Lake Bonneville Marl Chemistry and Lake Dynamics

Charles G. Oviatt

Integrated studies of shorezone clastic deposits and offshore chemical precipitates (marl) in Lake Bonneville are yielding information on lake-level history and lake dynamics. The calcium carbonate content, ratio of aragonite to calcite, and carbon and oxygen isotopic content of the marlin shallow cores from a number of localities around the lake basin suggest the following conclusions. 1) There is a strong contrast in marl composition between the hydrologically open Sevier subbasin and the hydrologically closed Great Salt Lake subbasin (or main body of Lake Bonneville). Sevier subbasin marl is richer in calcium carbonate, contains more aragonite, and isotopic ratios are higher than in main body marl. These contrasts held even during the period when the Sevier and main bo y were directly connected in Lake Bonneville. 2) During the transgressive phase of Lake Bonneville, Oviatt ^dgr¹⁸O and ^dgr¹³C strongly covaried in the main body marl, but the relationship was more scattered in Sevier marl. During the regressive phase of Lake Bonneville the isotopes in both basins covaried strongly, although they became lighter with time in the Sevier subbasin and heavier with time in the main body. 3) Marl composition is a direct clue to the history of the lake and its paleohydrology, but it is highly dependent on location within the lake basin. The most sensitive locations seem to have been areas where contrasting water masses mixed and in relatively shallow water sites distant from river inputs.

AAPG Search and Discover Article #91019©1996 AAPG Convention and Exhibition 19-22 May 1996, San Diego, California