Late Cambrian Carbonate sequences of the Argentine Precordillera and the Setptoan positive C-Isotope excursion (Spice)

SIAL, ALCIDES N.; PERALTA, SILVIO H.; FERREIRA, VALDEREZ P.; GAUCHER, CLAUDIO; TOSELLI, ALEJANDRO J.; ACEÑOLAZA, FLORENCIO G.; PARADA, MIGUEL ANGEL; PIMENTEL, MARCIO M.

Sao Paulo

Conferencia; International Meeting Project N° 478 IGCP; 2004

Universidad Sao Paulo - Project N° 478 IGCP

The highly oscillatory C-isotope record of the Late Neoproterozoic coincides with major glacial to interglacial fluctuations. Except for a glaciation at the Vendian/Cambrian boundary coincident with a large C negative excursion (Bertrand-Sarfati et al., 1995), in the Cambrian period  ?greenhouse? conditions seem to have predominated (Tucker, 1992). In addition, the widespread occurrence of phosphorites in the Early Cambrian suggest vigorous oceanic circulation and upwelling (Cook and Shergold, 1984). The falling amplitude of C-isotopic values between 750 and 500Ma may be related, somehow, to the change from glacial ?icehouse? conditions in the Cryogenian to ?greenhouse? conditions in the Middle Cambrian. C-isotope oscillations in the Early Cambrian result, probably, from climatic oscillations either than from glaciations that have not been proved to have occurred (Brasier and Sukhov, 1998). A large and global Steptoean positive carbon isotope excursion (SPICE; +5?PDB; Saltzman et al., 1998, 2000) has been reported from North America, Kazakstan, South China and Australia and is one of the largest Phanerozoic C-isotope excursions. It represents a major perturbation of the carbon cycle ~500Ma and, as a peculiarity, a worldwide mass extinction (trilobites) coincides with the onset of the positive shift (base of the Pterocephalyd biomere). SPICE is a valuable tool for precise regional and intercratonic correlations and can be used globally to locate primary subdivisions of the Cambrian system in unfossiliferous carbonate sequences.