Stratigraphic Evidence for Late Mississippian Instability in Western United States

Abstract

During Early Mississippian time tectonically stable conditions prevailed across most of the Cordilleran region. East of the Early Mississippian continental margin, which roughly corresponded to the position of the later Mississippian Antler orogenic belt, a relatively thin, uniform, shelf-carbonate lithosome was deposited across most of the western United States. Later Mississippian time was characterized by orogenic and epeirogenic unrest in the Cordilleran region. The first regionally significant tectonic pulse in the Antler belt took place during early Meramecian time and is reflected in the stratigraphic record by clastic wedges, unconformities, and structural complexities. Outside of the area adjacent to the Antler belt, Meramecian instability is reflected by the initiation of strongly subsiding basins in Utah and Idaho, and by an epeirogenically produced regional sub-Meramecian unconformity recognized through much of the western United States. Clastic wedges in Nevada and Idaho indicate a second major Mississippian pulse in the Antler orogenic belt during about Chesteran time. In many areas of the western United States, where Chesteran strata are preserved, a regional unconformity is recognized below or within the Chesteran succession. A complex facies configuration and local evidence of mild deformation indicate a complex paleogeography during Chesteran time. The Chesteran was a time of general regression of the seas in the Cordilleran region.