The Impact of Early-Diagenetlc Aluminophosphate Precipitation on the Oceanic Phosphorus Budget
Published:January 01, 2000
Birger Rasmussen, 2000. "The Impact of Early-Diagenetlc Aluminophosphate Precipitation on the Oceanic Phosphorus Budget", Marine Authigenesis: From Global to Microbial, Craig R. Glenn, Liliane Prévôt-Lucas, Jacques Lucas
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Early-diagenetic aluminophosphate minerals (mainly florencite) are ubiquitous in ancient (Archean to Cretaceous) marine-deposited sandstones. The crystals are >10 μm in diameter and are mostly associated with thin coatings or pockets of detrital clay particles lining quartz grain surfaces. Aluminophosphate crystals are also found in altered detrital aluminosilicate grains (e.g. feldspar).
The aluminophosphate minerals precipitated in sands deposited in shallow marine environments. Diagenetic textures and the presence of structural sulfate in the aluminophosphate minerals suggest that the authigenic crystals formed shortly after deposition, probably in the zones of sulfate reduction and methanogenesis. The aluminophosphate minerals formed as the concentrations of phosphate in the pore water increased and phosphate combined with various cations (e.g. calcium, barium, rare earth elements) to precipitate at sites of aluminum availability (e.g. detrital clay particles and aluminosilicate grains).
Although the aluminophosphate minerals are volumetrically minor constituents (<0.05 wt%), the authigenic crystals, which are present in >90% of samples studied, are spatially and temporally widespread in ancient Australian sandstones. Burial flux estimates show that phosphorus is removed at a rate of ~5.6 × 10-7g/cm2-yr. This value suggests that aluminophosphate precipitation was probably an important sink for oceanic phosphorus in the past, and possibly significant in present-day coastal environments. The discovery of the magnitude of the authigenic aluminophosphate sink has implications for models of the marine phosphorus cycle.
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Marine Authigenesis: From Global to Microbial
This volume is a collection of 33 state-of-the-art papers focusing on various aspects of authigenic and diagenetic marine minerals and related global elemental cycling. The commingling of the various studies of authigenic minerals in this volume, including the most recent advances in knowledge concerning the occurrence and origins of phosphorites, glauconites, dolomites, siderites, manganese-iron associations, barites, ironstones, and other marine chemical sediments/sedimentary rocks of early authigenic/diagenetic origin, is partly the result of the increasing awareness that there are many overlaps, even direct co-associations, between different authigenic minerals, both in time, space, and genesis. Taken together, this compilation represents a holistic approach towards marine authigenesis that considers the integrated whole more than the simple sum of its parts.