Poziomy morskie w obrębie serii iłów poznańskich

Abstract

MARINE HORIZONS WITHIN POZNAŃ CLAYS

Summary

Owing to the geological researches carried out to explain the development and the occurence of the Poznań clay series I could have stated that the extent of this series to the south and west is much greater than it has so it far been supposed. The results obtained are shown in Fig. 2. Within the south-western part of the basin, the Poznań clay series may be subdivided into three lithological horizons that differ from each other in having both various development of deposits and various genesis. The lower horizon of grey clays is developed mainly as clays and coal-bearing loams, grey and brown in colour. These are deposits of bog marshes gradually overflooded with marine waters. The middle horizon of green clays with glauconite is developed mainly in the form of green and blue clays with silt and sand intercalations with glauconite. Here are found also clay banks with marly concretions, or thin lenses of limestones and marls. In the sands and silts with glauconite are found horizons revealing silt intercalations with foraminifer assemblages. The horizon of green clays with glauconite and foraminifers is of marine origin. The upper part of the Poznań clay series is represented by variegated clay horizon. It is developed mainly as grey and green-grey clays with yellow-brown and red spots and bands. These deposits were formed during the shallowing and drying processes of the basin. The data mentioned-above show that the genesis of these formations is, too, much more complicated. It has so far been accepted that this is a deposit of a large inland lake. Some authors were, however, of the opinion that this lake could have had a temporary connection with the northern Pliocene sea (J. Łyczewska, 1958, 1959; A. Kowalska, 1960). The results of the researches suggest that the transgression could have come from the Carpathian foredeep area. The water masses, accumulated in the foredeep, poured into the Poznań clay basin formed at that time. This is proved by planktonic foraminifers that occur in the deposits of the green clay horizon with glauconite. The distribution of these foraminifers is fairly considerable (Figs. 1 and 3). At the close of the Pliocene time the Sudetes were uplifted. The basin of the Poznań clays gradually disappeared. The Pliocene sedimentation ended with a series of white gravels and kaolin clays. These deposits were overlain with the river deposits in the form of numerous alluvial cones, which join in the foreland area of the Sudetes to form piedmont flats.