Stratigraphy and Paleogeographic Setting of Mississippian Monte Cristo Group, Spring Mountains, Nevada

Paul Belasky

Rocks of the Monte Cristo Group exposed in the Spring Mountains, southern Nevada, represent a northwestward-deepening platform, which evolved from a carbonate ramp into a rimmed shelf during the early Late Mississippian. Sedimentological observations and biostratigraphic data on conodonts and colonial rugose corals suggest that relatively rapid subsidence resulted in the development of a carbonate ramp in the Spring Mountains during the early middle Osagean. A shelf-margin facies, represented by shallow-water pelmatozoan shoals and coral buildups, developed in the central part of the Spring Mountains during the late middle Osagean and prograded northwestward over moderately deep tempestite-rich deposits from the late Osagean through the middle Meramecian. Shoreward of the shoals were broad lagoons with good circulation in which dark fossiliferous micritic limestone was deposited.

The pattern of evolution of the Early and early Late Mississippian carbonate platform in the Spring Mountains generally is similar to that of platforms of the same age in east-central California and the Arrow Canyon Range in southeastern Nevada. The early Meramecian shelf margin in east-central California presently is offset approximately 160 km to the northwest relative to the shelf margin of the same age in the Spring Mountains area. The present position of the late Osagean shelf margin in the Arrow Canyon Range relative to that of the coeval margin in the Spring Mountains suggests an additional 70 km of right-lateral displacement along the Las Vegas Valley shear zone.

AAPG Search and Discovery Article #91024©1989 AAPG Pacific Section, May 10-12, 1989, Palm Springs, California.