El tránsito Cretácico-Terciario en Beloc, Haitíregistro micropaleontológico e implicaciones bioestratigráficas.

Resumen

The section studied is located immediately south of the village of Beloc, in the Southern Peninsula of Haiti. Rack sequences of that locality have the distinctive stratigraphic characteristic of yielding a series that spans the transition from the Cretaceous to the Tertiary (K/T boundary), which is distinguished by a conspicuous marker bed composed of spherulites. The micropaleontologic data based on foraminifers indicate the presence of several important biozones charateristics of the boundary zone, namely the uppermost part of the Abathomphalus mayaroensis Zone, part ? of the Guembelitria cretacea Zone,and the Parvularugoglobigerina eugubina Zone, respectively. The calcareous nannoplanktons also yield transitional taxa that concur wdh the foraminiferal data, as they are indicative of the Micula prinsii Zone (uppermost Maastrichtian), as well as the lower part of NP1 or basal Danian. The absolute frequency of the different groups greatly diminish at the level that is assigned to the lowest Danian, which is coincident with the biotic crisis of the K/T boundary event. The dramatic decrease is particularly evident in the nannofossils, which are reduced by 1/100 to 1/400 of the assemblages recorded toward the end of the Maastrichtian. The relatively high frequency of Thoracosphaera spp.(up to 8 percent total), the predominance of heterohelicids, and the remarkable abundance of juvenile globotruncanids (about 50 percent) in theCretaceous materials seem to also indicate a very unstable planktonic ecosystem toward the end of the Maastrichtian.