Cretaceous Oceanic Anoxic Event 2 in the Arobes section, northern Spain: nannofossil fluctuations and isotope events
Published:January 01, 2013
Mihaela C. Melinte-Dobrinescu, Enrique Bernárdez, Kunio Kaiho, Marcos A. Lamolda, 2013. "Cretaceous Oceanic Anoxic Event 2 in the Arobes section, northern Spain: nannofossil fluctuations and isotope events", Isotopic Studies in Cretaceous Research, A.-V. Bojar, M. C. Melinte-Dobrinescu, J. Smit
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The Cenomanian–Turonian boundary interval of the Arobes section, northern Spain, represents the maximum depth of a relatively shallow succession. The investigated section extends within the Rotalipora cushmani and Whiteinella archaeocretacea planktonic foraminiferal zones, and from UC3 up to UC8 nannofloral zones, respectively. The Oceanic Anoxic Event 2 (OAE2) is about 16 m thick and includes a positive δ13C excursion, from 3 up to 5.5‰. The first peak of δ13C is situated towards the upper part of the Rotalipora cushmani planktonic foraminiferal zone, while the second peak of δ13C is situated in the lower part of the Whiteinella archaeocretacea planktonic foraminiferal zone. The plateau, the youngest phase of OAE2, ends slightly above the first occurrence (FO) of the nannofossil Quadrum gartneri. Based on nannofloral fluctuation, an unstable environment is recognized from the last occurrence (LO) of the nannofossil Axopodorhabdus albianus up to the FO of the nannofossil Quadrum gartneri. Mesotrophic, eutrophic and oligotrophic nannofossils have successive peaks throughout the OAE2. In the lower part of OAE2, especially in the trough phase and second build-up, productivity increased. The calcareous dinoflagellate Thoracosphaera spp. peaks up to almost 30% in the lower part of the second build-up phase. The critical nannofloral turnover episode is characterized by impoverished calcareous nannofossil assemblages and temporary disappearances of high-fertility taxa, such as Biscutum constans and Zeugrhabdotus erectus. This shift in nannofloral assemblages starts in the last stages of OAE2; that is, towards the top of the second build-up phase and also covers the main part of the plateau phase of δ13C.
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Isotopic Studies in Cretaceous Research
The Cretaceous was a period characterized by very warm climate, oceanic anoxic and oxic events and enhanced volcanic activity. The end of the Cretaceous is punctuated by a well-documented asteroid impact and the extinction of, among other groups, the dinosaurs. This volume elucidates various aspects of Cretaceous marine and continental environmental conditions. The articles in this book present a broad range of interdisciplinary contributions, which are grouped into sections on marine environments(including anoxic and oxic events, volcanism and the Cretaceous–Palaeocene boundary); mixed marine–freshwater environments and continental records. The isotopic data are combined with further geochemical, palaeontological, lithological and mineralogical proxies. The interdisciplinary approach offered here gives a solid investigation base for this fascinating period. There are examples from Europe, Asia, South and North America, and from the Early Cretaceous to the Cretaceous–Paleogene boundary.