The Chromium Isotope composition of an Early to Middle Ordovician marine carbonate platform from the Eastern Precordillera, San Juan, Argentina

JOAN D´ARCY; GEO GILLEAUDEAU; ROBERT FREI; SILVIO PERALTA; LINDA KAH; CLAUDIO GAUCHER

Copenhagen

Conferencia; Conference University of Copenhagen Department of Geosciences and Natural Resource Management; 2015

Department of Geosciences and Natural Resource Manageme-University of Copenhagen

A broad suite of redox proxy data suggest that despite ocean and atmosphere oxygenation in the late Neoproterozoic, euxinic conditions persisted in the global deep oceans (1,2). However, major changes in the sulphur isotope composition of carbonate associated sulphate and co-existing pyrite in the Middle Ordovician are consistent with an abrupt flux of oxygen into the oceans resulting in the widespread ventilation of euxinic bottom waters (3).In this study we test the effect of mixing of a previously stratified ocean on Cr isotope fractionation. Cr is redox sensitive and its isotopes fractionate in response to changes in oxygen concentrations. To do this we measured the Cr isotope composition of an Early to Middle Ordovician marine carbonate platform from the Cerro La Silla section of the Precordillera, San Juan, Argentina (Figure 1,2).