Reconstructing the post-glacial history of the Tõrvajõe basin in NE Estonia

The Tõrvajõe basin is located in NE Estonia in the Estonian part of the Narva-Luga Klint Bay, between the Baltic Klint and Sininõmme costal dunes. Narva-Luga Klint Bay is characterized by slow post-glacial isostatic uplift (about 0-1mm/yr) and slowly undulating low topography (0-11 m a.s.l). Therefore even small increases in sea-level can easily lead to the flooding of substantial areas. The complex deglaciation history of the Baltic Sea area, with up-dammed lakes and early phases of post-glacial seas, has at times, left the area submerged, while at other times, has let it emerge as terrestrial land. Abundant archeological findings of Mesolithic and Neolithic settlement sites make the area interesting for reconstruction of palaeoenviromental history. The aim of our research was to investigate and associate paleoenvironmental conditions and waterlevel changes with Mesolithic settlement pattern in the Tõrvajõe area.

Developmental history of the basin was studied using lithostratigraphy, pollen, diatom, and loss-on-ignition analyses, radiocarbon dating, and GIS-based palaeogeographic reconstruction. Our results show four developmental stages in the postglacial history of the basin: Ancylus Lake lagoon, mire, freshwater lake/lagoon during the Litorina Sea and mire. During the Ancylus Lake transgression at about 10.8-10.2 cal ka BP a spit started to form north from the basin and a lagoon evolved behind it. Findings of fishing tools from the lagoon sediments at the Siivertsi site indicate human activity in the Tõrvajõe area already during the Mesolithic period. In relation to the regression of the Ancylus Lake, the basin dried up and formation of fen peat started to take place from at about 8.7 cal ka BP. During the Litorina Sea transgression at about 8.5-7.5 cal ka BP the Tõrvajõe basin filled again with water. It is not clear if the basin was connected with the open waters during the Litorina Sea or not. Diatom analysis results indicate freshwater conditions in the water body at that time. However, this could also be because of freshwater inflow from the palaeo Narva River which debouched to the Tõrvajõe basin. The shores of this lake/lagoon were preferred living environments for  Neolithic people between ca 7.1-6.0 cal ka BP. Altogether, 14 Neolithic settlement sites have been found from the shores of this water body. Later, due to drying up of the lake/lagoon, people abandoned the Tõrvajõe area and concentrated mostly along the ancient rivers in Narva-Luga Klint Bay.