Central Nevada Thrust Belt: Its Preseismic State of Knowledge

Dietrich Roeder, Gregory Cameron, Randolph Chamberlain

The Central Nevada thrust belt (CNTB) is an east-vergent intra-Cordilleran fold-thrust belt of probable Cretaceous age. It is 100 km (60 mi) wide and more than 300 km (190 mi) long and merges near Las Vegas with the Sevier segment of the Overthrust belt. The CNTB affects 7 km (22,000 ft) of Paleozoic shelf deposits and contains significant Paleozoic-sourced oil in Tertiary fault blocks with uncertain but possibly thrust-related internal structure. Ongoing frontier exploration in the CNTB looks for thrust juxtaposition (present over the full width of the CNTB) of Mississippian source rocks beneath Devonian reefal and fractured carbonate reservoirs. Source and reservoir are involved in subunconformity traps beneath the valley fill and in subthrust duplex traps anywhere. Sur ace sampling suggests that maturation of Mississippian organic matter was achieved by stratigraphic burial and was little affected by thrust loading and Neogene volcanism.

Present knowledge of the CNTB is based on early wells in foothills anticlines, extensive surface mapping, the Cordilleran COCORP line, and seismic data of limited scope. Our regional synthesis and chance location of some prospective trends have been done by arranging the data into semibalanced cross sections. We have used Dahlstromian and Suppean geometry, we have assumed crustal responses to thrusting, and we have applied a modified Wernicke model of Tertiary extensional tectonics.

With uncertainties, we recognize a classical strike-belt zonation by style and bulk strain. An undeformed foreland in the hanging wall of the Idaho-Utah Overthrust belt is strongly extended by several trends of Neogene detachments. A foothills foldbelt suggests detachment and blind thrusting in several layers of Ordovician to Mississippian age. A frontal complex shows 30 km (19 mi) of overlap on thrusts detaching in the Mississippian and soling near the Devonian base. The main body of the CNTB involves the Cambrian and suggests 100-200 km (60-75 mi) of thrust overlap. It is capped by the 300 to 400-m (10,000-13,000 ft) thick Antler allochthon emplaced in pre-Permian time for more than 50 km (31 mi) along a flat intra-Devonian detachment. In general, sub-Antler structures do not involv the Mississippian and are not considered prospective.

AAPG Search and Discovery Article #91022©1989 AAPG Annual Convention, April 23-26, 1989, San Antonio, Texas.