--> ABSTRACT: Seismic-Scale Outcrops of Oblique Clinoforms, Topatopa Mountains, Southern California, by Michael S. Clark, Ward Abbott; #91003 (1990).

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ABSTRACT: Seismic-Scale Outcrops of Oblique Clinoforms, Topatopa Mountains, Southern California

Michael S. Clark, Ward Abbott

The Devil's Heart region of the Topatopa Mountains offers an unusual opportunity to describe, measure, and interpret reservoir-scale facies distributions with respect to seismic-scale stratal geometries. Seismic-scale outcrops of middle Eocene siliciclastic, progradational deltas show stratal geometries and facies distributions parallel and perpendicular to paleoshoreline. Landward-stepping, shoaling-upward cycles with parallel-concordant geometries are overlain by oblique clinoforms. The clinoforms are truncated by toplap against a sequence-bounding disconformity that represents a surface of sediment bypass and erosion, The sequence boundary, in turn, is overlain by a second set of landward-stepping, shoaling-upward cycles with parallel-concordant geometries. Thus, the d ltas prograded episodically across a marine basin and filled the basin nearly to sea level. A deepening event ended progradation and marked a return to aggradational processes.

Stratal geometries, facies distributions, and petrophysical properties were used to generate a synthetic seismic profile on which sedimentary facies and depositional environments were superimposed. This synthetic profile was then restored to a depth of 13000 ft (2.0-2.1 sec) and used as a model to interpret the distributions of facies and depositional environments for actual seismic data from other areas. The model shows continuous reflections from basin facies to the delta top. This contrasts with observations of the outcrop that show discontinuity of strata at the upper sequence boundary. By superimposing the facies on the synthetic seismic line, it is possible to show that delta-front turbidites and slumped strata comprising the clinoform bottomsets and foresets are not connected t wave-dominated river and/or delta mouth bars comprising the topset strata. This underscores the importance of having the outcrop model to correctly interpret the seismic.

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