UPPER PALEOZOIC TECTONIC UNCONFORMITIES IN THE CENTRAL PEQUOP MOUNTAINS, NEVADA

In the central Pequop Mountains, angular relationships and significant missing stratigraphic intervals within the Late Mississippian-Early Permian succession document two newly recognized tectonic unconformities. The stratigraphy includes the Chesterian Diamond Peak Formation (>500m), conformably overlain by Morrowan-Atokan Ely Limestone (~660m), unconformably overlain by Desmoinesian Hogan Formation (~310m), and unconformably overlain by Sakmarian-middle Kungarian Pequop Formation (>1350m).

Deformation occurs within the upper 120 m of the Ely Formation and is characterized by minor thrusting, fault propagated folds, and localized marbleization. Bedding of outcrop scale folds gives a hinge line orientation of 075/27; hinge line geometry and the associated fold geometries gives a N/NW shortening direction. The Hogan strata that overlie the Ely do not display these structures. Stratigraphically lower Ely and Diamond Peak do not seem to display the sub-Hogan structures. Preliminary fusulinid identification gives an age of upper Atokan for the uppermost Ely in the area, whereas preliminary calls for the basal Hogan are lower Desmoinesian, constraining the deformation between upper Atokan-lower Desmoinesian (~ 5 ma). Basal limestones of the Pequop Formation contain Sakmarian fusulinids and bracket a hiatus from upper Desmoinesian to Sakmarian (~ 18 ma) between the Hogan and Pequop. The Pequop Formation truncates Hogan bedding to the north. However, about 10 miles to the south at Nine-Mile Canyon, Missourian through Sakmarian strata are preserved below the sub-Peqoup unconformity.

Thus, within the central Pequop Mountains, at least two major tectonic unconformities occur in the Pennsylvanian-Early Permian succession: upper Atokan- lower Desmoinesian (sub-Hogan) and upper Desmoinesian-Sakmarian (sub-Pequop). The N/NW contractional direction for the sub-Hogan deformation appears anomalous with the E/SE deformation noted elsewhere. A similar tectonic unconformity separates the Ely and Hogan-age strata at Buck Mountain, 150 km S/SW of the Pequops. This suggests that the sub-Hogan unconformity reflects a regional phase of deformation. The magnitude of the sub-Pequop lacuna varies throughout eastern Nevada suggesting regional differential uplift and erosion.