SEISMIC STRATIGRAPHY OF LATE QUATERNARY GLACIAL TO MARINE-SEDIMENTS OFFSHORE BORNHOLM, SOUTHERN BALTIC SEA

The Quaternary history of the southern Baltic is marked by a complex s equence of glacial, lacustrine and marine phases. Consequently, a larg e number of unconformities and erosional and depositional surfaces are present in the stratigraphic record. Over 600 km of high-resolution, single-channel reflection seismic profiles were collected offshore Bor nholm. A sequence stratigraphic interpretation of the seismic data, in combination with some available core data, has led to the identificat ion of two Quaternary depositional sequences unconformably overlying t he late Mesozoic deposits. The sequences contain up to nine different seismic-stratigraphic units, and are separated by sharp boundaries rep resenting strong erosional events. The lower depositional sequence con tains five units (A-E) of glacial and late-glacial origin. The unconfo rmity at its base is marked by a southward flowing channel drainage pa ttern, which may be related to the mid-Weichselian Alnarp River system . Units A and B contain till and moraine deposits, probably of middle or early-late Weichselian age. Units C-E consist of glaciolacustrine c lays, and most likely represent different Baltic Ice Lake phases of th e late Weichselian. The upper depositional sequence contains four unit s (F-I) of postglacial lacustrine and marine origin. Its sharp erosion al base possibly indicates subaerial exposure. Unit F consists of back stepping delta or beach deposits, which are partially interfingered wi th the lacustrine clays of unit G. Both units can most likely be corre lated with the Ancylus Lake. The marine mud deposits of units H and I represent the widespread Litorina transgression.