Abstract
Backscattered electron (BSE) imaging and electron probe-coupled analysis of bone debris in the Negev phosphorites (Israel) show that F concentrations vary considerably in these components, and that these variations are driven by microbial activity. The bone debris are microbially tunneled, commonly with a micritic carbonate fluorapatite (CFA) phase filling the tunnels and gradually replacing the bone matrix. As a rule, the micritic CFA within the microbial tunnels is significantly much more F-enriched (F/P 2 O 5 —0.106–0.125) than the bone matrix (F/P 2 O 5 —0.083–0.104). Similar results are obtained in bones at final stages of microbial infestation and micrite phosphate replacement. The infested-replacing envelope invading the bone debris is much F enriched (enrichment factor of about 1.27 on average) than the surviving bone that escaped boring. These results are explained by redeposition as CFA of the microbially bored and dissolved hydroxyapatite, presumably fostered by microbial F transfer from porewaters to the sites of CFA precipitation in bone microborings. This pathway of F-enrichment driven by microbial activity may also explain the enigmatic differential U-enrichment previously observed in Negev phosphorite bones.
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