Abstract

A skeletonized fauna of possible Tommotian age (earliest Cambrian) has been discovered in the Caborca region, Sonora, in a unit considered approximately equivalent to the basal part of the Wood Canyon Formation of the Death Valley region. Probable metazoan traces occur about 900 m stratigraphically below the shelly fossils and may be among the oldest trace fossils known in the southern Cordillera. About 1,200 m stratigraphically below the shelly fossils, a new filamentous algal microbiota has been found in silicified wackestone from the El Arpa Formation. These new fossil occurrences, found within three stratigraphically correlated upper Proterozoic through Middle Cambrian sections from the Caborca region, have significant paleobiologic and biostratigraphic implications for the “Precambrian-Cambrian boundary” and Proterozoic paleobiology in western North America.

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