The ⁴⁰Ar/³⁹Ar cooling ages of white micas from the Jegłowa Beds (Strzelin Massif, Fore-Sudetic Block, SW Poland)

Jacek Szczepański

Institute of Geological Sciences, Wrocław University, Pl. M. Borna 9, 50-204 Wrocław, Poland, js@ing.uni.wroc.pl

Key words: cooling, deformation, metamorphism, 40Ar/39Ar ages, Sudetes, Bohemian Massif, Variscides.

Abstract
The metamorphic rocks of the Strzelin Massif, in the Fore-Sudetic Block, underwent polyphase tectonothermal evolution terminating with late orogenic gravitational collapse. These rocks recorded Early Permian cooling ages in the range of 279-285 Ma, obtained on white mica concentrates derived from metasediments of the Jegłowa Beds. The obtained results correspond to the youngest group of ages presented by Maluski et al. (1995) from the northern part of the Jeseník Mts, the Moravo-Silesian Zone of the East Sudetes. They suggest very low exhumation rate.

Geologia Sudetica, 34: 9–16.

Middle ro early late Viséan onset of late orogenic sedimentation in the Intra-Sudetic Basin, West Sudetes: miospore evidence and tectonic

Elżbieta Turnau¹, Andrzej Żelaźniewicz² & Wolfgang Franke³

¹ Instytut Nauk Geologicznych PAN, Senacka 1, 31-002 Kraków, Poland, ndturnau@cyf-kr.edu.pl
² Instytut Nauk Geologicznych PAN, Podwale 75, 50-449 Wrocław, Poland, pansudet@pwr.wroc.pl
³ Institut für Geologie und Paläontologie der Johann-Wolfgang Goethe-Universität Senckenberganlage 32, D-60054 Frankfurt, Germany

Key words: miospores, biostratigraphy, geochronology, Viséan, West Sudetes.

Abstract
The Early Carboniferous fluvial and deltaic sequence of the Intra-Sudetic Basin remained undated until recently, except for a Late Viséan ammonoid fauna in its upper part. Current miospore data indicate that the oldest part of the sequence is not older than the mid Viséan Knoxisporites triradiatus-Knoxisporites stephanephorus biozone of the west European miospore division. This palynological age determination is consistent with the recently obtained Ar-Ar cooling ages of white micas from sheared metamorphic rocks at the NW margin of the basin. This suggests that the rapid late orogenic denudation of the northern and western flanks of the Intra-Sudetic Basin must have started at or shortly after c. 335 Ma.

Geologia Sudetica, 34: 17-38.

Offshore to onshore transition in the Upper Viséan paleontological record from the Paprotnia section (Bardo Mts., West Sudetes)

Joanna Haydukiewicz & Jolanta Muszer

Uniwersytet Wrocławski, Instytut Nauk Geologicznych, ul. Cybulskiego 30, 50-205 Wrocław, Poland; jhay@ing.uni.wroc.pl; jmus@ing.uni.wroc.pl

Key words: taphocoenosis succession, Upper Viséan, environment, West Sudetes.

Abstract
This report provides detailed information on the taphocenosis succession from the Paprotnia series exposed in the western part of the Bardo Mts. (West Sudetes) and regarded as a temporal equivalent of the pelagic crenistria Limestone (cd III a, Upper Viséan). Five taphocoenoses have been recognised in the investigated section, which is composed of claystone and mudstone shales, greywackes and subordinately by carbonates. They differ mainly in terms of the relative frequency, size and state of preservation of specimens, and less in terms of their taxonomical composition. Changes in their vertical succession are coincidental with changes in the lithological record. Analyses of their taxonomical composition and various parameters of their paleontological record, reviewed herein, were used to estimate the paleoenvironment. Taphocoenosis I was deposited under low-energy conditions, probably in oxygen-deficient waters below the wave base. Taphocoenosis II was most likely accumulated in the environment located between the storm wave and fair weather wave bases, in oxygenated water. The fossils of assemblage III developed in a turbulent environment of well-oxygenated and relatively high-temperature shallow water. The organisms of taphocoenosis IV reflect renewed settling of the shallow seafloor during a short period of low energy conditions interrupted by the rapid delivery of a large quantity of terrigenic deposits. The uppermost part of the section, composed mainly of greywackes, which contain only the remains of terrestrial plants (taphocoenosis V) may suggest proximity to land. Both the paleontological and lithological features of the Paprotnia series indicate gradual environmental changes from offshore to onshore conditions. Consequently, the Paprotnia series represents the shallower facies equivalent of the pelagic crenistria Limestone, which is widespread in the Kulm facies of Variscan Europe.

Geologia Sudetica, 34: 39-58.

The Variscan overthrust of the Lower Palaeozoic gneiss unit on the Cadomian basement in the Strzelin and Lipowe Hills massifs, Fore-Sudetic Block, SW Poland: is this part of the East-West Sudetes boundary?

Teresa Oberc-Dziedzic & Stanisław Madej

Institute of Geological Sciences, University of Wrocław, pl. M. Borna 9, 50-204 Wrocław, Poland; toberc@ing.uni.wroc.pl; smad@ing.uni.wroc.pl

Key words: Moravo-Silesian zone, East-West Sudetes boundary, Fore-Sudetic Block, Cadomian basement, Strzelin Thrust.

Abstract
The problem of the position of the boundary between the geological structures of the West and the East Sudetes has been a topic of discussion since 1912, when F.E. Suess developed the concept of the Moldanubian overthrust as a boundary between the Moldanubian and Moravo-Silesian zones. The West Sudetes comprise gneisses of Cambro-Ordovician protolith age with inclusions of high pressure metamorphic rocks. The Cadomian basement, referred to as the Brunovistulian and overlain by Devonian rocks, is characteristic of the East Sudetes. The location of the East-West Sudetes boundary is well-defined in the mountainous part of the Sudetes but still a matter of debate in the Fore-Sudetic Block. This paper puts forward a new approach to this problem.
The Proterozoic Strzelin gneiss with its Proterozoic (the older schist series) and Devonian envelope (the Jegłowa beds) are tectonically overlain by the Early Palaeozoic Gościęcice gneiss and the light Stachów gneiss with its envelope. The former occurs in the footwall and the latter in the hanging wall rocks of the Strzelin Thrust. This juxtaposition resembles the situation along the East-West Sudetes boundary separating two domains with contrasting protolith ages. Consequently, the Strzelin Thrust is considered part of the border zone between the East and West Sudetes, i.e. the northern continuation of the Ramzova/Nyznerov thrust to the Fore-Sudetic Block. At the present erosion level, the hanging wall rocks of the Strzelin Thrust are separated from their roots and form klippen. The minimum transport distance along the thrust is estimated at 10 km. The Strzelin Thrust forms a generally shallowly dipping domed surface. It becomes steeper east of the Strzelin massif, where it is hidden beneath Cenozoic sediments, and west of the Lipowe Hills, where it follows the eastern border of the Kamieniec Ząbkowicki Metamorphic Complex. The hanging wall is probably rooted in the strongly mylonitised mica schists exposed along the Mała Ślęza river. The thrust zone is a wide mylonitic belt carrying relatively HT and HP garnet-bearing amphibolites in the northern part of the Strzelin massif and the strongly mylonitised Henryków gneiss and quartzites in the southern part at the Lipowe Hills.
This paper discusses the problem of the East-West Sudetes boundary, mainly in the framework of the Strzelin massif. The attitude of this boundary in other parts of the Fore-Sudetic Block is still unclear because of poor exposure and numerous faults of E-W and NW-SE orientation that displace it from its original position.