MN-RICH AND FE-RICH BLACK TRAVERTINE SHRUBS - BACTERIALLY (AND NANOBACTERIALLY) INDUCED PRECIPITATES

Black shrubs (i.e., arborescent forms) are present within hot-water tr avertine deposits from Morocco, The shrubs are commonly a few centimet ers high and laterally grouped along individual laminae, Other than in mineral composition, the black shrubs closely resemble the calcite sh rubs from other hot-water travertine deposits (e.g., Bagni di Tivoli, Italy, and Mammoth Hot Springs, Yellowstone National Park). They are c omposed of a variety of minerals that are Mn-rich and also have a sign ificant Fe-oxide component. Similar Mn- and Fe-rich shrub-like forms h ave been described from desert varnish, deep sea Mn nodules, and marin e carbonates (Frutexites). SEM analyses show that bacterial bodies are densely packed within the Mn rich black travertine shrubs whereas no bacterial bodies are evident within the enclosing aragonite and calcit e laminae, The bacterial bodies range in shape and size from rods (com monly 0.8 mu m long by 0.1 mu m in diameter), to spherical forms (comm only 0.3 mu m in diameter) that form chains up to 1 mu m long, to nano bacterial spheres (150 to 200 nm in diameter) that make up densely pac ked chains commonly 15 mu m in length. It is well documented within th e microbiological literature that, not only do bacteria have the abili ty to induce the precipitation of Mn and Fe, they can concentrate Mn i n mineral precipitates from waters with very low to essentially undete ctable concentrations of Mn. The black Mn-rich shrubs within the Moroc can travertines, other hot-water travertines, and related features suc h as desert varnish, deep sea Mn nodules, and Frutexites are postulate d to also be the result of bacterially induced precipitation.