Some data on the Holocene deposits in the Mark and Weerijs valleys (prov. Of Noord-Brabant, the Netherlands)

Abstract

Descriptions of cores from Holocene sediments in the Mark and Weerijs valleys (Province of Noord-Brabant, The Netherlands) allow the distinction of two groups of profiles. Those of the first group show humous sand at the top, underlain by peat. The sand may be more clayey at the base. In the present paper, this sand is indicated as a type I deposit. In the second group of profiles the peat contains an intercalated fine-sandy clay layer, indicated as a type II deposit. The thickness of this layer varies strongly, and the over- and underlying peat may be partially or wholly absent. Field observations point to a high-water origin of the type I deposits. Micropaleontological data from deposits of type II appear to indicate deposition in a fresh-water environment. Heavy-mineral data from type I and II deposits suggest a common source of origin. Grain size analyses, however, show a marked difference between the two types. This difference in grain-size distribution is attributed to an enrichment of type I deposits by cover sand. Palynological investigation of four complete cores showed that sediments of type I have been deposited in both valleys since the early Middle Ages. In the Mark valley, the deposition of type II started with the Atlantic and continued at least up to the Subatlantic. The formation of this type of deposit in the Weerijs valley appears to be confined to the Subboreal. The earlier sedimentation in the Mark valley is thought to be due to the post-glacial rise of the phreatic surface and to a deeper level of the Mark valley bottom. The presence of type II sediments of Atlantic and Subboreal age intercalated in peat, suggest that this relative rise of the phreatic surface was stronger during the Atlantic and Subboreal.