Paleozoic-Mesozoic tectono-sedimentary evolution and magmatism of the Egersund Basin area, Norwegian central North Sea

Abstract

This study focuses on the tectonic evolution of the greater Egersund Basin in the Norwegian central North Sea, with special emphasis on Late Paleozoic extensional tectonics following Caledonian collapse and the Variscan Orogeny, and the impact of the basement structural grain on this evolution. The Caledonian collapse likely resulted in development/rejuvenation of the deepest E-W trending structures/depocenters by Late Devonian time. Thus, a late Devonian-?early Carboniferous age can be assigned to the initial extension, which was associated with the development of an E-W striking basin system, to be overprinted by N–S extensional structures of similar age. A phase of regional magmatism at the Carboniferous-Permian transition (≈300 Ma) may be associated with a large igneous province centred on the Skagerrak area. Faulting during late Carboniferous-early Permian was minor within the study area as reflected by uniform sedimentary thicknesses of the uppermost Carboniferous and lower Permian sequences. Major normal faults, mainly trending N–S, were active during a late Permian-Early Triassic rift phase affecting large parts of the central and northern North Sea area. A later phase of extension was initiated in late Middle Jurassic time and the Egersund Basin proper formed during the Late Jurassic-Early Cretaceous. The depocenters that developed during this phase was influenced by the deep Late Paleozoic (sub-salt) structural grain, including strike-slip movements along the Sorgenfrei-Tornquist Zone. Later events include mild inversion along the northern flank of the Egersund Basin, possibly as a Late Cretaceous response to far-field Alpine compression, and Cenozoic regional tilting.