REID, S. A., Bechtel Petroleum, Tupman, CA

ABSTRACT: An Overview of Miocene and Pliocene Depositional Systems of the Elk Hills Area, Kern County, California

The Miocene and Pliocene stratigraphic section at Elk Hills field contains a continuous record of deposition at the center of the southern San Joaquin basin. High sedimentation strong nearshore tidal currents resulted in a basin center that contains portions of sandy depositional systems derived from the west and east margins of the basin within an overwhelmingly muddy section.

The Miocene section contains three distinct deep water turbidite systems: (1) the lower Miocene Carneros Sandstone, a submarine fan with sand derived from a source area to the northwest, (2) the upper Miocene Stevens Main Body B sandstone, part of the westerly prograding Kern River submarine fan system, and (3) the upper Miocene Stevens 24Z and 26R sandstones, channel, and levee systems with sand originating from the Gabilan uplift west of the San Andreas fault. These sandstone units are encased in deep water organic and siliceous shales.

Depositional units in the Pliocene form a single basin-filling, mud-rich system. Slope mudstone of the Etchegoin Formation and delta front sands of the Gusher and Calitroleum indicate the progradation of the outer shelf edge. The Scalez sands mark the eastward progradation of nearshore barrier bars. The Pliocene section concludes with widespread lagoonal muds and tidal channels of the San Joaquin Formation.

The onset of Pleistocene deformation formed domal and faulted structures. Deeply buried organic shales near Elk Hills reached thermal maturity, generating and expelling hydrocarbons. The abundant claystone and shale were excellent trap seals, and all Miocene and Pliocene sands became flooded with hydrocarbons, many to their spill points. The result was the development of four major petroleum zones with recoverable reserves of more than 1.5 billion bbl.

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