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Wilfried Jokat - One of the best experts on this subject based on the ideXlab platform.
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Response of Cenozoic turbidite system to tectonic activity and sea-level change off the Zambezi Delta
Marine Geophysical Research, 2017Co-Authors: Jude A. Castelino, Christian Reichert, Wilfried JokatAbstract:Submarine fans and turbidite systems are important and sensitive features located offshore from river deltas that archive tectonic events, regional climate, sea level variations and erosional process. Very little is known about the Sedimentary Structure of the 1800 km long and 400 km wide Mozambique Fan, which is fed by the Zambezi and spreads out into the Mozambique Channel. New multichannel seismic profiles in the Mozambique Basin reveal multiple feeder systems of the upper fan that have been active concurrently or consecutively since Late Cretaceous. We identify two buried, ancient turbidite systems off Mozambique in addition to the previously known Zambezi-Channel system and another hypothesized active system. The oldest part of the upper fan, located north of the present-day mouth of the Zambezi, was active from Late Cretaceous to Eocene times. Regional uplift caused an increased sediment flux that continued until Eocene times, allowing the fan to migrate southwards under the influence of bottom currents. Following the mid-Oligocene marine regression, the Beira High Channel-levee complex fed the Mozambique Fan from the southwest until Miocene times, reworking sediments from the shelf and continental slope into the distal abyssal fan. Since the Miocene, sediments have bypassed the shelf and upper fan region through the Zambezi Valley system directly into the Zambezi Channel. The morphology of the turbidite system off Mozambique is strongly linked to onshore tectonic events and the variations in sea level and sediment flux.
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the Sedimentary Structure of the lomonosov ridge between 88 n and 80 n
Geophysical Journal International, 2005Co-Authors: Wilfried JokatAbstract:SUMMARY While the origin of the 1800-km-long Lomonosov Ridge (LR) in the Central Arctic Ocean is believed to be well understood, details on the bathymetry and especially on the sediment and crustal Structure of this unique feature are sparse. During two expeditions in 1991 and 1998 into the Central Arctic Ocean several high quality seismic lines were collected along the margin of the ridge and in the adjacent Makarov Basin (MB). The lines collected between 87 ◦ 36 � N and 80 ◦ N perpendicular to and along the LR show a sediment starved continental margin with av ariety of geological Structures. The different features may reflect the different geological histories of certain ridge segments and/or their different subsidence histories. The sediments in the deep MB have thicknesses up to 2.2 km (3 s TWT) close to the foot of the ridge. At least in part basement reflections characteristics suggest oceanic crust. The acoustically stratified layers are flat lying, except in areas close to the ridge. Seismic units on the LR can be divided into two units based on refraction velocity data and the internal geometry of the reflections. Velocities 4.0 km s −1 are associated with faulted sediments at deeper levels and may represent acoustic basement, which was affected by the Late Cretaceous/Early Cenozoic rift events. Along large parts of the ridge the transition of the two units is associated with an erosional unconformity. Close to the Laptev Sea such an erosional surface may not be present, because of the initial great depths of the rocks. Here, the deeper strata are affected by tectonism, which suggests some relative motion between the LR and the Laptev Shelf. Stratigraphic correlation with the Laptev Sea Shelf suggests that the ridge has not moved as a separate plate over the past 10 Myr. The seismic and regional gravity data indicate that the ridge broadens towards the Laptev Shelf. Although the deeper Structure may be heavily intruded and altered, the LR appears to extend eastwards as far as 155 ◦ E, a consequence of a long-lived Late Cretaceous rift event. The seismic data across LR support the existence of iceberg scours in the central region of the ridge as far south as 81 ◦ N. However, no evidence for a large erosional events due to a more than 1000-m-thick sea ice cover is visible from the data. South of 85 ◦ N the seismic data indicate the presence of a bottom simulating reflector along all lines.
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Sedimentary Structure of the nansen and amundsen basins arctic ocean
Geophysical Research Letters, 2004Co-Authors: Wilfried Jokat, Uli MickschAbstract:[1] The first continuous multichannel seismic profile to investigate the deeper Structure of the western Nansen Basin was acquired in 2001 with the German and US icebreakers RV Polarstern and USCGC Healy. The 550-km long profile provides detailed insight into the deeper Structure of this part of the Arctic Ocean. The sediments are up to 4.5 km thick close to the North Svalbard margin. The sediments thin continuously towards the north. The topography of the oceanic basement in the Nansen Basin is very rough, and it crops out north of 84°43'N 22°05'E. Here, it prevents the deposition of thicker sediment units. The rift valley of the Gakkel Ridge, with water depths around 4830 m, was crossed at 85°36'N 16°41'E. The top of the basement along the profile can be fit by a theoretical subsidence curve. In the Amundsen Basin, sediments are only 1.7–2.0 km thick and oceanic basement younger than chron 13 shallows abruptly some 100 km north of the median valley. The contrasting basement Structures are related in our interpretation to the differing depositional histories of the two basins, and to asymmetric spreading in Cenozoic times.
Geraldine Jacobsen - One of the best experts on this subject based on the ideXlab platform.
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determining flow patterns and emplacement dynamics from tsunami deposits with no visible Sedimentary Structure
Earth Surface Processes and Landforms, 2017Co-Authors: Claire L Kain, Patrick Wassmer, James Goff, Catherine Chaguegoff, Christopher Gomez, Deidre Hart, D Fierro, Geraldine JacobsenAbstract:In the absence of eyewitness reports or clear Sedimentary Structures, it can be difficult to interpret tsunami deposits or reconstruct tsunami inundation patterns. The emplacement dynamics of two historical tsunami deposits were investigated at seven transects in Okains Bay, New Zealand, using a combined geospatial, geomagnetic and sedimentological approach. The tsunami deposits are present as layers of sand and silt intercalated between soils and become finer and thinner with distance inland. The deposits are attributed to the 1960 and possibly the 1868 tsunamis, based on radiometric dating and correlation with historical records. Measurements of Magnetic Fabric (MF: Anisotropy of Magnetic Susceptibility) and particle size were used to reconstruct the evolution of flow dynamics laterally and vertically. A combination of statistical methods, including spatial autocorrelation testing, Spearman's rank order correlation, Principal Component Analysis (PCA) and K-means cluster analysis, was applied to examine relationships between MF parameters and sediment texture, and infer depositional hydrodynamics. Flow patterns deduced from MF show the estuary channel acted as a conduit for inundation, with flow commonly aligned sub-perpendicular to the estuary bed. MF and sediment data suggest deposition occurred from settling during laminar flow. Evidence of both uprush and backwash deposition, as well as wave reflection from infraStructure, was found. Statistical analysis of data showed significant relationships between grain size parameters and MF parameters associated with flow speed and magnetic fabric type. PCA and cluster analysis differentiated samples into two primary hydrodynamic groups: 1) samples deposited from laminar flow, and 2) samples deposited close to the limit of inundation, which includes samples deposited further inland, those affected by flow convergence, and those in the upper part of tsunami deposits. This approach has potential as a tool for reconstructing hydrodynamic conditions for palaeotsunamis and by combining spatial and statistical analyses, large-scale investigations can be more easily performed. This article is protected by copyright. All rights reserved.
Patrick Wassmer - One of the best experts on this subject based on the ideXlab platform.
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determining flow patterns and emplacement dynamics from tsunami deposits with no visible Sedimentary Structure
Earth Surface Processes and Landforms, 2017Co-Authors: Claire L Kain, Patrick Wassmer, James Goff, Catherine Chaguegoff, Christopher Gomez, Deidre Hart, D Fierro, Geraldine JacobsenAbstract:In the absence of eyewitness reports or clear Sedimentary Structures, it can be difficult to interpret tsunami deposits or reconstruct tsunami inundation patterns. The emplacement dynamics of two historical tsunami deposits were investigated at seven transects in Okains Bay, New Zealand, using a combined geospatial, geomagnetic and sedimentological approach. The tsunami deposits are present as layers of sand and silt intercalated between soils and become finer and thinner with distance inland. The deposits are attributed to the 1960 and possibly the 1868 tsunamis, based on radiometric dating and correlation with historical records. Measurements of Magnetic Fabric (MF: Anisotropy of Magnetic Susceptibility) and particle size were used to reconstruct the evolution of flow dynamics laterally and vertically. A combination of statistical methods, including spatial autocorrelation testing, Spearman's rank order correlation, Principal Component Analysis (PCA) and K-means cluster analysis, was applied to examine relationships between MF parameters and sediment texture, and infer depositional hydrodynamics. Flow patterns deduced from MF show the estuary channel acted as a conduit for inundation, with flow commonly aligned sub-perpendicular to the estuary bed. MF and sediment data suggest deposition occurred from settling during laminar flow. Evidence of both uprush and backwash deposition, as well as wave reflection from infraStructure, was found. Statistical analysis of data showed significant relationships between grain size parameters and MF parameters associated with flow speed and magnetic fabric type. PCA and cluster analysis differentiated samples into two primary hydrodynamic groups: 1) samples deposited from laminar flow, and 2) samples deposited close to the limit of inundation, which includes samples deposited further inland, those affected by flow convergence, and those in the upper part of tsunami deposits. This approach has potential as a tool for reconstructing hydrodynamic conditions for palaeotsunamis and by combining spatial and statistical analyses, large-scale investigations can be more easily performed. This article is protected by copyright. All rights reserved.
Catherine Chaguegoff - One of the best experts on this subject based on the ideXlab platform.
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determining flow patterns and emplacement dynamics from tsunami deposits with no visible Sedimentary Structure
Earth Surface Processes and Landforms, 2017Co-Authors: Claire L Kain, Patrick Wassmer, James Goff, Catherine Chaguegoff, Christopher Gomez, Deidre Hart, D Fierro, Geraldine JacobsenAbstract:In the absence of eyewitness reports or clear Sedimentary Structures, it can be difficult to interpret tsunami deposits or reconstruct tsunami inundation patterns. The emplacement dynamics of two historical tsunami deposits were investigated at seven transects in Okains Bay, New Zealand, using a combined geospatial, geomagnetic and sedimentological approach. The tsunami deposits are present as layers of sand and silt intercalated between soils and become finer and thinner with distance inland. The deposits are attributed to the 1960 and possibly the 1868 tsunamis, based on radiometric dating and correlation with historical records. Measurements of Magnetic Fabric (MF: Anisotropy of Magnetic Susceptibility) and particle size were used to reconstruct the evolution of flow dynamics laterally and vertically. A combination of statistical methods, including spatial autocorrelation testing, Spearman's rank order correlation, Principal Component Analysis (PCA) and K-means cluster analysis, was applied to examine relationships between MF parameters and sediment texture, and infer depositional hydrodynamics. Flow patterns deduced from MF show the estuary channel acted as a conduit for inundation, with flow commonly aligned sub-perpendicular to the estuary bed. MF and sediment data suggest deposition occurred from settling during laminar flow. Evidence of both uprush and backwash deposition, as well as wave reflection from infraStructure, was found. Statistical analysis of data showed significant relationships between grain size parameters and MF parameters associated with flow speed and magnetic fabric type. PCA and cluster analysis differentiated samples into two primary hydrodynamic groups: 1) samples deposited from laminar flow, and 2) samples deposited close to the limit of inundation, which includes samples deposited further inland, those affected by flow convergence, and those in the upper part of tsunami deposits. This approach has potential as a tool for reconstructing hydrodynamic conditions for palaeotsunamis and by combining spatial and statistical analyses, large-scale investigations can be more easily performed. This article is protected by copyright. All rights reserved.
Fulvio Zezza - One of the best experts on this subject based on the ideXlab platform.
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The Sedimentary Structure of Upper Pleistocene–Holocene deposits in Venice and its effects on the stability of the historic centre
RENDICONTI LINCEI, 2010Co-Authors: Fulvio ZezzaAbstract:The results of a recent study (Geologia e Progettazione nel centro storico di Venezia”, Secondo Convegno Nazionale: La riqualificazione delle città e dei territori, Venezia 7 dicembre 2007, Quad. IUAV 54, Il Poligrafo ed. 2008) focused on Venice’s historic centre have led to the identification of a peculiar Sedimentary Structure (multistorey sandbody). This Structure was created during the Upper Pleistocene by the multiple overlapping of sandbodies corresponding to stream channels, all of which crossed the area where the city now lies. The erosion and deposition events responsible for these stratigraphic conditions are the effects of both climatic variations during the Wurmian glaciation and changes in the fluvial regime. The Sedimentary Structure was completed during the Holocene by the deposition of sand in fluvial and tidal channels on top of the previous Pleistocene stream channel sediments. The deposits of this Structure are heteropic with those of the rhythmic succession (cyclothemic organization) belonging to the alluvial plain of the Upper Pleistocene and the Holocene lagoon facies of tidal plain found in the surrounding area. The geological model of the city is able to explain the mechanical behaviour of the soil in the western and eastern areas of the historic centre where the losses in elevation are considered at present as a consequence of the urban development in the last centuries, since the vertical movements due to groundwater exploitation of the deep aquifers have more than likely ended. According to a methodology known as operational facies concept, which first determines the facies relationship, then discriminates the intervals with lithological variability and finally fits together the information coming from the terrain properties, it can be inferred that the losses in elevation are related to the evolution of the deformation processes acting nowadays in the urban settlement. The results of the aforementioned study reveal, in fact, that these processes are provoked by the residual component of a long-term secondary consolidation and by the geochemical subsidence which occurs between salt water intrusion and clay containing organic matter and peat.
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the Sedimentary Structure of upper pleistocene holocene deposits in venice and its effects on the stability of the historic centre
Atti della Accademia Nazionale dei Lincei. Rendiconti Lincei. Scienze fisiche e naturali, 2010Co-Authors: Fulvio ZezzaAbstract:The results of a recent study (Geologia e Progettazione nel centro storico di Venezia”, Secondo Convegno Nazionale: La riqualificazione delle citta e dei territori, Venezia 7 dicembre 2007, Quad. IUAV 54, Il Poligrafo ed. 2008) focused on Venice’s historic centre have led to the identification of a peculiar Sedimentary Structure (multistorey sandbody). This Structure was created during the Upper Pleistocene by the multiple overlapping of sandbodies corresponding to stream channels, all of which crossed the area where the city now lies. The erosion and deposition events responsible for these stratigraphic conditions are the effects of both climatic variations during the Wurmian glaciation and changes in the fluvial regime. The Sedimentary Structure was completed during the Holocene by the deposition of sand in fluvial and tidal channels on top of the previous Pleistocene stream channel sediments. The deposits of this Structure are heteropic with those of the rhythmic succession (cyclothemic organization) belonging to the alluvial plain of the Upper Pleistocene and the Holocene lagoon facies of tidal plain found in the surrounding area. The geological model of the city is able to explain the mechanical behaviour of the soil in the western and eastern areas of the historic centre where the losses in elevation are considered at present as a consequence of the urban development in the last centuries, since the vertical movements due to groundwater exploitation of the deep aquifers have more than likely ended. According to a methodology known as operational facies concept, which first determines the facies relationship, then discriminates the intervals with lithological variability and finally fits together the information coming from the terrain properties, it can be inferred that the losses in elevation are related to the evolution of the deformation processes acting nowadays in the urban settlement. The results of the aforementioned study reveal, in fact, that these processes are provoked by the residual component of a long-term secondary consolidation and by the geochemical subsidence which occurs between salt water intrusion and clay containing organic matter and peat.
