Stojące pnie kalamitów w odsłonięciu cegielni Brynów i warunki ich pogrzebania

Bolesław Brzyski, Ryszard Gradziński, Roma Krzanowska


Upright Calamite stems from Brynów and conditions of their burial

A great number of upright calamité stems were found in the outcrop of the Brynów brick-tkiin (Katowice, Upper Silesia) in May, 1973. The sedimentological investigations in this locality were carried out by R. Gradziński and R. Krzanowska and the palaeobotanical ones by B. Brzyski . The sediments exposed in Brynów dip generally to SSW at an angle 3—5°. They are of the Uppermost Westphalian A age and belong to the upper part of the Załęże beds (according to the division of Stopa 1967) or to the lower part of the Orzesze beds according to the older division.

For purpose of general description, the sediments of the Brynów section were divided into eight main layers numbered I—VIII (fig. 2). The layers IV and V are composed of fine- and very fine-grained muddy sandstones with mudstone intercalations of secondary importance. These rocks are bedded but not very distinctly. The thickness of the individual beds and their lateral extension are variable. The lower bounding surfaces of both layers are slightly uneven (Pl. I, figs. 1, 2) but they do not have the character of wide-spread scoured surfaces. In the muddy sandstones the cross-stratification (of small- and large- -scaie) predominates; the bounding surfaces of the sets are often gradational or indistinct (fig. 4; H. IV, figs. 1, 2). In vertical cross-section the shape of cross-laminae is frequently sigmoidal. Climbing-ripple cross- -lamination may be observed in places. Horizontal, discontinuous lamination is rare. In both layers vertical and lateral passages from sandstone to mudstone (and vice versa) are of frequent occurrence; sharp 'contacts between these are also visible (Pl. Ill, fig. 1). Most mudstone intercalations are local, but a few ones have some greater lateral persistence and can be traced at a distance of at least ten or more metres. The mudstones display thin lenticular stratification (with delicate cross-lamination in lenses of coarser-grained sediment) and discontinuous lamination — horizontal or inclined. The layer V is Composed of mudstones ; muddy sandstone intercalations occur in places in its upper part. Sedimentary structures of these deposits are generally the same as those described above but in places the mudstones are structureless. A similar assemblage of sedimentary structures occurs in mudstones of the layers III and VII. Claystones (in the layers I, III and VII), as a rule, are structureless. The layer VIII consists of medium-grained sandstones. Its lower bounding surface displays a character of an extensive scoured surface. In the overlying bed some rare intraformational mudstone clasts and large tree trunks in horizontal position are visible. The upper part of the layer consists of sandstone beds inclined at an angle 15—20° to the principal surface of accumulation of this layer. Within these beds there occur structures of cross-stratification of large- and small-scale. Thus, these beds as a whole display the composite inclined stratification (according to the terminology of Gradziński 1970).

Most numerous calamité stems were found within the 14 m long section of the wall (fig. 3) in the upper part of the layer V and in the layer VI. This part of the wall, with about 70 stems visible, was examined in detail. Only the casts of stems are preserved. Vertical and steeply inclined casts predominate while horizontal ones are rare. Flattened rhizomes are very rare in the layer VI and more common in the layer V. The casts are 3—10 cm in diameter and attain a height of 180 cm. Probably all the calamités in the examined section belong to Calamités (Stylocalamites) suckowii Brgt. Upright casts pass, as a rule, throughout the alternating sandstones and mudstones (Pis. I, II, III). The arcuate bases of several stem-casts are evidently connected with the mudstone intercalations of greater lateral persistence. These bases marlk periods of renewed vegetation. It seems that they are more often related to the growth from rhizomes than to the „candelabrum” growth of the side stems.

The examinated sediments belong to the limnic part of the Upper Silesian coal-bearing series (cf. Unrug and Dembowski , 1971). The features of the Brynów sediments seem to imply a deposition on an alluvial aind/or deltaic plain. In the opinion of the authors, only sandstones of the layer VIII represent the channel deposits. Muddy sandstones of the layers IV and VI were most probably deposited in a crevasse-splay or a natural levee. This is indicated by: 1) the grain composition of the rocks, 2) the characteristic assemblage of sedimentary structures suggesting a rapid deposition from traction and suspension, 3) the lack of wide-spread scoured surfaces on t)he bottom of both layers, and 4) the position of these layers in the whole profile of the Brynów locality. Considering that the sediments are relatively coarse-grained, the authors suppose that the depositional sub-environment of both layers was rather a crevasse-splay than a natural levee.

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