Triassic-Jurassic tectonic evolution of the Baltic sector of the North German Basin: regional extension, salt movement and large-scale uplift

Abstract

<p>As a part of the intracontinental Central European Basin System, the Baltic sector of the North German Basin has a long and complex history of basin evolution strongly influenced by salt tectonics. In the scope of the DFG project StrucFlow, we investigate the Triassic – Jurassic phase of basin evolution of the Baltic sector of the North German Basin to deepen the understanding of regional tectonics and their relation to the initial development of Zechstein salt structures. We use a dense network of modern marine high-resolution 2D seismic profiles together with older seismic data and both onshore and offshore wells. Thereby, we strive for a detailed regional tectono-stratigraphic interpretation of Triassic and Jurassic deposits with improved stratigraphic subdivision. We interpret local thickness variations across salt structures, imaged by the seismic data, to identify phases of salt withdrawal in rim-synclines and accumulation within the salt structure. Our analysis covers the northernmost part of both the eastern Glückstadt Graben and the Eastholstein Mecklenburg Block as well as the northeastern basin margin close to Rügen Island. Relatively quiet tectonic conditions characterized by thermal subsidence during the Early and Middle Triassic persisted in the study area. In the Late Triassic, during deposition of the Keuper, Paleozoic faults were reactivated at the northeastern basin margin, which created a local depocenter with increased thickness of Keuper and Lower Jurassic deposits. We interpret this zone with increased Triassic – Jurassic sedimentary thickness as a transtensional graben system connected to deeper Paleozoic structures. Local thickness variations of Triassic units across salt structures and crestal faulting indicate initial salt movement in the eastern Glückstadt Graben and at the Kegnaes Diapir contemporaneous with the onset of Late Triassic regional extension and faulting at the northeastern basin margin. Salt movement continued at least until the early Jurassic. During the Triassic, the Eastholstein Mecklenburg Block formed a more stable area at the transition between the Glückstadt Graben and the fault systems of the northeastern basin margin. Within the Eastholstein Mecklenburg Block, salt movement started only in the latest Triassic and was of decreased intensity. From Middle Jurassic times until the Albian, the North Sea doming event subjected the study area to uplift and erosion, which removed much of the Jurassic and partly Upper Triassic deposits resulting in a study area-wide erosional unconformity.</p>