Abstract: An Example of Salt Tectonics Controlled by Regional Tectonics: The Nordkapp Basin, Norway
Kare T. Nilsen, Bruno C. Vendeville, Jan-Terje Johansen
Both seismic
data and experimental tectonic
modeling
indicate that the growth of salt structures in the Nordkapp basin, a deep late-Paleozoic basin in the Southeastern Barents Sea, was strongly influenced by regional tectonics. During regional extension in early Triassic times the sediment overburden deformed by normal faulting but overburden deformation was detached from that in the basement by the thick salt layer. Faulting triggered diapir rise below overburden grabens. Diapirs grew passively until mid-Triassic times by maintaining their crest at or near the sea floor while sediment accumulated into adjacent salt withdrawal basins. Deposition of horizontal, constant-thickness strata in mid-Triassic times indicates that the source layer was then depleted, marking the end of the pass
ve diapiric stage. Still, diapirs kept rising until late Triassic times and extruded enough salt on the sea floor to produce overhangs in the central and northern part of the basin. Overhang formation can be attributed to the combined effect of (1) decreasing sedimentation rate, (2) mid- and late-Triassic local extension, and (3) gravity gliding of the overburden along the basin slope toward the basin center, which squeezed salt out of diapir stems. By latest Triassic times, diapir rise slowed down, with only minor diapir growth in early Jurassic times before diapirs were buried under 1000 to 1500 meters of Cretaceous sediments. Late Cretaceous regional tectonics and mid-Tertiary compression allowed diapirs to lift their roof and rise actively. Stretching and faulting of upper Cretaceous
and Tertiary strata above diapirs during this latest stage overprinted earlier deformations.
AAPG Search and Discovery Article #90986©1994 AAPG Annual Convention, Denver, Colorado, June 12-15, 1994