Lateral variability and depositional trends in the siliceous mudstone lithofacies, Monterey/Modelo turbidite system, eastern Ventura basin, California
Abstract
The lateral transition between deepwater clastics and fine-grained siliceous mudstone in the Modelo Formation type area, known as the Piru submarine fan, in the eastern Ventura basin, has been poorly studied. The Modelo Formation is correlative with the Monterey Formation, whose siliceous lithofacies have been more extensively studied, and is the principal hydrocarbon source, and an important petroleum reservoir, in California. This sedimentologic study will identify, characterize and quantify facies abundance and relationships with lateral position from sandstone into the siliceous mudstones of the Modelo Formation. While both the sandstone and the fine-grained siliceous (originally diatomaceous) lithofacies have been individually well studied at different locations, the transition between them has not. Based on pilot work in Malibu Beach and the eastern Santa Monica Mountains, we suspect that a number of distinct gravity flow, tractive flow and suspension settling depositional processes interact in the transition zone, some being unique to diatomaceous sediment (e.g., “speckled beds”). The nature of the sandstone-siliceous mudstone/porcelanite transition holds potentially important implications for the zone’s ability to seal charged sandstone reservoirs or to provide a mixed/hybrid reservoir system. The Tarzana submarine fan system extends into the Los Angeles basin and has similarities with the Stevens Sand system in the San Joaquin basin, and therefore may provide insight beyond the Eastern Ventura Basin. Besides its applied economic significance, this study will also contribute to a fundamental scientific understanding of deep marine siliceous coarse-grained and siliceous mudstone sedimentology in a tectonically active depositional basin. Data obtained from field methods will include: detailed outcrop based studies including mapping and a lateral series of quantitative stratigraphic analyses, petrophysical logging by handheld spectral gamma ray, and analysis of sedimentary bedding, structure and paleocurrent. Lab methods to identify silica phases and mineralogically characterize the silica:detritus ratios in siliceous mudstones will include X-ray diffraction, Scanning Electron Microscopy, Total Organic Carbon, and hand sample and thin section analysis.
AAPG Datapages/Search and Discovery Article #90372 © 2020 AAPG Pacific Section Convention, 2020 Vision: Producing the Future, Mandalay Beach, Oxnard, CA, April 4-8, 2020 (Cancelled)