Lithology and Organic Matter in Bottom Sediments of Kaliningrad Bay in the Baltic Sea

Results of studying 13 lithological cores from Kaliningrad Bay in the Baltic Sea are presented. The texture features, grain-size distribution of sediments, natural moisture, and content of organic matter and vivianite mineral have been determined in the cores. This study reveals a regularity of changes in the grain-size distribution of sediments with the depth typical for all cores: sandy (0.25–0.063 mm) sediments in the upper part (to a depth of 32–65 cm) are underlain by homogeneous organic-rich tinted olive clay (less than 0.063 mm). Changes in other parameters are also observed in approximately the same layers. For example, the organic matter content averages 6% in the upper (0–65 cm) layer and 29% in deeper clay sediments. Moisture content varies from 45 to 90% in the upper layer and from 90 to 185% in the lower one. The vivianite mineral is formed exclusively in lower layers. Based on the changes in the sediments, two lithostratigraphic divisions are distinguished: the lower (I) and the upper (II) members, corresponding to different sedimentation stages. The lower member, formed during the period of predominance of the river flow, is composed of plastic, olive-colored clays identified as sapropel formations. They are classified as a mineralized type of sapropel with an ash content of 70–87%. The thickness of the sapropel layer averages about 1 m. Sapropel formations are identified in all cores, which enables us to suggest that they are widely distributed in the sedimentary layer.