Marine ecogeology in semi-closed basin: case study on a threat of geogenic pollution of the southern Baltic Sea (Polish Exclusive Economic Zone)

Abstract

Modern migration of harmful geogenic substances into bottom sediments and bottom water has been demonstrated in the Polish Exclusive Economic Zone of the Baltic Sea. A geogenic substance is a matter (gas or liquid) whose formation, chemical composition and physical properties result from natural geological processes. The bedrock of the Baltic Sea contains rocks which are sources of geogenic pollutants migrating along fault zones and pinchouts of sedimentary formations. The pollutant source rocks include: oil- and gas-bearing reservoir rocks (Middle Cambrian, Rotliegend, Zechstein and Carboniferous); black shales (lower Paleozoic); effusive rocks (Rotliegend); salts (Zechstein), reservoir rocks for mineral and thermal waters (Paleozoic and Mesozoic). The main sources of geogenic contamination are oil and natural gas deposits as well as zones prospective for hydrocarbon accumulations because they produce increased concentrations of liquid and gaseous hydrocarbons in bottom sediments and bottom water. Hydrocarbons cause a lethal deficit of oxygen in bottom water. The migration activity of the fault zones and regional pinchouts is shown, for instance, by increased concentrations of vanadium and strontium in bottom sediments. Strontium comes from Zechstein salts while vanadium is from lower Paleozoic black shales and/or hydrocarbon-bearing sediments. The whole Polish Exclusive Economic Zone of the Baltic Sea is threatened by geogenic pollution. Areas at greatest risk of geogenic pollution have been defined in both the eastern part (East European Craton: western part of the Courland Block, Rozewie Block, Łeba Block, eastern part of the Żarnowiec Block) and the western part of the zone (European Paleozoic platform: western part of the Kołobrzeg Block, and Gryfice and Wolin blocks).