Geomorphic and stratigraphic development of Lake Bonneville's Intermediate paleoshorelines during the late Pleistocene

摘要

During the height of the Last Glacial Maximum (LGM), multiple paleoshorelines of late Pleistocene Lake Bonneville formed within the Bonneville basin of western Utah, eastern Nevada, and southeast Idaho. The geomorphic and sedimentological history of the paleoshorelines related to the relict lake has been used as proxies to understand paleoclimatic shifts during the LGM. The depositional and chronologic history of the lake's more significant paleoshorelines is well established. However, multiple transgressive paleoshorelines, termed "Intermediate" paleoshorelines, have also been identified but poorly documented in the basin. Intermediate paleoshorelines are found between the altitudinal limits of the lake's Bonneville and Provo levels. The variations in the altitudinal limits of these paleoshorelines make their correlation and chronologic record difficult to decipher.;Geologic maps were produced for unconsolidated sediments near Stockton, Utah and in the Hogup Bar located southeast of Park Valley, Utah, to provide a geologic framework of the stratigraphic and geomorphic developmental and chronological record related to the Intermediate paleoshorelines. New stratigraphic and chronological data provided from these maps record two previously unpublished oscillatory events as well as evidence for previously proposed oscillatory events that occurred during the Intermediate (transgressive) phase of the lake. A model was also developed to correlate the Intermediate paleoshorelines within the basin, by updating and incorporating data from hydro isostatic rebound models, by incorporating data from a model that predicts potential wave energy, and by incorporating sedimentological and geomorphic data from the paleoshorelines to explain why variations exist in the altitudes of the Intermediate features. The potential correlation of six significant and multiple less substantial Intermediate paleoshorelines suggest that the chronologic record of these features can be established. However, more chronological and sedimentological evidence needs to be obtained before the proposed chronology of the Intermediate paleoshorelines and the observed oscillatory events can fully be demonstrated. As further documentation and chronology of these intermediate paleoshoreline features are obtained it will elucidate how the lake has responded to past submillennial climatic shifts associated with the LGM and will lead to a better understanding of the risk associated with future oscillations of the lake's surface.