Is the Late Paleozoic Ely-Bird Spring Basin of Nevada an Unrecognized Ancestral Rocky Mountains Basin?

Sturmer, Daniel M. and Trexler, James H., Jr.
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During Pennsylvanian to early Permian time, much of western Laurasia experienced broad deformation far from the nearest plate boundaries. Most of this deformation involved basement-cored uplifts and associated basins of the Ancestral Rocky Mountains (ARM) orogeny. Due to poor exposure and post-Paleozoic tectonics, driving mechanisms for these basins are not well understood or agreed upon. On the western Laurasian margin, a series of stacked, unconformity-bounded, tectonically generated basins formed as part of the Antler Overlap sequence. One of these basins, the Ely-Bird Spring (EBS) basin, initiated in latest Mississippian-earliest Pennsylvanian time, synchronous with many of the ARM basins. Though coeval with the ARM basins, the EBS basin is generally not considered as part of the ARM orogeny.

The purpose of this study is to test whether the ARM and EBS basins were related tectonically. Initially, the tectonic evolution of the EBS basin was elucidated by 1-D geohistory analyses of six stratigraphic sections throughout the EBS basin and detailed carbon isotope chemostratigraphy of those sections. Geohistory analysis was used to estimate the proportion of basin subsidence due to tectonics. The geohistory plots from the EBS basin were compared to existing plots from four western ARM basins (Oquirrh, Paradox, and Eagle basins; Wyoming Shelf) to evaluate the tectonic driving mechanism of basin formation by comparing each tectonic subsidence curve to plots from basins with known tectonic settings (cf. Xie and Heller, 2009). The geohistory analyses for the EBS basin suggest compatibility with foreland basin systems, whereas most ARM basins are similar to strike-slip tectonic settings. Carbon isotope chemostratigraphy in the EBS basin shows the most rapid sediment accumulation rates in the northwestern part of the basin, consistent with flexural response to loading to the west. Therefore, the EBS basin seems to have formed due to proximal loading at the northwest corner of the basin, not as a far-field ARM basin.

AAPG Search and Discovery Article #90162©2013 Pacific Section AAPG, SPE and SEPM Joint Technical Conference, Monterey, California, April 19-25, 2013