HR: 1340h
AN: H53D-0499    [Abstracts]
TI: Patterns of Fluvial Incision and Deposition Related to Climate Change Along the Colorado River at Lees Ferry, Arizona
AU: * Cragun, W
EM: scragun@cc.usu.edu
AF: Utah State University, 4505 Old Main Hill, Logan, UT 84322-4505 United States
AU: Pederson, J L
EM: bolo@cc.usu.edu
AF: Utah State University, 4505 Old Main Hill, Logan, UT 84322-4505 United States
AB: The influence of climate change on fluvial incision and terrace formation has received greater attention in the past several decades, especially as the precision, accuracy, and techniques of innovative dating methods have been refined. Evidence has recently been reported from several studies within or near glaciated terrain that suggests the timing and cyclic nature of terrace formation closely matches glacial-interglacial oscillations observed throughout the Quaternary. Studies in arid and semi-arid regions that receive water from glaciated headwaters but are not glaciated themselves are not well documented. In particular, large drainage basins that incorporate several bio-climatic and geomorphic terrains may exhibit fluvial activity that does not respond simultaneously everywhere along its length. The small-scale patterns of deposition and incision in these types of systems may be controlled by transient-fluvial signals working their way from the headwaters down or local conditions of sediment production and hydrology. We are working to establish an accurate chronostratigraphy of the fill terraces along the Colorado River at Lees Ferry through cosmogenic exposure (10Be) and optically stimulated luminescence (OSL) dating techniques. Additionally, we are employing stratigraphic and sedimentologic methods in order to examine the timing and processes of terrace formation and to further explore potential patterns of fluvial responses within a dry basin located approximately 950 km downstream of its glaciated headwaters. Seven distinct deposits (Qt1-Qt7) and two additional erosional terrace levels (Qt4y and Qt6y) have been mapped and surveyed with total-station equipment. Cosmogenic samples have been analyzed from desert pavement surfaces on six terraces, including two sets of cosmogenic depth profiles to correct for inheritance. In addition, several OSL samples have been analyzed from stratigraphic profiles in order to constrain the timing of deposition and subsequent floodplain abandonment and calculate long-term incision rates. Initial chronologic results suggest that three major episodes of terrace formation have occurred in the past 120 ka, associated with MIS stages 5b-c, 4, and a later Pleistocene event (MIS 3 or 2?). Interestingly, the most prominent deposit in the Lees Ferry area (Qt4) correlates to MIS stage 5b-c, a time in which no glaciations have been reported in headwater drainages. While climate change has likely influenced terrace formation at Lees Ferry during the Pleistocene, a complicated history of fluvial response to local controls may obscure any distinct correlation to glacial records within the region.
DE: 1803 Anthropogenic effects (4802, 4902)
DE: 1815 Erosion
DE: 1824 Geomorphology: general (1625)
DE: 1827 Glaciology (0736, 0776, 1863)
DE: 1860 Streamflow
SC: Hydrology [H]
MN: Fall Meeting 2005