Minerały ilaste poziomu iłów płomienistych serii poznańskiej

Abstract

CLAY MINERALS IN THE MOTTLED CLAY HORIZON OF THE POZNAŃ SERIES

Summary

Mottled day horizon represents the youngest member of the Poznań series referred to Pliocene. The thickness of the deposits of this horizon amounts to several to 20 m. These deposits have been formed in some sedimentary cycles. The cycles begin with a coarser material – sands and silts, and end with days. Most clays and silts are characterized by red and cherry-red colours, appearing in patches, and only a small part of the deposits is grey, greenish and brown in colour, without any patches.
The clay fractions have been separated from 22 samples. The examinations of this fraction were a basis to investigate clay minerals. Chemical composition of the fraction below 2 mm is given in Tabs 1–4, DTA curve – in Figs 2, 4, 7, 9 and 11, X-ray patterns in Figs. 3, 5, 6, 8, 10, 12, 13, l4 and 15.
The research yielded the following results. Samples of day deposits revealed 20–80% by weight of the fraction below 2 mm. The fraction contained the following minerals: beidellite, illite, kaolinite, lillite-beidellite mixed-layer phase, quartz, goethite, haematite, and anatase. Beidellite is here the main clay mineral prevailing quantitatively. It contains mainly cations characterized by a high electric field (Ca,
Mg and probably Fe³⁺) in exchangeable positions, rarely monovalent (mainly K) or monovalent and bivalent ones. As, a rule the mineral characterized by a poor crystallinity. The beidellite is accompanied by kaolinite and illite, the former prevailing over the later in most samples. In part, both minerals are in the same amount, illite only very rarely predominating over kaolinite.
X-ray examinations have demonstrated that the red and cherry-red patches are due to hematite.
The mottled day horizon reveals, within the entire occurrence area, the same associations of clay minerals. Differentiated are only their quantitative proportions in the deposits.