Contents

• Introduction • Sea-level change

• Sedimentology – concepts • Sequence stratigraphy – concepts
• Fluvial environments • Marine sequence stratigraphy
• Deltaic environments • Nonmarine sequence stratigraphy
• Coastal environments • Basin and reservoir modeling
• Offshore marine environments • Reflection

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 Sequence stratigraphy – concepts

• Sequence stratigraphy highlights the role of allogenic controls

on patterns of deposition, as opposed to autogenic controls that
operate within depositional environments
• Eustasy (sea level)
• Subsidence (basin tectonics)
• Sediment supply (climate and hinterland tectonics)

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 Sequence stratigraphy – concepts

• Accommodation is the space available, at any given point in

time, for sediments to accumulate; accommodation is created or
destroyed by RSL changes
• Water depth is controlled by changes in accommodation as well
as sedimentation
• Base level is the horizontal surface to which subaerial erosion
proceeds; therefore it corresponds to sea level
• Base level is a principal control of accommodation, and, hence,
whether erosion or deposition is likely to occur at any given
location; attempts to extend the concept landward are
controversial

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 Sequence stratigraphy – concepts

• Allostratigraphy is a relatively new approach to stratigraphic

subdivision, and is based on the separation of strata based on
unconformities or other discontinuities (e.g., paleosols)
• Sequence stratigraphy is the analysis of genetically related
depositional units bounded by unconformities and their
correlative conformities
• A depositional sequence is a stratigraphic unit bounded at its
top and base by unconformities or their correlative conformities
(=allostratigraphic unit), and typically embodies a continuum of
depositional environments, from updip (continental) to downdip
(deep marine)
• The subtle balance between RSL and sediment supply controls
whether aggradation, regression (progradation), forced
regression, or transgression (retrogradation) will occur

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 Sequence stratigraphy – concepts

• Allostratigraphy is a relatively new approach to stratigraphic

subdivision, and is based on the separation of strata based on
unconformities or other discontinuities (e.g., paleosols)
• Sequence stratigraphy is the analysis of genetically related
depositional units bounded by unconformities and their
correlative conformities
• A depositional sequence is a stratigraphic unit bounded at its
top and base by unconformities or their correlative conformities
(=allostratigraphic unit), and typically embodies a continuum of
depositional environments, from updip (continental) to downdip
(deep marine)
• The subtle balance between RSL and sediment supply controls
whether aggradation, regression (progradation), forced
regression, or transgression (retrogradation) will occur

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 Sequence stratigraphy – concepts

• Allostratigraphy is a relatively new approach to stratigraphic

subdivision, and is based on the separation of strata based on
unconformities or other discontinuities (e.g., paleosols)
• Sequence stratigraphy is the analysis of genetically related
depositional units bounded by unconformities and their
correlative conformities
• A depositional sequence is a stratigraphic unit bounded at its
top and base by unconformities or their correlative conformities
(=allostratigraphic unit), and typically embodies a continuum of
depositional environments, from updip (continental) to downdip
(deep marine)
• The subtle balance between RSL and sediment supply controls
whether aggradation, regression (progradation), forced
regression, or transgression (retrogradation) will occur

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 Sequence stratigraphy – concepts

• A RSL fall on the order of tens of meters or more will lead to a

basinward shift of the shoreline and an associated basinward
shift of depositional environments; commonly (but not always)
this will be accompanied by subaerial exposure, erosion, and
the formation of a widespread unconformity known as a
sequence boundary
• Sequence boundaries are the key stratigraphic surfaces (high-
order bounding surfaces) that separate successive sequences
and are characterized by subaerial exposure/erosion, a
basinward shift in facies, a downward shift in coastal onlap, and
onlap of overlying strata
• Parasequences are lower order stratal units separated by
(marine) flooding surfaces; they are commonly autogenic and
not necessarily the result of smaller-scale RSL fluctuations

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 Sequence stratigraphy – concepts

• Systems tracts are contemporaneous, linked depositional

environments (or depositional systems); they are the building
blocks of sequences and different types of systems tracts
represent different limbs of a RSL curve
• Falling-stage (forced regressive) systems tract (FSST)
• Lowstand systems tract (LST)
• Transgressive systems tract (TST)
• Highstand systems tract (HST)
• The various systems tracts are characterized by their position
within a sequence, by shallowing or deepening upward facies
successions, or by parasequence stacking patterns

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 Sequence stratigraphy – concepts

• Systems tracts are contemporaneous, linked depositional

environments (or depositional systems); they are the building
blocks of sequences and different types of systems tracts
represent different limbs of a RSL curve
• Falling-stage (forced regressive) systems tract (FSST)
• Lowstand systems tract (LST)
• Transgressive systems tract (TST)
• Highstand systems tract (HST)
• The various systems tracts are characterized by their position
within a sequence, by shallowing or deepening upward facies
successions, or by parasequence stacking patterns

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 Sequence stratigraphy – concepts

• Maximum flooding surfaces form during the culmination of

RSL rise, and maximum landward translation of the shoreline,
and constitute the stratigraphic surface that separates the TST
and HST
• In the downdip realm (deep sea), where sedimentation rates
can be very low during maximum flooding, condensed
sections may develop
• LSTs are separated from overlying TSTs by transgressive
surfaces; transgression is further characterized by coastal
onlap
• An alternative approach to sequence analysis uses genetic
stratigraphic sequences that are bounded by maximum
flooding surfaces

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 Sequence stratigraphy – concepts

• Maximum flooding surfaces form during the culmination of

RSL rise, and maximum landward translation of the shoreline,
and constitute the stratigraphic surface that separates the TST
and HST
• In the downdip realm (deep sea), where sedimentation rates
can be very low during maximum flooding, condensed
sections may develop
• LSTs are separated from overlying TSTs by transgressive
surfaces; transgression is further characterized by coastal
onlap
• An alternative approach to sequence analysis uses genetic
stratigraphic sequences that are bounded by maximum
flooding surfaces

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 Sequence stratigraphy – concepts

• In a very general sense, RSL fall leads to reduced deposition

and formation of sequence boundaries in updip areas, and
increased deposition in downdip settings (e.g., submarine fans)
• RSL rise leads to trapping of sediment in the updip areas (e.g.,
coastal plains with a littoral energy fence) and reduced transfer
of sediment to the deep sea (hemipelagic deposition;
condensed sections)

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 Sequence stratigraphy – concepts

• Seismic stratigraphy is based on the principle that seismic

reflectors follow stratal patterns and approximate isochrons
(time lines)
• Reflection terminations provide the data used to identify
sequence-stratigraphic surfaces, systems tracts, and their
internal stacking patterns
• Technological developments have been prolific:
• Vertical resolution improved to a few tens of meters
• Widespread use of 3D seismic
• Seismic data should preferably always be interpreted in
conjunction with well log or core data

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 Sequence stratigraphy – concepts

• Seismic stratigraphy is based on the principle that seismic

reflectors follow stratal patterns and approximate isochrons
(time lines)
• Reflection terminations provide the data used to identify
sequence-stratigraphic surfaces, systems tracts, and their
internal stacking patterns
• Technological developments have been prolific:
• Vertical resolution improved to a few tens of meters
• Widespread use of 3D seismic
• Seismic data should preferably always be interpreted in
conjunction with well log or core data

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 Sequence stratigraphy – concepts

• Seismic stratigraphy is based on the principle that seismic

reflectors follow stratal patterns and approximate isochrons
(time lines)
• Reflection terminations provide the data used to identify
sequence-stratigraphic surfaces, systems tracts, and their
internal stacking patterns
• Technological developments have been prolific:
• Vertical resolution improved to a few tens of meters
• Widespread use of 3D seismic
• Seismic data should preferably always be interpreted in
conjunction with well log or core data

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 Sequence stratigraphy – concepts

• A better understanding of stratigraphic sequences can be

obtained by the construction of chronostratigraphic charts
(‘Wheeler diagrams’); these can subsequently be used to infer
coastal-onlap curves
• Variations in sediment supply can produce stratal patterns that
are very similar to those formed by RSL change (except for
forced regression); in addition, variations in sediment supply
can cause stratigraphic surfaces at different locations to be out
of phase
• In principle, sequence-stratigraphic concepts could be applied
with some modifications to sedimentary successions that are
entirely controlled by climate change and/or tectonics (outside
the realm of RSL control)

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 Sequence stratigraphy – concepts

• A better understanding of stratigraphic sequences can be

obtained by the construction of chronostratigraphic charts
(‘Wheeler diagrams’); these can subsequently be used to infer
coastal-onlap curves
• Variations in sediment supply can produce stratal patterns that
are very similar to those formed by RSL change (except for
forced regression); in addition, variations in sediment supply
can cause stratigraphic surfaces at different locations to be out
of phase
• In principle, sequence-stratigraphic concepts could be applied
with some modifications to sedimentary successions that are
entirely controlled by climate change and/or tectonics (outside
the realm of RSL control)

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 Sequence stratigraphy – concepts

• The global sea-level curve for the Mesozoic and Cenozoic

(inferred from coastal-onlap curves) contains first, second, and
third-order eustatic cycles that are supposed to be globally
synchronous, but it is a highly questionable generalization
• Conceptual problems: spatially variable RSL change due to
differential isostatic and tectonic movements undermines the
notion of a globally uniform control
• Dating problems: correlation is primarily based on biostratigraphy
that typically has a resolving power comparable to the period of
third-order cycles

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