Abstract: Potential of the Evaporitic Environment as a Source of Petroleum

By

Robert Evans and Douglas W. Kirkland

Examination of modern saline lakes, solar evaporation ponds, and lagoons shows that the evaporitic environment can be very productive of organic matter. Few species survive in the brines, but those that do commonly are present in great profusion. In a marine evaporitic embayment, the flow of surface currents is persistently toward regions of highest salinity, so that a continual supply and concentration of nutrients exist. Prolific growth of phytoplankton may be similar to that in areas of upwelling in modern oceans.

Only carbonates precipitate in the "mesosaline" part (4- 12% salinity) of such an evaporitic environment, and no great dilution of organic matter by clastic or biogenic sediments occurs. Because stratification of brine may occur and reducing conditions may be associated with the bottom waters, much of the organic matter can be preserved. Maturation may produce a rich carbonate source rock, commonly unrecognized in the geologic column.

In the Middle East, mesosaline conditions occurred many times from the Triassic to the Cretaceous; they may be responsible for the vast reserves of petroleum in the area. Evaporitic conditions may also have played a part in the petroleum productivity of many other areas, including the Michigan and Paradox basins.

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