The Influence on Subrosion of Three Different Types of Salt Deposits

Abstract

In the study of salt-bearing deposits, the geologist has to bear in mind that salt is readily soluble. Since water is ubiquitously present in porous sedimentary rocks, salt is frequently dissolved. The residues of the subrosion processes are found in the cap-rocks or gypsum cap-rocks in salt domes. At the Hänigsen-Wathlingen salt dome within the northwest German Zechstein Basin it is shown that both the stratigraphy and the content of the insolubles of the cap-rocks depend on previous tectonic structures.

Apart from the diapiric salt structures, cap-rocks are also known from horizontally bedded salt deposits as shown in a deposit from the Khorat Plateau in Thailand. At the edges as well as in uplift areas the deposit is intensely subroded, and filled by insolubles such as anhydrite and clastic components of the preceding salt strata. Since the clastics occur as distinct and continuing layers, containing only minor amounts of salt, the stratigraphic section is still preserved even after subrosion has taken place.

Subrosion at the top of the salt body, called regular subrosion, is also common in the Fulda Basin of western Germany. In the horizontally layered salt strata of this area, a rare combination of regular and irregular subrosion at the bottom of the beds occurs. The top of the salt is covered by a thin sheet of layered cap-rock gypsum, overlain by a subrosion breccia consisting of a mixture of elastics and boulders of gypsum, and finally overlain by strata of brecciated overburden sediments. Beneath the salt horizons a collapse breccia composed of rock fragments from strata overlying the salt strata and displaying chaotic structures is found.