Depositional Belts in Nevada During the Famennian
COLES, KENNETH S., Purdue University, West Lafayette, IN
Deformed upper Famennian strata near the base of the Roberts Mountains allochthon in Nevada add detail to the paleogeography of the region at the time it was undergoing the transition from the shelf-slope setting of the early Paleozoic to the foreland basin and highland of the Antler orogeny.
The uppermost Devonian part of the Pinecone sequence and correlative rocks in central and northeastern Nevada consists of black chert and argillite, commonly with nodular phosphate. Deposition took place in a detritus-starved, oxygen-poor slope or foredeep setting east of the advancing, but still submerged, Roberts Mountains allochthon. The Pinecone is less far-traveled than much of the allochthon as the time interval from deposition to the end of thrust movement and deformation was shorter.
The late Famennian saw at least three contrasting belts of deposition in the vicinity of Nevada. First, black shale and micrite of the Leatham Member of the Pilot Shale in eastern Nevada and western Utah formed in the deep subtidal/dysaerobic belt described by Sandberg and coworkers. Second, a bathyal belt, in central Nevada to the west of the Pilot, contained black chert and phosphate in a zone of high surface productivity. Also present, but rare, were beds of carbonate detritus with a probable provenance to the east, and olistoliths(?) of quartz sandstone like that known in the approaching Roberts Mountains allochthon to the west. Third, greenstones and chert of the Schoonover sequence, described by E. Miller and co-workers, were being deposited somewhere beyond the allochthon in an oxygenated, oceanic setting.
AAPG Search and Discovery Article #91009©1991 AAPG-SEPM-SEG-SPWLA Pacific Section Annual Meeting, Bakersfield, California, March 6-8, 1991 (2009)