High resolution comparative palynostratigraphy and palaeoecology of Oligocene sequences in the terrestrial basins of the Western British Isles and the marine North Sea basin

Oligocene sediments from six terrestrial basins in western Britain and two boreholes from the North Sea Basin were studied. These Oligocene sequences are dominated by claystones with silts, sands, conglomerates and lignites. From these sediments 116 samples were processes for a quantitative palynological study. Taxa encountered included 142 genera and 264 species. Using palynological associations and the ranges o f taxa the two North Sea Basin sections could be correlated with the data from the western British Isles basins. A fall in sea level at the Rupelian/Chattian boundary was evident from the data enabling absolute ages to be defined for the correlative events between the marine sequences. Upto now the ages o f the terrestrial Oligocene sediments in western Britain have been poorly constrained. It was found that the pollen and spore events o f the marine sequences could be seen in the data from the western British Isles allowing, for the first time, a high resolution comparative palynostratigraphy for the Oligocene sequences o f North and West Britain. The distribution o f the taxa encountered and statistical tests on the data indicate a fall in sea level at the Rupelian/Chattian boundary and three local transgressive events (two in the Upper Rupelian and one in the Upper Chattain). The Rupelian palaeoecology suggests mixed mesophytic forests surrounding floodplain areas with floodplain swamp development. This changes into the Chattian with secondary dryland and primary forests taking over from the mixed mesophytic forests. The fall in sea level and associated fall in base level generates instability leading to fluctuating floodplain swamp environments. A similar situation is envisaged for eastern England where the dominance o f mixed mesophytic forests and coastal littoral swamp environments changes to more open, drier forests and unstable coastal swamps.