Stratigraphic Units in the Bolson of Las Vegas Valley, Nevada, with Emphasis on Hydrostratgraphic Units

Abstract

In the mid 1990's Donovan developed a set of formal Allostratgraphic (Geologic) and also Hydrostratigraphic (hydrogeologic) units. Subsequent analysis has shown the utility of these units in the upper 600 meters of the basin fill. There are over 10,000 wells in Las Vegas Valley however, wells drilled deeper than 250 meters are unusual, although relatively common for agricultural purposes from the 1940's through 1960's. Later, similar wells were drilled for large flow volume demands. There is also a small number of oil wells that fully penetrate the alluvium. Allostratigraphic units have been recognized and recommended, where appropriate, since 1983. Hydrostratigraphic units were proposed to be recognized in 1992, however the proposal was formally withdrawn in 2000. The reason both kind of units were mapped and described at the same time using the same lithologic and geophysical data was to document the differences between the two kinds of stratigraphic units. The type sections of both units are identical at 36°10′19.13′N 115°11′22.22′W however the units are not geometrically similar at other locations in the bolson. A reason for the formal withdrawal of Hydrostratigrahic units was a perceived limited utility for Petroleum applications and the longstanding use of less formal hydrogeological units and completely arbitrary ‘modeling units’, for hydrologic application. This presentation will show the use of Hydrostratigraphic units, with a possible improved characterization criteria, based on 21st century data.

AAPG Datapages/Search and Discovery Article #90266 © 2016 AAPG Pacific Section and Rocky Mountain Section Joint Meeting, Las Vegas, Nevada, October 2-5, 2016