Geomorphic thresholds and complex response of fluvial systems - some implications for sequence stratigraphy

Journal Article · Thu Jul 01 00:00:00 EDT 1993 · AAPG Bulletin (American Association of Petroleum Geologists); (United States)

OSTI ID:5940556

Wescott, W A ^[1]

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1. Amoco Production Company, Houston, TX (United States)

First-generation sequence stratigraphic models have dealt in a very rudimentary fashion with the response of fluvial systems to eustasy. A major element of presently accepted models is that rivers incise when sea level falls and aggrade during the ensuing rise. Geomorphic principles state that fluvial systems are complex, process-response systems that can adjust to internal and external changes in other ways besides incision and aggradation by modifying their stream patterns and channel geometries. Application of geomorphic principles to sequence stratigraphic models results in the following observations. During eustatic lowstands, rivers may adjust to lowered base levels and changes in slope by modifying channel patterns. Therefore, not all lowstands produce type 1 sequence boundaries. Type 1 sequence boundaries characterized by fluvial-valley incision are more likely to develop when sea level drops below the shelf-slope break, resulting in topological relief near the strandline in which headwardly eroding knickpoints form. Rate of eustatic change is sufficiently low that geomorphic systems can maintain their equilibrium during eustatic changes and migrate back and forth across the shelf without major modifications. Finally, under conditions of relatively static sea level, sequences and parasequences of the same scale in time and space can be deposited as the result of purely intrinsic causes and responses of a fluvial system. In general, eustasy controls the location of deposition and erosion, but the resultant stratal geometry is controlled by sediment supply and processes acting on the sediments as the shoreline moves across the shelf in response to eustasy. Sequence stratigraphy is frequently used in petroleum exploration and basin analysis. However, present models do not adequately in corporate modern principles of fluvial geomorphology and do not accurately predict sedimentary facies and surfaces in some basins. 33 refs., 14 figs., 4 tabs.

• OSTI ID: 5940556
• Journal Information: AAPG Bulletin (American Association of Petroleum Geologists); (United States), Vol. 77:7; ISSN 0149-1423
• Country of Publication: United States
• Language: English

Related Subjects

02 PETROLEUM
03 NATURAL GAS
GEOLOGIC STRATA
SEDIMENTATION
RIVERS
GEOMORPHOLOGY
STRATIGRAPHY
GEOLOGIC MODELS
EXPLORATION
PETROLEUM DEPOSITS
SEA LEVEL
SEDIMENTARY BASINS
GEOLOGIC DEPOSITS
GEOLOGIC STRUCTURES
GEOLOGY
LEVELS
MINERAL RESOURCES
RESOURCES
STREAMS
SURFACE WATERS
020200* - Petroleum- Reserves
Geology
& Exploration
030200 - Natural Gas- Reserves
Geology
& Exploration