New Mexico Geological Society Annual Spring Meeting — Abstracts

The Snowy River formation, a pool deposit located in a recently discovered passage in Fort Stanton Cave, New Mexico, may be the world’s longest continuous cave deposit. The formation is composed of tufa-like white coralloid calcite lining an old subsurface stream channel, and currently extends from north to south for >7 km with its southern terminus still undefined. Core samples collected from the Snowy River deposit reveal a laminated internal structure, indicating episodic deposition of sub-millimeter scale calcite laminae during periods when the passage is flooded by CaCO₃-saturated water. The basal layer has been dated with U-Th techniques at only 836 years BP, indicating an abrupt change in climatic or hydrochemical conditions within the past millennium. The Snowy River passage has been intermittently flooded for the past two years during the southwest monsoon season, during which a thin film of new calcite was deposited. The source of water in the passage is unknown. Water level data loggers show abrupt disappearance of floodwaters during winter months when the monsoonal rains are over, suggesting a point source of recharge to the cave system via a sinkhole or losing stream, and possibly an as yet undiscovered second entrance to the south.