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Nigel P. Mountney - One of the best experts on this subject based on the ideXlab platform.
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palaeohydrological characteristics and palaeogeographic reconstructions of Incised Valley fill systems insights from the namurian successions of the united kingdom and ireland
Sedimentology, 2020Co-Authors: Ru Wang, Luca Colombera, Nigel P. MountneyAbstract:Namurian (Carboniferous) eustatic fluctuations drove the incision and backfill of shelf‐crossing Valley systems located in humid subequatorial regions, which are now preserved in successions of the United Kingdom and Ireland. The infills of these Valleys archive the record of palaeoriver systems whose environmental, hydrological and palaeogeographic characteristics remain unclear. A synthesis of sedimentological data from fluvial strata of 18 Namurian Incised‐Valley fills in the United Kingdom and Ireland is undertaken to elucidate the nature of their formative river systems and to refine regional palaeogeographic reconstructions. Quantitative analyses are performed of facies proportions, of geometries of Incised‐Valley fills and related architectural elements, and of the thickness of dune‐scale sets of cross‐strata. Reconstruction of the size of the drainage areas that fed these Valleys is attempted based on two integrative approaches: flow‐depth estimations from dune‐scale cross‐set thickness statistics and scaling relationships of Incised‐Valley fill dimensions derived from late‐Quaternary examples. The facies organization of these Incised‐Valley fills suggests that their formative palaeorivers were perennial and experienced generally low discharge variability, consistent with their climatic context; however, observations of characteristically low variability in cross‐set thickness might reflect rapid flood recession, perhaps in relation to sub‐catchments experiencing seasonal rainfall. Variations in facies characteristics, including inferences of flow regime and cross‐set thickness distributions, might reflect the control of catchment size on river hydrology, the degree to which is considered in light of data from modern rivers. Palaeohydrological reconstructions indicate that depth estimations from cross‐set thickness contrast with observations of barform and channel‐fill thickness, and projected thalweg depths exceed the depth of some Valley fills. Limitations in data and interpretations and high bedform preservation are recognized as possible causes. With consideration of uncertainties in the inference of catchment size, the palaeogeography of the Valley systems has been tentatively reconstructed by integrating existing provenance and sedimentological data. The approaches illustrated in this work can be replicated to the study of palaeohydrological characteristics and palaeogeographic reconstructions of Incised‐Valley fills globally and through geological time.
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geological controls on the geometry of Incised Valley fills insights from a global dataset of late quaternary examples
Sedimentology, 2019Co-Authors: Ru Wang, Luca Colombera, Nigel P. MountneyAbstract:Incised Valleys that develop due to relative sea-level change are common features of continental shelves and coastal plains. Assessment of the factors that control the geometry of Incised-Valley fills has hitherto largely relied on conceptual, experimental or numerical models, else has been grounded on case studies of individual depositional systems. Here, a database-driven statistical analysis of 151 late-Quaternary Incised-Valley fills has been performed, the aim being to investigate the geological controls on their geometry. Results of this analysis have been interpreted with consideration of the role of different processes in determining the geometry of Incised-Valley fills through their effect on the degree and rate of river incision, and on river size and mobility. The studied Incised-Valley fills developed along active margins are thicker and wider, on average, than those along passive margins, suggesting that tectonic setting exerts a control on the geometry of Incised-Valley fills, likely through effects on relative sea-level change and river behaviour, and in relation to distinct characteristics of basin physiography, water discharge and modes of sediment delivery. Valley-fill geometry is positively correlated with the associated drainage-basin size, confirming the dominant role of water discharge. Climate is also inferred to exert a potential control on Valley-fill dimensions, possibly through modulations of temperature, peak precipitation, vegetation and permafrost, which would in turn affect water discharge, rates of sediment supply and Valley-margin stability. Shelves with slope breaks that are currently deeper than 120 m contain Incised-Valley fills that are thicker and wider, on average, than those hosted on shelves with breaks shallower than 120 m. No correlation exists between Valley-fill thickness and present-day coastal-prism convexity, which is measured as the difference in gradient between lower coastal plains and inner shelves. These findings challenge some concepts embedded in sequence stratigraphic thinking, and have significant implications for analysis and improved understanding of source-to-sink sediment route-ways, and for attempting predictions of the occurrence and characteristics of hydrocarbon reservoirs.
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Geological controls on the geometry of Incised‐Valley fills: Insights from a global dataset of late‐Quaternary examples
Sedimentology, 2019Co-Authors: Ru Wang, Luca Colombera, Nigel P. MountneyAbstract:Incised Valleys that develop due to relative sea-level change are common features of continental shelves and coastal plains. Assessment of the factors that control the geometry of Incised-Valley fills has hitherto largely relied on conceptual, experimental or numerical models, else has been grounded on case studies of individual depositional systems. Here, a database-driven statistical analysis of 151 late-Quaternary Incised-Valley fills has been performed, the aim being to investigate the geological controls on their geometry. Results of this analysis have been interpreted with consideration of the role of different processes in determining the geometry of Incised-Valley fills through their effect on the degree and rate of river incision, and on river size and mobility. The studied Incised-Valley fills developed along active margins are thicker and wider, on average, than those along passive margins, suggesting that tectonic setting exerts a control on the geometry of Incised-Valley fills, likely through effects on relative sea-level change and river behaviour, and in relation to distinct characteristics of basin physiography, water discharge and modes of sediment delivery. Valley-fill geometry is positively correlated with the associated drainage-basin size, confirming the dominant role of water discharge. Climate is also inferred to exert a potential control on Valley-fill dimensions, possibly through modulations of temperature, peak precipitation, vegetation and permafrost, which would in turn affect water discharge, rates of sediment supply and Valley-margin stability. Shelves with slope breaks that are currently deeper than 120 m contain Incised-Valley fills that are thicker and wider, on average, than those hosted on shelves with breaks shallower than 120 m. No correlation exists between Valley-fill thickness and present-day coastal-prism convexity, which is measured as the difference in gradient between lower coastal plains and inner shelves. These findings challenge some concepts embedded in sequence stratigraphic thinking, and have significant implications for analysis and improved understanding of source-to-sink sediment route-ways, and for attempting predictions of the occurrence and characteristics of hydrocarbon reservoirs.
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stratigraphic architecture of back filled Incised Valley systems pennsylvanian permian lower cutler beds utah usa
Sedimentary Geology, 2013Co-Authors: Oliver Wakefield, Nigel P. MountneyAbstract:The Pennsylvanian to Permian lower Cutler beds collectively form the lowermost stratigraphic unit of the Cutler Group in the Paradox Basin, southeast Utah. The lower Cutler beds represent a tripartite succession comprising lithofacies assemblages of aeolian, fluvial and shallow-marine origin, in near equal proportion. The succession results from a series of transgressive–regressive cycles, driven by repeated episodes of climatic variation and linked changes in relative sea-level. Relative sea-level changes created a number of Incised-Valleys, each forming through fluvial incision during lowered base-level. Aeolian dominance during periods of relative sea-level lowstand aids Incised-Valley identification as the erosive bounding surface juxtaposes Incised-Valley infill against stacked aeolian faces. Relative sea-level rises resulted in back-flooding of the Incised-Valleys and their infill via shallow-marine and estuarine processes. Back-flooded Valleys generated marine embayments within which additional local accommodation was exploited. Back-filling is characterised by a distinctive suite of lithofacies arranged into a lowermost, basal fill of fluvial channel and floodplain architectural elements, passing upwards into barform elements with indicators of tidal influence, including inclined heterolithic strata and reactivation surfaces. The Incised-Valley fills are capped by laterally extensive and continuous marine limestone elements that record the drowning of the Valleys and, ultimately, flooding and accumulation across surrounding interfluves (transgressive surface). Limestone elements are characterised by an open-marine fauna and represent the preserved expression of maximum transgression.
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Stratigraphic architecture of back-filled Incised-Valley systems: Pennsylvanian–Permian lower Cutler beds, Utah, USA
Sedimentary Geology, 2013Co-Authors: Oliver Wakefield, Nigel P. MountneyAbstract:The Pennsylvanian to Permian lower Cutler beds collectively form the lowermost stratigraphic unit of the Cutler Group in the Paradox Basin, southeast Utah. The lower Cutler beds represent a tripartite succession comprising lithofacies assemblages of aeolian, fluvial and shallow-marine origin, in near equal proportion. The succession results from a series of transgressive–regressive cycles, driven by repeated episodes of climatic variation and linked changes in relative sea-level. Relative sea-level changes created a number of Incised-Valleys, each forming through fluvial incision during lowered base-level. Aeolian dominance during periods of relative sea-level lowstand aids Incised-Valley identification as the erosive bounding surface juxtaposes Incised-Valley infill against stacked aeolian faces. Relative sea-level rises resulted in back-flooding of the Incised-Valleys and their infill via shallow-marine and estuarine processes. Back-flooded Valleys generated marine embayments within which additional local accommodation was exploited. Back-filling is characterised by a distinctive suite of lithofacies arranged into a lowermost, basal fill of fluvial channel and floodplain architectural elements, passing upwards into barform elements with indicators of tidal influence, including inclined heterolithic strata and reactivation surfaces. The Incised-Valley fills are capped by laterally extensive and continuous marine limestone elements that record the drowning of the Valleys and, ultimately, flooding and accumulation across surrounding interfluves (transgressive surface). Limestone elements are characterised by an open-marine fauna and represent the preserved expression of maximum transgression.
Nicolas Weber - One of the best experts on this subject based on the ideXlab platform.
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Incised-Valley morphologies and sedimentary-fills within the inner shelf of the northern Bay of Biscay
Journal of Marine Systems, 2008Co-Authors: Eric Chaumillon, Jean-noël Proust, David Menier, Nicolas WeberAbstract:This study is a first synthesis focused on Incised-Valleys located within the inner shelf of the Bay of Biscay. It is based on previously published results obtained during recent seismic surveys and coring campaigns. The morphology of the Valleys appears to be strongly controlled by tectonics and lithology. The Pleistocene sedimentary cover of the shelf is very thin and discontinuous with a maximum thickness ranging between 30 and 40 m in Incised-Valley fills. Thus the Incised bedrock morphology plays a key-role by controlling hydrodynamics and related sediment transport and deposition that explains some variations of those Incised-Valley fills with respect to the previously published general models.
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Incised-Valley morphologies and sedimentary-fills within the inner shelf of the Bay of Biscay (France): A synthesis
Journal of Marine Systems, 2008Co-Authors: Eric Chaumillon, Jean-noël Proust, David Menier, Nicolas WeberAbstract:International audienceThis study is a first synthesis focused on Incised-Valleys located within the inner shelf of the Bay of Biscay. It is based on previously published results obtained during recent seismic surveys and coring campaigns. The morphology of the Valleys appears to be strongly controlled by tectonics and lithology. The Pleistocene sedimentary cover of the shelf is very thin and discontinuous with a maximum thickness ranging between 30 and 40 m in Incised-Valley fills. Thus the Incised bedrock morphology plays a key-role by controlling hydrodynamics and related sediment transport and deposition that explains some variations of those Incised-Valley fills with respect to the previously published general models
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Incised-Valley morphologies and sedimentary-fills within the inner shelf of the Bay of Biscay (France): A synthesis
Journal of Marine Systems, 2007Co-Authors: Eric Chaumillon, Jean-noël Proust, David Menier, Nicolas WeberAbstract:This study is a first synthesis focused on Incised-Valleys located within the inner shelf of the Bay of Biscay. It is based on previously published results obtained during recent seismic surveys and coring campaigns. The morphology of the Valleys appears to be strongly controlled by tectonics and lithology. The Pleistocene sedimentary cover of the shelf is very thin and discontinuous with a maximum thickness ranging between 30 and 40 m in Incised-Valley fills. Thus the Incised bedrock morphology plays a key-role by controlling hydrodynamics and related sediment transport and deposition that explains some variations of those Incised-Valley fills with respect to the previously published general models.
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Architecture and morphology of the outer segment of a mixed tide and wave-dominated-Incised Valley, revealed by HR seismic reflection profiling: the paleo-Charente River, France
Marine Geology, 2004Co-Authors: Nicolas Weber, Eric Chaumillon, Michel Tesson, Thierry GarlanAbstract:Abstract We present new single-channel high-resolution seismic reflection profiles, ground-truthed by vibrocore data, dedicated to the outer segment of an Incised Valley connected to the Charente River (French Atlantic coast). The present-day Charente is located about 50 km northward of the well-known Gironde estuary. Those river mouths are comparable in terms of marine hydrodynamic parameters, but strongly differ by their water discharge and catchment area. Seismic data are processed and interpreted to develop a three-dimensional seismic stratigraphic framework for the Charente-Incised Valley fill. The channel network of the drowned Charente Valley is evidenced for the first time, and shows a seaward distributary pattern which is likely influenced by neotectonic control. Incision depth and width of the Charente and Gironde-Incised Valleys are similar, supporting the idea that correlation between Valley width and modern hydrology is poor. The internal geometry of the Charente Valley fill shows in seismic lines high to middle angle dipping reflectors at the base and a top of sequence with an intervening low angle seismic unit. This pattern is associated with a landward migration of the seismic unit depocentres. Sedimentary facies of the main seismic units suggests an upward and landward shift from estuarine mixed sands and muds, to estuary mouth massive sands, topped by fine marine sands. The described sedimentary and seismic characters, and the Holocene age of the Valley fill near the present-day Charente river mouth, suggest that the drowned Charente Valley infill mainly corresponds to a single transgressive sequence emplaced during the last sea level rise. Beyond the local interest, the dense seismic grid recorded across the Charente drowned Valley gives a seismic validation for the model of large Valley fill proposed by Ashley and Sheridan [Ashley, G.M., Sheridan, R.E., 1994. Depositional model for Valley fills on a passive continental margin. In: R.W. Dalrymple, R.J. Boyd, B.A. Zaitlin (Eds.), Incised Valley Systems: Origin and Sedimentary Sequences. SEPM (Soc. Sediment. Geol.) Spec. Publ., Tulsa, Vol. 51, pp. 285–301.]. We propose that high–low–high internal reflection pattern succession represents the “Seismic Sandwich” in reference to the Ashley and Sheridan [Ashley, G.M., Sheridan, R.E., 1994. Depositional model for Valley fills on a passive continental margin. In: R.W. Dalrymple, R.J. Boyd, B.A. Zaitlin (Eds.), Incised Valley Systems: Origin and Sedimentary Sequences. SEPM (Soc. Sediment. Geol.) Spec. Publ., Tulsa, Vol. 51, pp. 285–301.] “Sedimentary Sandwich”. Such seismic pattern is also recognized in the Gironde Valley [Mar. Geol. 175 (2001) 183.].
Andrew Green - One of the best experts on this subject based on the ideXlab platform.
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spatial and temporal variations in Incised Valley systems from the durban continental shelf kwazulu natal south africa
Marine Geology, 2013Co-Authors: Andrew Green, Nonkululeko Dladla, Luke G GarlickAbstract:Abstract The evolution of several Incised Valley systems from the KwaZulu-Natal shelf is compared over time. These represent the shelf extension of the collective Durban Harbour drainage system, and the Mgeni, Mhlanga, and Mdloti Rivers. Two main ages of incision are apparent; early Santonian (Cretaceous), and late Pleistocene/Holocene. The early Valleys formed by tectonic controls, namely phases of higher frequency base level fall superimposed on lower frequency, higher order transgression. The results are complex networks of stacked compound Valleys that have been exploited by some of the younger networks formed by glacio-eustatic fall prior to the last glacial maximum (LGM) of ~ 18 Ka BP. The Valley fills have evolved from high energy basal fluvial deposits, low-energy central basin fines, mixed-energy estuarine mouth plug deposits, clay-rich flood deposits through capping sandy shoreface deposits. The earliest fills are dominated by central basin deposits and were underfilled as a result of low gradient and limited sediment supply. The more recent late Pleistocene/Holocene fills have significantly thicker fluvial deposits as a result of increased gradient and stream competence during the later stages of Valley and shelf evolution. The youngest Valleys show a situation of differential evolution along the Valley length due to varying rates of sea level rise in the Holocene. Initial rapid sea level rise caused drowning and overstepping of the outer segment of the Incised Valley, whereas slower rates of sea level rise in the late Holocene caused shoreface ravinement of the inner-mid segments of the Valley. This differential exposure to accommodation has resulted in a sedimentological partitioning between tide-dominated facies in the outer Valley segment and river-dominated facies in the inner segment (cf. Cooper, 2001 ).
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evolution of an Incised Valley coastal plain estuary under low sediment supply a give up estuary
Sedimentology, 2012Co-Authors: Andrew J G Cooper, Andrew Green, Ian C WrightAbstract:The literature on Incised river Valley sedimentology is dominated by studies of sediment-rich systems in which the Valley has been filled during and/or shortly after drowning. In contrast, the Holocene evolution of the Kosi Lagoon, South Africa (an Incised coastal plain river Valley) took place under very low sedimentation rates which have produced a distinctive stratigraphy and contemporary sedimentary environments. The findings are based on a synthesis of the results of studies of seismic stratigraphy, sediment distribution, morphodynamics and geomorphology. Barrier migration was prevented by a high pre-Holocene dune barrier against which Holocene coastal deposits accumulated in an aggradational sequence. Holocene evolution of the back barrier involved: (i) drowning of the Incised Valley; (ii) wave-induced modification of the back-barrier shoreline leading to segmentation during the highstand; and (iii) marine sedimentation adjacent to the tidal inlet. Segmentation has divided the estuary into a series of geochemically and sedimentologically distinctive basins connected by channels in the estuarine barriers. The seismic stratigraphy of the back barrier essentially lacks a transgressive systems tract, shoreline modification and deposition having been accomplished during the highstand. The lack of historical geomorphological change suggests that the system has achieved morphological equilibrium with ambient energy conditions and low sediment supply. This study presents a classification for estuarine Incised Valley fills based on the balance between sea-level rise and sedimentation in which Kosi represents a ‘give-up’ estuary where much of the relict Incised channel form is drowned and preserved. It exhibits a fundamentally different set of evolutionary processes and stratigraphic sequences to those of the better known Incised Valley systems in which sedimentation either keeps pace with sea-level (‘keep-up’ estuaries) or occurs after initial drowning (‘catch-up’ estuaries).
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Evolution of an Incised Valley coastal plain estuary under low sediment supply: a ‘give‐up’ estuary
Sedimentology, 2011Co-Authors: J. Andrew G. Cooper, Andrew Green, C. Ian WrightAbstract:The literature on Incised river Valley sedimentology is dominated by studies of sediment-rich systems in which the Valley has been filled during and/or shortly after drowning. In contrast, the Holocene evolution of the Kosi Lagoon, South Africa (an Incised coastal plain river Valley) took place under very low sedimentation rates which have produced a distinctive stratigraphy and contemporary sedimentary environments. The findings are based on a synthesis of the results of studies of seismic stratigraphy, sediment distribution, morphodynamics and geomorphology. Barrier migration was prevented by a high pre-Holocene dune barrier against which Holocene coastal deposits accumulated in an aggradational sequence. Holocene evolution of the back barrier involved: (i) drowning of the Incised Valley; (ii) wave-induced modification of the back-barrier shoreline leading to segmentation during the highstand; and (iii) marine sedimentation adjacent to the tidal inlet. Segmentation has divided the estuary into a series of geochemically and sedimentologically distinctive basins connected by channels in the estuarine barriers. The seismic stratigraphy of the back barrier essentially lacks a transgressive systems tract, shoreline modification and deposition having been accomplished during the highstand. The lack of historical geomorphological change suggests that the system has achieved morphological equilibrium with ambient energy conditions and low sediment supply. This study presents a classification for estuarine Incised Valley fills based on the balance between sea-level rise and sedimentation in which Kosi represents a ‘give-up’ estuary where much of the relict Incised channel form is drowned and preserved. It exhibits a fundamentally different set of evolutionary processes and stratigraphic sequences to those of the better known Incised Valley systems in which sedimentation either keeps pace with sea-level (‘keep-up’ estuaries) or occurs after initial drowning (‘catch-up’ estuaries).
Paul Weimer - One of the best experts on this subject based on the ideXlab platform.
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reservoir geology of nicholas and liverpool cemetery fields lower pennsylvanian stanton county kansas and their significance to the regional interpretation of the morrow formation Incised Valley fill systems in eastern colorado and western kansas
AAPG Bulletin, 2004Co-Authors: David W. Bowen, Paul WeimerAbstract:Reservoirs in the lower Pennsylvanian Morrow Formation of eastern Colorado, southwestern Kansas, and northwestern Oklahoma have produced greater than 8 tcf of gas and 200 million bbl of oil. This prolific depositional system produces from reservoirs representing a range of depositional environments from updip, fluvial-dominated, Incised-Valley fills to deep-water basin-floor systems. The Valley fills of the Morrow Formation are of particular significance because they can be mapped in great detail from subsurface control over very long distances. Facies distributions in the Valleys change systematically downdip. As a result, reservoir characteristics and trapping mechanisms vary with these changes in internal Valley stratigraphy.This paper focuses on the reservoir geology of Nicholas and Liverpool Cemetery fields. These fields produce gas from the extreme downdip region of an Incised-Valley-fill system in the lower Morrow Formation. The Valley systems in this downdip region are deeper and wider and demonstrate greater marine influence than the updip regions of the Valley systems farther north and into the hinterland.Compartmentalization in these downdip reservoirs differs significantly from updip Valley-fill reservoirs. The reservoirs in this downdip region are more highly compartmentalized because the dominant reservoir facies in these fields is a series of bayfill delta deposits. These deposits are isolated by shale deposits in the Valley. This depositional setting contrasts markedly with predominantly fluvial reservoirs in updip regions of the Valleys. Understanding the scale, geometry, and internal complexity of this depositional system is important because the associated sandstones are important gas reservoirs in southwest Kansas. Cores, wire-line logs, pressure data, and production data collected from the Morrow Formation at Nicholas and Liverpool Cemetery fields provide valuable information from which to describe and interpret this downdip Valley fill. This paper describes the downdip Incised-Valley-fill reservoirs in this producing complex and documents the trapping relationships of these reservoirs and their production characteristics.
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Regional sequence stratigraphic setting and reservoir geology of Morrow Incised-Valley sandstones (lower Pennsylvanian), eastern Colorado and western Kansas
AAPG Bulletin, 2003Co-Authors: David W. Bowen, Paul WeimerAbstract:Oil and gas exploration for the lower Pennsylvanian Morrow Formation of eastern Colorado, western Kansas, and northwestern Oklahoma provides a subsurface data set that transects the entire range of lowstand depositional systems from Incised-Valley-fill systems to deep-water basin-floor systems in one composite depositional sequence. One compound Incised-Valley fill that is a part of this system contains three facies tracts with unique reservoir characteristics: (1) the updip facies tract is dominated by amalgamated fluvial channel sandstones, (2) the transition facies tract consists of fluvial channel sandstones interbedded with finer grained estuarine sandstones, and (3) the downdip facies tract consists of ribbonlike fluvial channel sandstones isolated in estuarine shale.A 175-mi-long (283-km-long) longitudinal cross section through one trunk of the Incised-Valley-fill drainage shows that internal Valley-fill strata change significantly as a function of the interplay of varying depositional systems down gradient in the Valley. Key contrasts in reservoir performance are documented as a function of changes in reservoir characteristics, trap controls, and trap configurations from updip to downdip in this Valley-fill drainage.The strata of the Morrow Formation were deposited in a cratonic basin during a period in the Earth's history when the climate was cooler than today. High-frequency changes of sea level across an extremely low-gradient depositional surface controlled erosion and deposition. These facies tracts reflect the response of Valley-fill sedimentary processes to high-frequency relative sea level changes resulting from glacio-eustasy. The resultant Valley-fill systems have many characteristics in common with published Valley-fill models, but have significant differences as well.
Antonio B. Rodriguez - One of the best experts on this subject based on the ideXlab platform.
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Controls on late quaternary Incised-Valley dimension along passive margins evaluated using empirical data
Sedimentology, 2010Co-Authors: C.r. Mattheus, Antonio B. RodriguezAbstract:Incised Valleys are canyon-like features that initially form near the highstand shoreline and evolve over geological time as rivers erode into coastal plains and continental shelves to maintain equilibrium-gradient profiles in response to sea-level fall. Most of these Valleys flood during sea-level rise to form estuaries. Incised-Valley morphology strongly controls the rate of creation of sediment accommodation, Valley-fill facies architecture and the preservation potential of coastal lithosomes on continental shelves, and affects coastal physical processes. Nonetheless, little is known about what dictates Incised-Valley size and shape and whether these metrics can be used to explain principal formation processes. The main control on alluvial channel morphology over human time scales is discharge; this is based on numerous empirical studies and is well-constrained because all variables are easily measured at this short time scale. Knowledge of long-term river evolution over a complete glacio-eustatic cycle, on the contrary, remains largely conceptual, experimental and based on individual systems because variables that are thought to drive morphological change are not easily quantified. In spite of this difficulty, existing models of Incised-Valley formation at the coast suggest that Valley evolution is driven largely by downstream forcing mechanisms, highlighting sea-level and shelf gradient/morphology as the dominant controls on Valley incision. Although Valleys are cut by rivers, whose channels are a direct reflection of discharge, little empirical data exist in coastal areas to address the degree to which Valley evolution is governed by upstream controls. The late Quaternary is the best time period to examine because it provides the most complete sedimentary record and many variables, including sea-level, tectonics, substrate lithology and drainage network characteristics, are accurately constrained. Here, 38 late Quaternary Valleys along the coast of two different passive continental margins are compared, which suggests that Valley shape and size are governed primarily by upstream, intrinsic controls such as discharge. Valley width, depth and cross-sectional area are found to be predictable at the highstand shoreline and are scaled with the size of their drainage basin, which has important implications for estimating sediment discharge to continental shelves and deep water environments during periods of low sea-level.
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Control of Upstream Variables on Incised-Valley Dimension
Journal of Sedimentary Research, 2007Co-Authors: C.r. Mattheus, Antonio B. Rodriguez, D. Lawrence Greene, Alexander R. Simms, John B. AndersonAbstract:Abstract It is well documented that sea level fell during the Last Glacial Maximum, shifting graded-stream profiles out of equilibrium and causing rivers to incise into continental shelves. Although Incised Valleys have been heavily researched, the interplay between upstream and downstream controls on Incised-Valley dimension are not well constrained. To address this lack of understanding, we examined the cross-sectional dimension of nine Incised Valleys located across the northern Gulf of Mexico margin and bounded by the sequence boundary associated with the last sea-level lowstand. These Incised Valleys are distinguished by drainage basins that vary in size by three orders of magnitude, cover a margin that presently has a steep climate gradient, and extend across a continental shelf that varies along strike in width and gradient. Incision depths vary for Valleys that have similar gradient profiles but different drainage-basin areas, suggesting significant control of upstream variables on Incised-Valley morphology. Additionally, these data show a strong linear correlation between drainage-basin area and Incised-Valley cross-sectional area. This suggests applicability of the empirically derived relationship between modern discharge and cross-sectional channel area to Incised Valleys when compared at the maximum highstand shoreline of the previous sequence. Incised-Valley dimension adjusts over a longer period than the lowstand and is in equilibrium with drainage-basin area, which is considered a proxy for long-term discharge. Although base-level fall promotes incision, upstream variables control Incised-Valley dimensions.
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Abstract: Control of Upstream Variables on Late Quaternary Incised-Valley Evolution along the Northern Gulf of Mexico Margin
2006Co-Authors: C.r. Mattheus, Antonio B. RodriguezAbstract:Abstract It is established that sea level along the northern Gulf of Mexico margin fell to ~120 m below present day level during the Last Glacial Maximum (~22-17 ka), exposing the continental shelf and promoting fluvial incision. The Incised-Valley systems formed during this lowstand in sea level have been well constrained by seismic and lithologic studies, aided by 14C dating techniques. However, a comparative study has not been attempted to determine relative controls of upstream (climate and drainage-basin characteristics) and downstream (fluvial and shelf gradients, rate and magnitude of base-level fall) controls on Incised-Valley evolution. To address this, Incised-Valley dimension was calculated for eight Oxygen Isotope Stage 2 Incised-Valley systems from core and seismic data at locations close to the highstand shoreline of the previous sequence along the margin. Studied systems cover a region presently characterized by steep precipitation gradients, are distinguished by drainage basins that vary in size by three orders of magnitude, and extend across a continental shelf that varies along strike in width (80-160 km) and gradient (1.0-2.0 m/km). Linear relationships between drainage-basin area and Incised-Valley cross-sectional area and width suggest a strong correlation between discharge and Incised-Valley dimension for systems along the northern Gulf of Mexico margin. These data suggest that the level of variability along the margin is not unique and comparison of Incised-Valley dimension therefore yields insight into respective drainage-basin sizes and/or climate gradients. Although the base-level fall promoted fluvial incision, Incised-Valley dimension was controlled by upstream variables.
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Abstract: Mapping Bay-Head Deltas Within Incised Valleys as an Aid for Predicting the Occurrence of Barrier Shoreline Sands: An Example From the Trinity/Sabine Incised Valley
2000Co-Authors: Antonio B. Rodriguez, John B. AndersonAbstract:Examination of the landward retreat history of bayhead deltas during transgressions will help predict the occurrence and location of barrier shorelines associated with Incised Valleys. During the last transgression (18,000 yr. BP to present) the Trinity/Sabine Incised Valley backfilled with continuous fluvial and bay-head delta facies and discontinuous middle-bay and coastal (tidal delta complex and barrier facies) deposits (Thomas and Anderson, 1994; Fig. 1A). Thomas and Anderson (1994) identified four packages of sediments bounded by flooding surfaces separating proximal coastal environments (bayhead delta and fluvial environments) from overlying distal coastal environments (middle bay, tidal delta, and barrier environments) within the Incised Valley. In places on the inner shelf banks (Sabine, Heald, Shepard, and Thomas banks) lie adjacent to and over the Incised Valley (Fig. 1A). These banks represent submerged paleoshorelines composed of three facies (from bottom to top): (1) a back barrier estuarine facies characterized by landward-dipping seismic reflectors and consisting of an interbedded sand and mud unit; (2) a fore-barrier, lower shoreface/ebb-tidal delta facies characterized by seaward-prograding to chaotic seismic reflectors and consisting of a muddy sand unit; and (3) a storm-reworked facies characterized by a chaotic to acoustically reverberating seismic reflection pattern consisting of an interbedded shell hash and sand
