Biogenic components of the Baltic Sea sediments☆

Abstract

Abstract The contents of biogenic components in 1511 samples of the Baltic Sea sediments (depth range 0–5 cm) are studied, and maps of their distribution are compiled. The sediments contain ≤ 13.03% Corg, ≤ 1.33% N, ≤ 9.0% SiO2am, ≤ 5.0% CaCO3, and ≤ 1.45% P. The maximum and elevated contents of components are found in the mud of the sea deeps. The more fraction < 0.01 mm the sediments contain, the higher are the contents of components. Four facies types of carbonaceous mud, precursors of shales, have been recognized: (1) shallow-water (lagoon) lime sapropel, (2) carbonaceous mud of the shallow-water Gulf of Finland, (3) carbonaceous mud of the middle-depth Baltic Sea, and (4) laminated carbonaceous metal-bearing mud. The latter type of mud is strongly enriched in manganese and ore-forming trace elements, which points to its formation in the stagnant environment. In composition the Baltic Sea mud is similar to petroliferous mudstones of the Bazhenov Formation in West Siberia and to ancient black shales.