Description
This is the first detailed biostratigraphic and lithostratigraphic analysis of the southwestern-most exposures of the Hidden Valley Dolomite. A nearly complete section in the Talc City Hills area of the southern Inyo Mountains is 1156 feet thick and has been divided into a lower member (266 feet thick) and an upper member (890 feet thick). Analysis of abundant and diverse age-diagnostic conodonts from this section is very significant because diagenesis and low grade metamorphism have destroyed much of the paleontologic record. Three Early Silurian to early Late Silurian conodont biozones are recognized within the lower member. They are: Spathognathodus celloni Biozone (Early Silurian, late Llandoverian age) from 0 - 15 feet; Pterospathodus amorphognathoides Biozone (late Early Silurian to early Late Silurian, late Llandoverian to early Wenlockian age) from 15 feet to 116 feet; and Kockelella ranuliformis Assemblage Biozone (early Late Silurian, Wenlockian age) from 116 feet to 286 feet. The upper member from 286 feet - 1156 feet is nearly barren of conodonts but combined evidence from several sources indicates the interval is Late Silurian, Ludlowian age. Interpretations of the depositional environments are based upon stratigraphic, sedimentologic, and paleontologic evidence. The lower member (0 - 266 feet) represents a marine transgressive phase with minor episodic regressive phases. Shallower normal marine subtidal (above effective wave base) environments to deeper normal marine subtidal (below effective wave base) environments prevailed. The upper member (266 - 1156 feet) represents a marine regressive phase. Barrier bars and ridges restricted normal marine current regimes resulting in limited ecosystems. Between 266 feet and 287 feet transitional marine environments are evident. Water depth ranged from shallower subtidal restricted environments to intertidal restricted environments. Supratidal environments may have also been significant.
