Development of Intra‐Rift Basins During Stress Field Change in the Central Upper Rhine Graben (SW Germany)

Abstract The essentially non‐magmatic continental rift system of the Upper Rhine Graben (URG) is segmented and characterized by intra‐rift sub‐basins that exhibit NE to NW trends suggesting complex basin development during rifting. Structural modeling and analyses of an about 40 km 2 3D seismic survey from the northern part of the central URG segment show deep rooted NNE‐striking faults controlling early, syn‐rift 1, extensional basin evolution from about 47 Ma to 27 Ma. The change in stress field at about 27 Ma and subsequent reactivation of these deep rooted basement faults resulted in a new set of shallow rooted en‐echelon faults. On a larger scale this change in stress field was accompanied by a shift of regional depocenters. The shallow rooted en‐echelon faults nucleated in 32–28 Ma old strata and are linked by conjugated relay ramps that control the development of latest Oligocene to early Miocene syn‐rift 2 basins trending N to NNW. Although we only studied a small part of the >11,000 km 2 large URG, we hypothesize that this type of intra‐rift basin development in the hanging wall of major deep rooted normal faults is more widespread in the graben and may represent a general style for the development of other late Oligocene‐early Miocene intra‐rift basins, such as for example, the distinct Heidelberg Basin. We suggest increasing mechanical coupling between the European lower plate and Adriatic upper plate at c. 30 Ma to 28 Ma as a possible cause for the Oligocene stress field change.