Late Paleozoic Tectonism in the Central Great Basin Requires Revision of Stratigraphic and Structural Interpretations
Recent studies in central Nevada show that stratigraphy
of Mississippian through Permian rocks is largely driven by late Paleozoic tectonism. At least eight tectonostratigraphic
boundaries have been identified. Most coincide with lithostratigraphic
boundaries and many are associated with regional unconformities. Some are
dramatic, preserving folding and faulting beneath the unconformity. Others are
subtle disconformities. All are regionally important markers recording tectonic
activity after the Antler orogeny and before the Sonoma orogeny.
A dramatic example is an upper Carboniferous
unconformity at Carlin, NV, where gently deformed Missourian strata overlie
highly folded and faulted Desmoinesian rocks.
Map-scale folds and thrust faults with 100s of meters of stratigraphic
throw record regional NW-SE contraction, with vergence
primarily to the NW. Biostratigraphy constrains this
deformation to early Missourian. The angular unconformity can be mapped
regionally, and correlated with equivalent disconformities and facies changes related to uplift.
Using these tectonostratigraphic
boundaries, we are reassessing the upper Paleozoic stratigraphy
of the Great Basin. This genetic approach has
both simplified correlation, and created some problems. Some units, especially
coarse clastic strata related to uplift and
reworking, take on new significance as indicators of tectonic activity. Other
units need to be redefined because they contain regional unconformities. In
addition, the recognition of upper Paleozoic deformation, some of which
coincides with Ancestral Rockies deformation to the east, requires revision of
tectonic models for western North America.