Abstract

Several breccia pipes crop out in rocks younger than the Cutler Formation in Lockhart Basin. Assuming that they bottom in the Paradox or Honaker Trail formations, the pipes are 2,000 feet high. Typical pipes in Lockhart Basin are exposed as hills of rubble. Wall rock-pipe fill contacts are sharp, and surrounded by inward dipping country rocks. Alteration is present in some pipe fills, which causes the rocks to have a bleached appearance. Downward displacements of material in the pipes is at least 100 feet in two of the pipes examined in Lockhart Basin.

A reasonable model to account for the development of the pipes is upward stoping from cavities in the Paradox and Honaker Trail formations which formed simultaneously with the collapse of a minor salt anticline that once occupied the Lockhart Basin area. The initial cavities allowing for gravity collapse of roof rocks were probably solutional voids in the dissolving salt core, or tensional openings in competent units that infolded into the shrinking salt core. Additional volume was progressively created within the pipes by the solutional removal of carbonate clasts and cements within the pipe fills, and by possible solutional enlargement of the pipes where carbonates or salts comprised the wall rocks.