Cretaceous calcareous nannofossil biostratigraphy of Sites 761, 762 and 763, Exmouth and Wombat Plateaus, northwest Australia

Abstract

Together, these sites contain an apparently complete, expanded Aptian-Maestrichtian record. Data indicate that traditional middle and Upper Cretaceous nannofossil biozonations are not entirely applicable in this region. Relative ranges of key Cretaceous nannofossil markers in the eastern Indian Ocean and in sections from Europe and North Africa are compared. The authors have determined which previously used events are applicable, and which additional markers have biostratigraphic utility in this region. Significant differences in Campanian-Maestrichtian assemblages exist between the more northern Site 761 and Sites 762 and 763. Such differences are surprising, considering that these sites are only separated by 3° of latitude. This is interpreted as marking a strong thermal gradient over the Exmouth Plateau region. Other results include the recovery of an expanded Albian-Cenomanian sequence containing a mixture of Austral and Tethyan floras, which will enable correlation of biozonations established for these two realms; the recovery of two condensed but apparently complete Cenomanian-Turonian boundary sections; correlation of Upper Cretaceous calcareous nannofossil biostratigraphy with magneto- and foraminifer stratigraphy; and correlation of portions of the Barrow Group equivalents to the Berriasian and Valanginian stages. -from Authors