Late Paleozoic deformation at Edna Mountain, Humboldt County, Nevada

Faulting, folding, and regionally significant unconformities provide evidence for five deformational events at Edna Mountain, Humboldt County, north central Nevada. Three of these events are restricted to the upper Paleozoic, a time interval when deformation is not predicted by traditional models. The Iron Point fault at Edna Mountain records deformation that pre-dates the Sonoma orogeny. The nature and timing of the Iron Point fault have been reinterpreted by this study. In addition to revisiting the Iron Point fault, this study has identified multiple, non-coaxial fold sets. Timing and kinematics of fold development are addressed. The Battle Formation as mapped at Edna Mountain has also been reexamined and renamed. Lastly, three late Paleozoic unconformities recognized at Edna Mountain can be correlated with regionally significant unconformities. One of the unconformities documented by this study was previously unrecognized.; Multiple fold generations record periods of deformation in Edna Mountain's geologic history. Locally overturned, southwest-vergent folds (F1) are developed in the Lower Pennsylvanian Iron Point Conglomerate (previously mapped as the Battle Formation) and Highway Limestone and erosionally truncated by an angular unconformity (C5). The C5 unconformity is overlain by the Highway Conglomerate at Edna Mountain and had been unrecognized due to the mapping of the Highway Conglomerate and Highway Limestone as a single formation. F 1 folds are truncated downward by the Iron Point fault. Upper Pennsylvanian Antler Peak Limestone overlies the Iron Point fault and a second unconformity (C6). Open, upright folds (F3), recording north-south shortening are developed in the Antler Peak Limestone and truncated upward by a third unconformity (P4). The P4 unconformity is overlain by the Lower to Middle Permian Edna Mountain Formation. Southeast-vergent folds (F4) are developed in the Edna Mountain Formation and all of the underlying units. These folds are interpreted as recording the Sonoma orogeny. A fourth fold set (F5) is recognized as post-dating the Sonoma orogeny.; The Iron Point fault is here reinterpreted as a low-angle normal fault. Truncated folds in the upper plate along with the juxtaposition of younger rocks in the hanging wall against older rocks in the footwall suggest that the Iron Point fault is extensional, rather than contractional in nature. Additionally, the average initial northeast dip of the fault and the presence of an immature conglomerate containing clasts from the lower Paleozoic Preble Formation support the interpretation that the Iron Point fault is a down-to-to-the-northeast normal fault. The Iron Point fault is interpreted here to have formed by gravitational collapse, in response to crustal thickening during the development of F 1 folds.; Three deformational events restricted to 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 Middle Pennsylvanian time. Initial motion along the Iron Point fault along with deposition of the Highway Conglomerate occurred during Middle to Late Pennsylvanian time, after the development of F1. Development of broad east-west folding (F3) followed between the Early and Middle Permian. F4 and F5 folds developed in response to the Sonoma orogeny and younger, Mesozoic shortening, respectively. Folding similar in style and timing to F1 and F3 at Edna Mountain is present to the east in Carlin Canyon.