Abstract:
Well-preserved and diverse assemblages of upper Campanian and Maastrichtian planktic foraminifera (PF) are compared from three ODP sites (Sites 1049, 1050 and 1052) along a 1300 m depth transect of Blake Plateau in the North Atlantic to develop a more reliable and higher resolution biostratigraphic scheme for subtropical latitudes. Integration of published calcareous nannofossil biostratigraphies and magnetostratigraphies enables refinement of age models and estimates of changes in sedimentation rates for each site, and affords more accurate age estimates for the biostratigraphic datum events. Special attention was dedicated to determining the stratigraphic distribution of the heterohelicid species of Pseudoguembelina and Planoglobulina, which are relatively abundant in low latitude Maastrichtian sediments. The lowest occurrence (LO) of Psg. palpebra is recorded in the lower PF Gansserina gansseri Zone and lower calcareous nannofossil CC24 Zone, and has proven to be a more reliable biomarker than Gansserina gansseri, which is very rare and sporadic at all three sites. Stratigraphically important PF events within in the upper part of the mid-Maastrichtian Racemiguembelina fructicosa Zone include the LO of Plg. acervulinoides followed by the LO of Plg. multicamerata. The LOs of Psg. hariaensis and a distinct morphotype of Rugoglobigerina can consistently be used to correlate the uppermost Maastrichtian interval of the Abathomphalus mayaroensis Zone at all three sites. However, Plummerita hantkenoides, which is recognized as a distinctive uppermost Maastrichtian biomarker in more nearshore settings, is absent at all three Blake Plateau sites and has not been found in any other deep-sea site. Observations from this study form the basis for proposing modifications to the standard Tethyan PF biozonation for the Maastrichtian Stage.