Tournaisian age of granitoids from the Odra Fault Zone (southwestern Poland): equivalent of the Mid-German Crystalline High?

The Odra Fault Zone of southwestern Poland is a NW-trending horst marked by gravimetric and magnetic anomalies and composed of high- to low-grade metamorphic and igneous rocks which are only known from boreholes. This zone embraces a concealed border between Variscan internides and externides. It also contains an array of several I-type, metaluminous to peraluminous, high potassic granitoid bodies which intruded earlier metamorphosed rocks. Except for one case, they remain unfoliated and undeformed, and presumably play a role of stitching plutons at the suture between two obliquely colliding terranes. U–Pb TIMS dating of single zircons from one foliated and one unfoliated granitoid samples yielded identical concordant ages of 344±1 Ma (Tournaisian). They resemble a Pb–Pb age of 350±5 Ma obtained for S-type granitoids from the Luckau area further west in Germany, which is generally regarded as an eastern segment of the Mid-German Crystalline High. Carboniferous granitic intrusions in the high are generally younger (340–290 Ma). Correlations of the the Odra Fault Zone with the Mid-German Crystalline High appear plausible, but by no means certain and require further confirmation.     

SPECIFIC EROSIONAL AND DEPOSITIONAL PROCESSES IN A PLEISTOCENE SUBGLACIAL TUNNEL IN THE WIELKOPOLSKA REGION,POLAND

The Pleistocene Cie?le succession accumulated in a subglacial tunnel and shows three sedimentological units: (1) trough cross‐stratified sand with granules deposited in deep channels up to 5.4 m, (2) trough stratified and massive gravels deposited in a very deep channel up to 6.2 m eroded by a catastrophic hyperconcentrated flow, and (3) a massive diamicton, interpreted as a basal till of melt‐out type. We focus on angular and deformed sandy clasts that occur in the second unit. It appears that thermal erosion, short transport in a sediment‐laden current and sudden sedimentation were responsible for the oversized sandy clasts that occur in the gravel glaciofluvial deposits. The deposits are characterized by large‐scale erosional scours, massive structure, and fluid‐escape deformations. This combination of features can be used as a key tool for the interpretation of hyperconcentrated‐flow conditions beneath Pleistocene ice sheets.     

Determination of recent deposition rates in Lake Constance with radioisotopic methods

Sedimentation rates were determined with the ²¹⁰Pb method in eight sediment cores from Lake Constance. The rate of deposition in the main basin (Obersee) varies from about 0.06 g cm^?2 y^?1 in the central part to 0.13 g cm^?2 y^?1 in the eastern part of the lake and then increases rapidly towards the Rhine delta. In the central lake area the rate of deposition has been approximately constant since 1900, and dating with the ²¹⁰Pb method is in good agreement with sedimentological observations. In the Konstanzer Trichter area, the deposition rate has been increasing since about 1955 as a result of eutrophication and subsequent high carbonate production. Dating with ¹³⁷Cs is fairly accurate for sediments deposited at a high rate, but is questionable for slowly accumulating ones. A positive correlation of ²¹⁰Pb fluxes and sedimentation rates indicates that ²¹⁰Pb flux into sediments follows the distribution pattern of solids. ²¹⁰Pb profiles in four sediment cores interpreted in terms of a constant flux model display synchronous fluctuations of the sedimentation rate; however, their relation to long-range particulate input variations remains to be proved. Sedimentation rates determined with the ²¹⁰Pb method were used to calculate recent nutrient and heavy metal fluxes. Anthropogenic fluxes of Zn and Pb are in the same range of magnitude as in other polluted areas in Europe and America.     

GEOMORPHOLOGICAL CHANGES WITHIN A HILLSLOPE CAUSED BY A WINDTHROW EVENT IN THE TATRA MOUNTAINS,SOUTHERN POLAND

Tree uprooting plays an important role in hillslope evolution. The geomorphological impact of tree uprooting after a foehn wind occurrence, in December 2013 in the Tatra Mountains, was investigated. Geomorphological mapping was conducted in three watersheds. Additionally, in one of the watersheds, 459 windthrow pits were measured, in an area of 6.4 ha. The mean volume of a pit was 2.41 m³, and the mean surface area was 5.47 m². 3.9% of the area was affected by windthrow pits, however locally the magnitude of changes was significantly higher, reaching up to 14.5% of the surface area. Slope inclination weakly influenced the effects of uprooting, and a decrease in the average depth of pits on steep slopes was observed. Individual windthrow pits (five cases) initiated the activity of geomorphological processes, and two cases of periodic springs were noted. Changes in the relief of small landforms caused by tree uprooting were documented. Windthrow creation facilitated the delivery of the soil material from the slopes into the channels.     

Saxothuringian zone in Germany and Poland: differences and common features

The classical correlation by kossmat (1927) of the Saxothuringian belt of Germany with the West Sudetes of Poland is re-evaluated with special reference to the crystalline massifs of Munchberg and the Góry Sowie and the surrounding areas. Important common features are: Cambro-Ordovician magmatism and sedimentation; Silurian to Devonian radiolarian cherts in the low grade to unmetamorphosed units; Early Devonian (and older?) pressure-dominated metamorphism followed by rapid uplift; the incorporation of high pressure and mantle rocks; and Early Carboniferous mass flow deposits with ‘Saxothuringian’ clasts. Differing features in the West Sudetes are: tectonic contacts in and around the Góry Sowie are mostly subvertical and mainly (semi-)brittle (in contrast with subhorizontal and ductile contracts in the Münchberg); the Góry Sowie has undergone late re-equilibration of the earlier tectonic fabrics; an ophiolite juxtaposed with the Góry Sowie crystallized in (?) Devonian time and became only statically metamorphosed, as opposed to the regionally metamorphosed Cambro-Ordovician mafic rocks of the Saxothuringian belt; localized depocenters with Upper Devonian to Lower Permian elastic rocks relating to north-west trending strike-slip faults instead of the north-east trending cylindroidal foreland basin in the Saxothuringian. It is possible that the West Sudetes originated as an easterly continuation of the Saxothuringian belt, but then became involved, from the Late Devonian onwards, in a strike-slip system parallel with the margin of the East European Platform.     

Uplift and late orogenic deformation of the Central European Variscan belt as revealed by sediment provenance and structural record in the Carboniferous foreland basin of western Poland

The Carboniferous foreland basin of western Poland contains a coherent succession of late Viséan through Westphalian turbidites derived from a uniform group of sources located within a continental magmatic arc. Detrital zircon geochronology indicates that two main crustal components were present in the source area of Namurian A sediments. They represent Late Devonian and Early Carboniferous ages, respectively. The detritus from Westphalian D beds is much more diversified and contains admixture of Late Carboniferous zircons suggesting rapid unroofing of Variscan igneous intrusions in the hinterland between Namurian A and Westphalian D times. Tectonic repetitions of tens of metres thick fault-bounded stratigraphic intervals, recorded in several wells, provide evidence for compressional regime that occurred in the SW part of the Carboniferous basin not earlier than during the Westphalian C and produced NW–SE trending folds, concordant with the structural grain of the adjacent, NE part of the Bohemian Massif.