Supervisor: TÜ ÖMI vanemteadur Igor Tuuling, PhD
Opponent: dotsent Riko Noormets, PhD (University Centre in Svalbard, Norway)
The increasing human activity in the sea and coastal areas (prospecting, constructing, engineering etc.) stimulates a consequent need for fundamental geological knowledge about the sea floor structure, formation and development of the basin.
The Gulf of Riga (GR), shared by Estonia and Latvia, is a semi-closed eastern branch of the Central Baltic Sea that from the Baltic Proper is isolated by the West Estonian Archipelago.
This thesis, based largely on the original marine geological data, presents a complex seismo-acoustic and lithologic study of the Lateglacial and postglacial sequence (LGPGS) of the northern GR and analysis of streamlined glacial relief features in and around the gulf.
The bedrock depression holding the GR is predetermined by deep tectonic structures. It was largely gouged/shaped by erosion of Pleistocene glaciers. Since then nearly a continuous LGPGS has settled in it.
Lithologically, nine layers were distinguished in the LGPGS of the northern GR that were correlated with seven seismic/acoustic units. They reflect largely different stages in the development of the Baltic Sea. Thus, a regular set of seismo-acoustic profiles enabled estimating distribution and thicknesses of different lithologic units with their depositional and environmental characteristics over a large area.
Two regional discontinuities divide the LGPGS 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.
NW-SE oriented glacier relief features prevail in the GR, which corroborates the S/SE direction of the main Riga ice stream. Occasional NE-SW deviations from this direction in the Pärnu Bay and around the Irbe Strait reflect local influence of the Sakala and Kurzeme ice divide zones, respectively. There is no evidence of an ice-marginal zone crossing the central part of the GR as was supposed earlier.