The Experts below are selected from a list of 2769 Experts worldwide ranked by ideXlab platform
Daniele Masetti - One of the best experts on this subject based on the ideXlab platform.
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Cyclic Sedimentation in the southern alpine rhaetic the importance of climate and eustasy in controlling platform basin interactions
Sedimentology, 1990Co-Authors: Mark T. Burchell, Marco Stefani, Daniele MasettiAbstract:Uppermost Triassic (Rhaetic) facies, as developed in the Southern Alpine region of Northern Italy, were deposited in a rapidly subsiding, fault-dissected trough (the Lombardy Basin) bounded by carbonate platforms. The main part of the Rhaetic succession consists of 10-m-scale asymmetric cycles, each divided into three parts: a lower shale portion; a central rhythmic portion consisting of repeated marl-limestone couplets, the limestone parts of which thicken upward; and an upper, wholly carbonate unit. A study of the diagenetic history of the series demonstrates that both the major asymmetric Cyclicity and the limestone-marl couplets of the central rhythmic member (together constituting a ‘compound’ Cyclic form) are fundamentally depositional in nature. It is suggested that this compound Cyclicity resulted from the superposition of a low-frequency (approximately 100 000-year periodicity) asymmetric carbonate mud signal with a higher-frequency terrigenous mud signal. Field, petrographic, and geochemical investigations suggest that the basinal carbonate is predominantly allochthonous in origin, having been derived as relatively pure aragonitic mud from adjacent carbonate platforms. It is postulated that the asymmetric carbonate signal was linked to the ecological effects of eustatic fluctuation on platform carbonate systems. Repeated subaerial exposure of subtidal muds in shallow areas indicates that such sea-level variations occurred. A model is presented in which the basinward export of carbonate was negligible in the deepening phase, increased to a maximum during shallowing and was finally halted by the emergence of large platform flats. In contrast, the higher frequency terrigenous mud signal of the basin is thought to have been climatically modulated; fluctuations of a shorter period than those predicted by the Milankovitch theory affected hinterland precipitation and runoff. Particularly rapid subsidence and high depositional rates may have allowed the preservation of this signal.
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Cyclic Sedimentation in the Southern Alpine Rhaetic: the importance of climate and eustasy in controlling platform‐basin interactions
Sedimentology, 1990Co-Authors: Mark T. Burchell, Marco Stefani, Daniele MasettiAbstract:Uppermost Triassic (Rhaetic) facies, as developed in the Southern Alpine region of Northern Italy, were deposited in a rapidly subsiding, fault-dissected trough (the Lombardy Basin) bounded by carbonate platforms. The main part of the Rhaetic succession consists of 10-m-scale asymmetric cycles, each divided into three parts: a lower shale portion; a central rhythmic portion consisting of repeated marl-limestone couplets, the limestone parts of which thicken upward; and an upper, wholly carbonate unit. A study of the diagenetic history of the series demonstrates that both the major asymmetric Cyclicity and the limestone-marl couplets of the central rhythmic member (together constituting a ‘compound’ Cyclic form) are fundamentally depositional in nature. It is suggested that this compound Cyclicity resulted from the superposition of a low-frequency (approximately 100 000-year periodicity) asymmetric carbonate mud signal with a higher-frequency terrigenous mud signal. Field, petrographic, and geochemical investigations suggest that the basinal carbonate is predominantly allochthonous in origin, having been derived as relatively pure aragonitic mud from adjacent carbonate platforms. It is postulated that the asymmetric carbonate signal was linked to the ecological effects of eustatic fluctuation on platform carbonate systems. Repeated subaerial exposure of subtidal muds in shallow areas indicates that such sea-level variations occurred. A model is presented in which the basinward export of carbonate was negligible in the deepening phase, increased to a maximum during shallowing and was finally halted by the emergence of large platform flats. In contrast, the higher frequency terrigenous mud signal of the basin is thought to have been climatically modulated; fluctuations of a shorter period than those predicted by the Milankovitch theory affected hinterland precipitation and runoff. Particularly rapid subsidence and high depositional rates may have allowed the preservation of this signal.
Mark T. Burchell - One of the best experts on this subject based on the ideXlab platform.
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Cyclic Sedimentation in the southern alpine rhaetic the importance of climate and eustasy in controlling platform basin interactions
Sedimentology, 1990Co-Authors: Mark T. Burchell, Marco Stefani, Daniele MasettiAbstract:Uppermost Triassic (Rhaetic) facies, as developed in the Southern Alpine region of Northern Italy, were deposited in a rapidly subsiding, fault-dissected trough (the Lombardy Basin) bounded by carbonate platforms. The main part of the Rhaetic succession consists of 10-m-scale asymmetric cycles, each divided into three parts: a lower shale portion; a central rhythmic portion consisting of repeated marl-limestone couplets, the limestone parts of which thicken upward; and an upper, wholly carbonate unit. A study of the diagenetic history of the series demonstrates that both the major asymmetric Cyclicity and the limestone-marl couplets of the central rhythmic member (together constituting a ‘compound’ Cyclic form) are fundamentally depositional in nature. It is suggested that this compound Cyclicity resulted from the superposition of a low-frequency (approximately 100 000-year periodicity) asymmetric carbonate mud signal with a higher-frequency terrigenous mud signal. Field, petrographic, and geochemical investigations suggest that the basinal carbonate is predominantly allochthonous in origin, having been derived as relatively pure aragonitic mud from adjacent carbonate platforms. It is postulated that the asymmetric carbonate signal was linked to the ecological effects of eustatic fluctuation on platform carbonate systems. Repeated subaerial exposure of subtidal muds in shallow areas indicates that such sea-level variations occurred. A model is presented in which the basinward export of carbonate was negligible in the deepening phase, increased to a maximum during shallowing and was finally halted by the emergence of large platform flats. In contrast, the higher frequency terrigenous mud signal of the basin is thought to have been climatically modulated; fluctuations of a shorter period than those predicted by the Milankovitch theory affected hinterland precipitation and runoff. Particularly rapid subsidence and high depositional rates may have allowed the preservation of this signal.
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Cyclic Sedimentation in the Southern Alpine Rhaetic: the importance of climate and eustasy in controlling platform‐basin interactions
Sedimentology, 1990Co-Authors: Mark T. Burchell, Marco Stefani, Daniele MasettiAbstract:Uppermost Triassic (Rhaetic) facies, as developed in the Southern Alpine region of Northern Italy, were deposited in a rapidly subsiding, fault-dissected trough (the Lombardy Basin) bounded by carbonate platforms. The main part of the Rhaetic succession consists of 10-m-scale asymmetric cycles, each divided into three parts: a lower shale portion; a central rhythmic portion consisting of repeated marl-limestone couplets, the limestone parts of which thicken upward; and an upper, wholly carbonate unit. A study of the diagenetic history of the series demonstrates that both the major asymmetric Cyclicity and the limestone-marl couplets of the central rhythmic member (together constituting a ‘compound’ Cyclic form) are fundamentally depositional in nature. It is suggested that this compound Cyclicity resulted from the superposition of a low-frequency (approximately 100 000-year periodicity) asymmetric carbonate mud signal with a higher-frequency terrigenous mud signal. Field, petrographic, and geochemical investigations suggest that the basinal carbonate is predominantly allochthonous in origin, having been derived as relatively pure aragonitic mud from adjacent carbonate platforms. It is postulated that the asymmetric carbonate signal was linked to the ecological effects of eustatic fluctuation on platform carbonate systems. Repeated subaerial exposure of subtidal muds in shallow areas indicates that such sea-level variations occurred. A model is presented in which the basinward export of carbonate was negligible in the deepening phase, increased to a maximum during shallowing and was finally halted by the emergence of large platform flats. In contrast, the higher frequency terrigenous mud signal of the basin is thought to have been climatically modulated; fluctuations of a shorter period than those predicted by the Milankovitch theory affected hinterland precipitation and runoff. Particularly rapid subsidence and high depositional rates may have allowed the preservation of this signal.
Mahmoud A. Aref - One of the best experts on this subject based on the ideXlab platform.
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Evaporitic and biosiliceous Cyclic Sedimentation in the Miocene of the Gulf of Suez—Depositional and diagenetic aspects
Sedimentary Geology, 1995Co-Authors: J.m. Rouchy, D. Noël, A.m.a. Wali, Mahmoud A. ArefAbstract:Abstract The Middle to Late Miocene evaporite-bearing formations which outcrop along the Gebel Zeit and Gems highs in the southwestern Gulf of Suez (Egypt), consist of thick calcium sulphate beds rhythmically interbedded with marlstones, siltstones and claystones containing various amounts of biogenic silica, as well as pure diatomites. The calcium sulphate beds are composed mainly of gypsum and anhydrite. Subaqueous crustallisation in subpermanent brine ponds of marine origin predominated during deposition of the selenite and laminated gypsum. Early diagenetic interstitial growth of nodular anhydrite occurred episodically when the water level dropped, in response to increasing salinity associated with the precipitation of halite in the deeper troughs. Nevertheless, most of the nodular facies resulted from the burial conversion of gypsum to anhydrite which has been sometimes rehydrated into gypsum. A last phase of gypsum dehydration has occurred at the surface, related to the present hot and dry climatic conditions. The biosiliceous deposits contain either well preserved (opal-A) or diagenetically altered (opal-CT, clinoptilolite, quartz and even clays) diatom frustules. Such diagenetic changes are commonly described in the oceanic biosiliceous deposits. The fossil content of these diatomitic layers implies shallow-marine conditions on the shelves of highs induced by block faulting. The Cyclic succession of evaporited and biosiliceous deposits recorded the alternation of high sea level stands associated with high organic productivity, probably enhanced by seasonal input of nutrients and low sea level stands associated with hypersaline conditions and evaporite deposition. Locally, the sharp contact between the diatomites and gypsum argues for a rapid evolution of salinity towards high concentration (up to gypsum saturation and more). The formation of finely laminated diatomitic sediments is known to require either high organic productivity or anoxic conditions in bottom/intermediate waters, and eventually both processes. In the Gebel Zeit and Gemsa areas, a local association of the biosiliceous sediments with diagenetic carbonates and native sulphur, resulting from processes of bacterial sulphate reduction, confirms that anoxic conditions occurred in the deep-water body or in the sediments. Large amounts of organic compounds were involved in these diagenetic processes. Immature organic matter was consumed during an early diagenetic stage of transformation. It is assumed that this organic matter was supplied either by the biosilica-rich interbeds or the organic-rich laminated carbonates. The initial organic content of the biogenic deposits was impoverished as early as the first stages of Sedimentation and diagenesis. Although a large part of the organic matter could have been destroyed by these early diagenetic processes and further oxidation in outcrops, these sediments can be considered as potential source rocks in nearby less exposed sequences.
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evaporitic and biosiliceous Cyclic Sedimentation in the miocene of the gulf of suez depositional and diagenetic aspects
Sedimentary Geology, 1995Co-Authors: J.m. Rouchy, D. Noël, A.m.a. Wali, Mahmoud A. ArefAbstract:Abstract The Middle to Late Miocene evaporite-bearing formations which outcrop along the Gebel Zeit and Gems highs in the southwestern Gulf of Suez (Egypt), consist of thick calcium sulphate beds rhythmically interbedded with marlstones, siltstones and claystones containing various amounts of biogenic silica, as well as pure diatomites. The calcium sulphate beds are composed mainly of gypsum and anhydrite. Subaqueous crustallisation in subpermanent brine ponds of marine origin predominated during deposition of the selenite and laminated gypsum. Early diagenetic interstitial growth of nodular anhydrite occurred episodically when the water level dropped, in response to increasing salinity associated with the precipitation of halite in the deeper troughs. Nevertheless, most of the nodular facies resulted from the burial conversion of gypsum to anhydrite which has been sometimes rehydrated into gypsum. A last phase of gypsum dehydration has occurred at the surface, related to the present hot and dry climatic conditions. The biosiliceous deposits contain either well preserved (opal-A) or diagenetically altered (opal-CT, clinoptilolite, quartz and even clays) diatom frustules. Such diagenetic changes are commonly described in the oceanic biosiliceous deposits. The fossil content of these diatomitic layers implies shallow-marine conditions on the shelves of highs induced by block faulting. The Cyclic succession of evaporited and biosiliceous deposits recorded the alternation of high sea level stands associated with high organic productivity, probably enhanced by seasonal input of nutrients and low sea level stands associated with hypersaline conditions and evaporite deposition. Locally, the sharp contact between the diatomites and gypsum argues for a rapid evolution of salinity towards high concentration (up to gypsum saturation and more). The formation of finely laminated diatomitic sediments is known to require either high organic productivity or anoxic conditions in bottom/intermediate waters, and eventually both processes. In the Gebel Zeit and Gemsa areas, a local association of the biosiliceous sediments with diagenetic carbonates and native sulphur, resulting from processes of bacterial sulphate reduction, confirms that anoxic conditions occurred in the deep-water body or in the sediments. Large amounts of organic compounds were involved in these diagenetic processes. Immature organic matter was consumed during an early diagenetic stage of transformation. It is assumed that this organic matter was supplied either by the biosilica-rich interbeds or the organic-rich laminated carbonates. The initial organic content of the biogenic deposits was impoverished as early as the first stages of Sedimentation and diagenesis. Although a large part of the organic matter could have been destroyed by these early diagenetic processes and further oxidation in outcrops, these sediments can be considered as potential source rocks in nearby less exposed sequences.
Marco Stefani - One of the best experts on this subject based on the ideXlab platform.
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Cyclic Sedimentation in the southern alpine rhaetic the importance of climate and eustasy in controlling platform basin interactions
Sedimentology, 1990Co-Authors: Mark T. Burchell, Marco Stefani, Daniele MasettiAbstract:Uppermost Triassic (Rhaetic) facies, as developed in the Southern Alpine region of Northern Italy, were deposited in a rapidly subsiding, fault-dissected trough (the Lombardy Basin) bounded by carbonate platforms. The main part of the Rhaetic succession consists of 10-m-scale asymmetric cycles, each divided into three parts: a lower shale portion; a central rhythmic portion consisting of repeated marl-limestone couplets, the limestone parts of which thicken upward; and an upper, wholly carbonate unit. A study of the diagenetic history of the series demonstrates that both the major asymmetric Cyclicity and the limestone-marl couplets of the central rhythmic member (together constituting a ‘compound’ Cyclic form) are fundamentally depositional in nature. It is suggested that this compound Cyclicity resulted from the superposition of a low-frequency (approximately 100 000-year periodicity) asymmetric carbonate mud signal with a higher-frequency terrigenous mud signal. Field, petrographic, and geochemical investigations suggest that the basinal carbonate is predominantly allochthonous in origin, having been derived as relatively pure aragonitic mud from adjacent carbonate platforms. It is postulated that the asymmetric carbonate signal was linked to the ecological effects of eustatic fluctuation on platform carbonate systems. Repeated subaerial exposure of subtidal muds in shallow areas indicates that such sea-level variations occurred. A model is presented in which the basinward export of carbonate was negligible in the deepening phase, increased to a maximum during shallowing and was finally halted by the emergence of large platform flats. In contrast, the higher frequency terrigenous mud signal of the basin is thought to have been climatically modulated; fluctuations of a shorter period than those predicted by the Milankovitch theory affected hinterland precipitation and runoff. Particularly rapid subsidence and high depositional rates may have allowed the preservation of this signal.
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Cyclic Sedimentation in the Southern Alpine Rhaetic: the importance of climate and eustasy in controlling platform‐basin interactions
Sedimentology, 1990Co-Authors: Mark T. Burchell, Marco Stefani, Daniele MasettiAbstract:Uppermost Triassic (Rhaetic) facies, as developed in the Southern Alpine region of Northern Italy, were deposited in a rapidly subsiding, fault-dissected trough (the Lombardy Basin) bounded by carbonate platforms. The main part of the Rhaetic succession consists of 10-m-scale asymmetric cycles, each divided into three parts: a lower shale portion; a central rhythmic portion consisting of repeated marl-limestone couplets, the limestone parts of which thicken upward; and an upper, wholly carbonate unit. A study of the diagenetic history of the series demonstrates that both the major asymmetric Cyclicity and the limestone-marl couplets of the central rhythmic member (together constituting a ‘compound’ Cyclic form) are fundamentally depositional in nature. It is suggested that this compound Cyclicity resulted from the superposition of a low-frequency (approximately 100 000-year periodicity) asymmetric carbonate mud signal with a higher-frequency terrigenous mud signal. Field, petrographic, and geochemical investigations suggest that the basinal carbonate is predominantly allochthonous in origin, having been derived as relatively pure aragonitic mud from adjacent carbonate platforms. It is postulated that the asymmetric carbonate signal was linked to the ecological effects of eustatic fluctuation on platform carbonate systems. Repeated subaerial exposure of subtidal muds in shallow areas indicates that such sea-level variations occurred. A model is presented in which the basinward export of carbonate was negligible in the deepening phase, increased to a maximum during shallowing and was finally halted by the emergence of large platform flats. In contrast, the higher frequency terrigenous mud signal of the basin is thought to have been climatically modulated; fluctuations of a shorter period than those predicted by the Milankovitch theory affected hinterland precipitation and runoff. Particularly rapid subsidence and high depositional rates may have allowed the preservation of this signal.
J.m. Rouchy - One of the best experts on this subject based on the ideXlab platform.
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Evaporitic and biosiliceous Cyclic Sedimentation in the Miocene of the Gulf of Suez—Depositional and diagenetic aspects
Sedimentary Geology, 1995Co-Authors: J.m. Rouchy, D. Noël, A.m.a. Wali, Mahmoud A. ArefAbstract:Abstract The Middle to Late Miocene evaporite-bearing formations which outcrop along the Gebel Zeit and Gems highs in the southwestern Gulf of Suez (Egypt), consist of thick calcium sulphate beds rhythmically interbedded with marlstones, siltstones and claystones containing various amounts of biogenic silica, as well as pure diatomites. The calcium sulphate beds are composed mainly of gypsum and anhydrite. Subaqueous crustallisation in subpermanent brine ponds of marine origin predominated during deposition of the selenite and laminated gypsum. Early diagenetic interstitial growth of nodular anhydrite occurred episodically when the water level dropped, in response to increasing salinity associated with the precipitation of halite in the deeper troughs. Nevertheless, most of the nodular facies resulted from the burial conversion of gypsum to anhydrite which has been sometimes rehydrated into gypsum. A last phase of gypsum dehydration has occurred at the surface, related to the present hot and dry climatic conditions. The biosiliceous deposits contain either well preserved (opal-A) or diagenetically altered (opal-CT, clinoptilolite, quartz and even clays) diatom frustules. Such diagenetic changes are commonly described in the oceanic biosiliceous deposits. The fossil content of these diatomitic layers implies shallow-marine conditions on the shelves of highs induced by block faulting. The Cyclic succession of evaporited and biosiliceous deposits recorded the alternation of high sea level stands associated with high organic productivity, probably enhanced by seasonal input of nutrients and low sea level stands associated with hypersaline conditions and evaporite deposition. Locally, the sharp contact between the diatomites and gypsum argues for a rapid evolution of salinity towards high concentration (up to gypsum saturation and more). The formation of finely laminated diatomitic sediments is known to require either high organic productivity or anoxic conditions in bottom/intermediate waters, and eventually both processes. In the Gebel Zeit and Gemsa areas, a local association of the biosiliceous sediments with diagenetic carbonates and native sulphur, resulting from processes of bacterial sulphate reduction, confirms that anoxic conditions occurred in the deep-water body or in the sediments. Large amounts of organic compounds were involved in these diagenetic processes. Immature organic matter was consumed during an early diagenetic stage of transformation. It is assumed that this organic matter was supplied either by the biosilica-rich interbeds or the organic-rich laminated carbonates. The initial organic content of the biogenic deposits was impoverished as early as the first stages of Sedimentation and diagenesis. Although a large part of the organic matter could have been destroyed by these early diagenetic processes and further oxidation in outcrops, these sediments can be considered as potential source rocks in nearby less exposed sequences.
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evaporitic and biosiliceous Cyclic Sedimentation in the miocene of the gulf of suez depositional and diagenetic aspects
Sedimentary Geology, 1995Co-Authors: J.m. Rouchy, D. Noël, A.m.a. Wali, Mahmoud A. ArefAbstract:Abstract The Middle to Late Miocene evaporite-bearing formations which outcrop along the Gebel Zeit and Gems highs in the southwestern Gulf of Suez (Egypt), consist of thick calcium sulphate beds rhythmically interbedded with marlstones, siltstones and claystones containing various amounts of biogenic silica, as well as pure diatomites. The calcium sulphate beds are composed mainly of gypsum and anhydrite. Subaqueous crustallisation in subpermanent brine ponds of marine origin predominated during deposition of the selenite and laminated gypsum. Early diagenetic interstitial growth of nodular anhydrite occurred episodically when the water level dropped, in response to increasing salinity associated with the precipitation of halite in the deeper troughs. Nevertheless, most of the nodular facies resulted from the burial conversion of gypsum to anhydrite which has been sometimes rehydrated into gypsum. A last phase of gypsum dehydration has occurred at the surface, related to the present hot and dry climatic conditions. The biosiliceous deposits contain either well preserved (opal-A) or diagenetically altered (opal-CT, clinoptilolite, quartz and even clays) diatom frustules. Such diagenetic changes are commonly described in the oceanic biosiliceous deposits. The fossil content of these diatomitic layers implies shallow-marine conditions on the shelves of highs induced by block faulting. The Cyclic succession of evaporited and biosiliceous deposits recorded the alternation of high sea level stands associated with high organic productivity, probably enhanced by seasonal input of nutrients and low sea level stands associated with hypersaline conditions and evaporite deposition. Locally, the sharp contact between the diatomites and gypsum argues for a rapid evolution of salinity towards high concentration (up to gypsum saturation and more). The formation of finely laminated diatomitic sediments is known to require either high organic productivity or anoxic conditions in bottom/intermediate waters, and eventually both processes. In the Gebel Zeit and Gemsa areas, a local association of the biosiliceous sediments with diagenetic carbonates and native sulphur, resulting from processes of bacterial sulphate reduction, confirms that anoxic conditions occurred in the deep-water body or in the sediments. Large amounts of organic compounds were involved in these diagenetic processes. Immature organic matter was consumed during an early diagenetic stage of transformation. It is assumed that this organic matter was supplied either by the biosilica-rich interbeds or the organic-rich laminated carbonates. The initial organic content of the biogenic deposits was impoverished as early as the first stages of Sedimentation and diagenesis. Although a large part of the organic matter could have been destroyed by these early diagenetic processes and further oxidation in outcrops, these sediments can be considered as potential source rocks in nearby less exposed sequences.
