Iron Oxide-Rich Filaments: Possible Fossil Bacteria in Lechuguilla Cave, New Mexico
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Abstract
Reddish filaments in two fragments of unusual iron oxide bearing stalactites, "the Rusticles" from Lechuguilla Cave, New Mexico, are found only within the central canals of the Rusticles. The curved, helical, and/or vibrioidal filaments vary from 1 to 6 w m in outer diameter and 10 to > 50 w m in length. SEM and TEM show the filaments have 0.5- w m diameter central tubes, with goethite crystals radiating outwardly along their lengths. The diameter of the central tubes is consistent with the diameter of many ironoxidizing filamentous bacteria. Although most iron oxide depositing bacteria do not deposit well-crystallized radiating goethite, we propose thick hydrous iron oxide was slowly crystallized from amorphous material to goethite, in place, over a relatively long period of time. From the gross morphology and the particular setting, we suggest this represents an occurrence of fossilized, acidophilic iron-oxidizing bacteria.
