THE INFLUENCE OF GLACIAL CYCLES ON PLEISTOCENE SEDIMENTATION OF THE LOWER AMERICAN RIVER (CALIFORNIA, USA)

During the Pleistocene Epoch, glaciers advanced and retreated, sea levels fell and rose, and rivers flowed across the landscape. As the American River flowed from the Sierra Nevada Mountains west to the Sacramento River, steep river channels eroded across the Central Valley and filled with gravel. After filling the channels with gravel, deposition switched to finer sands before the river relocated and incised new channels to the north. The present study investigates whether glacial and interglacial climate changes controlled this landscape evolution by varying sediment loads along the Lower American River. Dating fluvial sandstones with infrared stimulated luminescence (IRSL) of feldspars and reconstructing the depositional environment with grain size and mineralogical analyses reveals the relationship between glaciation and sedimentation. The hypothesis is that early glaciation created a steep gradient which cut down through the older alluvium, high quantities of large sediment were deposited during maximum glaciation, and paleosols developed over stable interglacial periods. However, preliminary IRSL data disputes this, with coarse sandstone deposition during an interglacial. Analyzing the formation of the Lower American River influences our understanding of the sedimentation in mid-latitude rivers draining glaciers and provides dating for Quaternary formations in California’s Central Valley.