GSA Annual Meeting in Phoenix, Arizona, USA - 2019

Paper No. 188-5
Presentation Time: 9:00 AM-6:30 PM


WU, Zequn, Department of Geosciences, Baylor University, Waco, TX 76798, FORMAN, Steven L., Institute of Archaeology, Baylor University, Waco, TX 76798; Department of Geosciences, Baylor University, Waco, TX 76798-7354, WIEST, Logan A., Department of Geosciences, Mansfield University of Pennsylvania, Mansfield, PA 16933, MAYHACK, Connor, Department of Geosciences, Baylor University, One Bear Place #97354, Waco, TX 76706 and BOLLES, Kasey, Department of Geology, Baylor University, Waco, TX 76706

Aeolian systems on the Great Plains of N. America are associated with major drainages that cross distinct north-south temperature gradient and an east-west precipitation gradient. The records of aeolian deposition shows peak activity across the Great Plains between ca. 1300 and 700 years ago, often associated with decadal-scale megadroughts during the Medieval Climate Anomaly (MCA). The Palmer Drought Severity Index (PDSI) network, indexing the drought variability with spatial significance, indicated multiple multi-decadal modest (–0.5 to -1) to severe (< -2) dry conditions, with intervening pluvial conditions characteristic of the of MCA in the Great Plains. Drainages may be particulate sources for adjacent aeolian deposit dependent of on river level, channel form and proximity. An earlier study documented for fifteen high-order streams across central Texas sustained fluvial degradation associated with drought conditions ca. 1 ka ago. However, the relative magnitudes and interactions of aeolian and fluvial systems are not well understood with hydroclimatic variability. The Red River aeolian-fluvial system developed perpendicular to an east-west decreasing precipitation gradient from mesic to semiarid environments. The distribution of river terraces and aeolian deposits, the terrace hierarchy, preserved paleo-hydrologic features, were initially discerned by surficial characteristics revealed from field-based mapping and 1930s aerial photography. We will present stratigraphic, sedimentologic, and pedologic observations and associated granulometry for sections in the Red River drainage. Retrieved 5-15 m long Geoprobe cores from terrace surfaces exposed stabilized dune landforms overlying fluvial terrace deposits. Analysis of one core from the second terrace at 6 m above the river shows 3 m thickness of aeolian sand, with a basal OSL age of ~8 ka, overlying 9 m of fluvial sand with four intercalated paleosols. This study is along the Red River and across the bioclimatic gradient, to contextualize the changes in depositional processes, landscape stability, and associated climate changes particularly during paleo- and historical megadroughts, such as during the 1930s, 16th century and the MCA, will provide insights on river system response to drought variability and concomitant with pronounced aeolian activity.