Paleoceanographic changes at the Jurassic–Cretaceous boundary in the Western Tethys, northeastern Mexico |
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| Authors: | Thierry Adatte Wolfgang Stinnesbeck Jürgen Remane Hans Hubberten |
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| Institution: | aInstitut de Géologie, 11 Rue Emile Argand, 2007 Neuchâtel, Switzerland;bFacultad de Ciencias de la Tierra, Universidad Autónoma de Nuevo León, Ap. Postal 104, 67700 Linares, NL, Mexico;cAlfred Wegener Institut für Polar und Meeresforschungs, Forschungstelle Potsdam, Telegraphenberg A 43, 0 1561 Potsdam, Germany |
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| Abstract: | Mexico is usually considered to have formed the western end of the Tethys during Late Jurassic and Early Cretaceous times. The circumstances of the opening of the Gulf of Mexico Basin towards the Tethys and the exact stratigraphic timing, however, are not clear. Four sections covering this time interval, located in northeastern Mexico, have been measured and sampled in detail, in order to clarify their stratigraphic position during the Late Jurassic to Early Cretaceous time interval and the paleogeographic and oceanographic changes that accompanied this opening. Our studies include microfacies, micro- and macropaleontology, whole rock and clay-mineral x-ray diffraction and stable isotopes analyses. Our data indicate that the Jurassic-Cretaceous boundary, as defined by the Lyon-Neuchâtel Colloquium of 1973, cannot be determined precisely in northeastern Mexico due to the near-absence of calpionellids and endemism of ammonite taxa. In the lower and upper Berriasian sediments, we detected Mediterranean ammonite taxa so far unknown from Mexico, corresponding to the appearance of typical calpionellid-rich facies. These faunas allow direct biostratigraphic correlation with European ammonite and calpionellid zones.We propose that a major oceanographic change occurred in the upper part of calpionellid Zone B of the Early Berriasian. At this time, sediments in northeastern Mexico present increasingly pelagic facies, a dramatic appearance of Tethyan microfossils (calpionellids) and ammonites, changes in stable isotopic values, whole rock and clay-mineral mineralogy. We suggest that these changes are due to a global sea-level rise that connected directly northeastern Mexico to the European Tethys and ended the endemic, semi-restricted and anoxic environment of the Late Jurassic La Casita and equivalent La Caja and La Pimienta Formations. |
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| Keywords: | Mexico Tithonian Berriasian ammonites calpionellids clay minerals stable isotopes correlation Tethys anoxia source-rocks sea-level rise |
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