Stratigraphy and tectonics of Permo-Triassic basins in the Netherlands and surrounding areas

This thesis addresses different aspects of the geological development during the Permian and Triassic (300 to 200 Ma) of the Netherlands and surrounding areas. The study area encompasses the Southern Permian Basin (SPB), a large intracratonic basin stretched out from the United Kingdom in the west to Lithuania in the east. This study revealed that, rather than one basin, the SPB actually comprised three basins, separated by subtle swells. The basins each originated differently with specific subsequent histories High-resolution stratigraphic correlations of the Permo-Triassic interval were carried out to (i) align the various stratigraphic schemes, and (ii) to define a single basin-wide stratigraphic framework for the SPB (Chapter 1). High resolution sequence stratigraphy as a correlation tool is presented in Chapter 2. Two new tectonic pulses in the Late Permian (Zechstein) are presented in Chapter 3. A detailed overview of the stratigraphy and tectonics of the Permian and Triassic in the Netherlands is presented in Chapter 4. The regional synthesis is presented in Chapter 5. It includes a series of new, high-resolution, paleogeographic maps illustrating the current insights in basin evolution. One of the recommendations of this study is a revision and redefinition of some units in the Permian and Triassic lithostratigraphy of the Netherlands (Appendix 1). Following the Variscan Orogeny, at the end of the Carboniferous (300 Ma), the Netherlands was situated in the interior part of the super-continent Pangea, north of the Alpine-style Variscan Mountain chain, which formed as a result of the accretion of the Gondwana to Laurussia plates. These mountains supplied the bulk of the sediments to the Netherlands until Mid Triassic times; further, they formed a barrier for humid air masses from the Tethys. Climatic conditions were arid to semi-arid for most of the Middle Permian to Middle Triassic, becoming slightly more humid during the Late Triassic. Marine incursions in the basin have been recorded in the Late Permian from the north, and from the late Early Triassic onwards from the Tethys. Late Carboniferous to Middle Permian rift/wrench tectonics triggered slab detachment and extrusive volcanism during a prolonged period (Early to Middle Permian). These processes resulted in the collapse of the Variscan Mountains. Initially molasse-type sediments were deposited, followed by eolian sediments and salts. Subsidence was essentially driven by thermal lithosphere contraction. Desert sediments (Rotliegend) were deposited during the Middle Permian, followed by cyclic evaporites of the Zechstein (Late Permian). The Triassic evolution is dominated by a complex interplay of climate, transgressions and short-lived pulses of rift tectonics. Cyclic sedimentation in the EarlyTriassic is attributed to climatic Milankovitch cyclicity. From the Middle Triassic onwards, rifting concentrated in the Central North Sea, Horn and Gluckstadt Grabens. During the pulses, up to 4,500 m of salt and fine-grained clastics accumulated here. Late Triassic compression, related to the closure of the Paleo-Tethys, resulted in the doming of Fennoscandia. Delta systems from the this high built out southward over the SPB during relatively humid periods. A major marine transgression flooded the area during the youngest part of the Triassic.