HR: 10:35h
AN: PP42A-02 INVITED     [Abstracts]
TI: Paleoceanographic Implications of the Terrestrial Carbon-Isotope Record of the Early Toarcian (Jurassic) Oceanic Anoxic Event
AU: * Hesselbo, S
EM: stephen.hesselbo@earth.ox.ac.uk
AF: University of Oxford, Department of Earth Sciences Parks Road, Oxford, OX1 3PR United Kingdom
AU: Jenkyns, H C
EM: hugh.jenkyns@earth.ox.ac.uk
AF: University of Oxford, Department of Earth Sciences Parks Road, Oxford, OX1 3PR United Kingdom
AU: Duarte, L V
EM: lduarte@dct.uc.pt
AF: Universidade de Coimbra, Departamento de Ciˆncias da Terra, Coimbra, 3000-272 Portugal
AB: Macrofossil wood in two European sections representing the Toarcian (Early Jurassic) Oceanic Anoxic Event (OAE) have previously been shown to exhibit a large (~ -6 to -7 %) shift in d13C values which has been interpreted as a massive and geologically short-lived perturbation to the global carbon cycle. This interpretation has recently been challenged on the basis of a compilation of carbon-isotope data from belemnites collected from sections in northern Europe that exhibit carbon isotope values that are heavier than expected at the peak of the OAE. Here we present new carbon isotope measurements from wood collected from a marine record of the early Toarcian at Peniche, Portugal, a section currently under consideration as a GSSP for the base of the Toarcian. A large negative excursion (~ -7%) is confirmed for the OAE in these samples. These cannot have been severely impregnated by hydrocarbons of marine origin and the ages are well defined by ammonite biostratigraphy and by Sr-isotope stratigraphy. Carbon-isotope data is also presented for an early diagenetic silica nodule that formed within jet from the Toarcian of the Yorkshire coast, northeast England; values are indistinguishable from those of stratigraphically equivalent jet samples from which solvent extractable hydrocarbons had been removed. Thus, the early Toarcian negative carbon-isotope excursion is confirmed as a phenomenon of the global shallow-ocean, biosphere and atmosphere. It is likely that the anomalously heavy values obtained from belemnites from the OAE interval derive their isotopic signature from localized and possibly seasonal water masses characterized by dissolved inorganic carbon strongly enriched in heavy carbon by very high organic productivity.
DE: 0428 Carbon cycling (4806)
DE: 0454 Isotopic composition and chemistry (1041, 4870)
DE: 1615 Biogeochemical cycles, processes, and modeling (0412, 0414, 0793, 4805, 4912)
DE: 4901 Abrupt/rapid climate change (1605)
SC: Paleoceanography and Paleoclimatology [PP]
MN: Fall Meeting 2005