Revised Volcanic Stratigraphy of Drill Hole J-13, Fortymile Wash, Nevada, Based on Petrographic Modes and Chemistry of Phenocrysts

摘要

The core and cuttings of water well J-13 below the lower contact of the Paintbrush Tuff at 1475 ft (449.6 m) to the total depth of 3498 ft (1066.2 m) have been reexamined in the light of recent core drilling at Yucca Mountain sponsored by the Nevada Nuclear Waste Storage Investigations of the US Department of Energy. An updated stratigraphic log is presented, showing the position of cored intervals and sample locations. The tuffs of Calico Hills were penetrated from 1475 to 1740 ft (449.6 to 530 m), a thickness of 265 ft (80.8 m). All three units of the Crater flat Tuff were penetrated: the Prow Pass from 1740 to 1956 ft (530.4 to 596.2 m), the Bullfrog from 2015 to 2320 ft (614.2 to 707.1 m), and the Tram unit from 2350 to 3200 ft (716.3 to 975.4 m). The lowermost ash-flow tuff penetrated from 3220 ft (982.5 m) to the bottom of the hole at 3498 ft (1066.2 m) is the tuff of Lithic Ridge, also penetrated in hole USW-G1. The units were identified by thin-section modal analysis and by electron microprobe analyses of the feldspar and biotite phenocrysts. (ERA citation 08:019006)