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Gary J. Hampson - One of the best experts on this subject based on the ideXlab platform.
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Characterization of Controls on High-Resolution Stratigraphic Architecture in Wave-Dominated Shoreface–Shelf Parasequences Using Inverse Numerical Modeling
Journal of Sedimentary Research, 2011Co-Authors: Karl Charvin, Gary J. Hampson, Joep E.a. Storms, Kerry Gallagher, Richard LabourdetteAbstract:Abstract A new inverse numerical modeling method is used to constrain the environmental parameters (e.g., relative-sea-level, sediment-supply, and wave climate histories) that control stratigraphic architecture in wave-dominated shallow-marine deposits. The method links a “process-response” forward stratigraphic model that simulates wave and storm processes (BARSIM) to a combination of inverse methods formulated in a Bayesian framework that allows full characterization of uncertainties. This method is applied for the first time to a real geologic dataset, collected at outcrop from two shoreface–shelf Parasequences in the Aberdeen Member, Blackhawk Formation of the Book Cliffs, east-central Utah, USA. The environmental parameters that controlled the observed stratigraphic architecture are quantified, and key aspects of stratigraphic architecture are successfully predicted from limited data. Stratigraphic architecture at Parasequence-stacking and intra-Parasequence scales was driven principally by relative sea level (varying by up to about 55 m) and sediment supply (varying by up to 70 m2/yr), whose interplay determines the shoreline trajectory. Within zones of distinctive shoreline trajectory, variations in wave climate (of up to about 3 m in fairweather-wave height) controlled superimposed variations in sandstone and shale content (e.g., the development of upward-coarsening and upward-fining bedsets). The modeling results closely match the observed stratigraphic architecture, but their quality is limited by: (1) the formulation and assumptions of the forward-modeling algorithms, and (2) the observed data distribution and quality, which provide poor age constraint.
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intra Parasequence architecture of an interpreted asymmetrical wave dominated delta
Sedimentology, 2010Co-Authors: Karl Charvin, Gary J. Hampson, Kerry Gallagher, Richard LabourdetteAbstract:Although modern wave-dominated shorelines exhibit complex geomorphologies, their ancient counterparts are typically described in terms of shoreface-shelf Parasequences with a simple internal architecture. This discrepancy can lead to poor discrimination between, and incorrect identification of, different types of wave-dominated shoreline in the stratigraphic record. Documented in this paper are the variability in facies characteristics, high-resolution stratigraphic architecture and interpreted palaeo-geomorphology within a single Parasequence that is interpreted to record the advance of an ancient asymmetrical wave-dominated delta. The Standardville (Ab1) Parasequence of the Aberdeen Member, Blackhawk Formation is exposed in the Book Cliffs of central Utah, USA. This Parasequence, and four others in the Aberdeen Member, record the eastward progradation of north/south-trending, wave-dominated shorelines. Within the Standardville (Ab1) Parasequence, distal wave-dominated shoreface-shelf deposits in the eastern part of the study area are overlain across a downlap surface by southward prograding fluvial-dominated delta-front deposits, which have previously been assigned to a separate ‘stranded lowstand Parasequence’ formed by a significant, allogenic change in relative sea-level. High-resolution stratigraphic analysis of these deposits reveals that they are instead more likely to record a single episode of shoreline progradation characterized by alternating periods of normal regressive and forced regressive shoreline trajectory because of minor cyclical fluctuations in relative sea-level. Interpreted normal regressive shoreline trajectories within the wave-dominated shoreface-shelf deposits are marked by aggradational stacking of bedsets bounded by non-depositional discontinuity surfaces. Interpreted forced regressive shoreline trajectories in the same deposits are characterized by shallow incision of fluvial distributary channels and strongly progradational stacking of bedsets bounded by erosional discontinuity surfaces that record enhanced wave-base scour. Fluvial-dominated delta-front deposits most probably record the regression of a lobate delta parallel to the regional shoreline into an embayment that was sheltered from wave influence. Wave-dominated shoreface-shelf and fluvial-dominated delta-front deposits occur within the same Parasequence, and their interpretation as the respective updrift and downdrift flanks of a single asymmetrical wave-dominated delta that periodically shifted its position provides the most straightforward explanation of the distribution and relative orientation of these two deposit types.
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three dimensional modeling of a shoreface shelf Parasequence reservoir analog part 2 geologic controls on fluid flow and hydrocarbon recovery
AAPG Bulletin, 2009Co-Authors: Matthew D Jackson, Gary J. Hampson, Richard P SechAbstract:Wave-dominated, shoreface-shelf Parasequences are commonly modeled as simple layer-cake reservoirs, yet analysis of modern and ancient analogs demonstrates that these intervals contain a more complex physical stratigraphy. We investigate the impact of depositional and diagenetic heterogeneity associated with gently dipping clinoform surfaces on fluid flow and recovery during water flooding, using a three-dimensional model reconstructed from a well-exposed outcrop analog. We demonstrate that the volume of oil in place is affected by variations in facies thickness associated with interfingering along clinoforms, whereas waterflood sweep efficiency is affected by barriers to flow along clinoform surfaces, such as calcite-cemented layers, mudstones, and siltstones. Sweep efficiency is low when water flooding is down depositional dip because oil is bypassed at the toe of each clinothem as water flows preferentially through high-quality sandstone facies in the upper part of the Parasequence. Sweep efficiency is higher when water flooding is up depositional dip because the gravity-driven, downward flow of water sweeps poorer-quality sandstone facies in the lower part of the Parasequence. In both cases, injectors may offer limited pressure support to producers. Water flooding along depositional strike yields good pressure support but poor sweep because the gravity-driven flow of water into the lower part of the Parasequence is significantly reduced. This yields highly variable fluid saturations but a uniform pressure gradient, which is consistent with pressure and fluid saturation data from the mature Rannoch Formation reservoir, Brent field, United Kingdom North Sea. Simple layer-cake models fail to capture the range of flow behaviors described above and overpredict recovery by up to 20% as a result.
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Geomorphological and sequence stratigraphic variability in wave‐dominated, shoreface‐shelf Parasequences
Sedimentology, 2008Co-Authors: Gary J. Hampson, Joep E.a. StormsAbstract:Physical stratigraphy within shoreface-shelf Parasequences contains a detailed, but virtually unstudied, record of shallow-marine processes over a range of historical and geological timescales. Using high-quality outcrop data sets, it is possible to reconstruct ancient shoreface-shelf morphology from clinoform surfaces, and to track the evolving morphology of the ancient shoreface-shelf. Our results suggest that shoreface-shelf morphology varied considerably in response to processes that operate over a range of timescales. (1) Individual clinoform surfaces form as a result of enhanced wave scour and/or sediment starvation, which may be driven by minor fluctuations in relative sea level, sediment supply and/or wave climate over short timescales (10 1 -10 3 years). These external controls cannot be distinguished in vertical facies successions, but may potentially be differentiated by the resulting clinoform geometries. (2) Clinoform geometry and distribution changes systematically within a single Parasequence, reflecting the cycle in sea level and/or sediment supply that produced the Parasequence (10 2 -10 5 years). These changes record steepening of the shoreface-shelf profile during early progradation and maintenance of a relatively uniform profile during late progradation. Modern shorefaces are not representative of this stratigraphic variability. (3) Clinoform geometries vary greatly between different Parasequences as a result of variations in Parasequence stacking pattern and relict shelf morphology during shore-face progradation (10 5 -10 8 years). These controls determine the external dimensions of the Parasequence.
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discontinuity surfaces clinoforms and facies architecture in a wave dominated shoreface shelf Parasequence
Journal of Sedimentary Research, 2000Co-Authors: Gary J. HampsonAbstract:ABSTRACT Detailed outcrop analysis of a wave-dominated, shoreface-shelf Parasequence exposed in the Book Cliffs, Utah reveals minor stratigraphic discontinuities, which define clinoforms. Two types of discontinuity are recognized, each with a distinctive lithologic character and geometry. Nondepositional discontinuities are marked by an abrupt decrease in the thickness and amalgamation of storm-generated event beds, and are interpreted to record hiatuses in sedimentation. These discontinuities define clinoforms with a concave-upward geometry that dip gently (0.02-0.58°) over distances of 800-6000 m down depositional dip. Erosional discontinuities are marked by an abrupt increase in event-bed amalgamation, grain size, and sand content, and are interpreted as enhanced storm-wave scours. These discontinuities define more steeply dipping (0.22-0.95°), concave-upward clinoforms that extend over 100-1600 m down depositional dip and 500-1500 m along depositional strike. The distribution and amalgamation of minor stratigraphic discontinuities defines linear zones of distinctive facies architecture that are oriented parallel to the paleoshoreline trend. Using the simple assumption that the shoreface-shelf equilibrium profile remained approximately constant for each type of discontinuity throughout shoreface migration (the "Bruun rule"), intra-Parasequence facies architecture can be speculatively interpreted in terms of shoreline trajectory, which reflects the balance between sediment supply and accommodation. The resulting interpretations support the notion that shoreline trajectory exerts a strong control on intra-Parasequence facies architecture and preservation of the shoreface-shelf profile.
Richard Labourdette - One of the best experts on this subject based on the ideXlab platform.
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Characterization of Controls on High-Resolution Stratigraphic Architecture in Wave-Dominated Shoreface–Shelf Parasequences Using Inverse Numerical Modeling
Journal of Sedimentary Research, 2011Co-Authors: Karl Charvin, Gary J. Hampson, Joep E.a. Storms, Kerry Gallagher, Richard LabourdetteAbstract:Abstract A new inverse numerical modeling method is used to constrain the environmental parameters (e.g., relative-sea-level, sediment-supply, and wave climate histories) that control stratigraphic architecture in wave-dominated shallow-marine deposits. The method links a “process-response” forward stratigraphic model that simulates wave and storm processes (BARSIM) to a combination of inverse methods formulated in a Bayesian framework that allows full characterization of uncertainties. This method is applied for the first time to a real geologic dataset, collected at outcrop from two shoreface–shelf Parasequences in the Aberdeen Member, Blackhawk Formation of the Book Cliffs, east-central Utah, USA. The environmental parameters that controlled the observed stratigraphic architecture are quantified, and key aspects of stratigraphic architecture are successfully predicted from limited data. Stratigraphic architecture at Parasequence-stacking and intra-Parasequence scales was driven principally by relative sea level (varying by up to about 55 m) and sediment supply (varying by up to 70 m2/yr), whose interplay determines the shoreline trajectory. Within zones of distinctive shoreline trajectory, variations in wave climate (of up to about 3 m in fairweather-wave height) controlled superimposed variations in sandstone and shale content (e.g., the development of upward-coarsening and upward-fining bedsets). The modeling results closely match the observed stratigraphic architecture, but their quality is limited by: (1) the formulation and assumptions of the forward-modeling algorithms, and (2) the observed data distribution and quality, which provide poor age constraint.
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intra Parasequence architecture of an interpreted asymmetrical wave dominated delta
Sedimentology, 2010Co-Authors: Karl Charvin, Gary J. Hampson, Kerry Gallagher, Richard LabourdetteAbstract:Although modern wave-dominated shorelines exhibit complex geomorphologies, their ancient counterparts are typically described in terms of shoreface-shelf Parasequences with a simple internal architecture. This discrepancy can lead to poor discrimination between, and incorrect identification of, different types of wave-dominated shoreline in the stratigraphic record. Documented in this paper are the variability in facies characteristics, high-resolution stratigraphic architecture and interpreted palaeo-geomorphology within a single Parasequence that is interpreted to record the advance of an ancient asymmetrical wave-dominated delta. The Standardville (Ab1) Parasequence of the Aberdeen Member, Blackhawk Formation is exposed in the Book Cliffs of central Utah, USA. This Parasequence, and four others in the Aberdeen Member, record the eastward progradation of north/south-trending, wave-dominated shorelines. Within the Standardville (Ab1) Parasequence, distal wave-dominated shoreface-shelf deposits in the eastern part of the study area are overlain across a downlap surface by southward prograding fluvial-dominated delta-front deposits, which have previously been assigned to a separate ‘stranded lowstand Parasequence’ formed by a significant, allogenic change in relative sea-level. High-resolution stratigraphic analysis of these deposits reveals that they are instead more likely to record a single episode of shoreline progradation characterized by alternating periods of normal regressive and forced regressive shoreline trajectory because of minor cyclical fluctuations in relative sea-level. Interpreted normal regressive shoreline trajectories within the wave-dominated shoreface-shelf deposits are marked by aggradational stacking of bedsets bounded by non-depositional discontinuity surfaces. Interpreted forced regressive shoreline trajectories in the same deposits are characterized by shallow incision of fluvial distributary channels and strongly progradational stacking of bedsets bounded by erosional discontinuity surfaces that record enhanced wave-base scour. Fluvial-dominated delta-front deposits most probably record the regression of a lobate delta parallel to the regional shoreline into an embayment that was sheltered from wave influence. Wave-dominated shoreface-shelf and fluvial-dominated delta-front deposits occur within the same Parasequence, and their interpretation as the respective updrift and downdrift flanks of a single asymmetrical wave-dominated delta that periodically shifted its position provides the most straightforward explanation of the distribution and relative orientation of these two deposit types.
Karl Charvin - One of the best experts on this subject based on the ideXlab platform.
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Characterization of Controls on High-Resolution Stratigraphic Architecture in Wave-Dominated Shoreface–Shelf Parasequences Using Inverse Numerical Modeling
Journal of Sedimentary Research, 2011Co-Authors: Karl Charvin, Gary J. Hampson, Joep E.a. Storms, Kerry Gallagher, Richard LabourdetteAbstract:Abstract A new inverse numerical modeling method is used to constrain the environmental parameters (e.g., relative-sea-level, sediment-supply, and wave climate histories) that control stratigraphic architecture in wave-dominated shallow-marine deposits. The method links a “process-response” forward stratigraphic model that simulates wave and storm processes (BARSIM) to a combination of inverse methods formulated in a Bayesian framework that allows full characterization of uncertainties. This method is applied for the first time to a real geologic dataset, collected at outcrop from two shoreface–shelf Parasequences in the Aberdeen Member, Blackhawk Formation of the Book Cliffs, east-central Utah, USA. The environmental parameters that controlled the observed stratigraphic architecture are quantified, and key aspects of stratigraphic architecture are successfully predicted from limited data. Stratigraphic architecture at Parasequence-stacking and intra-Parasequence scales was driven principally by relative sea level (varying by up to about 55 m) and sediment supply (varying by up to 70 m2/yr), whose interplay determines the shoreline trajectory. Within zones of distinctive shoreline trajectory, variations in wave climate (of up to about 3 m in fairweather-wave height) controlled superimposed variations in sandstone and shale content (e.g., the development of upward-coarsening and upward-fining bedsets). The modeling results closely match the observed stratigraphic architecture, but their quality is limited by: (1) the formulation and assumptions of the forward-modeling algorithms, and (2) the observed data distribution and quality, which provide poor age constraint.
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intra Parasequence architecture of an interpreted asymmetrical wave dominated delta
Sedimentology, 2010Co-Authors: Karl Charvin, Gary J. Hampson, Kerry Gallagher, Richard LabourdetteAbstract:Although modern wave-dominated shorelines exhibit complex geomorphologies, their ancient counterparts are typically described in terms of shoreface-shelf Parasequences with a simple internal architecture. This discrepancy can lead to poor discrimination between, and incorrect identification of, different types of wave-dominated shoreline in the stratigraphic record. Documented in this paper are the variability in facies characteristics, high-resolution stratigraphic architecture and interpreted palaeo-geomorphology within a single Parasequence that is interpreted to record the advance of an ancient asymmetrical wave-dominated delta. The Standardville (Ab1) Parasequence of the Aberdeen Member, Blackhawk Formation is exposed in the Book Cliffs of central Utah, USA. This Parasequence, and four others in the Aberdeen Member, record the eastward progradation of north/south-trending, wave-dominated shorelines. Within the Standardville (Ab1) Parasequence, distal wave-dominated shoreface-shelf deposits in the eastern part of the study area are overlain across a downlap surface by southward prograding fluvial-dominated delta-front deposits, which have previously been assigned to a separate ‘stranded lowstand Parasequence’ formed by a significant, allogenic change in relative sea-level. High-resolution stratigraphic analysis of these deposits reveals that they are instead more likely to record a single episode of shoreline progradation characterized by alternating periods of normal regressive and forced regressive shoreline trajectory because of minor cyclical fluctuations in relative sea-level. Interpreted normal regressive shoreline trajectories within the wave-dominated shoreface-shelf deposits are marked by aggradational stacking of bedsets bounded by non-depositional discontinuity surfaces. Interpreted forced regressive shoreline trajectories in the same deposits are characterized by shallow incision of fluvial distributary channels and strongly progradational stacking of bedsets bounded by erosional discontinuity surfaces that record enhanced wave-base scour. Fluvial-dominated delta-front deposits most probably record the regression of a lobate delta parallel to the regional shoreline into an embayment that was sheltered from wave influence. Wave-dominated shoreface-shelf and fluvial-dominated delta-front deposits occur within the same Parasequence, and their interpretation as the respective updrift and downdrift flanks of a single asymmetrical wave-dominated delta that periodically shifted its position provides the most straightforward explanation of the distribution and relative orientation of these two deposit types.
Grant Wach - One of the best experts on this subject based on the ideXlab platform.
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Firmgrounds – key surfaces in the recognition of Parasequences in the Aptian Lower Greensand Group, Isle of Wight (southern England)
Sedimentology, 2002Co-Authors: Alastair Ruffell, Grant WachAbstract:Aptian Lower Greensand Group exposures in the cliffs of the Isle of Wight (southern England) display a consistent coarsening-up cyclicity on the scale of centimetres to tens of metres that reflects the bed, bed-set, Parasequence, Parasequence set and sequence hierarchy. These coarsening-up cycles are most commonly recognized at the scale of Parasequences (20 cm to 10 m thick), genetically related groups of which form Parasequence sets. Both Parasequences and Parasequence sets contain the succession of biofacies that culminate in firmground development. Numerous episodes of erosion, deposition and colonization are recorded, reflecting multiple erosion/bypass events. The increase in mean grain-size through each cycle is reflected by changes in physical sedimentary structures; ichnofauna or bioturbational fabric; fossil fauna and diagenesis. Interbedded mudstones, siltstones and sandstones in the lower beds of each cycle display a variety of structures ranging from low-angle, hummocky, or tabular cross-strata, sandstone-filled erosional gutters and planar lamination. The cleaner sandstones found in the upper parts to each cycle are often completely bioturbated with only rare stratification and pebble/plant debris-filled scours preserved. Bioturbational fabrics change upward through each cycle from small, subhorizontal, mud- or sandstone-filled burrows to large, branching, clay-filled or cemented burrow systems. The top surface of each cycle is marked by a fossil epifauna indicative of firm to hard substrate conditions. Concentrations of bivalves, brachiopods, bryozoa, crinoids and corals are preferentially cemented by iron oxide, carbonate or phosphate. Such cements were early and thus utilized by firm or hard substrate dwellers. This fossiliferous, cemented sandstone is overlain by a flooding surface marked by the mudstone and silt-rich sandstones at the base of the next cycle. Together, the fauna and ichnofauna in each cycle represent the gradual development of firm substrate conditions, culminating in the diverse firmground fauna preserved at the top of each cycle. The fauna and changing substrate conditions reflect the hiatuses developed during successive episodes of marine flooding. High species diversity is matched by complex patterns of taphonomic feedback in the mature firmground faunas that mark major flooding surfaces. Increasing faunal maturity allows recognition of a hierarchy of hiatuses. This hierarchy is analogous to the Parasequence–Parasequence set division. The stratigraphic condensation of firmgrounds can be used to empirically define the condensed section, the thickness of sediment between firmgrounds being a function of sediment supply and water depth (accommodation space).
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firmgrounds key surfaces in the recognition of Parasequences in the aptian lower greensand group isle of wight southern england
Sedimentology, 1998Co-Authors: Alastair Ruffell, Grant WachAbstract:Aptian Lower Greensand Group exposures in the cliffs of the Isle of Wight (southern England) display a consistent coarsening-up cyclicity on the scale of centimetres to tens of metres that reflects the bed, bed-set, Parasequence, Parasequence set and sequence hierarchy. These coarsening-up cycles are most commonly recognized at the scale of Parasequences (20 cm to 10 m thick), genetically related groups of which form Parasequence sets. Both Parasequences and Parasequence sets contain the succession of biofacies that culminate in firmground development. Numerous episodes of erosion, deposition and colonization are recorded, reflecting multiple erosion/bypass events. The increase in mean grain-size through each cycle is reflected by changes in physical sedimentary structures; ichnofauna or bioturbational fabric; fossil fauna and diagenesis. Interbedded mudstones, siltstones and sandstones in the lower beds of each cycle display a variety of structures ranging from low-angle, hummocky, or tabular cross-strata, sandstone-filled erosional gutters and planar lamination. The cleaner sandstones found in the upper parts to each cycle are often completely bioturbated with only rare stratification and pebble/plant debris-filled scours preserved. Bioturbational fabrics change upward through each cycle from small, subhorizontal, mud- or sandstone-filled burrows to large, branching, clay-filled or cemented burrow systems. The top surface of each cycle is marked by a fossil epifauna indicative of firm to hard substrate conditions. Concentrations of bivalves, brachiopods, bryozoa, crinoids and corals are preferentially cemented by iron oxide, carbonate or phosphate. Such cements were early and thus utilized by firm or hard substrate dwellers. This fossiliferous, cemented sandstone is overlain by a flooding surface marked by the mudstone and silt-rich sandstones at the base of the next cycle. Together, the fauna and ichnofauna in each cycle represent the gradual development of firm substrate conditions, culminating in the diverse firmground fauna preserved at the top of each cycle. The fauna and changing substrate conditions reflect the hiatuses developed during successive episodes of marine flooding. High species diversity is matched by complex patterns of taphonomic feedback in the mature firmground faunas that mark major flooding surfaces. Increasing faunal maturity allows recognition of a hierarchy of hiatuses. This hierarchy is analogous to the Parasequence–Parasequence set division. The stratigraphic condensation of firmgrounds can be used to empirically define the condensed section, the thickness of sediment between firmgrounds being a function of sediment supply and water depth (accommodation space).
Massimo Zecchin - One of the best experts on this subject based on the ideXlab platform.
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Parasequences: Allostratigraphic misfits in sequence stratigraphy
Earth-Science Reviews, 2020Co-Authors: Octavian Catuneanu, Massimo ZecchinAbstract:Abstract Parasequences were introduced as the building blocks of seismic-scale systems tracts in the context of low-resolution seismic stratigraphy. Pitfalls of this concept relate to the definition of Parasequence boundaries as lithological discontinuities that mark episodes of abrupt water deepening. With this general meaning, ‘flooding surfaces’ may be facies contacts within transgressive deposits, or may coincide with different types of sequence stratigraphic surfaces (maximum regressive, transgressive ravinement, or maximum flooding). In all cases, flooding surfaces are allostratigraphic contacts restricted to coastal and shallow-water settings, where evidence of abrupt water deepening can be demonstrated. Flooding surfaces may also be absent from the shallow-water systems, where conformable successions accumulate during gradual water deepening. It follows that (1) Parasequences have smaller extent than systems tracts, and (2) systems tracts do not always consist of stacked Parasequences. These limitations prevent the dependable use of the Parasequence concept in sequence stratigraphy. Advances in high-resolution sequence stratigraphy show that the scales of sequences and Parasequences are not mutually exclusive; the two types of units define different approaches to the delineation of stratigraphic cycles at high-resolution scales. Sequences that develop at Parasequence scales provide a more reliable alternative for correlation, both within and outside of the coastal and shallow-water settings, rendering Parasequences obsolete. Every transgression that affords the formation of a flooding surface starts from a maximum regressive surface and ends with a maximum flooding surface observed at the scale of that transgression. These systems tract boundaries are invariably more extensive than any facies contacts that may form during the transgression. Flooding surfaces remain relevant to the description of facies relationships, but their stratigraphic meaning needs to be assessed on a case-by-case basis. The use of sequences and systems tracts in high-resolution studies provides consistency in methodology and nomenclature at all stratigraphic scales, irrespective of geological setting and the types and resolution of the data available.
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towards the standardization of sequence stratigraphy is the Parasequence concept to be redefined or abandoned
Earth-Science Reviews, 2010Co-Authors: Massimo ZecchinAbstract:After more than thirty years from the introduction of the sequence-stratigraphic concepts (Payton, 1977), and their refinement in the classic SEPM special publication 42 (Wilgus et al., 1988), sequence stratigraphy has becomemoremature and now represents a widely used tool to study sedimentary successions. More recently, review publications (e.g. Miall, 1997; Posamentier and Allen, 1999; Catuneanu, 2006; Catuneanu et al., 2009) have put order among the various sequence-stratigraphic models and attempted to standardize the terminology. Among the historical issues raised by sequence-stratigraphic concepts and terminology, one deals with the high-frequency cycles that compose sequences, which have been named Parasequences. A Parasequence was defined as ‘a relatively conformable succession of genetically related beds or bedsets bounded by marine flooding surfaces and their correlative surfaces... Parasequences are progradational and therefore the beds within Parasequences shoal upward’ (Van Wagoner et al., 1987, 1988, 1990). The flooding surface was defined as ‘a surface across which there is an abrupt shift of facies that may indicate an increase in water depth or a decrease in sediment supply’ (Van Wagoner et al., 1988, 1990). Parasequences may be stacked to form progradational, aggradational and retrogradational Parasequence sets, which typify systems tracts composing a sequence (VanWagoner et al., 1990), the latter being defined as ‘a stratigraphic unit composed of a relatively conformable succession of genetically related strata and bounded at its top and base by unconformities or their correlative conformities’ (Mitchum, 1977).
