HIGH-RESOLUTION SEQUENCE STRATIGRAPHY OF THE LOWER TRIASSIC BUNTSANDSTEIN IN THE NETHERLANDS AND NORTHWESTERN GERMANY

Detailed log correlations of the largely fluvio-lacustrine Lower Trias sic 'Buntsandstein' (Late Permian-Early Anisian), carried out on 80 we lls in the Dutch onshore and offshore areas, can be linked to northwes t-German high-resolution sequence stratigraphy. The correlations show that cyclic sedimentation occurred in large parts of the basin. Seven Ist-order sequences are recognised, namely the Main Claystone, Rogenst ein, Volpriehausen, Detfurth, Hardegsen, Selling and Lower Rot Sequenc es. They are overlain by the lower part of the Upper Rot-Lower Muschel kalk Sequence. Distinct sequence boundaries have been identified at th e bases of four sequences: Volpriehausen, Detfurth, Selling and Upper Rot. The higher-order sequences consist of fining-upwards cycles with a thickness of up to tens of metres. The sequences are laterally persi stent and have a characteristic expression on gamma-ray and sonic logs . In the Lower Buntsandstein, they display a uniform character through out most of the area, with only minor differences in thickness or lith ology. NNE-oriented lows and swells were formed during deposition of t he Volpriehausen, Detfurth and Hardegsen Sequences. Uplift prier to th e deposition of the Selling Sequence caused deep erosion on the swells in the basin and minor erosion in the lows. The high-resolution seque nces probably represent alternating, relatively wet and dry climatic p eriods, with a periodicity of about 100 000 years. An analysis of the sequences suggests that their reduced thickness on the swells is mainl y the effect of erosion. This is supported by analyses of the accumula tion patterns and rates.