The Valanginian δ 13 C excursion may not be an expression of a global oceanic anoxic event

• Published in: Earth and Planetary Science Letters
• Main Authors: Westermann, Stéphane, Föllmi, Karl B., Adatte, Thierry, Matera, Virginie, Schnyder, Johann, Fleitmann, Dominik, Fiet, Nicolas, Ploch, Izabela, Duchamp-Alphonse, Stéphanie
• Other Authors: Institut des Sciences de la Terre de Paris (iSTeP), Université Pierre et Marie Curie - Paris 6 (UPMC)-Centre National de la Recherche Scientifique (CNRS), Interactions et dynamique des environnements de surface (IDES), Université Paris-Sud - Paris 11 (UP11)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)
• Format: Article in Journal/Newspaper
• Language: English
• Published: HAL CCSD 2010
• Subjects: [SDU]Sciences of the Universe [physics]; Weddell; Weddell Sea; North Atlantic
• Online Access: https://hal-insu.archives-ouvertes.fr/insu-03641572; https://doi.org/10.1016/j.epsl.2009.12.011

International audience Marine and terrestrial sediments of the Valanginian age display a distinct positive δ 13 C excursion, which has recently been interpreted as the expression of an oceanic anoxic episode (OAE) of global importance. Here we evaluate the extent of anaerobic conditions in marine bottom waters and explore the mechanisms involved in changing carbon storage on a global scale during this time interval. We asses redox-sensitive trace-element distributions (RSTE; uranium, vanadium, cobalt, arsenic and molybdenum) and the quality and quantity of preserved organic matter (OM) in representative sections along a shelf-basin transect in the western Tethys, in the Polish Basin and on Shatsky Rise. OM-rich layers corresponding in time to the δ 13 C shift are generally rare in the Tethyan sections and if present, the layers are not thicker than several centimetres and total organic carbon (TOC) contents do not surpass 1.68 wt.%. Palynological observations and geochemical properties of the preserved OM suggest a mixed marine and terrestrial origin and deposition in an oxic environment. In the Polish Basin, OM-rich layers show evidence for an important continental component. RSTE exhibit no major enrichments during the δ 13 C excursion in all studied Tethyan sections. RSTE enrichments are, however, observed in the pre- δ 13 C excursion OM-rich "Barrande" levels of the Vocontian Trough. In addition, all Tethyan sections record higher Mn contents during the δ 13 C shift, indicating rather well-oxygenated bottom waters in the western Tethys and the presence of anoxic basins elsewhere, such as the restricted basins of the North Atlantic and Weddell Sea. We propose that the Valanginian δ 13 C shift is the consequence of a combination of increased OM storage in marginal seas and on continents (as a sink of 12 C-enriched organic carbon), coupled with the demise of shallow-water carbonate platforms (diminishing the storage capacity of 13 C-enriched carbonate carbon). As such the Valanginian provides a more faithful ...