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1 Zeszyty Naukowe. Marine Sciences / Uniwersytet Szczeciński

1 1998

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Możliwości wykorzystania standardowych badań uziarnienia i cech mineralno-petrograficznych w litodynamicznej interpretacji polskiej strefy brzegowej Bałtyku

Racinowski R., Dobrzyński S.

Zeszyty Naukowe. Marine Sciences / Uniwersytet Szczeciński

1998

Nr 4

75-90

Standard lithological investigations of the seashore zone rubble comprise the following analyses: grain size distribution, mineral-petrographic composition, heavy minerals composition, morphometric and morphoscopic characteristics of the cobbles, and abrasion of the quartz grains in the sandy fraction. The rubble shows a marked similarity to the mineral-petrographic composition throughout the Polish Baltic seashore and qualitatively it is linked up with initial Pleistocene material. The morphometric features of the gravels undergo a very rapid transformation in relation to the Pleistocene deposits. The farther away from the place where the glacial deposits are washed out, the smaller the quantity of components of low wear resistance - the gravels become more oblate and smooth. The qualitative composition of the rubble's heavy minerals is linked up with the Pleistocene deposits. As a result of rapid differentiation in the seashore environment there are small rubble centres enriched in heavy minerals (mainly on the shore), mainly garnets, zircon, rutile, disthene, staurolite. The rubble that is not enriched in heavy minerals contain larger quantities of amphiboles, pyroxenes, especially biotite, chlorite and muscovite. In the Polish seashore zone the rubble's thickness ranges from a dozen to several dozen centimetres and it is represented by middle-sized and fine sands. The analysis of its lithodynamic features (based on grain size distribution) shows that it is very susceptible to outwashing. The rank erosion velocities are ca 0,1 - 0,3 m/s. This means that in the shallow subshore (0 - 7m under sea level) the sediment transport starts developing at state of the sea 1 - 30B, and in the deeper subshore (7 - 14m under sea level) at sea of 5 - 60B. Basing on the lithological investigations of the rubble, attempts were made to designate local and regional directions of its displacement. To this end the following were used: indices of grain size distribution (mainly Mz and 1), the compositionof heavy minerals (mainly the heavy mineral's mass in the rubble; content of components with densities over 3,4 g/cm3, 2,9 - 3,4 g/cm3). Also the analyses of petrographic and morphometric composition of the cobbles proved instrumental. The findings on a local scale seem unquestionable, yet on a regional scale they are controversial and susceptible of various interpretations.