GIS-based multiproxy coastline reconstruction of the eastern Gulf of Riga, Baltic Sea, during the Stone Age

We present early to mid-Holocene palaeocoastline reconstructions for the Tolkuse-Rannametsa area on the eastern coast of the Gulf of Riga. Radiocarbon-dated sediment stratigraphies and diatom analyses, supported by ground-penetrating radar data and GIS-based modelling, were used in the palaeogeographical reconstructions to strip back younger sediments and landforms from the LiDAR-derived digital elevation model. The reconstructions show an open coast environment during the Ancylus Lake stage and the formation of a peatland after the lake drainage at about 9000-8600cal. a BP. The waters of the Litorina Sea flooded the study area between 8200 and 7700cal. a BP, forming a 25-km-long and up to 5.5-m-deep lagoon with two connections to the sea. This brackish water lagoon existed in the area for about 4000years and terminated around 3800-3500cal. a BP as a result of isostatic uplift and growth of the barrier spit. The reconstructions illustrate the relationships between the lagoonal system and three Mesolithic and Neolithic settlement sites found in the study area. A comparative analysis which besides palaeogeographical and ecological data included a data set with more than 100 Stone Age sites from the eastern Baltic region, was used to propose the most suitable locations for coastal settlements in the Tolkuse-Rannametsa area. However, some of these areas are presently covered by a peat layer that is several metres thick, which may explain the relative scarcity of the archaeological finds on the shores of the palaeo-lagoon. The proposed multiproxy approach has the capability to delimit the areas that would have been favourable for prehistoric habitation, but might not be observable in the present-day topography. In return, this increases the likelihood of locating any well-preserved preserved settlement sites and artefacts that are buried under the protective sediment layer.