Fault Mapping and Reconstruction of the Structural History of the Dutch Central Graben (2014)

This MSc thesis has been written by former intern Duncan Wijker.

This paper presents the results of a study focused on the structural development of the Dutch Central Graben and aims to provide a comprehensive description of the structural history of the main structural elements. The study makes use of the recently acquired NL-DEF-3D multi-client seismic survey which was designed to provide modern 3D long offset seismic data on large parts of the D, E and F blocks covering over 6,000 km2. The improved the imaging of the deepest parts of the Dutch northern offshore allows the identification of deep seated fault relations and improved insight into salt activity phases.

The data shows the existence of an intra-Carboniferous angular unconformity in a large part of the Step Graben. Based on both literature and well control the unconformity can be identied to be of Stephanian age, with Stephanian sequences onlapping onto strongly tilted late Westphalian strata. It is the first time a base Stephanian unconformity is identied on seismic in the Dutch offshore but it confirms earlier predictions.

The seismic profiles show a pre-Permian fault system already active at the site of the Dutch Central Graben. A few of these faults were reactivated during Triassic rifting phases. Thickness maps of Triassic strata together with cross fault thickness variations indicate fault activity already during Early Triassic times, much earlier than conventionally thought.

Several different models explaining features observed from the seismic data and describing the deformation history of the Dutch Central Graben have been analyzed. It followed that a model of moderate Triassic rifting, Late Jurassic rifting and Late Cretaceous inversion tectonics together with major halokinesis from Triassic times onward, ts best with the observation.