Eocene to Miocene U‐Pb Geochronology Evolution of the Rio Grande Rise, Southwestern Atlantic: A Paleoceanographic Approach

Abstract

The Rio Grande Rise (RGR) is a major submarine feature in the South Atlantic that plays an important role in regional oceanographic dynamics. This study presents new U‐Pb geochronology of sedimentary rocks from the RGR, offering direct age constraints on carbonate and apatite embedded within Fe‐Mn crusts and associated foraminifera fossils. Samples were analyzed using high‐patial resolution geochronological techniques to establish a comprehensive temporal framework from the Eocene to the Miocene. Our results reveal distinct stages of geological evolution of the RGR. In the Eocene (48.1 ± 0.8/1.4 Ma; 2s), the RGR was marked by a shallow carbonate platform with local areas submitted to subaerial exposure and the presence of Larger Benthic Foraminifera (LBF). In the Oligocene (31.5 ± 0.9/1.9 Ma; 2s), carbonate precipitates infilled pores of previously formed Fe‐Mn crusts, possibly during a period of tectonic subsidence. In the late Oligocene‐early Miocene (21.0 ± 2.0/2.0 Ma; 2s), we identified an episode of phosphatization associated with global changes in marine circulation. Finally, in the Miocene (15.6 ± 1.6/3.0 Ma; 2s), the presence of planktic foraminifera indicates pelagic, open‐marine depositional conditions over the RGR, consistent with its regional subsidence history. These findings enhance the understanding of the geological history of the RGR, its role in shaping South Atlantic oceanic circulation, and provide new insights on Fe‐Mn crust formation and phosphatization events in the region.