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DOI: http://dx.doi.org/10.21440/2307-2091-2017-4-46-51

Conditions and morphological features of gypsum crystallization in loose sediments (on the example of the Novoafon cave, Abkhazia) PDF

O. Ya. Chervyatsova, S. S. Potapov, V. I. Rakin, S. N. Sergeev, R. S. Dbar, J. A. Ekba

The article presents the results of investigations of sulfate (gypsum) mineral formation in the southern halls of the Novoafon cave in the conditions of a loose loamy aggregate. These sediments, which are sediments of cave lakes, refer to pseudomiosilites and myosilites – essentially quartz rocks, poor hydrolysates. The southern halls of the cave are characterized by air temperatures from 12.2 to 13.4 °C. The maxima and minima lag behind the surface for 2-3 months. Observations of the relative humidity of air are fragmentary, but there are data on its significant fluctuations, increased as a result of anthropogenic transformation of the air circulation system (the appearance of artificial tunnels). The studied aggregates of gypsum are characterized by a size range from less than 1 mm and up to 3-4 cm and a wide variety of morphological types. Gypsum is represented by skeletal crystals on which parts of facets of simple forms occur: {010}, {121} , {110} and rarely {011}. Rounded, lateral with respect to the planes of perfect cleavage {010} of the gypsum surface, speak of a diffuse growth regime. Such a regime can be explained by the composition of the sediments: the clay layers in their composition during the moistening of the cave accumulated capillary water, which was slowly deposited into the growth substrate during the dry periods. Most researchers indicate that in the processes of secondary redeposition of gypsum in caves (irrespective of its initial source) the main role is played by the processes of alternation of moisture with evaporation. Therefore, this type of secondary gypsum mineralization can be considered as an indicator of the microclimatic regime with high-amplitude fluctuations in the relative humidity of air, which has been preserved for a long time. Its further study using isotope techniques can help in the reconstruction of the natural regime of air humidity in the cave (before the anthropogenic transformation of the microclimatic regime).

Keywords: sulfates; secondary mineral formations; gypsum; morphology of crystals; genesis of minerals.

 

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