THE ORDOVICIAN–SILURIAN TRANSITION BEDS IN THE SEAFLOOR BETWEEN GOTLAND AND HIIUMAA ISLANDS, BALTIC PROPER

Abstract

High resolution continuous seismic profiles, shot during 1990-1992 between: Sweden and Estonia, have provided new details of the Lower Paleozoic seismic strati- graphy and especially on the traceability of seismic reflectors. Combined with recent lithologic and biostratigraphic information from onshore drillings these findings make it now possible to perform stratigraphic interpretations on epoch rather than period level. The onshore core studies show distinct differences in the facial pattern of the upper Ordovician and especially the lower Silurian deposits between the opposite sides of the sea. On the basis of the seismic recordings both gradual and local lateral changes in the thickness and the internal structure of the seismostratigraphic units have been distinguished. An updated map of the upper Ordovician and lower Silurian outcrops on the seabed has been compiled.