Transgressive-phase barriers as indicators of basin-wide lake-level changes in late Pleistocene Lake Bonneville, Utah, USA

Abstract

Lake Bonneville was the largest of the late Pleistocene pluvial lakes that once filled part of the Great Basin of the interior western United States. As the lake reached its highest level at the Bonneville shoreline and overflowed, it eroded through landslide deposits and alluvium near Red Rock Pass, Idaho, and quickly dropped over 100 m to the Provo shoreline. This unique flooding history and resulting rapid lake-level fall allows us to assume that all shorelines with elevations between the Bonneville and Provo levels (the intermediate shorelines) formed during the lake's transgressive phase. Various types of depositional features characterize the transgressive-phase shorelines, including barrier spits and bayhead barriers. This study uses 5 m auto-correlated digital elevation models (DEMs), airborne light detection and ranging (lidar), and ground penetrating radar (GPR) surveys to measure the internal and external structure of intermediate barriers. Analysis of 102 barriers at 26 different locations further documents the lake's constructional shorelines while employing a statistical approach to show patterns in basin-wide lake levels. These methods identify only one confidently correlatable intermediate shoreline at an adjusted elevation of 1530 m (±4 m), providing evidence of a still-water level during the late-transgressive phase of Lake Bonneville. The variability of elevations along barrier crests indicates that the formation of depositional features is highly dependent on local wave climate, in addition to basin-scale climatic controls.