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N. Vivian - One of the best experts on this subject based on the ideXlab platform.
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controls on Turbidite sand deposition during gravity driven extension of a passive margin examples from miocene sediments in block 4 angola
Marine and Petroleum Geology, 2000Co-Authors: J.e. Anderson, S. J. Drysdall, J. Cartwright, N. VivianAbstract:Abstract In recent years, exploration of the Lower Congo Basin in Angola has focused on the Neogene Turbidite sand play of the Malembo Formation. Gravity tectonics has played an important role during deposition of the Malembo Formation and has imparted a well-documented structural style to the post-rift sediments. An oceanward transition from thin-skinned extension through mobile salt and eventually to thin-skinned compressional structures characterises the post-rift sediments. There has been little discussion, however, regarding the influence of these structures on the deposition of the Malembo Formation Turbidite sands. Block 4 lies at the southern margin of the Lower Congo Basin and is dominated by the thin-skinned extensional structural style. Using a multidisciplinary approach we trace the post-rift structural and stratigraphic evolution of this block to study the structural controls on Neogene Turbidite sand deposition. In the Lower Congo Basin the transition from terrestrial rift basin to fully marine passive margin is recorded by late Aptian evaporites of the Loeme Formation. Extension of the overlying post-rift sequences has occurred where the Loeme Formation has been utilised as a detachment surface for extensional faults. Since the late Cretaceous, the passive margin sediments have moved down-slope on the Loeme detachment. This history of gravity-driven extension is recorded in the post-rift sediments of Block 4. Extension commenced in the Albian in the east of the block and migrated westwards with time. In the west, the extension occurred mainly in the Miocene and generated allochthonous fault blocks or “rafts”, separated by deep grabens. The Miocene extension occurred in two main phases with contrasting slip vectors; in the early Miocene the extension vector was to the west, switching to southwest-directed extension in the late Miocene. Early Miocene faults and half-grabens trend north–south whereas late Miocene structures trend northwest–southeast. The contrast in slip vectors between these two phases emphasises the differences in driving mechanisms: the early Miocene faulting was driven by basinward tilting of the passive margin, but gravity loading due to sedimentary progradation is considered the main driver for the late Miocene extension. The geological evolution of the late Miocene grabens is consistent with southwest-directed extension due to southwest progradation of the Congo fan. High-resolution biostratigraphic data identifies the Turbidite sands in Block 4 as early Miocene (17.5–15.5 Ma) and late Miocene (10.5–5.5 Ma) in age. Deposition of these sands occurred during the two main phases of gravity-driven extension. Conditions of low sedimentation rates relative to high fault displacement rates were prevalent in the early Miocene. Seafloor depressions were generated in the hangingwalls of the main extensional faults, ultimately leading to capture of the turbidity currents. Lower Miocene Turbidite sand bodies therefore trend north–south, parallel to the active faults. Cross-faults and relay ramps created local topographic highs capable of deflecting Turbidite flows within the half grabens. Flow-stripping of turbidity currents across these features caused preferential deposition of sands across, and adjacent to, the highs. Turbidite sands deposited in the early part of the late Miocene were influenced by both the old north–south fault trends and by the new northwest–southeast fault trends. By latest Miocene times Turbidite channels crosscut the active northwest–southeast-trending faults. These latest Miocene faults had limited potential to capture turbidity currents because the associated hangingwall grabens were rapidly filled as pro-delta sediments of the Congo fan prograded across the area from the northeast.
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Controls on Turbidite sand deposition during gravity-driven extension of a passive margin: Examples from Miocene sediments in Block 4, Angola
Marine and Petroleum Geology, 2000Co-Authors: J.e. Anderson, S. J. Drysdall, J. Cartwright, N. VivianAbstract:In recent years, exploration of the Lower Congo Basin in Angola has focused on the Neogene Turbidite sand play of the Malembo Formation. Gravity tectonics has played an important role during deposition of the Malembo Formation and has imparted a well-documented structural style to the post-rift sediments. An oceanward transition from thin-skinned extension through mobile salt and eventually to thin-skinned compressional structures characterises the post-rift sediments. There has been little discussion, however, regarding the influence of these structures on the deposition of the Malembo Formation Turbidite sands. Block 4 lies at the southern margin of the Lower Congo Basin and is dominated by the thin-skinned extensional structural style. Using a multidisciplinary approach we trace the post-rift structural and stratigraphic evolution of this block to study the structural controls on Neogene Turbidite sand deposition. In the Lower Congo Basin the transition from terrestrial rift basin to fully marine passive margin is recorded by late Aptian evaporites of the Loeme Formation. Extension of the overlying post-rift sequences has occurred where the Loeme Formation has been utilised as a detachment surface for extensional faults. Since the late Cretaceous, the passive margin sediments have moved down-slope on the Loeme detachment. This history of gravity-driven extension is recorded in the post-rift sediments of Block 4. Extension commenced in the Albian in the east of the block and migrated westwards with time. In the west, the extension occurred mainly in the Miocene and generated allochthonous fault blocks or "rafts", separated by deep grabens. The Miocene extension occurred in two main phases with contrasting slip vectors; in the early Miocene the extension vector was to the west, switching to southwest-directed extension in the late Miocene. Early Miocene faults and half-grabens trend north-south whereas late Miocene structures trend northwest-southeast. The contrast in slip vectors between these two phases emphasises the differences in driving mechanisms: the early Miocene faulting was driven by basinward tilting of the passive margin, but gravity loading due to sedimentary progradation is considered the main driver for the late Miocene extension. The geological evolution of the late Miocene grabens is consistent with southwest-directed extension due to southwest progradation of the Congo fan. High-resolution biostratigraphic data identifies the Turbidite sands in Block 4 as early Miocene (17.5-15.5 Ma) and late Miocene (10.5-5.5 Ma) in age. Deposition of these sands occurred during the two main phases of gravity-driven extension. Conditions of low sedimentation rates relative to high fault displacement rates were prevalent in the early Miocene. Seafloor depressions were generated in the hangingwalls of the main extensional faults, ultimately leading to capture of the turbidity currents. Lower Miocene Turbidite sand bodies therefore trend north-south, parallel to the active faults. Cross-faults and relay ramps created local topographic highs capable of deflecting Turbidite flows within the half grabens. Flow-stripping of turbidity currents across these features caused preferential deposition of sands across, and adjacent to, the highs. Turbidite sands deposited in the early part of the late Miocene were influenced by both the old north-south fault trends and by the new northwest-southeast fault trends. By latest Miocene times Turbidite channels crosscut the active northwest-southeast-trending faults. These latest Miocene faults had limited potential to capture turbidity currents because the associated hangingwall grabens were rapidly filled as pro-delta sediments of the Congo fan prograded across the area from the northeast. © 2001 Elsevier Science Ltd. All rights reserved.
Christopher A Scholz - One of the best experts on this subject based on the ideXlab platform.
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Turbidite systems of lacustrine rift basins examples from the lake kivu and lake albert rifts east africa
Sedimentary Geology, 2015Co-Authors: Xuewei Zhang, Christopher A ScholzAbstract:Abstract The Holocene Turbidite systems of Lake Kivu and the Pliocene Turbidite systems of Lake Albert in the East African Rift were examined using high-resolution 2-D and 3-D seismic reflection data and sediment core information. Based on investigations of seismic facies and lithofacies, several key turbidity-flow depositional elements were observed, including channels, overbank levees with sediment waves, and depositional lobes. Analyses of the sources of the recent and ancient Turbidite systems in these two extensional basins suggest that flood-induced hyperpycnal flows are important triggers of turbidity currents in lacustrine rift basins. From source to sink, sediment dispersal, facies distribution, and depositional thickness of the Turbidite systems are strongly influenced by rift topography. The Lake Kivu and Lake Albert rifts serve as excellent analogues for understanding the sedimentary patterns of lacustrine Turbidites in extensional basins.
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climatic control of the late quaternary Turbidite sedimentology of lake kivu east africa implications for deep mixing and geologic hazards
Geology, 2014Co-Authors: Xuewei Zhang, Christopher A Scholz, Robert E Hecky, Douglas Wood, C J EbingerAbstract:The Lake Kivu catchment in the East African Rift is subject to various geologic hazards, including frequent volcanic eruptions, earthquakes, and potential limnic overturns and degassing events. Integration of high-resolution seismic reflection data, 14 C dated sediment cores, and lake-floor bathymetry reveals large axial and transverse Turbidite systems in the eastern basin of the lake. The Turbidites were sourced by hyperpycnal river flows during exceptional floods, and the temporal occurrence of the Turbidites was climatically controlled. The Turbidite record over the past ∼12 k.y. is correlated with the regional paleohydrologic records from tropical East Africa. Our study suggests that flood-introduced Turbidites preserved in deep lakes are indicators of hydrological changes, and that extreme floods in Lake Kivu9s recent history may have triggered deep mixing events. This study also has implications for the current degassing efforts in Lake Kivu; potential geologic hazards may be triggered by extraordinary turbidity currents, and need to be considered in the design and deployment of gas extraction facilities.
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deltaic sedimentation in a modern rift lake
Geological Society of America Bulletin, 1995Co-Authors: Thomas C Johnson, John D Wells, Christopher A ScholzAbstract:Five of the largest deltas of Lake Malawi in Africa were surveyed to compare and contrast bathymetry, bedform distribution, and sedimentary facies using high-resolution seismic reflection profiling, side-scan sonar, and sediment coring. Striking variability in delta morphology and depositional facies was found, depending primarily on tectonic setting but also influenced strongly by lake processes and the significant past variability in lake level resulting from climatic change. Deltas on border faults and accommodation zones have much steeper offshore gradients than those on shoaling margins, resulting in narrow sandy shelves, abundant mass wasting, and sand bypass to the deep basins as Turbidites, either confined to turbidity channels or spread across sand ramps. At the axial margin of the lake, where the trend of faults is orthogonal to the shoreline, deltaic facies are dominated by mud, mass wasting is common, and numerous Turbidite channels coalesce into a single major, fault-controlled channel. In contrast, deltas on shoaling margins have broad, sandy shelves that are strongly influenced by coastal currents, which rework the sands into well-developed sand wave fields. Turbidites are not common in this setting, and the slope regions are covered with poorly sorted sandy muds with little evidence for downslope transport.
J.e. Anderson - One of the best experts on this subject based on the ideXlab platform.
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controls on Turbidite sand deposition during gravity driven extension of a passive margin examples from miocene sediments in block 4 angola
Marine and Petroleum Geology, 2000Co-Authors: J.e. Anderson, S. J. Drysdall, J. Cartwright, N. VivianAbstract:Abstract In recent years, exploration of the Lower Congo Basin in Angola has focused on the Neogene Turbidite sand play of the Malembo Formation. Gravity tectonics has played an important role during deposition of the Malembo Formation and has imparted a well-documented structural style to the post-rift sediments. An oceanward transition from thin-skinned extension through mobile salt and eventually to thin-skinned compressional structures characterises the post-rift sediments. There has been little discussion, however, regarding the influence of these structures on the deposition of the Malembo Formation Turbidite sands. Block 4 lies at the southern margin of the Lower Congo Basin and is dominated by the thin-skinned extensional structural style. Using a multidisciplinary approach we trace the post-rift structural and stratigraphic evolution of this block to study the structural controls on Neogene Turbidite sand deposition. In the Lower Congo Basin the transition from terrestrial rift basin to fully marine passive margin is recorded by late Aptian evaporites of the Loeme Formation. Extension of the overlying post-rift sequences has occurred where the Loeme Formation has been utilised as a detachment surface for extensional faults. Since the late Cretaceous, the passive margin sediments have moved down-slope on the Loeme detachment. This history of gravity-driven extension is recorded in the post-rift sediments of Block 4. Extension commenced in the Albian in the east of the block and migrated westwards with time. In the west, the extension occurred mainly in the Miocene and generated allochthonous fault blocks or “rafts”, separated by deep grabens. The Miocene extension occurred in two main phases with contrasting slip vectors; in the early Miocene the extension vector was to the west, switching to southwest-directed extension in the late Miocene. Early Miocene faults and half-grabens trend north–south whereas late Miocene structures trend northwest–southeast. The contrast in slip vectors between these two phases emphasises the differences in driving mechanisms: the early Miocene faulting was driven by basinward tilting of the passive margin, but gravity loading due to sedimentary progradation is considered the main driver for the late Miocene extension. The geological evolution of the late Miocene grabens is consistent with southwest-directed extension due to southwest progradation of the Congo fan. High-resolution biostratigraphic data identifies the Turbidite sands in Block 4 as early Miocene (17.5–15.5 Ma) and late Miocene (10.5–5.5 Ma) in age. Deposition of these sands occurred during the two main phases of gravity-driven extension. Conditions of low sedimentation rates relative to high fault displacement rates were prevalent in the early Miocene. Seafloor depressions were generated in the hangingwalls of the main extensional faults, ultimately leading to capture of the turbidity currents. Lower Miocene Turbidite sand bodies therefore trend north–south, parallel to the active faults. Cross-faults and relay ramps created local topographic highs capable of deflecting Turbidite flows within the half grabens. Flow-stripping of turbidity currents across these features caused preferential deposition of sands across, and adjacent to, the highs. Turbidite sands deposited in the early part of the late Miocene were influenced by both the old north–south fault trends and by the new northwest–southeast fault trends. By latest Miocene times Turbidite channels crosscut the active northwest–southeast-trending faults. These latest Miocene faults had limited potential to capture turbidity currents because the associated hangingwall grabens were rapidly filled as pro-delta sediments of the Congo fan prograded across the area from the northeast.
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Controls on Turbidite sand deposition during gravity-driven extension of a passive margin: Examples from Miocene sediments in Block 4, Angola
Marine and Petroleum Geology, 2000Co-Authors: J.e. Anderson, S. J. Drysdall, J. Cartwright, N. VivianAbstract:In recent years, exploration of the Lower Congo Basin in Angola has focused on the Neogene Turbidite sand play of the Malembo Formation. Gravity tectonics has played an important role during deposition of the Malembo Formation and has imparted a well-documented structural style to the post-rift sediments. An oceanward transition from thin-skinned extension through mobile salt and eventually to thin-skinned compressional structures characterises the post-rift sediments. There has been little discussion, however, regarding the influence of these structures on the deposition of the Malembo Formation Turbidite sands. Block 4 lies at the southern margin of the Lower Congo Basin and is dominated by the thin-skinned extensional structural style. Using a multidisciplinary approach we trace the post-rift structural and stratigraphic evolution of this block to study the structural controls on Neogene Turbidite sand deposition. In the Lower Congo Basin the transition from terrestrial rift basin to fully marine passive margin is recorded by late Aptian evaporites of the Loeme Formation. Extension of the overlying post-rift sequences has occurred where the Loeme Formation has been utilised as a detachment surface for extensional faults. Since the late Cretaceous, the passive margin sediments have moved down-slope on the Loeme detachment. This history of gravity-driven extension is recorded in the post-rift sediments of Block 4. Extension commenced in the Albian in the east of the block and migrated westwards with time. In the west, the extension occurred mainly in the Miocene and generated allochthonous fault blocks or "rafts", separated by deep grabens. The Miocene extension occurred in two main phases with contrasting slip vectors; in the early Miocene the extension vector was to the west, switching to southwest-directed extension in the late Miocene. Early Miocene faults and half-grabens trend north-south whereas late Miocene structures trend northwest-southeast. The contrast in slip vectors between these two phases emphasises the differences in driving mechanisms: the early Miocene faulting was driven by basinward tilting of the passive margin, but gravity loading due to sedimentary progradation is considered the main driver for the late Miocene extension. The geological evolution of the late Miocene grabens is consistent with southwest-directed extension due to southwest progradation of the Congo fan. High-resolution biostratigraphic data identifies the Turbidite sands in Block 4 as early Miocene (17.5-15.5 Ma) and late Miocene (10.5-5.5 Ma) in age. Deposition of these sands occurred during the two main phases of gravity-driven extension. Conditions of low sedimentation rates relative to high fault displacement rates were prevalent in the early Miocene. Seafloor depressions were generated in the hangingwalls of the main extensional faults, ultimately leading to capture of the turbidity currents. Lower Miocene Turbidite sand bodies therefore trend north-south, parallel to the active faults. Cross-faults and relay ramps created local topographic highs capable of deflecting Turbidite flows within the half grabens. Flow-stripping of turbidity currents across these features caused preferential deposition of sands across, and adjacent to, the highs. Turbidite sands deposited in the early part of the late Miocene were influenced by both the old north-south fault trends and by the new northwest-southeast fault trends. By latest Miocene times Turbidite channels crosscut the active northwest-southeast-trending faults. These latest Miocene faults had limited potential to capture turbidity currents because the associated hangingwall grabens were rapidly filled as pro-delta sediments of the Congo fan prograded across the area from the northeast. © 2001 Elsevier Science Ltd. All rights reserved.
Angel Pugabernabeu - One of the best experts on this subject based on the ideXlab platform.
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filling the gap a 60 ky record of mixed carbonate siliciclastic Turbidite deposition from the great barrier reef
Marine and Petroleum Geology, 2014Co-Authors: Jody M Webster, Robin J Beaman, Angel Pugabernabeu, Paula J Reimer, Willem RenemaAbstract:Abstract Late Pleistocene to Holocene margin sedimentation on the Great Barrier Reef, a mixed carbonate-siliciclastic margin, has been explained by a transgressive shedding model. This model has challenged widely accepted sequence stratigraphic models in terms of the timing and type of sediment (i.e. carbonate vs. siliciclastic) deposited during sea-level oscillations. However, this model documents only hemipelagic sedimentation and the contribution of coarse-grained Turbidite deposition, and the role of submarine canyons in this process, remain elusive on this archetypal margin. Here we present a new model of Turbidite deposition for the last 60 ky in the north-eastern Australia margin. Using high-resolution bathymetry, 58 new and existing radiometric ages, and the composition of 81 Turbidites from 15 piston cores, we found that the spatial and temporal variation of Turbidites is controlled by the relationship between sea-level change and the variable physiography along the margin. Siliciclastic and mixed carbonate-siliciclastic Turbidites were linked to canyons indenting the shelf-break and the well-developed shelf-edge reef barriers that stored sediment behind them. Turbidite deposition was sustained while the sea-level position allowed the connection and sediment bypassing through the inter-reef passages and canyons. Carbonate Turbidites dominated in regions with more open conditions at the outer-shelf and where slope-confined canyons dominated or where canyons are generally less abundant. The turn-on and maintenance of carbonate production during sea-level fluctuations also influenced the timing of carbonate Turbidite deposition. We show that a fundamental understanding of the variable physiography inherent to mixed carbonate-siliciclastic margins is essential to accurately interpret deep-water, coarse-grained deposition within a sequence stratigraphic context.
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late pleistocene history of Turbidite sedimentation in a submarine canyon off the northern great barrier reef australia
Palaeogeography Palaeoclimatology Palaeoecology, 2012Co-Authors: Jody M Webster, Robin J Beaman, Angel Pugabernabeu, Deane Ludman, Willem Renema, Raphael A J Wust, Nicholas P J GeorgeAbstract:Cores from slopes east of the Great Barrier Reef (GBR) challenge traditional models for sedimentation on tropical mixed siliciclastic-carbonate margins. However, satisfactory explanations of sediment accumulation on this archetypal margin that include both hemipelagic and Turbidite sedimentation remain elusive, as submarine canyons and their role in delivering coarse-grained Turbidite deposits, are poorly understood. Towards addressing this problem we investigated the shelf and canyon system bordering the northern Ribbon Reefs and reconstructed the history of Turbidite deposition since the Late Pleistocene. High-resolution bathymetric and seismic data show a large paleo-channel system that crosses the shelf before connecting with the canyons via the inter-reef passages between the Ribbon Reefs. High-resolution bathymetry of the canyon axis reveals a complex and active system of channels, sand waves, and local submarine landslides. Multi-proxy examination of three cores from down the axis of the canyon system reveals 18 Turbidites and debrites, interlayered with hemipelagic muds, that are derived from a mix of shallow and deep sources. Twenty radiocarbon ages indicate that siliciclastic-dominated and mixed Turbidites only occur prior to 31 ka during Marine Isotope Stage (MIS) 3, while carbonate-dominated Turbidites are well established by 11 ka in MIS1 until as recently as 1.2 ka. The apparent lack of siliciclastic-dominated Turbidites and presence of only a few carbonate-dominated Turbidites during the MIS2 lowstand are not consistent with generic models of margin sedimentation but might also reflect a gap in the Turbidite record. These data suggest that Turbidite sedimentation in the Ribbon Reef canyons, probably reflects the complex relationship between the prolonged period (> 25 ka) of MIS3 millennial sea level changes and local factors such as the shelf, inter-reef passage depth, canyon morphology and different sediment sources. On this basis we predict that the spatial and temporal patterns of Turbidite sedimentation could vary considerably along the length of the GBR margin.
Xuewei Zhang - One of the best experts on this subject based on the ideXlab platform.
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Turbidite systems of lacustrine rift basins examples from the lake kivu and lake albert rifts east africa
Sedimentary Geology, 2015Co-Authors: Xuewei Zhang, Christopher A ScholzAbstract:Abstract The Holocene Turbidite systems of Lake Kivu and the Pliocene Turbidite systems of Lake Albert in the East African Rift were examined using high-resolution 2-D and 3-D seismic reflection data and sediment core information. Based on investigations of seismic facies and lithofacies, several key turbidity-flow depositional elements were observed, including channels, overbank levees with sediment waves, and depositional lobes. Analyses of the sources of the recent and ancient Turbidite systems in these two extensional basins suggest that flood-induced hyperpycnal flows are important triggers of turbidity currents in lacustrine rift basins. From source to sink, sediment dispersal, facies distribution, and depositional thickness of the Turbidite systems are strongly influenced by rift topography. The Lake Kivu and Lake Albert rifts serve as excellent analogues for understanding the sedimentary patterns of lacustrine Turbidites in extensional basins.
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climatic control of the late quaternary Turbidite sedimentology of lake kivu east africa implications for deep mixing and geologic hazards
Geology, 2014Co-Authors: Xuewei Zhang, Christopher A Scholz, Robert E Hecky, Douglas Wood, C J EbingerAbstract:The Lake Kivu catchment in the East African Rift is subject to various geologic hazards, including frequent volcanic eruptions, earthquakes, and potential limnic overturns and degassing events. Integration of high-resolution seismic reflection data, 14 C dated sediment cores, and lake-floor bathymetry reveals large axial and transverse Turbidite systems in the eastern basin of the lake. The Turbidites were sourced by hyperpycnal river flows during exceptional floods, and the temporal occurrence of the Turbidites was climatically controlled. The Turbidite record over the past ∼12 k.y. is correlated with the regional paleohydrologic records from tropical East Africa. Our study suggests that flood-introduced Turbidites preserved in deep lakes are indicators of hydrological changes, and that extreme floods in Lake Kivu9s recent history may have triggered deep mixing events. This study also has implications for the current degassing efforts in Lake Kivu; potential geologic hazards may be triggered by extraordinary turbidity currents, and need to be considered in the design and deployment of gas extraction facilities.
