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The AAPG/Datapages Combined Publications Database

GCAGS Transactions

Abstract


Gulf Coast Association of Geological Societies Transactions
Vol. 27 (1977), Pages 134-138

Sub-Salt Origin of Salt Dome Cap Rock

Oscar L. Paulson, Jr.(1)

ABSTRACT

Previous theories for the origin of salt dome cap rock have relied in varying degrees on the introduction of minerals and fluids from the sediments surrounding the dome. This paper proposes a sub-salt origin for the minerals. The occurrence of cap rock minerals beneath the salt of most evaporate basins is a well-known fact, but the idea of these minerals becoming an integral part of the diapiric mass has not been broached. Studies of other diapiric structures have revealed that materials underlying the principal diapiric constituent can be incorporated into the diapiric mass.

Irregularities in the thickness of salt dome cap rock are associated with similar irregularities in the top of the salt. These irregularities may result from spines of movement which serve as avenues for the expulsion of cap rock minerals. The presence of hydrogen sulphide, sulphur and pressured brine at depth in salt domes adds support to a sub-salt origin for cap rock.

The species of minerals present in the cap rock of a particular dome are generally related to the amount of growth of the dome and its position in the evaporite basin. Domes which have undergone the most upward growth are more likely to have a greater number of the minerals which precipitated early in the evaporite sequence. Metallic sulphides found in some domes are commonly associated with sapropels which mark the beginning of the evaporite stage and, therefore, represent the oldest of the mineral species to reach the cap rock.


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