Exploration in Classic Thrust Belt and Its Foreland--Bavarian Alps, Germany: ABSTRACT

The Bavarian Alps are composed of a stack of thrust sheets, which have been transported northward onto the molasse of the Tertiary foredeep. Exploration in the Unfolded Molasse zone and its Mesozoic substrata has resulted in the discovery of a considerable number of oil and gas fields. Most of these fields are related to monoclines, which are aligned along west-east-striking, reverse growth faults. In addition, other fields are related to facies traps which were successfully located by improved seismic methods. The northern edge of the Alpine orogene is formed by the west-east-striking synclines of the Folded Molasse zone, which is thrust at least 20 km over the autochthonous Unfolded Molasse zone. Several wildcats reveal good porosities and oil and gas shows. Coalification studies have proved that even the deepest parts of the Molasse zones are within the oil window. The Helveticum zone is thrust over the Folded Molasse zone, and it contains potential reservoir rocks with gas shows. The Helveticum zone is tectonically overlain by the Flysch zone, which has no reservoir properties. The Kalkalpin zone (Cretaceous Alps) is the uppermost thrust complex. It was recently penetrated by the wildcat Vorderriss 1, which proved that the Kalkalpin consists of several nappes with a total thickness of 6,400 m. At Vorderriss the Flysch zone is not present and must have been tectonically removed; the Kalkalpin zone is thus underlain by allochthonous Helveticum zone. Minor oil and gas shows are present in the Vorderriss 1. In the Alps, seismic data are of satisfactory to good quality and major thrust planes can be mapped. The seismic data indicate that the molasse and its substrata extend far to the south beneath the Kalkalpin zone and, furthermore, they apparently form domal structures at several locations. At Vorderriss, seismic data indicate that the Helveticum zone, the molasse, and the Mesozoic substrata, which all underlie the Kalkalpin zone, have a total thickness of about 2,000 m. The crystalline basement is expected to be at a depth of 8,200 m. According to maturity studies this sedimentary complex is still within the oil window. End_of_Article - Last_Page 673------------