Devonian and Lower Carboniferous geology of the northern Dutch offshore

Abstract

The main purpose of this study is to investigate the paleogeographical and geological setting of the northern Dutch offshore in Devonian and Carboniferous times (including the A, the western B and northern E blocks). High-quality 3D seismic surveys reported on in this study made available a wealth of data. In addition, detailed core analysis and well log panels were used. The result of the project is a first geological overview and paleogeographic setting of the Devonian and Early Carboniferous in the northern Dutch offshore. Using seismic data, well logs and cores, a better understanding of the Devonian and Carboniferous geology was achieved. The granite of the ESH has been mapped in detail. Late Middle Devonian Kyle Limestone Group has strong reflectors which show onlap against the ESH. Using well logs and seismic data late Viséan tectonic tilting was interpreted on the ESH by late Viséan and early Namurian onlap against older sediments. Well logs show that the thickness of early Namurian sediments is thinner on top of the ESH in comparison to the well logs off the ESH and at the boundary of the ESH. This means late Viséan and Namurian is a period with tectonic activity. Paleogeographic maps in early Viséan, late Viséan and Namurian were made based on detailed core analysis and well log panels. Early Viséan is characterized by shoreline facies and fluvial facies in the north(west). These are lagoons and distributary channels with dominantly clastic sediment input. The shoreline was situated just south of the northern Dutch offshore. The ESH did not play a significant role. Late Viséan is characterized by carbonate deposits with flooding surfaces (clay) in between which point to a gradual increase in sea level. During Lower Carboniferous the sediment supply came from the northern highs. Tectonic tilting of the ESH started in late Viséan. However the ESH did not play a significant role in late Viséan. In early Namurian times active extension is said to cease and uniform regional subsidence took place; however the ESH shows tectonic activity. Tectonic tilting of the ESH started in late Viséan and caused the ESH to be a ‘high’ area in early Namurian. Shallow marine conditions dominated north of the ESH with more fluvial and foreshore deposits south of the ESH and on the ESH with abundant marine incursions. The ESH causes the division between facies.