Distribution of and hydrographic controls on ferromanganese crusts: Tropic Seamount, Atlantic

Yeo, Isobel; Howarth, Sarah A.; Spearman, J.; Cooper, Alan K.; Crossouard, N.; Taylor, Joan E.; Turnbull, M.; Murton, Bramley J.

doi:10.1016/j.oregeorev.2019.103131

Cited by 22 publications

(10 citation statements)

References 31 publications

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“…Compared with loose sediments, transitional zone deposits experience a lower degree of mobilisation on seamount slopes. Similar observations have been presented by Yeo et al 25 . All the lithotypes in this study are shown in Fig.…”

supporting

confidence: 92%

“…Intense topographical changes on the slope, such as landslides, slope collapse and volcanic activity (which ceased in the Late Cretaceous in this case) on intraplate seamounts 10,42 , play a role in clearing deposits from seamount slopes and burying old deposits on slopes 25 . After past deposits have been removed, the seamount flank would consist exposed rock and would eventually experience build-up of new deposits.…”

Section: Resultsmentioning

confidence: 94%

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Depositional patterns constrained by slope topography changes on seamounts

Yan

Yang

et al. 2020

Sci Rep

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Slope topography is known to control the spatial distribution of deposits on intraplate seamounts; however, relatively little is known about how slope topography changes constrain those depositional patterns. In this study, we analyse data on four lithotypes found on seamount slopes, including colloidal chemical deposits comprising mainly cobalt-rich crusts, and examine the relationships between the spatial distribution of these lithotypes and current slope topography. We use these relationships to discuss depositional patterns constrained by slope topography changes. Some depositional units in drill core samples are interpreted to have resulted from past topographic changes that created the current slope topography. Two or more types of deposits that accumulated at the same location implies that the slope topography changed over time and that the depositional patterns on seamount slopes are constrained by changes in slope topography.

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supporting

confidence: 92%

Section: Resultsmentioning

confidence: 94%

Depositional patterns constrained by slope topography changes on seamounts

Yan

Yang

et al. 2020

Sci Rep

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“…Eroded botryoids of the top surface of the second generation in some samples corroborated this erosional process. Bottom currents of more than 0.2 m/s may be capable of eroding Fe-Mn crust surfaces [53]. The prevalence of columnar and mottled texture is related to a higher amount of biogenic particle input that constrains or interrupts the formation of laminations [54].…”

Section: Two Generations Of Fe-mn Crusts On Rio Grande Risementioning

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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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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“…This is consistent with reported values for Fe‐Mn crusts surface scrapes from the Atlantic (Abouchami et al, 1999; Frank et al, 2002, 2003; Muiños et al, 2008). There is a systematic trend toward less radiogenic values with increasing water depth of the samples (Figure 4), which relates to erosive conditions on the summit of Tropic Seamount (Yeo et al, 2019) and loss of the most recent, more radiogenic part of the record in some samples.…”

Section: Resultsmentioning

confidence: 92%

Development of a Correlated Fe‐Mn Crust Stratigraphy Using Pb and Nd Isotopes and Its Application to Paleoceanographic Reconstruction in the Atlantic

Josso

Horstwood

Millar

et al. 2020

Paleoceanog and Paleoclimatol

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Eight ferromanganese crust samples spanning the complete depth range of Tropic Seamount in the northeast Atlantic were analyzed for Pb and Nd isotopes to reconstruct water mass origin and mixing over the last 75 Ma. Pb isotopes were determined by laser ablation multicollector inductively coupled plasma mass spectrometer (LA-MC-ICP-MS), which enables the rapid production of large, high spatial resolution data sets. This makes it possible to precisely correlate stratigraphy between different samples, compare contemporaneous layers, and create a composite record given the abundance of hiatuses in crusts. Pb and Nd isotope data show the influence of various oceanic and continental end-members in the northeast Atlantic Ocean. This reflects its evolution from a restricted, isolated basins in the Late Cretaceous with influxes from the Tethys Ocean, to an increasingly well-mixed, large-scale basin, with a dominant Southern Ocean signature until the Miocene. Less radiogenic Nd isotope signatures suggest Labrador Sea Water influenced the northeast Atlantic basin as early as 17-15 Ma, flowing through a northern route such as the Charlie-Gibbs Fracture Zone. Pb and Nd isotopes highlight the increasing influence of Saharan eolian dust input about 7 Ma, imparting a less radiogenic excursion to the binary mixing between North Atlantic water masses and riverine discharge from West and Central Africa. This highlights the influence of eolian dust input on the open ocean Pb and Nd budget and supports an early stage of North African aridification in the Late Miocene. This signature is overprinted about 3 Ma to the present by a strong North Atlantic Deep Water signature following the onset of Northern Hemisphere glaciation. This difference in residence time is recognized within the regional Nd isotope signature of water masses that influence different oceanic basins. For example, newly formed North Atlantic Deep Water (NADW) has a signature of −13.5 ƐNd (deviation of the determined 143 Nd/ 144 Nd ratio from the chondritic uniform reservoir CHUR in parts per 10,000) that originates from the mixing of Labrador Sea Water

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Distribution of and hydrographic controls on ferromanganese crusts: Tropic Seamount, Atlantic

Cited by 22 publications

References 31 publications

Depositional patterns constrained by slope topography changes on seamounts

Depositional patterns constrained by slope topography changes on seamounts

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

Development of a Correlated Fe‐Mn Crust Stratigraphy Using Pb and Nd Isotopes and Its Application to Paleoceanographic Reconstruction in the Atlantic

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