--> --> Newly discovered Chainman shale outcrops in the Spring Mountains west of Las Vegas extends the southern end of the Mississippian Antler foreland basin by about seventy-five miles

AAPG Pacific Section and Rocky Mountain Section Joint Meeting

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Newly discovered Chainman shale outcrops in the Spring Mountains west of Las Vegas extends the southern end of the Mississippian Antler foreland basin by about seventy-five miles

Abstract

Rapid Precision Mapping (RPM) in the Spring Mountains west of Las Vegas reveal about a thousand feet of Mississippian Antler siliciclastics (Mac), including organic-rich dark gray Chainman shale, which is not shown on existing maps. RPM mapping is a geologic mapping technique that combines high-resolution, sub-meter GPS Technology (Trimble Navigation) with Geographic Information System (MapInfo) to rapidly create geologic maps with precise attitude and sample locations. The newly discovered outcrops of Mac extend the southern end of the Antler foreland basin by about seventy-five miles. Before the discovery of the outcrop, the closest known outcrops of Chainman shale to Las Vegas are west of Alamo 75 miles north northwest of Las Vegas, Kane Spring Wash 70 miles northeast of Las Vegas and the shales in the equivalent Eleana Formation in the Nevada Test site 85 miles northwest of Las Vegas. A thin, approximately 25 foot bed of Mac between the Joana equivalent Monte Crystal or Redwall Formations and the Ely equivalent Bird Springs Formation is found in most thrust sheets in the ranges around Las Vegas including Frenchman Mountain, Apex, and the hanging wall of the Keystone thrust fault in the eastern Spring Mountains. It pinches out eastward to the East Mormon and Muddy Mountains ranges. However, in another thrust sheet above and west of Keystone hanging wall thrust sheet in the Spring Mountains the Mac with Chainman shale is about 1000 feet thick. The non-resistant Mac forms mostly covered slops above very resistant cliff-forming Joana Limestone and below ledge-forming Ely Limestone. The shale lies in mostly covered slopes below partly covered slopes of sandstone. Several popular hiking trails make easy access to some of the Mac outcrops.