Portal de Periódicos da CAPES

Artigo Produção Nacional Revisado por pares

BIBTEX RIS

Global perturbation of the marine Ca isotopic composition in the aftermath of the Marinoan global glaciation

2010; Elsevier BV; Volume: 182; Issue: 4 Linguagem: Inglês

10.1016/j.precamres.2010.06.015

1872-7433

Juan Carlos Silva‐Tamayo, Thomas F. Nägler, Alcídes N. Sial, Afonso César Rodrigues Nogueira, Kurt Kyser, Cláudio Riccomini, Noël P. James, Guy M. Narbonne, Igor M. Villa,

Geochemistry and Elemental Analysis

Ca isotopic compositions of Marinoan post-glacial carbonate successions in Brazil and NW Canada were measured. Both basal dolostones display δ44/40Ca values between 1 and 0.7‰, overlying limestones show a negative Ca isotope excursion to values around 0.1‰, and δ44/40Ca values rapidly increase up-section to near 2.0‰. In the Brazilian successions, those high δ44/40Ca values rapidly decrease and stabilize to values between 0.6 and 0.9‰. These Ca isotope secular variation trends are unlike those of Sturtian post-glacial carbonate successions, but similar to those of Marinoan post-glacial carbonate successions in Namibia, suggesting that the perturbation of the marine Ca cycle was global. This recommends Ca isotope stratigraphy as a tool to correlate Neoproterozoic post-glacial carbonate successions worldwide. While the lowermost and uppermost strata have δ44/40Ca values typical of Phanerozoic carbonates, the extremes, 0.1 and 2.0‰, have not been thus far reported for other marine carbonates. These extreme values suggest a short-lived, non-actualistic perturbation in the marine Ca cycle. Simple box modelling of the Marinoan post-glacial marine Ca cycle can reproduce the extreme values only by postulating a two-step process, with Ca input initially exceeding Ca removal trough carbonate precipitation, followed by precipitation overtaking a decreased Ca input.