Petrographic evidence for the nature of vertical permeability barriers: Temple Avenue fault, Wilmington oil field, Long Beach, California

The Temple Avenue fault is a north-trending east-dipping normal fault that cuts the north flank of the Wilmington anticline in the Wilmington oil field. The fault offsets strata of the Repetto Formation (lower Pliocene) and the Puente Formation (upper Mocene). Oil-water contact structural maps indicate that the fault acts as a permeability barrier.; Smectite to illite transition and the precipitation of authigenic clays and carbonate cements are responsible for the sealing properties of the Temple Avenue fault. Smectite-illite transition along the fault plane is not controlled by temperature alone, but by the chemistry of fluids migrating from lower structural levels along the fault. plane. The smectite to illite transition along the Temple Avenue fault. occurs at a very shallow depth (2,858 feet [871 meters] below sea level), and it is controlled mainly by K+ concentration.