Abstract

The Cenozoic section in the vicinity of Carlin, northeastern Nevada, comprises the following units, separated by erosional or slight angular unconformities: (1) several thousand feet of volcanic rocks ranging from rhyolite to basalt; diorite and granodiorite intrusive rocks (early Tertiary ?); (2) Rand Ranch formation (new name): 1700 feet of Paleozoic-pebble conglomerate and sandstone (Oligocene?); (3) Safford Canyon formation (new name): 700 feet of volcanic conglomerate and sandstone, rhyolitic tuff, and limestone (late Oligocene, early Miocene?); (4) Raine Ranch formation (new name): 2000 feet of pumice lapilli tuff, volcanic breccia, lava flows, conglomerate, rhyolitic tuff, diatomite, shale, and limestone (late Miocene); (5) 500 feet of rhyolite; (6) Carlin formation (new name): at least 600 feet of tuffaceous conglomerate and sandstone, rhyolitic and basaltic tuffs, diatomite, shale, and limestone (early Pliocene); (7) Hay Ranch formation (new name): several thousand feet of lacustrine clay, limestone, and rhyolitic ash with basin-border facies of conglomerate and fanglomerates (middle Pliocene–middle Pleistocene); (8) thin welded tuff (Pleistocene). Units 4, 6, and 7 are dated by vertebrate fossils.

Basin and Range faulting was active from late Miocene to Pleistocene and may have begun in Oligocene time.

Rhyolitic tuffs are extensively altered to zeolites. The transformation seems to have taken place under the influence of the water of the lakes in which the volcanic glass was deposited.

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