--> Abstract: Relating Depositional Facies to Seismic-Scale Stratal Geometries, Upper Jurassic Great Valley Sequence, Northern Sacramento Valley, California, by K. T. Lyons; #90987 (1993).

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LYONS, KEVIN T., The University of Texas at Austin, Austin, TX

ABSTRACT: Relating Depositional Facies to Seismic-Scale Stratal Geometries, Upper Jurassic Great Valley Sequence, Northern Sacramento Valley, California

Detailed lithologic mapping, combined with aerial photo interpretation, has been used to relate depositional facies to large-scale stratal geometries in the Upper Jurassic Great Valley Sequence of the northern Sacramento Valley, California. This turbidite complex is characterized by thick intervals of fine-grained deposits which have an internal offlapping stratal pattern, separated by coarse-grained channelized units with no systematic internal stratal pattern.

The most common lithofacies within the fine-grained deposits consists of unconfined low-density turbidity flows and possible slurry-deposit mudstones. Stratal lineations interpreted from aerial photos show very low-angle downlap within these packages which are up to 400 meters thick. Associated debris flows up to 35 meters thick and common slump deposits suggest deposition in a slope setting. Stratification types and paleocurrents within isolated sandstone-filled channels and flanking mudstones indicate the probable presence of channel-levee systems.

Channelized units consisting of the deposits of high-density turbidity flows are of two general types: (1) broad complexes up to 150 meters thick with 15 kilometer lateral extent in outcrop, consisting of amalgamated sand and gravel filled channels showing abundant internal scouring, and (2) single, isolated, conglomerate-filled channels up to 1 kilometer wide and 75 meters thick which show an internal offlapping pattern of fill when viewed parallel to sediment transport direction.

Comparison of multi-channel seismic data from the nearby subsurface Great Valley Sequence and modeled two-dimensional seismic sections based on outcrops (at similar wavelet frequencies) illustrate pitfalls of conventional stratigraphic interpretation. Major depositional features such as channels are imaged with adequate resolution to provide confident interpretation. Other depositional and stratigraphic features such as lobes and channel-levee elements are only poorly imaged at the scale of this analysis.

AAPG Search and Discovery Article #90987©1993 AAPG Annual Convention, New Orleans, Louisiana, April 25-28, 1993.