Size-related isotopic trends in Maastrichtian planktic foraminifera of DSDP Core 44-390A (Appendix B)

Stable isotope analyses were performed on ontogenetic dissections of four taxa of low latitude Late Cretaceous planktonic foraminifera from DSDP Hole 390A. The species studied include Planoglobulina acervulinoides, Planoglobulina multicamerata, Pseudoguembelina palpebra, and Racemiguembelina fructicosa. Delta18O and delta13C data indicate a deeper surface water paleohabitat for P. multicamerata than the other three taxa, and ontogenetic increases in delta18O values suggest all these taxa underwent vertical migrations from shallow to deeper surface waters. Changes in delta13C values through ontogeny include sharp increases in delta13C composition in the juvenile size intervals, a decrease in the rate of delta13C change through intermediate size intervals, and reversals to a negative trend in delta13C values in terminal size intervals. The intermediate and terminal growth changes in delta13C signals are similar to ontogenetic trends observed in some extant and Paleogene planktonic foraminifera and may result from decreasing metabolic rates through ontogeny or endosymbiont digestion prior to gametogenesis. The ontogenetic delta13C increases of 1.04?, 0.76?, 0.83?, and 0.77? in R. fructicosa, P. palpebra, P. acervulinoides, and P. multicamerata, respectively, may indicate the presence of photosymbionts. However, our review and critique of the current literature discussing photosymbiont effects on stable isotope values in living and fossil planktonic foraminifera suggests that conclusions regarding the presence of photosymbionts in fossil taxa may be more equivocal than previously thought.

Mineral and chemical compositions of sedimentary and volcano-sedimentary rocks drilled in DSDP Legs 43 and 44

Sedimentary cover on the bottom of the Northwest Atlantic Ocean is underlain by Late Jurassic - Cretaceous tholeiite-basalt formation. It consists of come sedimentary formations with different lithologic features and age. Their composition, stratigraphic position and, distribution are described on materials of deep-sea drilling. Mineralogical and geochemical studies of DSDP Leg 43 and Leg 44 holes lead to new ideas about composition and genesis of some sediment types of and their associations. High metal contents in the chalk formation of black clays on the Bermuda Rise probably result from exhalations. Connection of red-colored and speckled deposits with hiatuses in sedimentation is shown. Main stages of geological history of the North American Basin are reflected in accumulation of the followed formations: ancient carbonate formation (Late Jurassic - Early Cretaceous), formation of black clays rich in organic matter (Cretaceous), formation of speckled clays (Late Cretaceous), siliceous-clayey turbidite formation (Eocene), hemipelagic and pelagic clayey formation (Neogene), and terrigenous turbidite formation (Pleistocene).

Early Maastrichtian stable isotopes: changing deep water sources in the North Atlantic?

We propose that the observed short-term stable isotope fluctuations reflect changes in high- and low-latitude intermediate to deep water sources, based on a high-resolution stable isotope record of planktic and benthic foraminifera from the Early Maastrichtian (~71.3 to ~ 69.6 Ma) of Blake Nose (DSDP Site 390A, North Atlantic). Sources of these waters may have been the low-latitude eastern Tethys and high-latitude North Atlantic. Changes in intermediate to deep water sources were probably steered by eccentricity-controlled insolation fluctuations. Lower insolation favored the formation of high-latitude deep waters due to positive feedback mechanisms resulting in high-latitude cooling. This led to a displacement of low-latitude deep waters at Blake Nose. Higher insolation reduced intermediate to deep-water formation in high latitudes, yielding a more northern flow of low-latitude deep waters.