Deciphering the tectonostratigraphic history of the Ventura Basin using Automated Mineralogy

Abstract

The exact timing of the change from a convergent to a transform margin along the west coast of the United States is still debated. The eastern Ventura Basin, CA is hypothesized to have been translated 45-60 km northwest since the Oligocene. Detrital zircon geochronology data reveal four unique age modes that change in abundance from Eocene to Pliocene formations in the eastern Ventura Basin. These age mixtures likely record the erosion of distinct source terranes from the San Gabriel Mountains and transfer of that sediment into the basin. However, California has many source terranes of similar age, and an extra-regional source cannot be ruled out with my current data. Each potential parent source has a unique heavy mineral assemblage, and many contain minerals that degrade reservoir quality. I plan to utilize the heavy mineral suites from existing samples as an independent and unique provenance characteristic that will aid in reconstructing the Ventura Basin. Scanning electron microscopy is widely used in mapping mineral composition in crystalline rocks. In the stratigraphy community, however, these methods are not commonly utilized. Provenance prediction is often entirely based on U-Pb geochronology data due to the time-consuming and subjective methods of traditional sandstone petrography (i.e., point counting). SEM-based automated mineralogy can objectively and quantitatively identify heavy mineral assemblages in sedimentary rocks in less time. This study will conduct SEM-based automated mineralogy analyses on sandstone petrographic thin sections and heavy mineral grain mounts to enable a more confident provenance prediction for sediments of the Ventura Basin, CA.

AAPG Datapages/Search and Discovery Article #90351 © 2019 AAPG Foundation 2019 Grants-in-Aid Projects