With the emergence of the Mississippian Leadville Limestone, a climatically specific subaerial tower-karst surface developed in the Molas Pass area, with 80 ft of local relief. Much of this surface is buried under different thicknesses of the Early Pennsylvanian Molas Formation, in part a regolith of siltstone and residual clays from the limestone solution.

Rising like small peaked knobs from a plain are three examples of the tower karst found near Molas Pass, the Molas Lake tower, Waterfall tower, and Sultan Creek tower. These illustrate the relatively low limestone solubility, strong fracturing, both joint and fault, and high water-table variations conducive to both tower and the related Kegelkarst formation. Folding may produce adverse conditions for the karst tending to hasten cavern integration and limestone removal.

Tower karst and the predominance of kaolinite in the lower Molas, together with silica and hematite produced from soil ferralitization, suggest a subtropical to tropical climate with heavy rainfalls followed by rapid evaporation. The modern localization of this type of karst to areas below 30° of latitude implies a northward migration of the Molas Pass area since the Early Pennsylvanian.

The complex stratigraphic relations between the fine-grained Leadville Limestone and the underlying Ouray dolomitic grainstone have made their field separation difficult and may indicate which areas were above and below sea level during the karst formation. This suggests a relative elevation of 100-200 ft for the Leadville at the time of the maximum tower-karst formation.

The geologic controls on tower-karst development as observed in the Molas Pass area correlate well with the climate and geologic controls in a modern tower-karst analogue, central Jamaica.

An understanding of the mechanisms of tower-karst formation and burial is directly applicable to petroleum stratigraphic trap location as in the Elk Basin field of northern Wyoming-southern Montana, and the localization of base metal sulfide ore deposits as at Gilman, Colorado.

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