Dolnodewońskie skały polimiktyczne i tufogeniczne w regionie kieleckim Gór Świętokrzyskich

Abstract

LOWER-DEVONIAN POLYMICT AND TUFACEOUS ROCKS IN THE KIELCE REGION OF THE ŚWIĘTOKRZYSKIE MOUNTAINS

Summary 

Recently, some complete profiles of the Lower Devonian have been investigated in several bore holes (Haliszka-1, Zaręby-2, Zdobiec-1 and Cedro-1) situated within the Klelce region of the Świętokrzyskie Mountains. In the eastern part of the Kielce-Łagów synclinorium (near Iwaniska), the real thickness of the Lower Devonian amounts approximately to 130 m. In the western part, in turn (vicinity of Radlino) - approximately 80 m. The Lower Devonian age is evidenced here by the fragments of placoderms and ostracoderms of the genus Psammosteidae sp.(Table I, Fig. 5), fragments o. pelecypods (Table I. Fig. 3), psilophytes (Table I, Fig. 4) and by a rich microflora assemblage examined by L. Jakubowska (1968). The Lower Devonian profile is characterized by some distinctive lithological complexes. Here belong, from bottom to top: lower variegated siltstone-sandstone complex, middle sandstone complex, upper variegated siltstone-sandstone complex and upper sandstone complex (Fig. 1). These complexes are considerably regionally widespread and may be investigated in a dozen of bore holes in the vicinity of Iwaniska, Łagów, Radlin, and Bieliny, as well as at exposures. At the lower part of the Devonian formations three sedimentary cycles are distinguished: Lower Emsian cycle that includes the lower variegated complex with the polymict conglomerates at the bottom; Upper Emsian cycle that make the middle sandstone complex with psephites at the bottom and the upper varigated complex; and Emsian-Eifelian cycle built of conglomerates, sandstones, clastic-carbonate rocks and Eifelian dolomites (Fig. 1). In the Kielce region, the coloured polymict rocks appear in the Lower Devonian profile at two horizons only. For the most part they are found in the lower portion of the profile, where intertonguing with quartz sandstones, clay siltstones and tuffites, they constitute the so-called lower variegated complex. In the middle sandstone complex built almost completely of white psammitic quartzite sandstones, no polymict and tufaceous rocks have been ascertained. On the other hand, above the middle complex, the main part is played again by the ferruginous polymict siltstones with intercalations of sandstones, tufaceous claystones and tuffites (Fig. 1). The polymict rocks are built of feebly sorted different mineral components (quartz, muscovite, rizzite, biotite, rarely kaolinized feldspars, chlorites, haematite, goethite, chalcedony, rutile, zircon, tourmaline) and of fragments of sedimentary rocks, at places also of metamorphic and volcanic rocks. Psammitic-aleuritic fragmental material occurs in changing amounts; quartz is here a prevailing constituent (Tabl. II, Fig. 6). Cementing material makes 70% of rock, and is differentiated, mainly clayey (illite), clayey-feruginous, locally ferruginous, and at basal, partly of porous-contact nature. Fe₂O₃ content ranges from 5 to 20%. Most rocks examined are determined as polymict siltstones; part of them represent transition varieties to quartz-clay sandstones and greywackes of lower rank. In tuffites the clastic material (quartz, feldspars, fragments of volcanic rocks) is cemented with abundant, devitrified clay mass characterized by a montmorillonite-illite composition. Thermal-differential analyses of the clay fraction of the tuffite (Fig. 2, curves 1, 2, 3), and chemical nature (Table 1, No 7) show a resemblance to tufaceous siltstones. These in turn contain a slight adimixture of pyroclastic material mixed with the local sedimentary rocks (Tabl. IV, Fig. 12).
Frequently non uniform red and spoty colour of the polymict rocks most probably is an effect of diagenetic processes responsible for the transition of goethite into haematite. These rocks frequently reveal fine haematite concretions of diagenetic origin (Tabl. III, Fig. 9 and 11). In the Lower Devonian the transgression periods, which are represented by sandstone complexes, are separated with a period of reduced transgression, shallowing of the basin, strong denudation of elevated areas and intense volcanic activity all recorded in the upper variegated complex. Similar conditions of intense weathering processes and volcanic activity were at the time of the lower cycle of the Lower Devonian sedimentation. The occurrence of numerous intercalations of tuffites and tufaceous rocks in the Lower Devonian profile proves an intense volcanic activity at that time.