Seismic stratigraphy, tectonics and gas migration in the Åland Sea, northern Baltic Proper

Abstract

The Aland Islands, which form the threshold between the Baltic Proper in the south and the Bay of Bothnia in the north, are dominated by a sheet-like intrusion of Lower Riphean Rapakivi granites resting on and within Svecofennian crust. West of the Aland Islands lies a semi-circular tectonic depression, the Aland Sea Basin. The Svecofennian crystalline basement slopes gently away from the Rapakivi massif here and the depression terminates westwards against a stepwise fault which reaches a maximum height of about 1700 metres along the Swedish coastline at Vaddo Island. The Aland Sea Basin is infilled with Middle Riphean to Early Paleozoic sedimentary bedrock sequences which in their lower parts are intruded by Middle Riphean dolerite sills and dikes