The Toarcian Oceanic Anoxic Event (Early Jurassic) in the Neuquen Basin, Argentina: a reassessment of age and carbon-isotope stratigraphy

AL-SUWAIDI, A.H.; HESSELBO, S.P.; DAMBORENEA, S.E.; MANCEÑIDO, M.O.; JENKYNS, H.C.; RICCARDI, A.C.; ANGELOZZI, G.N.; AL-SUWAIDI, A.H., ANGELOZZI, G.N., BAUDIN, F., CONDON, D., DAMBORENEA, S.E., HESSELBO, S.P., JENKYNS, H.C., MANCEÑIDO, & RICCARDI, A.C.,

JOURNAL OF GEOLOGY

UNIV CHICAGO PRESS

Lugar: Chicago; Año: 2016 vol. 124 p. 171 - 193

0022-1376

The Toarcian oceanic anoxic event (T-OAE) is recorded by the presence of globally distributed marine organic carbon¨Crich black shales and a negative carbon isotope shift, with ¦Ä13Corg values as low as −33¡ë, interrupting an overarching positive excursion. Here we present new biostratigraphic data and high-resolution ¦Ä13Corg data from two Southern Hemisphere localities: Arroyo Serrucho in the north and Arroyo Lapa in the south of the Neuqu¨¦n Basin, Argentina. Previous studies at these localities aimed to provide an accurate numerical age for the T-OAE and characterization of its carbon isotope stratigraphy. The new carbon isotope data and ammonite biostratigraphy presented here from Arroyo Serrucho show the T-OAE to be recorded lower in the section than supposed by previous authors, thus calling into question the published age of the T-OAE in this section. A newly investigated exposure at Arroyo Lapa North shows a complex carbon isotope record with at least three high-amplitude fluctuations in the hoelderi zone (equivalent to the serpentinum zone in northwestern Europe), with ¦Ä13Corg values of <−28¡ë, and two intervening positive isotope excursions, with ¦Ä13Corg values around −24¡ë. At Arroyo Lapa South, the characteristic major stepped negative carbon isotope excursion is recorded, with ¦Ä13Corg values of <−30¡ë and total organic-carbon contents increasing to 11%; above this level an erosional surface of a submarine channel truncates the section. These new data are globally correlative and unambiguously illustrate the global reach of the T-OAE.