REVISED TAXONOMIC FRAMEWORK AND PHYLOGENY OF TURONIAN BISERIAL PLANKTONIC FORAMINIFERA

Cretaceous biserial planktonic foraminifera have been underutilized in biostratigraphic studies because of taxonomic confusion and inadequate documentation of their evolutionary and phylogenetic history. Recent efforts to develop an evolutionary classification of the biserial taxa have led to a radical revision of their species and genus level taxonomy. Foraminiferal assemblages from boreholes drilled as part of the Cretaceous Tanzania Drilling Program are ideal for testing proposed revisions to the Late Cretaceous biserial taxonomy and phylogeny because of the nearly continuous Cenomanian-Maastrichtian recovery and unusually good shell preservation. To investigate proposed species concepts and to clarify their identification, we have undertaken a quantitative approach to describing key characteristics of each species. In doing so we use SEM and X-ray images of well-preserved Cenomanian-Santonian biserial specimens, including Planoheterohelix moremani, Pl. postmoremani, Pl. globulosa, Pl. reussi, Protoheterohelix washitensis, Pr. obscura, Laeviheterohelix pulchra, Pseudotextularia nuttalli, Huberella praehuberi, and Hu. huberi. The study is based on over 200 specimens picked from Tanzania Drilling Program Site 31 as well as a few from IODP Site 463 and ODP Hole 1050C. In addition, new SEM images were taken of all available primary type specimens, enabling quantitative comparison with data collected from the core samples. The qualitative and quantitative observations to describe the Late Cretaceous biserial populations are not only useful for testing proposed taxonomic concepts, but also in helping to identify key features that allow for a clearer distinction between biserial species. This added resolution will help future bio- and chemostratigraphic studies.