Charakterystyka litologiczna osadów powierzchniowych Ławicy Odrzanej

Zofia Jurowska, Ryszard Kotliński




The present characteristic of the surface deposits of Ławica Odrzana is basednon the results of granulometric, mineralogical and petrographic studies made in the Department of the Geology of the Sea at the Geological Institute. Fine-grained sands and local medium-grained sands represent the predominant type of deposits.

An analysis of the statistical parameters of grain size distribution shows that the mean grain diameters (Mz) range from 2 to 3 j (0.25–0.125 mm) and that the deposits are well sorted on the whole (standard deviation 01 varies from 0.35 to 0.50).

Those deposits which occur in the top part of Ławica Odrzana are very well sorted (s1 > 0.35). SKG varies from –0.68 to +0.80, most of the values varying from –0.10 to +0.10. Oblateness (KG) ranges from 0.90 to1.11 in most of the deposits.

An analysis of the morphology of quartz grains shows the predominance of partly rounded grains, the percentage of rounded grains being quite large. Most of the grains are characterized by unpolished, rough and fine-porous surfaces. The mineral composition shows that quartz is the predominant component (91.3 per cent on the average), followed by feldspars (3.1 per cent) and fragments of crystalline rocks (about 1.5 per cent). Transparent grains with intergrowths, semitransparent grains and fractured grains are the prevailing physiographic types. Among heavy minerals predominate those from the group of garnets, amphiboles, epidotes and pyroxenes.

The differentiation in the mineral composition of surface sandy deposits is connected with the activity of bottom currents. The zonal differentiation in the mineral composition of these deposits results from the separation of grains in the course of displacements, generally speaking from the north-west to the south-east. Material is accumulated in the central, top part of Ławica Odrzana and on its south-eastern slope. The formation of the sandy cover of Ławica Odrzana and its contemporary morphological character represent the combined effect of processes taking place in two different environments – marine and aeolian


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