Late W eichselian and H olocene seismostratigraphy and depositional history of the G ulf of R iga, NE B altic S ea

The L ateglacial and postglacial sequence in the northern G ulf of R iga is sedimentologically subdivided into nine distinctive layers. In the seismo‐acoustic sequence these layers are correlated with seven seismic/acoustic units, which largely reflect different stages in the development of the B altic S ea. A uniform layer of the L ate W eichselian till, a layer of waterlain glacial diamicton ( WGD ), a varved succession of the B altic I ce L ake, a brackish‐water/freshwater sandy/silty clay of Y oldia S ea, a FeS ‐rich layer of A ncylus L ake and discordantly bedded sand of the L itorina S ea and present‐day gyttja are revealed both in sediment cores and in acoustic recordings. In general, the lateral extent of the distinguished sediment layers is gradually shrinking upwards in the Quaternary sequence towards the deepest, central depression of the gulf. Two distinguished regional discontinuities divide the L ateglacial and postglacial sediment sequence into three allounits: glacial diamicton deposits in the lower part; ice‐proximal WGD , glaciolacustrine and postglacial lake/marine deposits in the middle; and brackish‐water marine deposits in the uppermost part of the sequence. The presented detailed seismostratigraphic subdivision of the Quaternary sediment sequence of the G ulf of R iga permits a correlation/comparison with similar sequences across the B altic S ea and in other former glaciated basins.