Podstawowe problemy geologiczne dewonu dolnego Gór Świętokrzyskich

Abstract

MAIN GEOLOGICAL PROBLEMS OF THE LOWER DEVONIAN IN THE ŚWIĘTOKRZYSKIE MTS.SummaryIn the Lower Devonian deposits, younger than Gedinnan, developed characteristic sedimentary cyclothems in the north (Łysogóry region) and in the south (Kielce region) (Fig. 2). In the Łysogóry region are found at least three such cyclothems, whereas in the Kielce region there are two only. The cyclothems disclose the following sequence of complexes: conglomerates - gravelstones – quartz sandstones - quartzite sandstones (in the lower cyclothems with placoderms, and in higher ones – with spirifers) – variegated, ferruginous siltstones, sandstones and claystones (with detritus of psilophyte flora), and again quartz sandstones - quartzite sandstones. The individual cyclothems are not everywhere completely and identically developed. In the Kielce region the lower cyclothems reveal a well developed bottom conglomerate-gravel series (e.g. Miedziana Góra conglomerates), locking, however, the upper sandstone members (either eroded or not laid down). In the Devonian cyclothems of the Łysogóry region reduced are bottom coarse-detrital complex, whereas the top sandstones are better developed. The lower conglomerate and sandstone complexes (if preserved) were formed, according to the author’s opinion, in the lagoon basins during the expansive movement of water of the transgreding Devanian sea. Sedimentation of variegated deposits (black-grey-rusty-celadon in colour, ferruginous, locally bituminous and with flora remains) took place in the stagnant lagoon basins that little by little changed into limnic large lakes and morasts, disclosing type reduction conditions of the environment. In the Lower Devonian time the area of the Świętokrzyskie Mts. was characterized by the presence of alternating (intertonguing also horizontally) lagoon and limnic facies. Sea transgression developed systematically and little by little comprised the irregularly uplifted (more in the south and south-east, less in the north and west) Young-Caledonian ridges. The transgression of the sea changed, and the lagoons lost their contact with the Devonian open sea basins. Successive and more and more intense ingressions disturbed later the limnic basins and morasts, and the sea extended over new areas. The last of these ingressions appears to-day in the form of the transgressive Bielino conglomerate (Fig. 2). The oscillatory development of the Devonian transgression was related to the general, though decreasing Young-Caledonian mobility of the Świętokrzyskie Mts. region. Uplifting movements that conditioned the pre-Eifelian erosion an development of the Bielino conglomerates at the base of the Eifelian were the last stronger phase of these processes. When correlating the sections of the Lower Devonian from both regions of the Świętokrzyskie Mts. we are based on scarce palaeontological data only and on widely extending tuffites and Bielino conglomerates. In the light of this conception (see Fig. 2) the I – lower cyclothem of the Łysogóry area (lower part of the Barcz series) would not have any equivalent in the Kielce region. Possibly the Miedziana Góra conglomerate may partly correspond to its upper members here. Stratigraphically, this cyclothem represents probably the Upper Siegen. As far as age is concerned the II cycothem from the Łysogóry Mts. (upper part of the Barcz series) is related to the rocks of the I cyclothem in the Kielce region (the Miedziana Góra conglomerate, “the lower sandstone complex” and “the lover variegated complex” with tuffites). The series here considered represents probably the Lower Emsian. III cyclothem known to occur in the north (Zagórz Beds) and II cyclothem – in the south (“middle sandstone complex”, and “upper variegated complex”) in the Świętokrzyskie Mts. represent the Upper Emsian. The notion of the “Zagórz Beds” was introduced into the regional geological literature by H. Łobanowski (1965). He distinguished here three lithological complexes. On the other hand, M. Tarnowska distinguished in the Kielce region three “sandstone complexes” and “two variegated complexes” (Fig. 2). In both parts of the Świętokrzystkie Mts. the IV sedimentary cyclothem is developed above the Bielino conglomerates. This cyclothem may be referred to the Eifelian sensu lato, i.e. it may be a basis of the Eifelian-Givetian sub-cycle. At the bottom it is represented by the Bielino conglomerates and quartz sandstones, yellow in colour, overlain immediately with dolomites or with dark claystones and marly dolomites. Hypothetical stratigraphic boundaries of the Lower Devonian in the Świętokrzyskie Mts. are drawn by the present author along the boundaries of the successive sedimentary cyclothems. Calling in question only the continental origin of the Siegen deposits the present author is of the opinion that the sedimentary environment of the Upper Emsian and even of the lowermost Eifelian was not of marine character too. The sea invasion reached the region of the Łysogóry Mts. earlier (at the Upper Siegen time?) than the Kielce region (at Lower Emsian time?). In the southern area of the Świętokrzyskie Mts. the mountain ranges projected longer above the waves of the transgreding sea (still at the beginning of the Eifelian time). The thickness of the Lower Devonian deposits, many times greater in the northern areas of the Świętokrzyskie Mts. (Fig. 3) than in the Kielce region, is a result of the sinking tendencies considerably stronger at that time in the Łysogóry Mts. region.