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Concept
Salt dome
Summary
A salt dome is a type of structural dome formed when salt (or other evaporite minerals) intrudes into overlying rocks in a process known as diapirism. Salt domes can have unique surface and subsurface structures, and they can be discovered using techniques such as seismic reflection. They are important in petroleum geology as they can function as petroleum traps.
Stratigraphically, salt basins developed periodically from the Proterozoic to the Neogene. The formation of a salt dome begins with the deposition of salt in a restricted basin. In these basins, the outflow of water exceeds inflow. More concretely, the basin loses water through evaporation, resulting in the precipitation and deposition of salt. While the rate of sedimentation of salt is significantly larger than the rate of sedimentation of clastics, it is recognized that a single evaporation event is rarely enough to produce the vast quantities of salt needed to form a layer thick enough for the formation of salt diapirs, indicating that a sustained period of episodic flooding and evaporation of the basin must occur.
Over time, the layer of salt is covered with deposited sediment, becoming buried under an increasingly large overburden. Previously, researchers believed that the compaction of overlying sediment and subsequent decrease in buoyancy led to salt rising and intruding into the overburden due to its ductility, thereby creating a salt diapir. However, after the 1980s, the primary force that drives the flow of salt is considered to be differential loading.
Differential loading can be caused by gravitational forces (gravitational loading), forced displacement of salt boundaries (displacement loading), or thermal gradients (thermal loading). The flow of the salt overcomes the strength of the overburden as well as boundary friction aided by overburden extension, erosion, thrust faults, ductile thinning, or other forms of regional deformation. The vertical growth of salt formations creates pressure on the upward surface, causing extension and faulting (see salt tectonics).
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