Highstand Shelf-Edge Deltas: An Example from High-Latitude Eocene West Spitsbergen, Norway

Carlos A. Uroza and Ronald J. Steel
The University of Texas, at Austin, Austin, TX

Highstand shelf-edge deltas are able to reach the shelf margin during rising relative sea level. They are important because they cause retention of high volumes of sand on the aggrading shelf and there may be a much-reduced sandy sediment volume available for deepwater deposition. Some high-latitude Eocene shelf-edge deltas of the Battfjellet Formation, West Spitsbergen, are identified as highstand deltas based on: 1- An aggradational tendency with stacked parasequences suggesting relative sea level rise during progradation, 2- A high sediment supply from the nearby uplifted West Spitsbergen Orogenic Belt, 3- A context of longer term rising shelf-edge trajectory, and 4- A narrow shelf (about 20 km) and therefore short transit time for the deltas, thus reducing the likelihood of auto-retreat. These deltas can be seen to occupy a shelf-edge location, and they are wave-dominated as would be predicted at such a shelf-margin site.

These Eocene deltas form fine to medium-grained, progradational, and stacked sandbodies up to 25 m thick and are exposed along a 4 km-dip-oriented transect in the Van Kuelenfjorden area. They represent the regressive part of each of three well-defined parasequences (encompassed within a 4th-order stratigraphic sequence) with a predominance of wave-generated structures (swaley and hummocky cross-stratification, flat lamination, and wave-ripple lamination). The delta topsets contain tidal-influenced distributary channels or are truncated by estuarine deposits.

The slope succession beyond the shelf edge contains thin sheet sands deposited as tempestites, within an otherwise shale-dominated environment. There are no sand-rich slope channels and probably no basin-floor fans.