Seismo-acoustic profiling helped to determine the boundaries of two main members overlaying crystalline bedrocks: fluvio-glacial sediments (mainly the moraine of the last glaciation) up to 150 m thickness and recent marine sediments of small thickness. These loose sediments do not occur continuously. Graben-like depressions a 100-300 m deep occur on the sea bottom, divided by barriers. There are no evidences of older then Valdai sediments' existence in this area.