SAND INJECTITE ARCHITECTURE AND PETROGRAPHIC PROPERTIES OF THE PANOCHE GIANT INJECTION COMPLEX, PANOCHE HILLS, CA

The Panoche Giant Injection Complex (PGIC) is exposed at outcrop for 300-400km² and has a unique hierarchal three-part architecture of sandstone parent units, intrusive dikes and sills and extrusive units recording a regional overpressure event where fluidized marine Cretaceous sands were forcefully injected into natural hydraulic fractures in overlying low permeability shale of the Moreno Formation. Existing pressure and depth models of the PGIC show the sandstone parent units were buried to approximately 1.5 km before the overlying seal was breached and the sand was injected. Petrographic and petrophysical properties of sand injectites and their spatial distribution throughout a sand injectite complex are important for understanding the process of sand injection and sand injectite fluid flow characteristics, yet there has been limited work done detailing such relationships, especially at outcrop scale. Although two separate parent units of the PGIC have been identified through outcrop observations; namely the Upper Panoche Formation and the Dos Ados Sandstone Member, they haven’t been identified mineralogically. Depending on which parent unit sourced the PGIC there may be implications for existing geopressure models as well as observed phenomena at the macro and microscopic scale. This study will serve to identify the parent units by comparing the mineralogy of the parent units with injected sands and examine petrographic and petrophysical properties of a sand injectite complex and their relationship with outcrop-based observations through mapping and stratigraphic logging.