Formation and Evolution of Phosphorite Grains and Nodules on the Namibian Shelf, From Recent to Pleistocene

Baturin, G. N.

doi:10.2110/pec.00.66.0185

Cited by 28 publications

(36 citation statements)

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“…6A). The CFA occurs as elongate pods up to 1 lm in length similar in texture to Holocene CFA observed off Walvis Bay (Baturin, 2000). The dolomite occurs as submicrometer-sized crystals that together form 10 lm spherical clusters or pods (Fig.…”

Section: Cementation Of Pan Sedimentsmentioning

confidence: 53%

Holocene evolution of the Anichab Pan on the south‐west coast of Namibia

Compton¹

2006

Sedimentology

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Coastal sediment-filled depressions (pans) are one of the few areas that contain Quaternary records of sea-level and palaeoenvironmental change along the western margin of southern Africa. Anichab is a 128 km 2 salt-encrusted pan on the hyper-arid southern coast of Namibia with an emergent, well-preserved and in-place mid-Holocene mollusc assemblage. The molluscs are typical of subtidal sands on the sheltered side of offshore islands but include several warm-water species no longer found living along this coast. The Holocene evolution of the pan was largely influenced by changes in sea level and supply of sand along the coast. Calibrated radiocarbon ages of mollusc shells indicate a maximum Holocene sea level of ca 2 m above mean sea level (msl) from 7AE0 to 6AE3 ka and a return to near present-day sea level by 5AE3 ka. The pan surface is 2 m below msl and has been emergent since 4AE9 ka from the build up of sandy beaches and coastal dunes. A thin (1-4 cm) halite crust occurs over much of the pan surface but a layer of halite-cemented sand up to 40 cm thick is restricted to the central pan. Gypsum occurs near the subsurface brine interface and is limited by calcium to the edges of the pan. Nodules of calcite-cemented sand are forming in brackish, relatively high alkalinity subsurface waters in the southeast corner of the pan and nodules of aragonite-cemented sand are forming in brines 1 m below the central pan surface. Although modern dolomite has been reported from coastal lagoons of Brazil and Australia, carbonate cements are a minor feature of Anichab Pan and dolomite was restricted to a single reworked nodule most likely of Late Pleistocene age. Therefore, Anichab Pan does not appear to be a modern analogue to extensive, mixed-water dolomite cements found in Upper Pleistocene sediment-filled depressions on the Namibian shelf.

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Section: Cementation Of Pan Sedimentsmentioning

confidence: 53%

Holocene evolution of the Anichab Pan on the south‐west coast of Namibia

Compton¹

2006

Sedimentology

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“…In the case of phosphorite deposits, authigenic apatite is precipitated in relatively shallow marine sediments during early diagenesis. The precipitates are often overgrowths on diatomaceous earths made up of amorphous, opaline silica (see for example, the photomicrographs in Baturin, 2000). Moreover, magnesium, a major ion in natural solutions such as seawater and blood, is known to inhibit inorganic and biological apatite precipitation.…”

mentioning

confidence: 99%

Modeling apatite nucleation in the human body and in the geochemical environment

Sahai¹

2005

American Journal of Science

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ABSTRACT. This paper serves to show that under similar physicochemical conditions, universal chemical reaction pathways can be involved in the interactions of fluids, biomolecules and minerals, whether in the human body or in the geochemical environment. The concept is illustrated by comparing heterogeneous apatite nucleation at bone sialoprotein (BSP) surfaces, bioceramic implant surfaces and on marine, diatomaceous sediments where phosphorite deposits are formed. The present approach combines crystallographic considerations, experimental NMR data and ab initio molecular orbital calculations of NMR parameters to elucidate reactive site geometry, mineral nucleation and inhibition reaction pathways. This technique may be applicable in future investigations of biomineralization mechanisms.The peptide sequence, S(P)EE, is proposed to constitute an active site on BSP, where the three acidic groups are arranged at 60°from each other. The equilateral triangle provides a stereochemical match for Ca 2؉ on the (001) face of apatite. The analogous active site on silicate bioceramics is the cyclic silicate trimer or three-ring containing surface silanol groups. One possible reaction pathway for calcium phosphate (CaP) nucleation consistent with experimental 31 P NMR data involves the following steps: Ca 2؉ sorption at the active site and HPO 4 2؊ attachment resulting in the critical nucleus, followed by nucleus growth and phase transformation to apatite. The present ab initio calculations cannot provide information on which CaP phase is nucleated, so we assume that the CaP nucleus is amorphous. Magnesium inhibits nucleation by adsorbing faster than calcium, as an outer-sphere surface complex, at the active site.

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“…The phosphate content of known deposits varies considerably and is seldom more than 29 wt. % (Baturin & Savenko, 1985;Baturin 1998;Rao & Nair, 1991). Figure 1.…”

Section: Marine Phosphorite Depositsmentioning

confidence: 99%

“…Figure 1. Location of known marine phosphorite deposits (in light black -after Baturin and Savenko, 1985;Baturin 1998;Rao and Nair, 1991;Earney, 1990) and evaporite deposits (in dark grey -after Cronan, 1980;Earney, 1990;Warren, 1999;Teleki et al, 1987 and others cited in the text) with reference to the ELCS regions (in pale grey) and EEZ areas (outlined by thin curved grey lines) -modified after Prescott, 1985.…”

Section: Marine Phosphorite Depositsmentioning

confidence: 99%

A global review of non-living resources on the extended continental shelf

Murton¹

2000

Rev. Bras. Geof.

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Formation and Evolution of Phosphorite Grains and Nodules on the Namibian Shelf, From Recent to Pleistocene

Cited by 28 publications

References 0 publications

Holocene evolution of the Anichab Pan on the south‐west coast of Namibia

Holocene evolution of the Anichab Pan on the south‐west coast of Namibia

Modeling apatite nucleation in the human body and in the geochemical environment

A global review of non-living resources on the extended continental shelf

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