Quantitative Determination of Tertiary Sediment Supply to the North Sea Basin

Abstract

Sediment supply comprises a major family of regime variables that influence geomorphic surface grade. Spatial and temporal changes in total sediment supply and sediment texture (gravel:sand:mud ratio) will cause reconfiguration of depositional and erosional profiles, potentially creating or influencing the sequence stratigraphic framework of the basin. Sequence grain volume, which is defined as the volume of sedimentary grains in an individual stratigraphic sequence (total sequence volume minus cement and porosity volume), has been quantitatively determined for each of 16 genetic stratigraphic sequences in the North Sea Basin. Rates of total sediment supply to the basin in both time and space were then calculated. Sand grain volume and sand:mud ratio were also calculated for each sequence. These data define four principal episodes of Tertiary sediment supply. The most significant episode occurred in the late Paleocene and was followed by secondary episodes in the Eocene and Oligocene. A fourth Neogene episode extends through the present. All episodes correlate to source-terrain tectonic pulses related to evolution of the North Atlantic Basin, to intraplate stress changes associated with successive phases of the Alpine orogeny, or to the late Cenozoic epeirogenic uplift of Scandinavia. The major episodes, in turn, contain secondary sequence-to-sequence variations that correspond to changes in spatial or temporal values of one or both of the supply regime variables. Again, most changes closely reflect details within the histories of the principal tectonic phases. The history of changing source-area relief and resulting topographic grades and related changes in sediment yield into the basin was a principal control on North Sea Cenozoic sequence development. Source-basin relief, in turn, was largely determined by regional tectonism.