Chronostratigraphy, paleotemperature change, and mosasaur paleoecology at the late Cretaceous South Atlantic margin, Bentiaba, Angola

The delta13C stratigraphy derived from marine bivalve shells, including fossils belonging to Inoceramus, for Cenomanian-Maastrichtian marine strata at the coast of southern Angola is anchored by an intercalated basalt with a whole rock 40Ar/39Ar radiometric age of 84.6 +/- 1.5 Ma. This is the first African stable carbon isotope record correlated to significant events in the global carbon cycle spanning the Late Cenomanian to latest Campanian. A positive ~ 3‰ excursion observed in bivalve shells below the basalt indicates the Cenomanian-Turonian Boundary Event at 93.9 Ma, during Oceanic Anoxic Event 2. Additional excursions above the basalt are correlated to patterns globally up to the Campanian-Maastrichtian Boundary, which occurred during a period of global cooling. Bench 19, a single horizon that has produced a diverse assemblage of fossil vertebrates, is constrained to the Campanian-Maastrichtian Boundary Events and was deposited between 72.8 to 71.5 Ma. The age of the basalt ties the Bentiaba section to a pulse of Late Cretaceous magmatic activity around the South Atlantic and significant tectonic activity in the African continent. Subsidence and sedimentation rates are lower in southern Angola than concurrent rates elsewhere along the western coast of Africa and are consistent with observations of a relatively thin Late Cretaceous sequence in the offshore Namibe Basin.;The delta18O values derived from bivalves indicate a long-term increase from -4.5‰ in the Late Cenomanian to -1.2‰ in the Late Campanian. Assuming a constant oceanic delta18O value, the 3.3‰ increase reflects cooling of the shallow marine environment at Bentiaba by ~16°. A positive ~2‰ shift at the Cenomanian-Turonian Boundary is observed in non-inoceramid bivalves delta18O values from -4.5‰ to -2.4‰. Early to Late Campanian inoceramids yield the highest delta18O values, between -1‰ to -2‰, and are offset by about +1‰ from published records for benthic foraminifera and bathyal Inoceramus at Walvis Ridge. This offset in delta18O values indicates a temperature difference of ~5° between coastal and deeper water offshore Angola. The stratigraphic distribution of marine amniotes at Bentiaba coincides with cooler temperatures inferred from delta18O values derived from bivalves. Bench 19 has produced a diverse marine amniote fauna at the Campanian-Maastrichtian Boundary, during a period of increased global ocean connectivity and circulation of cooler productive high latitude-derived waters.;delta13C values of mosasaur and plesiosaur tooth enamel range from -5 to -16 /, showing a negative trend with increasing body size. This pattern is similar to that observed in marine mammals, in which more negative delta13C values correlate with deep diving behavior and foraging habitats distant from the shoreline. Specimens of the mosasaur Globidens yielded values more negative than expected for their body size, and are interpreted as being due to a diet consisting of lower trophic level prey relative to other marine amniotes examined in this study. Prognathodon specimens yielded delta 13C values between -5 to -14 /, and the large range in values reflects taxonomic differences or varied diets due to habitat partitioning among individuals. The diversity of niches utilized by large bodied marine amniotes implied by these results suggests a high level of productivity during the Late Cretaceous across a range of habitats along the coast of Angola.