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Quantifying the Bed-scale Architecture of Submarine Lobe Deposits, Point Loma Formation, California


Submarine lobe deposits form the largest sediment accumulations on Earth and host significant reservoirs for hydrocarbons. While many studies of modern and ancient lobe deposits describe facies changes (e.g., axis-to-fringe, proximal-to-distal), these facies relationships are rarely quantified. This study pairs traditional field methods and newly developed 3D geomodelling workflows to quantify lateral and vertical facies relationships in outcropping lobe deposits. Submarine lobe strata of the Upper Cretaceous Point Loma Formation crop out in coastal cliff exposures near San Diego, CA. These lobe deposits are part of a coarse-grained system, locally-sourced features deposited in a forearc basin setting, likely with a steep slope gradient. Laterally extensive cliff exposures near the Cabrillo National Monument offer a rare opportunity to observe bed-scale architecture and facies changes within the distal portion of these lobe deposits. We characterize these lobe deposits using centimeter-scale measured sections, bed and bedset correlations, paleocurrent analysis, and measurements derived from a drone photogrammetry-based 3D model. These datasets are assembled into a geospatial framework that enables recognition of key parameters that control the lateral and vertical facies architecture. This analysis of the Point Loma Formation is merged with published bed-scale correlation panels from other outcropping lobe deposits. This combined dataset enables comparison of facies parameters and relationships that summarize submarine lobe architecture within and between systems. These quantified facies trends also provide input data for fine-scale reservoir models of submarine lobe deposits.