STREAM PIRACY, TILTING, AND INCISION IN THE UPPER ARKANSAS RIVER BASIN: EVIDENCE FROM HIGH PLAINS TERRACES

The Upper Arkansas River shows a peculiar map-view drainage pattern with a main stem displaying several nearly 90 degree turns that are thought to represent points of late Cenozoic stream capture events; however, the timing, magnitude, and drivers of stream capture and associated drainage reorganization are poorly understood. This knowledge gap is largely due to poor preservation of geomorphic markers in the Upper Arkansas drainage basin where most studies of river capture have focused, and limited diagnostic source area bedrock units that make traditional provenance analysis challenging. Previous models invoke regional tilting due to the Rio Grande rifting and/or recent dynamic topography as the mechanism driving drainage reorganization in the Upper Arkansas, yet direct supporting evidence is generally lacking. Here we present a new approach to unravel and quantify the recent drainage reorganization of the Upper Arkansas using river terraces preserved in the High Plains and a one-dimensional numerical river incision model. Using hypothesized points of river capture near the towns of Salida, Coaldale, and Canon City, we simulate the downcutting response of the Arkansas River to instantaneous drainage area gain and compare the model results to incision patterns recorded by the High Plains terraces. Our preliminary results suggest that large magnitude river capture events explain much of the incision history of the Arkansas basin in the High Plains. Future modeling, field, and geochronology studies are aimed at untangling the relative role of stream capture versus hypothesized regional tilting on the incision history of the Arkansas River. The preliminary and future results will explore and improve understanding of the role of geodynamic tilting as a driver of drainage reorganization, as well as the impact of stream piracy on geomorphic archives, which are often used to constrain tectonic signals.