THIRD-ORDER SEQUENCE BOUNDARIES IN THE UPPERMOST CAMBRIAN (?) TO LOWER SILURIAN SECTION IN EAST-CENTRAL CALIFORNIA

Uppermost Cambrian (?) through Lower Silurian strata in Mazourka Canyon (MC) and Talc City Hills (TCH) in the Inyo Mountains region of east-central California can be grouped into four third-order sequences bounded by facies that represent abrupt changes in depositional environments, unconformities marked by basal conglomerates and development of karst features, and changes in systems tract architecture.

The lowest sequence boundary separates the Upper Cambrian (?) Tamarack Canyon from the overlying Ordovician Al Rose Formation at the base of which there are local occurrences of carbonate lithoclasts. The second sequence boundary is placed at the base of the Eureka Quartzite (EQ) in the TCH and about 10 m below the top of the Badger Flat Limestone in MC. In the TCH this boundary is marked by quartzite-filled solution cavities extending deeply into the upper part of the Badger Flat Limestone and carbonate lithoclasts in the basal beds of the EQ. In MC the boundary is placed below the lowest of several sandstone beds near the top of the Badger Flat Limestone. The third boundary lies at the base of the Johnson Spring Formation (partially equivalent to EQ) in MC where it is marked by an abrupt change from fine-grained offshore sediments of the Barrel Spring Formation to intertidal quartzites of the Johnson Spring Formation, the base of which locally contains reworked quartzite clasts. The boundary in the TCH is placed 24 m above the base of the EQ where impure quartzites, probably equivalent to the Barrel Spring Formation, are overlain by vitreous orthoquartzite. The fourth boundary separates the lower (Upper Ordovician) and middle (Lower Silurian) members of the Ely Springs Dolomite. Karst features and a basal conglomerate occur along this unconformity throughout the region.

Correlation of the above sequence boundaries cratonward is somewhat problematic due to their outboard position on the paleoshelf.