Abstract: Petroleum Geology of Marine Evaporites

S. M. Billo

The conditions necessary for evaporite deposition are also important with respect to genesis of source beds for petroleum. In a restricted basin marked by large-scale salt successions, it is presumed that the basin proper is separated from the open sea either by structural or physiographic barriers. These barriers may elevate the effective wave base so that much of the basin is in the stagnant zone or in reducing environment, where sediments rich in organic matter may be deposited. Such shallow barriers increase the conditions favorable for the generation of petroleum. Since marine evaporitic basins are not ideally closed systems, but are subject to influxes and perhaps refluxes of sea water or brine, much petroleum associated with evaporites is generated from dissolved and particulat organic matter swept from the normal marine into the evaporitic environments. Only carbonates precipitate in the mesosaline part (4-12% salinity) of such evaporitic environments. They are of great significance in source rock origin. The huge reserves of petroleum in the Mesozoic of the Middle East, and many other areas including the Michigan, Paradox, and Delaware basins, owe their origin to the thick sequences of carbonates and evaporites of the mesosaline environments. Repeated cycles of oil and gas formation in the stratigraphic record are related to tectonic, climatic, or eustatic events or both, and to increasing sedimentary overburden.

AAPG Search and Discovery Article #90984©1994 AAPG Annual Convention, East Lansing, Michigan, September 18-20, 1994