SNOWY RIVER: A NEW DISCOVERY FROM AN OLD CAVE

Fort Stanton Cave, New Mexico is an historic cave, recently designated as a National Conservation Area within the Bureau of Land Management. The cave hosts an important new discovery: the Snowy River passage, an unusual passage with walls and ceilings coated with jet-black manganese oxide and a white calcite "river" on the floor of the borehole-like passage. Currently explored to 7.4 km long, with no end in sight, the unique Snowy River formation may be the world's longest continuous speleothem. The cave, and especially this new passage, is the subject of intense exploration and scientific study. The research group is a multidisciplinary team of geochronologists, hydrologists, mineralogists, molecular biologists, and microbiologists working on an integrated understanding of the cave, including the hydrology of the cave, the age and origin of the unusual formation, the origin of the manganese wall deposits, biogenicity of cave formations, and the potential for human impact in this mostly pristine passage.

The Snowy River formation is a thinly laminated carbonate pool crust. The bottom of the calcite, younger than expected, has been dated at 820 (+/-200) yrs BP and the top is recent, with new calcite precipitated with each flooding event. The laminae vary from microns to millimeters in thickness and appear to be continuous across cores taken several km apart. The minor element chemistry, particularly SrO, SO₃, and P₂O₅ determined by microprobe traverses across one core, varies significantly from layer to layer. The lamellae suggest episodic flooding events of variable duration.

Black Mn-oxides on the walls of the passage coat centimeter-thick clay and silt that was deposited on the limestone bedrock prior to the deposition of the white Snowy River calcite. The layers in the wall and floor sediments also suggest episodic deposition during an earlier era when the passage was apparently open to the surface. In cross-section, the Mn-oxide coating consists of discontinuous dendritic clusters and laminated structures. DNA sequence results from the manganese crusts in Snowy River indicate that closest relatives of some organisms in the Mn crust are from other caves (ferromanganese deposits in Lechuguilla Cave, NM; Frassasi Cave, Italy; and Weebubbie Cave on the Nullabor Plain, Australia) and soil and rhizosphere communities.