Pacific Section AAPG, SPE and SEPM Joint Technical Conference

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Chemostratigraphy Of Hemipelagic Facies Of The Monterey Formation And Equivalent Sedimentary Rocks, Los Angeles Basin, California


The submarine-fan-dominated, proximal Los Angeles basin contains interstratified hemipelagic strata coeval with the widespread Miocene Monterey Formation that accumulated in other California margin basins. Although more detrital-rich and containing greater abundance of plagioclase and muscovite than more distal, outboard basins, a four-part compositional zonation is recognized in the fine-grained facies, similar to the stratigraphic succession of the Santa Barbara coastal area. In ascending stratigraphic order, these include a basal interbedded calcareous-siliceous zone, a phosphatic zone, a calcareous-siliceous zone, and an uppermost siliceous zone. To establish these zonations, 125 samples from five wells in a north-south transect across the western basin from East and West Beverly Hills, Inglewood, and Wilmington oil fields were analyzed for bulk chemical composition by XRF and quantitative mineralogy by XRD and FTIR. The mineralogic composition of the fine-grained detrital fraction makes use of geochemical equations for sedimentary components developed elsewhere unsuitable to the Los Angeles basin.