Late Vendian-Early Palaeozoic tectonic evolution of the Baltic Basin: regional tectonic implications from subsidence analysis

Subsidence analysis was performed on 43 boreholes penetrating the Upper Ven dian-Lower Palaeozoic sedimentary succession of the Baltic Basin, The resul ts were related to lithofacial and structural data to elucidate subsidence mechanisms and the regional tectonic setting of basin development. Tectonic subsidence patterns are consistent throughout the basin for the time perio d studied. An extensional tectonic subsidence event, possibly of two phases , is indicated from the Late Vendian to the beginning of the Middle Cambria n. This event is seen in the southwestern part of the Baltic Basin (Peri-To rnquist zone) until the earliest Cambrian after which it is also observed i n the SW-NE-trending Baltic Depression part of the basin, Basin development during this time is interpreted as recording the latest stages of break-up of the Precambrian super-continent Rodinia and ultimately the formation of the Tornquist Sea. The late Middle Cambrian to Middle Ordovician tectonic subsidence pattern of the Baltic Basin is characteristic of post-rift therm al subsidence of the newly formed passive continental margin of Baltica, de veloped along its southwestern edge. A gradual increase in subsidence rate is observed from the (Middle?) Late Ordovician and throughout the Silurian (particularly for Ludlow and Pridoli times) creating subsidence curves with convex shapes typical of foreland basin development. The rate of Late Silu rian tectonic subsidence increases significantly towards the southwest marg in of the Baltic basin, adjacent to the present location of the North Germa n-Polish Caledonides. The Baltic Basin therefore appears to have developed primarily as a flexural foreland basin during Silurian oblique collision of Baltica and Eastern Avalonia. A foreland setting is supported by the influ x of distal turbidites into the basin from southwest sources in the Late Si lurian. Compressional deformation structures of Early Devonian (Lochkovian) age are seen in seismic sections in the central part of the Baltic Basin ( Lithuania). These, together with a change in subsidence pattern, mark the e nd of the Caledonian stage of basin development of the Baltic Basin. (C) 19 99 Elsevier Science B.V. Ail rights reserved.