Distal Ancestral Rocky Mountains tectonism: Evolution of the Pennsylvanian-Permian Oquirrh-Wood River basin, southern Idaho

摘要

Strata of the Oquirrh–Wood River basin in southern Idaho and northeastern Nevada provide a record of the northern extent of basin development related to the Pennsylvanian-Permian Ancestral Rocky Mountains. Sedimentary facies distributions, sediment dispersal patterns, provenance analyses, and subsidence analysis suggest that reactivated thrusting within a segment of the Devonian-Mississippian Antler orogenic belt (Roberts Mountains allochthon) caused subsidence of the Oquirrh–Wood River basin. Reactivated thrusting within the Antler belt was apparently the primary expression of Ancestral Rocky Mountains tectonism in southern Idaho and northeastern Nevada. Stratigraphic architecture of the Oquirrh–Wood River basin was generally controlled by deformation of the Roberts Mountains allochthon to the west of the basin. The Oquirrh–Wood River basin trends north-northwest and is obliquely superposed on the eastern margin of the generally north-trending Roberts Mountains allochthon. Uplift of part of the allochthon resulted in complex sediment dispersal patterns during early basin development. Early basin fill includes Middle Pennsylvanian chert-pebble conglomerate derived from chert-rich Roberts Mountains allochthon strata to the northwest and west of the basin. These conglomerates were deposited in a shallow-marine setting on the northwestern to western basin margin and were progressively reworked to the southeast. Continued reactivation of the Antler belt in Late Pennsylvanian and Early Permian time resulted in the deposition of a thick quartzite-pebble conglomerate sequence along the western basin margin. Crustal loading during this phase of deformation created a generally north-trending foredeep, in which as much as 3000 m of mixed siliciclastic-carbonate turbidites were deposited in an anoxic marine environment. The siliciclastic turbidite fraction was derived from the craton interior to the northeast of the basin, whereas the carbonate fraction was derived from a carbonate platform on the eastern basin margin. Facies relationships, sandstone and conglomerate provenance, and basin-subsidence history constrain the tectonic setting and evolution of the Oquirrh–Wood River basin. The Oquirrh–Wood River basin probably developed as a flexural foredeep in front of a reactivated Antler thrust belt in a compressional or transpressional setting. If basin formation were driven by transpression, the basin could be explained by models of the Ancestral Rocky Mountains that relate deformation to the Ouachita-Marathon orogenic belt on the southern margin of North America. Alternatively, a recently proposed model relates the Ancestral Rocky Mountains to Pennsylvanian-Permian Andean-style convergence on the southwestern margin of North America. Although the age and location of the convergent margin are poorly constrained in this model, it is generally supported by the west-east to southwest-northeast compression needed to form the Oquirrh–Wood River basin.