O wieku trzeciorzędowej flory Turowa k. Bogatyni (Górne Łużyce)

Abstract

ON THE AGE OF TERTIARY FLORA OF TUROW (UPPER LUSATIA)*SummaryThe Żytawa basin in which the mine Turów is situated, is to be found in the northward continuation of the fault-along the eastern border of Kruëne Hory. The latter range originated at Oligo-Miocene time; due to the following erosion it became the source of sand, gravel, silt and plant remains transformed subsequently into the browncoal strata: they were deposited in a flat depression in granite. Of two coal seams present exploatation takes place only at the upper one, where its thickness amounts to about 60 m. The open work Turów I became the source of extremely abundant palaeobotanical materials, collected in the course of 20 expeditions (1947-1969) by the staff of the Palaeobotanical Laboratory of Muzeum Ziemi (Museum of the Earth). The collections consist of: loose fragments of fossil wood or torn off the stumps in situ (which constitute 30 foreat beds - Fig. 1), impressions of leaves in silts and sphaerosiderite concretions, abundant chared fruits and seeds, found mainly in sand-gravel lenses (Figs 1 and 4), small particles of leaves brought by water from the higher regions (excellent material for cuticular studies); several hundred samples have been taken for palynological researches. The diversity of material required the application of the numerous ways of working them out, whereas the subtropical aspect of the plant remains has caused the necessity to consult the foreing herbaria: the flora has proved to resemble that of the mountain area of south-west China, of Birma, Indochina and the Philippine islands.So far 82 species, representing 30 families, have been determined. Most probably, the number of determined species may be redoubled. Hence the drawing of any ultimate conclusion as to the age of this unique flora in Poland would be premature.Some common features, however, displays the flora from Osieczów: it contains many leathery leaves with the entire margin, of large size testifying to very warm and humid climate; another feature, shared in common by both floras in question (Turów and Osieczów) is the abundance of evergreen oaks and the representatives of the family Lauraceae, as well as the palms. However, as concerns the plant communities, the flora of Osieczów is more uniform, and the habitat suggested is: "sand dunes along a water course" (J. Raniecka-Bobrowska, 1962).The flora of Turów is much more diversified: numerous water plants and trees peculior to wet grounds and swamps (Glyptostrobus, Alnus, 7 species of Carya, Pterocarya and so on) seem to have been common in the lower zone, while oak-laurel forests and a plant complex called "Mastixia-flora", after its principal member belonging to the family Cornaceae, probably covered the mountain slopes; their remains, being brought down by the water joined the common deposits with the former group. The warm character of the Turów flora is emphasized, on the one hand, by the lack of fir, spruce, larch, scarcity of pine and on the other – by the presence of exotic genera, e. g. two species of Podocarpus, widespread nowadays mainly in the southern hemisphere, Athrotaxis - today only on Tasmania, and Widdringtonia - at present in South Africa only.The abundance of species of the genus Symplocos, presently wide-spread in south-eastern Asia, is worth mentioning. Still more so that one of the large-leaved specimen of Symplocos found in Turów resembles, on the one hand the present-day species Symplocos rigida C l a r k e of India, on the other hand it seems to be identic with an Upper Eocene species of the well-know Bohemian deposit of Stare Sedlo (Tab. II, Fig. 5) - Phyllites juglandoides R o s s m. E. A. Rossm¬ssler, l840; H. Czeczott and A. Skirgiełło, 1967). This fact proves that even in the same area the individual genera may exist several million years, thus making the age determination very difficult.When at the early period of her researches of the Turów flora the author noticed that no one of the Tortonian floras from Silesia, and even from Lusatian area (Senftenberg - the upper seam) corresponds to the Turów flora, she resumed the study of the numerous Tertiary floras of north-western Bohemia, and she found that some of the floras in the Chomutów-Most-Cieplice basin, for instance the one of Béestiany of the Aquitanian-Burdigalian age (Knobloch, 1967) reveal a composition very near to that of Turów. In her study of 1959 she referred it to the III group, i. e. Lower Miocene-probably Burdigalian (H. Czeczott, 1959).The Lower Miocene age of the floras from the Żytawa basin was proved also by the geological works conducted by Fr. Berger (1940) and W. Klupfel (1941), who tried to refute the misconception of        F. Kirchheimer (1938) and others, who referred the floras (thus also that of the Żytawa basin) which disclose a complex of fruit and seeds of the "Mastixia flora" - to the Oligocene. Presently, the younger age of the Turów flora and, generally, that of the second coal seam, may be considered as already determined: at the German-Bohemian boundary a small basin occurs at Seifhennrsdorf that discloses a flora complex of Chattian age. The determination of age has been based on fossil remains of Anthracoterium, and on the position of coal under a thick basalt cover. In the Turów basin, basalts have been found under the two coal seams. There exists, however, a divergence of opinion, whether the flora from Turów should, ar should not be referred to the Helvetian. The author leans to a conception of referring the Turów flora to the Lower Miocene. This, among others, is proved by the results of pollen analysis made by R. Hunger (1951): the beds adjacent to the upper seam, thus synchronous with the second seam at Turów, are referred by him to the Chattian-Aquitanian, mainly on the presence of Lygodium and Sapotaceae pollen grains (which, according to P. W. Thompson (1951) are components characteristic of the synchronous coals from Rhineland). The Turów flora also reveals the presence of Lygodium and Sapotaceae, the latter found not only in the form of pollen grains, but also as seeds.To make sure of the Lower Miocene age of the Turów flora, the author under take to marked on the map of Europe all the so far discovered sites of the fern Cyclosorus stiriacus (U n g.) C h i n g. et T a k h t. (Figures 2, 3 and also Table I). The nervation of the last order is so characteristic that its determination could have easily been made on the basis of numerous remains found to occur almost in all strata of the overburden at Turów I (even - what is rather rarely observed - a sporangiferous specimen was found. Tab. III. Fig. 6; Tab. IV, Fig. 7). Afterwarded, it has been observed, however, that this problem is not so simple, since both the depth of incisions and the density of nerves of the last order are variable. Apart from several most contrasting species, 64 sites were taken into account (on the small-scale map, only 35 determinations are visible) and the age of the relative flora analysed. Older scientists (W. Ph. Schimper, 1859; A. Dotzler, 1937; W. Gothan, 1945; W. Berger, 1950 and others) were of the opinion that some regularity may be observed in the location of flora with the fern examined; the older floras comprising this fern would appear at higher latitudes than the younger ones. C. F. Zincken (1867) maintained that the fern "Goniopteris" stiriaca U n g. was an element characteristic of the Aquitanian in the sub-Alpine area. The present author's conclusions, drawn from the distribution of the sites in space and time, preved that opinions of the older scientists, in general true, deviate, in many details. Indeed, the sites in South England (Fig. 3, p. 2a, 2b - Upper Oligocene, end Lower, or Middle Eocene) are markedly older than for example those in the south-eastern areas (3 sites in the Caucasus – 30-32 which of Sarmatian-Pliocene age). In addition to this we observe a series of sites not too remote from each other, but strongly varying in age. Here belong the sites in Bulgaria (Palaeogene - in the Rhodopes, Upper Miocene - in the northern part), Handlov« in Slovakia (34) - probably the youngest site at this latitude (Lower Tortonian), Haselbach near Altenburg (7) which, although not so remote from the sites of the north-western depression in Bohemia (from Upper Oligocene to Lower Miocene), is several million years older. What is the matter here? It seems that the simplified conception as to the occurrence of this highly thermophilic fern is disturbed by orogenic processes and sea transgressions. So, the Tortonian transgression in Bulgaria completely eroded the strata, Aquitanian, Burdigalian and Helvetian in age. A site (Lower Tortonian) persisted in Slovakia, because it was protected from the north by the then emerging Carpathian Mts. The lack of Cyclosorus in the Tortonian of the Silesian area is explained by somewhat cooler climate in the areas situated north of the Sudetes.Distinctly thermophylic character of G. stiriaca and of the related species is unquestionable. It results from the studies of pteridologists and modern plant geographer that Cyclosorus, with about 75% of ferns, developed in the Antarctic region (L. Croizat, 1952; E. B. Copeland, 1947). This is evidenced by the present area of about 300 sub-tropical species of which the modern genus consists. Two of them occur in New Zeland, five in South Africa, and even in dry inland areas of Australia (herein one species in the beds of intermittent streams). In the south-eastern areas of Asia the distribution is strongly differentiated (R. E. Holltum, 1959): no less than 26 species have been observed in the Indochina. They differ in the depth of leaflet incisions, the density of nervation, the presence or lack of indusia. The fern is a repent plant, the rhizoms have been frequently encountered in Turów, (that from Turów does not reviel any indusia). Ecology is different too. Some of the ferns grow in forests, others within the open areas, or are found only in the marsh areas (to these belongs the fern from Turów), or occur only in mountainous regions. The Palaeogene sites in Europe prove that the fern Cyclosorus has long ago migrated from the Antarctic regions to Europe, to reach remote areas of South England, and perhaps even Greenland.