The Colorado Plateau (CP) region of the United States contains numerous examples of surface drainages that have been disrupted by megalandslides. Two types of drainage disruption due to landslippage have been recognized in the CP; the damming of surface streams and the formation of closed basins within headscarp grabens. These traps tend to accumulate lacustrine, aeolian, debris flows/fans, and colluvial materials, often eroded from the headscarps. We recently employed palynology, the study of pollen, spores, and other organic walled microfossils, on sediments trapped within the headscarp graben of the Surprise Valley Landslide Complex in an attempt to determine the paleoclimate when the megalandslide occurred. Most sediments sampled were reddish, indurated shallow lacustrine deposits. Previous researchers have assumed that sediments in the arid Southwest have been oxidized, destroying the palynomorphs. Sampling and analysis has yielded palynomorphs describing both paleo and recent environments. Landslides are inherently difficult to date because secondary movements disrupt the processes required for accurate dating using direct methods, resulting in biases towards more recent secondary slide events. The analysis of local sediment trapped by landslides provides an additional tool to indirectly date sequences of landslippage dating back tens, or even hundreds of thousands of years. Identification of palynomorphs complements dates obtained using other methods by providing insights into paleoenvironment/paleoclimate during each movement sequence.
Available at: http://works.bepress.com/j-rogers/81/