BELL, PATRICIA, Mission Geoscience, Bakersfield, CA

ABSTRACT: Geological Significance of Depositional Interbeds of the Tulare Formation, Westside San Joaquin Valley, California

The Tulare Formation extends along the west side of the San Joaquin Valley and is well exposed in oil-producing anticlines from Coalinga to Elk Hills. Depositional facies analysis has revealed the formation of Lake Tulare, a somewhat brackish lake which became more fresh, then began to fill in with alluvial then braided-stream fluvial sediments. The Tulare Formation contains the Corcoran clay, which may contain evidence of the 700,000-yr-old formation of the Long Lake Caldera. This clay formed during a lacustrine period of deposition and is best seen in the northern San Joaquin Valley. It apparently breaks up and is not found in the southern San Joaquin Valley. Another lacustrine unit, the Amnicola, is well exposed at Coalinga and is shown to be locally a coquina of the eponymous snai . Overlying are fan-delta to braided-stream sediments which contain evidence of glacially related cycles of deposition.The Tulare locally has been structurally deformed by apparent thrust faulting and by strike-slip motion, which in conjunction with rapid facies changes can make correlations difficult in the subsurface. The Tulare acts as reservoir to low-gravity oils, as does its correlative, the Kern River Formation of the east side of the San Joaquin Valley. The Tulare Formation sands also act as conduits for freshwater recharge from the Temblor Range. The Temblor Range apparently acts as the source of mercury which has been found during oil field operations within the Tulare Formation.

AAPG Search and Discovery Article #90992©1993 AAPG Pacific Section Meeting, Long Beach, California, May 5-7, 1993.