FAR-FIELD FLEXURAL RESPONSE OF LAKE BONNEVILLE FROM PALEOPLUVIAL LAKE ELEVATIONS

There are 18 paleopluvial lakes in east-central Nevada that were contemporaneous with ancient Lake Bonneville. Shoreline elevations from three of these lakes (lakes Waring, Clover and Franklin) have been measured at 201 locations. The measurements reveal that these shorelines record the far-field flexural response of an isostatically rebounding Lake Bonneville. Linear regression analysis on each shoreline data set yields west-dipping slope values of 0.23 m km-1, 0.19 m km-1 and 0.11 m km-1 for lakes Waring, Clover and Franklin, respectively. These values decrease in magnitude with increasing distance from the point of maximum uplift and are consistent with flexure theory. An east-west profile of the ancient shoreline elevations provides an extended lithospheric deflection datum for comparison of various lithospheric models. The new data support the results of Bills and May and suggest that the lithosphere underlying the Bonneville basin is 21-25 km thick and overlies mantle with an effective viscosity of (1.0-1.4) x 10(20) Pa s.