New Carbon isotope records of the Early Jurassic Toarcian Oceanic Anoxic Event from the Neuquén Basin, Argentina

AL-SUWAIDI, A.; BAUDIN, F.; DAMBORENEA, S.E.; HESSELBO, S.; JENKYNS, H.; MANCEÑIDO, M.O.; RICCARDI, A.C

Trelew, Chubut

Simposio; 5° Simposio Argentino del Jurásico; 2013

Museo Paleontológico Egidio Feruglio

The Neuquén Basin is located in Argentina, between 32° and 41° S latitude. The basin is a back-arc with a multiphase tectonic history dominated by rifting related to the break up of Gondwana and extension of the South American Plate. New biostratigraphy and organic-carbon isotope data (δ13Corg) from two locations, Arroyo Serrucho, and Arroyo Lapa reveals a stepped negative (-6%o) excursion at the boundary of the tenuicostatum-hoelderi Andean ammonite Zones. This excursion corresponds with the Early Toarcian Oceanic Anoxic Event (T-OAE; Early Jurassic, tenuicostatum-falciferum ammonite Zones: ~183 Ma), which is characterized by globally near-synchronous deposition of black shales relatively enriched in organic carbon and a broad positive and intervening stepped negative excursion in δ13C (-2 to -7 %o) recorded in marine and terrestrial organic matter and in pelagic and shallow-water carbonates deposited during the event. This negative excursion is also captured in the fossil wood record from Arroyo Lapa, with lowest values of ~ -32.5 %o, typical for Early Toarcian black shales in Europe. In addition to the Early Toarcian record, new data from two locations, Chacay Melhue and Arroyo Lapa, show a ~ -2%o excursion in δ13Corg at the Pliensbachian-Toarcian boundary, which is correlative with an excursion of similar magnitude at this boundary recorded in Europe. These new data provide further support that the Pliensbachian?Toarcian carbon isotope excursion and the T-OAE are global events likely caused by a globally synchronous increase in organic productivity with coincident injection of isotopically light carbon into the ocean-atmosphere system.