The Bornholm horst block is composed of Precambrian crystalline basement overlain by Palaeozoicand Mesozoic cover rocks. The cover intervals are separated by an angular unconformity and a hiatus spanning the Devonian through Middle Triassic interval. Late Palaeozoic faulting of the Early Palaeozoic Baltica platform is correlated with early-middle Carboniferous deformation in the Variscan foreland and with faulting associated with dolerite dyke injection in Skåne in the Late Carboniferous-Early Permian. The Palaeozoic fault systems are striking NW-SE and WNW-ESE and the platform series are dipping towards the SE and ESE respectively. The Mesozoic faulting was associated with the development of a horst-graben framework in the Bornholm-Skåne segment of the Sorgenfrei-Tornquist Zone. Mesozoic fault subsidence started in the Rønne Graben in the Triassic. In the Jurassic the Arnager-Sose block became active, cut off from the Bornholm block; in addition the Læså Graben (new) and the Øle Å fault block complex (new) were cut into the central Bornholm block from the south. In the Late Cretaceous the central Bornholm block was perforated by isolated fault blocks, i.e. the Nyker block, the Bøsthøj block and the Lobbæk block (new) along with subsidence of the Holsterhus block and renewed subsidence of the Arnager-Sose block. The Mesozoic series are dipping towards the southwest.The Palaeozoic fault systems were associated with two-dimensional plane strain during ENE-WSW and NNE-SSW extension. By contrast the Jurassic and Cretaceous fault systems were associated with three-dimensional strain with maximum extension striking NE-SW and secondary extension striking NW-SE. The Mesozoic palaeostress fields were associated with the break down of the Pangea supercontinent.

Keywords: Tornquist Zone, Bornholm horst block, superposed fault systems, two-dimensional plane Tornquist Zone, Bornholm horst block, superposed fault systems, two-dimensional plane  strain, three-dimensional strain.