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The field of provenance analysis has seen a revival in the last decade as quantitative data-acquisition techniques continue to develop. In the 20th century, many heavy-mineral data were collected. These data were mostly used as qualitative indications for stratigraphy and provenance, and not incorporated in a quantitative provenance methodology. Even today, such data are mostly only used in classic data tables or cumulative heavy-mineral plots as a qualitative indication of variation. The main obstacle to rigorous statistical analysis is the compositional nature of these data which makes them unfit for standard multivariate statistics. To gain more information from legacy data, a straightforward workflow for quantitative analysis of compositional datasets is provided. First (1) a centred log-ratio transformation of the data is carried out to fix the constant-sum constraint and non-negativity of the compositional data. Next, (2) cluster analysis is followed by (3) principal component analysis and (4) bivariate log-ratio plots. Several (5) proxies for the effects of sorting and weathering are included to check the provenance significance of observed variations and finally a (6) spatial interpolation of a provenance proxy extracted from the dataset can be carried out. To test this methodology, available heavy-mineral data from the southern edge of the Miocene North Sea Basin are analysed. The results are compared with available information from literature and are used to gain improved insight into Miocene sediment input variations in the study area.
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 Cl-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.
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