Nanofósiles del límite Cretácico/Terciario cerca de Beloc (Haití): bioestratigrafía, composición de las asociaciones e implicaciones paleoclimáticas

Abstract

The Beloc Formation, (Southern Peninsula of Haiti) includes a well preserved record of the Cretaceous/Tertiary boundary materials with a distinct spherulithic layer interpreted as a result of the Chicxulub impact. A quantitative nannofossil study of four sections spanning the K/T boundary has led to identify the interval corresponding to the Micula murus/Nephrolithus frequens (CC25c/CC26a) Subzones and a thick Micula prinsii (CC26b) Subzone for the Upper Cretaceous materials. Also, the Subzone of Cruciplacolithus primus (CP1a) has been identified in the lowest Paleogene materials. Two intervals that are characterised by an in Aguado et al. / Journal of Iberian Geology 31 (2004) 9-24 10 crease in the relative proportions of Prediscosphaera stoveri and Ahmuellerella regularis, also show a parallel decrease in the warm water indicator Watznaueria barnesae. They occur whithin Subzone CC26b, and are interpreted as short periods of climatic cooling. Successive blooms of Thoracosphaera spp. and Neobiscutum are the most significant nannofossil events registered in the lower Tertiary materials. A small increase in Thoracosphaera spp. observed within the last centimeters of the uppermost Maastrichtian materials, just below the base of the spherulithic layer, may be interpreted as the result of a more stressed environment. Contrary to what is generally found in other sections from low palaeo-latitude regions, no Braarudosphaera bloom was observed at Beloc, and the presence of this taxon is only nominal. Rare and occasional occurrence of Biantholithus specimens (including B. sparsus) constitutes the only typically Tertiary taxa found above the spherulithic layer.