HYPOGENIC SPELEOGENESIS WITHIN SEVEN RIVERSEVAPORITES: COFFEE CAVE, EDDY COUNTY,NEW MEXICO

摘要

Coffee Cave, located in the lower Pecos region of southeastern New Mexico, illustrates processes of hypogenic speleogenesis in the middle Permian Seven Rivers Formation. Coffee Cave is a rectilinear gypsum maze cave with at least four stratigraphically-distinct horizons of development. Morphological features throughout the cave provide unequivocal evidence of hypogenic ascending speleogenesis in a confined aquifer system driven by mixed (forced and free) convection. Morphologic features in individual cave levels include a complete suite that defines original rising flow paths, ranging from inlets for hypogenic fluids (feeders) through transitional forms (rising wall channels) to ceiling half-tube flow features and fluid outlets (cupolas and exposed overlying beds). Passage morphology does not support origins based on epigenic processes and lateral development, although the presence of fine-grained sediments in the cave suggests minimal overprinting by backflooding. Feeder distributions show a lateral shift in ascending fluids, with decreasing dissolutional development in upper levels. It is likely that additional hypogenic karst phenomena are present in the vicinity of Coffee Cave because regional hydrologic conditions are optimum for confined speleogenesis, with artesian discharge still active in the region.