Chemostratigraphy of Hemipelagic Facies of the Monterey Formation and Equivalent Sedimentary Rocks, Los Angeles Basin, California

Lanners, Rebecca; Behl, Richard J.; and Herzig, Charles
[email protected]

We are constructing a mineralogical and geochemical stratigraphy of the fine-grained, Monterey-equivalent facies in the subsurface of the Los Angeles basin. Although the petroliferous Los Angeles basin has been extensively explored and characterized for more than 100 years, the principal focus has been on coarse-grained reservoir rocks. It is unknown whether the basin contains the same 3-part calcareous-phosphatic-siliceous hemipelagic stratigraphy of the Monterey that is recognized in better-studied central California basins that accumulated in response to major shifts in tectonic, oceanographic and climatic conditions. In the inboard Los Angeles basin, the Monterey Formation and its stratigraphic equivalents – the Modelo, Puente, and Topanga formations – contain much higher detrital content than distal “outboard” locations such as the Santa Barbara and Santa Maria basins. This necessitates careful hand-picking and ultrasonic cleaning of fine-grained lithologies from well cuttings to study the hemipelagic succession in the subsurface. We are studying four wells in the East and West Beverly Hills, Inglewood, and offshore Wilmington oil fields that form a north-south transect across the western Los Angeles basin. Approximately 100 samples are analyzed for bulk chemical composition by X-ray fluorescence (XRF) and quantitative mineralogy by X-ray diffraction (XRD). The wells show large lateral variability in detrital content that could be explained by evolution and migration of submarine fan distribution systems, however there are striking similarities of siliceous, organic-rich, and phosphatic fine-grained sediments between the oil fields and with other basins. Preliminary data from the northern basin reveal a detrital-rich upper section and calcareous- and phosphatic-rich lower sections, similar to the stratigraphic successions present in other basins. Chemostratigraphic and mineralogic data will be used to characterize the Monterey and equivalent stratigraphic successions in the Los Angeles basin, determine the degree of lateral similarity across the basin, identify unique marker horizons, and attempt intra- and interbasinal correlation.

AAPG Search and Discovery Article #90162©2013 Pacific Section AAPG, SPE and SEPM Joint Technical Conference, Monterey, California, April 19-25, 2013