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ABSTRACT: Sequence Stratigraphy of the Monterey Formation, Santa Barbara County: Integration of Physical, Chemical, and Biofacies Data from Outcrop and Subsurface

K. M. Bohacs

Deep basinal rocks of the Monterey Formation can be allocated to different depositional environments based on an integration of bedding, facies stacking patterns, lithology, biofacies, and inorganic and organic chemistry. These rocks show evidence of systematic changes in depositional environments that can be related to eustatic sea level changes and basin evolution. Even deep-basinal environments are affected by changing sea level through changes in circulation patterns and intensities, nutrient budgets and dispersal patterns, and location and intensity of the oceanic oxygen minimum.

The sequence-stratigraphic framework was constructed based on the physical expression of the outcrop strata and confirmed by typing the outcrop sections to an integrated well-log/seismic grid through outcrop gamma-ray-spectral profiles. Interpretation of a sequence boundary was based on increased proportions of hemipelagic facies, evidence of increased bottom-energy levels above the boundary, and local erosion and relief on the surface. The proportion of shallower water and reworked dinoflagellates increased to a local maximum above the boundary. Downlap surfaces exhibited increased proportions of pelagic facies around the surface, evidence of decreased bottom-energy levels and terrigenous sedimentation rates, and little or no significant erosion on the surface. The proportion of deep r water dinoflagellates increased to a local maximum at or near the downlap surface; there was no evidence of reworked individuals.

The detailed sequence-stratigraphic framework makes it possible to tie rock properties to genetic processes for construction of predictive models.

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