Late Devonian to Mississippian arkosic rock derived from a granitic terrane in northwestern Nevada adds a new dimension to the Antler orogeny

New paleontologic and stratigraphic evidence indicates the coarse-grained
arkosic deposits of northwestern Nevada, including the “Cambrian” Harmony Formation
are of Late Devonian to Mississippian age. The large size, poor rounding, and
poor sorting of feldspar and quartz clasts indicate first-cycle derivation from a nearby
granitic terrane. The U-Pb ages of single zircon detrital grains from these deposits, as
determined by G.E. Gehrels and co-workers, suggest a probable source of the arkosic
sediments was Precambrian rock of the Peace River area near northern British
Columbia. Transport of the arkosic debris by turbidity currents from northern
British Columbia to northwestern Nevada, as proposed by those authors, is unlikely
because the immaturity of the deposits indicates a local source, and because the entire
western Canadian Shield was the site of deposition, not erosion, in Late Devonian and
Mississippian time. The evidence leads to the conclusion that the provenance of the
Late Devonian to Mississippian arkosic rocks was a fragment of the Canadian shield
tectonically transported to northwestern Nevada from the latitude of northern British
Columbia. Because the miogeocline in British Columbia is intact, this exotic terrane
must have been rifted from the North American plate prior to formation of the Upper
Precambrian and Paleozoic miogeocline, and was transported southward by strikeslip
faults. Its time of arrival in Nevada was certainly before the Late Devonian and
probably before the Late Ordovician. The presence in Nevada of an exotic terrane
shedding coarse arkosic sediments eastward across a strike-slip fault in Late Devonian
and Mississippian time adds new factors to the Late Devonian and Mississippian
Antler orogeny and has implications for the entire western margin of North America.