The Effects of Magmatism on the Reservoir Potential of Sandy Deep Marine Successions of Southern California and the Borderland Region

Marsaglia, Kathleen M.¹, David A. Clague², Alice S. Davis² (1) California State University Northridge, Northridge, CA (2) Monterey Bay Aquarium Research Institute (MBARI), Moss Landing, CA

The dominantly quartzofeldspathic (arkosic) compositions of Upper Cretaceous to Paleogene sandstones in southern California are products of batholith unroofing and dissection. Locally, these sandstones exhibit significant compaction and cementation by carbonate, and lesser clay-mineral, quartz and feldspar cements. Oligocene-Miocene triple-junction formation and plate reorganization resulted in local changes in sand composition associated with magmatism, recycling of uplifted sedimentary units, and crustal extension. These trends are apparent from onshore (mainland and island) outcrop and subsurface studies as well as from offshore Deep Sea Drilling Project sites and dredges located in the outer California borderland region. Our recent deep marine exploration of the outer California borderland using MBARI's (Monterrey Bay Aquarium Research Institute) R/V Western Flyer and the ROV (remotely operated vehicle) Tiburon suggests a complex felsic to mafic magmatic history for the area that includes a distinct period (~16 Ma) of calcalkaline volcanism on the Patton Ridge. Because volcanic components (e.g., vitric ash and crystals) add diagenetic complexity to potential reservoir sandstones, understanding the distribution and chemistry of offshore magmatism is important in predicting the reservoir characteristics of post-Oligocene deep-marine sandy facies within the region.