Siliciclastic Sequence Stratigraphy

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Siliciclastic Sequence Stratigraphy

• A short course
• John Holbrook
• Department of Earth and Environmental Sciences
• University of Texas at Arlington

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I. Definitions

• A. Sequence Stratigraphy (Non-formal definition)
• The subdivision of sedimentary basin fills into
  genetic packages bounded by unconformities and
  their correlative conformities Emery, 96
• B. Sequence (Non-formal definition)
• A stratigraphic unit composed of a relatively
  conformable succession of genetically related
  strata bounded at its top and base by
  unconformities or their correlative conformities
  Van Wagoner, 88
• C. Sequence Boundary (Non-formal definition)
• A surface separating younger from older strata
  along which there is evidence of subaerial
  erosion and truncation and subaerial exposure and
  along which a significant hiatus is indicated
  Van Wagoner, 88
• 1. Sequences subdivided by a series of lesser
  surfaces

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II. Sequence Stratigraphy in the Context of
Stratigraphy

• What is stratigraphy?
• 1. the study of large-scale vertical and lateral
  relationships between units of sedimentary rock
  that are defined on the basis of lithological or
  physical properties, paleontological
  characteristics, geophysical characteristics,
  geophysical properties, age relationships and
  geographic position and distribution. (i.e., its
  the filing system for the rock record)
• a. Stratigraphy is based on Stenos and Huttons
  laws.
• b. The fact that rocks were originally laid down
  in a fluidized form was noted by medieval and
  renaissance scientists (e.g. Steno, Da Vinci).

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B. Formal vs. Informal Schemes in Stratigraphy
Formal Schemes(as espoused by the ICSN
NACSN)

• Lithostratigraphy
• Allostratigraphy
• Sequence Stratigraphy
• Genetic Sequence stratigraphy
• Depositional sequence stratigraphy

• Biostratigraphy
• Chronostratigraphy
• Cyclostratigraphy
• Magnetostratigraphy
• Pedostratigraphy
• Event Stratigraphy
• Morphostratigraphy

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B. Formal vs. Informal Schemes in Stratigraphy
Informal Schemes

• Lithostratigraphy
• Allostratigraphy
• Sequence Stratigraphy
• Genetic Sequence stratigraphy
• Depositional sequence stratigraphy

• Biostratigraphy
• Chronostratigraphy
• Cyclostratigraphy
• Magnetostratigraphy
• Pedostratigraphy
• Event Stratigraphy
• Morphostratigraphy

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C. Sequence stratigraphy as a subset of
allostratigraphy?
(NACSN, 1981)
(Holbrook, 2001)
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III. The Roots of Sequence Stratigraphy

• A. Modern sequence stratigraphic concepts stem
  from work of Grabau (1906), Blackwelder (1909),
  Barrell (1917), Wheeler (1958) and Sloss (1963).
• B. Holy sea level change
• Noah, the Old Testament,
• and the Koran
• 2. The Renaissance
• Barnet (1681) Scared
• Theory of the Earth
• b. de Maillet (1748) Telliamed
• i. Spawned the Neptunists

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C. Early ideas for mechanisms of sea-level
fluctuation 1. Lyell, 1835 and raised
beaches 2. MacLaren (1842) and glacial
advances and Agassiz (1840) 3. Croll
(1864) and orbital cycles
Quaternary oxygen isotope stages
(Stanley, 2005)
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• D. Early ideas on sea level and stratigraphic
  control
• 1. Hutton 1788 and the concept of the
  unconformity
• Basalt, cross-cutting relationships, and the
  sinking of the Neptunists
• 2. Chamberlain (1898 and 1909) and world-wide
  diastrophic control on stratigraphy
• 3. Suess (1906) and eustasy
• 4. Grabau (1906) and concepts of
• lapping relationships

Grabau (1906)
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Penn. cyclothems
E. Relationship between time and stratigraphy 1.
This figure was driven by early attempts to use
sedimentation rates to calculate the age of the
Earth. F. Wanless and Shepard (1935) and
Pennsylvanian cyclothems
(Barrell, 1917)
(Stanley, 2005)
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G. Sloss, Krumbein and Dapple (1949) the
interregional unconformity, and the Sequence
H. Wheeler (1958) and the Wheeler
diagrams I. Sloss Sequences
from Larry Sloss (1963)
(Stanley, 2005)
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J. The Seismic Revolution in subsurface
stratigraphy
1. Explosion of subsurface data driven by need to
fuel WW1 and WW2. a. Development of Well logs,
Cores and Seismic 2. Seismic data was acquired
for petroleum exploration during latter half of
the 20th C. a. Seismic imaging developed form
technology used in WW2 to locate submarines. 3.
Several advantages a.Provided continuous
subsurface image of sedimentary basin fills. b.
Structure and stratigraphic relationships
observed in areas not previously accessible. c.
Could compare seismic data from around the world.
4. Developed science of seismic
stratigraphy. 5. Scientists at Exxon recognized
the stratigraphic significance of the seismic
tool (Vail et al., 1977). a. New data amenable to
analysis using concepts developed by Wheeler and
others.
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• K. 1977, the research group at Exxon, Peter Vail,
  and AAPG Memoir 26
• 1. The Slug Diagram and the transgressive/regres
  sive and chronostratigraphic framework
• a. Lapping Relationships

(Holbrook, 2006, AGI Data Sheets)
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2. The Vail Curves of absolute sea level
(Van Wagoner, et al., 1990)
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• L. A watershed event SEPM Special Publication 42
  Sea Level Changes an Integrated Approach 1988
• 1. Spelled out detailed mechanisms of sequence
  stratigraphy
• 2. Opened sequence stratigraphy to non-industry
  scrutiny
• a. Attacks on the Vail Curves (e.g., Miall, 1991)
• b. Modified for non-shelf settings, non-seismic
  data sources, and impractical assumptions
• 3. We will start from SEPM SP 42 less the Vail
  Curves

(Van Wagoner, et al., 1990)
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M. What is the Power of the Technique? 1. Higher
resolution for reservoir and seal prediction
Lithostratigraphic vs.
Sequence Stratigraphic
c.o. Janok Bhattacharya
From Van Wagoner et al., 1990
Cretaceous - Book Cliffs, Utah
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2. More effective predictive interpretation of
seismic data
http//strata.geol.sc.edu/
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3. More robust interpretive template

• We suggest that many of these deposits are
  top-eroded deltas formed where rivers delivered
  sediment to lowstand coastlines.

• Key Evidence
• Deltaic Depositional Systems
• lobate to elongate geometry
• radiating paleocurrents,
• basinward dipping internal clinoform beds,
• upward coarsening facies successions.

c.o. Janok Bhattacharya
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IV. Basic Concepts

• Accommodation
• Space available for sediment to accumulate at any
  point in timecontrolled by base level (Jervey,
  1988)
• 1. Marine settings
• 2. Alluvial settings

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B. Allocyclic controls on accommodation that form
Sequences 1. Sea Level 2. Tectonics 3. Climate
Sea Level
Climate
Triassic rift basin cycles?
(Stanley, 2005)
Tectonics
Estimated temperatures from leaf margins
(Stanley, 2005)
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C. Lapping relationships as seen on seismic lines
and recognition of surfaces 1. Coastal onlap
2. Marine onlap 3. Offlap 4.
Downlap 5. Toplap 6. Internal
convergence
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D. The Parasequence 'a relatively conformable
secession of beds or bedsets bound by
marine-flooding surfaces' (Van Wagoner,
1985) 1. A marine flooding surface is sharp
boundary across which an abrupt deepening of
water is recorded by a sudden shift toward more
basinal facies 2. Parasequences and
progradation
Parasequences
(Posamentier and Allen, 1999)
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3. Parasequences in outcrop, well log, and core
(Van Wagoner, et al., 1990)
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4. Parasequence sets 1. Progradational
sets 2. Retrogradational sets 3.
Aggradational sets
(Van Wagoner, et al., 1990)
4. Parasequences in well logs
(Van Wagoner, et al., 1990)
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V. Systems Tracts 'a linkage of contemporaneous
depositional systems' Van Wagoner (1985) A. Some
initial comments 1. Defined objectively on the
basis of reflector/surface/parasequence set
configuration and position in a sequence 2.
Originally defined for the continental shelf a.
Shelf-margin assumptions i. Tectonics, basin
physiography, and sediment supply
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• B. The four original systems tracts
• Lowstand
• a. Wedge
• b. Fan
• c. Valley Fill

(Van Wagoner, et al., 1990)
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2. Transgressive
(Van Wagoner, et al., 1990)
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3. Highstand
(Van Wagoner, et al., 1990)
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4. Lowstand (return)
(Van Wagoner, et al., 1990)
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Missing In Action?
Type 2 Sequence Boundary?
Shelf-Margin Wedge?
5. Shelf-Margin Wedge a. Type 1 vs. Type 2
unconformity b. Use
(AGI Data Sheets, Holbrook)
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C. Variations from the basic shelf model to
ramp settings 1. Generalizations a. Ramp has
no shelf/slope brake b. Ramp slopes and
variable subsidence i. Minor changes may have
big results
Ramp-type Basins
(Van Wagoner, et al., 1990)
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2. Variations in systems tracts in ramp
sequences a. Lowstand i. Incised valley
fills ii. The lowstand wedge iii. The
lowstand fan b. Transgressive systems tract i.
Often muted -Slopes, sediment supply, and
subsidence -The transgressive surface of
erosion and the condensed section c. Highstand
deposition i. Sea level, downstepping, and
distinguishing the systems tract
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Normal Regression

• 3. Falling-stage systems tract
• Normal regression when regression occurs during
  increased or stable accommodation and is driven
  by sediment supply
• b. Forced regression - when relative sea level
  fall causes a regression as the only option
  generally resulting in downstepping of the
  shoreface system

Forced Regression
(Posamentier and Allen, 1999)
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c. Falling-stage systems tract of Nummedal et
al. 1993
Lowstand Falling Stage
(Posamentier and Allen, 1999)
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4. Some other generalizations a. Systems tracks
and boundaries tend to be more widespread b.
Individual units commonly thin i. Seismic is
often useless c. Outcrop and well-log data are
commonly plentiful
(Van Wagoner, et al., 1990)
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VI. Differing Approaches to Identification of a
Sequence A. The Six Surfaces of Embry
(Embry, 2002)
(Holbrook, AGI data sheets)
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B. Traditional approaches 1.The Posamentier, et
al., 1992 view (Type 1 of Embry) a. Early vs.
late lowstand systems tracts and placement of the
sequence boundary b. -Pros and cons
2. The Hunt and Tucker 1992 view (Type 2 of
Embry) a. Falling stage vs. lowstand systems
tract and the placement of the sequence
boundary b. Pros and cons
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3. Transgressive-Regressive Sequence Stratigraphy
(Embry, 2002) 4. Genetic Sequence
Stratigraphy (Galloway,1988)
(Embry, 2002)
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VII. Recognition of Systems Tracts and
Application of Sequence Stratigraphy a Summary
of the Tools A. Characteristics used for
distinguishing systems tracts 1. Internal facies
(Facies present Facies arrangement) 2.
Geometry 1. Surface configurations 2.
Parasequence sets 3. General shape 3.
Boundaries 1.Lapping relationships 2. Facies
contrasts 3. Surface characteristics (Morphology
sediment contrasts)
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B. Primary tools for recognizing
characteristics 1. Outcrop description 2.
Well-log correlations 3. Seismic
lines C. Which tools are best?
SB
SB
SB
SB
Shoreface
SB
Fluvial
Shelf
RSE
SB
Pennsylvanian, New Mexico
(Posimentier and Allen, 1999)
Florida Aquifer, Kisseme
TSE
Incised Valley
SB
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C. Warning Signs on the Road Ahead 1. Descriptive
Genetic? 2. Sequence Vs Seismic
stratigraphy
(Posimentier and Allen, 1999)
Van Wagoner et al. (1988)
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VIII. Interpretation of Sequences from Seismic
data A. What is seismic reflection data and how
is it processed? 1. Terms sources, impedance,
geophones, stacking, Fourier analysis, frequency
filtering, moveout correction, Snell's law
(Sin01/Sin02 V2/V1), reflectors, two-way travel
time
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2. Resolution (Individual beds can be resolved
down to about 1/4 wavelength In general, beds as
thin as about 1m down to about 75m beds only as
thin as about 15m thick at a kilometer or two)
Seismic Trace
GPR Trace
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3. General factors to consider when interpreting
time sections a. Fast beds will appear thinner
than they actually are and vise versa b.
Velocity generally increases with depth c.
Dipping beds will always appear to have shallower
dips than they actually do (migration)
(Tearpock and Bischke, 1991)
(Tearpock and Bischke, 1991)
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d. Steeply dipping surfaces may be more prone to
migration errors or may not show up at all e.
Multiples f. Point-source diffractions
g. There is room for some interpretation
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B. Sequence-stratigraphic interpretation of
seismic lines 1. Mostly already covered a.
The slug diagram idealized case b.. The
importance of lapping relationships and
arrangement of surfaces
(Posamentier and Allen, 1999)
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(Posamentier and Allen, 1999)

• 2. Some realities of interpretation
• a. Transgressive systems tract is commonly thin
  and hard to spot
• i. Healing phase expression
• ii. Highstands may appear dominant

(Posamentier and Allen, 1999)
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b. Lowstand fans generally only visible where
large drop-off occurs
(Posamentier and Allen, 1999)
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c. Lapping relationships may not be apparent
where i. Section is dominated by non-prograding
systems ii. Progradation angle is
low -Improvement by vertical exaggeration
iii. Trace is lateral along strike to
main prograding body
(Posamentier and Allen, 1999)
(Tearpock and Bischke, 1991)
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d. Sequences may be hierarchical and thus complex
(Posamentier and Allen, 1999)
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e. Use well data if you have it f. Plainview
of reflectors is a help (3-D seismic)
(Weimer, et al., 1998)
(Posamentier and Allen, 1999)
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Cape May Seismic Line Sequence Stratigraphic Inte
rpretation
Line Location