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Ashton EmbryGeological Survey of Canada
Sequence Stratigraphic Analysis of Mixed, Reefal Carbonate and
Siliciclastic Systems
Outline• Sequence Stratigraphy
• Sequence Surfaces and Sequence Boundaries for Siliciclastics
• Sequence Surfaces and Sequence Boundaries for Carbonates/Reefs
• Sequence Surfaces and Sequence Boundaries for Mixed Reef and Siliciclastic Successions
• Correlating a Reef/Siliciclastic Succession
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How do we use sequence stratigraphy to correlate from a reef to off-reef siliciclastics?
Where is the sequence boundary?
REEF SILICICLASTICS
Importance of Doing Sequence Stratigraphy Properly
Sequence stratigraphy provides an excellent methodology for:
• Correlating a stratigraphic succession.
• Subdividing it into genetic, quasi-chronostratigraphic units for facies analysis and paleogeographic reconstruction.
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SEQUENCE STRATIGRAPHY
Consists of :
• The recognition and correlation of stratigraphic surfaces which represent depositional breaks or changes in depositional trend in the rock record.
SEQUENCE STRATIGRAPHY
• Sequence surfaces are recognized by sedimentological criteria and geometrical relationships between the surface and strata above and below the surface.
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SEQUENCE STRATIGRAPHY
Consists of :
• The description and interpretation of resulting, genetic stratigraphic units bound by those sequence surfaces.
1) For constructing an approximate chronostratigraphic, correlation framework to facilitate facies analysis and related endeavours.
USINGSEQUENCE STRATIGRAPHY
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2) For bounding individual sequence stratigraphic units for mapping and communication purposes.
USINGSEQUENCE STRATIGRAPHY
3) For allowing the sedimentary record to be interpreted in terms of base level changes.
USINGSEQUENCE STRATIGRAPHY
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USINGSEQUENCE STRATIGRAPHY
4) In conjunction with facies analysis, for providing a framework and theoretical basis for interpreting depositional history and paleogeographic evolution.
The Five Material-Based Surfaces of Sequence Stratigraphy
1) Subaerial Unconformity (SU)
2) Shoreline Ravinement (SR)
3) Maximum Regressive Surface (MRS)
4) Maximum Flooding Surface (MFS)
5) Slope Onlap Surface (SOS)
Unconformities (time barriers) or low diachroneity surfaces (approx. time surfaces)
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The Five Material-Based Surfaces of Sequence Stratigraphy
1) Subaerial Unconformity (SU)
2) Shoreline Ravinement (SR)
3) Maximum Regressive Surface (MRS)
4) Maximum Flooding Surface (MFS)
5) Slope Onlap Surface (SOS)
Unconformities (time barriers) or low diachroneity surfaces (approx. time surfaces)
Slope Onlap Surface
An unconformable stratigraphic surface which is developed in marine slope strata and onto which there is demonstrable onlapby marine strata.
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Posamentier and Vail, 1988
SOS forms in siliciclastic successions when the shoreline reaches the shelf edge and
much of the slope becomes starved.
SOS
Posamentier and Vail, 1988
SOS is onlapped by slope deposits during both base level fall and base level rise.
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Seismic from Posamentier, 2003
SR-U
Slope Onlap Surface (SOS) Quaternary Strata, Gulf of Mexico
When the shelf is exposed during base level fall, carbonate sedimentation essentially ceases except for
rock falls and localized carbonate production which onlap the starved slope (SOS).
Grammer et al, 2005
SOS
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MaximumFloodingSurface
Inductive Model for Material-Based
T
MaximumRegressive
Surface
Start Transgression
ShorelineRavinement
Start Regression
SubaerialUnconformity
Base Level Fall
Embry, 1995
Slope Onlap
Surface
Sequence Stratigraphic Surfaces inSiliciclastics
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Early Base Level Fall
End Base Level Fall
Mid Base Level Rise
Early Base Level Fall
Sequence Stratigraphic Surfaces inCarbonates
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SR-U
In most cases, the strata directly overlying an unconformity in carbonate strata are marine in origin. The is indicates that a previously formed subaerial unconformity (SU) was modified during transgression. In such cases, the surface is best referred to as an Unconformable Shoreline Ravinement (SR-U).
Fairholme Gp (Late Devonian), Rocky Mtns, Slope Onlap Surfaces
Whalen et al., 2000
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Sequence Stratigraphic Surfaces Bahamas Bank
Grammer et al, 2005
Sequence Stratigraphic Surfaces Carbonate Platform/Slope/Basin
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Sequence Stratigraphic Surfaces Reefal Carbonate
Sequence Stratigraphic Surfaces Reefal Carbonate
Wheeler Diagram
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Where’s the Sequence Boundary
Next Question
Depositional Sequence
A depositional sequence is a stratigraphic unit bound by subaerial unconformities and their correlative surfaces (Van
Wagoner et al, 1988).
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Depositional Sequence Boundaries (Subaerial unconformities/shoreline ravinements
on the basin flank and correlative surfaces basinward )
SU/SR-UCorrelative SurfacesSU/SR-U
Correlative surfaces are sequence stratigraphic surfaces which join with the end of the SU/SR-U and with each other, so as to form a single,continuous, through going boundary.
Correlative Surfaces
SU/SR-U Correlative Surfaces
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Given that: ` 1) The correlative surfaces must adjoin to the basinward termination of the SU.
2) The Subaerial Unconformity reaches its maximum basinward extent at the end of base level fall (start base level rise).
The correlative surfaces must develop at, or soon after, the start of base level rise to be able to join with the end of the SU/SR-U.
SU/SR-U Correlative Surfaces
The marginal unconformity (SU/SR-U) and the correlative surfaces must adjoin so as to form
one continuous boundary.
Developed well after Rise
Developed at or soon after start Rise
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Due to the requirement that the correlative surfaces portion of the SB develop at and soon after the start of base level rise:
“All sediments deposited during the previous base level fall must
lie below the depositional sequence boundary.”
Depositional Sequence Boundary Placement
Over the past 30 years many workers have put the sediments deposited during base level fall on top of the sequence boundary.
Schlager, 2005
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The Depositional Sequence Boundary must be placed ABOVE the truncated strata which were deposited during base level fall.
SU/SR-U
Revised
Attached Debris
Detached debris
Attached Debris
Detached Debris
Handford and Loucks, 1993
SB
This SB is unacceptable because it places sediments deposited during base level fall (orange) above the SB.
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Sediments Deposited During Base Level Fall (orange) Are Placed Below the SB
Attached Debris
Detached debris
Revised
SU/SR-U
SB
SB
X
Anselmetti et al., 1997
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Sequence Stratigraphic Surfaces Carbonate Platform/Slope/Basin
Depositional Sequence Boundary Placement
Sequence Stratigraphic Surfaces Reefal Carbonate
Depositional Sequence Boundary Placement
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Wheeler Diagram
Depositional Sequence Boundary Placement
Sequence Stratigraphic
Surfaces in Mixed Reefal Carbonates and Siliciclastics
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Sequence Stratigraphic Model Mixed Reefal Carbonates and Siliciclastics
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SR-U
Ladinian Carbonate Platform, Lombardy Basin, ItalyBerra, 2007
SU/SR-U
Berra, 2007
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Berra, 2007
SR-U
Ladinian Carbonate Platform, Lombardy Basin, ItalyBerra, 2007
MRS
MFS
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Kendall, pers.comm., 2008
Depositional Sequence Boundaries in the Brushy Canyon Formation of the Permian Basin are usually placed at the base of deep water sandstone units (red lines) which are interpreted to have been deposited during base level fall.
Permian Basin
Kendall, pers.comm., 2008
Permian Basin
Depositional Sequence Boundaries (red) are best placed near or at the top of sandstone units
Revised
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Depositional Sequence Boundaries (red) are best placed near or at the top of sandstone units rather than at the base of them.
Depositional Sequence Boundaries Were Inappropriately Placed Below the Deep Water Sandstones Deposited During Base Level Fall
Sarg, 1988
Carbonates and Basinal Siliciclastic Turbidites
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The Depositional Sequence Boundary is most reasonably placed on top of the deep water
clastics rather than at the base.
Sarg, 1988
Carbonates and Basinal Siliciclastic Turbidites
Depositional Sequence Boundary Carbonate Platform/Slope and Deep Water Siliciclastics
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SOS
Fairholme Gp (Late Devonian), Rocky Mtns, Slope Onlap Surfaces and Sequence Boundaries
Whalen et al., 2000
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Correlating from Reef to Siliciclasticswith Sequence Stratigraphy
SR-U
MRS
MFS
Correlating from Reef to Siliciclasticswith Sequence Stratigraphy
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Subsurface Correlation from Reef to Siliciclastics with Sequence Stratigraphy
Sequence Stratigraphic Surfaces – Reefal Carbonate and Adjacent Siliciclastics