Sedimenty permokarbonu v Kraskove (vrt KS-1) a jejich zdrojovy material

Only scarce data exist on sedimentary relic of the so-called Kraskov Permian. Although the sediments studied remind red-bed clastics, their Permian age and stratigraphy have never been confirmend, because fossiliferous sediments are missing or were not yet identified. The Kraskov relic is supposed to belong to the Permo-Carboniferous only by analogy with lithologies of other Permo-Carboniferous relics occurring in the Bohemian Massif. It extends along NW-SE direction, and covers an area of approx. 15 km2. Data acquired from older boreholes indicate that the basement of the Kraskov relic, including adjacent area, have a complex geological structure (Fig.1). In order to obtain more information about this Permo-Carboniferous unit, which is a part of the Železné hory Mts. Geopark, a borehole KS-1 was suggested and later drilled to a depth of 27 m near the village of Kraskov. It proved an occurrence of Permo-Carboniferous clastic deposits some 21.5 m thick, lying on a granitoid basement. However, this thickness is smaller than that in the northern part of the relic where the Permo-Carboniferous siliciclastic sediments attained a thickness of 80 m. Coarse to very coarse pebbly arcosic sandstones and conglomerates constitute the major lithology in poorly preserved drill core of borehole KS-1. Microscopic study revealed numerous angular to subrounded clasts of polycrystalline quartz, then metamorphic, metagranite, quartzite and metasediments lithoclasts (Figs 3–5) in poorly sorted sandstones and conglomerates. Close to the bottom of drill core there prevail gray consolidated conglomerates, arcosic sandstones and arcoses with clasts up to 12 cm large in very coarse matrix, cemented by carbonate and sericite (Fig. 6). The deposits in the upper section of drill core are poorly consolidated, and exhibit red, brown or violet colour shades, being rich in biotite (Fig. 2). The assemblage of heavy minerals studied consists of garnet, biotite, staurolite, tourmaline and also apatite (Table 1), which indicate that the source area lies in metamorphic and alternatively magmatic rocks of the Kutná Hora and Oheb Crystalline Complexes, and/or in the Železné hory Plutonic Complex. Very abundant biotite in the matrix and poor sorting and reworking of clasts suggest that the source area is close to the depositional area.

References

Abraham, M. – Březina, S. – Grym, V.– Jurák, L. – Kincl, P. – Kopecký, P. – Kubíček, Č. – Procházka, Z. – Špaček, J. – Zelinková, Z. – Žáček, M. (1983): Železné hory – fluorit. Etapa průzkumu vyhledávací. Stav ke dni 30. 9.1983. – MS Čes. geol. služba. Praha.

Chmelař, J. (2008): Hydrogeologické vyjádření k povolení odběru podzemní vody z vrtu HVPí-4 – Podhradí v Železných horách dle § 9 Vodního zákona. – MS Čes. geol. služba. Praha.

Tůma, W. (1992): Prachovice, hydrogeologický průzkum. – MS Čes. geol. služba. Praha.

Pešek, J. – Holub, V. – Petránek, J. – Vodičková, J. – Chaloupský, J. – Jetel, J. – Kaiserová, M. – Martínek, K. (2001): Geologie a ložiska svrchnopaleozoických limnických pánví České republiky. – 243 str. Čes. geol. služba. Praha.

Smolíková, L. (1966): Nález araukaritů v severozápadním okolí Seče v Železných horách. – Čas. Mineral. Geol. 11, 1, 85–86.

Tucker, M. E. (1991): Sedimentary Petrology, An Introduction to the Origin of Sedimentary Rocks. – 260 str. Blackwell Sci. publ. London,

Veselá, M. (1976): Jihlavská brázda ve vývoji geologické stavby okolí Jihlavy. – Sbor. geol. Věd, Geol. 28, 189–205.