Geochemistry of Evaporitic Lacustrine Deposits

To most of us, evaporites are the products of sea water evaporation. Sea salts have long been important to man and they have played an increas­ ingly significant role since the industrial revolution (see Multhauf 1978). To the geologist, the thick accumulations of marine salts found through­ out the geologic column are testimony to unusual conditions of climate, hydrology, sedimentation, and tectonics. And yet years of s tudy have left unresolved some of the basic controversies with respect to deposi­ tional processes and environments. In part this is because the giant deposits of the past appear to lack contemporary analogues. In contrast, scant attention has been paid to continental evaporites, even though thousands of saline lakes exist on all continents except Europe. Saline lake deposits, however, are usually restricted and ephemeral. Very few nonmarine evaporites can rival their marine counterparts on economic terms, the Green River Formation of Wyoming and Searles Lake of California being the exceptions. This neglect is unfortunate, because evaporitic lacustrine deposits abound in problems of significance to climate, hydrology, tectonics, sedi­ mentation, geochemistry, and mineralogy. Their compositional range is much wider than that of marine evaporites and the formational processes can be s tudied r ight now in a variety of settings. Quantitatively insigni­ ficant compared to marine rocks, chemical sediments of closed basins can teach us much about important processes that have modified the earth's surface throughout geologic time. Those of us who have spent time and effort studying such deposits have not been disappointed. For this review, which focuses mainly on geochemical and related