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ABSTRACT: Relationships of Depositional Sequence Stratigraphy and Facies in a Deep-Sea Clastic System, Great Valley Sequence, Northern California

Robert K. Suchecki, Rosemary C. Paramore

Lineations interpreted from aerial photographs and field analysis reveal stratal geometries of deep-sea clastic deposits along the Jurrasic-Cretaceous basin margin of the Great Valley, northern California. These stratal patterns of principal stratigraphic sequences in steeply dipping Tithonian to Valanginian sediments in combination with lithic facies, biostratigraphy, and interpretation of sedimentation processes illustrate the depositional sequence stratigraphy that resulted from eustatic and tectonic variations.

Consistently repetitious sequences, which were deposited seaward of the ancient shelf edge, contain the following components. (1) Basal, sharply prograding to mounded conglomerate-sand-shale accumulations that have local bidirectional downlap of internal strata. These accumulations, up to 250 m thick and 3 km lateral extent in outcrop, are interpreted as basin-floor deposits that formed principally from massive failure and slumping of the penecontemporaneous shelf and upper slope. (2) Clinoformal wedges of sandstone and lesser mudstone that contain prominent internal downlapping and toplapping strata. Locally, at the top of these wedges are stratal geometries and sandstone deposits that are interpreted as nested channel-lobe systems. This stratigraphic component is up to 1.1 km thick nd has lateral extent to 15 km. (3) Multiple prograding, clinoformal wedges with complex downlapping and toplapping internal strata. These are composed dominantly of mudstone and thin-bedded sandstone turbidite successions and have up to 2 km cumulative thickness in a single principal sequence. Stratal lineations and facies mimic inferred slope channel-levee complexes in other ancient systems.

The component geometries and internal stratal patterns of the sequences are similar in detail to seismically defined stratigraphic sequences of Vail and illustrate deep-sea clastic stratigraphic and facies relationships based on a depositional sequence stratigraphic framework.

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