Mn-Fe-Enhancing Budding Bacteria in Century-Old Rock Varnish, Erie Barge Canal, New York

Abstract

AbstractFossil remnants of bacteria involved in the enhancement of manganese and iron rarely occur within the microstratigraphy of rock varnishes collected from warm desert environments, because varnish formation processes ultimately destroy these microfossils through remobilization of Mn-Fe and reprecipitation in a clay-mineral matrix. In contrast, Mn-Fe encrustations on budding bacteria commonly occur within varnishes that formed within just a century along the Erie Barge Canal, New York. Nanoscale imagery and elemental analyses reveal that these budding bacterial forms greatly enhance Mn, Fe, or both in encrustations surrounding hyphae and cells. The Mn and Fe precipitates have a granular texture on the scale of <1 nm to ∼10 nm. The precipitates also have a stringy texture, where strings are typically only a few nanometers wide. These in situ observations are consistent with expectations from studies of budding-bacteria cultures and with the polygenetic model of varnish formation. Given that the Erie C...