GSA Annual Meeting in Phoenix, Arizona, USA - 2019

Paper No. 90-9
Presentation Time: 10:25 AM


HOSE, Louise D., Department of Geological Sciences and Engineering, University of Nevada-Reno, 1664 N. Virginia, Reno, NV 89557 and HAVLENA, Zoe E., Earth and Environmental Science, New Mexico Institute of Mining and Technology, SOCORRO, NM 87801

The geology of Lehman Caves in Great Basin National Park within the Southern Snake Range of eastern Nevada, is remarkably understudied. All geologic maps show the cave encased in a single block of Cambrian Pole Canyon Limestone that extends to the surface. All published descriptions fail to recognize that the host rock is a mylonitic marble, that the older Cambrian Pioche Shale crops out at the farthest western cave passage, and that an extensive, apparently faulted block of Late Proterozoic Prospect Mountain Quartzite overlies much of the cave. The geologic setting of the cave is much more complex than previously understood.

Lehman demonstrates no relationship with modern drainage patterns or surface features. Compelling evidence that it formed from sulfidic, hypogenic (rising) fluids has been documented in the Gypsum Annex (GA) passages. Extensive Pleistocene intrusion of epigenic waters has mostly (or entirely) removed the evidence of early sulfidic origins in the remaining cave passages but there are ample remnants of the cave’s hypogenic roots.

The host rock is extensively sheared Pole Canyon Limestone, which likely metamorphosed as the ~6-km thick sedimentary rock overburden slid along the overlying, Miocene Snake Creek Range Décollement. Release of the overburden pressure and the beginning of Basin-and-Range faulting introduced extensive fractures into the mylonite.

The first stage of speleogenesis appears caused by warm waters rising along the fractures. Sulfide-driven condensation corrosion processes dominated as air filled the passages. Extensive “gypsum paste” coated the walls as evidenced today by preserved, lithified gypsum crusts in the GA.

The second stage probably extended from the latter Miocene through most of the Pliocene as the water table dropped and corrosive gases withdrew.

Pleistocene water infiltration resulted in the iconic and abundant calcite dripstone, flowstone, and shields of Lehman Caves during the third stage. Any gypsum, formed in Stage 1 and lithified in Stage 2, was likely removed from most passages by the abundant epigenic water.

Stage 4 (probably Holocene through modern day) sub-aerial, carbon dioxide-driven, condensation-corrosion processes have severely altered the cave walls and speleothems. Sub-aerial cave coral is also abundant and commonly directional.