Analysis of 66 samples from DSDP Site 263 (Cores 263-4R-4 to 263-29R-4) reveals a unique faunal composition with a predominance of agglutinated taxa, many of them previously unrecorded from any other DSDP and ODP Indian Ocean sites. A total of 66 agglutinated and 31 calcareous taxa are documented and five new species are described: Hippocrepina gracilis n.sp., “Textulariopsis” elegans n.sp., Aaptotoichus challengeri n.sp., “Gaudryinopsis” pseudobettenstaedti n.sp. and “Gaudryina” cuvierensis n.sp. Three assemblages are recognized based on changes in the composition of dominant taxa and occurrences of stratigraphically important species: (1) a high-diversity Valanginian to Barremian Bulbobaculites-Recurvoides Assemblage (Cores 263-29R to -18R), comprised of numerous elongate agglutinated forms, rare nodosariids, and variable numbers of tubes and ammodiscids; (2) a moderately diverse Aptian to Albian Rhizammina-Ammodiscus-Glomospira Assemblage (Cores 26318R to -7R) with highly fluctuating numbers of the nominate taxa and Haplophragmoides, Trochammina, Verneuilinoides spp., and Vemeuilina howchini; (3) a very low diversity Albian or younger Assemblage (Cores 263-6R to -4R) containing sparse agglutinated foraminifera, rare nodosariids and rotaliids. We interpret the assemblages as shelf to lower slope and consider them to reflect a deepening palaeobathymetry as the Cuvier margin subsided after the initial breakup of East Gondwana during the Valanginian. Our interpretation is in sharp contrast with initial palaeodepth estimates of less than 100 m, as well as with original chronostratigraphic interpretations based on foraminifera and nannofossils which correlated the base of the recovered interval with the Aptian. The absence of many cosmoplitan forms, despite high diversity, suggests strong faunal differentiation in the Austral realm or endemisn within the Cuvier Basin during the Early Cretaceous.

A Valanginian to Barremian bathyal foraminiferal assemblage (118 taxa belonging to 51 genera) is documented from ODP Site 766, drilled near the foot of the Exmouth Plateau off northwest Australia. The majority of taxa are cosmopolitan species previously described from the boreal assemblages of northern Europe and the northern margins of the Tethys, but 32 taxa could not be assigned to previously described species and are left in open nomenclature. The chronostratigraphy of this section is based upon nannofossils, palynomorphs, and radiolarians. The foraminiferal succession is divided into four assemblages based on the first and last occurrences of characteristic benthic foraminifera: 1) An upper Valanginian Lenticulina ouachensis - Textularia bettenstaedti assemblage with Ammodiscus tenuissimus, Bulbobaculites sp., and Aaptotoichus clavellatus. The last occurrences of these taxa are observed near the transition between the Valanginian and Hauterivian. 2) A lower Hauterivian assemblage is characterized by Lenticulina heiermanni and Saracenaria forticosta. 3) An upper Hauterivian assemblage contains Planularia crepidularis, Patellina subcretacea, and Reinholdella hofkeri. A major faunal discontinuity is observed at the top of this assemblage between Cores 766A-32R and 766A-30R, probably associated with a depositional gap between the late Hauterivian and the Barremian. 4) The overlying Barremian assemblage is characterized by Gavelinella barremiana, Glomospira spp., and Pseudogaudryinella sp. This record enables long-distance comparisons of the stratigraphic ranges of benthic foraminiferal species in the austral bioprovince with their reported ranges in the North Atlantic region and the northern Tethys. Although the assemblages at Site 766 consist of ca. 74% cosmopolitan species, they differ from Tethyan assemblages in the rarity or absence of index taxa such as Praedorothia spp., Lenticulina nodosa and L. eichenbergi, as well as ornamented, palmate morphotypes such as Citharina spp., Flabellina spp., and Frondicularia spp. They differ from the typical boreal assemblages by the lack of diverse agglutinated taxa. As a result, benthic foraminiferal zonations established for the Lower Cretaceous of the northern Tethys and Tethyan DSDP sites could not be applied at Site 766. Taxonomic and biostratigraphic differences at Site 766 support the existence of a taxonomically distinct Early Cretaceous austral bioprovince.