HISTORY OF SEDIMENTATION IN BEAR LAKE, UTAH-IDAHO, OVER THE LAST 250,000 YEARS: LINKS TO PACIFIC CLIMATE

Sediments deposited over the last 250,000 years in Bear Lake, Utah/Idaho are predominantly calcareous silty clay, with calcite as the dominant carbonate mineral. The abundance of siliciclastic sediment indicates that Bear River usually was connected to Bear Lake. However, three aragonitic marl intervals were deposited during the Holocene and the last two interglacial intervals, equivalent to oxygen isotope stages (OIS) 5 and 7. These high carbonate, aragonitic intervals coincide with warm interglacial continental climates, warm Pacific SSTs, increased coastal upwelling under the California Current, and increased organic productivity, all recorded in marine sediments off the western margin of North America. This implies that the subtropical (Hawaiian) high-pressure system that today drives the California Current during the summer had a longer residence time during interglacials. During the last three glacial interval (OIS 2, 4, and 6), the Aleutian low-pressure system, presently dominant during the winter, had a longer residence time, producing storms and precipitation that increased the levels of Lake Bonneville and Lake Lahontan, and increased the flow of Bear River. On the California margin, the California Current upwelling system was greatly reduced during glacial intervals. Sediments deposited on the margins of North America during glacial intervals indicate that organic productivity was considerably lower than during interglacials. These climatic patterns over the North Pacific are recorded in Bear Lake by river-borne detrital clastic sediments deposited during glacial intervals, and carbonate sediments, dominated by aragonite, during the more arid interglacials.