Dewon i karbon w podłożu południowej części niecki miechowskiej

Jan Kicuła, Halina Żakowa


Devonian and Carboniferous in the basment of the southern part of the Miechów syncline

Deep bore-holes drilled in Southern Poland under a joint programme of the Oil Industry and the Geological Institute brought important data on the pre-Mesozoic structural stage of this region. Five bore-holes reached the Precambrian directly under the Mesozoic cover; 24 other penetrated or pierced the Palaeozoic rocks in which the Devonian and Carboniferous systems play a predominant role (Fig. 1). The study of materials from the bore-holes Marszowice 1, Koniusza 1, Skalbmierz 3 and 4, Strożyska 5, Załucze 1, and partly Słomniki 1 and Mędrzechów 1 is already completed. With the exception of the bore-holes Koniusza 1, Skalbmierz 4 and Mędrzechów 1, some preliminary stratigraphic conclusions are modified in the present paper. General informations on the bore-holes Rudno 1, Mniszów 16, Zielona 1 and Grobla 28 were published by E. Jawor (1970). Detailed paleontological and stratigraphic investiga tions of cores from the bore-holes Grobla 1, Kazimierza Wielka 1 and 10, Dobiesławice 1, Kobylniki 1 and Pacanów 1 were carried out, comprising studies of conodonts (determined by M. Chorowska who prepared the Plates XX—XXIII), microflora (determined by A. Jachowicz and E. Turnau), macrofauna (determined by H. Żakowa), microfauna (determined in macerated samples by H. Jurkiewicz and in thin section by H. Żakowa who consulted the determinations of some forms with Professor R. Conil and Professor B. L. Mamet ). The more important fossils are presented in Plates XXIV—XXIX. Geophysical logs were used for stratigraphic correlation also for bore- -holes which did not provide palaeontological data, and for determination of boundaries of systems and stages lying in most cases in non-cored depth intervals. Profiles of the bore-holes Dobiesławice 1 and Kobylniki 1 important both from the methodological and the stratigraphical ppint of view are given in the Polish text. The profiles of other bore-holes are described in detail in an unpublished report (J. Kicuła and H. Żakowa, 1971). The lithological and facial development and the stratigraphic division of the Devonian and Carboniferous strata is presented in the present paper. Included are informations on the bore-hole Liplas 2, situated beyond the described region. Index fossils found in this bore-hole (Table 1) permitted to establish a preliminary division of the Carboniferous, for which there was only few data in earlier papers.

In some bore-holes drilled in the investigated region only a tentative determination of various stages of the Devonian and Carboniferous systems is possible. These bore-holes will be discussed first. In the bore-hole Klonów 1 (Fig. 2) a dolomitic conglomerate 10 m thick is tentatively assigned to the Devonian. In the bore-hole Radzanów 2 the Palaeozoic limestones with intercalations of dolomites and clastic rocks are tentatively assigned to the Devonian (300 m) and to the Carboniferous (c. 200 m). In the bore-hole Radzanów 4 carbonate rocks with undeterminable corals, 610 m thick, are assigned to the Devonian and Lower Carboniferous. In the bore-hole Słomniki 1 the Devonian-Carboniferous boundary is not precised, and the carbonate Devonian rocks are tentatively assigned to the Middle and Upper Devonian (S. Bukowy, 1964 b). Carbonate Devonian rocks in the bore-holes Skalbmierz 3 and 4, 385—500 m thick represent the stratigraphic interval Middle Devonian—Frasnian but the fossils present did not permit a more detailed determination of age (J. Kicuła and H. Żakowa, 1966). In the bore-hole Strożyska 5 the Emsian-Eifelian boundary is not determined, and the total thickness of these two stages amounts to c. 70 m (W. Bednarczyk, K. Korejwo , H. Łobanowski, L. Teller, 1968).

The Emsian is developed as variegated siltstones with rare intercalations of quartzitic sandstones and orthoquartzites containing a psilophytes flora (Table 1). In the bore-holes Kazimierza Wielka 1, Kobylniki 1, and Radzanów 4 (Fig. 2) the Emsian rocks are overlying directly the Precambrian, with dips 2—5°, and only at Kobylniki 1 dipping 10—30°. The Emsian was not pierced in the bore-holes Słomniki 1 (siltstones and quartzitic sandstones) and Skalbmierz 3 (claystones).

Givetian rocks documented by fossils (stromatoporoidea, brachiopods, Table 1) consist of dolomitic limestones, and dolomites, locally with intercalations of anhydrites (bore-hole Załucze 1) and of clastic rocks at the base (bore-hole Kobylniki 1). They occur in the bore-holes Kobylniki 1 (thickness 190 m lying on Emsian), Strożyska 5 (501 m, on Eifelian) Racławice 2 (260 m), lying there directly on the Precambrian, and in the bore-holes Dobiesławice 1 (220 m), and Załucze 1 (153 m) dipping at an angle of 10—20° (Fig. 2). According to the present authors the Frasnian and Famennian stage (except Etroeungtian) are absent in the profile of the bore-hole Załucze 1. The carbonate rocks with clastic intercalations at the base, and dips ranging from 2° to 30° in the bore-holes Kazimierza Wielka 1 and 4 (thickness 100—110 m), Kalina 1 (250 m) and Radzanów 4 (170 m), are tentatively assigned to the Givetian, on the base of the presence of fossils in the bore-hole Kazimierza Wielka 1 and lithologic and geophysical correlation in the remaining ones.

This stage is tentatively determined (Fig. 2) in the bore-holes Kazimierza Wielka 1 (thickness 340 m), Kazimierza Wielka 4 (120 m), Dobiesławice 1 (240 m), Kobylniki 1 (125 m), Radzanów 4 (270 m) and Strożyska 5 (250 m). As a rule, direct palaeontological evidence is lacking, and the presence of the Frasnian is assumed on the basis of analysis of thickness distribution of other stages developed in carbonate facies, supplemented by lithologic and geophysical correlations. The Frasnian consists of carbonate rocks, mostly limestones, inclined at an angle of 2—30°. Conodonts assigned to the Palmatolepis sp. were found in the bore-hole Kazimierza Wielka 1 (Table 1). Undeterminable corals, and foraminifers, algae and microflora with no stratigraphic value occur also in Frasnian rocks.

Well documented Famennian rocks are present in the bore-hole Kazimierza Wielka 1 (Fig. 2), where brachiopods indicating the Dancov-Lebedyan horizon were found in the Upper Famennian (Table 1). The Famennian rocks are 450 m thick, and dip at an angle of 2—5°. In the bore-hole Dobiesławice 1 the Famennian rocks are 500 m thick and dip at an angle of 10—20°. Rich assemblages of conodonts are documenting the Lower Famennian in this bore-hole (quadratinodosa zone, and the lower part of the crepida zone, see Table 1). Also brachiopods of the Plectorhynchella genus and some foraminifers found in this bore-hole have a stratigraphic value. In the bore-hole Dobiesławice 1 the thickness of the Lower Famennian is estimated as 300 m, and the strata assigned to the Cheiloceras stage are probably c. 250 m thick. No index fossils of the Upper Famennian were found in this bore-hole. Famennian rocks with a less characteristic fauna are present in the bore-hole Kobylniki 1 (120 m), while in the bore-hole Radzanów 4 the Famennian was determined tentatively, and its thickness is estimated as 230 m. The uppermost Famennian (Etroeungtian), only a few m thick was determined in the bore-hole Załucze 1. The paleontological documentation was given by H. Żakowa , E. Głowacki and H. Jurkiewicz (1963). The presence of this stage is related with the transgression of the Carboniferous sea, which reached first the Załucze area, after a break in marine sedimentation caused by Bretonian tectonic movements. The Famennian is represented by limestones, locally dolomitic in all bore-holes described above.

The Tournaisian marls and limestones were pierced by the bore-holes Kobylniki 1 (thickness 135 m), Skalbmierz 3 (c. 180 m), Mędrzechów 1 (above 120 m) and Załucze 1 (84 m), and penetrated by the bore-holes Grobla 1 and Pacanów 1. Brachiopods and other fossils found in these beds are listed in Table 1. Index foraminifers permitted a subdivision of the Tournaisian in the bore-hole Grobla 1.

Lower and Middle
Visean Undifferentiated Lover and Middle Visean limestones and marls with clastic intercalations, 140 m thick, are present in the bore-hole Kazimierza Wielka 10 (Fig. 2). The age is documented by foraminifers, goniatites and flora (Table 1). Similar rocks, 370 m thick are present in the bore-hole Skalbmierz 3 (J. Ki cuł a , H. Żakowa, 1966). Fossiliferous carbonate rocks assigned to the Lower and Middle Visean (thickness above 130 m) occur in the bore-hole Mędrzechów 1 (S. Czarniecki and S. Kwiatkowski, 1961, P. Karnkowski and E. Głowacki, 1961). Fossiliferous rocks of the same age, lithologically similar, but with intercalations of shales, c. 280 m thick, were described from the bore-hole Załucze 1 (S. Czarniecki and S. Kwiatkowski, 1961, H. Żakowa, E. Głowacki and H. Jurkiewicz, 1963). The Lower and Middle Visean consisting of limestones with intercalations of claystones is 440 m thick in the bore-hole Kobylniki 1. Index foraminifers enable to separate the Lower Visean (Table 1) while the Middle Visean tentatively determined, as palaentological evidence is lacking, is only a few tens of metres thick. Middle Visean rocks, tentatively determined in the bore-hole Słomniki 1, directly overlying the Devonian, are 103 m thick (K. Bojkowski and S. Bukowy, 1966). Limestones with intercalations of clastic rocks, 180 m thick and occurring under the Upper Visean in the bore-hole Koniusza 1, were tentatively assigned to the Middle Visean (K. Korejwo and L. Teller, 1968). Index foraminifers and algae permitted to determine the presence of the Middle Visean limestones c. 120 m thick also in the profile of the bore-hole Strożyska 5 (Table 1).

Upper Visean
Upper Visean rocks were determined in the bore-hole Strożyska 5 in the eastern part of the investigated area, and in three bore-holes in western part. In the bore-hole Strożyska 5 the Upper Visean consists of clastic rocks 202 m thick. Fossils collected by H. Żakowa (Table 1) and microflora determined by A. Jachowicz permitted to establish the presence of the Goniatites crenistria zone. In the bore-hole Słomniki 1 (Fig. 1) the Upper Visean clastic rocks with a basal conglomerate and intercalations of limestones, marls and tuffites are c. 860 m thick (K. Bojkowski and S. Bukowy, 1966). The presence of the zones Goa and Goß has been established on the basis of goniatites, and the zone Goy on the basis of lamellibranchs. H. Żakowa (1971) expressed some doubt as to the validity of the determination of the latter zone. Clastic and calcareous rocks 930 m thick present in the bore-hole Marszowice 1 were assigned to the zones Goy and Goß on the evidence provided by goniatites and lamellibranchs (K. Korejwo and L. Teller, 1968). According to H. Żakowa (1971) the determination of some goniatites from Goy zone of this bore-hole is no valid. In the bore-hole Koniusza 1 the Upper Visean lithologically similar, is 340 m thick. Index fossils are documenting the presence of the Goa zone.

Namurian siltstones and claystones containing animal and plant fossils were found in the investigated area in the bore-holes Słomniki 1 (thickness c. 90 m) and Marszowice 1 (more than 160 m).

Remarks on palaeogeography and tectonics
The development of Devonian and Carboniferous rocks in the basement of the southern part of the Miechów syncline was depending chiefly upon the morphology of the pre-Devonian rocks deformed during the Caledonian orogeny, and upon epeirogenic movements accompanying the Variscan sedimentary cycle. These factors influenced the distribution of facies and thickness of rocks, rates of subsidence of the sedimentary basin during various epochs, and rejuvenation of ancient (Caledonian and older) dislocations. The transversal elevation of Miechów—Książ Wielki—Chomentów (Fig. 1) was one of principal tectonic structures influencing the development of the Devonian and Carboniferous in the described area (H. Jurkiewicz and H. Żakowa, 1972). The present-day „mosaic structure” of the Upper Palaeozoic in this area is resulting also from post-Bretonian and post-Variscan erosion, and also from younger tectonic movements. The present complicated structure is hampering the reconstruction of the original Devonian and Carboniferous sedimentary basin, which is outlined below. The post-Caledonian denudation formed a morphologically diversified surface on Precambrian, Silurian and Ordovician rocks. This surface is discordantly overlain by Emsian deposits forming the lowermost part of the new sedimentary cycle. The Emsian rocks, 20—135 m thick formed in a continental environment and represent the Old-Red Sandstone facies developed over large areas in southern Poland (M. Pajchlowa, 1968). The area described was covered by a marine transgression at the beginning of the Eifelian. The determination of the limits of the transgression is difficult, as the paleontological evidence of the Eifelian is scanty. The sea covered probably new areas in Givetian times e. g. the area of Racławice. Carbonate sediments with local supply of detrital material (e. g. in the region of Kazimierza Wielka) formed in the shallow Givetian sea. The floor of the basin subsided rapidly in the region of Strożyska where the Givetian is 501 m thick, while less pronounced subsiding zones developed in the regions of Skalbmierz—Dobiesławice and of Racławice—Kalina (thickness exceeding 200 m). Another belt of subsidence is present north of the transversal elevation Miechów-Chomentów, where in the region of Węgrzynów the Givetian reaches a thickness of 460 m (H. Jurkiewicz and H. Żakowa, 1969 a, 1972). During Frasnian times the depth and the extent of the sea did not change much, and the zones of pronounced subsidence had the same position as during the Givetian. During the Famennian the region of Kazimierza Wielka—Dobiesławice was subsiding at a high rate, as the thickness of the Famennian amounts there to 500 m. The subsidence was strongest during the Early Famennian — the Cheiloceras zone is particularly thick. A similar course of subsidence is known from the region of Bolechowice in the Holy Cross Mts (H. Żakowa, 1967). The Famennian sea transgreded eastward to the region of Kobylniki and Radzanów, where the thickness of deposits reached to 230 m. Bretonian movements activating structural elements of the pre-Devonian basement caused the regression of the sea already at the beginning of the Famennian in some areas (bore-holes Skalbmierz 3, Strożyska 5), or even earlier (? bore-hole Racławice 2). The exact determination of the area subject to Late Devonian emergence is not possible, as in many cases the Devonian is overlain directly by Mesozoic rocks, and the lack of the Carboniferous may be caused by later erosion. The sea probably persisted in the region of Kobylniki—Radzanów, and possibly also in the region of Kazimierza Wielka—Dobiesławice. The Tournaisian marine ingression came probably from the south, through the region of Grobla, and joined the embayment formed in the Etroeungtian in the region of Załucza, where the sea advanced from the area of the Holy Cross Mts. The sea was bordering from the west a relatively large land extending from the region of Racławice to the region of Kraków (J. Kicuła and H. Żakowa, 1966). Limestones exceeding 100 m in thickness accumulated in the shallow Tournaisian sea, surrounding at least the elevation of Strożyska. In Early Visean times the extent of the sea did not change much, but the sediments, containing clastic intercalations among the limestones, are much thicker. During the Middle Visean the hitherto elevated region of Strożyska and the zone of Łobzów—Słomniki—Koniusza were incorporated into the sedimentary basin. During the Tournaisian and the Tournaisian — Visean boundary palaeogeographic changes occurred also in the central part of the Miechów area, where diastrophic conglomerates are known at Węgrzynów and Łobzów. These conglomerates contain among others fragments of Precambrian rocks, which at least partly could be derived from the Opatkowice— Książ Wielki elevation, or from the western margin of the hypothetical land in the area of Skalbmierz. Erosion of the latter was probably related with rejuvenation of longitudinal dislocations extending far to the south (Fig. 1). The large regression at the Middle-Upper Visean boundary included also the southern part of the described area. The Upper Visean rocks known from the bore-hole Strożyska 5 are developed in a clastic facies similar to that present in the region of Podborze (H. Żakowa, A. Jachowicz, 1963). A zone of rapid subsidence developed in the Late Visean in the region of Słomniki—Marszowice, where the thickness of clastic rocks reaches c. 1 000 m. The remaining part of the described area were probably entirely emerged after the Lower Carboniferous times. The epeirogenic movements of synvariscan and younger age resulted in the formation of a system of longitudinal and transversal dislocations (Fig. 1) many of which are rejuvenated Caledonian and older faults. Rejuvenation of older faults is especially well marked in the case of NW-SE dislocations along which the elevations of Precambrian rocks of Opatkowice, Puszcza and Kwików are formed. The vertical displacement of the Pre-Cambrian rocks exceed 1 800 m, as indicated by data from closely spaced bore-holes (e. g. the bore-holes Skalbmierz 3 and Opatkowice 1, Fig. 3). Thus the described area displays a block structure, expressed by a great stratigraphic diversification of sedimentary rocks on small areas, with small dips in Palaeozoic and younger strata. The opinions on the absence of fold deformations of Variscan age are confirmed.

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