Late Permian to Triassic basin infill history and palaeogeography of the Mid-Norwegian shelf—East Greenland region

Abstract

In the Late Permian to Triassic, the present Mid-Norwegian shelf and East Greenland represented an extensional basinal region, c. 400 km wide and 800 km long, composed of several sub-basins. This basinal region was the site of a highly varied sediment infill history during Late Permian to Late Triassic time, controlled by changes and variations in tectonic development, climate and eustasy. In the Late Permian minor movements along some intra-basinal faults resulted in the formation of several sub-basins. This tectonic event is defined as an initial rift phase . In the Mid-Norwegian shelf—East Greenland region the Permian-Triassic transitional interval is represented by a major shift in basin infill style, including erosion of carbonate margins and influx of silisiclastic sediments to marine sub-basins. This combination of processes is controlled by increased fault activity and fault block rotation, which was accompanied by a fall in the relative sea level. The Early Triassic (early Scythian) represents the syn-rift phase when the dominantly marine sediment infill pattern was controlled by continued fault-block rotation and tectonic activity along several structural lincaments. The basin infill in the late Scythian represents an overall shallowing up of the basinal region, and a marginal marine to continental depositional environment became established. The Middle Triassic post-rift phase 1 is represented by a dominantly aggrading continental succession on the Mid-Norwegian shelf, probably with some short-lived marine transgressions. In East Greenland, this phase is characterised by a great variability of continental facies with a minor marine incursion. The establishment of a continental depositional environment is caused by a decrease in rate of accommodation relative to rate of sediment input, brought about by cessation in fault activity and reduced tectonic subsidence. However, the Vingleia Fault Zone was still active during deposition of the Middle Triassic succession. This indicates that certain structural elements continued to be tectonically active during the ‘post-rift phase’. A second tectonic event influenced the basin infill of the lower part of the Upper Triassic succession in the post-rift phase 2 . Thick evaporites formed in isolated marine sub-basins, was triggered by an arid climate, oscillation in the relative sea level, and likely, the establishment of a structural threshold to the Borealic open marine seaway. The upper part of the Upper Triassic succession of post-rift phase 3 represents the establishment of a fluviolacustrine depositional environment. This facies shift was probably caused by reduced rate of subsidence, tectonic uplift in the hinterland and more humid conditions.