Seismic Stratigraphy and Tectonics of Sedimentary Basins around Bornholm Southern Baltic

Abstract

Identification of structural elements in the offshore area around Bornholm has been possible with the use of reflection seismic data. The area straddles the Fennoscandian Borderzone, extending into the Danish Polish Trough. Major structural depressions are the Rønne Graben, the Arnager Graben (new name), the Christiansø Half-graben and the Hano Bay Basin. Structural highs are the Christiansø High, the Hammervand High, the Bornholm Gat Uplift, The Dueodde High (new name), the Southern Bornholm High (new name) and Bornholm High. The Palaeozoic sediments show rapidly increasing thicknesses to the south towards the Caledonian deformation front, and to the east towards the Peribaltic Syneclise. The present distribution of thick Palaeozoic sediments is however primarily a result of Late Palaeozoic–Early Mesozoic erosion. Occurences of Triassic, Jurassic and Lower Cretaceous sediments are primarily restricted to graben areas. These were generated in a Late Carboniferous-Early Permian tension dominated right-lateral wrench fault system parallel to the Tornquist line. The Mesozoic sediments of the above-mentioned ages were deposited in expanding basins interrupted by tectonic activity, which resulted in renewed restriction of sediments to graben areas accompanied by erosion on structural highs. Late Jurassic and Late Early Cretaceous tectonic events are identified. The most spectacular tectonic event is of an Early Tertiary age. The Rønne Graben and the Arnager Graben were subjected to compression in a right lateral fault system during this phase, and were subsequently uplifted and erosion occurred accompanied by reverse faulting and minor folding.