Ichnological evidence of j?kulhlaup deposit recolonization from the Touchet Beds, Mabton, WA, USA

摘要

The late Wisconsinan Touchet Beds section at Mabton, Washington reveals at least seven stacked j?kulhlaup deposits, five showing evidence of post-flood recolonization by vertebrates. Tracemakers are attributed to voles or pocket mice (1-3. cm diameter burrows) and pocket gophers or ground squirrels (3-6. cm diameter burrows). The Mount St. Helens S tephra deposited between flood beds contains the invertebrate-generated burrows Naktodemasis and Macanopsis. Estimates of times between floods are based on natal dispersal distances of the likely vertebrate tracemakers (30-50. m median distances; 127-525. m maximum distances) from upland areas containing surviving populations to the Mabton area, a distance of about 7.9. km. Tetrapods would have required at least two to three decades to recolonize these flood beds, based on maximum dispersal distances. Invertebrate recolonization was limited by secondary succession and estimated at only a few years to a decade. These ichnological data support multiple floods from failure of the ice dam at glacial Lake Missoula, separated by hiatal surfaces on the order of decades in duration. Ichnological recolonization times are consistent with published estimates of refill times for glacial Lake Missoula, and complement the other field evidence that points to repeated, autogenically induced flood discharge.