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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 surfaces are recognized by sedimentological criteria and geometrical relationships between the surface and strata above and below the surface.

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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.


3) For allowing the sedimentary record to be interpreted in terms of base level changes.


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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


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




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Wheeler Diagram


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

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