Utwory syluru i dewonu w południowej części struktury bardzkiej (Sudety)

Maria Chorowska

Abstract


W rejonie Boguszyna i Wojciechowic występują głównie, jeśli nie wyłącznie, utwory starsze od karbonu dolnego. Są to szarogłazy, mułowce i iłowce dewonu, w większości górnego, podrzędnie sylurskie i dolno dewońskie lidyty i iłowce z wkładkami radiolarytów. Brak tu utworów ordowiku. W sylurze i dewonie czynny był wulkanizm kwaśny i zasadowy. Tektonika utworów syluru i dewonu jest wynikiem zbrekcjowania sekwencji skalnych w toku ześlizgów podmorskich oraz późniejszego stektonizowania tak powstałej megabrekcji.

 

THE SILURIAN AND DEVONIAN DEPOSITS IN THE SOUTHERN PART OF THE BARDO STRUCTURE - THE SUDETY MTS.

In the Boguszyn and Wojciechowice region greywacke, siltstones and claystones described till now as Lower Carboniferous represent likely exclusively various links of Devonian, mainly the Upper one. The subordinately occurring Silurian deposits consist of the Ludlow deposits and known till now the Llandovery and Wenlock lydites and graptolithic shales. Rhyolites, tuff, and volcanic breccia are stratigraphically connected with the Ludlow claystones in Mariańska Górka. There are no Ordovician deposits in the studied area. Orthoquartzitic sandstones described till now as "the Ordovician quartzites of Jodłownik" are stratigraphically connected with the Emsian sequence of shales interbedded with siltstones and orthoquartzitic sandstones.

The age of the rocks in exposures and in the Boguszyn IG 1 borehole (Tab. 1) was determined on the base of fauna with a varied accuracy. This age was specified in many cases by taking into consideration the lithology (Tab. 2; Fig. 2).

In Silurian and lowest Devonian originated pelites - mainly siliceous, claystones and clastic deposits - mostly black with a large quantity of radiolarians and spicules of sponges and with occasional pelecypods and brachiopods (solely Lingula sp.) with very small valves, which occur only in the light claystones. These deposits are interbedded by tuffs and tuffites. Rhyolites and volcanic breccia occur also in the Ludlow deposits.

Clastic deposits began to originate in Emsian. Initially there were sandstones and fine- or medium-grained greywackes and also coarse-grained, sometime conglomeratic greywackes in the Frasnian and Famennian sequences.

In the Emsian and Frasnian deposits (the outcrop in Boguszyn) and in the Eifelian and Frasnian sequences (the Boguszyn IG 1 borehole) were stated the tuff and tuffite bands of acid and basic volcanism. In the Boguszyn IG 1 borehole profile the age of spilite is not identified; this spilite forms a sill in thermal contact with the Frasnian claystone and greywacke.

The Silurian and Devonian deposits show a deep water, pelagic character; they were formed chiefly in reduction conditions. The Middle and Upper Devonian sequences are developed in a flysch facies. Clastic deposits originated from suspension currents occur in Emsian for the first time. Tectonics in the Silurian and Devonian deposits is very complex. This can be explained as the result of brecciation of large masses of deposits (during submarine slides) lithified in a various degree and then processed tectonically. Occurrence on the surface and up to the depth of 2000 m (the Boguszyn IG 1 borehole bottom) of blocks of various size, consisting of rocks of various age, chaotically distributed, variously positioned (often up side down) establishes the main cause of absence connections amongs lithostratigraphical profiles. The later rigid deformations manifested anisotropic fractures, originated from at least five phases of fracturing, and brecciation or even crushing the rocks, previously dislocated gravitationally. The complex tectonics of the area is described variously. J. Oberc and R. Wilczyński (1987) showed the indications of folding tectonics, B. Wajsprych (1986) showed melange texture.

 


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