Calcareous nannofossil during the Paleocene Eocene Thermal Maximum in sediments of Walvish Ridge

Compositions and abundances of calcareous nannofossil taxa have been determined in a ca 170 kyrs long time interval across the Paleocene/Eocene boundary at 1-cm to 10-cm resolution from two ODP Sites (1262, 1263) drilled along the flank of the Walvis Ridge in the South Atlantic. The results are compared to published data from ODP Site 690 in the Weddell Sea. The assemblages underwent rapid evolution over a 74 kyrs period, indicating stressed, unstable and/or extreme photic zone environments during the PETM hyperthermal. This rapid evolution, which created 5 distinct stratigraphic horizons, is consistent with the restricted brief occurrences of malformed and/or weakly calcified morphotypes. The production of these aberrant morphotypes is possibly caused by major global scale changes in carbon cycling in the ocean-atmosphere system, affecting also photic zone environments. No marked paleoecologically induced changes are observed in abundances of the genera Discoaster, Fasciculithus and Sphenolithus at the Walvis Ridge sites. Surprisingly, there is no significant correlation in abundance between these three genera, presumed to have had a similar paleoecological preference for warm and oligotrophic conditions.

Bulk stable carbon and oxygen isotopes from ODP Site 1258, and Fe intensities from ODP Site 1262, and minimal tuning age model options for ODP Site 1258 and 1262

Timing is crucial to understanding the causes and consequences of events in Earth history. The calibration of geological time relies heavily on the accuracy of radioisotopic and astronomical dating. Uncertainties in the computations of Earth's orbital parameters and in radioisotopic dating have hampered the construction of a reliable astronomically calibrated time scale beyond 40 Ma. Attempts to construct a robust astronomically tuned time scale for the early Paleogene by integrating radioisotopic and astronomical dating are only partially consistent. Here, using the new La2010 and La2011 orbital solutions, we present the first accurate astronomically calibrated time scale for the early Paleogene (47-65 Ma) uniquely based on astronomical tuning and thus independent of the radioisotopic determination of the Fish Canyon standard. Comparison with geological data confirms the stability of the new La2011 solution back to ~54 Ma. Subsequent anchoring of floating chronologies to the La2011 solution using the very long eccentricity nodes provides an absolute age of 55.530 {plus minus} 0.05 Ma for the onset of the Paleocene/Eocene Thermal Maximum (PETM), 54.850 {plus minus} 0.05 Ma for the early Eocene ash -17, and 65.250 {plus minus} 0.06 Ma for the K/Pg boundary. The new astrochronology presented here indicates that the intercalibration and synchronization of U/Pb and 40Ar/39Ar radiometric geochronology is much more challenging than previously thought.

Sapientia, 2000, Vol. LV, nº 208 (número completo)

Contenido: Estructuras mentales y principios racionales / Lorenzo Vicente Burgoa – Autonomía moral y deliberación en Santo Tomás de Aquino / Ciro E. Schmidt Andrade – Thomas Aquinas and the reality of time / Steven C. Snyder – Fe y razón en Ramón Llull / Marc Egea I Ger – Idealismo y personalismo en Husserl / Francisco Leocata – El discurso no consensuado de Jürgen Habermas / Marisa Villalba de Tablón – Hacia el tercer milenio : el clima posmoderno y la recuperación de la naturaleza humana del hombre (observaciones tomistas) / William R. Darós – Razón, voluntad y praxis / María Celestina Donadío Maggi de Gandolfi – Meditación sobre la felicidad / Alberto Caturelli – “Y llegarán a ser virtuosos” : ley jurídica positiva penal y educación / Héctor H. Hernández – Todos los hombres desean la felicidad / Ignacio E. M. Andereggen – Justicia y derecho en Ley Natural y Derechos Naturales de John Finnis / Carlos I. Massini Correas – El itinerario antiguo y medieval de la negación nominalista de la metafísica / Mario Enrique Sacchi – Notas y comentarios -- Bibliografía