The palaeo-ecology and biostratigraphy of foraminiferal, radiolarian and diatom assemblages have been studied through the upper Aptian to Maastrichtian sedimentary succession of the Sergipe Basin, northeastern Brazil. The systematic taxonomy of the microfauna studied is documented and completely revised. Palaeo-environmental models, mostly derived from micropalaeontological and sedimentological criteria, are proposed for the distribution of the foraminiferal morphogroups. The palaeogeographic reconstruction of the studied area, from the upper Aptian to Maastrichtian, is presented. A refined microbiostratigraphic zonation scheme, based on all sections studied, is proposed and primarily defined for regional application. The composition and distribution patterns of the foraminiferal assemblages (diversity and abundance of morphogroups) are shown to be a direct response to overall palaeoceanographic conditions and to community strategies of exploitation of the trophic resources in the microhabitats. The foraminifera recovered - from the oldest, late Aptian, marine sediments reveal a characteristic Tethyan affinity and suggest that this area had at least minimal surface water exchange with low latitude central North Atlantic-western Tethyan bioprovinces, even possibly at intermediate (epi- to mesopelagic) water depths.

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