Correlation of a Valanginian Stable Isotopic Excursion in Northeastern Mexico with the European Tethys
Thierry Adatte, Wolfgang Stinnesbeck, Hans Hubberten, Jürgen Remane, José Guadalupe López-Oliva, 2001. "Correlation of a Valanginian Stable Isotopic Excursion in Northeastern Mexico with the European Tethys", The Western Gulf of Mexico Basin: Tectonics,Sedimentary Basins, and Petroleum Systems, Claudio Bartolini, Richard T. Buffler, Abelardo Cantú-Chapa
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In the Sierra Madre Oriental of northeastern Mexico, two sections (La Huasteca and San Lucas) spanning Berriasian to lower Hauterivian rocks were analysed and are correlated by mean of calpionellid and ammonite ocurrences, microfacies, and stable isotopes (bulk rock). A major isotopic excursion (approximately 3‰) of both δ13C and δ18O was recognized in an interval of pelagic mudstone corresponding to the upper Valanginian. A similar δ13C excursion was also observed in coeval strata of the southern Italian Alps and Appennines (Weissert and Channell., 1985; Weissert et al., 1989; Weissert and Lini, 1991; Lini et al., 1992); the northern Tethys margin (Föllmi et al. 1994); the Gulf of Mexico (Patton et al., 1984); and the North Atlantic (Robertson and Bliefnick, 1983) and Pacific (Douglas and Savin, 1973) Oceans. The δ13C shift is independent of changes in microfacies, contents in organic matter, and mineralogical composition of the sediment. This stable isotopic pattern was also identified in the Vocontian basin in France (Hennig et al., 1999), and calibrated to the Campylotoxus-Verrucosum zones of the early/late Valanginian. Integration of our biostratigraphic and isotopic data indicates the presence, at San Lucas, of a complete Valanginian sequence in terms of European ammonite and calpionellid zones, whereas at La Huasteca some of the zones may be absent.
This late Valanginian δ13C excursion is generally interpreted to be the first episode of Cretaceous greenhouse conditions. It reflects a major change in the global carbon budget that could have resulted from increased tectonic/volcanic activity, such as the Paraná continental flood basalts leading to increased atmospheric CO2 and, consequently, greenhouse conditions.
Oxygen-isotopes data in the Mexican sections trend toward higher values, but with a significant temporal lag, as compared with the δ13C curve. This indicates seawater and/or climatic cooling, which can be linked either to negative feedback (e.g., increase in weathering) leading to a decrease in atmospheric CO2 or to intense oceanic spreading and a subsequent global sea-level rise.
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Carbon dioxide (CO 2) is the main compound identified as affecting the stability of the Earth's climate. A significant reduction in the volume of greenhouse gas emissions to the atmosphere is a key mechanism for mitigating climate change. Geological storage of CO 2, or the injection and long-term stabilization of large volumes of CO 2 in the subsurface in saline aquifers, in existing hydrocarbon reservoirs or in unmineable coal seams, is one of the more technologically advanced options available. A number of studies have been carried out and are reported here. They are aimed at understanding the safety, physical and chemical behaviour and long-term fate of CO 2 when stored in geological formations. Until efficient, alternative energy options can be developed, geological storage of CO 2, the subject of this volume, provides a mechanism to reduce carbon emissions significantly whilst continuing to meet the global demand for energy.