LATE QUATERNARY ALLUVIAL HISTORY OF THE OWL CREEK DRAINAGE BASIN: A GEOMORPHIC RESPONSE TO ENVIRONMENTAL CHANGE

Because of the paucity of radiocarbon datable materials, late Pleistocene deposits in central Texas have been poorly documented. This has limited our understanding of alluvial landscape evolution during this important time period. As such, we proceeded to date a series of late Pleistocene deposits in the Owl Creek drainage basin with OSL to test the validity of this methodology in this environmental setting. The analysis of the alluvial history along modern fluvial systems has proven to be effective for understanding periods of environmental stability and flux during the Late Quaternary. This period marks the last cycle of interglacial-glacial events with extreme environmental fluctuations and the colonization of North America by pre-Clovis and Clovis peoples. Investigation of fluvial responses by sediment accumulation and erosion in tributary-trunk streams is a viable method for examining internal and external thresholds during this critical time period. The analysis of Red Bluff along Owl Creek at Fort Hood, Texas will provide valuable data that will be analyzed to examine tributary-trunk stream relationships and landscape evolution of low-order steams in central Texas. Episodes of fluvial deposition and incision are preserved in Quaternary sediments at Red Bluff along Owl Creek. This investigation characterizes landscape development by: (1) mapping allostratigraphic units, (2) chronologically constraining the units using OSL dating, (3) inferring environments of deposition, (4) assessing potential response of the allostratigraphic record to climate, base level, and intrinsic factors and (5) comparing the Owl Creek record to other regional data. Soil descriptions, stratigraphy, OSL assays, and 14C dates suggest periods of deposition and incision were punctuated by pedogenic events from the beginning of the Late Pleistocene until modern times. Preliminary analysis suggests initial valley incision pre-dating fluvial deposition around 117,000 years ago. Periods of sediment accumulation, erosion and stability continue throughout the record at Owl Creek. On-going research will focus on refining the chronology at Red Bluff and the evaluation landscape changes through time.