Abstract

Høgsnyta is one of the (1 x 5 km [0.6 x 3.0 mi] scale) mountainside outcrops that expose shelf-margin clinoform complexes in the Eocene Central Basin of Spitsbergen. The Høgsnyta shelf margin in Reindalen, exposed on a dip-parallel, steep mountainside, is a wedge-shaped turbidite sandstone body, 70 m (230 ft) thick at the shelf edge, that thins downslope and pinches out above the base of slope, approximately 5 km (3 mi) from the shelf edge. The 200 m (656 ft) height of the clinoform complex gives a direct estimate for the paleo-water depth. The outcrop also exposes older marine mudstone below the studied shelf-margin clinoform complex, the shelf reaches of younger clinoform complexes, and a younger coastal-plain succession above the shelf-margin complex documented in this paper.

The Høgsnyta turbidite system is a slope-turbidite apron that is attached to a fluvial shelf-edge delta system. Fluvial distributary channels fed into delta-front sheets or into slope channels (chutes); the slope channels terminated with slope lobes on the upper and middle slope, or with turbidite sheets on the lower slope.

The internal architecture of the Høgsnyta shelf-margin clinoform complex reflects the following timing of deposition in a sea level cycle: (1) shelf-margin progradation during the falling stage; (2) lower-slope aggradation during the early lowstand; (3) intralowstand flooding back onto the shelf edge; and (4) shelf-margin progradation during the late lowstand. The Spitsbergen data show that sands were distributed beyond the shelf edge during the falling stage and the lowstand, whereas the sandy sediments were deposited largely onto the shelf and coastal plain during the development of transgressive and highstand systems tracts.

Two types of shelf margins in the Eocene Central Basin produce turbidites. Type I shelf margins produce basin-floor fans, whereas Type II shelf margins, like the Høgsnyta margin, have slope-turbidite systems. Both systems reflect broadly similar timing of deposition in a sea level cycle and indicate a sea level fall below the shelf edge. However, in Type I systems significant shelf-edge erosion, slope bypass, and basin-floor deposition occur, whereas in Type II shelf margins the turbidite systems are attached to shelf-edge deltas and confined to the slope. The conventional explanation for the architectural and sediment partitioning (distribution) differences between Type I and II margins is that the magnitude or duration of sea level fall was greater in the case of Type I. We propose that higher rates of sediment fallout at the shelf edge and upper slope during the falling stage can dampen incision and prevent deep channeling at the shelf margin.