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The AAPG/Datapages Combined Publications Database

AAPG Bulletin


Volume: 9 (1925)

Issue: 1. (January-February)

First Page: 42

Last Page: 78

Title: Petrography of Salt Dome Cap Rock

Author(s): Marcus I. Goldman


Two kinds of cap rock are differentiated: the gypsum Previous HitanhydriteNext Hit-cap and the calcite cap. The gypsum is derived from the Previous HitanhydriteNext Hit by hydration and is characteristic of the upper part of the cap, where it contains much calcite and sulphur. The deeper, less altered part of the Previous HitanhydriteNext Hit cap shows parallel banding, which may be the result of diffusion, and breccia fragments of a parallel-banded, finer-grained Previous HitanhydriteNext Hit, which give evidence of sedimentary origin. Therefore, although no detrital minerals have been found in specimens of Previous HitanhydriteNext Hit cap, this cap is believed to be of sedimentary origin, brought up by an intrusive salt plug from depth. Possible explanations of the presence or absence of Previous HitanhydriteNext Hit caps on salt domes are offered. The calcite cap is the product of repl cement and penetration by calcite of the sedimentary beds adjacent to the gypsum-Previous HitanhydriteNext Hit cap and probably of the upper part of the gypsum-Previous HitanhydriteNext Hit cap itself. The sulphur in cap rock is characteristically associated with this calcite. The calcite and sulphur are probably the result of reduction of the outer parts of the Previous HitanhydriteNext Hit cap by hydrocarbons from adjacent beds. Constituents of minor importance are sulphides, carbonates of an early generation, barite, celestite, bipyramidal quartz crystals, and inclusions of sandstone in Previous HitanhydriteTop.

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