Gipsy w utworach plioceńskich

Ryszard Wyrwicki



In the Pliocene of Poland are found gypsums of two main generations. Younger gypsums Occur in the near-surface zone of Pliocene deposits, not deeper than 8 m. They are developed as single crystals and concretions in clay, and as crystals grown up in the Pliocene carbonate concretions, as well as together with jarosite and goethite make vein stuff. The gypsum is colourless and transparent, its content in clay amounting to 10%, Nests and lenses of clay with younger gypsum are arranged irrespective of the course of the Pliocene clay beds. Older gypsums occur at various depths, down to over 200 m. Their occurrence is connected with the given strata. In one clay bed they may appear in one or several horizons. In each of these horizons the individual crystals and concretions may be variously developed (Fig. 1). Gypsums of older generation as a rule contain numerous inclusions of matrix that increases their cloudiness and decreases their transparency. Both crystals and concretions frequently show disturbances in growth. The gypsums occur at small depth in the weathering zone, arid reveal traces of solution. The amount of gypsums in the individual beds reaches as much as 20%. The older gypsums occur in the grey-green clays that frequently contain pyrite (Fig. 8). Genesis of both generations of gypsums is different. The older gypsums were formed during the early diagenesis of clays at the Pliocene time. The younger gypsums, in turn, originated as a weathering product of pyrite in the Pliocene clays and as a result of leaching of calcium carbonate from the overlying Quaternary boulder clays (pliocene clays are lacking calcium). Younger gypsums were produced during the Quaternary period and along with other sulphate minerals are also being formed at present. At certain exposures of the Pliocene clays gypsums of both generations occur together.

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