactivation stage, characterized by a resurfacing of the ooid and a subsequent shift towards photoautotrophs. The sleeping stage is presumably a stage of ooid degradation where bioerosion, mainly by heterotrophic fungi and bacteria is particularly active.","PeriodicalId":21838,"journal":{"name":"Sedimentology","volume":"5 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-10-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"136034339","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}
Dylan McGowan, Amisha Salian, Jaco H. Baas, Jeff Peakall, Jim Best
ABSTRACT Understanding of the formative conditions of many sole structures is limited, with chevron marks and striated groove marks being particularly enigmatic. These sedimentary structures are examined here through laboratory modelling. An idealized tool, resembling an armoured mud clast, was dragged through substrates of kaolinite–seawater mixtures of different yield strengths while submerged in seawater. The experiments suggest that armoured mud clasts are the likely tools producing fine striae in striated grooves and given the common occurrence of striated groove marks in outcrops, that these clasts are more prevalent in deep‐marine settings than previously thought. Chevron marks were observed to form over a narrow range of substrate yield stresses, likely explaining their relative rarity. Furthermore, their form is shown to be a function of substrate rheology, with chevron angle relative to the movement direction of the tool being less in weaker substrates. Moreover, the size of cut chevron marks, characterized by a narrow central cut, bears no relationship to the size of the incising tool, but rather reflects a substrate with a low yield stress that is sufficiently mobile to close behind the tool. In contrast, interrupted chevron marks, characterized by a distinct central groove, reflect greater substrate strength. Striated grooves without chevrons formed at the highest yield stresses simulated in the experiments. The relationship between tool mark type and yield stress, in combination with changes in chevron angle, enables these sole structures to be utilized as indicators of palaeosubstrate rheology. The conditions required to preserve such features include a prolonged period of bed consolidation, flow bypass and lack of bioturbation. Given changes in seafloor communities and bioturbation over time and their impact on substrate rheology, particularly during the early Palaeozoic, the present work supports the idea that the frequency of these sole structures likely changed over geological time.
{"title":"On the origin of chevron marks and striated grooves, and their use in predicting mud bed rheology","authors":"Dylan McGowan, Amisha Salian, Jaco H. Baas, Jeff Peakall, Jim Best","doi":"10.1111/sed.13148","DOIUrl":"https://doi.org/10.1111/sed.13148","url":null,"abstract":"ABSTRACT Understanding of the formative conditions of many sole structures is limited, with chevron marks and striated groove marks being particularly enigmatic. These sedimentary structures are examined here through laboratory modelling. An idealized tool, resembling an armoured mud clast, was dragged through substrates of kaolinite–seawater mixtures of different yield strengths while submerged in seawater. The experiments suggest that armoured mud clasts are the likely tools producing fine striae in striated grooves and given the common occurrence of striated groove marks in outcrops, that these clasts are more prevalent in deep‐marine settings than previously thought. Chevron marks were observed to form over a narrow range of substrate yield stresses, likely explaining their relative rarity. Furthermore, their form is shown to be a function of substrate rheology, with chevron angle relative to the movement direction of the tool being less in weaker substrates. Moreover, the size of cut chevron marks, characterized by a narrow central cut, bears no relationship to the size of the incising tool, but rather reflects a substrate with a low yield stress that is sufficiently mobile to close behind the tool. In contrast, interrupted chevron marks, characterized by a distinct central groove, reflect greater substrate strength. Striated grooves without chevrons formed at the highest yield stresses simulated in the experiments. The relationship between tool mark type and yield stress, in combination with changes in chevron angle, enables these sole structures to be utilized as indicators of palaeosubstrate rheology. The conditions required to preserve such features include a prolonged period of bed consolidation, flow bypass and lack of bioturbation. Given changes in seafloor communities and bioturbation over time and their impact on substrate rheology, particularly during the early Palaeozoic, the present work supports the idea that the frequency of these sole structures likely changed over geological time.","PeriodicalId":21838,"journal":{"name":"Sedimentology","volume":"76 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-10-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"136113669","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}
Toms Buls, Kresten Anderskouv, Patrick L. Friend, Charlotte E. L. Thompson, Lars Stemmerik
ABSTRACT Bottom current activity has been responsible for the formation of a multitude of erosional and depositional features recorded in chalk. Advanced knowledge on the mobility and transport of unlithified calcareous nannofossil ooze by bottom currents is increasingly important not only for understanding the deposition of ancient chalk, but also for modelling the behaviour of modern pelagic carbonate sediments. Whereas the erosional behaviour of very pure calcareous nannofossil ooze has recently been investigated, the effect of organic matter and clay minerals on the erosional behaviour of calcareous nannofossil ooze is as yet unquantified. The results of the present study are based on laboratory flume studies utilizing chalk ooze with varying concentrations of smectite clay (1 to 30 wt. %), two types of organic matter and bed porosity. Phytoplankton ( Pavlova lutheri ) was used as a proxy for particulate marine organic matter, and xanthan gum as a proxy for extracellular polymeric substances. The results show a significant decrease in nannofossil ooze mobility with increasing content of clay or marine organic matter. Organic matter is found to reduce erodibility at much lower concentrations than clay minerals at porosities equivalent to those of the sea floor. At lower porosities, corresponding to some depth below the sea floor, organic matter and clay minerals are less effective in bed stabilization. This suggests that clay minerals and especially organic matter will affect the likelihood of initiation of severe erosion on the sea floor, whereas their inhibiting effect will decrease as erosion scours progressively deeper into the sediment column. The effect of extracellular polymeric substances is more complex than marine organic matter, probably due to detachment of large aggregates from the bed and resulting increase in bed roughness. The choice of organic matter in sedimentological experiments may lead to significant differences in sediment behaviour and should therefore involve careful consideration.
{"title":"Effects of clay and organic matter on calcareous nannofossil ooze erodibility","authors":"Toms Buls, Kresten Anderskouv, Patrick L. Friend, Charlotte E. L. Thompson, Lars Stemmerik","doi":"10.1111/sed.13150","DOIUrl":"https://doi.org/10.1111/sed.13150","url":null,"abstract":"ABSTRACT Bottom current activity has been responsible for the formation of a multitude of erosional and depositional features recorded in chalk. Advanced knowledge on the mobility and transport of unlithified calcareous nannofossil ooze by bottom currents is increasingly important not only for understanding the deposition of ancient chalk, but also for modelling the behaviour of modern pelagic carbonate sediments. Whereas the erosional behaviour of very pure calcareous nannofossil ooze has recently been investigated, the effect of organic matter and clay minerals on the erosional behaviour of calcareous nannofossil ooze is as yet unquantified. The results of the present study are based on laboratory flume studies utilizing chalk ooze with varying concentrations of smectite clay (1 to 30 wt. %), two types of organic matter and bed porosity. Phytoplankton ( Pavlova lutheri ) was used as a proxy for particulate marine organic matter, and xanthan gum as a proxy for extracellular polymeric substances. The results show a significant decrease in nannofossil ooze mobility with increasing content of clay or marine organic matter. Organic matter is found to reduce erodibility at much lower concentrations than clay minerals at porosities equivalent to those of the sea floor. At lower porosities, corresponding to some depth below the sea floor, organic matter and clay minerals are less effective in bed stabilization. This suggests that clay minerals and especially organic matter will affect the likelihood of initiation of severe erosion on the sea floor, whereas their inhibiting effect will decrease as erosion scours progressively deeper into the sediment column. The effect of extracellular polymeric substances is more complex than marine organic matter, probably due to detachment of large aggregates from the bed and resulting increase in bed roughness. The choice of organic matter in sedimentological experiments may lead to significant differences in sediment behaviour and should therefore involve careful consideration.","PeriodicalId":21838,"journal":{"name":"Sedimentology","volume":"4 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-10-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"136113211","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 Both igneous and sedimentary rocks affected by water–rock interaction commonly form rhythmic Fe‐oxide bands that provide information on palaeo‐groundwater. This study investigated the formation of Fe‐oxide banded patterns of concentrically banded concretions from the Jurassic Navajo Sandstone (United States) and banded claystone ‘zebra rock’ from the Neoproterozoic Johnny Cake Shale Member (Western Australia). Micro‐X‐ray fluorescence imaging of both samples revealed uniformly banded patterns of asymmetrical Fe content peaks. This study proposes that their formations were caused by diffusion, with a pH buffering reaction of Fe 2+ and O 2 due to dissolution of earlier materials by acidic fluids. Based on the model, it is suggested that the acid fluids for Navajo diffused towards the inner side of the concretion, and that for Kimberley they penetrated oblique or perpendicular to bedding. In addition, the Fe‐oxide precipitation has resulted from pH rises of acidic fluids because of diagenetic alteration of earlier calcite concretion in Navajo and that of earlier pyrite‐bearing claystone in Kimberley. The interpretation for Kimberley is based on the δ 34 S values (<−20‰) of zebra rock, suggesting that the alunite and Fe‐oxide resulted from the supply of and Fe 2+ produced as a result of pyrite oxidation in earlier rocks. The formation rate of the Fe‐oxide band was estimated from the constant width of the Fe peaks and the expected diffusion coefficient for Fe 2+ through the rock matrix, and it was found to be on the order of years for Navajo and on the order of tens of years for Kimberley.
{"title":"Rhythmic iron‐oxide bands of Navajo Sandstone concretions and Kimberley banded claystone: Formation process and buffering reaction rate by diagenetic alteration","authors":"Nagayoshi Katsuta, Sin‐ichi Sirono, Ayako Umemura, Hirokazu Kawahara, Yuma Masuki, Chikage Yoshimizu, Ichiro Tayasu, Takuma Murakami, Hidekazu Yoshida","doi":"10.1111/sed.13135","DOIUrl":"https://doi.org/10.1111/sed.13135","url":null,"abstract":"Abstract Both igneous and sedimentary rocks affected by water–rock interaction commonly form rhythmic Fe‐oxide bands that provide information on palaeo‐groundwater. This study investigated the formation of Fe‐oxide banded patterns of concentrically banded concretions from the Jurassic Navajo Sandstone (United States) and banded claystone ‘zebra rock’ from the Neoproterozoic Johnny Cake Shale Member (Western Australia). Micro‐X‐ray fluorescence imaging of both samples revealed uniformly banded patterns of asymmetrical Fe content peaks. This study proposes that their formations were caused by diffusion, with a pH buffering reaction of Fe 2+ and O 2 due to dissolution of earlier materials by acidic fluids. Based on the model, it is suggested that the acid fluids for Navajo diffused towards the inner side of the concretion, and that for Kimberley they penetrated oblique or perpendicular to bedding. In addition, the Fe‐oxide precipitation has resulted from pH rises of acidic fluids because of diagenetic alteration of earlier calcite concretion in Navajo and that of earlier pyrite‐bearing claystone in Kimberley. The interpretation for Kimberley is based on the δ 34 S values (<−20‰) of zebra rock, suggesting that the alunite and Fe‐oxide resulted from the supply of and Fe 2+ produced as a result of pyrite oxidation in earlier rocks. The formation rate of the Fe‐oxide band was estimated from the constant width of the Fe peaks and the expected diffusion coefficient for Fe 2+ through the rock matrix, and it was found to be on the order of years for Navajo and on the order of tens of years for Kimberley.","PeriodicalId":21838,"journal":{"name":"Sedimentology","volume":"52 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-10-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"136078554","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}
Luca Colombera, Arnold J.H. Reesink, Robert A. Duller, Victoria A. Jeavons, Nigel P. Mountney
ABSTRACT Strata produced by fluvial dunes can provide insight into the hydrological regime of ancient rivers. Recent experiments indicate that conditions of disequilibrium between bedforms and formative flows may be inferred from the coefficient of variation of preserved dune cross‐set thickness, suggesting that this quantity may act as a proxy for the flashiness of river floods relative to the time required for full bedform translation. To assess whether this idea is applicable to interpretations of the stratigraphic record, this study examines published data relating to more than 2600 cross‐sets from 53 sedimentary units of 19 river systems. The presented analyses must not be over interpreted, because the considered rivers span different environmental settings, the data sources are heterogeneous in terms of type and dimensionality, and some variables were established by applying empirical relationships. Yet, significant findings are revealed. Larger rivers exhibit discharge and bedform characteristics that are more conducive to disequilibrium; however, a modest increase in the coefficient of variation of cross‐set thickness, CV(D st ) , as opposed to the expected decrease, is seen as a function of river size. Crucially, smaller CV(D st ) values are not systematically associated with conditions that should favour dune disequilibrium. Meanwhile, only ca 25% of the studied examples demonstrate cross‐set thickness statistics compatible with quantitative formulations of the autogenic control by variable dune topography – the notion of ‘variability‐dominated’ preservation. These findings indicate that the variability in cross‐set thickness may be a poor predictor of discharge variability, perhaps because of the multiplicity of factors controlling dune preservation, such as bedform hierarchy, transport stage and depth‐dependent variations in dune disequilibrium. To improve interpretations of cross‐stratified deposits, further research is needed to: (i) establish the value of process‐to‐product models for reverse product‐to‐process interpretations; and (ii) to define representative samples for preserved dune deposits accounting for temporal and spatial variability in preservation potential.
{"title":"The thickness variability of fluvial cross‐strata as a record of dune disequilibrium and palaeohydrology proxy: A test against channel deposits","authors":"Luca Colombera, Arnold J.H. Reesink, Robert A. Duller, Victoria A. Jeavons, Nigel P. Mountney","doi":"10.1111/sed.13147","DOIUrl":"https://doi.org/10.1111/sed.13147","url":null,"abstract":"ABSTRACT Strata produced by fluvial dunes can provide insight into the hydrological regime of ancient rivers. Recent experiments indicate that conditions of disequilibrium between bedforms and formative flows may be inferred from the coefficient of variation of preserved dune cross‐set thickness, suggesting that this quantity may act as a proxy for the flashiness of river floods relative to the time required for full bedform translation. To assess whether this idea is applicable to interpretations of the stratigraphic record, this study examines published data relating to more than 2600 cross‐sets from 53 sedimentary units of 19 river systems. The presented analyses must not be over interpreted, because the considered rivers span different environmental settings, the data sources are heterogeneous in terms of type and dimensionality, and some variables were established by applying empirical relationships. Yet, significant findings are revealed. Larger rivers exhibit discharge and bedform characteristics that are more conducive to disequilibrium; however, a modest increase in the coefficient of variation of cross‐set thickness, CV(D st ) , as opposed to the expected decrease, is seen as a function of river size. Crucially, smaller CV(D st ) values are not systematically associated with conditions that should favour dune disequilibrium. Meanwhile, only ca 25% of the studied examples demonstrate cross‐set thickness statistics compatible with quantitative formulations of the autogenic control by variable dune topography – the notion of ‘variability‐dominated’ preservation. These findings indicate that the variability in cross‐set thickness may be a poor predictor of discharge variability, perhaps because of the multiplicity of factors controlling dune preservation, such as bedform hierarchy, transport stage and depth‐dependent variations in dune disequilibrium. To improve interpretations of cross‐stratified deposits, further research is needed to: (i) establish the value of process‐to‐product models for reverse product‐to‐process interpretations; and (ii) to define representative samples for preserved dune deposits accounting for temporal and spatial variability in preservation potential.","PeriodicalId":21838,"journal":{"name":"Sedimentology","volume":"2015 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-10-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135044578","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 Hummocky cross‐stratification is commonly observed in the marine offshore transition to lower shoreface environments. However, to date, the origins of hummocky cross‐stratification and its associated hummocky bedforms and hydrodynamic processes remain controversial and enigmatic. In the present study, a large‐scale flume experiment was conducted to study the formation of hummocky bedforms. In the central test area of the flume, combined flow with water waves, with period of 2 s and velocity of 0.34 m/s, progressed at a right angle to a current with velocity of 0.17 m/s, whereas a wave‐alone condition pertained upstream and downstream of the test area. The combined‐flow ripples in the test area had smaller dimensions than wave ripples, but their cross‐section geometries were very similar. Most importantly, the experimental results, for the first time, revealed that humps occur with lengths up to approximately 40 mm beneath combined flow ripples. The formation of these structures appears to relate to the enhanced turbulence for the combined flow, because the turbulence kinetic energy for combined flow was ca 50% higher than that under the wave‐only condition. Moreover, the observed small‐scale humps in the present experiment had comparable cross‐section geometries with hummock‐like bedforms previously reported in laboratories and fields under storm conditions. Additionally, these humps could scale up to large‐size hummocks under waves with longer period and faster velocity than the present conditions. The present experiment indicates that waves perpendicular to a current do generate hummock‐like structures in association with ripples and therefore provide a new perspective for future study of the origins of hummocky cross‐stratification.
{"title":"Hummocky sedimentary structures within rippled beds due to combined orbital waves and transverse currents","authors":"X. Wu, P.A. Carling, D. Parsons","doi":"10.1111/sed.13145","DOIUrl":"https://doi.org/10.1111/sed.13145","url":null,"abstract":"ABSTRACT Hummocky cross‐stratification is commonly observed in the marine offshore transition to lower shoreface environments. However, to date, the origins of hummocky cross‐stratification and its associated hummocky bedforms and hydrodynamic processes remain controversial and enigmatic. In the present study, a large‐scale flume experiment was conducted to study the formation of hummocky bedforms. In the central test area of the flume, combined flow with water waves, with period of 2 s and velocity of 0.34 m/s, progressed at a right angle to a current with velocity of 0.17 m/s, whereas a wave‐alone condition pertained upstream and downstream of the test area. The combined‐flow ripples in the test area had smaller dimensions than wave ripples, but their cross‐section geometries were very similar. Most importantly, the experimental results, for the first time, revealed that humps occur with lengths up to approximately 40 mm beneath combined flow ripples. The formation of these structures appears to relate to the enhanced turbulence for the combined flow, because the turbulence kinetic energy for combined flow was ca 50% higher than that under the wave‐only condition. Moreover, the observed small‐scale humps in the present experiment had comparable cross‐section geometries with hummock‐like bedforms previously reported in laboratories and fields under storm conditions. Additionally, these humps could scale up to large‐size hummocks under waves with longer period and faster velocity than the present conditions. The present experiment indicates that waves perpendicular to a current do generate hummock‐like structures in association with ripples and therefore provide a new perspective for future study of the origins of hummocky cross‐stratification.","PeriodicalId":21838,"journal":{"name":"Sedimentology","volume":"61 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-10-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135197609","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}
Chaojin Lu, Ardiansyah Koeshidayatullah, Fei Li, Huan Cui, huayao zou, Peter K. Swart
ABSTRACT While marine dolomites formed under near surface conditions have been considered to be potentially reliable archives of past oceanic conditions, this interpretation comes with significant challenges because diagenetic alteration frequently produces diverse fabrics with large geochemical variability. It has been suggested that the Ediacaran dolomites in South China (Hamajing Member, Dengying Formation) recorded the oceanic conditions present at the time they formed, yet these dolomites are composed of five different fabrics (stromatolitic, micritic, oolitic, saddle dolomites and fibrous–radial dolomite cements) and show large variations in multiple geochemical isotope proxies (carbon, oxygen, clumped, magnesium and the sulphur of carbonate‐associated sulphate). This study establishes a paragenetic sequence for these dolomites by combining the clumped and the oxygen isotopic compositions, thereby assessing whether they are geochemically representative of the original seawater. Using this diagenetic framework, the micritic and stromatolitic dolomites show a closed‐system behaviour (low water–rock ratios; <0.3) and are largely resistant to the hydrothermal alteration during late diagenesis. In contrast, the ooid and cement fabrics have been affected by the hydrothermal fluid precipitating saddle dolomite in the open‐system condition with the high stimulated water–rock ratios (>1). Furthermore, in a closed‐system environment, the elevated δ 24 Mg and δ 34 S values in the stromatolitic dolomite reflect the isotopic Rayleigh fractionation that enriches the 26 Mg and 34 S through rock‐buffered recrystallization, coupled with microbial sulphate reduction. These results demonstrate that the complex signals in early marine dolomite should be carefully evaluated when used as a palaeoproxy.
{"title":"A clumped isotope diagenetic framework for the Ediacaran dolomites: Insights to fabric‐specific geochemical variabilities","authors":"Chaojin Lu, Ardiansyah Koeshidayatullah, Fei Li, Huan Cui, huayao zou, Peter K. Swart","doi":"10.1111/sed.13144","DOIUrl":"https://doi.org/10.1111/sed.13144","url":null,"abstract":"ABSTRACT While marine dolomites formed under near surface conditions have been considered to be potentially reliable archives of past oceanic conditions, this interpretation comes with significant challenges because diagenetic alteration frequently produces diverse fabrics with large geochemical variability. It has been suggested that the Ediacaran dolomites in South China (Hamajing Member, Dengying Formation) recorded the oceanic conditions present at the time they formed, yet these dolomites are composed of five different fabrics (stromatolitic, micritic, oolitic, saddle dolomites and fibrous–radial dolomite cements) and show large variations in multiple geochemical isotope proxies (carbon, oxygen, clumped, magnesium and the sulphur of carbonate‐associated sulphate). This study establishes a paragenetic sequence for these dolomites by combining the clumped and the oxygen isotopic compositions, thereby assessing whether they are geochemically representative of the original seawater. Using this diagenetic framework, the micritic and stromatolitic dolomites show a closed‐system behaviour (low water–rock ratios; <0.3) and are largely resistant to the hydrothermal alteration during late diagenesis. In contrast, the ooid and cement fabrics have been affected by the hydrothermal fluid precipitating saddle dolomite in the open‐system condition with the high stimulated water–rock ratios (>1). Furthermore, in a closed‐system environment, the elevated δ 24 Mg and δ 34 S values in the stromatolitic dolomite reflect the isotopic Rayleigh fractionation that enriches the 26 Mg and 34 S through rock‐buffered recrystallization, coupled with microbial sulphate reduction. These results demonstrate that the complex signals in early marine dolomite should be carefully evaluated when used as a palaeoproxy.","PeriodicalId":21838,"journal":{"name":"Sedimentology","volume":"26 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-10-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135301118","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}
From numerous modern gently inclined coastal areas and deltas around the world carbonate-cemented sandstone slabs and pebbles have been reported. Such sandstones collected at the coast of the German North Sea and the Mediterranean Sea (Rhône Delta) are cemented by calcite derived from the anaerobic oxidation of methane, as evidenced by biomarkers and δ13C isotope values <−35‰ typical of anaerobic oxidation of methane. The methane originated from peat, which formed in coastal lowlands, deltas and channels during the Pleisto–Holocene transgression due to the concomitant rise of the groundwater level. During ongoing transgression, the peat became overlain by marginal-marine mud, acting as a seal, and finally by marine sand. In shallow-marine settings, wave-pumping effects during storms led to seal failure and methane could migrate upward. This scenario matches recent observations in the German North Sea where a pockmark field formed during the winter storm season. The emanating methane was eventually oxidized aerobically or anaerobically by anaerobic oxidation of methane in the sand cover. The CH4 generated in the peat underneath contains ‘old’ carbon that becomes, in the case of anaerobic oxidation of methane, incorporated into bicarbonate, which in turn facilitates cementation of sand and, thus, causes the peculiar situation that the C-14 age of the cement is older than the bioclasts embedded in the sandstone. Such authigenically cemented sandstones have environmental significance for flooding of gently inclined coastal plains.
{"title":"Authigenic-cemented pebbles formed during Pleisto–Holocene transgression of gently inclined coastal plains","authors":"Andreas Wetzel, Helge Niemann","doi":"10.1111/sed.13143","DOIUrl":"https://doi.org/10.1111/sed.13143","url":null,"abstract":"From numerous modern gently inclined coastal areas and deltas around the world carbonate-cemented sandstone slabs and pebbles have been reported. Such sandstones collected at the coast of the German North Sea and the Mediterranean Sea (Rhône Delta) are cemented by calcite derived from the anaerobic oxidation of methane, as evidenced by biomarkers and δ<sup>13</sup>C isotope values <−35‰ typical of anaerobic oxidation of methane. The methane originated from peat, which formed in coastal lowlands, deltas and channels during the Pleisto–Holocene transgression due to the concomitant rise of the groundwater level. During ongoing transgression, the peat became overlain by marginal-marine mud, acting as a seal, and finally by marine sand. In shallow-marine settings, wave-pumping effects during storms led to seal failure and methane could migrate upward. This scenario matches recent observations in the German North Sea where a pockmark field formed during the winter storm season. The emanating methane was eventually oxidized aerobically or anaerobically by anaerobic oxidation of methane in the sand cover. The CH<sub>4</sub> generated in the peat underneath contains ‘old’ carbon that becomes, in the case of anaerobic oxidation of methane, incorporated into bicarbonate, which in turn facilitates cementation of sand and, thus, causes the peculiar situation that the C-14 age of the cement is older than the bioclasts embedded in the sandstone. Such authigenically cemented sandstones have environmental significance for flooding of gently inclined coastal plains.","PeriodicalId":21838,"journal":{"name":"Sedimentology","volume":"61 3","pages":""},"PeriodicalIF":3.5,"publicationDate":"2023-10-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"138509470","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}
Katarina Gobo, Ervin Mrinjek, Vlasta Ćosović, Roko Ramov, Karla Vlatković
ABSTRACT Mass‐transport deposits are products of resedimentation phenomena involving a broad spectrum of gravity‐driven processes, and commonly have a high preservation potential in deep‐marine environments. This study documents various types of mass‐transport deposits that are interbedded with intensely bioturbated shallow‐marine calciclastic sediments deposited along a reflective coast during the middle and late Eocene. The sedimentary succession, located in the vicinity of Novigrad in northern Dalmatia, Croatia, comprises sediments deposited in a range of nearshore and carbonate ramp environments, and represents the infill of a thrust‐top (piggyback) basin of the North Dalmatian foreland basin. Five types of mass‐transport deposits, ranging in thickness from 13 cm to 6 m, have been identified: (i) calcilutite and calcarenite slumps; (ii) conglomeratic slump‐debrites with a ‘dough‐like’ appearance; (iii) blocky‐flow deposits bearing large blocks of beachface and/or shoreface deposits; (iv) rockfall deposits comprising scattered blocks of beachface conglomerates and shoreface calcarenites; and (v) ‘classical’ matrix‐supported debrites. Calciturbidites are rare and mainly comprise Ta and Tb divisions. Conglomeratic slump‐debrites are mostly found in association with offshore‐transition deposits, suggesting that mass flows were triggered above the storm wave base likely due to a combined effect of: (i) strong earthquakes related to the tectonic development of the basin; (ii) sediment destabilization due to pore‐water overpressure during forced regressions; and (iii) storm‐wave loading affecting the shallow seabed. Progressive deepening likely favoured mass‐flow transformations, although the overall paucity of turbidites suggests relatively short mass‐flow transport distance and turbidity current bypass to deeper realms. Multiple erosion phases and resedimentation processes from the Cretaceous to the late Eocene contributed to the diverse suite of extraformational clasts in the mass‐transport deposits studied. The mass‐transport deposits may be triggered and emplaced in shallow‐marine settings mainly during regressive stages of basin development, as the diverse gravel clast composition suggests significant tectonic influence. Although the mass‐transport deposits reported herein are relatively small, some of their peculiar sedimentary features and occurrence within shallow‐marine calciclastic deposits render them rather unique and suitable for a re‐assessment of the nature and evolutionary continuum of processes involved in subaqueous sediment mass transport, as well as the preservation potential of sedimentary features in high‐energy wave‐reworked environments.
{"title":"Shallow‐marine calciclastic mass‐transport deposits in an evolving thrust‐top basin: A case study from the North Dalmatian foreland basin, Croatia","authors":"Katarina Gobo, Ervin Mrinjek, Vlasta Ćosović, Roko Ramov, Karla Vlatković","doi":"10.1111/sed.13142","DOIUrl":"https://doi.org/10.1111/sed.13142","url":null,"abstract":"ABSTRACT Mass‐transport deposits are products of resedimentation phenomena involving a broad spectrum of gravity‐driven processes, and commonly have a high preservation potential in deep‐marine environments. This study documents various types of mass‐transport deposits that are interbedded with intensely bioturbated shallow‐marine calciclastic sediments deposited along a reflective coast during the middle and late Eocene. The sedimentary succession, located in the vicinity of Novigrad in northern Dalmatia, Croatia, comprises sediments deposited in a range of nearshore and carbonate ramp environments, and represents the infill of a thrust‐top (piggyback) basin of the North Dalmatian foreland basin. Five types of mass‐transport deposits, ranging in thickness from 13 cm to 6 m, have been identified: (i) calcilutite and calcarenite slumps; (ii) conglomeratic slump‐debrites with a ‘dough‐like’ appearance; (iii) blocky‐flow deposits bearing large blocks of beachface and/or shoreface deposits; (iv) rockfall deposits comprising scattered blocks of beachface conglomerates and shoreface calcarenites; and (v) ‘classical’ matrix‐supported debrites. Calciturbidites are rare and mainly comprise Ta and Tb divisions. Conglomeratic slump‐debrites are mostly found in association with offshore‐transition deposits, suggesting that mass flows were triggered above the storm wave base likely due to a combined effect of: (i) strong earthquakes related to the tectonic development of the basin; (ii) sediment destabilization due to pore‐water overpressure during forced regressions; and (iii) storm‐wave loading affecting the shallow seabed. Progressive deepening likely favoured mass‐flow transformations, although the overall paucity of turbidites suggests relatively short mass‐flow transport distance and turbidity current bypass to deeper realms. Multiple erosion phases and resedimentation processes from the Cretaceous to the late Eocene contributed to the diverse suite of extraformational clasts in the mass‐transport deposits studied. The mass‐transport deposits may be triggered and emplaced in shallow‐marine settings mainly during regressive stages of basin development, as the diverse gravel clast composition suggests significant tectonic influence. Although the mass‐transport deposits reported herein are relatively small, some of their peculiar sedimentary features and occurrence within shallow‐marine calciclastic deposits render them rather unique and suitable for a re‐assessment of the nature and evolutionary continuum of processes involved in subaqueous sediment mass transport, as well as the preservation potential of sedimentary features in high‐energy wave‐reworked environments.","PeriodicalId":21838,"journal":{"name":"Sedimentology","volume":"42 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-10-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135696333","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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