Title: Sequence Stratigraphy
1Sequence 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
2Why 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
3Sequence Stratigraphy
A framework of genetically related stratigraphic
facies geometries and their bounding surfaces
used to determine depositional setting
4Sequence 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".
5Talk 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
6Sequence 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).
7 'Depositional' sequence Vail et al 1971
8SB
mfs
TS
Establish a framework of genetically related
stratigraphic facies geometries and their
bounding surfaces to determine depositional
setting
9Barrier Coastal Elements
10Sedimentary Analysis
Potential flow of interpretation Scheme
used to characterize depositional systems so they
can be compared
data
data
interpretation
interpretation
interpretation
11Power 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
12Building 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
13Fluvial - Architectural Elements
14Deepwater - Architectural Elements
15Deepwater - Architectural Elements
16Deepwater - Architectural Elements
17Hierarchy of Carbonate Shelf Architectural
Elements
PROGRADING MARGIN
ONLAPPING MARGIN
PROGRADING MARGIN
PROGRADING MARGIN
18Elements 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
19History 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
20Sloss Unconformities Eustasy
After Lowell Thwaite
21 1st Seismic Sequence Interpretation
Vail et al, 1976
Mesozoic through Tertiary of Offshore Morocco
22 'Depositional' sequence Vail
Jervey Posmentier Van Wagoner
23Sequence 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?
24Sequence 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
25Sequence 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
26Unconfined 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)
27Stacking Patterns - Unconfined
After Van Wagoner
28Confined 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
29Confined Sedimentary Fill - Channels
30Stacking 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
31Stacking, 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
32 System Tracts - Reviewed
33System 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
34Surfaces, 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
35Bounding 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).
36Conceptual 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
37'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
38 '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
39'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'
40Boundaries Conceptual Models
After Catuneanu, 2007
41SequenceStratigraphyModelTree
After Catuneanu, 2002
42Application 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
43Caveats
- 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
44Why 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
45Terms 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
46Terms 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
47Terms 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
48Terms 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
49Definitions Points to consider
- Definition
- Alternate terms
- Origin of Feature
- Absolute time or Fuzzy time significance if any?
50 "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
51Sequence 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
52Sequence 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
53Which 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!
54