| The geochemical evolution of Great Salt Lake, Utah, during the past 30,000 plus years is presented. Major factors influencing the system during this period are changes in hydrologic and hydrochemical conditions in the basin, mineral precipitation resulting from evaporitic concentration, and diffusive mass transport.;Lake elevation fluctuations are used as indicators of past hydrologic conditions. Lake elevation curves are constructed using information obtained from sedimentologic, biostratigraphic, and mineralogic analyses of piston cores which penetrated up to 6.4 metres of sediment beneath the present lake. This information was combined with published C('14) ages from wood along former lake shorelines to obtain a consistent physical history for the lake. Prior to approximately 32,000 years B.P., an ephemeral lake playa system existed in the basin. For the past 32,000 years a perennial lake has been present, initially as a shallow saline brine, followed by a brackish lake, at intermediate levels, between 25,000 and 19,500 years B.P. Between 19,500 and 17,500 years B.P. a fresher but somewhat restricted lake near the Provo level occupied the basin. Fresh water conditions and a stand near the Bonneville level existed from about 17,000 to 15,000 years B.P. About 15,000 years ago a sharp drop in lake elevation occurred. Between 15,000 and 8,000 years B.P. the lake was at extremely low levels and appears at times to have been divided into two separate basins. For the past 8,000 years the lake has fluctuated near its present level.;Three major types of inflow to the present system have been recognized. These are concentrated Na('+)- Cl('-) dominant spring waters, dilute Ca('2+)- HCO(,3)('-) river waters, and dilute Ca('2+)- HCO(,3)('-) precipitation. Changes in the proportion of each type of water entering the system under variable past hydrologic conditions has resulted in a change in the sequence of minerals precipitated during evaporative concentration. Between 15,000 and 8,000 years B.P. mirabilite was precipitated at low lake stands but not halite. Since that time a higher proportion of spring waters have entered the lake which has become Cl('-)-rich; halite is precipitated prior to mirabilite. |
