In this thesis, a detailed tectonic and stratigraphic reconstruction of the development of the southern part of the Late Palaeocene - Oligocene Dutch North Sea Basin is presented. The research concentrates on fault geometry and sedimentary architecture in response to tectonic activity. The aim of this research is to gain an improved insight in the mechanics of inversion tectonics, when multiple inversion phases occurred in separate pulses. The research is based on seismic and well data, which cover a significant part of the Dutch offshore territory. Tectonic subsidence and uplift are quantified, and sources of lithospheric stress identified. Sequence stratigraphic correlation improves the temporal resolution of reconstructions.
keywords: North Sea Basin, Broad Fourteens Basin, Palaeogene, inversion, sequence stratigraphy
The Dutch part of the North Sea Basin has experienced distinct pulses of tectonic activity since the Late Palaeozoic. Activity started with rifting, which resulted in the formation of the Broad Fourteens Basin (BFB), and continued with tectonic inversion and associated uplift during the Mesozoic and Early Cenozoic.
After cessation of the Palaeocene Laramide phase, several episodes of minor tectonic activity have been detected, which occurred from the Late Ypresian to the Bartonian. These tectonic pulses resulted in reduced subsidence and uplift. Unfortunately, Early Oligocene erosion removed much of the Ypresian-Bartonian sediments in the study area, which obscured the evidence of these intervals of tectonic activity. It is, therefore, not a surprise that this activity has been unnoticed until now. However, the events can be correlated to intervals of tectonic activity in areas surrounding the Netherlands territory, which indicates their regional importance.
The inverted BFB and the southern North Sea were uplifted in response to compressional stress associated with the Eocene-Oligocene Pyrenean phase. The response is of a different nature than during earlier phases of compression. An area more than twice the width of the Mesozoic BFB was uplifted. This is probably the result of a difference in the direction of the Pyrenean compressive stress field with respect to earlier pulses of inversion. The thick Palaeocene and Eocene sedimentary cover, which had been deposited in the area after cessation of the Laramide phase, might have enhanced this effect by deflecting the local stress directions even further and by favouring reactivation of normal faults in a strike-slip sense over formation of new, low-angle thrust faults.
After the Oligocene, tectonic activity ceased in the study area. The neighbouring Roer Valley Graben, which until the Oligocene experienced a similar tectonic evolution as the BFB, was tectonically reactivated in response to stress induced by the Alpine orogenic belt. The Roer Valley Graben experienced rapid subsidence, which continues until present times. A comparison of both areas shows that this different evolution is not caused by a difference in local stress or existing fault directions. Again, overburden thickness might have been an important factor in prohibiting the reactivation of faults in the southern North Sea. Additionally, absorption of compressive stress emanating from the Alpine belt by the grabens of the West European Rift System might result in a decrease in intensity of tectonic activity towards the southern North Sea.