CONICET | Buscador de Institutos y Recursos Humanos

Stromatolites are relevant in palaeoenvironmental and palaeoecological studies. In this work the isotopic signatures of a stromatolitic carbonate level from the Cerro de las Cabras Formation (Anisian) are analyzed in order to unravel the paleoenvironmental conditions affecting carbonate precipitation during active microbial growth. Cerro de las Cabras Formation corresponds to the first sequence of the synrift of the Cuyana basin and is interpreted as playa lakes deposits that include ephemeral rivers. Along with the isotopic analysis a microfacies characterization was carried out determining a marginal palustrine environment with a shallow tendency upwards. δ13C and δ18O were determined on the different laminae of the stromatolite. We found good correlation between the isotope values and the environmental changes. The carbon isotope variability within the central laminae is related to changes in biological productivity associated with inflowing waters and nutrient inputs. The δ13C values obtained for the lower and upper lamina are related with changes in water level. The oxygen isotope ratios reflect hydrological variations in a water body with short residence time.