AAPG Foundation 2019 Grants-in-Aid Projects

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Comparison of active margin basin-floor fan architecture: Are basin floor fans dominated by sheets and lobes?

Abstract

A drone dataset from the Juncal Formation basin floor fans in California suggests a large degree of channelization, and significant deposition from Froude supercritical flow turbidites even in the outer fan. Outer fan channels and a lower volumetric proportion of lobes has been suggested from some modern and recent systems. For example, the Navy and the Congo fan datasets suggest that submarine fans consists of a multitude of channels and related smaller heterolithic lobes, with sands dominantly deposited in channels, even on outer fan. Sedimentary structures originating from supercritical flow conditions have been identified in other ancient and modern submarine fans. These data arise questions whether a high degree of channelization is a common features in basin floor fans or just occurs in specific conditions and fan types. To explore these questions, we propose the Point Loma Formation, San Diego, California as our research area to study the architecture using drone photography and measured sections. This work aims to document the architecture and facies of submarine fan deposits of the Cretaceous Point Loma Formation in San Diego, California. The purpose is to test the hypothesis that the Point Loma Formation consists of small heterolithic lobes interbedded with sandstone-filled channels, by documenting the bed geometries and architecture, lithological variability and bed thinning patterns. The proposed research will utilize a drone survey, measured sections, and a comparative literature analyses of modern and ancient systems. Our reconnaissance observations show considerable lithological variability in this outer fan succession, with sandstones occurring in erosionally based lenticular units, and the lobe deposits show variability in bed thickness and thinning rate. Field studies will be accompanied by a literature study of well documented outcrop examples of basin floor fans where significant channelization and supercritical flow structures have been documented (Ainsa, Sorbas, Tabernas, and Sandino basin floor fans). The aim is to compare lithology and architecture to assess which features are common to all the fans.