Structure and Prospects of Alpine Basins and Foredeep

Abstract

The sedimentary history of the German Molasse basin is characterized by three stages separated by major unconformities: (1) Permian-Carboniferous siliciclastic graben sedimentation, (2) Mesozoic mixed carbonate-siliciclastic shelf sedimentation, and (3) Tertiary siliciclastic foredeep sedimentation. The southern-most part of the basin was overthrust by the Alpine nappes. The hydrocarbon source rocks are Toarcian and Oligocene shales as well as Permian-Carboniferous coals. Most of the oil kitchen is to the north of the thrust front, whereas the gas kitchen is primarily in the subthrust zone. Some biogenic gas occurs in the shallower northeastern parts of the basin. The chief reservoir rocks are Triassic and Jurassic sandstones in the central and western part, and Tertiary sandstones and carbonates in the eastern part of the basin. They are commonly sealed by marine shales. Most traps are on the upthrown side of basin-parallel antithetic normal faults. The Molasse basin is in a mature stage of exploration, with relatively low remaining recoverable reserves. Additional exploration potential is inferred in stratigraphic traps in the foreland basin, as well as in structural traps in the subthrust zone and the nappes.