Authors: Manuel Montes1, Elisabet Beamud2, Francisco Nozal1 & Sergio Santillana3
1 Instituto Geológico y Minero de España (IGME). Área de Geología, Geomorfología y Cartografía Geológica. Calera 1, 28760-Tres Cantos, Madrid, Spain;
2 Paleomagnetic Laboratory CCiTUB-Instituto de Ciencias de la Tierra ‘Jaume Almera’-CSIC, Sole i Sabaris, s/n, 08028-Barcelona, Spain;
3 Instituto Antártico Argentino, 25 de Mayo 1143, San Martín, provincia de Buenos Aires, Argentina
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Abstract: The Paleocene (66–56 Ma) was a critical time interval for understanding the geological history in high palaeolatitudes after the end of Cretaceous event (recovery from mass extinction, palaeoclimate, global sea level changes, among others). The sedimentary succession from Seymour Island (Antarctic Peninsula) provides key reference material from this important phase of the early Cenozoic. A detailed age model is proposed for the López de Bertodano (LBF), Sobral (SF) and Cross Valley-Wiman (CVWF) formations based on a new magnetostratigraphic section which integrates previous dinoflagellate cyst biostratigraphy, Iridium anomaly (K-Pg boundary), U–Pb zircon dating (airfall tuff) and strontium isotope values from macrofossils. The new composite magnetostratigraphic section, which includes the Cretaceous–Paleogene boundary, has been correlated to the GPTS from C29r up to C24r. The top of the LBF is confirmed as latest Maastrichtian to earliest Danian (~65.4 Ma) in age. The overlying SF is mostly Danian in age (~65.2-~63 Ma) and CVWF is Selandian-Thatenian (~61.3-56.9 Ma). LBF, SF and CVWF are unconformity-bounded units (alloformations) that record the geological evolution of the James Ross Basin during a period of relative decreasing tectonism but coeval with volcanic activity. Unconformity based internal units have been recognized, dividing each formation into allomembers (LBF: Molluscan and Cenozoic; SF: A, B and C; CVWF: Díaz, Arañado, Bahía Pingüino). The new age model allows correlation of base-level changes with eustatic sea-level fluctuations. The bases of the SF and CVWF are correlated with the 65.3 and 61.5 Ma sea level lowstands.
Keywords: Paleocene; Magnetostratigraphy; Antarctic Peninsula; James Ross Basin; Seymour Island