Stratigraphy and structure of the Schoonover Sequence, northeastern Nevada; implications for Paleozoic plate-margin tectonics

Radiolarian biostratigraphy and detailed geologic mapping have been used to resolve the complex structure and stratigraphy of part of the Golconda Allochthon in the Independence Mountains, Nevada. Here, the Schoonover Sequence is latest Devonian to Early Permian in age, spanning the time interval from the emplacement of the Roberts Mountains Allochthon onto the shelf in the earliest Mississippian Antler Orogeny to the inception of the Sonoma Orogeny. The history of the Schoonover Basin is tied to that of the adjacent shelf in Nevada and provides important insights into the upper Paleozoic paleogeographic framework of the continental margin. The stratigraphic relations documented in the Schoonover Sequence are compatible with a back-arc thrusting model for the formation of both the Roberts Mountains and Golconda allochthons, but they are more difficult to reconcile with models that interpret the allochthons as accretionary prisms developed in front of farther-traveled arcs that collided with a passive margin. Data suggest that the western United States was a Southwest Pacific-style active margin at least as far back as the Devonian.--Modified journal abstract.