HR: 0830h
AN: PP41B-0835    [PDF]
TI: The Mid-Barremian Event (MBE): the Prelude to the OAE1a
AU: * Coccioni, R
EM: cron@info-net.it
AF: University of Urbino, Istituto di Geologia e Centro di Geobiologia Campus Scientifico, Localit… Crocicchia, Urbino, PU 61029 Italy
AU: Galeotti, S
EM: s.galeotti@uniurb.it
AF: University of Urbino, Istituto di Geologia e Centro di Geobiologia Campus Scientifico, Localit… Crocicchia, Urbino, PU 61029 Italy
AU: Sprovieri, M
EM: sprovier@gms01.geomare.na.cnr.it
AF: IAMC, Sezione Geomare Sud-CNR, Calata Porto di Massa, NAPOLI, NA 80100 Italy
AB: Detailed litho-, bio- and chemostratigraphic investigations of the Hauterivian-lowermost Aptian Maiolica pelagic limestones in the Umbria-Marche sequence, allowed to identify that the Selli Level, which is the regional sedimentary expression of the OAE 1a, represents the climax of a ca. 5 myr-long cycle of black shale deposition starting at the lower/upper Barremian boundary within polarity Chronozone M3 and H. similis-H. kutznetsovae planktonic foraminiferal Zone, that is in the lowermost part of the calcareous nannofossil Zone NC 5D. This long-term cycle starts with a prominent short-term event, here named mid-Barremian Event (MBE), which is associated with several changes in the biotic and abiotic records. In particular, a comparison of the available chemo- litho-, and biostratigraphic data from the Umbria-Marche Basin, allows to recognise that the MBE is defined by: 1) a 0.5 per mil positive shift in the carbon isotope values (Hadji, 1993; unpublished data); 2) a major step in the initial evolutive radiation of planktonic foraminifera (unpublished data); 3) a major turnover in the radiolarian assemblages (Jud, 1994; O'Dogherty, 1994). The above mentioned change in carbon isotope values can be confidently correlated over the Mediterranean Tethys which is the sole area where a detailed isotopic record is available for the entire Barremian (Erba et al., 1999; Wissler et al., 2002). These lines of evidence concur to define the MBE as an outstanding event associated with large scale changes in the ocean-climate system likely related to the rapid oceanic Ontong-Java Plateau formation, which eventually led to OAE1a. Remarkably, the MBE largely predates the well known series of biotic and geochemical events occurring prior to the OAE1a and may be considered as the real turning point in the Barremian-Aptian long-term cycle of black-shale deposition and evolutionary turnovers in several fossil groups. References Erba, E., Channell, J.E.T., Claps, M., Jones, C., Larson, R., Opdyke, B., Premoli Silva, I., Riva, A., Salvini, G., and Torricelli, S., 1999, Integrated stratigraphy of the Cismon Apticore (Southern Alps, Italy): a "reference section" for the Barremian-Aptian interval at low latitudes. Journal of Foraminiferal Research, v. 29, pp. 371-391. Hadji, S., 1993, Stratigraphie isotopique des carbonates p‚lagiques (Jurassique sup‚rieur-Cr‚tac‚ inf‚rieur) du bassin d'Ombrie-Marches (Italie). PhD Thesis, Univ. Pierre et Marie Curie, Paris, 118 pp. O'Dogherty, L., 1994, Biochronology and Paleontology of Mid-Cretaceous Radiolarians from Northern Apennines (Italy) and Betic Cordillera (Spain): M‚moires de G‚ologie (Lausanne), v. 21, 413 pp. Rud, J., 1994, Biochronology and Systematics of Early Cretaceous Radiolaria of the Western Tethys: M‚moires de G‚ologie (Lausanne), v. 21, 147 pp. Wissler, L., Weissert, H., Masse, J.P., and Bulot, L., 2002, Chemostratigraphic correlation of Barremian and lower Aptian ammonite zones and magnetic reversal: Int. J. Earth Sci. (Geol. Rundsch.), v. 91, pp. 272-279.
DE: 4267 Paleoceanography
DE: 4802 Anoxic environments
DE: 4805 Biogeochemical cycles (1615)
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2003 Fall Meeting