Stable isotope characterization of a saline paleolake of the Cañadón Asfalto Formation (Middle-Upper Jurassic), Cañadón Carrizal, Cerro Cóndor, Chubut province, Argentina

CAGNONI, MARIANA; CABALERI, NORA; ARMELLA, CLAUDIA; PANARELLO, HÉCTOR

Brasilia

Simposio; VII South American Symposium on Isotope Geology; 2010

<!-- /* Style Definitions */ p.MsoNormal, li.MsoNormal, div.MsoNormal {mso-style-parent:""; margin:0cm; margin-bottom:.0001pt; mso-pagination:widow-orphan; font-size:12.0pt; font-family:"Times New Roman"; mso-fareast-font-family:"Times New Roman"; mso-ansi-language:EN-US; mso-fareast-language:EN-US;} @page Section1 {size:612.0pt 792.0pt; margin:70.85pt 3.0cm 70.85pt 3.0cm; mso-header-margin:36.0pt; mso-footer-margin:36.0pt; mso-paper-source:0;} div.Section1 {page:Section1;} --> The Cañadón Asfalto Formation crops out in Chubut province, Argentina and consists of a thick volcano-sedimentary continental sequence that represents one of the most important continental Jurassic records of South America. The carbonate-evaporite sequence that crops out in Cañadón Carrizal belongs to the Las Chacritas Member and is characterized by a shallow lacustrine facies association. This sequence includes an extensive biohermal belt, flood facies of high and low lake-level stages and desiccation -evaporation facies. The basin was defined as a hydrologically- closed saline lake. Isotopic data do not show definitive covariance between delta 13C and delta18O as could be expected for a dominant hydrological closed lake. However, there is a good correlation between delta18O and delta13C values and lake-level fluctuations. The delta 18O variations are linked to changes in the hydrologic balance and delta13C variability is linked to modifications in bio productivity, sometimes adapted to special chemical conditions due to the extreme salinity of the lake waters.