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The diversity of morphological features of Mesozoic inversion structures in NW Germany as representatives of inversion structures in northern Europe is presented and their origin analysed and geologically dated. The particular role of salt in inverted basins and the re-shaping of pre-existing salt structures during the inversion act is demonstrated and the term 'salt wedge', a Zechstein salt intrusion into salt layers within the Triassic sedimentary pile, introduced. The leading theories on inversion (continent-continent collision, re-activation Variscan features) are discussed and discarded, but no new comprehensive theory was developed. The impact of inversion on HC prospectivity of sedimentary basins is debated and proposals for future interdisciplinary research are made.

Since the beginning of the development of the North German Basin in Stephanian to Early Rotliegend times, rifting played a major role. Nearly all structures in NW-Germany and the German North Sea -(more than 800) -salt diapirs, grabens, inverted grabens and inversion structures -are genetically related to rifting. Today, the rifting periods are well dated. We find signs of dilatation at all times except from the Late Aptian to the end of the Turonian. To the contrary, the period of the Coniacian and Santonian, lasting only five million years was a time of compression, transpression, crustal shortening and inversion. Rifting activities decreased notably after inversion in Late Cretaceous times. Tertiary movements concentrated on a limited number of major, long existing lineaments. Seismically today NW-Germany and the German North Sea sector is one of the quietest regions in Central Europe.

The 'Northwest European Gas Atlas' comprises maps on characteristics (e.g. molecular and isotopic compositions) of natural gases in northwest European gas fields, on the distribution and facies of source and reservoir rocks, on maturities, and other relevant geological information.

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Thermal history and evolution of the Palaeozoic petroleum system of the western Lower Saxony Basin as well as charge history of the Apeldorn gas field was reconstructed using 2-D forward basin modelling software. The Apeldorn gas field is located on an inverted western rim of the Lower Saxony Basin (LSB) and belongs with its relatively anomalous nitrogen content of 73.9 vol. % to one of the most unique gas accumulations in North Germany. Based on thermal calibration studies utilising both, vitrinite reflectance and corrected bottom hole temperatures as calibration parameters, a shallow burial model and an anomalous event of Coniacian high heat flow of 80 to 120 mW/m2 was derived. As result, Lower Triassic and younger successions became subjected to slight changes in thermal maturity as opposed to Carboniferous and Permian successions, which show no assessable impact of the high heat flow event on the coalification pattern. The deep burial model in contrary to the shallow burial model is not supported by the structural reconstruction and backstripping in this more marginal setting. According to the modelling results, the key charge of the present Apeldorn gas field began in Tithonian (late Upper Jurassic) during the major phase of rifting in the Lower Saxony Basin. The present Westphalian coal-derived gas accumulations of the Lower Triassic Buntsandstein reservoir were sourced directly from modelled methane pools at top Rotliegend level. The hydrocarbon potential of the Westphalian source rocks became exhausted in Oxfordian (early Upper Jurassic). Reduction of the hydrostatic pressure during the Coniacian high heat flow event together with uplift during the Coniacian-Santonian inversion led to an extensive free gas exsolution. The resulting gas mixture between the exsolved free gas and the Westphalian coal-derived gas reached and saturated Buntsandstein reservoir. The structural trap became destroyed in course of the inversion leading to a sharp decrease of methane and nitrogen saturation.

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