METAL SORPTION AND MINERAL PRECIPITATION BY BACTERIA IN 2 AMAZONIAN RIVER SYSTEMS - RIO-SOLIMOES AND RIO-NEGRO, BRAZIL

Citation
Ko. Konhauser et al., METAL SORPTION AND MINERAL PRECIPITATION BY BACTERIA IN 2 AMAZONIAN RIVER SYSTEMS - RIO-SOLIMOES AND RIO-NEGRO, BRAZIL, Geology, 21(12), 1993, pp. 1103-1106
Citations number
22
Categorie Soggetti
Geology
Journal title
ISSN journal
00917613
Volume
21
Issue
12
Year of publication
1993
Pages
1103 - 1106
Database
ISI
SICI code
0091-7613(1993)21:12<1103:MSAMPB>2.0.ZU;2-7
Abstract
The surfaces of epiphytic and episammic bacteria from the solute-rich waters of the Rio Solimoes, Brazil, interacted with available cations in solution and provided major sites for iron deposition. Once bound t o the bacteria, the iron served as nucleation sites for the formation and growth of fine-grained authigenic mineral phases. Because of progr essive mineralization, the precipitates exhibited a wide range of morp hologies, from amorphous ''gel-like'' to crystalline structures. Compl ete encrustation of some bacterial cells was observed. The most abunda nt mineral phase associated with the bacteria was a complex (Fe,Al) si licate with a variable composition. Energy-dispersive X-ray spectrosco py suggested that the gel-like structures were similar in composition to a chamositic clay, whereas the crystalline phases were increasingly kaolinitic. Bacteria collected from the solute-deficient waters of th e Rio Negro remained conspicuously unmineralized, suggesting that meta l sorption and biomineralization largely reflect the availability of d issolved metals in the water column. In a solute-rich river system, th e fate of the metal-loaded bacteria has profound implications for the transfer of metals from the hydrosphere to the sediment. Through diage nesis, the bound metals may either be recycled to the overlying water column or become immobilized as stable mineral phases. If the latter o ccurs, microorganisms will have played an important role in metal depo sition, low-temperature clay formation, and, invariably, mudstone diag enesis. This implies that in the geologic record, microorganisms may h ave been instrumental in the genesis of many sedimentary rocks of fluv ial origin.