Karbońskie wapienie i zlepieńce zachodniej części struktury bardzkiej

Abstract

 Wapienie górnodewońsko-turnejskie, tzw. dewonu okolic Kłodzka, nie tworzą odrębnej formacji.

Występują one jedynie jako detrytus wapienny w utworach zróżnicowanych genetycznie, powstałych od schyłku wizenu górnego po najniższą część namuru A. W artykule przedstawiono charakterystykę wapieni obszaru alimentacyjnego. Na podstawie następstwa stratygraficznego warstw w odsłonięciach między Dzikowcem. Nową Wsią i Srebrną Górą opracowano schemat sedymentacji. Stwierdzono, że z serią fliszową, szarowakowo-iłowcową wiążą się tufity ryolitowe.

CARBONIFEROUS LIMESTONES AND CONGLOMERATES

IN WESTERN PART OF THE BARDO STRUCTURE

The paper presents results of studies on rock complexes hitherto treated as Upper Devonian limestone formation with limestones of the Gattendorfia stage at the top, i.e. “Devonian of the vicinities of Klodzko”, and gneiss conglomerates and Lower Coal Limestone. The studies on composition and development of these rocks, analyses of microfacies, including identifications of organic structures in thin sections, and studies on conodonts made it possible to state that: 1 – Upper Devonian and Tournaisian limestones, i.e. ”Devonian of-the vicinities of “Klodzko”, do not represent a separate formation but detritus of limestones (limestone fragments varying in size up to blocks and olistolites) in strata formed not before the end of Late Visean; 2 – in the Bardo structure, thick and genetically differentiated rock series originated in time interval from the end of Visean to the beginning of Namurian A: limestone-gabbro conglomerates (hitherto treated as basal limestone of Upper Devonian formation) and gneiss-limestone conglomerates which represent alluvial cone deposits with laminites typical of the wadi zone; limestone conglomerates (a part of Lower Coal Limestone) – fine- to coarse-clastic rocks, the origin of which has been partly related to reworking of material from alluvial cones (including gneiss-limestone conglomerates) and its redeposition in deeper parts of sea by storm waves; knobby limestones (a part of Lower Coal Limestone), thin-bedded and representing deposits of turbidites, subjected to submarine slides as partly semiplastic but already knobby material; limestone breccias with detritus and large olistolites of Upper Devonian limestones (Main Litnestone and Clymenia Limestone) and Tournaisian and Visean ones, i.e. olistostrome deposits formed in result of gravity slides; graywacke-claystone and flysch rocks and related rhyolite tuffs.

Figure 6 shows scheme of sedimentation of the above mentioned rocks, reconstructed on the basis of succession of strata in outcrops between Dzikowiec, Nowa Wieś and Srebrna Góra (Fig. I).

Contact of sandy series with gneiss-limestone conglomerates at the top and olistostrome breccia in the quarry D-5 at Dzikowiec is found to be tectonic in character (Fig. 3).

The available data appear insufficient to precise the upper time limit of sedimentation of the above discussed strata. It may be only assumed that sedimentation of the flysch series and, therefore, also underlaying conglomerates and limestones was not continuing after the beginning of the Namurian A as this was the time of onset of sedimentation of coal-bearing Wałbrzych Beds.

Origin of thick and genetically differentiated rock series in so narrow time interval (end of Late Visean – beginning of Namurian A) was possible under conditions of accelerated sedimentation, related to rapid erosion of uplifting areas, and high rate of subsidence of basin floor. The erosion was also accelerated in the early Early Carboniferous, which is shown by the nature of detrital rocks from the turn of Devonian and Carboniferous and Early Visean, corresponding in composition and possibly origin to gneiss-limestone conglomerates from the end of Late Visean. The older conglomerates are here represented by boulders varying in size and usually rounded, embedded in gneiss-limestone conglomerates cropping out in the vicinities of Srebrna Góra.

Source areas of detrital material of the above conglomerates remain unknown. On the basis of differences in its petrographic composition it may be assumed that individual deltaic cones were supplied with material from various directions. That is why some of them mainly yield detritus of gneisses and others – gabbros. Limestorie material, very common in these cones and the remaining conglomerate-limestone deposits, was presumably coming from vast neighbouring area. This conclusion is supported, for example, by generally normal position of large olistolites of limestones of Upper Devonian and Gattendorfia stage in olistostrome displayed in the quarry D-5 at Dzikowiec.

The alimentary area was characterized by intense development of limestones of the Waulsortian type as well as those originating in deeper part of sublittoral and hemipelagic zones (from Famennian to Late Visean, inclusively).

The studies showed that limestone-gabbro conglomerates and olistostrome breccia from the quarry D-5 at Dzikowiec correspond in origin and age to conglomerates and limestone breccias from Gołogłowy and outcrops near Półwiejska and Podgrodzie Streets in Kłodzko. This made it possible to state that clay and clay-siliceous shales from the Gołogłowy section do not represent sedimentary cover of Upper Devonian limestones as the latter occur in the form of various-sized blocks and fragments in flow deposits, presumably deposited not before the end of Late Visean.

The finding that Upper Devonian and Gattendorfia stage limestones of the so-called Devonian of the vicinities of Kłodzko merely form fragments and blocks in strata of the uppermost Upper Visean age makes it necessary to revise age of metamorphism in the Kłodzko structure, previously assumed as pre-Late Devonian. It is also stated that the section of eastern wall in the quarry D-5 at Dzikowiec cannot be treated as example of tectonic disturbances of the Nassau phase.

The fauna found in detrital rocks of the latest Late Visean or younger age appears to have been inappropriately interpreted in the past as it is partly mixed.