Mapa geologiczna dna Bałtyku w skali 1:200 000

Abstract

Omówiono treść Mapy geologicznej dna Bałtyku w skali 1:200000 oraz zakres i metody prac rejsowych i laboratoryjnych. Przedstawiono też nowsze osiągnięcia w zakresie rozpoznania osadów czwartorzędowych oraz ich podłoża.GEOLOGICAL MAP OF THE BALTIC SEA BOTTOM IN A SCALE OF 1:200,000 Contents of the Geological Map of the Baltic Sea Bottom in a scale of 1:200,000 is described together with rage and methods of cruise and laboratory works. The Geological Map of the Baltic Sea Bottom is composed of 17 sheets (Fig. 1). It contains the map of bottom sediments in a scale of 1:200,000, general geological sections, geological profiles and also maps in a scale of 1:500,000 i.e. geomorphological, lithodynamic ones, of sediments at depth of 1 m beneath the bottom surface and of resource forecast, as well as explanatory text. The map is based on results of cruise and laboratory works. Standard studies of a sea bottom comprise: echo sounding (at least 1 Mm long per 1 Mm2 of bottom surface), collecting of scoop samples (at least 1 sample per 1.5 Mm2), collection of cores (at least 1 core per 1.5 Mm2). Standard studies comprise also seismoacoustic sounding and boreholes to 30 m depth (Fig. 2). Samples of sediments are subjected to laboratory analyses. Principal analyses include: grain size analysis, mineral-petrographical analysis of the fraction 1.0-0.5 mm, quantitative and qualitative analyses of heavy minerals in fraction 0.25-0.125 mm, analysis of roundness degree of quartz grains, analysis of contents of organic matter, quantitative (derivatographic) analysis of clay minerals, biostratigraphic analysis, analysis of principal chemical composition and absolute datings by 14C method of organic sediments and by thermoluminescence method of tills and clastic deposits. Range of cruise and laboratory studies enables a vast and detailed description of sediments distinguished on the map. Geological symbols present age, origin and grain size composition of sediments. Deposits in the present Baltic Sea area were formed during the Late Glacial and the Holocene, and are subdivided into 3 lithostratigraphical units: sediments of the Baltic ice-dam lake, sediments of the Yoldia sea and Ancylus lake, sediments of the Litorina and the present Baltic seas. Grain size types of superficial sediments were distinguished on the basis of classification of F.P. Shepard (1954). Besides the sands are subdivided into four grain size subtypes (Fig. 3).