LATE MAASTRICHTIAN FORAMINIFERAL POPULATION DYNAMICS AND THEIR RELATIONSHIP TO PARALLEL STABLE ISOTOPIC MEASUREMENTS

By measuring stable isotopic ratios in parallel with foraminiferal population counts across cyclic intervals in the upper Maastrichtian of Ocean Drilling Program Site 1050, we have tested conclusions regarding the species-level paleoecology and short term oceanographic variability within a greenhouse ocean. During the Maastrichtian Site 1050 was located at ~30°N latitude in the western North Atlantic. The Maastrichtian section shows dark-light color alternations that have been attributed to precessional cycles. In a previous study across the most prominent Maastrichtian cycles, light colored intervals were found to be associated with relatively high productivity, relatively cool temperatures, and higher relatively abundances of Heterolix spp. and Globigerinelloides spp.; darker intervals were associated with relatively low productivity, relatively warm temperatures, and higher relative abundances of Globotruncana spp. and Pseudoguembelina spp.

Preliminary results suggest these relationships break down in an interval where cyclicity is less dramatic. Across low amplitude cycles in a younger interval from the same hole, we have found that light colored intervals are associated with the highest d¹³C values for Heterolix globulosa, and Rugoglobigerina rugosa consistent with high relative productivity in these intervals. However, the largest variations in d¹³C values are seen in Pseudoguembelina palpebra, and these values show no apparent relationship to cyclic color changes. Further, whereas bulk carbonate and H. globulosa have d¹⁸O values that suggest the light intervals were relatively cool, d¹⁸O values of the presumed surface dwellers R. rugosa and P. palpebra suggest, if anything, the opposite. Finally, most taxa studied have their peak abundances in a sample from a relatively light interval, but not in all samples from light interval. These results demonstrate that neither the local water column nor planktic foraminiferal distributions responded in a consistent fashion to Milankovitch-scale forcing.  With further work on this interval, we believe we will find that certain taxa were relatively abundant during either high or low productivity intervals and that the complexity seen is due in part to variation in the surface mixed layer being out of phase with variation deeper in the water column.