Quantitative clay mineralogy as provenance indicator for recent muds in the southern North Sea

Abstract

The origin of recent mud deposits as well as the coastal turbidity maximum in the French-Belgian-Dutch nearshore area of the southern North Sea is still under debate in the literature. Some models favor the erosion of the Cretaceous chalk cliffs along the English Channel and subsequent NE ward directed transport, other models focus on the erosion of Eocene to earliest Oligocene, and Pleistocene to Holocene clays outcropping on the seafloor off the Belgian coast. In order to validate these hypotheses, the detailed qualitative and quantitative clay mineral composition of these sediments was used as a provenance indicator. By comparing the clay mineral composition of the mud deposits and the associated suspended particulate matter (SPM) with the composition of potential nearby and more remote sources such as the present day marine environment, estuaries and rivers, coastal erosion areas and the geological substratum, the origin of the mud deposits and the SPM could be traced. Results showed that only the clay composition of the Scheldt estuary coincides with those of the mud deposits and the coastal turbidity maximum and that all other potential sources could be excluded. Our data suggest that the clay mineral composition of the mud deposits has a similar composition since at least about 100.000 years, indicating that these deposits originate from a paleo-Scheldt river rather than from the recent river system, as the present-day Scheldt estuary is not source of fine-grained sediments. The present-day SPM in the Belgian-Dutch nearshore area originates mainly from the erosion and resuspension of the existing mud deposits situated in the Belgian nearshore. This study demonstrates the value and suitability of quantitative bulk and clay mineralogy techniques in sediment provenance studies and highlights the importance of incorporating the recent geological history in hydrodynamic studies of sedimentary basins.