THE REAL ANTLER OROGENY:EVIDENCE IN NEVADA

Palinspastically restored maps of Mississippian rocks in Nevada reveal the evolution of the “type locality” for the Antler orogeny. The initial tectonism was in late Middle Mississippian time; there is no evidence of a latest Devonian-earliest Mississippian orogeny. The late Meramecian-early Chesterian (C2) unconformity records tectonic shortening, uplift and subaerial exposure across northern and central Nevada, while marine deposition continued to the south. Both the geographic distribution and the erosional depth of the unconformity indicate that the tectonic uplift was greatest to the north and northwest. The Mississippian sedimentary and structural records are consistent with deformation along a sinistral-oblique convergent margin rather than west-to-east emplacement of oceanic over continental rocks at a convergent plate boundary, the previous model for the Antler orogeny.

The maps combine stratigraphic, sedimentological, and structural data to show the evolving Mississippian paleogeography in unprecedented detail. Biostratigraphic age control permits construction of maps for specific time intervals, as well as distinction between tectonic and glacioeustatic influences. Many of the glaring anomalies of the “Antler orogeny” as originally defined are resolved by our thorough re-examination of the rocks. Lower Mississippian mudrocks overlie the Devonian carbonates, recording transgression following the latest Devonian SL lowstand, and a basin starved of coarse clastic sediment. Coarse-grained siliciclastic turbidites were deposited in Osagean (late Early Mississippian) through Meramecian (late Middle Mississippian) time. The turbidity currents flowed south, parallel to the continental margin. Structures below the C2 unconformity record northwest-southeast to west-east shortening and southeast to east vergence. The C2 surface was subsequently buried by Chesterian (Upper Mississippian) fluvial-deltaic deposits prograding southeast from a tectonic highland.