Jurassic giant erg deposits, flexure of the United States continental interior, and timing of the onset of Cordilleran shortening

Abstract

The requirement of long-term accommodation space for preservation in the geological record is particularly acute in the case of thick wind-blown deposits that accumulate to heights well above the regional elevation. The Mesozoic of the western United States contains a number of well-developed erg systems. The clue to their formation and preservation is the combination of a positive sand budget and the generation of shortening events in the early Mesozoic continental margin arc of the U.S. Cordillera, which flexed the continental interior downward. The combination of the creation of a wide topographic depression representing a retro-foreland basin, sheltered behind a mountain belt exerting a rain shadow effect, and a background dynamic subsidence, produced optimum conditions for the preservation of thick eolian deposits during the Jurassic. The onset of flexural subsidence in Utah is thought to have been as early as Early Jurassic on the basis of the characteristic signature of the subsidence profiles, which is in agreement with the recent documentation of Early Jurassic igneous and structural activity west of the Luning-Fencemaker thrust belt in Nevada.