A north-flowing precursor to the Pecos River in the Gatu�a formation of southeastern New Mexico and Texas

Abstract

Axial-fluvial deposits in the Gatuña Formation of southeastern New Mexico have been recognized for decades. Contrary to existing models, 725 paleocurrent measurements presented here indicate this axial river flowed north, with mean values for individual localities ranging from northwest to north-northeast. Axial sediments were deposited by a regional braided paleoriver within evolving solution-subsidence basins near the modern, south-flowing Pecos River. These dissolution features preserved Gatuña deposits from paleo-landscape positions possibly hundreds of meters above the modern Pecos Valley. Most of the fluvial sedimentary fill within major solution-subsidence features is likely Miocene–Pleistocene, whereas the thin alluvial and eolian Gatuña on the margins of the modern Pecos Valley may be largely Pleistocene. Northward paleoflow (and its subsequent reversal) in southeastern New Mexico resulted largely from epeirogenic warping of the Llano Estacado region since the Oligocene. 90