Valouny granitoidu ve slepencich skryjsko-tyrovickeho kambria

Pebbles of light granitoid rocks were found in conglomerates of the Buchava Formation of the Skryje-Týřovice Basin at three localities. They occur both in the so-called Kettner´s profile below Studená hora in a road cut of highway leading from Roztoky to Týřovice (Fig. 1). Similar pebbles were also newly identified around Kouřimecká Rybárna hamlet, NE of Týřovice, and in Karáskova rokle (gully), NE of Skryje.
Petromict conglomerates near Studená hora and at the Kouřimecká Rybárna hamlet correspond to the earlier distinguished Vosník Conglomerates (Kettner 1923), to the Týřovice Conglomerates occurring in Karáskova rokle (gully), and today they are all ranked among the Slapnice Member of the Buchava Formation (Fatka et al. 2011). The age of conglomerates corresponds to the Drumian stage of the Cambrian (504.5 to 500.5 Ma). Granitoid pebbles found at the localities near Studená hora and Kouřimecká Rybárna (each located on opposite banks of the river Berounka) are confined to the same layer of conglomerates the development and strike of which at both outcrops are almost the same, i.e. NE-SW to ENE–WSW. The size of granitoid pebbles at all three sites ranges most often between 2.6 and 3.6 cm, max. 4.4 cm. A total of 10 pieces of these pebbles were found.
Granitoid pebbles in the Vosník Conglomerates found in a few pieces (3 identifiable pebbles) have already been mentioned in a study by Kettner and Dudek (1956). In this paper, however, the localities are described in detail, including two new localities, and accompanied by photographic documentation of thin sections, and including discussion regarding a potential source of magmatic rocks based on the current knowledge of absolute age of the surrounding plutons.
The following three basic types of granitoid rocks were identified in conglomerates of the Buchava Formation at the above-mentioned localities: (1) light granites (leucogranites or porphyries, Fig. 2) with distinct intergrowths of quartz and feldspar, (2) fine-grained granites with pinkish feldspars (Figs 3, 4), and (3) tectonized, cataclastic granitoids penetrated with tiny quartz veinlets (Fig. 5). All types are usually fine- to medium-grained, but they may also represent just varieties of one type of granite.

References

Fatka, O. - Micka, V. - Szabad, M. - Vokáč, V. - Vorel, T. (2011): Nomenclature of Cambrian lithostratigraphy of the Skryje-Týřovice Basin. - Bull. Geosci. 86, 4, 841-858.

Fiala, F. (1980): Valouny granitoidů ze spodnokambrických žiteckých slepenců. - Čas. Mineral. Geol. 25, 4, 351-368.

Cháb, J. - Stráník, Z. - Eliáš, M. (2007): Geologická mapa České republiky 1 : 500 000. - Čes. geol. služba. Praha.

Kettner, R. (1923): Kambrium skrejsko-tejřovické a jeho okolí. - Sbor. St. geol. Úst. Čs. Republ. 3, 5-63.

Kettner, R. - Dudek, A. (1956): Vosnické slepence ve skryjsko-týřovickém kambriu. - Sbor. k osmdesátinám akad. F. Slavíka, 133-157.

Kettner, R. - Slavík, F. (1928): Nový profil v algonkiu a kambriu tejřovickém. - Rozpr. Čes. Akad. Věd Umění, Tř. II 38, 10, 1-30.

Kukal, Z. (1966a): Petrografický výzkum skryjsko-týřovického kambria. - Zpr. geol. Výzk. v Roce 1965, 105-107.

Kukal, Z. (1966b): Zdroje klastického materiálu sedimentů příbramsko-jineckého kambria. - Sbor. geol. Věd, Geol. 10, 83-116.

Kukal, Z. (1971): Sedimentology of Cambrian deposits of the Barrandian area (Central Bohemia). - Sbor. geol. Věd, Geol. 20, 53-100.

Petránek, J. (1952a): Skrytá diskordance ve skryjském kambriu. - Rozpr. Čes. Akad. Věd Umění, Tř. II 62, 4, 1-12.

Petránek, J. (1952b): Zpráva o výzkumu týřovických a vosnických slepenců v skryjském kambriu. - Věst. Ústř. Úst. geol. 27, 5, 219-221.

Vorel, T. - Stárková, M. - Hradecký, P. - Holásek, O. - Adamová, M. - Dušek, K. - Hrazdíra, P. - Klečák, J. - Krmíček, L. - Krupička, J. - Lysenko, V. - Mašek, D. - Müller, P. - Skácelová, D. - Skácelová, Z. (2012): Základní geologická mapa České republiky 1 : 25 000 s Vysvětlivkami, list 12-321 Panoší Újezd. - 106 str. Čes. geol. služba. Praha.