Clinoforms, Clinoform Trajectories and Deepwater Sands

Ron Steel, Institute of Energy Research, University of Wyoming, Laramie, WY 82071, and Torben Olsen, Statoil, Forus, Norway

Abstract

Clinoforms, which have heights up to 350 meters and lengths of 25km in the Eocene strata of Spitsbergen, represent morphological surfaces (time lines) that pass from nearly flat-lying coastal and shelf environments, through gently-dipping (2-5 degrees) deep-water slopes to nearly flat-lying basin-floor fans. These clinoform surfaces are an order of magnitude larger than the delta/strandplain clinoforms from which they are constructed. Repeated regressive-transgressive transits of the deltas and strandplains, between lowstand shelf edge and highstand embayments, have created the morphological shelf and caused the coastal plain, shelf, and basin floor to aggrade, while the shelf margin accreted.

Four different types of shelf-slope clinoform are documented, classed according to (1) the process regime on the outer shelf, (2) the degree of fluvial incision, if any, on the shelf margin, and (3) the volume partitioning of the sand budget between shelf-edge, slope and basin-floor sites.

A nearly dip-oriented transect has been selected across a Spitsbergen basin whose shelf edge has accreted some 40 km in less than 6my. A clear relationship can be seen between the growth trajectory of the shelf margin and the dominant types of clinoform in any particular growth segment. Low-angle accretionary trajectories have been created by clinoform sets dominated by Types 1 and 2, which have partitioned much of their sand budget onto the turbidites of the slope and basin floor. In contrast, high-angle accretionary trajectories result from clinoform sets that are dominated by Types 3 and 4, that have stored most of their sand budget in the coastal plain and on the shelf.