Geochemical Investigation of Sediments from the Brazil Basin and the Rio Grande Rise

Emelyanov, Emelyan M; Trimonis, E.S.

doi:10.2973/dsdp.proc.72.112.1983

Cited by 5 publications

(8 citation statements)

References 4 publications

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“…Organic carbon maxima in sediments from Deep Sea Drilling Project (DSDP) Site 516 in the RGR [18] coincide well with ages determined by magnetobiostratigraphy of 19.09 Ma and 15.5 Ma [114]. These organic carbon peaks reflect enhanced biological productivity in surface waters that exported high amounts of P to the RGR seabed that likely facilitated the phosphatization.…”

Section: History Of Phosphatization Of Fe-mn Crusts On the Summit Of Rgrsupporting

confidence: 62%

“…Once the volcanic activity ceased, thermal subsidence again took place and the islands were eroded and leveled by waves and currents as they subsided, creating the flat-topped edifice (guyot) characteristic of RGR's highest elevations of today. Since then, accumulation of pelagic sediment composed mainly by nannofossils and planktonic foraminifera with a small amount of terrigenous components has been the dominant sedimentation processes along RGR [18].…”

Section: Study Areamentioning

confidence: 99%

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Genesis and Evolution of Ferromanganese Crusts from the Summit of Rio Grande Rise, Southwest Atlantic Ocean

et al. 2020

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The Rio Grande Rise (RGR) is a large elevation in the Atlantic Ocean and known to host potential mineral resources of ferromanganese crusts (Fe–Mn), but no investigation into their general characteristics have been made in detail. Here, we investigate the chemical and mineralogical composition, growth rates and ages of initiation, and phosphatization of relatively shallow-water (650–825 m) Fe–Mn crusts dredged from the summit of RGR by using computed tomography, X-ray diffraction, 87Sr/86Sr ratios, U–Th isotopes, and various analytical techniques to determine their chemical composition. Fe–Mn crusts from RGR have two distinct generations. The older one has an estimated age of initiation around 48–55 Ma and was extensively affected by post-depositional processes under suboxic conditions resulting in phosphatization during the Miocene (from 20 to 6.8 Ma). As a result, the older generation shows characteristics of diagenetic Fe–Mn deposits, such as low Fe/Mn ratios (mean 0.52), high Mn, Ni, and Li contents and the presence of a 10 Å phyllomanganate, combined with the highest P content among crusts (up to 7.7 wt %). The younger generation is typical of hydrogenetic crusts formed under oxic conditions, with a mean Fe/Mn ratio of 0.75 and mean Co content of 0.66 wt %, and has the highest mean contents of Bi, Nb, Ni, Te, Rh, Ru, and Pt among crusts formed elsewhere. The regeneration of nutrients from local biological productivity in the water column is the main source of metals to crusts, providing mainly metals that regenerate rapidly in the water column and are made available at relatively shallow water depths (Ni, As, V, and Cd), at the expense of metals of slower regeneration (Si and Cu). Additionally, important contributions of nutrients may derive from various water masses, especially the South Atlantic Mode Water and Antarctic Intermediate Water (AAIW). Bulk Fe–Mn crusts from the summit of RGR plateau are generally depleted in metals considered of greatest economic interest in crusts like Co, REE, Mo, Te, and Zr, but are the most enriched in the critical metals Ni and Li compared to other crusts. Further investigations are warranted on Fe–Mn crusts from deeper-water depths along the RGR plateau and surrounding areas, which would less likely be affected by phosphatization.

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Section: History Of Phosphatization Of Fe-mn Crusts On the Summit Of Rgrsupporting

confidence: 62%

Section: Study Areamentioning

confidence: 99%

Genesis and Evolution of Ferromanganese Crusts from the Summit of Rio Grande Rise, Southwest Atlantic Ocean

et al. 2020

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“…10.1029/2020PA004197 12 of 24 and S2b, S2f, and S2g) and, less often, larger mollusk shells (Figures S2g and S2h). This is in accordance with the dominant type of sedimentation on RGR that took place since the Eocene being largely pelagic carbonates, a foraminifera-nannofossil ooze (Emelyanov & Trimonis, 1983;Florindo et al, 2015). EDS maps reveal the cement is CFA (Ca and P, Figures 4h and S2d), which is more frequently cryptocrystalline (crystals are too small to be distinguished).…”

Section: Formation Of Cement In Phosphorite Rocks and Lensessupporting

confidence: 80%

“…We can infer periods of stronger OMZ in the RGR in the early to middle Miocene from enhanced biological productivity and organic carbon peaks in the sediments. For example, DSDP site 516 sediment cores at RGR revealed enhanced biological productivity from 23.9 to 22.9 Ma based on the accumulation of foraminifera tests (Florindo et al., 2015) and organic carbon peaks at about 19.1 Ma and 15 Ma (Berggren et al., 1983; Emelyanov & Trimonis, 1983). In addition, stable C and O isotopes compositions (δ 18 O and δ 13 C) of the planktonic foraminifers and alkenones data all point to an incursion of a cold, nutrient‐rich intermediate water mass from high southern latitudes at ∼20.3 Ma in the RGR area, caused by more dynamic circulation in the early Miocene in the South Atlantic (Pagani et al., 2000).…”

Section: Resultsmentioning

confidence: 99%

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

Benites

Hein

Mizell

et al. 2021

Paleoceanog and Paleoclimatol

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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-

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“…On the Rio Grande Rise, biogenic carbonate sediments accumulated from Early Cretaceous to Holocene (Emelyanov and Trimonis, 1983).…”

Section: Sediment Seriesmentioning

confidence: 99%

Bottom sediments and near-bottom currents in the Southwestern Atlantic

Emelyanov

2015

Russian Geology and Geophysics

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On the basis of the author's data on the composition of sediments and seismic cross sections, together with literature data, the bottom topography was described and the main structural features of the top 10-100 m thick sedimentary sequence in the Southwestern Atlantic (Brazil Basin) were identified. The presence of a heavy northward flow of Antarctic bottom water (AABW) and its active erosive activity were confirmed. The AABW caused the erosion or redeposition of red pelagic clays and hemipelagic clays, which accumulated in the Brazil Basin in the Holocene and Pleistocene; the clays contain abundant redeposited Pleistocene diatoms and Neogene and Paleogene discoasters. In most of the sediment cores of the Brazil Basin, the red pelagic clays are of Pleistocene age. Contourites and sandy microlayers have been found in the sediments at the foot of the continental slope of South America; this is the effect of the Deep Western Boundary Current on the ocean floor. The AABW transfers Antarctic diatom species along the continental slope of South America to 10º-5º S. The presence of the Equatorial Midocean Channel with a relative depth of 149 m in the western pelagic equatorial part of the Atlantic was confirmed, and new channels, such as Vavilov and Akademik Ioffe, have been found. The AABW flows northward along the Equatorial Mid-Ocean Channel. Apparently, the Akademik Ioffe Channel is not a proper midocean channel. At 20º S (at a depth of 5000 m), Pleistocene diatomic (Ethmodiscus rex) ooze containing up to 74% amorphous SiO 2 was detected. On the Amazon-Mid-Atlantic Ridge profile, the AABW flows into the Guyana Basin through only one valley of the Nara Plain, with a depth of 4620 m. Near the Ceara Rise and on the Amazon Fan, no geologic traces of the AABW flow into the Guyana Basin were found. Near the Rio Grande Rise, the AABW might have appeared in the Eocene. The formation of the Vema Channel, which separates the Rio Grande Rise from South America, also began at that time. The AABW flows were the heaviest before the largest glaciations (particularly at isotopic stages 7/6 and 3/2).

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Geochemical Investigation of Sediments from the Brazil Basin and the Rio Grande Rise

Cited by 5 publications

References 4 publications

Genesis and Evolution of Ferromanganese Crusts from the Summit of Rio Grande Rise, Southwest Atlantic Ocean

Genesis and Evolution of Ferromanganese Crusts from the Summit of Rio Grande Rise, Southwest Atlantic Ocean

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

Bottom sediments and near-bottom currents in the Southwestern Atlantic

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