RECOVERY STRATEGIES AND PALEOENVIRONMENTAL CHANGES ACROSS THE CRETACEOUS-PALEOGENE BOUNDARY AND DANIAN AT SOUTH ATLANTIC LOW LATITUDES: THE FORAMINIFERAL RECORD

Two Cretaceous-Paleogene (K/Pg) boundary sections in the northern South Atlantic (the Poty section, and offshore Campos basin, in NE and SE Brazil, respectively) yield an abundant foraminiferal record which demonstrate the sequence of events which happened across the boundary transition in low-latitudes. A clear community shift in the benthic foraminifera is observed, which is consistent with a sharp sea-level drop, in the order of magnitude of 100 to 300m, across the boundary transition, which has been similarly recorded elsewhere. Maastrichtian assemblages comprised complex deep-slope dwellers of mixed trophic structure, dominated by well-diversified infaunal detritivores with variable numbers of epifaunal/shallow infaunal morphotypes and epifaunal suspension feeders. These were replaced in the Danian by non-specialized shelf-upper slope dwelling assemblages, dominated by epifaunal/shallow infaunal active herbivores/detritivores, which are probably opportunistic immigrant forms adapted to decreased levels of particulate organic matter in the substrate. Three main dwarf-size planktonic foraminifera lineages are characteristic of the Danian, which jointly gave rise to all the subsequent Globigerinida families: (i) the microperforate, non-spinose, Guembelitria-Woodringina-Chiloguembelina (Guembelitriidae) lineage; (ii) the cancellate, spinose, Eoglobigerina-Parasubbotina-Subbotina (Globigerinidae) lineage; and (iii) the cancellate, non-spinose, Praemurica (Globorotaliidae) lineage, the last two evolved from a Hedbergella stock. The nearly coeval main diversification/radiation episodes among these early lineages, which give rise to a number of other dwarf-size opportunistic forms, are evidence of parallel evolutionary trends. Common patterns and processes underlie these events, most probably induced by major changes in oceanic water-masses as environmental conditions progressively improved, in the aftermath of the K/Pg mass-extinction event. The episodes of maximum radiation appear to be coeval with the progressive recovery of the surface water productivity and the oceanic carbon cycle, coupled with expanded surface-water oligotrophic settings, and the return to background oceanic conditions similar to those observed in the latest Cretaceous.