Reimers, C. E., Kastner, M. and Garisson, R. E. (1990) The role of bacterial mats in phosphate mineralization with particular reference to the Monterey Formation. In: Phosphate Deposits of the World Vol. 3: Neogene to modern phosphorites. , ed. by Burnett, W. C. and Riggs, S. R.. Cambridge University Press, Camridge, England, pp. 300-311.

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Abstract

Organic-rich shales sampled from the aples Beach section of the Monterey Formation. Califomia. contain authigenic phosphorite phases which apparently formed within bacterial mat laminations. Light and scanning electron microscope observations show that the fossilized remains ofthese mats are similar to communities of filamentous sulfur-oxidizing bacteria found
today at slope-depth, sediment, oxic anoxic interfaces. The crystal size and habits ofthe phosphatic minerals resemble contemporaf)
prec1pitates in contact with pore water solutions. Mineralogical and chemical analyses ofthe most phosphatic layers show that some are a nearly pure carbonate fluorapatite (or
francolite). These la)ers are lightly colored and are sandwiched between black siliceous muds with <0.2% CaCOJ . and organic carbon contents that excecd 25%. In othcr phosphatic intcrvals
of thc Naplcs Beach section. ca leite is a major diluent oflight and dark layers.
The C:P ratio of a single modern bacterial mat sample shows that these benthic communities are more enriched in phosphorus than planktonic organic matter. Thus, the generally believed
premise that authigenic phosphorite formation results from organic matter diagenesis in near-surface anoxic sediments is hcre modified by the contention that such transformations are more
highly favored in sediments supporting massive microbial communities.

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