LATE PALEOZOIC DEFORMATION AT EDNA MOUNTAIN, HUMBOLDT COUNTY, NEVADA

Folding, faulting, and regionally significant unconformities provide evidence for four previously undocumented late Paleozoic deformational events in the Edna Mountain area. Antler Overlap Assemblage rocks at Edna Mountain record pre-Sonoman deformation that was first recognized by Erickson and Marsh (1974). The geology at Edna Mountain provides a unique opportunity to constrain the timing and kinematics of deformation in rocks from the Antler Overlap Assemblage and both the Roberts Mountains and Golconda allochthons.

The Pennsylvanian to Permian units of the Antler Overlap Assemblage contain multiple fold generations constrained by faulting and unconformities. Along the northern and eastern edges of Edna Mountain, locally overturned, southwest-verging folds in the Early Pennsylvanian Battle Formation and Highway Limestone (F₁) are truncated by an angular unconformity (C5 or C6). Late Pennsylvanian to Early Permian Antler Peak Limestone overlies this unconformity; it contains open folds with sub-horizontal east-west axes (F₂), recording north-south contraction. Both fold sets are truncated by the sub-horizontal Iron Point fault. The Middle Permian Edna Mountain Formation rests in angular unconformity (P1 or P2) on older units in the Antler Overlap assemblage, on the Cambrian Preble Formation, and on the Iron Point fault. The Edna Mountain Formation is folded in tight, southeast-vergent folds (F₃).

Four deformational events during the late Paleozoic are recognizable at Edna Mountain; some of these are synchronous with late Paleozoic deformation elsewhere in north-central Nevada. Southwest-vergent folding (F₁) occurred in mid-Pennsylvanian time. Broad east-west folding (F₂), followed by the Iron Point fault, occurred between Early and Middle Permian time. Folding similar in style and timing to F₁ and F₂ at Edna Mountain is present to the east in Carlin Canyon. Direct evidence for the sense of motion on the Iron Point fault is lacking. Its younger-on-older relationship suggests that it may record top-to-the-west low-angle normal faulting off of a tectonic high somewhere to the east, but a thrust fault origin cannot be ruled out. The Late Permian Edna Mountain Formation post-dates the Iron Point fault, and pre-dates the east-vergent folding (F₃) which may represent the Sonoma orogeny in this area.