Salt tectonics in intracontinental sedimentary basins: Triassic – Jurassic salt movement in the Baltic sector of the North German Basin and its relation to post-Permian regional tectonics

Abstract

The formation and structural evolution of complex intracontinental basins, like the North German Basin, mark fundamental earth processes. Understanding these is not only essential to basic research but also of socioeconomic importance because of the multitude of resources, potential hazards and subsurface use capability in such basins. As part of the Central European Basin System, major subsidence and structural differentiation affected the Baltic sector of the North German Basin in Permian to Jurassic times. A dense network of high-resolution 2D seismic data together with nearby wells allow creating regional maps with refined stratigraphic subdivision of unprecedented spatial resolution covering the bays of Kiel and Mecklenburg (Baltic Sea). Cross sections along the basin margin allow reconstructing the structural evolution of the Zechstein salt and its overburden. At the northern basin margin, near the Kegnaes Diapir, thinning of the Buntsandstein and divergent reflectors indicate Early Triassic faulting and salt movement. In the Late Triassic, tectonic activity increased as expressed by the onset of salt movement in the northeastern Glückstadt Graben, major growth of the Kegnaes Diapir and faulting at the northeastern basin margin during deposition of the Keuper (Erfurt, Grabfeld, Stuttgart and Weser formations). At the northeastern basin margin, we interpret the accumulation of Keuper and Jurassic deposits as an infill of a local sub-basin bordered by the Werre Fault Zone and Agricola Fault System. Between the Glückstadt Graben and the northeastern basin margin, the Eastholstein-Mecklenburg Block formed a more stable area, where salt movement first began during the latest Triassic. In the peripheral part of the basin, salt movement was triggered by thin-skinned extension associated with thick-skinned faulting within the axial parts of major graben systems. Indications for gravity gliding are absent. Reactive diapirism is restricted to the basin margin, where reduced overburden thickness and Late Triassic erosion allowed diapiric breakthrough.