Tectonic and Depositional Evolution of the Loppa High Area, Norwegian Barents Sea

Tore Amund Svånå

The Loppa High is a distinct structural element with the crest striking in a general north-south direction. The eastern flank is dipping towards the deeper areas of the Bjarmeland Platform / Ottar Basin. The mid-Carboniferous and younger sedimentary cover unconformably overlies a basement of folded and fractured strata over parts of the Loppa High and its northeastern extension towards the Maud Basin (herein informally called the Aurelia High). In well 7220/6-1 these basement rocks are dominated by quartzitic metasandstones of uncertain age. A correlation to comparable facies in the Late Precambrian Sørhamna Formation on Bjørnøya is suggested. Seismic examples illustrate how the tectonic events have left their depositional footprints in the sedimentary cover. The first event that is discussed in more detail deals with how differential subsidence has determined the geometry of the carbonate platform that was established in the Loppa High area in Moscovian time. In the surrounding basinal areas thick deposits of salt and associated evaporites and carbonates accumulated. Seismic and well data suggest that the two main evaporitic events occurred in Moscovian and Asselian time respectively. The salt onlaps the flanks of the Loppa and Aurelia highs. Lateral to the salt pinch-out, several Barents Sea wells show that thick anhydrite beds were deposited. The salt has acted as a detachment for later tectonism, including large scale gravity gliding of the overlying sedimentary package. Close to the pinch-out area of the salt, the combined effects of rifting and uplift of the Loppa / Aurelia highs have caused this gliding to form distinct graben structures. Along the northern margin of the Aurelia High, this applies to the western extension of the Hoop Fault Complex (situated southwest of the Svalis Dome / Maud Basin). And along the Aurelia High’s southern margin the same mechanisms resulted in formation of the Swaen Graben and its continuation along the eastern flank of the Loppa High. The tectonic events that triggered this gravity gliding and graben formation were most active in Late Jurassic and Earliest Cretaceous time. The rotated fault blocks with the Skrugard and Havis hydrocarbon discoveries were formed by the same tectonic event. West of the Loppa High continued and rapid subsidence led to accumulation of thick Cretaceous and Cenozoic sedimentary packages.

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