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ABSTRACT: Effects of Pressure Solution on Petroleum Migration in the Miocene Monterey Formation, Southern San Joaquin Basin, California

Chung-I Lee

Pressure-solution features are common in the Monterey Formation and occur as bedding-parallel stylolites and solution cleavages at high angle to bedding. Both structures are visible in hand specimen, but they occur abundantly at a microscale. Petrographic study of siliceous rocks of the Monterey Formation shows that stylolites and solution cleavages provide horizontal (bedding parallel) and vertical avenues for petroleum migration, respectively. Together with tectonic fractures, they are major migration pathways of petroleum.

Pressure solution is a dissolution process that involves volume reduction of the rock and concentration of insoluble rock components, including organic matter, along pressure-solution features. Previous geochemical studies have shown the concentration of organic matter along stylolites, but no previous work has demonstrated it petrographically. Petrographic examination of siliceous rocks in the Monterey Formation under transmitted, reflected, and fluorescent light, shows the occurrence of liptinite and inertinite along stylolites. Petrographic evidence suggests that removal of rock mass by pressure solution can concentrate organic matter and help the development of a three-dimensional organic network believed to play an important role in primary migration.

AAPG Search and Discovery Article #91003©1990 AAPG Annual Convention, San Francisco, California, June 3-6, 1990