Quantitative Analysis of the Bed-Scale Facies Architecture of Submarine Lobe Deposits

Abstract

Submarine lobe deposits form the largest sediment accumulations on Earth and host significant reservoirs for hydrocarbons. While many studies of ancient lobe deposits qualitatively describe lateral architectural variability (e.g., axis-to-fringe, proximal-to-distal), these relationships are rarely quantified. This study pairs traditional field methods and geomodelling workflows to quantify lateral architecture relationships in outcropping lobe deposits.

Submarine lobe strata of the Upper Cretaceous Point Loma Formation form coastal cliff exposures at Cabrillo National Monument near San Diego, California. These fine-grained turbidites are interpreted as distal submarine lobes deposited in a forearc basin setting. The strike-oriented, laterally-extensive exposure offers a rare opportunity to observe bed-scale architecture and facies changes in turbidites and hybrid event beds over 1 km lateral distance. We characterize these deposits using centimeter-scale measured sections, bed and bedset correlations, paleocurrent analysis, and measurements derived from a photogrammetry-based 3D outcrop model. Individual beds show thickness changes of 2 to 20 cm over short lateral distances (25 m), resulting in a 10x variation in thinning rates. Similarity in thinning rates among multiple beds within the same section may more objectively define related packages of beds (i.e., lobe elements). Rapid thickness changes at the bed scale with clear onlap surfaces indicate complex flow behaviors and bed geometries not typical of distal submarine lobes.

In order to enable comparison of key relationships that control the lateral architecture of submarine lobe deposits, we also digitized published bed-scale correlation panels from different outcropping submarine depositional environments. Quantitative comparison of architectural components (e.g. bed thinning ratios, N:G and amalgamation ratios) between these panels and the Point Loma Fm. provide a framework to quantitatively compare facies architecture of submarine lobe deposits to other

AAPG Datapages/Search and Discovery Article #90323 ©2018 AAPG Annual Convention and Exhibition, Salt Lake City, Utah, May 20-23, 2018