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Geological Society, London, Special Publications; 2001; v. 183; p. 131-148;
DOI: 10.1144/GSL.SP.2001.183.01.07
© 2001 Geological Society of London

Geochemistry of the Cretaceous-Tertiary boundary at Blake Nose (ODP Leg 171B)

F. Martínez-Ruiz1, M. Ortega-Huertas2, D. Kroon3, J. Smit4, I. Palomo-Delgado2 & R. Rocchia5

1 Instituto Andaluz de Ciencias de la Tierra, CSIC-Universidad de Granada, Facultad de Ciencias, Avda. Fuentenueva s/n, 18002 Granada, Spain fmruiz{at}goliat.ugr.es
2 Departamento de Mineralogía y Petrología, Facultad de Ciencias, Universidad de Granada, Avda. Fuentenueva s/n, 18002 Granada, Spain
3 Department of Geology and Geophysics, University of Edinburgh, Grant Institute, West Mains Road, Edinburgh EH9 3JW, UK
4 Department of Sedimentary Geology, Vrije Universiteit, 1081 HV Amsterdam, Netherlands
5 Centre des Faibles Radioactivités, Laboratoire CEA-CNRS, 91198 Gif-sur-Yvette Cedex, France

The Cretaceous-Tertiary (K-T) boundary at Blake Nose, in the NW Atlantic, is recorded by a coarse, poorly graded and poorly cemented layer mostly consisting of green spherules that are mainly composed of smectite. Geochemical patterns across the boundary are governed by the source material of the spherule bed and postdepositional processes. The chemical composition and the nature of this bed indicate that it derived from melted target rocks from the Chicxulub impact structure. Ir and other typical extraterrestrial elements do not present significant enrichments, which suggests that the spherule bed material derived from crustal rocks. Ir instead reaches its highest concentration in the burrow-mottled calcareous ooze above the spherule bed, suggesting that it is associated to the finest fraction deposited after the target-rock-derived material. Only the Ni and Co content show slight enrichments within the upper part of the spherule layer, although most of the trace element profiles resulted from diagenetic alteration. During the alteration of glass to smectite, the concentrations of certain trace elements, such as the rare earth elements, were severely changed. In addition, oxygen-poor conditions also led to the remobilization of redox-sensitive elements, which show enhanced concentration at the top or above the spherule bed. Diagenetic remobilization may have also affected the Ir concentration.





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Review of the mineralogy of the Cretaceous-Tertiary boundary clay: evidence supporting a major extraterrestrial catastrophic event
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