Modes of Deformation in Sedimentary Multilayers Interacting With Sub-Décollement Structures: Insights From 3D Seismic Interpretation in the Eastern Jura Fold and Thrust Belt

The Jura fold and thrust belt is characterized by dominant thin-skinned thrusting and variable interaction with inherited structures and deep-seated (i.e., sub-d & eacute;collement) faults. Using 3D seismic data, the styles of deformation and the relationships with inherited structures at the eastern termination of the fold and thrust belt are documented in an area located NW of the city of Z & uuml;rich. The investigated seismic volume includes two major, ENE trending fold-thrust zones involving the Triassic-Jurassic epicontinental platform succession and the stratigraphically overlying Cenozoic Molasse Basin deposits. The location of both fold-thrust zones appears to be controlled by variable interaction between the d & eacute;collement level hosted in the Triassic evaporites of the Muschelkalk Group and faults linked to an underlying Permian-Carboniferous graben. Different modes of interaction of the Mesozoic multilayer (including the weak evaporite level close to its base) and underlying upper Paleozoic basin fill with inherited faults produced a marked contrast in structural style (pop-up and triangle zone geometry) between the N and S fold-thrust zones. We suggest that the different types of structures provide an unprecedented record of the transition from thin-skinned thrusting (dominant in the N fold-thrust zone) to deeply rooted deformation controlled by the inherited structural architecture of the upper Paleozoic basin. Such a transition was characterized by focusing of strain from the upper Paleozoic section to a narrow belt of Mesozoic strata, triggering coeval buckling and reverse faulting (manifested in the S fold-thrust zone). Propagation of sub-d & eacute;collement faults and segment linkage eventually led to breaching of the regional detachment.