HOW CAVES INFORM OUR UNDERSTANDING OF THE GEOMORPHOLOGIC AND TECTONIC HISTORY OF EAST-CENTRAL NEVADA OVER THE LAST 12 MILLION YEARS

Speleogenesis in Great Basin National Park and the Humboldt-Toiyabe National Forest, Nevada, within the central Great Basin, USA, occurred in at least five distinct stages, which are all directly tied to the Miocene through Pliocene tectonism and Pleistocene glacially induced geomorphic instability of the area. 1) The earliest caves formed along north-trending, listric fault gaps that opened between 17-10 Ma. 2) Hypogenic, CO₂-charged and sulfidic groundwater enlarged extensional fractures, both the listric gaps and other normal faults, and lined many of them with calcite mammillaries precipitated in established voids. Mammillaries, grown near the top of the descending, regional water tables, were dated as over 10 Ma by U-Pb. The oldest is 13.08 +0.84 Ma old. These dates provide a minimum age of speleogenesis. Studied hypogenic caves are mostly concentrated in the upper plate of the Snake Range décollement and scattered throughout the area from low knolls in the Snake Valley desert to alpine ridges above timberline. The demonstrated antiquity of the mammillaries informs us about the rate of relative uplift and stream incision since the Miocene as most of these caves are now hundreds of meters above the adjacent stream beds and major basins. 3) Later epigenic infiltration, likely in the late Pliocene to Recent, modified many ancient, hypogenic caves and also formed late-stage resurgence caves along extensional Basin and Range faults. 4) Mass wasting formed the youngest caves, probably in the late Pleistocene or later. Large blocks slid into newly deepened canyons to form deep open fractures up to 130-m deep that trend parallel to the adjacent stream bottoms. 5) One studied cave formed within talus below steep, glacier-carved cliffs.

This >12 Ma history of speleogenesis preserves records of the evolving landscape and its water table as well as the region’s climatic history. The potential of these caves to inform our understanding of regional geohistory has only been barely explored and deserves much more attention.

This research was funded by the Southern Nevada Public Land Management Act program. All caves in the study area (White Pine County) formed in Paleozoic carbonates and range in elevation from ~1750m to ~3500 m msl. Thirty-eight studied caves are in the Northern and Southern Snake Range with three in the Schell Creek, one in the Egan, and three in the Ruby Ranges.