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Abstract

The Northwest-German basin is the classic area of salt plugs (Figure 1). So far more than 200 of them have been discovered (Jaritz, 1973). Thus the "halokinesis," (the processes connected with the isostatic movements of salt; Trusheim 1957, 1960) determines to a large extent the distribution of sediments and the structural geology of Northwest Germany.

Round salt plugs (German: Salzstock) in Germany are 2 to 8 km (1.2 to 5 mi) in diameter. Other salt plugs average 4 to 5 km (2.5 to 3 mi) in width and range from 10 to 20 km (6 to 12 mi) to more than 100 km (62 mi) long. They are sometimes also referred to as salt walls (German: Salzwall). As pointed out by Trusheim (1957, 1960), salt walls are especially common in the deepest part of the basin, where the salt is the thickest. Most German salt plugs consist of the Upper Permian Zechstein salt, although some in the center of the basin also contain Lower Permian Rotliegend salt.

The economic value of the salt plugs is considerable. They are mined for both halite and potassium salt, and they are suitable as artificial solution caverns for the storage of crude oil and natural gas, and are intended for the dumping of hazardous waste. Rising salt plugs have also formed traps for oil and gas.

The salt plug is located near to the Dutch-German border, northeast of the city of Emden. It is 1.5 to 4 km (1 to 2.5 mi) wide and 50 km (31 mi) long stretching from north to south. The seismic line crosses the salt plug in its southern part from northwest to southeast.

The deepest strong reflection in the section at about 2.5 ms corresponds to the base of the Zechstein (i.e. the boundary Upper/Lower Permian). This very distinct seismic marker can readily be correlated and mapped in Northwest Germany. It is dislocated by faults, but not affected by halokinesis. The reflection is of utmost importance for the exploration of the pre-Zechstein, as normally no distinct and correlative reflections occur below it.

The mapping of the base Zechstein reflection encountered a low-relief anticline of 150 to 250 m (492 to 820 ft) closure under the salt plug. in the time section it appears exaggerated by the velocity pullup of the salt. A wildcat discovered a gas field in the Rotliegend red beds. Several other Rotliegend gas fields are known nearby; the biggest is the Dutch Groningen field some 25 km (15 mi) to the southwest.

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