REMMELTS, GIJS, Geological Survey of the Netherlands, Haarlem, Netherlands
ABSTRACT: Salt Tectonics in the Southern North Sea, Netherlands
Large parts of the southern North Sea are underlain by Upper Permian Zechstein salt. A vast amount of this sequence, originally more than 1000 m thick, has migrated into salt structures. Many hydrocarbon accumulations are related to these structures. The formation of the salt structures may have created structural traps or (by influencing the sedimentation pattern) stratigraphic traps. Salt generally acts as a seal, but depletion of salt can create migration routes into higher strata for hydrocarbons originating from underlying source rocks. The thermal conductivity of the salt can influence the maturity of source rocks in its direct vicinity.
Salt structures are formed almost exclusively by Zechstein salt. Minor movement occurred in Triassic evaporites.
The development of salt structures is influenced strongly by regional tectonics. Basement faulting probably triggered the salt movement. The dominant structural grain is reflected in the orientation and location of the salt structures. Periods of increased growth rates coincide with tectonic phases.
Long walls of salt formed in the northern area where the Triassic north-south orientated faults (which were rejuvenated in Late Jurassic) predominate. Toward the south, the northwest-southeast direction of the Late Jurassic interferes with the north-south trend and gradually becomes the dominant direction. This is reflected in the shortening of the north-south salt structures and eventually in the change in their orientation.
Average vertical growth rates have been calculated to be around 0.005-0.035 mm/yr. When correction for suberosion and erosion processes could be quantified and applied to the growth rates, they were significantly higher.
AAPG Search and
Discovery Article #90990©1993 AAPG International Conference and Exhibition, The
Hague, Netherlands, October 17-20, 1993.