The earliest Cambrian record of animals and ocean geochemical change

The Cambrian diversification of animals was long thought to have begun with an explosive phase circa 530 million years ago. Recent stratigraphic discoveries, however, suggest that many taxa appeared more gradually over the preceding 12 million years. We map earliest Cambrian carbonate carbon isotope records from Sibieria, Mongolia and China onto a carbon isotope record from morocco that is calibrated by five uranium-lead zircon ages from interbedded volcanic ashes. The correlations ignore fossil tie points, so we assume synchroneity in the carbon isotope composition of the global ocean, rather than synchroeity in the first appearances of animal taxa. We present new organic carbon isotopes, strontium isotopes, and uranium and vanadium concentrations from the same carbonate samples that define the age model. The result is a new absolute timeline for first appearances of skeletal animals, in the context of the changing isotope and redox geochemistry of the oceans. The timeline suggests that the diversification of skeletal animals began early, and that three pulses of fossil first appearances are associated with rapid reorganization of the carbon cycle, and are superimposed on long term increases in sea level and the hydrothermal flux of strontium. https://www.princeton.edu/geosciences/people/maloof/