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A Skeptic’s Conclusion:

The Model-based Clastic Sequence Stratigraphic Paradigm Was and Is Fatally Flawed.*

By

William E. Galloway1

 

Search and Discovery Article #70020 (2006)

Posted August 4, 2006

 

*Oral presentation at AAPG-SEPM Annual Convention, Houston, Texas, April 9-12, 2006. SEPM Forum: High-Resolution sequence stratigraphy: Is the Model Breaking Apart 

Click to view presentation in PDF format. 

 

1University of Texas, Austin, Texas ([email protected])

 

Limitations of a Model-Based Sequence Paradigm 

  • A “sequence boundary” is a conceptual surface that is a composite of multiple physical stratigraphic surfaces.

  • The composite fluvial incision surface is demonstrably not a single, regionally isochronous boundary.

  • Basin Previous HitpaleogeographyNext Hit is a 3D mosaic of sediment dispersal systems that cannot be captured by 2D models.

  •   Corollary: Clastic sediment supply rate and texture are not uniquely predictable by base level change history.

  • The sequence model and terminology inadequately reflects the diversity of slope and basin facies.

 

 

 

uLimitations

uFigure captions

uTypes of surfaces

uPhysical surfaces

uGeometric surfaces

uConceptual surfaces

uPliocene deposode

uGood bits

uReference

uNote

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

uLimitations

uFigure captions

uTypes of surfaces

uPhysical surfaces

uGeometric surfaces

uConceptual surfaces

uPliocene deposode

uGood bits

uReference

uNote

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

uLimitations

uFigure captions

uTypes of surfaces

uPhysical surfaces

uGeometric surfaces

uConceptual surfaces

uPliocene deposode

uGood bits

uReference

uNote

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

uLimitations

uFigure captions

uTypes of surfaces

uPhysical surfaces

uGeometric surfaces

uConceptual surfaces

uPliocene deposode

uGood bits

uReference

uNote

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

uLimitations

uFigure captions

uTypes of surfaces

uPhysical surfaces

uGeometric surfaces

uConceptual surfaces

uPliocene deposode

uGood bits

uReference

uNote

 

 

 

 

 

Figures

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Three Types of Stratigraphic Surfaces 

Physical Surfaces 

  • Physical manifestation in the stratigraphic record--you can put your hammer on it.

  • Record physical processes and environment.

  • Reproducible by competent geoscientists.

 

Geometric Surfaces 

  • Defined by angular relationship between beds or reflections.

  • Record progressive deposition along erosional or non-depositional discontinuity

 

Conceptual Surfaces 

  • Ideals created in the minds of geoscientists to organize stratigraphy.

  • Have no objective reality; nature does not create them.

  • Operator, objective, database, and paradigm dependent.

 

Physical Stratigraphic Surfaces 

Fluvial entrenchment surface

  • Valley cut

  • Fluvial planation

  • Interfluve exposure

 

Regressive ravinement surface

  • Wave-cut ravinement

  • Tidal ravinement

 

Transgressive ravinement surface

  • Wave-cut ravinement

  • Tidal ravinement

 

Shelf/slope starvation surface

  • Condensed section

 

Shelf erosion (“deflation”) surface

  • Mud bypass

  • Marine current scour

  • Tidal scour

 

Slope entrenchment surface

  • Submarine canyon cut

  • Mass-wasting surface

  • Contour current scour

 

Geometric Surfaces 

Downlap surface 

Onlap surface 

Toplap surface

 

Etc.

 

Conceptual stratigraphic surfaces

(see Figure 1) 

Correlative conformity

 

Maximum flooding surface

  • = non-marine correlative conformity + transgressive ravinement surface + shelf starvation surface ± shelf erosion surface ± slope entrenchment surface + basinal condensed section

 

Sequence boundary

  • = fluvial entrenchment surface ± regressive ravinement surface ± slope entrenchment surface + marine correlative conformity + maximum regressive surface, etc.

 

Pliocene Globoquadrina altispira Deposode

(Figure 2) 

WRLU System

  1. Mixed-load fluvial system

  2. Wave-dominated delta

  3. Salt-convolved retrogradational slope apron

  4. Abyssal plain fan

 

Mississippi/Red River System

  1. Mixed-load fluvial system

  2. Fluvial-dominated delta

  3. Salt-convolved progradational delta-fed apron

  4. Sandy abyssal plain

 

Features Associated with Deepwater Megaslide

  1. Coastal stream plain

  2. Wave-dominated shore zone

  3. Muddy shelf

  4. Megaslideàshelf-fed apron

  5. Mass transport complexàmuddy abyssal plain

 

The Good Bits 

  • Recognition and integration of physical surfaces

  • Parasequences and their stacking patterns

  • Recognition/interpretation of stratal architecture

 

Reference 

Otvos, E.G., 2005, Chronology of Gulf coastal plain and valley terrace aggradation during Pleistocene lowstands. Limitations of base level control: Quaternary International, v. 135, p. 91-113.

 

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Note: concerning SEPM Forum: SEPM Forum: High-Resolution sequence stratigraphy: Is the Model Breaking Apart? 

The objective of this forum was to have an open debate about the controversies associated with sequence stratigraphic interpretation in high resolution data sets. Several researchers are puzzled with questions arising from interpretation in high resolution surveys. What is the relationship between sea level and systems tracts during the last glacial cycle? Are the sequence stratigraphic surfaces in fact time transgressive? What surfaces are more likely to be synchronous? What are the implications for reservoir correlation and Previous HitmappingTop?  This research forum addresses these and other questions. Vitor Abreu (SEPM Research Councilor) moderated this forum, and seven invited guests from industry and academia led the discussion with different approaches and points of view. This allowed for different opinions to be expressed and defended on a scientific basis, and we hope shed a light on this controversial subject.

 

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