--> ABSTRACT: Stratigraphic Signatures Separating Tectonic, Eustatic, and Sedimentologic Effects on Sedimentary Sections, by Peter R. Vail, Felipe Audemard, Pablo N. Eisner, Guillermo A. Perez-Cruz; #91003 (1990).

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ABSTRACT: Stratigraphic Signatures Separating Tectonic, Eustatic, and Sedimentologic Effects on Sedimentary Sections

Peter R. Vail, Felipe Audemard, Pablo N. Eisner, Guillermo A. Perez-Cruz

The depositional patterns of sedimentary rocks are controlled by the complex interaction of tectonics, eustasy, and sediment supply. Tectonic and eustatic effects combine to cause relative changes of sea level that control the space available for sediments (accommodation space). Sediment supply controls how much of the accommodation space, created by the relative changes of sea level, is filled. The signature of each of these variables can be recognized and quantified in the stratigraphic record.
Tectonism has the greatest effect on accommodation. Its imprint on the sedimentary record is divided into three hierarchical groups. Evolution of sedimentary basins is interpreted as a first-order tectonic event. Second-order tectonic events are created by increases in the rate of tectonic subsidence. Major transgressive-regressive facies cycles are their stratigraphic signature. Folds, faults and magmatism make up the third-order tectonic events. Folds and faults tend to enhance or obscure eustatically caused sequences and systems tract boundaries, but do not change their age when dated at their correlative conformities. Third-order tectonic events may trigger stratigraphic marker beds, such as slumps and megaturbidites. Volcanism will produce bentonite marker beds and datable igneous s lls and dikes.

Eustasy controls the rate of relative sea level change and is the major controlling factor on the timing of stratigraphic discontinuities. The discontinuities create the boundaries between sequences and systems tracts. Eustatic effects are divided into two stratigraphic signatures: major continental flooding cycles are depositional sequence cycles. Major continental flooding cycles are believed to be caused by tectonoeustasy (changes in ocean basin volume). Depositional sequence cycles are thought to be caused by glacioeustasy (changes in water volume).

The sedimentologic effect is episodic in nature and local in distribution. The stratigraphic signature is the sedimentary structures related to sedimentary processes, such as storms, tides, and floods.

AAPG Search and Discovery Article #91003©1990 AAPG Annual Convention, San Francisco, California, June 3-6, 1990