THE ROLE OF DESERT BASIN PALEOLAKE GEOMORPHOLOGY IN PALEOENVIRONMENTAL RECONSTRUCTION

Although occasionally portrayed as a less important part of late Quaternary paleolake studies, geomorphology is as fundamental to that work as sedimentology and stratigraphy. Furthermore, studies of desert basin paleolakes, such as those in the North American Great Basin, typically involve at least two of those disciplines because lacustrine depositional landforms are composed of sediment, and depositional environments change over time. Nevertheless, earlier studies of Great Basin paleolakes tended to emphasize geomorphology whereas much of the work since the mid-20th century has focused on stratigraphic evidence. An initial emphasis on geomorphology is not surprising because most of the Great Basin paleolakes were discovered by recognizing abandoned shorelines in the landscape, and it is logical to first seek basic information on lake extent and open- or closed-basin status, which are typically accomplished by geomorphic observations. Geomorphology, however, is fundamental to paleolake studies conceptually as well as historically. A lake’s existence, extent, and changing size are influenced by its basin’s geomorphology as well as by climate, while the lake, in turn, creates coastal landforms in the basin. Preserved shoreline segments offer the most direct evidence of lake level, and fully reconstructing the shoreline around the basin typically requires geomorphic interpretation for stretches between preserved segments. In some cases shoreline elevations have been altered by postlake neotectonism, and partial alteration of coastal landforms by postlake exogenic geomorphic processes must also be considered. Once complete, careful shoreline mapping allows an accurate determination of lake surface area, which through the pluvial hydrologic index is the principal link to the effective moisture at the time the shoreline was formed. Evidence of stillstands or fluctuations in the size of a paleolake, however, do not always represent climate stability or change, respectively, but can reflect subbasin integration and isolation, threshold dynamics, changes in the drainage area, or other geomorphic factors. In these and other ways, geomorphology remains critical to the study of paleolakes and to the accuracy of paleoenvironmental reconstructions derived from evidence of them.