Paper No. 11
Presentation Time: 4:30 PM
IS THE EARLY–LATE PLIENSBACHIAN CARBON ISOTOPIC RECORD A PRELUDE OF THINGS TO COME?
SILVA, Ricardo L.1, DUARTE, Luís V.
1, COMAS-RENGIFO, María J.
2, MENDONÇA FILHO, João G.
3 and AZERÊDO, Ana C.
4, (1)Departamento de Ciências da Terra and IMAR-CMA, Faculdade de Ciências e Tecnologia, Universidade de Coimbra, Largo Marquês de Pombal, Coimbra, 3000-272, Portugal, (2)Departamento-UEI de Paleontología, Facultad de Ciencias Geológicas, Universidad Complutense de Madrid-CSIC, José Antonio Novais 2, Madrid, 28040, Spain, (3)Departamento de Geologia, Instituto de Geociências, Centro de Ciências Matemáticas e da Natureza, Universidade Federal do Rio de Janeiro, Cidade Universitária, Ilha do Fundão, Rio de Janeiro, 21949-900, Brazil, (4)Departamento de Geologia and Centro de Geologia, Faculdade de Ciências, Universidade de Lisboa, Campo Grande, Lisboa, 1749-016, Portugal, ricardo.silva@student.dct.uc.pt
We present a high-resolution carbon and oxygen isotopic record of organic-rich hemipelagic series of Pliensbachian age (top Ibex-Margaritatus Zones), which predates the Toarcian Oceanic Anoxic Event, one of the most important carbon cycle perturbation and extinction events of Mesozoic age. In the Lusitanian Basin (Portugal), three positive excursions are defined in the Peniche section, corresponding to the Luridum (Ibex Zone), Capricornus–lowermost Figulinum? (Davoei Zone) and uppermost Stokesi–Gibbosus subzones (Margaritatus Zone). These excursions are associated with organic-rich facies intervals. The Ibex and Margaritatus excursions can, although hampered by the lack of high-resolution data from other locations, be traced in contemporaneous basins, thus reflecting the global character of these features.
It has been proposed that the Margaritatus excursion is the result of a worldwide deposition of isotopically-light organic matter in a transgressive context, probably triggering worldwide oceanic anoxia in the Subnodosus or Gibbosus subzones. The burial of the isotopically-light organic matter, which ultimately is reflected in carbon storage, may have had important consequences. For instance, CO2 depleted atmospheric levels, resulting from the carbon storage, have been implied as a mechanism to the onset of the transient icehouse climatic conditions that operated during the uppermost Margaritatus Zone (Gibbosus Subzone)–Spinatum Zone. This event may also be related to biotic disruptions. As an example, and although highly debatable, in the Gibbosus Subzone the first of a succession of ammonite extinction episodes is recorded, occurring during the latest Pliensbachian–early Toarcian, associated with the onset and development of the palaeoenvironmental conditions that ultimately led to the Toarcian Oceanic Anoxic Event.
