Chemostratigraphic Correlation of Terminal Neoproterozoic Units from Caborca, Mexico
The lithologic, isotopic and CAS concentration trends are quite similar to the Death Valley Succession, located ~700 kilometers to the northwest, although the absolute value of δ34SCAS between Caborca and Death Valley is slightly different. Sulfur isotope data from Oman and China do not match the trends recognized in Death Valley and Caborca, nor do they agree with one another. The differences in δ34SCAS among these sites suggests that such proxies can be influenced by regional and/or diagenetic processes and do not necessarily reflect a global oceanic sulfate isotopic signal.
The cause(s) of these sulfur and carbon perturbations is unknown. One possibility is that an increase in terminal Neoproterozoic oceanic O2 (or alternate oxidizing compound) caused the oxygenation of isotopically-light, reduced phases of sulfur and carbon. An increase in oceanic oxygen was likely a necessary threshold to overcome in order to allow the proliferation of more complex life forms during the Cambrian Explosion.