Sand-grade density flow evolution on a shelf-edge–slope–basin-floor complex in the Upper Jurassic Olympen Formation, East Greenland

Abstract

The uppermost Callovian–Middle Oxfordian Olympen Formation is part of the early syn-rift succession of Jameson Land and Traill O, East Greenland and was deposited in prograding shelf-edge, slope and basin-floor environments. The formation consists of: (1) coarsening-upward units of sand-rich, prograding shelf-edge wedges; (2) slope and basin-floor mudstone; and (3) lenticular elongate and sheet-like, massive sandstone bodies deposited by sedimentary density flows on the slope, base-of-slope and basin floor. Systematic spatial and temporal variations in sandstone body geometry reflect down-slope transformations of the density flows. Lenticular and down-slope elongate sandstones mainly occur randomly scattered within prograding shelf-edge sandstone and slope mudstone. They represent short-travelled, hyperconcentrated density flows, filling pre-existing gullies that formed by retrogressive slumping. Sheet-like sandstones encased in mudstone were deposited from unconfined, concentrated density flows transitional to turbidity flows at the base-of-slope and on the basin floor. The Olympen Formation provides a well-exposed example of a sand-dominated shelf-edge–slope–basin-floor dispersal system in which the down-slope transformation of sand-grade density flows and resultant sandbody geometries can be demonstrated effectively. It may serve as a useful field analogue for a poorly understood but important type of hydrocarbon reservoir.