The origin of crude oil in the German sector of the North Alpine Foreland Basin

The German sector of the North Alpine Foreland Basin contains more than 50 oil and gas fields. To determine the origin of the oils, Lower Oligocene source rocks—the only significant source rock for which no modern data is available—were examined and compared with recently published data from the Jurassic Posidonia Shale and from Permo-Carboniferous rocks. In addition, the source potential of other Mesozoic units was evaluated. Finally, oil families were identified and correlated with specific source intervals, based on biomarkers and compound-specific carbon isotope data. The investigation shows that the Lower Oligocene can yield approximately 0.5 tHC/m 2 . Facies, depositional environment, and petroleum potential correspond to those of their counterparts in the Austrian part of the basin and reflect varying degrees of Paratethys isolation. Apart from the Lower Oligocene, only the Toarcian Posidonia Shale and Permian lacustrine shales are prolific oil-prone source rocks. Oil from Mesozoic reservoirs in the Lake Constance area originates mainly from the Posidonia Shale, although a contribution from Permian lacustrine shales cannot be excluded. Oil samples from Miocene reservoirs (Lower Freshwater Molasse) overlying the Mesozoic reservoirs exhibit an additional contribution from a Cenozoic source rock, which is probably not the Lower Oligocene. To the east, there is an approximately 150 km-long belt where oil is found predominantly in Oligocene reservoirs (Baustein Beds). The oil fields in the westernmost part of the belt also contain oil from Mesozoic and Cenozoic sources. All other oils, including oil in Eocene deposits, originate from Lower Oligocene source rocks.