Minerały ilaste osadów serii poznańskiej z profilu Rogaczewo

Ryszard Wyrwicki, Andrzej Wiewióra




In the Rogaczewo borehole (SW of Poznań) sediments of thePoznańseries,89.1 mthick, were found under12.5 mQuaternary deposits cover.

Three following stratigraphic horizons were distinguished:

- a mottled clays (Pliocene;14.5 mthick), composed of variegated clays, grey clays and silts and fine-grained sands in the lowermost layer,

- a green clays (Miocene; 70.3 thick), in which are present clays, muds, silts mostly grey-green, rarely brown in colour, rich in marlaceous, calcareous, dolomitic-calcareous and syderitic concretions of various sizes,

- a grey clays (Miocene;4.3 mthick), composed of greenish-grey clays rich in pirite and sideritic concretions, as well as rich in grey clays and silts containing carbonized plant remains.

Clay mineral components of < 2 mm particle size fractions separated from samples of the three stratigraphic horizons has been determined by the thermal and the X-ray methods.

In the mottled clays, beidellite variety of smectites with divalent cations in the interlayer space is a major clay mineral. It is accompanied by kaolinite, illite, mixed-layer randomly interstratified illite-beidellite and accesory anatase (DTA curves – Fig. 1; diffractograms – Figs. 8, 9).

In the green clays, beidellite is the major mineral, again, but it shows variations in a structural order, caused by various interlayer cations – mono- and divalent in the uppermost layer, divalent in the middle layer and alterating mixed or divalent in the base layer of the sediments. Kaolinite, illite and traces of chlorite are the minor clay constituents (DTA curves – Figs. 2–5; diffractograms – Figs. 10–12). Beidellite, kaolinite and illite occur in clay fractions of all the samples, neglecting a presence or absence of the concretions in the sediments.

In the grey clays (DTA curves – Fig. 6; diffractograms – Figs. 11, 12) beidellite with mostly monovalent cations in the interlayer positions slightly prevails in quantity over kaolinite and illite. Kaolinite contents is rather high in this horizon.

Mineral composition of clay fractions in the sediments of Rogaczewo is very similar to this of the sediments previously studied. It is typical for thePoznańseries.


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