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

The requirement of long-term accommodation space for preservation in the ge ological record is particularly acute in the case of thick wind-blown depos its that accumulate to heights well above the regional elevation, The Mesoz oic of the western United States contains a number of wed-developed erg sys tems. The clue to their formation and preservation is the combination of a positive sand budget and the generation of shortening events in the early M esozoic continental margin arc of the U.S. Cordillera, which flexed the con tinental interior downward. The combination of the creation of a wide topog raphic depression representing a retro-foreland basin, sheltered behind a m ountain belt exerting a rain shadow effect, and a background dynamic subsid ence, produced optimum conditions for the preservation of thick eolian depo sits during the Jurassic. The onset of flexural subsidence in Utah is thoug ht to have been as early as Early Jurassic on the basis of the characterist ic signature of the subsidence profiles, which is in agreement with the rec ent documentation of Early Jurassic igneous and structural activity west of the Luning-Fencemaker thrust belt in Nevada.