The characterization of carbonate production on rift basins is critical for understanding the nucleation and demise of reefs in tectonically active areas. A new petrographic and mineralogical analysis of Cambrian strata from the Avalon Zone in Newfoundland, based on scanning electron microscopy – back-scattered electron detector and Raman spectrometer analyses, facilitates recognition of several episodes of Terreneuvian–Miaolingian carbonate production and associated precipitation of ironstone and phosphorite. These distinct units mainly developed on uplifted rift shoulders and basaltic lava palaeoreliefs, and reflect amalgamated high-energy events, interrupted by scouring discontinuities (diastems) commonly lined by phosphatized and ferruginized microbial crusts. Mud-mounds, in contrast, nucleated under calm conditions episodically punctuated by high-energy episodes, where scattered thromboid structures occur as both clotted textures and distinct calcimicrobes. Precipitation of hematite/goethite versus chamosite couplets, both occluding primary porosities and replacing interlaminae and cortices of oncoids and coated aggregates, point to marine substrates close to the Fe-redox boundary. Upwelling of phosphate-rich ferruginous hydrothermal waters contributed to the precipitation of ironstone and phosphate interbeds. Ferruginous waters related to penecontemporaneous hydrothermal activity, reflected by the record of synsedimentary fissuring and stockwork ore bodies, were delivered to confined rift-related horst-and-graben settings, largely controlled by the development of specific Cambrian carbonate and associated ironstone facies. The influence of ferruginous waters necessarily affected the record of climatically sensitive evaporitic pseudomorphs, reefs/mounds and phosphorites, which are then not suitable criteria to discriminate palaeolatitude, as demonstrated by a comparison of low-latitude to middle-latitude margins fringing Baltica, and the Avalonian and Atlas – Ossa-Morena – Northarmorican rift transects of West Gondwana.
{"title":"Carbonate production and reef building under ferruginous seawater conditions in the Cambrian rift branches of the Avalon Zone, Newfoundland","authors":"J. Javier Álvaro, Andrea Mills","doi":"10.1111/sed.13172","DOIUrl":"https://doi.org/10.1111/sed.13172","url":null,"abstract":"The characterization of carbonate production on rift basins is critical for understanding the nucleation and demise of reefs in tectonically active areas. A new petrographic and mineralogical analysis of Cambrian strata from the Avalon Zone in Newfoundland, based on scanning electron microscopy – back-scattered electron detector and Raman spectrometer analyses, facilitates recognition of several episodes of Terreneuvian–Miaolingian carbonate production and associated precipitation of ironstone and phosphorite. These distinct units mainly developed on uplifted rift shoulders and basaltic lava palaeoreliefs, and reflect amalgamated high-energy events, interrupted by scouring discontinuities (diastems) commonly lined by phosphatized and ferruginized microbial crusts. Mud-mounds, in contrast, nucleated under calm conditions episodically punctuated by high-energy episodes, where scattered thromboid structures occur as both clotted textures and distinct calcimicrobes. Precipitation of hematite/goethite versus chamosite couplets, both occluding primary porosities and replacing interlaminae and cortices of oncoids and coated aggregates, point to marine substrates close to the Fe-redox boundary. Upwelling of phosphate-rich ferruginous hydrothermal waters contributed to the precipitation of ironstone and phosphate interbeds. Ferruginous waters related to penecontemporaneous hydrothermal activity, reflected by the record of synsedimentary fissuring and stockwork ore bodies, were delivered to confined rift-related horst-and-graben settings, largely controlled by the development of specific Cambrian carbonate and associated ironstone facies. The influence of ferruginous waters necessarily affected the record of climatically sensitive evaporitic pseudomorphs, reefs/mounds and phosphorites, which are then not suitable criteria to discriminate palaeolatitude, as demonstrated by a comparison of low-latitude to middle-latitude margins fringing Baltica, and the Avalonian and Atlas – Ossa-Morena – Northarmorican rift transects of West Gondwana.","PeriodicalId":21838,"journal":{"name":"Sedimentology","volume":null,"pages":null},"PeriodicalIF":3.5,"publicationDate":"2023-12-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"138715244","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}
Nevena Andrić-Tomašević, Vladimir Simić, Dragana Životić, Nenad Nikolić, Aleksandra Pavlović, Tobias Kluge, Aratz Beranoaguirre, Jeroen Smit, Achim Bechtel
Travertines are terrestrial carbonates that are commonly associated with fault activity in extensional and transtensional basins. The faults serve as conduits for the rise and mixing of carbonate enriched fluids with thermal and meteoric CO2 inputs promoting travertine precipitation at the surface. Therefore, travertine successions provide key constrain on the faulting, depositional environments, fluid flow and climate. This work focuses on the travertine succession in the Miocene Levač Basin, the marginal basin of the Morava Corridor situated at the junction of the Dinarides and the southernmost Carpathians. Detailed sedimentological, geochronological (U-Pb age, laser ablation – inductively coupled plasma – mass spectrometry) and structural analyses of the travertines are used to reconstruct the evolution of the feeding hydrothermal system. Furthermore, these data were used to understand the controlling factors governing alternation of fluid flows enriched in thermally generated and meteoric CO2, and precipitation of travertines in Levač Basin, and finally to elucidate the late stage of basin evolution. Four facies associations are distinguished within the succession, i.e. travertine slope, ridge, flat, and travertine flat under the fluvial influence. The results demonstrated that travertine deposition was controlled by north-west/south-west and north-east/south-east normal fault arrays. Stable isotope data show positive δ13C values (with δ18O being negative) shifting to negative in the distal and stratigraphically younger deposits implying dilution of deep hydrothermal fluids by mixing with meteoric waters. Finally, travertine deposits yielded a new U-Pb age of ca 14 Ma indicating that the Middle Miocene extensional phase known from other intermountain basins in the Dinarides reached as far east as the Levač Basin and Morava Corridor.
{"title":"Tectonically induced travertine deposition in the Middle Miocene Levač intramountain basin (Central Serbia)","authors":"Nevena Andrić-Tomašević, Vladimir Simić, Dragana Životić, Nenad Nikolić, Aleksandra Pavlović, Tobias Kluge, Aratz Beranoaguirre, Jeroen Smit, Achim Bechtel","doi":"10.1111/sed.13171","DOIUrl":"https://doi.org/10.1111/sed.13171","url":null,"abstract":"Travertines are terrestrial carbonates that are commonly associated with fault activity in extensional and transtensional basins. The faults serve as conduits for the rise and mixing of carbonate enriched fluids with thermal and meteoric CO<sub>2</sub> inputs promoting travertine precipitation at the surface. Therefore, travertine successions provide key constrain on the faulting, depositional environments, fluid flow and climate. This work focuses on the travertine succession in the Miocene Levač Basin, the marginal basin of the Morava Corridor situated at the junction of the Dinarides and the southernmost Carpathians. Detailed sedimentological, geochronological (U-Pb age, laser ablation – inductively coupled plasma – mass spectrometry) and structural analyses of the travertines are used to reconstruct the evolution of the feeding hydrothermal system. Furthermore, these data were used to understand the controlling factors governing alternation of fluid flows enriched in thermally generated and meteoric CO<sub>2</sub>, and precipitation of travertines in Levač Basin, and finally to elucidate the late stage of basin evolution. Four facies associations are distinguished within the succession, i.e. travertine slope, ridge, flat, and travertine flat under the fluvial influence. The results demonstrated that travertine deposition was controlled by north-west/south-west and north-east/south-east normal fault arrays. Stable isotope data show positive δ<sup>13</sup>C values (with δ<sup>18</sup>O being negative) shifting to negative in the distal and stratigraphically younger deposits implying dilution of deep hydrothermal fluids by mixing with meteoric waters. Finally, travertine deposits yielded a new U-Pb age of <i>ca</i> 14 Ma indicating that the Middle Miocene extensional phase known from other intermountain basins in the Dinarides reached as far east as the Levač Basin and Morava Corridor.","PeriodicalId":21838,"journal":{"name":"Sedimentology","volume":null,"pages":null},"PeriodicalIF":3.5,"publicationDate":"2023-12-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"138715078","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}
Yang Lu, Boriana Mihailova, Thomas Malcherek, Carsten Paulmann, Daniel Smrzka, Jennifer Zwicker, Zhiyong Lin, Gerhard Bohrmann, Jörn Peckmann
Climate change poses a significant challenge for life on Earth. Different climate modes have been shown to come along with changes of the magnesium/calcium (Mg/Ca) ratio of seawater, and such changes are believed to control the primary mineral phase of marine authigenic carbonates. However, factors controlling marine carbonate phases other than seawater Mg/Ca ratios exist. Fibrous cements forming at methane seeps in the Black Sea provide new insight into the factors governing elemental and mineral phase compositions of fibrous carbonates. In this study, the distribution of aragonite and fibrous Mg calcite cements from three seep sites in the Black Sea is described as a function of water depth. The Mg/Ca ratio of seawater, as well as the ratio in shallow pore water, is close to four at the examined sites. Fibrous Mg calcite postdated aragonite cement in seep carbonates from shallow water depth of 120 to 190 m, whereas Mg calcite is the only cement at a greater depth of ca 2000 m. The primary formation of fibrous Mg calcite is confirmed by its zonation under cathodoluminescence, crystal morphologies agreeing with competitive growth, uniformly distributed MgCO3 contents and precipitation in equilibrium with local conditions calculated from δ18O values. The MgCO3 contents (4.5 to 12.2 mol%) are negatively correlated with δ13C values, indicating that the incorporation of Mg into the calcite crystal structure was favoured by high concentrations of sulphide generated by sulphate-driven anaerobic oxidation of methane. Unlike open oceanic basins, stratification in the Black Sea leads to euxinic conditions in the deeper water column, favouring fibrous Mg calcite formation. This observation is consistent with sulphide catalysis as a critical agent for the formation of low-Mg calcite to very high-Mg calcite at high Mg/Ca ratios and is possibly relevant to carbonate cements forming during times of oceanic euxinia.
{"title":"Role of bottom water chemistry in the formation of fibrous magnesium calcite at methane seeps in the Black Sea","authors":"Yang Lu, Boriana Mihailova, Thomas Malcherek, Carsten Paulmann, Daniel Smrzka, Jennifer Zwicker, Zhiyong Lin, Gerhard Bohrmann, Jörn Peckmann","doi":"10.1111/sed.13170","DOIUrl":"https://doi.org/10.1111/sed.13170","url":null,"abstract":"Climate change poses a significant challenge for life on Earth. Different climate modes have been shown to come along with changes of the magnesium/calcium (Mg/Ca) ratio of seawater, and such changes are believed to control the primary mineral phase of marine authigenic carbonates. However, factors controlling marine carbonate phases other than seawater Mg/Ca ratios exist. Fibrous cements forming at methane seeps in the Black Sea provide new insight into the factors governing elemental and mineral phase compositions of fibrous carbonates. In this study, the distribution of aragonite and fibrous Mg calcite cements from three seep sites in the Black Sea is described as a function of water depth. The Mg/Ca ratio of seawater, as well as the ratio in shallow pore water, is close to four at the examined sites. Fibrous Mg calcite postdated aragonite cement in seep carbonates from shallow water depth of 120 to 190 m, whereas Mg calcite is the only cement at a greater depth of <i>ca</i> 2000 m. The primary formation of fibrous Mg calcite is confirmed by its zonation under cathodoluminescence, crystal morphologies agreeing with competitive growth, uniformly distributed MgCO<sub>3</sub> contents and precipitation in equilibrium with local conditions calculated from δ<sup>18</sup>O values. The MgCO<sub>3</sub> contents (4.5 to 12.2 mol%) are negatively correlated with δ<sup>13</sup>C values, indicating that the incorporation of Mg into the calcite crystal structure was favoured by high concentrations of sulphide generated by sulphate-driven anaerobic oxidation of methane. Unlike open oceanic basins, stratification in the Black Sea leads to euxinic conditions in the deeper water column, favouring fibrous Mg calcite formation. This observation is consistent with sulphide catalysis as a critical agent for the formation of low-Mg calcite to very high-Mg calcite at high Mg/Ca ratios and is possibly relevant to carbonate cements forming during times of oceanic euxinia.","PeriodicalId":21838,"journal":{"name":"Sedimentology","volume":null,"pages":null},"PeriodicalIF":3.5,"publicationDate":"2023-12-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"138529986","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}
Charlie Y.C. Zheng, Charles Kerans, Luis A. Buatois, M. Gabriela Mángano, Lucy T. Ko
Oxygen concentration in the ocean is vital for sustaining marine ecosystems. While the potential impacts of deoxygenation on modern oceans are hard to predict, lessons can be learned from better characterizing past geological intervals formed under a greenhouse climate. The greenhouse Cretaceous containing several oceanic anoxic events characterized by widespread oxygen-deficient water is ideal in this regard. The Austin Chalk Group in south Texas (USA) shows organic-rich intervals that can be linked to oxygen depletion in the ocean, but the exact bottom water oxygenation conditions have not been estimated. This study aims to reconstruct both sediment interstitial and bottom water oxygenation history during Austin Chalk Group deposition by integrating detailed ichnological, sedimentological and geochemical (X-ray fluorescence and X-ray diffraction) analyses, thereby providing a consistent model that may be applicable across a range of marine shelf settings. The 141.12 m Gise #1 core contains a continuous record of the Austin Chalk Group, providing an opportunity for unravelling oxygenation and deoxygenation events. Whereas the anaerobic–exaerobic deposits are essentially nonbioturbated, four oxygen-related ichnocoenoses are defined, further refining the transition of aerobic to dysaerobic conditions in the sediment interstitial water. Omission surfaces and glauconitic grains, products of current-induced scouring and condensation, suggest sporadic high-energy events in the Austin Chalk Group ramp that drove elevated terrestrial inputs. Geochemical data further help to identify anoxic bottom water conditions within the anaerobic facies. Additionally, the lowermost part of Austin Chalk Group illustrates redox cycles, whereas dilution events characterized by elevated terrestrial input are identified throughout the rest of Austin Chalk Group. The evolution of oxygenation levels in sediment interstitial water and bottom water disputes the existence of a long-lasting oxygen-deficient sea in south Texas. The refined depositional model may be applicable to coeval shelfal settings. Moreover, the results provide insights into variable, evolving palaeoclimatic and palaeoceanographic conditions of the greenhouse Late Cretaceous.
{"title":"Sedimentary environment and benthic oxygenation history of the Upper Cretaceous Austin Chalk Group, south Texas: An integrated ichnological, sedimentological and geochemical approach","authors":"Charlie Y.C. Zheng, Charles Kerans, Luis A. Buatois, M. Gabriela Mángano, Lucy T. Ko","doi":"10.1111/sed.13169","DOIUrl":"https://doi.org/10.1111/sed.13169","url":null,"abstract":"Oxygen concentration in the ocean is vital for sustaining marine ecosystems. While the potential impacts of deoxygenation on modern oceans are hard to predict, lessons can be learned from better characterizing past geological intervals formed under a greenhouse climate. The greenhouse Cretaceous containing several oceanic anoxic events characterized by widespread oxygen-deficient water is ideal in this regard. The Austin Chalk Group in south Texas (USA) shows organic-rich intervals that can be linked to oxygen depletion in the ocean, but the exact bottom water oxygenation conditions have not been estimated. This study aims to reconstruct both sediment interstitial and bottom water oxygenation history during Austin Chalk Group deposition by integrating detailed ichnological, sedimentological and geochemical (X-ray fluorescence and X-ray diffraction) analyses, thereby providing a consistent model that may be applicable across a range of marine shelf settings. The 141.12 m Gise #1 core contains a continuous record of the Austin Chalk Group, providing an opportunity for unravelling oxygenation and deoxygenation events. Whereas the anaerobic–exaerobic deposits are essentially nonbioturbated, four oxygen-related ichnocoenoses are defined, further refining the transition of aerobic to dysaerobic conditions in the sediment interstitial water. Omission surfaces and glauconitic grains, products of current-induced scouring and condensation, suggest sporadic high-energy events in the Austin Chalk Group ramp that drove elevated terrestrial inputs. Geochemical data further help to identify anoxic bottom water conditions within the anaerobic facies. Additionally, the lowermost part of Austin Chalk Group illustrates redox cycles, whereas dilution events characterized by elevated terrestrial input are identified throughout the rest of Austin Chalk Group. The evolution of oxygenation levels in sediment interstitial water and bottom water disputes the existence of a long-lasting oxygen-deficient sea in south Texas. The refined depositional model may be applicable to coeval shelfal settings. Moreover, the results provide insights into variable, evolving palaeoclimatic and palaeoceanographic conditions of the greenhouse Late Cretaceous.","PeriodicalId":21838,"journal":{"name":"Sedimentology","volume":null,"pages":null},"PeriodicalIF":3.5,"publicationDate":"2023-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"138530002","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}
Jie Wang, Zhijun Dai, Sergio Fagherazzi, Yaying Lou, Xuefei Mei, Binbin Ma
Deltas are crucial for land building and ecological services due to their ability to store mineral sediment, carbon and potential pollutants. A decline in suspended sediment discharge in large rivers caused by the construction of mega-dams might imperil deltaic flats and wetlands. However, there has not been clear evidence of a sedimentary shift in the downstream tidal flats that feed coastal wetlands and the intertidal zone with sediments. Here, integrated intertidal/subaqueous sediment samples, multi-year bathymetries, fluvial and deltaic hydrological and sediment transport data in the Nanhui tidal flats and Nanhui Shoal in the Changjiang (Yangtze) Delta, one of the largest mega-deltas in the world, were analyzed to discern how sedimentary environments changed in response to the operations of the Three Gorges Dam. Results reveal that the coarser sediment fractions of surficial sediments in the subaqueous Nanhui Shoal increased between 2004 to 2021, and the overall grain size coarsened from 18.5 to 27.3 μm. Moreover, intertidal sediments in cores coarsened by 25% after the 1990s. During that period, the northern part of the Nanhui Shoal suffered large-scale erosion, while the southern part accreted in recent decades. Reduced suspended sediment discharge of the Changjiang River combined with local resuspension of fine-grained sediments are responsible for tidal flats erosion. that the spatial pattern of grain-size parameters has shifted from crossing the bathymetric isobaths to being parallel to them. Higher tide level and tidal range induced by sea-level rise, an upstream increase in bed shear stress and larger waves likely further exacerbated erosion and sediment coarsening in deltaic flats. As a result, this sediment-starved estuary coupled with sea-level rise and artificial reclamations have enhanced the vulnerability of tidal flats in Changjiang Delta, this research is informative to the sedimentary shift of worldwide mega-deltas.
{"title":"Large-scale sedimentary shift induced by a mega-dam in deltaic flats","authors":"Jie Wang, Zhijun Dai, Sergio Fagherazzi, Yaying Lou, Xuefei Mei, Binbin Ma","doi":"10.1111/sed.13168","DOIUrl":"https://doi.org/10.1111/sed.13168","url":null,"abstract":"Deltas are crucial for land building and ecological services due to their ability to store mineral sediment, carbon and potential pollutants. A decline in suspended sediment discharge in large rivers caused by the construction of mega-dams might imperil deltaic flats and wetlands. However, there has not been clear evidence of a sedimentary shift in the downstream tidal flats that feed coastal wetlands and the intertidal zone with sediments. Here, integrated intertidal/subaqueous sediment samples, multi-year bathymetries, fluvial and deltaic hydrological and sediment transport data in the Nanhui tidal flats and Nanhui Shoal in the Changjiang (Yangtze) Delta, one of the largest mega-deltas in the world, were analyzed to discern how sedimentary environments changed in response to the operations of the Three Gorges Dam. Results reveal that the coarser sediment fractions of surficial sediments in the subaqueous Nanhui Shoal increased between 2004 to 2021, and the overall grain size coarsened from 18.5 to 27.3 μm. Moreover, intertidal sediments in cores coarsened by 25% after the 1990s. During that period, the northern part of the Nanhui Shoal suffered large-scale erosion, while the southern part accreted in recent decades. Reduced suspended sediment discharge of the Changjiang River combined with local resuspension of fine-grained sediments are responsible for tidal flats erosion. that the spatial pattern of grain-size parameters has shifted from crossing the bathymetric isobaths to being parallel to them. Higher tide level and tidal range induced by sea-level rise, an upstream increase in bed shear stress and larger waves likely further exacerbated erosion and sediment coarsening in deltaic flats. As a result, this sediment-starved estuary coupled with sea-level rise and artificial reclamations have enhanced the vulnerability of tidal flats in Changjiang Delta, this research is informative to the sedimentary shift of worldwide mega-deltas.","PeriodicalId":21838,"journal":{"name":"Sedimentology","volume":null,"pages":null},"PeriodicalIF":3.5,"publicationDate":"2023-11-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"138530005","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}
Ariana Osman, Ronald J. Steel, Ryan Ramsook, And Cornel Olariu
Compound clinoforms are well-recognized in modern large muddy deltas and in some ancient deltas, but there is still a lack of understanding regarding their lithology variations and the process by which sand from the shoreline clinothem reaches the subaqueous clinothem foresets that are sometimes 100 km away. Net-to-gross, thickness and facies association evaluation show overall coarsening-upward through a 191 m thick exposure of the late Pliocene Orinoco, Lower Morne L'Enfer Formation, with a distinct tripartite lithology distribution. The subaqueous clinothem records a lower, relatively muddy coarsening-upward interval, 112 m thick, with net-to-gross increasing from zero to 60%. On the lower delta front, zero net sand units show graded beds of silt and mud with occasional spring–neap rhythmites, strongly suggesting gravity flows influenced by tidal currents. These foreset beds are overlain by structureless very fine sand, interbedded with deformed wavy to lenticular, grey fluid mud layers that rapidly accumulated near the subaqueous clinoform rollover point. The tidally dominated subaqueous platform (subaqueous delta topset), 1 to 4 m thick, shows zero net sand units with anomalously high mud content, >70%, due to the high near-bed suspended sediment concentration of externally derived fluid mud that migrated littorally alongshore from the Amazon Delta. The interaction of freshwater river flood discharge with fluid-mud banks gave rise to density stratification with fine sand hypopycnally dispersing as a turbulent layer above the denser fluid-mud carpet. The shoreline clinothem (<8 m thick) has high net-to-gross, >85%, attributed to winnowing of sediment by waves and tides. Utilizing net-to-gross trends and facies changes provide useful criteria to identify compound clinoforms in the rock record. The Orinoco Delta deposits, however, are unusual, since fluid mud hinders sand deposition on the platform, allowing for easy identification of platform facies and a clear distinction between the subaqueous and shoreline clinothem in outcrop.
{"title":"Impact of wave, tides, and fluid mud on fluvial discharge across a compound clinoform (Pliocene Orinoco Delta)","authors":"Ariana Osman, Ronald J. Steel, Ryan Ramsook, And Cornel Olariu","doi":"10.1111/sed.13167","DOIUrl":"https://doi.org/10.1111/sed.13167","url":null,"abstract":"Compound clinoforms are well-recognized in modern large muddy deltas and in some ancient deltas, but there is still a lack of understanding regarding their lithology variations and the process by which sand from the shoreline clinothem reaches the subaqueous clinothem foresets that are sometimes 100 km away. Net-to-gross, thickness and facies association evaluation show overall coarsening-upward through a 191 m thick exposure of the late Pliocene Orinoco, Lower Morne L'Enfer Formation, with a distinct tripartite lithology distribution. The <i>subaqueous clinothem</i> records a lower, relatively muddy coarsening-upward interval, 112 m thick, with net-to-gross increasing from zero to 60%. On the lower delta front, zero net sand units show graded beds of silt and mud with occasional spring–neap rhythmites, strongly suggesting gravity flows influenced by tidal currents. These foreset beds are overlain by structureless very fine sand, interbedded with deformed wavy to lenticular, grey fluid mud layers that rapidly accumulated near the subaqueous clinoform rollover point. The tidally dominated <i>subaqueous platform</i> (subaqueous delta topset), 1 to 4 m thick, shows zero net sand units with anomalously high mud content, >70%, due to the high near-bed suspended sediment concentration of externally derived fluid mud that migrated littorally alongshore from the Amazon Delta. The interaction of freshwater river flood discharge with fluid-mud banks gave rise to density stratification with fine sand hypopycnally dispersing as a turbulent layer above the denser fluid-mud carpet. The <i>shoreline clinothem</i> (<8 m thick) has high net-to-gross, >85%, attributed to winnowing of sediment by waves and tides. Utilizing net-to-gross trends and facies changes provide useful criteria to identify compound clinoforms in the rock record. The Orinoco Delta deposits, however, are unusual, since fluid mud hinders sand deposition on the platform, allowing for easy identification of platform facies and a clear distinction between the subaqueous and shoreline clinothem in outcrop.","PeriodicalId":21838,"journal":{"name":"Sedimentology","volume":null,"pages":null},"PeriodicalIF":3.5,"publicationDate":"2023-11-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"138529987","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Alexandre Normandeau, Lynn T. Dafoe, Michael Z. Li, D. Calvin Campbell, Kimberley A. Jenner
The evolution of submarine canyons is primarily controlled by turbidity currents, which erode and fill them over time; however, many other hydrodynamic currents operate within canyons. Bottom currents from these other hydrodynamic processes, including internal tides can be dominant processes, but their deposits are seldom recognized in sediment cores or the rock record. This study combines autonomous underwater vehicle swath bathymetry imagery and sub-bottom profiles, high-resolution sediment core analyses (X-ray imagery and thin sections), and previously collected seabed video and flow measurements within Logan Canyon head (eastern Canada) to provide a detailed, modern record of facies associated with hydrodynamic processes in a canyon head. These results suggest that bottom currents are responsible for maintaining gullies on canyon sidewalls and an axial channel on the canyon floor. Thin sections of sediment cores reveal that muddy sand in the canyon head consists of mud aggregates and silt and fine-grained sand, both behaving similarly in terms of flow dynamics. Three facies are present at macro-scale and micro-scale: laminated, partially laminated and bioturbated sandy mud. Sedimentary structures include rhythmic sand and mud aggregate couplets, planar to wavy laminations, current ripple cross-laminations and fining-upward successions, which is attributed to bottom currents induced by internal tides. Bioturbated facies, characterized by discrete biogenic structures and cross-cutting relationships, predominate and overprint a mottled background. A mottled bioturbation fabric also alternates with or locally disrupts layering within the partially laminated facies. Internal tide currents, capable of bedload transport and forming ripples, were measured during a monitoring period in the canyon head, followed by rapid re-establishment of benthos and associated biogenic structures, confirming the core interpretations. Preservation of sedimentary facies associated with these internal tides occurs when the sedimentation rate outpaces the rate of bioturbation, likely during stormier conditions on the shelf. These results represent observations of sedimentary facies associated with modern bottom currents and internal tides, and can be used to interpret similar occurrences within the rock record.
{"title":"Sedimentary record of bottom currents and internal tides in a modern highstand submarine canyon head","authors":"Alexandre Normandeau, Lynn T. Dafoe, Michael Z. Li, D. Calvin Campbell, Kimberley A. Jenner","doi":"10.1111/sed.13165","DOIUrl":"https://doi.org/10.1111/sed.13165","url":null,"abstract":"The evolution of submarine canyons is primarily controlled by turbidity currents, which erode and fill them over time; however, many other hydrodynamic currents operate within canyons. Bottom currents from these other hydrodynamic processes, including internal tides can be dominant processes, but their deposits are seldom recognized in sediment cores or the rock record. This study combines autonomous underwater vehicle swath bathymetry imagery and sub-bottom profiles, high-resolution sediment core analyses (X-ray imagery and thin sections), and previously collected seabed video and flow measurements within Logan Canyon head (eastern Canada) to provide a detailed, modern record of facies associated with hydrodynamic processes in a canyon head. These results suggest that bottom currents are responsible for maintaining gullies on canyon sidewalls and an axial channel on the canyon floor. Thin sections of sediment cores reveal that muddy sand in the canyon head consists of mud aggregates and silt and fine-grained sand, both behaving similarly in terms of flow dynamics. Three facies are present at macro-scale and micro-scale: laminated, partially laminated and bioturbated sandy mud. Sedimentary structures include rhythmic sand and mud aggregate couplets, planar to wavy laminations, current ripple cross-laminations and fining-upward successions, which is attributed to bottom currents induced by internal tides. Bioturbated facies, characterized by discrete biogenic structures and cross-cutting relationships, predominate and overprint a mottled background. A mottled bioturbation fabric also alternates with or locally disrupts layering within the partially laminated facies. Internal tide currents, capable of bedload transport and forming ripples, were measured during a monitoring period in the canyon head, followed by rapid re-establishment of benthos and associated biogenic structures, confirming the core interpretations. Preservation of sedimentary facies associated with these internal tides occurs when the sedimentation rate outpaces the rate of bioturbation, likely during stormier conditions on the shelf. These results represent observations of sedimentary facies associated with modern bottom currents and internal tides, and can be used to interpret similar occurrences within the rock record.","PeriodicalId":21838,"journal":{"name":"Sedimentology","volume":null,"pages":null},"PeriodicalIF":3.5,"publicationDate":"2023-11-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"138529988","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Distinguishing between shallow-water delta and fluvial fan deposits in the subsurface of lacustrine basins is challenging due to their similar depositional characteristics and distribution patterns. This study focuses on the Middle Jurassic Shaximiao Formation in the central Sichuan Basin using core observations, seismic analyses, petrology analyses, zircon analyses, palaeoclimate indicators and palaeocurrent analyses to address this issue. Fifteen sedimentary lithofacies and eight lithofacies associations were established, corresponding to channelized fluvial deposits, non-channelized fluvial deposits and shallow-water delta deposits. Shallow-water deltas are dominated by channels and mouth-bar complexes with grey, red and green interbedded mudstone. Shingled seismic reflection, green mud clasts, small burrows and wave ripples are common with occasional palaeosols. Fluvial fans are dominated by channels and crevasse-splays with pink colour and accompanied by red coloured floodplain deposits. Bright spot seismic reflection, red mud clasts, big burrows, current ripples and palaeosols are common. The increased uplift of the Dabashan Mountains controls the palaeocurrent direction, promoting the evolution from a shallow-water delta in relatively humid environments to a fluvial fan in relatively arid environments. The channel widths in shallow-water deltas are wider than those in fluvial fans, whereas the opposite applies for the channel amalgamation rate. Highly frequent channel-width variations are controlled by short-cycle climate fluctuation, corresponding to chemical index of alteration value fluctuations in different sandstone groups. The channel width in the relatively humid environments is wider than those in arid environments for both shallow-water deltas and fluvial fans. It is likely that the sedimentary evolution from shallow-water deltas to fluvial fans is relatively common in lacustrine basins in relatively arid environments with wide and gentle slope landforms.
{"title":"Evolution from shallow-water deltas to fluvial fans in lacustrine basins: A case study from the Middle Jurassic Shaximiao Formation in the central Sichuan Basin, China","authors":"Tian Yang, Xiaofang Li, Yu Yang, Long Wen, Zhenglin Cao, Xiaojun Wang, Shaomin Zhang, Qiangshao Liang","doi":"10.1111/sed.13163","DOIUrl":"https://doi.org/10.1111/sed.13163","url":null,"abstract":"Distinguishing between shallow-water delta and fluvial fan deposits in the subsurface of lacustrine basins is challenging due to their similar depositional characteristics and distribution patterns. This study focuses on the Middle Jurassic Shaximiao Formation in the central Sichuan Basin using core observations, seismic analyses, petrology analyses, zircon analyses, palaeoclimate indicators and palaeocurrent analyses to address this issue. Fifteen sedimentary lithofacies and eight lithofacies associations were established, corresponding to channelized fluvial deposits, non-channelized fluvial deposits and shallow-water delta deposits. Shallow-water deltas are dominated by channels and mouth-bar complexes with grey, red and green interbedded mudstone. Shingled seismic reflection, green mud clasts, small burrows and wave ripples are common with occasional palaeosols. Fluvial fans are dominated by channels and crevasse-splays with pink colour and accompanied by red coloured floodplain deposits. Bright spot seismic reflection, red mud clasts, big burrows, current ripples and palaeosols are common. The increased uplift of the Dabashan Mountains controls the palaeocurrent direction, promoting the evolution from a shallow-water delta in relatively humid environments to a fluvial fan in relatively arid environments. The channel widths in shallow-water deltas are wider than those in fluvial fans, whereas the opposite applies for the channel amalgamation rate. Highly frequent channel-width variations are controlled by short-cycle climate fluctuation, corresponding to chemical index of alteration value fluctuations in different sandstone groups. The channel width in the relatively humid environments is wider than those in arid environments for both shallow-water deltas and fluvial fans. It is likely that the sedimentary evolution from shallow-water deltas to fluvial fans is relatively common in lacustrine basins in relatively arid environments with wide and gentle slope landforms.","PeriodicalId":21838,"journal":{"name":"Sedimentology","volume":null,"pages":null},"PeriodicalIF":3.5,"publicationDate":"2023-11-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"138509496","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Stephanie Neuhuber, Susanne Gier, Erich Draganits, Peter Steier, Monika Bolka, Franz Ottner, Christoph Spötl, Dorothee Hippler, Patrick Meister
Authigenic Mg-calcite and dolomite are frequently observed in restricted, evaporative environments, such as lagoon or lake systems, but their formation is difficult to capture due to slow growth rates. Lake Neusiedl, an alkaline and subhaline lake with a mean water depth of 0.7 m in Austria, offers a natural system to study the precipitation of Ca-Mg-carbonate phases, which occur as fine-grained, unconsolidated and largely homogenized mud. To elucidate the timing and formation mechanisms of these authigenic carbonate phases, the mineralogical and isotopic composition and radiocarbon age of different sediment grain-size fractions from <0.2 to >3.0 μm were analysed. X-ray diffraction analyses show two broad peaks of Mg-calcite and protodolomite (lacking ordering peaks), suggesting that the carbonates are authigenic rather than detrital in origin. Calibrated carbon-14 ages range between 200 cal yr BP and 3700 cal yr BP. The linear correlation of age and grain size suggests a very slow growth rate of single crystals of 0.23 to 0.60 μm/ka. These rates suggest an extremely slow sedimentation rate in a shallow lake that existed during most of the Holocene. The higher abundance of protodolomite in older grain fractions, in contrast to the presence of high-Mg calcite in the youngest fractions, suggests a growth succession where high-Mg calcite develops first and subsequently transforms into protodolomite. Much higher ages of 6 cal ka BP to 15 cal ka BP are measured in carbonates of lake deposits exposed on land, in a section northwest of the recent lake, suggesting a growth rate of those carbonate minerals of 0.13 μm/ka. These time constraints further suggest that some carbonate grains could already have nucleated from lake water before or during the last glacial maximum, although under slightly different hydrochemical conditions.
自生镁方解石和白云石经常在有限的蒸发环境中观察到，如泻湖或湖泊系统，但由于生长速度缓慢，它们的形成很难捕捉。Neusiedl湖位于奥地利境内，平均水深0.7 m，为研究ca - mg -碳酸盐岩相的沉淀提供了一个自然系统，ca - mg -碳酸盐岩相以细粒、松散、均质化的泥浆形式存在。为了阐明这些自生碳酸盐相的形成时间和形成机制，分析了<0.2 ~ >3.0 μm不同沉积物粒度组分的矿物学、同位素组成和放射性碳年龄。x射线衍射分析显示镁方解石和原白云岩有两个宽峰(无序峰)，表明碳酸盐为自生而非碎屑成因。校正后的碳14年龄范围在200至3700 cal - year BP之间。年龄与晶粒尺寸的线性关系表明单晶生长速率非常缓慢，为0.23 ~ 0.60 μm/ka。这些速率表明，在全新世的大部分时间里，一个浅湖的沉积速率极其缓慢。在较老的颗粒组分中原白云石的丰度较高，而在较年轻的颗粒组分中则存在高镁方解石，这表明了一个生长演替过程，即高镁方解石首先发育，随后转化为原白云石。在新近形成的湖泊西北剖面上，裸露在陆地上的湖泊沉积物碳酸盐的年龄在6 ~ 15 cal ka BP之间，表明这些碳酸盐矿物的生长速率为0.13 μm/ka。这些时间限制进一步表明，在末次极大期之前或期间，一些碳酸盐颗粒可能已经从湖水中成核，尽管水化学条件略有不同。
{"title":"Radiocarbon ages of microcrystalline authigenic carbonate in Lake Neusiedl (Austria) suggest millennial-scale growth of Mg-calcite and protodolomite","authors":"Stephanie Neuhuber, Susanne Gier, Erich Draganits, Peter Steier, Monika Bolka, Franz Ottner, Christoph Spötl, Dorothee Hippler, Patrick Meister","doi":"10.1111/sed.13161","DOIUrl":"https://doi.org/10.1111/sed.13161","url":null,"abstract":"Authigenic Mg-calcite and dolomite are frequently observed in restricted, evaporative environments, such as lagoon or lake systems, but their formation is difficult to capture due to slow growth rates. Lake Neusiedl, an alkaline and subhaline lake with a mean water depth of 0.7 m in Austria, offers a natural system to study the precipitation of Ca-Mg-carbonate phases, which occur as fine-grained, unconsolidated and largely homogenized mud. To elucidate the timing and formation mechanisms of these authigenic carbonate phases, the mineralogical and isotopic composition and radiocarbon age of different sediment grain-size fractions from <0.2 to >3.0 μm were analysed. X-ray diffraction analyses show two broad peaks of Mg-calcite and protodolomite (lacking ordering peaks), suggesting that the carbonates are authigenic rather than detrital in origin. Calibrated carbon-14 ages range between 200 cal yr BP and 3700 cal yr BP. The linear correlation of age and grain size suggests a very slow growth rate of single crystals of 0.23 to 0.60 μm/ka. These rates suggest an extremely slow sedimentation rate in a shallow lake that existed during most of the Holocene. The higher abundance of protodolomite in older grain fractions, in contrast to the presence of high-Mg calcite in the youngest fractions, suggests a growth succession where high-Mg calcite develops first and subsequently transforms into protodolomite. Much higher ages of 6 cal ka BP to 15 cal ka BP are measured in carbonates of lake deposits exposed on land, in a section northwest of the recent lake, suggesting a growth rate of those carbonate minerals of 0.13 μm/ka. These time constraints further suggest that some carbonate grains could already have nucleated from lake water before or during the last glacial maximum, although under slightly different hydrochemical conditions.","PeriodicalId":21838,"journal":{"name":"Sedimentology","volume":null,"pages":null},"PeriodicalIF":3.5,"publicationDate":"2023-11-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"138530004","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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