The evolution of Late Cretaceous deep-ocean circulation in the Atlantic basins: Neodymium isotope evidence from South Atlantic drill sites for tectonic controls

The South Atlantic basins during the Late Cretaceous were characterized by overall expansion and the opening of deep-water connections, eventually permitting deep-ocean circulation with the Indian and North Atlantic basins. However, the evolving pattern of deep-ocean circulation through the Late Cretaceous, particularly the timing of the connection between various basins, is not well constrained. Here we present new neodymium isotope data from five sites in the South Atlantic to reconstruct water mass chemistry and circulation patterns. The new data combined with previously published data indicate deep-water formation occurred in the high-latitude South Atlantic throughout the Late Cretaceous. Tectonic boundaries restricted the circulation of Southern Component Water until the opening of the Equatorial Atlantic Gateway and the subsidence of Rio Grande Rise between approximate to 79 and 75 Ma. Subsidence of these features permitted the northward flow of Southern Component Water, which then ventilated the deep North Atlantic. Nd isotope data indicate that the South Atlantic water column during the Cenomanian to Santonian was vertically stratified between intermediate and deep waters, with increased mixing evident during the Campanian and Maastrichtian.