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Jean-claude Faugères - One of the best experts on this subject based on the ideXlab platform.
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Hummocky Cross-Stratification-like structures in deep-sea turbidites: Upper Cretaceous Basque basins (Western Pyrenees, France)
Sedimentology, 2009Co-Authors: Thierry Mulder, Philippe Razin, Jean-claude FaugèresAbstract:Hummocky Cross-Stratification is a sedimentary structure which is widely interpreted as the sedimentary record of an oscillatory current generated by energetic storm waves remobilizing surface sediment on the continental shelf. Sedimentary structures named Hummocky Cross-Stratification-like structures, similar to true Hummocky Cross-Stratification, have been observed in the Turonian–Senonian Basque Flysch Basin (south-west France). The bathymetry (1000 to 1500 m) suggests that the observed sedimentary structures do not result from a hydrodynamic process similar to those acting on a continental shelf. The morphology of these three-dimensional structures shares similarities with the morphology of Hummocky Cross-Stratification despite a smaller size. The lateral extent of these structures ranges from a few decimetres to many decimetres; they consist of convex-up domes (hummock) and concave-up swales with a non-erosive base. Four types of Hummocky Cross-Stratification-like geometries are described; they occur in association with structures such as climbing current ripple lamination and synsedimentary deformations. In the Basque Flysch, Hummocky Cross-Stratification-like structures are only found in the Tc interval of the Bouma sequence. Hummocky Cross-Stratification-like structures are sporadic in the stratigraphic series and observed only in few turbidite beds or bed packages. This observation suggests that Hummocky Cross-Stratification-like structures are linked genetically to the turbidity current but form under a very restricted range of parameters. These structures sometimes show an up-current (upslope) migration trend (antidunes). In the described examples, they could result from standing waves forming at the upper flow interface because of Kelvin–Helmholtz instability.
Giorgio Basilici - One of the best experts on this subject based on the ideXlab platform.
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Hummocky cross stratification like structures and combined flow ripples in the punta negra formation lower middle devonian argentine precordillera a turbiditic deep water or storm dominated prodelta inner shelf system
Sedimentary Geology, 2012Co-Authors: Giorgio Basilici, Pedro Henrique Vieira De Luca, Daniel Gustavo PoireAbstract:Abstract Turbidity-current and storm-induced deposits may exhibit similarities, in particularly when the latter is laid down by a combination of oscillatory and unidirectional flows. Recent progress in facies analysis helps to discriminate the sedimentary effects of oscillatory from unidirectional components of the flow. On the basis of detailed analysis of sedimentary facies, strata geometry, and palaeocurrent data, the present study reinterprets the Punta Negra Formation (PNF) (Lower-Middle Devonian, Argentine Precordillera), previously considered as a depositional system of deep-water, as a storm-dominated prodeltaic shelf depositional system. In the sandstone beds of the PNF, planar, low-angle and undulating laminations with weakly asymmetric Hummocky and swaley bedforms, combined-flow ripples, accretionary Hummocky Cross-Stratification-like (HCS-like), and anisotropic HCS-like suggest the action of oscillatory currents combined with unidirectional currents in forming the deposits. Different hypotheses on the origin of the oscillatory currents have been examined. The most convincing interpretation is that the oscillatory component of the velocity is attributed to storm-induced waves. The palaeocurrent data indicate offshore current directions, suggesting that the unidirectional flow was a gravity-induced bottom current. Inverse grading at the base and overlying normally graded divisions of the sandstone beds testify to waxing–waning behaviour of the depositional flows; interbedding of sedimentary structures (undulating laminations, low-angle and parallel laminations, and combined-flow ripples) in the lower and intermediate divisions of the beds indicate fluctuations of flow velocity. This organisation of the sedimentary structures permits association of the unidirectional component with hyperpycnal bottom currents. The terrestrial origin of the hyperpycnal flows is suggested by the abundance of terrestrial plant remains, the mineralogical and textural immaturity of the sandstone composition, and the relative scarcity of bioturbation, which was likely controlled by fresh-water input and a high rate of sedimentation. Storm-influenced, hyperpycnal flows generated subaqueous channelised forms at the mouth of the river deltas, which later filled with sand. At the distal end of the channelised forms, lobe-shaped sandstone beds were deposited, evolving distally into thin sandstone beds alternating with sandy mudstone.
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A depositional model for a wave‐dominated open‐coast tidal flat, based on analyses of the Cambrian–Ordovician Lagarto and Palmares formations, north‐eastern Brazil
Sedimentology, 2012Co-Authors: Giorgio Basilici, Pedro Henrique Vieira De Luca, Elson P. OliveiraAbstract:Open-coast tidal flats are hybrid depositional systems resulting from the interaction of waves and tides. Modern examples have been recognized, but few cases have been described in ancient rock successions. An example of an ancient open-coast tidal flat, the depositional architecture of the Lagarto and Palmares formations (Cambrian–Ordovician of the Sergipano Belt, north-eastern Brazil) is presented here. Detailed field analyses of outcrops allowed the development of a conceptual architectural model for a coastal depositional environment that is substantially different from classical wave-dominated or tide-dominated coastal models. This architectural model is dominated by storm wave, low orbital velocity wave and tidal current beds, which vary in their characteristics and distribution. In a landward direction, the storm deposits decrease in abundance, dimension (thickness and spacing) and grain size, and vary from accretionary through scour and drape to anisotropic Hummocky Cross-Stratification beds. Low orbital wave deposits are more common in the medium and upper portion of the tidal flat. Tidal deposits, which are characterized by mudstone interbedded with sandstone strata, are dominant in the landward portion of the tidal flat. Hummocky Cross-Stratification beds in the rock record are believed, in general, to represent storm deposits in palaeoenvironments below the fair-weather wave base. However, in this model of an open-coast tidal flat, Hummocky Cross-Stratification beds were found in very shallow waters above the fair-weather wave base. Indeed, this depositional environment was characterized by: (i) fair-weather waves and tides that lacked sufficient energy to rework the storm deposits; (ii) an absence of biological communities that could disrupt the storm deposits; and (iii) high aggradation rates linked to an active foreland basin, which contributed definitively to the rapid burial and preservation of these Hummocky Cross-Stratification deposits.
M. F. Howells - One of the best experts on this subject based on the ideXlab platform.
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A shallow marine volcaniclastic facies model: an example from sedimentary rocks bounding the subaqueously welded Ordovician Garth Tuff, North Wales, U.K.
Sedimentary Geology, 1991Co-Authors: William J. Fritz, M. F. HowellsAbstract:Abstract Volcaniclastic sedimentary rocks bounding the Ordovician Garth Tuff in North Wales were deposited in a shallow marine setting adjacent to a magmatic arc. The volcaniclastic sedimentary rocks are primarily of angular to euhedral quartz, angular euhedral feldspar, and volcanic rock fragments. These grains are of a pyroclastic origin, but have been reworked to various degrees. Sedimentary rock fragments, rounded quartz, muscovite, biotite, iron-rich chlorite and various clay minerals occur in lesser amounts. The sedimentary rocks can be divided into a proximal offshore to foreshore facies association (POFFA) and an offshore to lower shoreface facies association (OLSFA). The sand-dominated POFFA, exposed near Capel Curig, is characterized by large wave ripples, Hummocky Cross-Stratification, co-sets of trough cross-beds, reactivation surfaces, plane beds, and graded turbidite layers in suspension-deposited mudstone. Water depths calculated from bedding plane exposure of large wave ripples and determined by the presence of Hummocky Cross-Stratification and by facies association vary from a few meters to around 30 m (45–50 m theoretical maximum) in a 45 m-thick stratigraphic section beneath the tuff. Eight kilometers to the southeast, the Garth Tuff is bounded by a thick sequence of suspension-deposited laminated mudstone with thin graded beds of siltstone and fine-grained sandstone. This facies association (OLSFA) represents the introduction of material by distal turbidites and by pelagic sedimentation. The OLSFA was deposited in water depths well below storm wave base, possibly in excess of 200 m. No evidence of storm waves or surface-generated currents occur until over 40 m above the tuff. This study documents marine sedimentary rocks, deposited in water depths ranging from foreshore to offshore, as the bounding facies of the Garth Tuff. It is, thus, reasonable to conclude that the Garth Tuff was emplaced and welded in water depths greater than the thickness of the tuff in the area of this study.
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Volcaniclastic sedimentation in and around an Ordovician subaqueous caldera, Lower Rhyolitic Tuff Formation, North Wales
Geological Society of America Bulletin, 1990Co-Authors: William J. Fritz, M. F. Howells, A. J. Reedman, S. D. G. CampbellAbstract:The Lower Rhyolitic Tuff Formation of Ordovician age in North Wales records the collapse, infilling, and subsequent resurgence of a volcanic caldera with an original diameter of about 15 km. This volcanic center controlled patterns of volcaniclastic sedimentation, providing enough topographic relief for both a shallow-lagoon depositional basin within the caldera and a source of sediment derived from the rim. Within the caldera, sediment consists of tuffaceous laminated siltstone and immature, coarse-grained, volcaniclastic sandstone containing plane beds, ripple cross-laminations, symmetrical wave ripples, and Hummocky Cross-Stratification. Coarse-grained, matrix-supported, conglomerate layers and layers of ash-flow tuffs are also present. These sediments accumulated in shallow water above fair-weather wave base. Conglomerate units represent debris flows from the caldera rim, a nearby shoreline, and elevated areas associated with resurgent domes. Sedimentation outside of the caldera consisted of deposition of background suspension and volcanic-ash suspension, and turbidite deposition on a pyroclastic apron. The outer margin of the apron was dominated by fine-grained suspension and turbidite deposition, whereas the inner margin of the apron contains Hummocky Cross-Stratification and other evidence of reworking by episodic storm waves. Local highs with associated shallow-water sedimentation existed outside the caldera. Even though deposited in high-energy marine environments, all sedimentary rocks are both texturally and mineralogically very immature. This textural immaturity differs from the typical very mature marine sediments and was caused by rapid depositional rates and a local volcanic sediment source.
William J. Fritz - One of the best experts on this subject based on the ideXlab platform.
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A shallow marine volcaniclastic facies model: an example from sedimentary rocks bounding the subaqueously welded Ordovician Garth Tuff, North Wales, U.K.
Sedimentary Geology, 1991Co-Authors: William J. Fritz, M. F. HowellsAbstract:Abstract Volcaniclastic sedimentary rocks bounding the Ordovician Garth Tuff in North Wales were deposited in a shallow marine setting adjacent to a magmatic arc. The volcaniclastic sedimentary rocks are primarily of angular to euhedral quartz, angular euhedral feldspar, and volcanic rock fragments. These grains are of a pyroclastic origin, but have been reworked to various degrees. Sedimentary rock fragments, rounded quartz, muscovite, biotite, iron-rich chlorite and various clay minerals occur in lesser amounts. The sedimentary rocks can be divided into a proximal offshore to foreshore facies association (POFFA) and an offshore to lower shoreface facies association (OLSFA). The sand-dominated POFFA, exposed near Capel Curig, is characterized by large wave ripples, Hummocky Cross-Stratification, co-sets of trough cross-beds, reactivation surfaces, plane beds, and graded turbidite layers in suspension-deposited mudstone. Water depths calculated from bedding plane exposure of large wave ripples and determined by the presence of Hummocky Cross-Stratification and by facies association vary from a few meters to around 30 m (45–50 m theoretical maximum) in a 45 m-thick stratigraphic section beneath the tuff. Eight kilometers to the southeast, the Garth Tuff is bounded by a thick sequence of suspension-deposited laminated mudstone with thin graded beds of siltstone and fine-grained sandstone. This facies association (OLSFA) represents the introduction of material by distal turbidites and by pelagic sedimentation. The OLSFA was deposited in water depths well below storm wave base, possibly in excess of 200 m. No evidence of storm waves or surface-generated currents occur until over 40 m above the tuff. This study documents marine sedimentary rocks, deposited in water depths ranging from foreshore to offshore, as the bounding facies of the Garth Tuff. It is, thus, reasonable to conclude that the Garth Tuff was emplaced and welded in water depths greater than the thickness of the tuff in the area of this study.
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Volcaniclastic sedimentation in and around an Ordovician subaqueous caldera, Lower Rhyolitic Tuff Formation, North Wales
Geological Society of America Bulletin, 1990Co-Authors: William J. Fritz, M. F. Howells, A. J. Reedman, S. D. G. CampbellAbstract:The Lower Rhyolitic Tuff Formation of Ordovician age in North Wales records the collapse, infilling, and subsequent resurgence of a volcanic caldera with an original diameter of about 15 km. This volcanic center controlled patterns of volcaniclastic sedimentation, providing enough topographic relief for both a shallow-lagoon depositional basin within the caldera and a source of sediment derived from the rim. Within the caldera, sediment consists of tuffaceous laminated siltstone and immature, coarse-grained, volcaniclastic sandstone containing plane beds, ripple cross-laminations, symmetrical wave ripples, and Hummocky Cross-Stratification. Coarse-grained, matrix-supported, conglomerate layers and layers of ash-flow tuffs are also present. These sediments accumulated in shallow water above fair-weather wave base. Conglomerate units represent debris flows from the caldera rim, a nearby shoreline, and elevated areas associated with resurgent domes. Sedimentation outside of the caldera consisted of deposition of background suspension and volcanic-ash suspension, and turbidite deposition on a pyroclastic apron. The outer margin of the apron was dominated by fine-grained suspension and turbidite deposition, whereas the inner margin of the apron contains Hummocky Cross-Stratification and other evidence of reworking by episodic storm waves. Local highs with associated shallow-water sedimentation existed outside the caldera. Even though deposited in high-energy marine environments, all sedimentary rocks are both texturally and mineralogically very immature. This textural immaturity differs from the typical very mature marine sediments and was caused by rapid depositional rates and a local volcanic sediment source.
Pedro Henrique Vieira De Luca - One of the best experts on this subject based on the ideXlab platform.
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Hummocky cross stratification like structures and combined flow ripples in the punta negra formation lower middle devonian argentine precordillera a turbiditic deep water or storm dominated prodelta inner shelf system
Sedimentary Geology, 2012Co-Authors: Giorgio Basilici, Pedro Henrique Vieira De Luca, Daniel Gustavo PoireAbstract:Abstract Turbidity-current and storm-induced deposits may exhibit similarities, in particularly when the latter is laid down by a combination of oscillatory and unidirectional flows. Recent progress in facies analysis helps to discriminate the sedimentary effects of oscillatory from unidirectional components of the flow. On the basis of detailed analysis of sedimentary facies, strata geometry, and palaeocurrent data, the present study reinterprets the Punta Negra Formation (PNF) (Lower-Middle Devonian, Argentine Precordillera), previously considered as a depositional system of deep-water, as a storm-dominated prodeltaic shelf depositional system. In the sandstone beds of the PNF, planar, low-angle and undulating laminations with weakly asymmetric Hummocky and swaley bedforms, combined-flow ripples, accretionary Hummocky Cross-Stratification-like (HCS-like), and anisotropic HCS-like suggest the action of oscillatory currents combined with unidirectional currents in forming the deposits. Different hypotheses on the origin of the oscillatory currents have been examined. The most convincing interpretation is that the oscillatory component of the velocity is attributed to storm-induced waves. The palaeocurrent data indicate offshore current directions, suggesting that the unidirectional flow was a gravity-induced bottom current. Inverse grading at the base and overlying normally graded divisions of the sandstone beds testify to waxing–waning behaviour of the depositional flows; interbedding of sedimentary structures (undulating laminations, low-angle and parallel laminations, and combined-flow ripples) in the lower and intermediate divisions of the beds indicate fluctuations of flow velocity. This organisation of the sedimentary structures permits association of the unidirectional component with hyperpycnal bottom currents. The terrestrial origin of the hyperpycnal flows is suggested by the abundance of terrestrial plant remains, the mineralogical and textural immaturity of the sandstone composition, and the relative scarcity of bioturbation, which was likely controlled by fresh-water input and a high rate of sedimentation. Storm-influenced, hyperpycnal flows generated subaqueous channelised forms at the mouth of the river deltas, which later filled with sand. At the distal end of the channelised forms, lobe-shaped sandstone beds were deposited, evolving distally into thin sandstone beds alternating with sandy mudstone.
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A depositional model for a wave‐dominated open‐coast tidal flat, based on analyses of the Cambrian–Ordovician Lagarto and Palmares formations, north‐eastern Brazil
Sedimentology, 2012Co-Authors: Giorgio Basilici, Pedro Henrique Vieira De Luca, Elson P. OliveiraAbstract:Open-coast tidal flats are hybrid depositional systems resulting from the interaction of waves and tides. Modern examples have been recognized, but few cases have been described in ancient rock successions. An example of an ancient open-coast tidal flat, the depositional architecture of the Lagarto and Palmares formations (Cambrian–Ordovician of the Sergipano Belt, north-eastern Brazil) is presented here. Detailed field analyses of outcrops allowed the development of a conceptual architectural model for a coastal depositional environment that is substantially different from classical wave-dominated or tide-dominated coastal models. This architectural model is dominated by storm wave, low orbital velocity wave and tidal current beds, which vary in their characteristics and distribution. In a landward direction, the storm deposits decrease in abundance, dimension (thickness and spacing) and grain size, and vary from accretionary through scour and drape to anisotropic Hummocky Cross-Stratification beds. Low orbital wave deposits are more common in the medium and upper portion of the tidal flat. Tidal deposits, which are characterized by mudstone interbedded with sandstone strata, are dominant in the landward portion of the tidal flat. Hummocky Cross-Stratification beds in the rock record are believed, in general, to represent storm deposits in palaeoenvironments below the fair-weather wave base. However, in this model of an open-coast tidal flat, Hummocky Cross-Stratification beds were found in very shallow waters above the fair-weather wave base. Indeed, this depositional environment was characterized by: (i) fair-weather waves and tides that lacked sufficient energy to rework the storm deposits; (ii) an absence of biological communities that could disrupt the storm deposits; and (iii) high aggradation rates linked to an active foreland basin, which contributed definitively to the rapid burial and preservation of these Hummocky Cross-Stratification deposits.