Source-Rock Potential of Evaporitic Environment

Abstract

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 exist in great profusion. In a marine evaporitic embayment, the flow of surface currents is persistently toward regions of highest salinity, so that there is a continual supply and concentration of nutrients. Prolific growth of phytoplankton may be similar to that in areas of upwelling in modern oceans. Only carbonates precipitate in the part (4 to 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 a sociated with the bottom waters, much of the organic matter produced can be preserved. Upon maturation, the result may be a rich carbonate source rock, frequently unrecognized in the geologic column. In the Middle East, mesosaline conditions are known to have occurred many times from the Triassic to Cretaceous and 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.