QUANTITATIVE-DETERMINATION OF TERTIARY SEDIMENT SUPPLY TO THE NORTH-SEA BASIN

Sediment supply comprises a major family of regime variables that infl uence geomorphic surface grade. Spatial and temporal changes in total sediment supply and sediment texture (gravel:sand:mud ratio) will caus e reconfiguration of depositional and erosional profiles, potentially creating or influencing the sequence stratigraphic framework of the ba sin. Sequence grain volume, which is defined as the volume of sediment ary grains in an individual stratigraphic sequence (total sequence vol ume minus cement and porosity volume), has been quantitatively determi ned for each of 16 genetic stratigraphic sequences in the North Sea Ba sin. Rates of total sediment supply to the basin in both time and spac e were then calculated. Sand grain volume and sand:mud ratio were also calculated for each sequence. These data define four principal episod es of Tertiary sediment supply. The most significant episode occurred in the late Paleocene and was followed by secondary episodes in the Eo cene and Oligocene. A fourth Neogene episode extends through the prese nt. Ail episodes correlate to source-terrain tectonic pulses related t o evolution of the North Atlantic Basin, to intraplate stress changes associated with successive phases of the Alpine orogeny, or to the lat e Cenozoic epeirogenic uplift of Scandinavia. The major episodes, in t urn, 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 changin g source-area relief and resulting topographic grades and related chan ges in sediment yield into the basin was a principal control on North Sea Cenozoic sequence development. Source-basin relief, in turn, was l argely determined by regional tectonism.