Ediacaran and Cambrian index fossils from Sonora, Mexico

Abstract

The Cambrian index fossil Treptichnus pedum is reported freom the Puerto Blanco Formation near Pitiquito, Sonora, Mexico, and new occurrences of the Neoproterozoic index fossil Cloudina are reported freom the underlying La Cienega Formation. Considered together, these fossils constrain the location of the Ediacaran/Cambrian boundary in Mexico. The suite of fossils in this sequence is important because it provides an independent biostratigraphic datum for constraining the position of Laurentia during the onset of metazoan diversification, for testing proposed lithostratigraphic correlations among western North American NeoproterozoicCambrian successions, and for testing regional tectonic paradigms such as the MojaveSonora Megashear hypothesis.