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1 Geological Quarterly

1 2004

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Entropy of Pleistocene till composition as an indicator of sedimentation conditions in Southern Lithuania

Baltrūnas V., Gaigalas A.

Geological Quarterly

2004

Vol. 48, No 2

115--122

The two most complete and stratigraphically most reliably identified Pleistocene sections in Southern Lithuania were chosen as the object of this study. Variations in relative entropy were assessed from the average data on the grain size,mineral and petrographic composition of the individual stratigraphically identified till beds. Data obtained in the current study showed that the relative entropy of till composition, which characterises the even distribution of the components according to relative parameters (such as the fraction intervals and, the number of minerals), indicates that the till composition was modified by matter dispersion (mixing) and condensation (concentration). The relative entropy of the content of different till components (grain size fractions, heavy and light minerals, petrographic groups) in glacial units of various ages is different and indicates different parameters of glacial dynamics and different routes of glacier movement. Also, the relative entropy of till composition in the direction of glacier movement shows repetitive patterns, which are predetermined by loading of the bottom layers of the glacier with till material up to its maximum concentration, followed by their settling. Ice loading with till material proceeds by grinding and mixing the transit and indigenous exarational material until the till mixture reaches its maximum density (volumetric weight) and becomes close to the optimum mixture.