Sequence Stratigraphy

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Sequence Stratigraphy Template for Conceptual
Models Used to Interpret Depositional
Systems - beauty but not truth? -
Christopher G. St. C. Kendall University of South
Carolina kendall_at_sc.edu 803 978 7523
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Why codify rules for sequence stratigraphic
nomenclature?

• We use common terms and know their meaning
• Have a standard hierarchy of subdivisions
• Have a uniform methodology
• Guidance for revision
• Teaching resource each new generation of
  students practitioners have a common
  understanding

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Sequence Stratigraphy
A framework of genetically related stratigraphic
facies geometries and their bounding surfaces
used to determine depositional setting
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Sequence Stratigraphy Terminology

• Stratigraphers have a position on terminology
  similar to the of Humpty Dumpty's from Lewis
  Carrolls Through the Looking Glass
• "When I use a word, it means just what I choose
  it to mean - nothing more nor less".

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Talk Organization

• Sedimentary Analysis Sequence Stratigraphy
• History of Sequence Stratigraphy
• Sequence Stratigraphy Analysis Defined
• Geometries Stacking Patterns
• System Tracts Relative Sea Level
• Bounding Surfaces
• Conceptual Models
• Terminology That Should be Defined
• Conclusions

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Sequence Stratigraphy The process

• Interpretation of the Sedimentary section
  involves
• From oldest to youngest, identify the
  subdividing surfaces that envelope enclose the
  discrete geometric bodies of sediment of the
  sedimentary section build a template
• Backstrip these geometries then use the
  template of surfaces to reassemble them in order
  of their accumulation
• The subdividing surfaces, geometry, lithofacies
  fauna are input to a conceptual model to
  determine the evolving character of the
  depositional setting
• Each stratal unit is defined and identified
  only by physical relationships of the strata,
  including lateral continuity and geometry of the
  surfaces bounding the units, vertical stacking
  patterns, and lateral geometry of the strata
  within the units." (Van Wagoner et al., 1990).

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'Depositional' sequence Vail et al 1971
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SB
mfs
TS
Establish a framework of genetically related
stratigraphic facies geometries and their
bounding surfaces to determine depositional
setting
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Barrier Coastal Elements
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Sedimentary Analysis
Potential flow of interpretation Scheme
used to characterize depositional systems so they
can be compared
data
data
interpretation
interpretation
interpretation
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Power of Sequence Stratigraphy

• Determines depositional setting by
• Establishing the order in which strata were laid
  down in
• Explains the geometric hierarchy of sedimentary
  strata the elements they form
• Uses the major surfaces marking breaks in the
  character of sedimentary section as a template
  for conceptual depositional models, independent
  of time (relative ages)
• Geologic time derived from
• Radiometric markers
• Biostratigraphic markers

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Building Block Sedimentary Fill Hierarchy

• Sediment body characterization in order of
  decreasing complexity
• Complex Set
• Complex
• Story
• Element
• Bed
• These are the fundamental components of Sequences
  and System tracts

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Fluvial - Architectural Elements
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Deepwater - Architectural Elements
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Deepwater - Architectural Elements
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Deepwater - Architectural Elements
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Hierarchy of Carbonate Shelf Architectural
Elements
PROGRADING MARGIN
ONLAPPING MARGIN
PROGRADING MARGIN
PROGRADING MARGIN
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Elements Sequence Building Blocks

• Definition of element hierarchy
• Framework for systematic description comparison
  of deposits of a depositional setting (fluvial,
  deltaic, deepwater etc)
• Based on physical organization of strata
  (geometry) the surfaces bounding them
• Genetically-related stratigraphic elements form
  the hierarchy
• Independent of type of setting
• Applicable at all scales to all sedimentary
  systems
• Purpose
• Analysis comparison of the elements of similar
  depositional systems
• Provide the detailed character of a sequence
  and/or system tract
• Net to-gross, aspect ratio, connectivity
• Lithofacies type aquifer/reservoir quality
• Application
• Better defined depositional geometries and so
  depositional models
• More accurate aquifer/resource assessment
• Optimize strategy for depletion of
  aquifer/resource

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History of Sequence Stratigraphy

• Sloss recognized intercontinental-unconformities
  related them to eustasy
• Vail extrapolated eustatic signals to seismic
  sequence boundaries
• Jerveys simulations showed seismic sequences
  product of cyclic sea level (base level) change
• Van Wagoner Posamentier related unconformities,
  transgressive surfaces maximum flooding
  surfaces to boundaries of system tracts in
  depositional sequences responding to sea level
  change
• Hydrocarbon exploration models production
  reservoir models use bounding surfaces, facies
  assemblages system tracts as templates for
  depositional models lithofacies geometry
  predictions

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Sloss Unconformities Eustasy
After Lowell Thwaite
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1st Seismic Sequence Interpretation
Vail et al, 1976
Mesozoic through Tertiary of Offshore Morocco
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'Depositional' sequence Vail
Jervey Posmentier Van Wagoner
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Sequence stratigraphy

• Analytical protocol marries rules of thumb
  (heuristics) to conceptual models
• Interprets general depositional setting of
  layered clastic carbonate sedimentary strata
• Models developed to interpret variety of
  datasets
• Work best with combination of outcrop, core, well
  log, seismic data
• May work with two or more of these data sources
  but are least reliable for a single data source
• Local differences in depositional processes,
  topography, and tectonics and, base level
  position, mean a model more appropriate to one
  setting, than others?

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Sequence Stratigraphys Fuzzy Rules

• Lithofacies geometries confining surfaces
  transgress time
• Different geometries for a specific time interval
  
• Local variations in rates direction of tectonic
  movement
• Local rates of sediment supply accumulation
• Not all erosional or depositional surfaces are
  product of base level change

Depositional models successfully predict
lithofacies geometry for exploration reservoirs
Depositional model is refined as data base grows
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Sequence stratigraphic analysis
Fundamental to sequence stratigraphic analysis

• Strata deposited in order
• Surfaces subdivide strata into packages of beds
  with common depositional origin
• Geometric arrangement of strata packages of
  strata reflect
• Basin filling
• Erosional events
• Commonly sequence stratigraphiy applied to
  sediment accumulation at basin margins in
  continental, marginal marine, and/or down-slope
  settings
• Fill accumulates either as
• Unconfined fill over these settings
• Confined within erosional down-cut topography

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Unconfined geometric architecture
Stacked layers tend to have three basic patterns

• Aggrading (lie above one another vertically)
• Prograding (inclined in order over and beside one
  another in a seaward direction)
• Retrograding (inclined in order over beside one
  another in a landward direction)

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Stacking Patterns - Unconfined
After Van Wagoner
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Confined geometric architecture
Fill post erosional down-cutting expressed by a
geometric architecture of stacked layers in
either succession of

• Organized offset bodies and/or
• Randomly ordered disorganized offset bodies

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Confined Sedimentary Fill - Channels
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Stacking Pattern Rules Problems

• End member stratal stacking patterns reflect
  interplay of accommodation (space available for
  sediments to fill) rates of sediment
  accumulation
• Local vagaries in
• Depositional processes
• Topography
• Tectonics so base level position
• mean stacking styles of geometry may merge with
  one another but are tied to system tracts

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Stacking, Surfaces System tracts!
Geometric architecture of stacked layers are
inferred to be related to eustatic events

• Lowstand - Progradation-to-aggradational (PA)
• Transgression - Retrogradational geometries (R),
• Highstand - Aggradational-to-progradation
  geometries (AP) system tracts (Van Wagoner et
  al., 1988 Neil and Abreu, 2008)
• As many as five system tracts recognized but
  above three are most commonly used

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System Tracts - Reviewed
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System Tracts - Unconfined
3-D facies assemblages of common genetic origin
with unconfined geometric architecture are
interpreted to form during phases of relative
sea-level cycle (Posamentier, et al, 1988)

• System tracts defined by
• Bounding surfaces
• Position within a sequence
• Geometric stacking pattern
• Lowstand - Progradation-to-aggradational (PA)
• Transgression - Retrogradational geometries (R),
• Highstand - Aggradational-to-progradation
  geometries (AP) system tracts (Van Wagoner et
  al., 1988 Neil and Abreu, 2008)
• As many as five system tracts recognized but
  above three are most commonly used

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Surfaces, System tracts Sequences

• Role of conceptual depositional models

System tracts are inferred to be related to
accommodation generation and fill. This
relationship is explained using conceptual models
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Bounding Surfaces
Identification interpretation of bounding
surfaces that separate layered clastic and
carbonate sedimentary strata into genetically
related packages, system tracts, a key to
Sequence Stratigraphy

• Maximum Flooding Surfaces (MFS)
• Transgressive Surfaces (TS) (maximum regressive
  surfaces transgressive ravinement surfaces)
• Sequence Boundaries (SB) (subaerial
  unconformities, regressive surfaces of marine
  erosion correlative conformities).

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Conceptual Models

• Three conceptual models commonly used in sequence
  stratigraphy are separated from each other on
  basis of bounding subdividing boundaries of
  system tracts

• 'Depositional' sequence of Vail et al 1971
• 'Genetic Stratigraphic' sequence model of
  Galloway, 1989
• 'Transgressive-Regressive' (T-R) sequence model
  of Embry and Johannessen, 1992

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'Depositional' Sequence (Vail et al 1971)

• Bounded by subaerial unconformities marine
  correlative conformities
• Bounding surface assumed genetically connected
  with stratigraphic hiatus associated with
  subaerial unconformity that is progressively
  younger in seaward direction
• No matter systems-tract terminology used bounding
  surfaces of this sequence enclose
• Forced regressive
• Normal regressive (lowstand and highstand)
• Transgressive sedimentary packages

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'Genetic Stratigraphic' Sequence Galloway,
1989

• Bounded by maximum flooding surfaces.
• These surfaces interpreted to form as sea level
  rises rapidly, sediment supply slows organic
  matter accumulates sequestering radioactive
  materials
• Sequence encloses
• Forced regressive deposits
• Normal regressive (lowstand and highstand)
  deposits
• Transgressive deposits

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'Transgressive-Regressive' (T-R) sequence (Embry
Johannessen, 1992)

• Composite sequence boundary includes subaerial
  unconformity marine portion of maximum
  regressive surface
• Normal' 'forced' regressive deposits are
  included within the 'regressive systems tract'

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Boundaries Conceptual Models
After Catuneanu, 2007
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SequenceStratigraphyModelTree
After Catuneanu, 2002
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Application nomenclature of conceptual models
subject to debate

• Nomenclature of systems tracts sequence
  stratigraphic surfaces
• Surfaces that should be ranked as 'sequence
  boundary
• Framework of surfaces, systems tracts, selection
  of sequence boundaries may vary with approach,
  available data sets, depositional setting
• Good news!!
• Sequence stratigraphic method determines
  depositional setting of section
• Identification of genetic units bounding
  surfaces mostly model independent.
• For both non-marine and marine systems, no
  matter characterization of 'sequence boundary',
  these boundaries envelope sedimentary section as
  through-going physical surface from basin margin
  to depocenter

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Caveats

• Sequence stratigraphic surfaces serve, at least
  in part, as boundaries between different genetic
  types of deposit
• Not all data lend themselves to identification of
  all sequence stratigraphic surfaces
• Not all sequence stratigraphic surfaces are
  present in every depositional section
• Depositional settings of nearshore to just
  offshore generate an array of depositional and
  erosional surfaces, many of incorporated into
  sequence stratigraphy
• In contrast, within either fluvial and/or
  deep-water systems, conditions favor formation of
  fewer key bounding sequence stratigraphic surfaces

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Why codify rules for sequence stratigraphic
nomenclature?

• We use common terms and know their meaning
• Have a standard hierarchy of subdivisions
• Have a uniform methodology
• Guidance for revision
• Teaching resource each new generation of
  students practitioners have a common
  understanding

45
Terms to Define

• Surfaces
• Separate layered clastic and carbonate
  sedimentary strata into genetically related
  packages, system tracts
• System Tract
• Specific three-dimensional facies assemblages of
  common genetic origin, associated with unconfined
  geometric architecture interpreted as formed
  during phases of a relative sea-level cycle
• Conceptual Models
• Explains configuration of surfaces and
  geometries that occur in layered sedimentary
  record in terms of
• Basinal setting
• Rates of sediment supply erosion (accumulation)
• Eustasy
• Tectonic movement

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Terms to Define - Surfaces
Separate layered clastic carbonate sedimentary
strata into genetically related packages, or
system tracts

• Subaerial unconformity
• Correlative conformity (sensu Posamentier, and
  sensu Hunt and Tucker the former have renamend
  Posamentiers CC as the basal surface of forced
  regression). (Two different surfaces).
• Regressive surface of marine erosion
• Maximum regressive surface
• Maximum flooding surface
• Transgressive ravinement surfaces

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Terms to Define Systems Tracts
Specific three-dimensional facies assemblages of
common genetic origin, associated with unconfined
geometric architecture interpreted as formed
during phases of a relative sea-level cycle

• Falling Stage Systems Tract (FSST)
• Lowstand Systems Tract (LST)
• Transgressive Systems Tract (TST)
• Highstand Systems Tract (HST)
• Regressive System Tract
• Low-accommodation systems Tract
• High-accommodation Systems Tract
• Forced regression
• Normal regression
• Transgression

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Terms to Define Conceptual Models
Models that explain surfaces geometries of
layered sediments in terms of basinal setting,
rates of supply erosion (accumulation),
eustasy, and tectonics

• Depositional sequence model
• Genetic Stratigraphic sequence model
• Transgressive-Regressive sequence model

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Definitions Points to consider

• Definition
• Alternate terms
• Origin of Feature
• Absolute time or Fuzzy time significance if any?

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"What's in a name? That which we call a rose.
By any other name would smell as
sweet.Shakespeare's Romeo and Juliet (II, ii,
1-2)
WHAT, YOU THINK IM AN IDIOT? OF COURSE I WROTE
DOWN WHAT WENT WHERE. OH.. WAIT IS THAT AN
H OR AN I
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Sequence Stratigraphy

• The fundamental key to sequence stratigraphic
  interpretation is the surfaces that subdivide the
  sedimentary section.
• Unfortunately the nomenclature of each of these
  sequence stratigraphic surfaces is constantly
  changing as our understanding of sedimentary
  systems their interpretation improves
• Though changes in nomenclature are well
  intentioned they add to the confusion to a
  scientific methodology that is already overlaid
  with complex multi-syllable terminology
• A surface can be given a name that has been used
  before for a different surface. The innocent,
  not knowing the terminology has been changed, may
  lack understanding of the reason for the change,
  feel that they are going stark raving mad

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Sequence Stratigraphy Conclusions
Subdivision interpretation of sedimentary
record using a framework surfaces seen in
outcrops, well logs, 2-D and 3-D seismic.
Include

• Surfaces of erosion non-deposition (Sequence
  Boundaries, Forced Regression Erosion Surface,
  Regressive Surface of Marine Erosion)
• Flooding (Trangressive Surfaces TS or Max
  Regressive Surface /or maximum flooding
  surfaces mfs Ravinement Surfaces RS-
  transgressive )

This template is used to predict the extent of
sedimentary facies geometry, lithologic
character, grain size, sorting reservoir quality
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Which way now?

• Paul Dimitri Krynines alleged mantra was that
• Stratigraphy is the triumph of terminology over
  common sense
• Our collective hope is to circumvent this cynical
  position propose a more consistent practical
  set of terminology!

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