Abstract

Exploration drilling for potassium ore in the 1950’s established that Palangana Dome contains an internal evaporite stratigraphy more consistent than that of any other known Gulf Coast salt stock. However, the internal structure was formerly regarded as too complex for the large-scale fold geometry to be resolved. By analogy with models and on theoretical considerations, Palangana Dome is shown to be a mushroom structure. Salt rose up a stem into a sheathlike core of the cap before spreading radially sideways near the crest and moving downward relative to the core into a peripheral synformal anticline. An antiformal syncline, consisting of evaporites (internal mushroom) or cover rocks infolded from below the cap (external mushroom), separates the periphery from the core. Tectonically disrupted sandstone is found in this infold. The infold of an external mushroom structure represents a new class of intradomal petroleum trap. Only two of the four possible zones of sylvite ore indicated by our reinterpretation have been adequately explored. We recognize other types of mushroom structure in evaporite diapirs in Iran, Germany, and Canada, and think that more examples will be found as dome interiors are further explored.