Maastrichtian foraminiferal and paleoceanographic changes on Milankovitch timescales

Milankovitch-scale alternations in Maastrichtian hemipelagic strata from Ocean Drilling Program Hole 1050C (Blake Nose) provide a natural experiment of paleoceanography and foraminiferal paleoecology in a tropical/subtropical greenhouse ocean. Cycles are 30–50 cm thick and thought to reflect the ∼21 kyr precessional cycle. High planktic δ18O values are correlated with high planktic but low benthic δ13C values, indicating that cooler and/or more saline surface waters were associated with higher productivity. High-productivity intervals are also characterized by high Ca concentrations; enrichment in feldspar and kaolinite; and high relative abundance of Heterohelix spp., Globigerinelloides spp., and Laeviheterohelix glabrans. Conversely, low-productivity intervals have low planktic δ18O values; high Fe and Ti concentrations; enrichment in quartz, illite, and chlorite; and relative increases in Globotruncana spp. and Pseudoguembelina spp. Potential forcing mechanisms for observed covariation include cyclic variation in water column stratification, variation in continental nutrient fluxes, and changes in the intensity of upwelling.