Goliath's and Mystery Caves Minnesota: Epigenic Modifications and Extension of Preexisting Hypogenic Conduits

Mystery and Goliath's Caves are developed in the Ordovician Dubuque and Stewartville Formations of the Galena Group in Fillmore County, MN. Both caves currently function as epigenic karst systems with allogenic surface streams sinking into the caves, running underground through the caves and ultimately resurging a surface springs a few kilometers away. Passages in both caves are locally controlled by vertical joints in the nearly flat-lying carbonate bedrock, but the water flow directions are from the recharge points to the springs and do not correspond to the systematic joint directions. Both caves contain major, often straight, joint-controlled, passages that appear to pre-date the current epigenic drainage systems. These old passages contain clear hypogenic features (Klimchouk, 2007) and strong indicators of slow paleoflows opposite of the current, more rapid vertical and horizontal epigenic water flow directions. The older hypogenic passages are connected and modified by distinct, younger epigenic passages – often with very sharp transitions back and forth between the two passage types. The epigenic flows are sometimes actively removing sediment accumulations that have partially clogged the hypogenic passages. In other places the epigenic water flow is currently incising vadose canyons into the hypogenic passages. The hypogenic passages evidently represent ancient, deep, compartmentalized flow systems that predate the present topography. “Ancient” is poorly constrained to be older than the oldest speleothems (>300 ka) and younger than the bedrock (~440 Ma). These ancient cave passages are being reactivated by epigenic systems – in the process of their destruction by general erosion of the landscape. The authors hope that the current active discussion about hypogene versus epigene speleogenesis does not degenerate into a “one or the other” debate. Both processes happen and are important parts of the development of karst aquifers and caves.