Postglacial seismogenic deformations of an esker in the Northern Karelian Isthmus (south-east Fennoscandia)

The research area is located in the Northern part of the Karelian Isthmus between Lake Ladoga and the Gulf of Finland of the Baltic Sea. The terrain features are closely related to the tectonic structure of the crystalline basement, partially covered with thin deposition layer of the Last Glaciation and Holocene mostly. Accumulative forms are rarely but strongly correlated with the tectonic structure also. Most expressive features of accumulative topography are esker ridges that stretch for tens of kilometers. Analysis of eskers spatial distribution shows their close connection with the structural plan of the crystalline basement. One of the ridges under study was described in three sections where a lot of deformations in soft sediments, accompanied by deformations of the esker’s topography (in one case) were found. The nature and stratigraphic position of deformations indicates their appearance during the period of existence of the Baltic Ice Lake after the retreat of the ice sheet. Post-sedimentary deformations were accompanied by partial re-deposition of sedimentary strata. Deformations are represented by several types and generations. The ensembles of faults and fold deformations in the esker deposition kinematically connected with each other and coinciding along the strike with the structural lineaments demonstrate the influence of the activated tectonic structure to the formation of the sedimentary cover. The conjugation of normal and thrust faults, the presence of several “event horizons” with traces of liquefaction testify to the seismotectonic genesis of deformations and several strong earthquakes that occurred at different stages of the existence of the Baltic Ice Lake in the period 13.0–11.6 thousand years BP.