| dc.description.abstract | In this study, the subsurface of the M- and N-blocks of the Dutch North Sea was analysed and modelled. An emphasis was put on the Late Pleistocene and Holocene sediments via the use of cores and seismic imagery of the study area. The M- and N-blocks of the Dutch North Sea are part of the North Sea Basin and is located north of the Dutch Wadden Islands. The study area was divided into the twelve-mile zone, the coastal proximal part, and the distal part of the blocks.
This research was initiated by the sand dredging planning project carried out by Deltares and TNO – Geological Survey of the Netherlands (TNO-GDN). Cores and seismic imagery from this project and the TNO-GDN database (Dinoloket) were collected to create a large database for the study area. With cores from the database and core samples, cross-sections with facies classes and formations were made. The formations and facies were interpreted and spatially explained via a paleogeographical description of the area. For a large part of the cores in the database the sediments were divided into formations, members and beds and the formation boundaries were imported and added into a 2.5D-layer model to show the three-dimensional distribution of the formations in the subsurface of the
study area.
Resulting from the extensive research and interpretation of the sediments in the cores and seismic imagery a clear succession of formations was found. In the northeast and southwest part of the twelve-mile zone glacial sediments of the Peelo Formation were found, interpreted as tunnel valley-fills of the Elsterian glacial period. During the following Saalian glacial period the Scandinavian ice sheet deposited the Gieten Member of the Drente Formation in the study area as an irregular surface. At these locations, the Drente Formation and younger Holocene sediments are found directly on top of the Peelo Formation, resulting in a hiatus of respectively 200 kyr and 400 kyr, due to the erosion of the Saalian ice sheet. During the following Eemian interglacial period the study area was covered by a
shallow to deep sea and deposited the marine sediments of the Eem Formation. During this research there was a focus on the division of the Eem Formation into multiple facies classes, as only a small amount of information about the division of the Eemian sediments was available from previous studies. The Eem Formation together with the Boxtel Formation, deposited by terrestrial and wind processes during the Weichselian glacial period, covered the irregular surface left after the last coverage of the ice sheet during the Saalian. The Holocene sediments in the subsurface consist of the Nieuwkoop, Naaldwijk and Southern Bight Formation. The Nieuwkoop Formation can be found as the Basal Peat Bed deposited in marshes at the start of the sea-level rise during the Early Holocene. As the sea level rose further above the ground surface a shallow sea with lagoons formed, in which the Velsen Bed of the Naaldwijk Formation was deposited. The most prominently present deposits in the subsurface of the study area are the tidal channel fill deposits of the Naaldwijk Formation. The tidal channels were high energy environments eroding into the substrate beneath the channels, such as the Velsen Bed, the Basal Peat Bed, the Boxtel Formation and the Eem Formation, but also in older tidal channel fills of the Naaldwijk Formation. After the infill of the tidal channels the Southern Bight Formation was and continues to be deposited in the study area. This formation is found directly under the sea bottom and is mostly associated with the sand waves structures present at the sea bottom. | |
