A Salt Pillow Structure in the Southern North Sea
P.F. Owen, N.G. Taylor, 1983. "A Salt Pillow Structure in the Southern North Sea", Seismic Expression of Structural Styles: A Picture and Work Atlas. Volume 1–The Layered Earth, Volume 2–Tectonics Of Extensional Provinces, & Volume 3–Tectonics Of Compressional Provinces, A. W. Bally
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This note describes the major features of a seismic section recorded over a Zechstein salt pillow in the southern North Sea. We made an attempt to explain these in terms of the geological history of the area.
The seismic data were acquired and processed in 1979 as part of a regional survey to give improved data at the deeper levels. in this example the migrated version of the line was used for the interpretation because it shows the detailed structure more clearly than the normal stacked section. The features illustrated are: (1) the asymmetric shape of the pillow; (2) listric faulting on the northeast side of the pillow wall; and (3) the displacement of the crest of the Base Tertiary reflector which does not lie immediately over the crest of the Triassic.
Permian — in this part of the salt basin some 500 m (1,640 ft) of halite were deposited with the dolomites and anhydride of the Upper Permian (Zechstein). The Zechstein evaporites overlie continental sediments of Permian age, and Carboniferous Coal Measures. We have termed these earliest units "Basement" on Figure 4, since they do not affect the subsequent structural history.
Triassic — Regional studies show that the Early Triassic deposits, mainly mudstones, were evenly distributed. This section shows that: (1) over 1,000 m (3,281 ft) of Triassic sediments were deposited by the Late Triassic; and (2) the youngest Triassic sediments thin by 150 m (492 ft) over the present day pillow.
This indicates that halokinesis could have begun as early as the Late Triassic. A 1,000 m (3,281 ft) overburden is probably sufficient to make underlying salt unstable (Trusheim, 1960). Alternatively, movement of the basement horst feature may have itself induced salt pillowing above it.
Jurassic — There is no evidence of thinning in the Lower to Middle Jurassic interval against the pillow, and therefore it is unlikely that there was any growth of the pillow at this time.
Between the Middle Jurassic and Lower Cretaceous, two closely related processes occurred: (1) major growth of the salt pillow; and (2) listric faulting on the northeast flank.