Transcript Document

Sequence Stratigraphy
Template for “Conceptual Models”
Used to Interpret
Depositional Systems
- beauty but not truth? Christopher G. St. C. Kendall
University of South Carolina
[email protected]
803 978 7523
Sequence Stratigraphy Defined
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

Sequence Stratigraphy Defined
Sequence Stratigraphy
A framework of genetically related
stratigraphic facies geometries and
their bounding surfaces used to
determine depositional setting
Sequence Stratigraphy Defined
Sequence Stratigraphy –
Terminology
Stratigraphers have a
position on terminology
similar to the of Humpty
Dumpty's from Lewis
Carroll’s Through the
Looking Glass

"When I use a word, it
means just what I
choose it to mean nothing more nor less".
Sequence Stratigraphy Defined
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
Sequence Stratigraphy Defined
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).
Sequence Stratigraphy Defined
'Depositional' sequence Vail et al 1971
Sequence Stratigraphy Defined
SB
mfs
TS
Establish a framework of genetically
related stratigraphic facies geometries
and their bounding surfaces to
determine depositional setting
Sequence Stratigraphy Defined
Coast
Types
Sequence Stratigraphy Defined
Sedimentary Analysis
Potential flow of
interpretation
data
data
Scheme used
to characterize
depositional systems
so they can be
compared
interpretation
interpretation
interpretation
Sequence Stratigraphy Defined
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
Sequence Stratigraphy Defined
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
Sequence Stratigraphy Defined
Fluvial - Architectural Elements
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Deepwater - Architectural Elements
Sequence Stratigraphy Defined
Deepwater - Architectural Elements
Sequence Stratigraphy Defined
Deepwater - Architectural Elements
Sequence Stratigraphy Defined
Hierarchy of Carbonate Shelf
Architectural Elements
PROGRADING MARGIN
PROGRADING MARGIN
ONLAPPING MARGIN
PROGRADING MARGIN
BED,
LITHOLOGY,
SEDIMENTARY
STRUCTURES
FAUNADefined
Sequence Stratigraphy
STACKED
BED
CYCLES
SHELF
COMPLEX
MARGIN
COMPLEX
ALLOCHEMS
CEMENTATION
& DIAGENESIS
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

Application
Provide the detailed character of a sequence and/or system tract
Net to-gross, aspect ratio, & connectivity
Lithofacies type & aquifer/reservoir quality
Better defined depositional geometries and so depositional models
More accurate aquifer/resource assessment
Optimize strategy for depletion of aquifer/resource
Sequence Stratigraphy Defined
History of Sequence Stratigraphy
Sloss recognized intercontinental-unconformities & related
them to eustasy
 Vail extrapolated eustatic signals to seismic sequence
boundaries
 Jervey’s 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

Sequence Stratigraphy Defined
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
Sequence Stratigraphy Defined
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?
Sequence Stratigraphy Defined
Sequence Stratigraphy’s 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
Sequence Stratigraphy Defined
Sequence stratigraphic analysis
Fundamental to sequence stratigraphic analysis:

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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
Sequence Stratigraphy Defined
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)
Sequence Stratigraphy Defined
Stacking Patterns - Unconfined
After Van Wagoner
Sequence Stratigraphy Defined
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
Sequence Stratigraphy Defined
Confined Sedimentary Fill - Channels
Sequence Stratigraphy Defined
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
Sequence Stratigraphy Defined
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

Sequence Stratigraphy Defined
System Tracts - Reviewed
Sequence Stratigraphy Defined
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

Sequence Stratigraphy Defined
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
Sequence Stratigraphy Defined
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).
Sequence Stratigraphy Defined
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
Sequence Stratigraphy Defined
'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
Sequence Stratigraphy Defined
'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
Sequence Stratigraphy Defined
'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'
Sequence Stratigraphy Defined
Boundaries & Conceptual Models
After Catuneanu, 2007
Sequence Stratigraphy Defined
Sequence
Stratigraphy
Model
Tree
After Catuneanu, 2002
Sequence Stratigraphy Defined
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
Sequence Stratigraphy
Defined
surface from basin margin
to depocenter
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

Sequence Stratigraphy Defined
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

Sequence Stratigraphy Defined
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
Sequence Stratigraphy Defined
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 Posamentier’s 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

Sequence Stratigraphy Defined
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









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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
Sequence Stratigraphy Defined
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
Sequence Stratigraphy Defined
Definitions – Points to consider
Definition
 Alternate terms
 Origin of Feature
 Absolute time or Fuzzy time significance if any?

Sequence Stratigraphy Defined
"What's in a name?
That which we call a
rose. By any other
name would smell as
sweet.“
WHAT, YOU THINK
I’M AN IDIOT?
OF COURSE I
WROTE DOWN
WHAT WENT
WHERE.
OH….. WAIT…… IS
THAT AN “H” OR AN
“I”
Shakespeare's Romeo
and Juliet (II, ii, 1-2)
Sequence Stratigraphy Defined
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
Sequence Stratigraphy Defined
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 &Sequence
reservoir
Stratigraphyquality
Defined
Which way now?
Paul Dimitri Krynine’s 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!
Sequence Stratigraphy Defined
Sequence Stratigraphy Defined