Integrated chronostratigraphy of the Pliocene-Pleistocene interval and its relation to the regional stratigraphical stages in the southern North Sea region

Abstract

Time-stratigraphic interpretations of Late Pliocene to Early Pleistocene sediments from onshore locations and from marginal marine settings of the North Sea Basin often refer to the subdivision of the Dutch and British ‘Quaternary’ regional stratigraphic stages. Since age control for these stages and their stage boundaries are based on relative dating methods, in this study pollen, dinoflagellate cysts and foraminiferal assemblages were investigated to correlate the regional stratigraphic stages independently to the global chronostratigraphy and the paleomagnetic timescale. The data were obtained from eight boreholes located in the depocentre setting of the Late Pliocene North Sea Basin comprising a 1000 m thick sedimentary succession. The British Gedgravian and Waltonian stages, the Dutch Reuverian to Brunssumian as well as published foraminiferal zones (NSB 14, FB and the lower part of the FA2 zone) fall within the Zanclean and Piacenzian. The lower boundaries of the Pre-Ludhamian and Pretiglian stages and of the NSB 14 to 15 zones are close to the paleomagnetic Gauss-Matuyama boundary. The Pre-Ludhamian, Ludhamian, Thurnian and the Pretiglian, Tiglian A and Tiglian B stages presumably cover the marine isotope stages 103 to 95. It is proposed that the Ludhamian, Thurnian and the Tiglian A were short lasting, warm, periods during which sea level highstand facilitated sedimentary deposition at the marginal areas of the North Sea Basin. The lower boundary of the paleomagnetic Olduvai subchron is situated in the Tiglian C1-4b stage while the TC4c stage is found within the Olduvai subchron. Foraminiferal NSB 15 and NSB 16 zone as well as the upper part of the FA2 and FA1 zone fall within the Gelasian and cover the Matuyama chron as well as the lower part of the Olduvai subchron. Comparison with formerly dated North Sea sediments shows a good agreement between foraminiferal zonations on a broader scale but significant differences in absolute ages occur. Strontium isotope values indicate approximately 1 Ma younger ages as expected from our chronostratigraphic model. This discrepancy is explained by the dominance of freshwater from river discharge contributing high amounts of eroded material to the basin, leading to an increase of the 87Sr/86Sr ratio in the shelf-sea water.