R. Weibel, H. Vosgerau, M. Larsen, P. Guarnieri, T. Kokfelt, K. Dideriksen, T. Balić-Žunić, B. Bell
Siliciclastic and volcaniclastic sediments in a volcanic rifted margin succession may experience a complex diagenetic history during burial that can have a large impact on sandstone reservoir properties. To understand such changes, variations in initial sediment composition and succeeding diagenetic changes have been studied for a Palaeogene outcrop analogue in the Kangerlussuaq area, East Greenland. The nature of mafic volcanic-bearing succession, which consists of intra-volcanic sandstones, accommodated over quartz-rich pre-volcanic fluvial sandstones, are comparable to the settings of recently discovered hydrocarbon-producing sandstones in the Faroe-Shetland Basin on the conjugate Atlantic margin. Our petrographic and provenance investigations of the pre- and intra-volcanic sandstones are supported by geochemical and X-ray diffraction analyses. The intra-volcanic sandstones were deposited in shallow marine environments with mixed siliciclastic and volcaniclastic input, the latter rich in felsic to m afic volcanic rock fragments and feldspar grains. Similar zircon age distributions of pre- and intra-volcanic sandstones support a continued supply from the same siliciclastic sediment source after the onset of volcanism. Variations in initial detrital grain and pore-fluid (fresh to marine) compositions resulted in different diagenetic changes in the pre- and intra-volcanic sandstones. However, where siliciclastic sandstones were overlain by volcaniclastic rocks rather than massive lava flows, the diagenetic changes resemble those of the intra-volcanic sandstones. The cementing phases are typically quartz, illite (probably illitized kaolinite), and rare anatase in the pre-volcanic sandstones. Chlorite, calcite, zeolite/feldspar, opal/quartz and titanite are characteristic authigenic phases in the intra-volcanic sandstones. Precipitation of different minerals in the pre- and intra-volcanic sandstones show that the detrital composition (and to a lesser extent depositional environment) played a major role du ring early and late diagenesis after deep burial (up to 6–8 km). Inter-eruptive siliciclastic units may prove to form highly valuable reservoirs when they are composed of mixed siliciclastic and volcaniclastic material. In the stratigraphically youngest intra-volcanic sandstones and pre-volcanic sandstones overlain by hyaloclastite or tuff, there is a high potential for interparticle porosity preservation during burial (less than 5 km) due to early chlorite rims and the generation of secondary porosity after the dissolution of early zeolite cement.
{"title":"Diagenetic effect on reservoir quality of siliciclastic and volcaniclastic sandstones from a Palaeogene volcanic rifted margin, East Greenland","authors":"R. Weibel, H. Vosgerau, M. Larsen, P. Guarnieri, T. Kokfelt, K. Dideriksen, T. Balić-Žunić, B. Bell","doi":"10.2110/jsr.2021.127","DOIUrl":"https://doi.org/10.2110/jsr.2021.127","url":null,"abstract":"Siliciclastic and volcaniclastic sediments in a volcanic rifted margin succession may experience a complex diagenetic history during burial that can have a large impact on sandstone reservoir properties. To understand such changes, variations in initial sediment composition and succeeding diagenetic changes have been studied for a Palaeogene outcrop analogue in the Kangerlussuaq area, East Greenland. The nature of mafic volcanic-bearing succession, which consists of intra-volcanic sandstones, accommodated over quartz-rich pre-volcanic fluvial sandstones, are comparable to the settings of recently discovered hydrocarbon-producing sandstones in the Faroe-Shetland Basin on the conjugate Atlantic margin. Our petrographic and provenance investigations of the pre- and intra-volcanic sandstones are supported by geochemical and X-ray diffraction analyses. The intra-volcanic sandstones were deposited in shallow marine environments with mixed siliciclastic and volcaniclastic input, the latter rich in felsic to m afic volcanic rock fragments and feldspar grains. Similar zircon age distributions of pre- and intra-volcanic sandstones support a continued supply from the same siliciclastic sediment source after the onset of volcanism. Variations in initial detrital grain and pore-fluid (fresh to marine) compositions resulted in different diagenetic changes in the pre- and intra-volcanic sandstones. However, where siliciclastic sandstones were overlain by volcaniclastic rocks rather than massive lava flows, the diagenetic changes resemble those of the intra-volcanic sandstones. The cementing phases are typically quartz, illite (probably illitized kaolinite), and rare anatase in the pre-volcanic sandstones. Chlorite, calcite, zeolite/feldspar, opal/quartz and titanite are characteristic authigenic phases in the intra-volcanic sandstones. Precipitation of different minerals in the pre- and intra-volcanic sandstones show that the detrital composition (and to a lesser extent depositional environment) played a major role du ring early and late diagenesis after deep burial (up to 6–8 km). Inter-eruptive siliciclastic units may prove to form highly valuable reservoirs when they are composed of mixed siliciclastic and volcaniclastic material. In the stratigraphically youngest intra-volcanic sandstones and pre-volcanic sandstones overlain by hyaloclastite or tuff, there is a high potential for interparticle porosity preservation during burial (less than 5 km) due to early chlorite rims and the generation of secondary porosity after the dissolution of early zeolite cement.","PeriodicalId":17044,"journal":{"name":"Journal of Sedimentary Research","volume":null,"pages":null},"PeriodicalIF":2.0,"publicationDate":"2023-08-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"43337147","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Playa basins contain saline lakes and the evaporitic mudflats around them. However, playa basins can be different depending if they are fed by marine incursions, dominated by perennial lakes of brackish or fresh water, or dominantly dry. A discrimination of playa types, which originated under such different conditions, can be difficult in the rock record. The present study contributes to our understanding of these settings by reconstructing the evaporitic facies evolution in the German Keuper Basin after the retreat of an epeiric sea. The Middle to Late Triassic Grabfeld Formation (ca. 237–233 Ma) consists of weathered gypsum and dolomitic marl at the surface. Non-weathered, anhydrite and dolomitic marl successions were studied at the tunnel face and on drillcores for the Stuttgart 21 construction project around Stuttgart. From oldest to youngest, the following facies were recognized: (1) The Grundgipsschichten facies represents an environment of large, shallow, sulfate lagoonal lakes (“saltern”). Aren itic sulfate was deposited in very shallow waters, comprising many tepee-like structures, enterolithic folds and numerous truncation surfaces. (2) The Bochingen-Horizont facies is characterized by greenish gray laminated mudstone and dolomite deposited in perennial saline lakes. Anhydrite was locally altered by brackish or fresh water. (3) The Dunkelrote Mergel facies contains the sediments of a dominantly dry playa basin, red mudstone and nodular anhydrite. Sheetfloods resulted in ephemeral lakes under a monsoonally controlled climate. Sedimentation was sparse with numerous truncation surfaces. Large, festoon-like structures on the tunnel face were interpreted as paleo-gilgai structures. The study concludes that an evaporative environment of a coast (“coastal sabkha”) can never be undoubtedly distinguished from a playa basin in the sedimentary record.
{"title":"Saltern, mudflat, and dry playa: playa basin types of a retreating epeiric sea (Keuper, Germany)","authors":"C. Leitner, M. Köster, F. Finger","doi":"10.2110/jsr.2023.013","DOIUrl":"https://doi.org/10.2110/jsr.2023.013","url":null,"abstract":"Playa basins contain saline lakes and the evaporitic mudflats around them. However, playa basins can be different depending if they are fed by marine incursions, dominated by perennial lakes of brackish or fresh water, or dominantly dry. A discrimination of playa types, which originated under such different conditions, can be difficult in the rock record. The present study contributes to our understanding of these settings by reconstructing the evaporitic facies evolution in the German Keuper Basin after the retreat of an epeiric sea. The Middle to Late Triassic Grabfeld Formation (ca. 237–233 Ma) consists of weathered gypsum and dolomitic marl at the surface. Non-weathered, anhydrite and dolomitic marl successions were studied at the tunnel face and on drillcores for the Stuttgart 21 construction project around Stuttgart. From oldest to youngest, the following facies were recognized: (1) The Grundgipsschichten facies represents an environment of large, shallow, sulfate lagoonal lakes (“saltern”). Aren itic sulfate was deposited in very shallow waters, comprising many tepee-like structures, enterolithic folds and numerous truncation surfaces. (2) The Bochingen-Horizont facies is characterized by greenish gray laminated mudstone and dolomite deposited in perennial saline lakes. Anhydrite was locally altered by brackish or fresh water. (3) The Dunkelrote Mergel facies contains the sediments of a dominantly dry playa basin, red mudstone and nodular anhydrite. Sheetfloods resulted in ephemeral lakes under a monsoonally controlled climate. Sedimentation was sparse with numerous truncation surfaces. Large, festoon-like structures on the tunnel face were interpreted as paleo-gilgai structures. The study concludes that an evaporative environment of a coast (“coastal sabkha”) can never be undoubtedly distinguished from a playa basin in the sedimentary record.","PeriodicalId":17044,"journal":{"name":"Journal of Sedimentary Research","volume":null,"pages":null},"PeriodicalIF":2.0,"publicationDate":"2023-08-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"67684028","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Brooks H. Ryan, S. Petersen, J. Rivers, Stephen E. Kaczmarek
Dolomite textures are widely interpreted to reflect physical, mineralogical, and geochemical conditions of crystal growth. In particular, nonplanar dolomites, which display non-faceted crystal boundaries and a low percentage of crystals with compromise boundaries with preserved crystal-face junctions, have long been cited as evidence of crystal growth in fluids warmer than a theoretical dolomite critical roughening temperature (CRT) of ~50-100°C. No direct empirical evidence exists, however, to support the claim that nonplanar dolomites form exclusively above the CRT. The present study offers new Δ47 clumped isotope data from nonplanar dolomites from the Paleocene-Eocene Umm er Radhuma Formation (Qatar) that show nonplanar dolomite can form below the proposed CRT. These dolomites are interpreted to have experienced only near-surface to shallow burial conditions since deposition, and lack common burial features such as two-phase liquid-vapor inclusions, stylolites, compaction reduced porosity, and buria l cements. Scanning electron microscope images reveal that relatively large dolomite crystals (typically > 100 µm) comprise non-faceted mosaics with indistinct crystal boundaries, indicating a nonplanar texture. Thin-section petrographic measurements confirm the nonplanar texture, as the proportion of dolomite crystals with compromise boundaries with preserved crystal-face junctions ranges from 9% to 20% with an average of 14%, defining these dolomites as nonplanar sensu stricto (≤ 30%). The new Δ47 clumped isotope data from these nonplanar dolomites reveals average crystallization temperatures ranging from 38.8 to 54.2°C and overall averaging 44.1°C. Calculated uncertainties, however, indicate the nonplanar dolomites could have formed at temperatures as low as 29.1°C or as high as 65.3°C. More than three quarters (~78%) of the samples have mean temperatures that fall below 50°C, and all samples have calculated uncertainties indicating possible temperatures below 50°C but not all indicate possible tempera tures above 50°C. Furthermore, these calculated uncertainties overlap with the crystallization temperatures of planar and mimetic dolomites higher in the section, suggesting that all dolomites formed under similar temperature conditions, and therefore texture is unlikely driven solely by crystallization temperature. Cumulatively, these results indicate that the nonplanar dolomite formed in a shallow burial setting at temperatures near or below the proposed dolomite CRT. The new Δ47 data, in conjunction with textural observations from natural dolomites and hundreds of published high-temperature experiments, suggest that nonplanar dolomite cannot be reliably used as an indicator of high-temperature environments of dolomitization.
白云石结构被广泛解释为反映晶体生长的物理、矿物学和地球化学条件。特别是，非平面白云岩，其显示出无面晶界和低百分比的晶体妥协的边界与保留晶面结，长期以来被引用为晶体生长的流体高于理论白云岩临界粗化温度(CRT) ~50-100°C的证据。然而，没有直接的经验证据支持非平面白云岩只在阴极射线管上方形成的说法。本研究提供了来自古新世-古新世Umm er Radhuma组(卡塔尔)的非平面白云岩的Δ47团块同位素数据，表明在建议的CRT下可以形成非平面白云岩。这些白云岩被解释为自沉积以来只经历过近地表到浅层的埋藏条件，并且缺乏常见的埋藏特征，如两相液-气包裹体、茎杆岩、压实降低孔隙度和埋藏胶结物。扫描电镜图像显示，相对较大的白云石晶体(通常为bbb100µm)由无面马赛克组成，晶体边界不清晰，表明非平面纹理。薄片岩相测量证实了白云岩的非平面结构，具有妥协边界和保留晶面结的白云岩晶体比例为9% ~ 20%，平均为14%，定义为非平面严格意义上的白云岩(≤30%)。这些非平面白云岩的Δ47团块同位素数据显示，平均结晶温度范围为38.8 ~ 54.2℃，整体平均温度为44.1℃。然而，计算的不确定性表明，非平面白云岩可能形成于最低29.1°C或最高65.3°C的温度。超过四分之三(~78%)的样品的平均温度低于50°C，所有样品的计算不确定度表明可能的温度低于50°C，但并非所有样品都表明可能的温度高于50°C。此外，这些计算的不确定性与剖面中较高的平面白云岩和模拟白云岩的结晶温度重叠，表明所有白云岩都是在相似的温度条件下形成的，因此结构不太可能完全由结晶温度驱动。总的来说，这些结果表明，非平面白云岩形成于浅埋环境，温度接近或低于所提出的白云岩CRT。新的Δ47数据，结合天然白云岩的结构观测和数百个已发表的高温实验，表明非平面白云岩不能可靠地用作白云化高温环境的指示物。
{"title":"Clumped isotope evidence for the formation of nonplanar dolomite textures at near-surface temperatures","authors":"Brooks H. Ryan, S. Petersen, J. Rivers, Stephen E. Kaczmarek","doi":"10.2110/jsr.2022.117","DOIUrl":"https://doi.org/10.2110/jsr.2022.117","url":null,"abstract":"Dolomite textures are widely interpreted to reflect physical, mineralogical, and geochemical conditions of crystal growth. In particular, nonplanar dolomites, which display non-faceted crystal boundaries and a low percentage of crystals with compromise boundaries with preserved crystal-face junctions, have long been cited as evidence of crystal growth in fluids warmer than a theoretical dolomite critical roughening temperature (CRT) of ~50-100°C. No direct empirical evidence exists, however, to support the claim that nonplanar dolomites form exclusively above the CRT. The present study offers new Δ47 clumped isotope data from nonplanar dolomites from the Paleocene-Eocene Umm er Radhuma Formation (Qatar) that show nonplanar dolomite can form below the proposed CRT. These dolomites are interpreted to have experienced only near-surface to shallow burial conditions since deposition, and lack common burial features such as two-phase liquid-vapor inclusions, stylolites, compaction reduced porosity, and buria l cements. Scanning electron microscope images reveal that relatively large dolomite crystals (typically > 100 µm) comprise non-faceted mosaics with indistinct crystal boundaries, indicating a nonplanar texture. Thin-section petrographic measurements confirm the nonplanar texture, as the proportion of dolomite crystals with compromise boundaries with preserved crystal-face junctions ranges from 9% to 20% with an average of 14%, defining these dolomites as nonplanar sensu stricto (≤ 30%). The new Δ47 clumped isotope data from these nonplanar dolomites reveals average crystallization temperatures ranging from 38.8 to 54.2°C and overall averaging 44.1°C. Calculated uncertainties, however, indicate the nonplanar dolomites could have formed at temperatures as low as 29.1°C or as high as 65.3°C. More than three quarters (~78%) of the samples have mean temperatures that fall below 50°C, and all samples have calculated uncertainties indicating possible temperatures below 50°C but not all indicate possible tempera tures above 50°C. Furthermore, these calculated uncertainties overlap with the crystallization temperatures of planar and mimetic dolomites higher in the section, suggesting that all dolomites formed under similar temperature conditions, and therefore texture is unlikely driven solely by crystallization temperature. Cumulatively, these results indicate that the nonplanar dolomite formed in a shallow burial setting at temperatures near or below the proposed dolomite CRT. The new Δ47 data, in conjunction with textural observations from natural dolomites and hundreds of published high-temperature experiments, suggest that nonplanar dolomite cannot be reliably used as an indicator of high-temperature environments of dolomitization.","PeriodicalId":17044,"journal":{"name":"Journal of Sedimentary Research","volume":null,"pages":null},"PeriodicalIF":2.0,"publicationDate":"2023-08-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"45879494","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Luís Fernando Silveira, L. Borghi, Fabia Emanuela Rafaloski Babco, B. C. Araújo, Mateus Kroth, G. Duarte, Laís Oliveira Ferreira, J. O. Mendonça
There is wide recognition of lacustrine sediments as excellent archives of a basin's depositional history due to their high sensibility to environmental changes. Among them, microbial limestones are one of the most valuable tools for paleoenvironmental reconstruction, as the biological agents responsible for their genesis tend to respond to short-lived variations of the depositional setting creating specific precipitation patterns. We here document and investigate the sedimentary features of a specific sedimentary layer, remarkable by the extraordinary lateral continuity of its textural attributes over kilometer distances. This marker horizon occurs among the first carbonate layers of the Crato Member (Aptian, Araripe Basin, NE Brazil), commonly assigned as a paleolacustrine system. We build upon a multiscale comparative analysis (mesoscale, microscale, and chemical) to outline the main processes and paleoenvironmental settings that prompted this interval's widespread and laterally almost uniform depos ition. A lamination pattern identified in different well cores was scrutinized and compared, proving the striking lateral continuity of the layer and attesting that autochthonous biologically-induced mineralization was the primary mechanism of the formation of the microbialites. Compositional and stable isotope results also show similar trends throughout the well cores, where minor differences represent the influence of local processes. The studied interval encompassed a relatively swift transition of organic shales rich in ostracod valves to planar stromatolites, where both developed in the anoxic benthonic zone of a freshwater lake. The precipitation of the overlying finely laminated limestones is related to a change in the carbonate genetic mechanism as a response to a more stable lacustrine stratification. The widespread formation of microbialites preserving an almost identical textural pattern must be related to a regional event, constituting a rare example of a preserved ancient biostrome. Moreover, the investigation of this sedimentary layer can further contribute to determining the roles of different biotic and abiotic processes in microbialite precipitation over large areas.
{"title":"Multiscale characterization of an extensive stromatolites field: a new correlation horizon for the Crato Member, Araripe Basin, Brazil","authors":"Luís Fernando Silveira, L. Borghi, Fabia Emanuela Rafaloski Babco, B. C. Araújo, Mateus Kroth, G. Duarte, Laís Oliveira Ferreira, J. O. Mendonça","doi":"10.2110/jsr.2022.090","DOIUrl":"https://doi.org/10.2110/jsr.2022.090","url":null,"abstract":"There is wide recognition of lacustrine sediments as excellent archives of a basin's depositional history due to their high sensibility to environmental changes. Among them, microbial limestones are one of the most valuable tools for paleoenvironmental reconstruction, as the biological agents responsible for their genesis tend to respond to short-lived variations of the depositional setting creating specific precipitation patterns. We here document and investigate the sedimentary features of a specific sedimentary layer, remarkable by the extraordinary lateral continuity of its textural attributes over kilometer distances. This marker horizon occurs among the first carbonate layers of the Crato Member (Aptian, Araripe Basin, NE Brazil), commonly assigned as a paleolacustrine system. We build upon a multiscale comparative analysis (mesoscale, microscale, and chemical) to outline the main processes and paleoenvironmental settings that prompted this interval's widespread and laterally almost uniform depos ition. A lamination pattern identified in different well cores was scrutinized and compared, proving the striking lateral continuity of the layer and attesting that autochthonous biologically-induced mineralization was the primary mechanism of the formation of the microbialites. Compositional and stable isotope results also show similar trends throughout the well cores, where minor differences represent the influence of local processes. The studied interval encompassed a relatively swift transition of organic shales rich in ostracod valves to planar stromatolites, where both developed in the anoxic benthonic zone of a freshwater lake. The precipitation of the overlying finely laminated limestones is related to a change in the carbonate genetic mechanism as a response to a more stable lacustrine stratification. The widespread formation of microbialites preserving an almost identical textural pattern must be related to a regional event, constituting a rare example of a preserved ancient biostrome. Moreover, the investigation of this sedimentary layer can further contribute to determining the roles of different biotic and abiotic processes in microbialite precipitation over large areas.","PeriodicalId":17044,"journal":{"name":"Journal of Sedimentary Research","volume":null,"pages":null},"PeriodicalIF":2.0,"publicationDate":"2023-08-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"48743706","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
In some wave-exposed coasts, sandy clinoforms occur with rollovers (locations where their surfaces steepen) at ∼ 20–60 m depth. They have been suggested to have formed from sand mobilized by strong wave agitation in shallow water that has deposited in more tranquil deeper water beyond the rollover, although other suggested origins of clinoforms might also apply. In situ information on active sediment transport is needed to address their origins. Here, we assess sediment transport across a sandy clinoform rollover at 25–30 m depth using legacy data from current meters installed across the Southern California shelf near Del Mar in depths of 15, 30, and 60 m. Although lasting only 25 hours, the data captured conditions during the passage of a cyclone, which occurs frequently along this coast. Information from a global meteorological model reveals that waves were 1–2 m in height during the cyclone passage. Using the mean particle size from vibracores (0.129 mm), sand at the 15-m-depth site would have been continuously agitated above its threshold of motion during the 25-hour period, whereas sand at the 30-m site was mobile over 17 hours. Total-load fluxes of sand estimated from the waves and currents were strong at the 15-m site and comprised mostly suspended particles. The cyclone winds drove water, including bottom water, mostly parallel to the coast, but that movement was accompanied by a downwelling component over the first ∼ 10 hours. That downwelling likely moved suspended particles from the topset of the clinoform onto the foreset. A later upwelling component may have partially reversed that particle movement but was unlikely to have been so effective. The results suggest how wave effects, coupled with downwelling currents, dominated the sand transport and deposition over this short 25-hour period, contributing to the clinoform morphology.
{"title":"Effects of currents and waves on the morphologies of coastal sandy clinoforms: sediment mobility calculations based on current meter and wave data from Southern California, U.S.A.","authors":"N. Mitchell, Zhongwei Zhao","doi":"10.2110/jsr.2023.002","DOIUrl":"https://doi.org/10.2110/jsr.2023.002","url":null,"abstract":"\u0000 In some wave-exposed coasts, sandy clinoforms occur with rollovers (locations where their surfaces steepen) at ∼ 20–60 m depth. They have been suggested to have formed from sand mobilized by strong wave agitation in shallow water that has deposited in more tranquil deeper water beyond the rollover, although other suggested origins of clinoforms might also apply. In situ information on active sediment transport is needed to address their origins. Here, we assess sediment transport across a sandy clinoform rollover at 25–30 m depth using legacy data from current meters installed across the Southern California shelf near Del Mar in depths of 15, 30, and 60 m. Although lasting only 25 hours, the data captured conditions during the passage of a cyclone, which occurs frequently along this coast. Information from a global meteorological model reveals that waves were 1–2 m in height during the cyclone passage. Using the mean particle size from vibracores (0.129 mm), sand at the 15-m-depth site would have been continuously agitated above its threshold of motion during the 25-hour period, whereas sand at the 30-m site was mobile over 17 hours. Total-load fluxes of sand estimated from the waves and currents were strong at the 15-m site and comprised mostly suspended particles. The cyclone winds drove water, including bottom water, mostly parallel to the coast, but that movement was accompanied by a downwelling component over the first ∼ 10 hours. That downwelling likely moved suspended particles from the topset of the clinoform onto the foreset. A later upwelling component may have partially reversed that particle movement but was unlikely to have been so effective. The results suggest how wave effects, coupled with downwelling currents, dominated the sand transport and deposition over this short 25-hour period, contributing to the clinoform morphology.","PeriodicalId":17044,"journal":{"name":"Journal of Sedimentary Research","volume":null,"pages":null},"PeriodicalIF":2.0,"publicationDate":"2023-07-31","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"44775913","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Dongwei Li, C. Gong, Daoyao Ge, G. Fan, R. Steel, D. Shao, Kun Qi
3-D seismic data from the Bengal Fan along with spectral decomposition and RGB color blending techniques display stratigraphic architectures and spatiotemporal distribution patterns of submarine fan-reservoir elements in stark detail. Seven reservoir elements are recognized in Pliocene and Pleistocene channel–lobe complexes (i.e., subfans) developed on the northeastern fringe of the Bengal Fan. Among them, crevasse, overbank, and avulsion splays are not well acknowledged by standard models of submarine fan-reservoir elements. Crevasse splays decrease in thicknesses towards ancestral channels, and are capped by overlying levees, whereas overbank and avulsion splays increase in thicknesses towards ancestral channels and cap underlying levees. Crevasse and avulsion splays exhibit lobate planform morphology and are linked updip to ancestral channels by feeder channels, whereas overbank splays display tongue-like planform morphology and lack feeder channels. Fills of laterally migrated channel-complex sets (CCSs) appear only in early stage of subfan evolution, whereas fills of vertically stacked CCSs can appear either in middle or late stages of subfan evolution. The inner segment of the documented subfans fostered infills of both laterally migrated and vertically stacked CCSs, whereas the outer segment of the studied subfans contains terminal lobe complexes and distributary-channel fills. Crevasse, overbank, and avulsion splays can appear either in middle or late stages of subfan evolution, and mainly occur in overbank environments of middle segments of the documented subfans, which are dominated by muddy facies as predicted by the standard model of submarine fan-reservoir elements. Pliocene and Pleistocene subfans demonstrate the importance of splay processes in submarine-fan evolution, and this has implications for understanding the evolution of the volumetrically largest sediment accumulations on Earth and the distribution of submarine fan-reservoir components. The downlap of subsequent levees onto crevasse splays and overbank splays created stratigraphic traps with the potential for large hydrocarbon accumulations.
{"title":"Stratigraphic architecture and distribution patterns of submarine fan-reservoir elements: insights derived from the Pliocene and Pleistocene Bengal Fan","authors":"Dongwei Li, C. Gong, Daoyao Ge, G. Fan, R. Steel, D. Shao, Kun Qi","doi":"10.2110/jsr.2021.118","DOIUrl":"https://doi.org/10.2110/jsr.2021.118","url":null,"abstract":"\u0000 3-D seismic data from the Bengal Fan along with spectral decomposition and RGB color blending techniques display stratigraphic architectures and spatiotemporal distribution patterns of submarine fan-reservoir elements in stark detail. Seven reservoir elements are recognized in Pliocene and Pleistocene channel–lobe complexes (i.e., subfans) developed on the northeastern fringe of the Bengal Fan. Among them, crevasse, overbank, and avulsion splays are not well acknowledged by standard models of submarine fan-reservoir elements. Crevasse splays decrease in thicknesses towards ancestral channels, and are capped by overlying levees, whereas overbank and avulsion splays increase in thicknesses towards ancestral channels and cap underlying levees. Crevasse and avulsion splays exhibit lobate planform morphology and are linked updip to ancestral channels by feeder channels, whereas overbank splays display tongue-like planform morphology and lack feeder channels. Fills of laterally migrated channel-complex sets (CCSs) appear only in early stage of subfan evolution, whereas fills of vertically stacked CCSs can appear either in middle or late stages of subfan evolution. The inner segment of the documented subfans fostered infills of both laterally migrated and vertically stacked CCSs, whereas the outer segment of the studied subfans contains terminal lobe complexes and distributary-channel fills. Crevasse, overbank, and avulsion splays can appear either in middle or late stages of subfan evolution, and mainly occur in overbank environments of middle segments of the documented subfans, which are dominated by muddy facies as predicted by the standard model of submarine fan-reservoir elements. Pliocene and Pleistocene subfans demonstrate the importance of splay processes in submarine-fan evolution, and this has implications for understanding the evolution of the volumetrically largest sediment accumulations on Earth and the distribution of submarine fan-reservoir components. The downlap of subsequent levees onto crevasse splays and overbank splays created stratigraphic traps with the potential for large hydrocarbon accumulations.","PeriodicalId":17044,"journal":{"name":"Journal of Sedimentary Research","volume":null,"pages":null},"PeriodicalIF":2.0,"publicationDate":"2023-07-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"44991382","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The relationship between fluvial systems and base-level changes, controlled mainly by sea-level fluctuations and tectonic activity, on time scales of 103–104 years, is important for evaluating and improving nonmarine sequence stratigraphy and numerical and physical alluvial architecture models. However, there are not enough quantitative data available from field studies, especially for periods of rapid base-level rise. The Echigo Plain, Japan, is a fluvial–coastal lowland where the tidal range is very small and where a very deep valley was incised by the Shinano River during the latest Pleistocene. The depth of the incised valley near the shoreline, 160 m below mean sea level, is greater than the amount of sea-level fall during the Last Glacial Maximum (LGM) because of tectonic subsidence. We studied an approximately 100-m-long borehole sediment core obtained from the landward part of the plain, where thick fluvial deposits have accumulated since the LGM. Sediment facies, diatom assemblages, sulfur content, carbon to sulfur ratios, and radiocarbon age dates indicate that most of the core sediments were deposited in a fluvial environment during the past 12 kyr. Sediment accumulation rates were 10–15 m/kyr between 12 and 8 cal kyr BP, and relatively low (less than 5 m/kyr) subsequently, mainly because of glacio-eustatic sea-level rise. The timing of the reduction in the accumulation rate is one possible indicator of the position of the maximum-flooding surface in a sequence composed only of fluvial sediments. The presence of many thin layers of very fine to fine-grained sand (20–80 cm thick), interpreted as crevasse-splay deposits, that formed between 11 and 8 cal kyr BP, when the base level was rising rapidly, implies that crevasse-splay deposits are characteristic of aggrading fluvial sediments and the transgressive systems tract in nonmarine sequence stratigraphy. Tectonic subsidence at approximately 2 m/kyr has contributed markedly to the larger accumulation rate of fluvial sediments of the highstand systems tract on the Echigo Plain, compared with rates in other fluvial–coastal lowlands, since 5–6 cal kyr BP, when the eustatic sea-level rise had mostly ceased.
{"title":"Accumulation of thick fluvial sediments in the Shinano River incised-valley fills: implications for sequence stratigraphy and alluvial architecture","authors":"K. Hori, S. Tanabe, A. Urabe","doi":"10.2110/jsr.2022.049","DOIUrl":"https://doi.org/10.2110/jsr.2022.049","url":null,"abstract":"\u0000 The relationship between fluvial systems and base-level changes, controlled mainly by sea-level fluctuations and tectonic activity, on time scales of 103–104 years, is important for evaluating and improving nonmarine sequence stratigraphy and numerical and physical alluvial architecture models. However, there are not enough quantitative data available from field studies, especially for periods of rapid base-level rise. The Echigo Plain, Japan, is a fluvial–coastal lowland where the tidal range is very small and where a very deep valley was incised by the Shinano River during the latest Pleistocene. The depth of the incised valley near the shoreline, 160 m below mean sea level, is greater than the amount of sea-level fall during the Last Glacial Maximum (LGM) because of tectonic subsidence. We studied an approximately 100-m-long borehole sediment core obtained from the landward part of the plain, where thick fluvial deposits have accumulated since the LGM. Sediment facies, diatom assemblages, sulfur content, carbon to sulfur ratios, and radiocarbon age dates indicate that most of the core sediments were deposited in a fluvial environment during the past 12 kyr. Sediment accumulation rates were 10–15 m/kyr between 12 and 8 cal kyr BP, and relatively low (less than 5 m/kyr) subsequently, mainly because of glacio-eustatic sea-level rise. The timing of the reduction in the accumulation rate is one possible indicator of the position of the maximum-flooding surface in a sequence composed only of fluvial sediments. The presence of many thin layers of very fine to fine-grained sand (20–80 cm thick), interpreted as crevasse-splay deposits, that formed between 11 and 8 cal kyr BP, when the base level was rising rapidly, implies that crevasse-splay deposits are characteristic of aggrading fluvial sediments and the transgressive systems tract in nonmarine sequence stratigraphy. Tectonic subsidence at approximately 2 m/kyr has contributed markedly to the larger accumulation rate of fluvial sediments of the highstand systems tract on the Echigo Plain, compared with rates in other fluvial–coastal lowlands, since 5–6 cal kyr BP, when the eustatic sea-level rise had mostly ceased.","PeriodicalId":17044,"journal":{"name":"Journal of Sedimentary Research","volume":null,"pages":null},"PeriodicalIF":2.0,"publicationDate":"2023-07-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"44723883","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Basin-wide accommodation production and associated sediment mass deposition exert fundamental controls on stratigraphic architecture, but the details of this relationship are not fully understood. This is because it is unknown how accommodation production directly influences morphodynamics both in terms of channel process (i.e., channel migration, channel avulsion) and floodplain process, both of which are themselves coupled dynamically and are critical to the nature of stratigraphic architecture. To address this, we expand upon existing theory that links sediment mass balance and resultant stratigraphic architecture. We use two fan-delta experiments that each experience different rates of accommodation production to measure key surface morphometrics and subsurface sedimentary characteristics. Importantly, sediment was transported in bedload and suspension in these experiments, allowing for construction of strata characterized by channel bodies surrounded by overbank strata deposited from suspension fallout. From these data we use three key timescales to capture the overall behavior of the system when placed into mass balance space; avulsion setup timescales (TA) and channel mobility timescales (TV) that define short-term surface autogenics, and an accretion timescale (TC) that incorporates longer term deposition. We find that the ratio of both TC/TA and TC/TV are independent of accommodation production rate in mass-balance space, which supports a self-organized response of channel dynamics to environmental boundary conditions. The fraction of strata generated from key depositional environments largely supports this behavior, particularly for channel sand bodies that resulted in deposition from bedload transport. As such, our results suggest that channel body density is independent of accommodation production rate in a mass-balance space. We found that, although contributing to a significant fraction of the basin strata, far-field overbank deposition rates are insensitive to accommodation production and that differences in autogenic timescales between experiments largely resulted from differences in channel deposition rates, highlighting the close coupling between channel dynamics and accommodation generation. More generally the observed self-organized response of surface morphodynamics to accommodation production in mass-balance space provides a process-based framework to explain the utility of balancing mass for the prediction of down-system sediment size fractionation and sedimentary architecture.
{"title":"Coupled channel-floodplain dynamics and resulting stratigraphic architecture viewed through a mass-balance lens","authors":"K. Straub, R. Dutt, R. Duller","doi":"10.2110/jsr.2022.012","DOIUrl":"https://doi.org/10.2110/jsr.2022.012","url":null,"abstract":"Basin-wide accommodation production and associated sediment mass deposition exert fundamental controls on stratigraphic architecture, but the details of this relationship are not fully understood. This is because it is unknown how accommodation production directly influences morphodynamics both in terms of channel process (i.e., channel migration, channel avulsion) and floodplain process, both of which are themselves coupled dynamically and are critical to the nature of stratigraphic architecture. To address this, we expand upon existing theory that links sediment mass balance and resultant stratigraphic architecture. We use two fan-delta experiments that each experience different rates of accommodation production to measure key surface morphometrics and subsurface sedimentary characteristics. Importantly, sediment was transported in bedload and suspension in these experiments, allowing for construction of strata characterized by channel bodies surrounded by overbank strata deposited from suspension fallout. From these data we use three key timescales to capture the overall behavior of the system when placed into mass balance space; avulsion setup timescales (TA) and channel mobility timescales (TV) that define short-term surface autogenics, and an accretion timescale (TC) that incorporates longer term deposition. We find that the ratio of both TC/TA and TC/TV are independent of accommodation production rate in mass-balance space, which supports a self-organized response of channel dynamics to environmental boundary conditions. The fraction of strata generated from key depositional environments largely supports this behavior, particularly for channel sand bodies that resulted in deposition from bedload transport. As such, our results suggest that channel body density is independent of accommodation production rate in a mass-balance space. We found that, although contributing to a significant fraction of the basin strata, far-field overbank deposition rates are insensitive to accommodation production and that differences in autogenic timescales between experiments largely resulted from differences in channel deposition rates, highlighting the close coupling between channel dynamics and accommodation generation. More generally the observed self-organized response of surface morphodynamics to accommodation production in mass-balance space provides a process-based framework to explain the utility of balancing mass for the prediction of down-system sediment size fractionation and sedimentary architecture.","PeriodicalId":17044,"journal":{"name":"Journal of Sedimentary Research","volume":null,"pages":null},"PeriodicalIF":2.0,"publicationDate":"2023-07-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"45197022","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The Eocene Uteland Butte Member of the Green River Formation in the Uinta Basin is characterized by lacustrine carbonate depositional cycles consisting of calcareous shales, limestones, and dolomites that have been interpreted to reflect climatically driven lake level fluctuations. Previous work suggests that dolomitization of three distinct stratigraphic intervals in the Uteland Butte Member—the PZ-1, PZ-1′, and PZ-2—occurred during low lake levels and was driven by a combination of density-driven downward reflux and evaporative pumping of concentrated brines. The current study uses a novel high-resolution mineralogical dataset to evaluate these proposed dolomitization mechanisms. Mineralogical data from three drill cores show that the dolomitized intervals are characterized by variations in dolomite abundance (relative to calcite), dolomite stoichiometry, and cation ordering (015:110), all of which covary with depositional facies. In the near-basin margin core and near-basin center cores, the PZ-1 interval is characterized by a shallowing-upward facies trend that corresponds to an increase in stoichiometry, dolomite abundance, and cation ordering. In the PZ-1′ interval both the near-basin margin and near-basin center cores exhibit shallowing to deepening facies patterns up core that correspond to an increase and a subsequent decrease in dolomite stoichiometry. Similarly, dolomite abundance in this interval exhibits an increase then a decrease. The PZ-2 interval is also characterized by a shallowing to deepening facies pattern, which corresponds with an increase then a decrease in stoichiometry. Lateral trends between cores indicate that basinward facies have less dolomite, and that the dolomite is less stoichiometric compared to their more landward counterparts. Collectively, these observations argue against a simple model of top-down reflux dolomitization driven by evaporative pumping. Instead, the vertical and lateral relationships between depositional facies and mineralogical properties in the PZ-1′ and PZ-2 intervals suggest that dolomitization may have occurred syndepositionally, and that the observed mineralogical patterns were driven by differences in fluid chemistry associated with lake level fluctuations through time. These findings are broadly consistent with previous studies on peritidal marine carbonates showing that dolomite mineralogy can record temporal and spatial paleoenvironmental changes that can be utilized to evaluate dolomitization mechanisms.
{"title":"Dolomite mineralogy as a proxy record for lake level fluctuations: a case study from the Eocene Uteland Butte Member of the Green River Formation, Uinta Basin, Utah, U.S.A.","authors":"C. Manche, Stephen E. Kaczmarek","doi":"10.2110/jsr.2022.060","DOIUrl":"https://doi.org/10.2110/jsr.2022.060","url":null,"abstract":"\u0000 The Eocene Uteland Butte Member of the Green River Formation in the Uinta Basin is characterized by lacustrine carbonate depositional cycles consisting of calcareous shales, limestones, and dolomites that have been interpreted to reflect climatically driven lake level fluctuations. Previous work suggests that dolomitization of three distinct stratigraphic intervals in the Uteland Butte Member—the PZ-1, PZ-1′, and PZ-2—occurred during low lake levels and was driven by a combination of density-driven downward reflux and evaporative pumping of concentrated brines. The current study uses a novel high-resolution mineralogical dataset to evaluate these proposed dolomitization mechanisms. Mineralogical data from three drill cores show that the dolomitized intervals are characterized by variations in dolomite abundance (relative to calcite), dolomite stoichiometry, and cation ordering (015:110), all of which covary with depositional facies. In the near-basin margin core and near-basin center cores, the PZ-1 interval is characterized by a shallowing-upward facies trend that corresponds to an increase in stoichiometry, dolomite abundance, and cation ordering. In the PZ-1′ interval both the near-basin margin and near-basin center cores exhibit shallowing to deepening facies patterns up core that correspond to an increase and a subsequent decrease in dolomite stoichiometry. Similarly, dolomite abundance in this interval exhibits an increase then a decrease. The PZ-2 interval is also characterized by a shallowing to deepening facies pattern, which corresponds with an increase then a decrease in stoichiometry. Lateral trends between cores indicate that basinward facies have less dolomite, and that the dolomite is less stoichiometric compared to their more landward counterparts. Collectively, these observations argue against a simple model of top-down reflux dolomitization driven by evaporative pumping. Instead, the vertical and lateral relationships between depositional facies and mineralogical properties in the PZ-1′ and PZ-2 intervals suggest that dolomitization may have occurred syndepositionally, and that the observed mineralogical patterns were driven by differences in fluid chemistry associated with lake level fluctuations through time. These findings are broadly consistent with previous studies on peritidal marine carbonates showing that dolomite mineralogy can record temporal and spatial paleoenvironmental changes that can be utilized to evaluate dolomitization mechanisms.","PeriodicalId":17044,"journal":{"name":"Journal of Sedimentary Research","volume":null,"pages":null},"PeriodicalIF":2.0,"publicationDate":"2023-07-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"47742858","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Gunnar Saelen, L. Spalluto, Niels Bo Jensen, Ivar Gunnaleite, Atle Jørgen Hestad Sande, Per Olav Eide Svendsen, Osso Gaetano, Talbot Michael R.
Thin-section investigation (polarized-light, cathodoluminescence and ultraviolet microscopy) combined with isotopic ( d18O, d13C, 87Sr/86Sr) analyses of bulk carbonate samples formed the basis for evaluating the diagenetic alteration of Albian – Cenomanian and Maastrichtian density-flow deposits off two segments of the Apulia Carbonate Platform in the Gargano promontory, Italy. We propose that differential platform uplift south and north of the Mattinata Fault controlled the diagenesis of density-flow deposits during Albian – Cenomanian times. In both cases, the (i) abundant blocky cement and vuggy pores in clasts, and (ii) remnant blocky cement on allochems in the corresponding matrix samples with interparticle pores, indicate disintegration of at least partially cemented deposits before failure and reworking into density flows. The abundant rudist fragments suggest that they were sourced from the margin and upper slope. However, the d13C compositions of the density-flow deposits south and no rth of the Mattinata Fault are different, and geochemical modelling based on presumed marine and terrestrial d13C compositions indicates: (A) The marine d13C values of deposits south of the Mattinata Fault suggest that the margin- and upper-slope deposits were subjected to predominantly marine-burial diagenesis before failure. Albian–Cenomanian Sr-isotope ages support the marine-burial diagenetic scenario where strontium was redistributed locally during calcitization of aragonitic allochems, and during precipitation of calcite cements. However, post-uplift precipitation of vadose cement in pores formed during marine-burial diagenesis has lowered the d13C and increased the 87Sr/86Sr ratio in many of the samples. (B) Twenty-five km north of the Mattinata Fault, the negative d13C values suggest that oxidation of terrestrial plants supplied 12C-enriched CO2 to the pore-water carbon pool during subaerial exposures, thus lowering the d13C compositions of the margin- and upper-slope deposits from values obtained during marine-burial diagenesis. This diagenetic model requires that residual aragonitic and high-Mg calcitic allochems were available in the deposits during penetration of meteoric water. However, the Albian – Cenomanian Sr-isotope ages and the geochemical modelling support a predominantly marine-burial scenario, with intraformational redistribution of strontium during meteoric diagenesis. A similar diagenetic model is envisaged for the Maastrichtian density-flow deposits south of the Mattinata Fault, but the less negative d13C and geochemical modelling suggest less influence of meteoric diagenesis before reworking. The majority of separate- and touching-vug pores likely also formed during marine-burial prior to failure and reworking of the margin- and upper-slope deposits. The large range in porosity (4 – 31 %) of density-flow deposits with predominantly interparticle pores are inferred to reflect varying degrees of compaction caused by variable overburd
{"title":"Diagenesis of carbonate density-flow deposits controlled by differential uplift of platform segments: Examples from the Cretaceous of the Gargano Promontory (Italy)","authors":"Gunnar Saelen, L. Spalluto, Niels Bo Jensen, Ivar Gunnaleite, Atle Jørgen Hestad Sande, Per Olav Eide Svendsen, Osso Gaetano, Talbot Michael R.","doi":"10.2110/jsr.2020.062","DOIUrl":"https://doi.org/10.2110/jsr.2020.062","url":null,"abstract":"Thin-section investigation (polarized-light, cathodoluminescence and ultraviolet microscopy) combined with isotopic ( d18O, d13C, 87Sr/86Sr) analyses of bulk carbonate samples formed the basis for evaluating the diagenetic alteration of Albian – Cenomanian and Maastrichtian density-flow deposits off two segments of the Apulia Carbonate Platform in the Gargano promontory, Italy. We propose that differential platform uplift south and north of the Mattinata Fault controlled the diagenesis of density-flow deposits during Albian – Cenomanian times. In both cases, the (i) abundant blocky cement and vuggy pores in clasts, and (ii) remnant blocky cement on allochems in the corresponding matrix samples with interparticle pores, indicate disintegration of at least partially cemented deposits before failure and reworking into density flows. The abundant rudist fragments suggest that they were sourced from the margin and upper slope. However, the d13C compositions of the density-flow deposits south and no rth of the Mattinata Fault are different, and geochemical modelling based on presumed marine and terrestrial d13C compositions indicates: (A) The marine d13C values of deposits south of the Mattinata Fault suggest that the margin- and upper-slope deposits were subjected to predominantly marine-burial diagenesis before failure. Albian–Cenomanian Sr-isotope ages support the marine-burial diagenetic scenario where strontium was redistributed locally during calcitization of aragonitic allochems, and during precipitation of calcite cements. However, post-uplift precipitation of vadose cement in pores formed during marine-burial diagenesis has lowered the d13C and increased the 87Sr/86Sr ratio in many of the samples. (B) Twenty-five km north of the Mattinata Fault, the negative d13C values suggest that oxidation of terrestrial plants supplied 12C-enriched CO2 to the pore-water carbon pool during subaerial exposures, thus lowering the d13C compositions of the margin- and upper-slope deposits from values obtained during marine-burial diagenesis. This diagenetic model requires that residual aragonitic and high-Mg calcitic allochems were available in the deposits during penetration of meteoric water. However, the Albian – Cenomanian Sr-isotope ages and the geochemical modelling support a predominantly marine-burial scenario, with intraformational redistribution of strontium during meteoric diagenesis. A similar diagenetic model is envisaged for the Maastrichtian density-flow deposits south of the Mattinata Fault, but the less negative d13C and geochemical modelling suggest less influence of meteoric diagenesis before reworking. The majority of separate- and touching-vug pores likely also formed during marine-burial prior to failure and reworking of the margin- and upper-slope deposits. The large range in porosity (4 – 31 %) of density-flow deposits with predominantly interparticle pores are inferred to reflect varying degrees of compaction caused by variable overburd","PeriodicalId":17044,"journal":{"name":"Journal of Sedimentary Research","volume":null,"pages":null},"PeriodicalIF":2.0,"publicationDate":"2023-07-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139357503","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"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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