A total of 113 species belonging to 54 genera are recovered from a study of the Maastrichtian and Danian deposits in the Cerro Azul section of the Neuquén Basin, west‐central Argentina. Of these, 9 new genera, 38 new species and 28 species in open nomenclature are recorded. These form the basis of the present study and are listed below. Genera: Phelocyprideis gen. nov., Aleisocythereis gen. nov., Apatoleberis gen. nov., Mimicocythereis gen. nov., Castillocythereis gen. nov., Hysterocythereis gen. nov., Orthrocosta gen. nov., Petalocythereis gen. nov. and Sthenarocythereis gen. nov. Species: Cytherella saraballentae sp. nov., Cytherella semicatillus sp. nov., Paracypris bertelsae sp. nov., Paracypris imaguncula sp. nov., Argilloecia abnormalis sp. nov., Argilloecia concludus sp. nov., Argilloecia hydrodynamicus sp. nov., Bythoceratina cheleutos sp. nov., Phelocyprideis acardomesido sp. nov., Eucythere dinetos sp. nov., Krithe crepidus sp. nov., Cytheropteron hyperdictyon sp. nov., Cytheropteron bidentinos sp. nov., Cytheropteron translimitares sp. nov., Aversovalva glochinos sp. nov., Eucytherura stibaros sp. nov., Hemingwayella verrucosus sp. nov., Heinia prostratopleuricos sp. nov., Loxoconcha (s.l.) posterocosta sp. nov., Keijia circulodictyon sp. nov., Keijia kratistos sp. nov., Paramunseyella epaphroditus sp. nov., Munseyella costaevermiculatus sp. nov., Ameghinocythere archaios sp. nov., Aleisocythereis polikothonus sp. nov., Castillocythereis multicastrum sp. nov., Castillocythereis albertoriccardii sp. nov., Cythereis stratios sp. nov., Cythereis clibanarius sp. nov., Cythereis trajectiones sp. nov., Henryhowella (Wichmannella) praealtus sp. nov., Hysterocythereis paredros sp. nov., Hysterocythereis coinotes sp. nov., Hysterocythereis diversotuberculatus sp. nov., Orthrocosta decores sp. nov., Orthrocosta atopos sp. nov., Orthrocosta phantasia sp. nov. and Sthenarocythereis erymnos sp. nov. The nature of the fauna and aspects of its evolution are discussed.

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Biostratigraphic results obtained with a systematic study of the planktic foraminiferal assemblages recovered from Upper Cretaceous-Lower Paleogene strata (Turonian? to early Danian in age) of Deep Sea Drilling Program (DSDP) Site 356, São Paulo Plateau, are presented and discussed herein. Fifty-nine planktic foraminiferal species were identifi ed within the studied interval, enabling the identifi cation of 11 planktic foraminiferal zones (Turonian? to early Danian in age): Marginotruncana schneegansi, Dicarinella concavata, Dicarinella asymetrica, Globotruncanita elevata, Contusotruncana plummerae, Radotruncana calcarata, Globotruncanella havanensis, Pseudoguembelina palpebra, Abathomphalus mayaroensis, Pseudoguembelina hariaensis and Pα. An unconformity spanning at least 0.96 Ma could also be suggested within core 31 (Maastrichtian in age), due to the absence of the Racemiguembelina fructicosa Interval Zone from the studied section. High sedimentation rates were estimated within the Santonian (Dicarinella asymentrica Total-range Zone) and the uppermost Maastrichtian (Pseudoguembelina hariaensis Interval Zone) of DSDP site 356, while lower and more constant values were suggested for the Campanian-lower Maastrichtian interval (Globotruncanita elevata Partial-range Zone to Pseudoguembelina palpebra Interval Zone). The reliability in identifying the Contusotruncana plummerae Interval Zone (Campanian in age) in Cretaceous sections of the South Atlantic Ocean is confi rmed herein.

A total of 479 samples from five drill-holes of the Pelotas Basin were analysed. Despite the huge number of samples, only 98 specimens were recovered, belonging to nine families, 21 genera and 34 species (most in open nomenclature). Due to the paucity and poor preservation of this material, just seven taxa were identified or tentatively identified at the species level: Cytherella cf. C. araucana Bertels, Cytherelloidea spirocostata Bertels, Bairdoppilata triangulata Edwards, Actinocythereis indigena Bertels, Brachycythere gr. sapucariensis Krömmelbein, Wichmannella araucana Bertels and Wichmannella meridionalis Bertels. Four taxa could not even be identified at the generic level and are referred as "gen. et sp. indet.". Trachyleberididae and Cytherellidae were the most diversified and abundant families while Cytherella and Paracypris were the most diversified genera, with seven and four species, respectively. The K-Pg boundary in the Pelotas Basin is marked by a faunal change with the local disappearance of the genera Cytherelloidea, Argilloecia, Cythereis, Brachycythere, Pondoina and Rostrocytheridea, and the first local occurrence of Neonesidea?, Bairdoppilata, Ambocythere, Buntonia, Langiella?, Trachyleberis and Krithe. The genera Cytherella, Paracypris, Wichmannella and Actinocythereis are recorded in the Cretaceous as well as the Paleogene. This faunal study suggests a neritic marine environment for the analysed interval.