--> Unraveling the Complex Tectonostratigraphic Evolution of the Ventura Basin, California, Using Detrital Zircon Mixture Modeling

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Unraveling the Complex Tectonostratigraphic Evolution of the Ventura Basin, California, Using Detrital Zircon Mixture Modeling

Abstract

Reservoir quality is fundamentally linked to the composition of its source sediment, and thus the character of source terranes. Despite advances in tools, deciphering sedimentary provenance in complex tectonic environments remains a challenge. The fraction of igneous and metamorphic versus recycled sedimentary source terranes can control the type and amount of clays and sand-grain maturity in a reservoir. The exact timing of the change from a convergent to transform margin along the west coast of the United States is still debated. In the eastern Ventura Basin, California, complex structural deformation and poor stratigraphic correlations to nearby basins have furthered hampered these efforts. Previous workers interpreted the sediments in the study area to be sourced from the San Gabriel Mountains to the east. The Ventura Basin has been translated 45-60 km to the northwest since at least 18 Ma, potentially receiving sediment from unique source ages and mineralogical composition through time. Sediment mixture modeling applied to detrital zircon U-Pb geochronology is a useful tool for provenance studies because it enables tracing of sediment in the basin (or ‘sink’) back to its original source. This technique can be applied in source-to-sink studies of active and passive margin basins where source terranes have unique ages. In this study, we utilize detrital zircon mixture modeling from Eocene-Pliocene sedimentary rocks to unravel the Miocene slip history of the San Gabriel strike-slip fault, which forms the eastern boundary of the Ventura Basin. We dated detrital zircons of seven Eocene-Pliocene formations with n=120 analyses per sample using U-Pb geochronology, then modeled what percentage of the nearby source terranes contributed to the detrital zircon population of each sample. Matching the sediments to their likely origins allows paleogeographic interpretations of where the Ventura Basin and precursor forearc basin were located through time. The relative abundances of Proterozoic, Triassic, Jurassic and Cretaceous age peaks in the Ventura Basin sediments record the erosion of distinct source terranes in the San Gabriel Mountains. The abundance of each peak changes through time in a manner consistent with locally-derived sediment and records the basin’s northward translation. The sandstones in the Ventura Basin show increasing maturity with time, which is consistent with the detrital zircon data and suggesting changing source terranes.