13 Clastic Sedimentology, Stratigrapy, and Paleontology

Saturday, 9 May 2009
8:30 AM - 12:30 PM

EARLY JURASSIC FOSSILS - SNOW LAKE PENDANT, EMIGRANT WILDERNESS, CA

Paper number: 13-4
Program: Technical Sessions
Time: 8:50 AM – 9:10 AM

Authors

Abstract

Snow Lake pendant exposes Neoproterozoic to Cambrian metasedimentary strata and unconformably overlying Mesozoic strata, all cut by 148- Ma dikes. Our previous work indicates that these units have been transported ~ 400 km northward from the Mojave region along the Mojave-Snow Lake fault (MSLF) (Lahren, 1989; Lahren et al., 1990). Fossils have been recovered from the overlap unit, which has previously been correlated with the Fairview Valley Formation (FVF) in the Mojave region. The FVF at Snow Lake pendant consists of ~ 500 m of metamorphosed sandstone, siltstone, mudstone, limestone and sandy/silty limestone. A discontinuous basal conglomerate, up to about 4m thick, contains clasts of marble and quartzite. Ammonites, bivalves, and echinoids were found about 5m above the base of the unit. Identifiable fossils include Coroniceras cf. C. volcanoense, of Early Sinemurian age and Agerchlamys cf. A. boellingi, of latest Rhaetian to Early Sinemurian age.

This fossil find supports our previous correlation of the overlap unit with the FVF in the Mojave region, which is now also regarded as Early Jurassic in age (Stone et al., 2005) and lends further support to the existence of the MSLF which was active between 148 Ma, the age of the Independence dike swarm, and 110 Ma, the age of plutons along the trace of the fault. We have also previously correlated these strata with lithologically similar strata bearing Sinemurian ammonites in the Sweetwater-Pine Grove Hills areas, near the CA-NV border. These units may be part of the Snow Lake block, which may have been oroclinally bent along with the MSLF (Lahren and Schweickert, 1995). Further tectonic and paleogeographic implications and possible connections with the Sunrise Formation in NV are now under study. We thank fieldtrip guests M. Bebout, A. Colwell, V. Memeti, and R. Muller (first fossil find) for helping find fossils.