Absence of major vegetation and palaeoatmospheric pCO₂ changes associated with oceanic anoxic event 1a (Early Aptian, SE France)

verfasst von

Ulrich Heimhofer, Peter A. Hochuli, Jens O. Herrle, Nils Andersen, Helmut Weissert

Abstract

The deposition of organic-rich sediments during the late Early Aptian Oceanic Anoxic Event (OAE) 1a has been interpreted to result in a major decrease of palaeoatmospheric CO₂ concentrations, accompanied by significant changes in the terrestrial flora. In order to test this hypothesis, the OAE 1a interval in the Vocontian Basin (SE France) has been studied with a combined approach including stable carbon isotopes, organic geochemistry and palynology. To estimate changes in palaeoatmospheric CO₂ levels across the OAE 1a, the δ ¹³C composition of presumed algal biomarkers (low molecular weight n -alkanes, steranes) and of bulk carbonate carbon are used. Our results yield estimated Early Aptian carbon dioxide partial pressure (pCO₂) values three to four times the preindustrial level and only a moderate drop across the black shale event. This moderate drop in pCO₂ is supported by palynological results. The frequency patterns of climate-sensitive sporomorphs (incl. pteridophyte spores, bisaccate pollen and Classopollis spp.) display only minor fluctuations throughout the studied section and indicate relatively stable patterns of terrestrial vegetation during and after formation of the OAE 1a black shale. The occurrence of a characteristic Early Aptian carbon isotope pattern across the OAE 1a interval permits accurate chemostratigraphic correlation with the well-studied Livello Selli interval of the Cismon record (N Italy). The contemporaneous formation of individual black shale layers at both sites indicates that transient episodes of dysoxic-anoxic bottom waters prevailed over large areas in the W Tethys Ocean independent of depositional setting. Comparison of the palynological data from the two locations displays significant differences in the frequency patterns of bisaccate pollen. The contrasting pollen spectra are interpreted to reflect prominent changes in the palaeoceanographic current patterns and/or selective sorting due to sea-level rise rather than latitudinal shifts of the major floral belts.

Externe Organisation(en)

ETH Zürich
Universität Zürich (UZH)
National Oceanography Centre
Christian-Albrechts-Universität zu Kiel (CAU)

Typ

Artikel

Journal

Earth and Planetary Science Letters

Band

223

Seiten

303-318

Anzahl der Seiten

16

ISSN

0012-821X

Publikationsdatum

15.07.2004

Publikationsstatus

Veröffentlicht

Peer-reviewed

Ja

ASJC Scopus Sachgebiete

Geophysik, Geochemie und Petrologie, Erdkunde und Planetologie (sonstige), Astronomie und Planetologie

Ziele für nachhaltige Entwicklung

SDG 13 – Klimaschutzmaßnahmen

Elektronische Version(en)

https://doi.org/10.1016/j.epsl.2004.04.037 (Zugang: Unbekannt)