LATE MAASTRICHTIAN-EOCENE BENTHIC FORAMINIFERA OF BRAZILIAN MARGINAL BASINS THE WESTERN SOUTH ATLANTIC

<jats:title>Abstract</jats:title> <jats:p>We present a detailed taxonomy of late Maastrichtian through Eocene benthic foraminifera from the southwest Atlantic Ocean, with a discussion on their paleogeographic and paleobathymetric distributions and assemblages across the Cretaceous/Paleogene and Paleocene–Eocene boundaries. The taxonomy of faunas from the Brazilian marginal basins has not yet been broadly compared with that of open ocean deep-sea taxa over this time. Here we, for the first time, compare continental margin and open ocean assemblages by integration of data from ten industry wells along the Brazilian margin with data from DSDP Sites 356 and 20 (Hole 20C).</jats:p> <jats:p>Maastrichtian through upper Paleocene assemblages of the deep-water Velasco-type, dominated by calcareous taxa (e.g., Stensioeina beccariiformis, Nuttallides truempyi, Cibicidoides hyphalus, Cibicidoides velascoensis), are most abundant at the most distal sites. In the marginal basins, this Velasco-type assemblage occurs as a minor component associated with flysch-type assemblages dominated by agglutinated taxa with mostly non-calcareous cement (e.g., the genera Rhizammina, Bathysiphon, Nothia, Haplophragmoides, Cribrostomoides,and Psammosiphonella).</jats:p> <jats:p>During the Eocene, differences between the distal and marginal assemblages decreased: most Brazilian marginal basins assemblages changed from agglutinated-dominated to calcareous-dominated, except in the Campos basin, where agglutinated forms dominated until the late Eocene. The most common species in the Eocene calcareous assemblages are Globocassidulina subglobosa, Nuttallides truempyi, Cibicidoides eocaenus, Cibicidoides havanensis, Planulina costataand Paralabamina lunata. At the open ocean sites, calcareous-dominated assemblages persisted across the Paleocene–Eocene boundary. The Benthic Extinction Event (BEE) at the base of the Eocene was recorded in both regions, although it was most severe at the open ocean sites. In the marginal basins the BEE was also reflected in a major turnover from agglutinated to calcareous assemblages, possibly due to the associated increased siliciclastic input that led to margin progradation and shallowing of the carbonate compensation depth (CCD) in some of the marginal basins.</jats:p>