Basin tectonics and erg response

Abstract

The alignment and distribution of facies in the major erg (eolian sand sea) deposits in the Permian and Jurassic systems on the Colorado Plateau show remarkable coincidence with modern tectonic elements. This indicates that subtle tectonic elements, precursors to the present ones, were coeval with ancient eolian deposition and controlled erg geometry and facies distribution. No other known controls or processes were capable of producing the observed patterns. Facies and architectural analysis of the Permian and Jurassic erg deposits define several major trends across the Colorado Plateau. The High Plateaus trend, parallel to and slightly east of the Wasatch line, is defined by a zone of thinning and facies change of several erg deposits. The Zuni trend lies along the Zuni lineament and is coincident with facies changes or erg margins of several units. The Colorado trend lies along the course of the modern Colorado River and a number of erg margins and several facies changes coincide with it. Most erg centers, as defined by facies and thickness, lay within paleobasins that include the Circle Cliffs trough, Holbrook, Black Mesa, and Blanding basins, and southern Cordilleran Miogeocline. Most erg deposits thin or pinch out across paleoarches, which include the Sedona, Monument, Emery and Defiance arches. Although the exact relation between the paleostructures and facies distribution is uncertain, it appears likely that some of the structural elements defined areas of greater and less sand accumulation. Areas of greater sand accumulation would be expected to be dominated by facies typical of erg centers and areas of lesser sand accumulation would be expected to be dominated by facies typical of the erg margin and eolian sand sheets. The structures may have also formed straight margins in aqueous environments such as rivers and marine coasts; straight, vertically stacked facies changes are commonly associated with erg margins in the stratigraphic record. Early post-depositional uplift of some arches may have defined straight, thin edges of some eolian sequences. The knowledge that subtle intrabasinal tectonic elements had an effect on eolian deposition can be used to reconstruct basin history; therefore, the mapping of eolian geometry and facies patterns can provide powerful information concerning the tectonic evolution of a sedimentary basin.