Miocene Phosphatization of Rocks From the Summit of Rio Grande Rise, Southwest Atlantic Ocean

Abstract

Phosphate is an essential nutrient and energy carrier for living organisms and a limiting nutrient for ocean productivity. On a long-term basis, the phosphorus cycle controls oceanic primary production and has a feedback mechanism with global climate, environment, and ecology (Elser et al., 2007;Follmi, 1996;Tyrrell, 1999). Marine phosphorites and phosphate-rich rocks are an important sink of P in the oceans (Follmi, 1996). Thus, determining the timing of the formation of phosphate-rich seafloor deposits can shed light on past climatic changes and the global P cycle.Although marine phosphorites have been more extensively studied in areas of high P and organic matter input to sediments from strong primary productivity along continental margins, significant phosphorite deposits also formed in more oxygenated low-organic-carbon environments at open-ocean seamounts, pla-

Reconstruction of the Paleo‐Ocean Environment Using Mineralogical and Geochemical Analyses of Mixed‐Type Ferromanganese Nodules From the Tabletop of Western Pacific Magellan Seamount

“…The presence of CFA indicates increased input of phosphorus. The input of phosphorus to the ocean during sea-level elevations occurs in two ways; vertical mixing (upwelling) and remineralizing inorganic P by primary productivity (Benites et al, 2020(Benites et al, , 2021. The Magellan Seamount cluster, the study area, was formed southward of the equator during the Cretaceous period (∼120 Ma) and moved northward according to the movement of tectonic plates; hence, the possible location at the time could have been in the equatorial high-productivity zone.…”

“…Therefore, during the mid-Miocene (19-16 Ma) phospha tization event, OSM9-1 would have already passed the equatorial high-productivity zone. During the mid-Miocene (19-16 Ma), when a phosphatization event occurred, the seawater temperature gradient between latitudes increased, accelerating ocean currents' circulation; various nutrients, including phosphates, were supplied to the sea surface using the enhanced upwelling, because of which the primary production would have increased rapidly (Benites et al, 2020(Benites et al, , 2021. Therefore, the OMZ was considerably expanded, and the OSF of the sediment at the tabletop of the Magellan Seamount rose closer to the surface.…”

A study of volcanic rocks and ferromanganese crusts through marine geophysical methods integration in the north portion of Cruzeiro do Sul Rift in the Rio Grande Rise

“…This report indicates the presence of pebbles of metamorphic rocks, mudstone, siltstone, pyroclastic, and pegmatitic rocks in smaller to almost absent concentrations. The substrate rocks supporting the FeMn crusts display basalt, carbonates, and phosphorates, or ironstone (Benites et al, 2020;Benites et al, 2021;Benites et al, 2022). Praxedes et al (2019) characterize the Cruzeiro do Sul Rift as a rotated block set separated by antithetic normal faults which extend until the acoustic basement.…”

Benthic megafauna habitats, community structure and environmental drivers at Rio Grande Rise (SW Atlantic)

“…Most of the knowledge about RGR geology was collected during the Deep-Sea Drilling Project (DSDP) in the mid-1980s (Baker, 1983) and just in the last ten years, more expeditions were made in this area. The genesis of Fe-Mn crust deposits is still being discussed (Benites et al, 2020(Benites et al, , 2021Mohriak et al, 2010;Ussami et al, 2013).…”