Composition and Origin of Phosphorite Deposits of the Blake Plateau

Manheim, Frank T.; Pratt, Robert G.; McFarlin, Peter F.

doi:10.2110/pec.80.29.0117

Cited by 29 publications

(22 citation statements)

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“…Shallower crusts may be more phosphatized because they experience higher phosphate concentrations during phosphatization than deeper crusts, and they may contain higher amounts of carbonate debris that can be easily replaced by CFA since they are closer to primary productivity and associated biogenic particle flux. Similar mixed Fe-Mn phosphorite pavements occur along the Blake Plateau in the northwest Atlantic Ocean [61] at comparable depths (500-800 m).…”

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

confidence: 59%

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

confidence: 59%

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

et al. 2020

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“…Almost all were either weathered, diagenetically altered, or of questionable age. Most phosphorites contain more than one generation of apatite, for example as authigenic pelloids and diagenetic cements (Ganison et nl., 1990;Summerhayes and McArthur, 1990;Manheim et al, 1980). The microsampling technique of Carpenter et a\.…”

Section: Dating Episodes Of Phosphogenesismentioning

confidence: 99%

Recent trends in strontium isotope stratigraphy

1994

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An introduction to Sr‐isotope stratigraphy can be obtained from several recent reviews (Elderfield, 1986; Veizer, 1989; McArthur, 1991, 1992a). The purpose of this article is not to repeat these reviews but to give to those not expert in the field, but who may be prospective users, a summary of aspects of the method not covered elsewhere, and some examples of recent applications of the technique and the problems that affect it. Highlighting problems inevitably means highlighting the publications in which they occur; I hope the authors will forgive me for spotlighting their work. Neither is this article intended to be a review of all that has been written on the use of Sr isotopes in low‐temperature geochemistry; it concentrates on their use in stratigraphy and dating, rather than how they may be used to elucidate geochemical processes. Many excellent papers are thereby excluded from consideration. Implicit in this article is the view that the successful application of strontium isotope stratigraphy requires an application of good methodology in both geochemistry and stratigraphy.

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“…Many mechanisms have been suggested for the formation of marine phosphorites, including : inorganic precipitation from seawater (Kazakov, 1937;Sheldon, 1980) or porewater (Burnett, 1977;Baturin, 1982;Froelichetal., 1988); replacement of carbonates (Ames, 1959;Kennedy & Garrison, 1975a,b;Manheim et al, 1975Manheim et al, , 1980McArthur et al, 1980); phosphatization of faecal pellets (d'Anglejan, 1967); formation of mollusc kidney stones (Doyle et at., 1978); and mineralization of bacteria (Cayeux, 1936;O'Brien et al, 1981;Soudry & Champetier, 1983;Zanin et al, 1985). With the possible exception of a molluscan origin, these different mechanisms are not necessarily mutually exclusive but, in many cases, merely represent different manifestations of the same phosphogenic processes.…”

Section: Phosphogenic Processesmentioning

confidence: 99%

Sedimentology, geochemistry and origin of phosphatic chalks: the Upper Cretaceous deposits of NW Europe

Jarvis

1992

Sedimentology

100

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Santonian‐Lower Campanian and Lower Maastrichtian phosphatic chalks in northern France, southern England and Belgium are Europe's largest sedimentary phosphatc deposits. The stratigraphy, sediment‐ology, petrography, mineralogy and geochemistry of the lithofacies are reviewed and new data presented. Depositional and diagenetic models for phosphatic chalk deposits are developed using published experimental work and from observations of modern high‐ and low‐productivity phosphogenic systems. It is concluded that phosphatic chalks were deposited in well‐oxygenated, current‐swept environments. Phosphatization required a delicate balance to be maintained between moderate organic carbon and carbonate sedimentation rates, reduced bulk sediment accumulation rate and an enhanced rate of bioturbation. Precipitation of carbonate‐fluorapatite (francolite) accompanied the bacterially mediated decomposition of organic matter, occurring within centimetres of the sediment‐seawater interface, and taking place preferentially within microbial bodies and coatings. In addition to the organically derived component, pore water phosphate levels were enhanced by phosphate absorbed on ferric oxyhydroxides which was liberated during iron reduction. Mineralization was probably a dominantly post‐oxic process, but occurred in a thick sediment mixed layer in which marine organic matter was undergoing intense mixed aerobic and anaerobic microbial degradation. Phosphogenesis occurred predominantly on the NE margins of the Anglo‐Paris Basin where shallower sea floors and suitable palaeoceanographic conditions prevailed. Phosphogenic episodes were limited by sea level fluctuations'which controlled the effectiveness of the erosional currents that formed and maintained the phosphatic basins and may have stimulated local productivity.

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Composition and Origin of Phosphorite Deposits of the Blake Plateau

Cited by 29 publications

References 0 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

Recent trends in strontium isotope stratigraphy

Sedimentology, geochemistry and origin of phosphatic chalks: the Upper Cretaceous deposits of NW Europe

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