Cave Ferromanganese Deposits (a.k.a corrosion
residues)
Caves offer accessible subterranean environments in which to study the
diversity of microbial life. These ecosystems are exposed to extreme
environmental stresses and may be based on inorganic energy sources
rather than sunlight. An excellent example of subterranean microbial
life is found in Lechuguilla Cave (New Mexico), the deepest cave in the
continental United States. Lechuguilla Cave, an immense, ancient cave in
near pristine condition, contains sulfur, iron, and manganese deposits
and extremely low nutrient environments harboring diverse microbial
life. The carbonate wall rock and overlying corroded limestone provide
an excellent model for studying how life has survived, adapted, and
altered this rock environment. Preliminary evidence suggests that the
diverse community of microorganisms inhabiting corrosion residues
includes fungi and bacteria that live by using manganese and iron. We
are investigating the nature of the unusual microorganisms present, the
means by which they adapt to their extreme environment, the energy
sources that they use, and the overall level of biological activity of
the communities. Because of the potential for subsurface life on other
planets and possible chemical similarity to Lechuguilla Cave, our
research will also explore the relevance of cave communities to those
that may exist elsewhere.
We are currently using Scanning Electron Microscopy (SEM) and Electron
Dispersive Spectroscopy (EDS) analysis to study sites in Lechuguilla
Cave to search for evidence of bacteria and their potential energy
sources.
Corrosion residues occur in many colors, including
black, gun metal gray, red, brown, yellow, ocher, pink, and orange. EDS has
shown us that black residues contain the highest concentration of manganese oxides, while reds and browns contain the
highest amounts of iron oxides. Using SEM, we are
scanning samples of corrosion residue from Lechuguilla Cave and Spider
Cave, and punk rock. The combination of SEM/EDS has
revealed different morphologies of calcite,
dolomite, gypsum,
quartz, clays, iron oxides in the shape of discs,
balls, and stars on the order of less than a micron
to a few microns in diameter, manganese oxides,
svanbergite, barite,
and rutile, zirconium,
apatite. Some samples of corrosion residue
and wall rock reveal the presence of rare earth elements.
The calcium carbonate associated with corrosion residues shows pitting of various types, including pits in the wall
rock behind the corrosion residues that contain putative bacterial filaments. Other bacterial
morphologies have been observed in corrosion residues and punk rock.
Corrosion residues are also found in Jewel Cave (Jewel Cave National
Monument). These residues are mainly browns and blacks and EDS analysis shows high iron content.
For more information about Lechuguilla:
This web site Copyright 2007, 2011, Kenneth
Ingham