Abstract: Syndepositional Tectonic Control of Turbidite Sedimentation Patterns

PATTERSON, JOSEPH E, and KENNETH D. WOLCOTT

Reservoir characterization of the Webster Formation (Upper Miocene Antelope Shale/Monterey equivalent) at Mobil's MOCO Lease, in the Midway-Sunset Field, suggests syndepositional tectonic movement of the "35 Anticline", a northwest-southeast trending intraslope basin/anticline developing subparallel to the San Andreas Fault, directly influenced the deposition of these turbidite deposits. The lower Webster Main turbidites represent more distal, laterally continuous depositional lobes which gradually filled, onlapped and overlapped the intraslope basin upslope of the anticline. The subsequent change in depositional slope resulted in a gradual transition from a depositional lobe facies to channel fill deposits representing sedimentary bypass of the infilled basin/anticline system. Syndepositional tectonic movement, both compressional and extensional (parallel to the axis of the anticline) is evidenced by formation dips increasing with depth in the syncline and an asymmetric transverse breach in the crest of the anticline which controlled the position of the depositional axis of the Webster Intermediate channel fill facies. Extensional faulting of the anticline resulted in the development of a half graben dipping to southeast and is illustrated by a gradual shift in the depositional axis of the channel deposits which migrated southeastward and climbed stratigraphically through time.

Detailed stratigraphic correlations both across the anticline and in the subsequently upended (60 degree dips) and erosionally truncated upslope deposits were necessary to initiate and manage the continuous injection steamflood. Pattern configuration was particularly important in the "steep dip" area to ensure proper continuous injection response which resulted in a production increase of 3000 BOPD.

Search and Discovery Article #90945©1997 AAPG Pacific Section Meeting, Bakersfield, California