Lower Paleozoic stratigraphy and structure of central Nevada: Comparisons and contrasts between the lower and upper plates of the Roberts Mountains thrust
Stanley C. Finney, Paula Noble, J. Kelly Cluer, 2000. "Lower Paleozoic stratigraphy and structure of central Nevada: Comparisons and contrasts between the lower and upper plates of the Roberts Mountains thrust", Great Basin and Sierra Nevada, David R. Lageson, Stephen G. Peters, Mary M. Lahren
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The Roberts Mountains of north-central Nevada is a classic area in which to examine the Roberts Mountains thrust, the thick Cambrian-Devonian section of carbonate-platform rocks of the lower plate, and the structurally complex basinal stratigraphic succession of the Roberts Mountains allochthon (RMA). The highest carbonate unit of the lower plate, the Middle Devonian Devils Gate Limestone, is overlain by the parautochthonous Misisisippian Webb Formation. It accumulated in a foreland basin as the carbonate platform subsided in front of the advancing allochthon, and locally it was incorporated into the basal RMA and translated a relatively short distance relative to overlying thrust nappes. Unnamed Devonian shale/ chert/limestone, variably developed, occupies the next higher nappe. These rocks were incorporated in the allochthon and transported from a deep-water basinal depositional location beyond the shelf margin. Higher nappes are composed of the Upper Cambrian-Ordovician Vinini Formation and the Silurian Elder Sandstone, although structural complexity higher in the allochthon repeats and imbricates lower and upper nappes.The Vinini Formation includes two prominent quartz sandstone intervals that can be recognized throughout much of the allochthon and provide direct sedimentological ties to the carbonate platform succession. An older, lower Whiterockian unit, which correlates with the uppermost Ninemile Shale and lower Antelope Valley Limestone of the platform, records a great sea-level lowstand that produced the unconformity between the Sauk and Tippecanoe cratonic sequences. The younger, upper Whiterockian unit is composed of the same quartz sands as the Eureka Quartzite. A facies succession in the uppermost Vinini Formation and the disconformable contact between the Vinini and Elder Formations are distinct records of Late Ordovician glacioeustatic sea-level fall and subsequent rise that are also represented in the carbonate platform succession. This is another precise sedimentological tie between platform and basin successions.The close stratigraphic ties between the Vinini Formation and correlative strata of the platform succession are strong evidence that rocks of RMA were deposited in a basin directly adjacent to, and along, the Cordilleran margin of Laurentia and that the RMA is not a far-traveled exotic terrain.