Early Permian Freshwater Silicified Stromatolites and Oolites from the Krkonoše Piedmont Basin (Bohemian Massif): Paleobiology, Environmental Setting and Early Diagenesis

A new actinopterygian species from lacustrine Lower Permian deposits of the Krkonose Piedmont Basin (Bohemian Massif, Czech Republic) is assigned to the genus Igornichthys Heyler, 1972. Present study of this new species reveals several anatomical structures that markedly advance our knowledge and make the generic diagnosis of Igornichthys more precise. Characters that include sharply pointed spines on the scales, a supraorbital sensory canal continuing from the frontal on to the dermopterotic, a maxilla with the maxillary plate protruding at a ventro-posteriorly angle, dentition forming a single row of similar conical teeth, and an oblong operculum are diagnostic of the new species. Igornichthys is placed within Igornichthyidae Heyler, 1977 together with Igornella Heyler, 1969, Setlikia Stamberg & Zajic, 1994 and Commentrya Sauvage, 1888 from the Stephanian and Lower Permian of the French Massif central and the Bohemian Massif. Analysis of the anatomical features of Igornichthys and other members...

Actinopterygians of the Stephanian sediments of the Krkonoše Piedmont Basin (Bohemian Massif) and their palaeobiogeographic relationship

Re–Os isotopic constraints on the source of platinum-group minerals (PGMs) from the Vestřev pyrope-rich garnet placer deposit, Bohemian Massif

Late Paleozoic volcanic rocks of the Intra-Sudetic Basin, Bohemian Massif: petrological and geochemical characteristics

Sporadic grains of the Sr-Ca-REE-rich members of the plumbogummite and beudantite groups were identified in a heavy mineral concentrate separated from Upper Carboniferous freshwater sandstone/arkose of the Semily Fm. at the Semily site (Krkonoše Piedmont Basin, Bohemian Massif, Czech Republic). These minerals display very fine-grained nature, increased porosity and contain abundant inclusions of both detrital (quartz, illite-muscovite) and authigenic (Fe-oxides, anatase) phases. The electron microprobe study revealed four phases including predominant crandallite, less frequent goyazite, and rare woodhouseite and florencite-(Ce), which, however, display great similarities on both cationic (Sr, REE, Ca, Fe contents) and anionic (As and S contents) sites of the formula. Cerium is always the dominating cation among REEs. The studied phases show low degree of fractionation of REEs (La/SmCN = 2.0 - 8.1), absence of CeCN anomaly and mostly slightly positive EuCN anomaly. They likely originated during diagenetic processes operating in the host sediments. When compared with other occurrences of these minerals in the area of Czech Republic, a very low level of REE fractionation is obvious, which can be explained either due to significant contribution of basic volcanites in the host rock environment and/or due to low activity of strong REE-complexing ligands in the parent fluids. However, the character of Ce and Eu anomalies is similar to other occurrences suggesting for similarities of temperature and redox conditions during crystallization.

A new aeduellid actinopterygian from the Lower Permian of the Krkonoše Piedmont Basin (Bohemian Massif) and its relationship to other Aeduellidae

Here we present preliminary information on the fossil content of a rediscovered fossiliferous locality in the Late Carboniferous (Stephanian; Kasimovian/Gzhelian) Ploužnice Horizon, Semily Formation, in the Krkonoše Piedmont Basin of the Bohemian Massif. Several meters thick reddish to grey tuffaceous siltstones of this lacustrine horizon contain centimetre thick bone-bed layers and sporadically distributed plant remains. Common are isolated fish remains of actinopterygians, chondrichthyans, and acanthodians as well as isolated insect wings, mainly from blattoids. The biostratigraphic age is determined by blattoid insects as Stephanian B/C (Kasimovian/Gzhelian).

Permo-Carboniferous volcanism in late Variscan continental basins of the Bohemian Massif (Czech Republic): geochemical characteristic

A new aeduellid actinopterygian Amelangia ornata gen. et sp. nov. is described from the Lower Goldlauter Formation of the Thuringian Forest (Lower Permian, Germany). Distinguishing characters of the newly described taxon are a large dermosphenotic, an unusually large number of suborbital bones, a maxilla with a low maxillary plate, a distinct sculpture consisting of tubercles on the operculum and suboperculum, the presence of a single branchiostegal ray, and a pectoral fin with a scaly basal lobe. The preserved characters place the new genus close to the genera Aeduella and Bourbonnella. The newly described genus and species is similar to an isolated operculum and suboperculum recovered from the Lower Permian of the Krkonoše Piedmont Basin in the Bohemian Massif.

The Krkonoše Piedmont Basin, an early post-Variscan basin (c. 310–280 Ma) located in the NE Bohemian Massif (Czech Republic, central Europe), contains up to 300-m-thick non-marine Lower Permian (Asselian) deposits of the Vrchlabí Formation that crop out in its western part. The Early Permian Krkonoše Piedmont Basin exhibits striking similarities—in terms of tectonostratigraphic evolution, depositional patterns, and volcanism—to other early post-Variscan, near-equatorial intermontane basins. This work focuses on sedimentological analysis of the Vrchlabí Formation using outcrop data, combined with borehole and newly acquired field gamma spectrometry data. The formation consists predominantly of fluvial deposits in the southern part of the basin that pass laterally into deltaic and lacustrine deposits of the Rudník Member, located in the central part of the basin. Fluvial deposits are formed by sandstone and conglomeratic bodies, decimeters to several meters thick, interpreted as single-story and multi-story channel fills as well as various macroforms (e.g., bars) deposited by a low-sinuosity fluvial system. Channel fills intercalate with floodplain deposits centimeters to few meters thick. Vertically, the studied fluvial succession is divided into five intervals based on i) variable preservation ratio between channel fill and floodplain deposits and ii) external and internal geometries of sandstone and conglomerate channel bodies. In order to explain the observed vertical changes in fluvial style and to determine the main controlling factors, the interaction of the fluvial system with the contemporaneous lake was investigated by interpreting base-level changes of the fluvial system and their correlation with lake level changes. In the central part of the basin the transition from fluvio-deltaic to lacustrine deposits is represented by alternating beige to gray sandstones centimeters to few meters thick and by dark gray mudstones up to several meters thick that pass northwards into shales. At the outcrop scale, the new sedimentological data in combination with newly acquired gamma-ray logs enabled tracing the lateral extent of individual fluvial bodies. The integration of the new data with older borehole data leads to a substantially better understanding of lateral and vertical relationship between the fluvio-deltaic and the lacustrine facies at the basin scale. Tectonic subsidence played a substantial role during the initial deposition of the Vrchlabí Formation. However, the external geometries, the internal architecture of fluvial channel bodies, and the variable degree of floodplain preservation throughout the entire Vrchlabí Formation cannot be explained by tectonics only, but requires the consideration of climatic controls. The Early Permian fluvial system is interpreted to reflect seasonal discharge variability with dry and wet periods under long-term subhumid climatic conditions that shifted towards more arid conditions during the latest depositional stage of the Vrchlabí Formation.

First anatomical description of silicified calamitalean stems from the upper Carboniferous of the Bohemian Massif (Nová Paka and Rakovník areas, Czech Republic)

Early diagenesis in Canadian Shield lakes

ABSTRACTThis paper describes a new 3‐D forward numerical model (CARBONATE 3D) that simulates the stratigraphic and sedimentological development of carbonate platforms and mixed carbonate–siliciclastic shelves by simulating the following sedimentary processes: (1) Carbonate shallow, open‐marine production, dependent on water depth, restriction and sediment input; (2) Carbonate shallow, restricted‐marine production, dependent on water restriction; (3) Pelagic sediment production and deposition; (4) Coarse and fine siliciclastic input; (5) Erosion, transport and redeposition of sediment, dependent on currents, slope, depth and restriction as well as sediment grain‐size and composition; (6) Dissolution of subaerially exposed carbonate. In this paper the model is used to investigate the controlling mechanisms on the sequence stratigraphy of isolated carbonate platforms and atolls and to predict distinctive architectural signatures from different drowning mechanisms. Investigation of the mechanisms controlling atoll strata shows that although relative sea‐level is the major control, antecedent topography, environmental setting and early diagenesis have profound influence on what stratigraphic geometries and facies develop. Hence care must be taken if sea‐level curves are interpreted from real stratigraphies. Atoll drowning by fast sea‐level rise, by lowered production and by repeated exposure and fast subsequent sea‐level rises are investigated and different stratigraphic signatures for the respective mechanisms predicted. A fast relative sea‐level rise results in a bucket‐shaped morphology developed prior to drowning and a sharp transition from the platform margin facies to a pelagic cover. Drowning caused by lowered platform margin production is predicted to result in the development of a dome‐shaped, shallow‐water shoal over the whole platform top prior to drowning. Fourth order amplitudes of several tens of metres, typical of ‘icehouse’ settings, cause atoll drowning at subsidence rates where atolls subject to fourth order amplitude of only a few metres, typical of ‘greenhouse’ settings, can keep up with the rising sea‐level. In the resultant strata, vertical facies belts are less well developed but horizontally extensive facies bands are more prominent. High fourth order amplitudes (up to 80 m) without sufficient third order scale subsidence will not lead to drowning, however, as the platform can recover in each fourth order lowstand. These results suggest that atolls might be easier to drown in ‘icehouse’ rather than in ‘greenhouse’ conditions but only in situations with suitably high rates of longer‐term relative sea‐level rise or sufficient lag times.

The Mesozoic and Tertiary basins of the Bohemian Massif and their evolution

A succession of the early Permian (Asselian) Rudník member exposed at the locality Škodějov – Hrádecký potok in the northwestern part of the Krkonoše Piedmont Basin (eastern Bohemia) contains light-colored clastic rocks with macroscopically conspicuous lamination, overlying lacustrine bituminous claystones and siltstones (ʻblack shalesʻ). This work aims to constrain the origin of those laminated strata. They can be macroscopically described as heterolithic sequence formed by fine- to medium-, exceptionally coarse-grained sandstone with intraclasts of mudstone, calcified fine-grained sandstone, mudstone and claystone with interlayers of organic-rich laminae. Volcaniclastic rocks are also present. The heterolithic volcanosedimentary sequence comprises cyclic (up to 4 dm), mostly horizontally laminated rocks, in places with soft- sediment deformation structures. Diagenetic phenomena, related to calcification of volcaniclastic layers and growth of pyrite crystals and framboids, are common. Volcaniclastic rocks with a predominance of albitized volcanic glass fragments are interpreted as vitritic tuffs. Fragments of volcanic glass floating in silty to fine-grained sandy matrix contain vesicules and are locally brown- colored. They are reinterpreted as being derived from contemporary intermediate (andesitic) volcanism, most likely extrabasinal. Extensive alteration of volcanic material makes characterization of the original composition of volcaniclastic deposits difficult. Trace element analysis using a portable XRF spectrometer revelaed negligible concentrations of V, Ni and Ti, which are indicative of rather basic volcanism. Results of outcrop-scale gammaspectrometry are presented here as trends of Th/U ratio of relevant lithotypes from several localities of the Rudník member. Organic-rich laminae present within the heterolithic succession at Hrádecký potok section are commonly rich in pyrite clusters. Those are the most probably related to formation of algal mats stimulated by input of fine-grained volcaniclastic material into the Rudník Lake. However, elevated siliciclastic and volcaniclastic input, particularly during periods of intensified volcanic activity, with related seismic events (that may have triggered gravity flows), may have disturbed or punctuated growth of algae on the lake floor. Our work has shown that the volcanic activity at the onset of deposition of the Rudník member in the northwestern part of Krkonoše Piedmont Basin (Škodějov – Hrádecký potok) was probably of intermediate nature and that it influenced depositional environment. Particularly, the fluctuating input of clastic and volcanogenic material could have caused an alternation of oxic and dysoxic conditions in the lake lacustrine environment over time. The intermediate character of volcanism in this locality contrasts with confirmed acidic volcanism documented in volcaniclastic layers in another lacustrine succession at Vrchlabí – roadcut (Martínek et al. 2006) that probably represent a different eruptive phase recorded within the Rudník member.