Long-Term Delivery and Distribution of Sediments from River Catchments to Basin Floor Fans

Sømme, Tor O.¹, William Helland-Hansen¹, Ole J. Martinsen², John B. Thurmond² (1) University of Bergen, N-5007 Bergen, Norway (2) Norsk Hydro Research Centre, N-5020 Bergen, Norway

To pursue a best-possible understanding of deep-water subsurface reservoir distribution, investigation of quantitative aspects of sediment delivery and storage along entire source-to-sink profiles are required. 28 erosional-depositional systems associated with both active and passive margins, and with different types of climate and basin morphology, have been examined in order to identify the main controls on timing, volume and spatial distribution of sediments delivered to and beyond the shelf break. Detailed digital elevation models provided information on drainage and basin parameters (e.g. length, gradient and area). Furthermore, an extensive literature search gained further knowledge on sediment dispersal patterns and basin floor fan characteristics.

Rivers are the primary source for deep-water sediments, and a close relationship between the size and morphology of a given drainage area, and the associated sediment load, transportation pattern and volume of the deep-sea fan is shown. The link between the river mouth and the shelf break is of primary importance in controlling sediment dispersal, as the shelf functions as storage for river-fed material. Narrow and steep shelves, strong littoral and tidal currents, and submarine canyons incising the shelf are most important for sediment transport to the basin floor.

The maximum/minimum river discharge ratio and sediment load variations, however, control sediment supply to the river mouth. These factors operating within individual drainage areas are considered as internal variables. The cross-sectional shape and plan-view morphology of the source-, shelf- and basin floor transects are external factors, governing long-term storage and transportation of sediments to basins.