Exploring the Triassic of the Northern Barents Shelf – Sag-basins Interacting with Growth-faults

Alvar Braathen

"We challenge the common geological belief that the Triassic evolution of the northern and eastern Barents Shelf is a tectonically quiescent period. This is based on work with onshore exposures in Svalbard and 2D seismics, addressing (i) shallow-shelf infill of regional sag-type basins, (ii) normal growth faulting in the distribution of deltaic (or estuarine) reservoir sandstones, and (iii) patterns of interaction between shelf progradation and faulting. Towards the north and east especially the Triassic successions of the Barents Shelf reflect the impact of the crustal-scale Uralian mountain belt in the east. Gradual infill of the foreland basin by sediments sourced from the east and southeast, with significant influence by sea-level changes during clinoform progradation and aggradation, is reflected in various depocenters, highs and platform areas across the Barents Sea. This gentle basin configuration is contrasted by the East Svalbard offshore realm, where conventional 2D seismic data suggests that the northern Barents Shelf experienced extensional movements on many deep-rooted faults, with renewed minor activity during the Triassic. These deep-rooted faults are steep shallower levels, curving into more gentle dips in the Permo-Carboniferoussuccessions. Most faults show offsets around 50-100 ms-1 (ca. 100-200 m) at Triassic levels, where many tip out. At this level a possible two-level fault system and small offsets on faults, combined with high seismic velocities offshore, make the fault systems and growth basins complicated to resolve in seismic data. Accordingly, observations from onshore exposures of fault geometries and growth-basin configurations yield important guidelines for the analysis of faults in the seismic data. Onshore upper Triassic exposures on Edgeøya (East Svalbard) display growth-faults with throws of 50-100 m in the sedimentary successions of two interacting types; (i) listric faults that sole out in pro-delta/marine shales, and (ii) steeper, more planar faults that have a deeper-seated origin. Cross-cutting relationships suggest linked movements of the two extensional fault types. The succession can be subdivided into two parts: a lower faulted array of half-graben basins with a complex stratigraphic architecture related to syndepositional faulting, and an overlying, less disturbed succession. These parts are separated by an unconformity overlain by a stratigraphic interval that drapes the lower, faulted succession, marking a major transition. For the growth-basins, sedimentary facies is consistent with a deltaic to estuarine depositional system, suggesting there is a link between a nearby deltaic sand-prone point-source(s) and shallow marine to tidal reworking of sediments. We hypothesize that Triassic faulting halted regional clinoform progradation, by arresting and redirecting deltaic/coastal sand distribution. "

AAPG Search and Discovery Article #90177©3P Arctic, Polar Petroleum Potential Conference & Exhibition, Stavanger, Norway, October 15-18, 2013