Functional groups in a single pteridosperm species: Variability and circumscription (Pennsylvanian, Nova Scotia, Canada)

Multiple foliar specimens of the Late Pennsylvanian fossil pteridosperm [gymnosperm] Alethopteris zeilleri (Ragot) Wagner were collected from one restricted stratigraphical horizon in the Canadian Sydney Coalfield. Variability of functional-group distribution using FTIR technique was studied in compressions, adaxial versus abaxial cuticles, and in unseparated cuticles as a function of maceration time from 48 to 168 h. The results obtained document spectral variability that could be expected within specimens of one species. For example, CH₂/CH₃ and Al/ox ratios can differ by as much as 20% of the values. Moreover, the experiments performed confirm that by using a previously established maceration protocol, long maceration periods do not bias FTIR spectra in terms of oxygenation overprinting. The inference that this cuticle is robust, under the given diagenetic level, probably reflects a reassuring degree of chemical fidelity of the Pennsylvanian plant to support Carboniferous chemotaxonomic observations.     

Chemometric study of functional groups in different layers of Trigonocarpus grandis ovules (Pennsylvanian seed fern, Canada)

We examined four dispersed, coalified ovules, Trigonocarpus grandis, of medullosalean seed-fern affinity from the Late Pennsylvanian age Sydney Coalfield, Canada, which represent the larger type of the 7–8 cm trigonocarpalean form species. At first glance it appears that the ovules are preserved like the usual Carboniferous foliar compressions, i.e. one coalified layer with one preserved anatomical tissue, the cuticle. However, careful sample preparation uncovered at least three coalified layers, and Schulze’s oxidative maceration process, which dissolves the coalified material, revealed several tissue layers. Altogether, eight sample forms were defined: (i) coalified layer, (ii) cuticle A, (iii) cupric + vitrain, (iv) vitrain, (v) cupric, (vi) cuticle B, (vii) alkaline solution and (viii) added coal seam material. The purpose of the study was twofold: first, to systematically analyze the forms by way of Fourier transform infrared (FTIR) spectrometry to fill a gap in chemical information that exits for coalified trigonocarpalean ovules of Carboniferous seed ferns; second, to use principal component analysis to focus on groupings as a function of chemical structure (functional groups) and to assess the different fossil forms in terms of FTIR chemical parameters, based on a 8 × 49 data matrix.Results include distinction among the three coaly sample forms, coalified layer (i), cupric + vitrain (iii) and cupric (v), based mainly, but not exclusively, on differences in carbonyl content, as well as length and branching of the polymethylenic chains. Important to note is the high aliphatic content of the cuticles as a signature of the biomacromolecules cutan/cutin. In particular, new insights into the structure of the original ovule are presented, and differences in chemistry are mainly a result of the complex structure of the precursor plant organ.     

Role of vegetation in shaping Early Pennsylvanian braided rivers: Architecture of the Boss Point Formation,Atlantic Canada

Vegetation is a major driver of fluvial dynamics in modern rivers, but few facies models incorporate its influence. This article partially fills that gap by documenting the stratigraphy, architecture and palaeobotany of the Lower Pennsylvanian Boss Point Formation of Atlantic Canada, which contains some of the Earth's earliest accumulations of large woody debris. Braided‐fluvial systems occupied channel belts of varied scale within valleys several tens of metres deep and more than 12 km wide, and their deposits predominantly consist of sandy and gravelly bedforms with subordinate accretionary macroforms, high flow‐strength sand sheets and rippled abandonment facies. Discrete accumulations of clastic detritus and woody debris are up to 6 m thick and constitute at least 18% of the in‐channel deposits; they represent lags at the base of large and small channels, fills of minor channels and sandy macroforms that developed in central positions in the upper parts of channel fills. Sandstones with roots and other remnants of in situ vegetation demonstrate that vegetated islands were present, and the abundance of discrete channel fills suggests that the formation represents an anabranching, island‐braided sandbed river, the earliest example documented to date. Although some sphenopsid and lycopsid remains are present, most woody fragments are derived from cordaitalean trees, and the evolution of this group late in the Mississippian is inferred to have exerted a significant influence on fluvial morphodynamic patterns. The formation records a landscape in which active channel belts alternated with well‐drained floodplains colonized by dense, mature forests and local patches of pioneering, disturbance‐tolerant vegetation. Lakes and poorly drained floodplains dominated by carbonate and organic deposition, respectively, were also present. A large supply of woody debris triggered channel blockage and avulsion, and active channel margins and islands within the channel belts were initially colonized by pioneer vegetation and subsequently stabilized by large trees. A similar alternation of stable and unstable conditions is observed in modern braided rivers actively influenced by vegetation.     

Facies,geometry and growth phases of the Valdorria carbonate platform (Pennsylvanian,northern Spain)

The 14 km wide Valdorria outcrop (Pennsylvanian, northern Spain) is one of the few examples of entirely exposed flat‐topped and high‐relief carbonate platforms reported in the fossil rock record. Laterally and vertically traceable stratal patterns expose three phases of growth. Phase I is a 430 m thick platform to slope succession that prograded over 6 km, and is dated as Early Bashkirian (Akavasian–Askynbashian). Phase II aggraded and prograded, exhibiting 180 m thickness of cyclical platform top deposits, dated as Late Bashkirian (Asatauian). Phase III is a mound‐shape structure that developed over the platform top of Phase II as a new phase of platform nucleation. It is 535 m thick and 2 km wide, and dated as Late Bashkirian (Asatauian–Transition interval). The observed changes of growth styles during platform evolution, from a prograding to an aggrading–prograding system, and a rapid aggradational phase, are inferred to be controlled by flexural subsidence in the active Cantabrian foreland basin, at the Variscan orogenic front. The metre‐scale shallowing‐upward cycles of the platform top are most probably due to glacioeustasy, as evidenced by well‐recorded subaerial exposure surfaces superimposed on subtidal deposits, and by a stratal pattern recurrent in a short interval of about 160 kyr. Observations of outcropping Bashkirian cyclothems in an isolated carbonate system, devoid of siliciclastic input, are relevant for a better understanding of the impact of high‐frequency sea‐level fluctuations on the carbonate factory. Moreover, progradation of the platform margin during Phase I reaches a rate of 2500 m/Myr, and 1810 m/Myr during Phase II; rates that are high when compared to other Pennsylvanian examples. The aggradation rate of 447 m/Myr calculated for the Late Bashkirian–Transition interval (Phases II and III; uncorrected for compaction, missing beats and erosion) is uncommonly high in comparison to coeval Pennsylvanian examples. The platform exhibits a self‐nourishing prograding microbial boundstone‐dominated slope. Thus, the slope‐shedding model applies well to Valdorria. However, Phase II recorded eustatic variations able to inhibit the slope microbial boundstone factory during low sea‐level stands; this is marked by common slope red‐stained breccias synchronous to platform top subaerial exposure phases. Contrarily, periods of relative high sea‐level and rapid subsidence in Phase III registered a greater development of cemented microbial boundstone. These observed, partly opposing relationships of sea‐level stands, shedding modes and slope architecture provide an improvement of the currently used slope‐shedding model. The overall architecture of the Valdorria outcrop compares well with that of other contemporaneous platforms, such as Sierra del Cuera and Bolshoi Karatau. Valdorria shares the high‐relief and flat‐topped, steep slopes, cyclothemic patterns and occurrence of karst features with the Pricaspian Basin platforms (Tengiz, Karachaganak and Kashagan), with minor variations in facies distribution of the internal platform. Furthermore, the continuous seismic‐scale outcrop of Valdorria, together with its isolated setting and asymmetrical growth, makes it a very good candidate for potential subsurface analogues of hydrocarbon‐bearing systems.     

Sumixam maximus gen. and sp. nov., a New Pennsylvanian Species of Archaeorthoptera (Neoptera; Indiana, USA)

A new Mazon-Creek-type fossil specimen is described as Sumixam maximus gen. and sp. nov., assigned to the taxon Archaeorthoptera Béthoux and Nel, 2002 (composed of Orthoptera and some fossil relatives): it exhibits one of the diagnostic character states of this taxon, which is the fusion of CuA (emerging from M + CuA) with CuP, or a branch of it. A more precise taxonomic assignment is out of reach. The new taxon exhibits a fusion of the anterior branch of MA with RP, and a point of divergence of MA and MP located near the point of divergence of CuA (from M + CuA), but lack a branching of CuPa. This unique combination of character states is probably derived with respect to a number of contemporaneous species. Sumixam maximus gen. and sp. nov. is most likely the closest known relative of the panorthopterans, which include all the recent Archaeorthoptera.     

似犬齿珊瑚属Caninophyllum Lewis，1929（四射珊瑚）两个种个体系统发育特征研究

四射珊瑚似犬齿珊瑚属Caninophyllum Lewis,1929广泛发育于欧洲、亚洲和北美地区石炭纪至早二叠世,以成年期主隔壁缩短且不发育轴部构造为特征,由于该属一些种的主、对隔壁特征及轴部构造在成年期特征与原始定义不符,导致关于Caninophyllum Lewis,1929定义存在分歧。根据准噶尔盆地东北缘上石炭统石钱滩组发现的保存较完整的Caninophyllum shuangjingziense Zeng,1983与Caninophyllum yui Wang,1989个体系统发育特征,并结合模式种及原始描述,认为Caninophyllum在早期个体发育阶段,原生隔壁（轴连隔壁）便分离为主隔壁与对隔壁,成年期主隔壁整体呈现缩短趋势,对隔壁与对部其余一级隔壁等长,轴部构造不发育。     

Upper Famennian and Lower Tournaisian sections of the Moravian Karst (Moravo‐Silesian Zone,Czech Republic): a proposed key area for correlation of the conodont and foraminiferal zonations

Foraminiferal and conodont faunas at the Devonian–Carboniferous (D–C) boundary in the southern part of the Moravian Karst (Czech Republic) were studied in different facies of the basin slope. The joint presence of foraminifers and conodonts in calciturbidites along with a positive δ¹³C excursion of the Hangenberg anoxic event enabled the high‐resolution calibration of the late Famennian–early Tournaisian interval (Upper expansa–crenulata conodont zones). The conodont stratigraphic and biofacies succession reveals a strong correlation with other European areas. The Siphonodella sulcata morphotype (close to Group 1 sensu Kaiser and Corradini and “nov. gen. nov. sp. 1” sensu Tragelehn) enters prior to the Hangenberg Event, which resembles Upper and Uppermost Famennian conodont successions from Franconia, Bavaria and Morocco. The diversification of the early siphonodellids takes place after the Hangenberg Event and after the protognathodid radiation. In terms of foraminiferal biostratigraphy, the D–C boundary interval is characterized by the first appearance datum (FAD) of Tournayellina pseudobeata close below the D–C boundary followed by a sequence of Tournaisian bioevents, where apart from the last appearance datums (LADs) of quasiendothyrs, the FADs of the Neoseptaglomospiranella species and chernyshinellids play an important role in a similar manner as in Eastern Europe. The correlation of these bioevents elsewhere is often hindered by glacioeustatically‐driven unconformities and widespread occurrences of unfavourable facies for plurilocular foraminifers (Malevka beds and Bisphaera beds). Copyright © 2013 John Wiley & Sons, Ltd.     

重庆万州盐井沟地区黄昏爪兽(爪兽科, 奇蹄目)化石新发现

黄昏爪兽（Hesperotherium）是我国早更新世代表物种之一,因发现标本稀少,其形态特征和灭绝时间是存疑的。重庆市万州区盐井沟大垭口地点发现了多件Hesperotherium化石,其中多数骨骼属首次发现,新材料增加了我们对该类动物的骨骼形态学的认识,其后肢骨骼在进化过程中较为保守,可能正是这种进化过程中的保守性导致其不能适应第四纪多变的气候环境,最终灭绝。同时通过对已知含Hesperotherium动物群的分析,认为Hesperotherium可以作为早更新世早-中期的代表物种,对应于邱占祥命名的NCMQ 1或欧洲的维拉方中-晚期。

     

Chemometric analysis of functional groups in fossil remains of the Dicroidium flora (Cacheuta, Mendoza, Argentina): Implications for kerogen formation

Studied samples include eight Gondwanan species of the Dicroidium flora: seed ferns (3), conifer (1), cycad-related (1), unknown affinity gymnosperms (2), and one undetermined axis from two Middle to Upper Triassic localities (Cacheuta, Mendoza, central western Argentina). Based on differing preservation states and sample treatments, four sample forms are established: (1) compressions, (2) cuticles, (3) cuticle-free coalified layers, and (4) associated coal samples. The purpose of the study is firstly to analyze the sample forms using Fourier transform infrared (FTIR) spectrometry, contributing to filling an existing gap of chemical information for Gondwanan pant fossil remains. Secondly, semi-quantitative chemical parameters, calculated by area integration of infrared spectra, are treated using principal component analysis to infer statistical groupings as a function of chemical structures (functional groups). From the initial two-component solution, based on the 8 × 41 data matrix, a subset matrix (4 × 29) could be isolated which also yielded a two-component solution (in each case, cumulative explained variance is at least 89%). Results include the distinction between the coaly forms (1) compressions and (3) cuticle-free coalified layers mainly based on the carbonyl contents and branching and length of the hydrocarbon side chains. The highly aliphatic nature of cuticles, which is indicative of biomacromolecules (cutin), is noted. Similarities in functional groups are recorded with types of kerogen and coal macerals. The result enables us to postulate that the functional groups characterizing the different modes of preservation of our fossil remains are likely related to the propensity to generate oil and gas/condensate from the kerogen. Our data have the potential for future studies with implications for chemotaxonomy, molecular taphonomy, and paleoclimatology.     

Systematically variable geometry and architecture of incised-valley fills controlled by orbital forcing: A conceptual model from the Pennsylvanian Breathitt Group (Kentucky,USA)

Incised-valley fills preserved within ancient coastal to shallow-marine successions represent important archives of environmental and sea-level change. Most current knowledge about the origin of incised valleys stems from Quaternary case studies; however, research on pre-Quaternary examples can shed light on valley formation and evolution across longer timespans. This article describes different types of incised-valley fills from Lower to Middle Pennsylvanian fluvio-deltaic successions of the Breathitt Group (eastern Kentucky), accumulated in the Central Appalachian Foreland under prevalent glacioeustatic forcing driven by Gondwanan glaciations. Based on well-established criteria for their recognition, numerous incised-valley fills were identified from outcrop and subsurface data through more than 300 m of clastic successions consisting of fourth-order stratigraphic sequences stacked into third-order composite sequences. Incised-valley fills were categorized into three archetypes based on lateral extent and aspect ratio (relatively wide versus narrow valley fills), nature of infill (fully continental versus mixed marine and continental facies associations) and relationships to underlying coal zones (truncating versus non-truncating). The systematic occurrence of each incised-valley fill type at specific stratigraphic positions within every third-order sequence suggests control by a periodic allogenic factor. Valley-fill archetypes are interpreted in terms of variable accommodation-supply ratios driven by variable duration of formative base-level cycles. For example, relatively wide incised-valley fills with alluvial infill evolved during long-lived cycles whose prolonged base-level drawdown maintained low accommodation/supply ratios. Deeper valleys with low aspect ratios and mixed marine-continental infills were generated by short-lived base-level drawdown that forced higher accommodation/supply ratios. Available chronological data for the studied successions consent to estimate base-level cycles spanning 10^4–5 years that were likely modulated by interference patterns of orbital parameters (obliquity and eccentricity) via global climate and glacioeustatic fluctuations. This conceptual model, relating incised-valley fill morphometry and internal architecture to orbital forcing patterns, provides a possible approach to predicting and interpreting incised-valley fill variability through successions accumulated during icehouse conditions.     

Palynological evidence for Pennsylvanian (Late Carboniferous) vegetation change in the Sydney Coalfield,eastern Canada

The palynology of clastic samples from seven stratigraphical levels in the late Moscovian Sydney Mines Formation, exposed along the shore at Bras d'Or, Nova Scotia, has been investigated. Most of the samples were from roof shales of major coals; the one sample that was not yielded a much higher proportion of pollen derived from extra‐basinal vegetation. The four stratigraphically lower roof shale samples yielded essentially similar palynological spectra, with 39 ± 4% lycophytes, 9 ± 4% sphenophylls, 23 ± 4% tree‐ferns, 12 ± 4% other ferns and 5 ± 3% cordaites. The palynology of the upper part of the investigated succession suggests a shift in vegetation towards one favouring more marattialean tree‐ferns, cordaites and conifers, and fewer lycophytes. This correlates with changes in drainage patterns as the alluvial plain migrated seawards and thus changed water tables. No evidence was found to suggest significant climate change at this time. Copyright © 2009 John Wiley & Sons, Ltd.     

New remains of Eremotherium laurillardi (Lund, 1842) (Megatheriidae, Xenarthra) from the coastal region of Ecuador

New remains of Eremotherium were recovered from the Pacific coast of Ecuador’s Manabi province. The Machalilla fossiliferous locality records the northernmost presence of Eremotherium along the Pacific coast of South America. Most of the fossil remains belong to the same individual, mainly its posterior half, but other individuals are represented. Among the better-preserved specimens are skull fragments, most of the hind limb bones and a number of trunk and caudal centra. These remains were compared with samples collected during the 20th century along the southern coastal regions of Ecuador and northern Peru. Many characters of the long bones and tarsals testify to a possibly different lineage despite the closeness of other Eremotherium populations. Some metric and morphological aspects suggest a different space-temporal southern Caribbean provenance. Other Eremotherium specimens, coming from other Ecuadorian localities, were studied and compared with classic Eremotherium samples. Interesting morpho-functional aspects are pointed out with regard to the tail and its importance in the bipedal stance.     

Holocene reactivations of catastrophic complex flow-like landslides in the Flysch Carpathians (Czech Republic/Slovakia)

Complex flow-like landslides (CFLLs) are important geomorphic agents of Late Quaternary mountain evolution in the Flysch Belt of the Outer Western Carpathians. The CFLLs are characterised by the upper section of deep-seated, retrogressive landslide of structurally unfavourably oriented rocks and lower sections composed of earthflows originated due to liquefaction of material accumulated from the upper slopes. Radiocarbon dating of organic matter incorporated into landslide debris or related deposits suggests that most of the CFLLs collapsed repeatedly throughout the Holocene with typical recurrence intervals of approximately 1–2 ka. Catastrophic landslides that occurred during extreme hydrometeorological events in recent decades displayed evidence of Holocene activity. Most of the CFLLs dammed and steepened adjacent valleys. Our chronological dataset is biased by erosion of older landforms, but most of the dated reactivations correlate to regional increases in humidity identified by previous paleoenvironmetal studies.     

Zalesskioxylon xiaheyanense sp. nov., a gymnospermous wood of the Stephanian (Late Pennsylvanian) from Ningxia, northwestern China

A new Late Pennsylvanian species of gymnospermous fossil wood, Zalesskioxylon xiaheyanense sp. nov. is described from the Lower Taiyuan Formation (Stephanian B-C) near the village of Xiaheyan, Ningxia Hui Autonomous Region, northwestern China. The specimen consists only of silicified secondary xylem. The tracheids are pycnoxylic with 2–3 seriate bordered pits, arranged in subcircular or hexagonal alternate (araucaroid) pattern. The pores of the pits are small, linear, and regularly tilted. Xylem rays are homogeneous, uniseriate, 1–25 cells high. Cross-fields are filled with numerous mixed simple pits of various sizes. Growth rings, axial parenchymatous elements and resin canals are absent. The geographic distribution of Zalesskioxylon woods is reviewed. Zalesskioxylon xiaheyanense sp. nov. grew at low latitudes, and because of the lack of growth rings, probably lived under relatively uniform climatic conditions. Our new species supplements the poorly known distribution of Carboniferous wood in China.     

Geochemistry of Miocene lacustrine sediments from the Sokolov Coal Basin (Czech Republic)

Sediments of the upper part of the Sokolov Formation of the Sokolov Brown Coal Basin consist mostly of brown lacustrine clays and claystones enriched in organic matter (2–18% TOC). The lower portion of the stratigraphic profile is formed mostly by kaolinite–illite clays and claystones, while the montmorillonite content increases in the upper portion. The change in the lithology of sediments is caused by the gradual erosion of the weathering crust in the source areas of the clastic material. Inversion of the weathering profile during erosion is manifested geochemically in a decrease in the Al₂O₃/Na₂O ratio and an increase in the SiO₂/Al₂O₃, Na₂O/K₂O and K₂O/TiO₂ ratios from the base to the top of the studied part of the Sokolov Formation. The amounts of trace elements (La, Ce, Nb, Zr, Cr, V, Sn) also decrease in the same direction. On the other hand, the amounts of Rb and Sr increase. The organic matter of the upper part of the Sokolov Formation consists primarily of Types I and II kerogen. Only near the base of the studied part of the formation, i.e., in the coal stringer, kerogen of Type III prevails. The extremely low degree of thermal maturity permits determination of the source of the organic matter and characterization of its accumulation environment. The organic material in the sediments is predominantly of algae origin. Relatively high amount of pentacyclic triterpanes of the hopane series indicates either the occurrence of cyanobacteria as primary producers or bacterial reworking during sedimentation and diagenesis. Organic matter accumulated under the conditions of a fresh-water lake or lake with slightly elevated salinity, in a dysoxic aqueous environment. The alternation of organic carbon-rich layers with layers low in organic matter is explained in terms of changes in the degree of dysoxia of the aqueous environment and a variation in the intensity of oxidation and mineralization of the organic material.     

Grain size,geochemistry and organic pollutants in modern fluvial deposits in eastern Moravia (Czech Republic)

Modern fluvial deposits from both small and large rivers were studied at 14 monitoring sites over 2 years (4 successive sampling seasons) in the area of eastern Moravia (Czech Republic). Grain size, geochemistry, content of persistent organic pollutants (PAHs, PCBs, HCHs, DDTs, HCBs and PeCB) and TOC were examined with the aim to understand their mutual relations and seasonal variations in sediment character and pollutant content. Sand and silt fraction predominate and the clay content is relatively low. Differences in provenance for various river systems were recognised. Both regional and seasonal variations in terms of content of persistent organic pollutants were documented. The content of TOC and mud was shown to play an important role in the accumulation of chlorinated persistent organic pollutants PCBs, HCHs, DDTs and HCB.     

Mineralogical characteristics of upper Jurassic Mikulov Marls,the Czech Republic,in relation to their thermal maturity

The Upper Jurassic Marls of Mikulov present a formation that is considered to be the most promising strata to produce hydrocarbons in the Vienna basin. The marls are composed of dark pelagic marlstones that frequently contain layers of limestone with thickness reaching several hundreds of meters. Twenty-seven core samples from selected wells located in the south-eastern portion of the Czech Republic representing depths ranging from 2300 to 4500 m were analyzed by x-ray diffraction to assess bulk mineralogy and the progress of smectite illitization.Bulk mineralogy of the Mikulov Marls comprises carbonates (mean value = 54.4 mass%), clay minerals (26.6 mass%), quartz (15.0 mass%), and feldspar (1.6 mean%). In the decreasing order, the clay mineral fraction is composed of illite/mica, kaolinite, illite-smectite, and chlorite. The amount of smectite in illite-smectite decreases with depth from 70% to 28%. There is a change from random to ordered interstratification at the depth of 3300 m. The transition from short-range ordering (R1) to long-range ordering (R3) occurs at depths greater than 4,500 m.There was a good correspondence between thermal maturity parameters: the percentage of smectite in illite-smectite structures and vitrinite reflectance as a parameter of organic matter. The increase of the metamorphic grade was compared in respect to the geothermal gradient with adjacent basins.     

Spatial distribution of lead and lead isotopes in soil B-horizon, forest-floor humus, grass (Avenella flexuosa) and spruce (Picea abies) needles across the Czech Republic

Lead concentrations were determined in samples of soil B-horizon (N = 258), forest-floor humus (O-horizon, N = 259), grass (Avenella flexuosa, N = 251) and spruce (Picea abies, N = 253) needles (2nd year) collected at the same locations evenly spread over the territory of the Czech Republic at an average density of 1 site/300 km². Median Pb concentrations differ widely in the four materials: soil B-horizon: 27 mg/kg (3.3-220 mg/kg), humus: 78 mg/kg (19-1863 mg/kg), grass: 0.37 mg/kg (0.08-8 mg/kg) and spruce needles: 0.23 mg/kg (0.07-3 mg/kg). In the Pb distribution maps for humus, grass and spruce a number of well-known Pb-contamination sources are indicated by unusually high concentrations (e.g., the Pb smelter at Pribram, the metallurgical industry in the NE of the Czech Republic and along the Polish border, as well as the metallurgical industry in Upper Silesia and Europe’s largest coal-fired power plant at Bogatynia, Poland). The ratio ²⁰⁶Pb/²⁰⁷Pb was determined in all four materials. The median value of the ²⁰⁶Pb/²⁰⁷Pb isotope ratio in the soil B-horizon is 1.184 (variation: 1.145-1.337). In both humus and grass the median value for the ²⁰⁶Pb/²⁰⁷Pb isotope ratio is 1.162 (variation: 1.130-1.182), in spruce needles the median ratio is 1.159 (variation: 1.116-1.186). In humus, grass and spruce needles the known contamination sources are all marked by higher ²⁰⁶Pb/²⁰⁷Pb isotope ratios in the maps. Furthermore, the soil B-horizon, humus, grass and spruce needles show distinctly different spatial distribution patterns of the ²⁰⁶Pb/²⁰⁷Pb isotope ratios. The B-horizon does not provide a viable background value for metal concentrations in the O-horizon or plant materials. None of the maps provides evidence for the importance of traffic-related emissions for the observed isotope ratios at the scale of the Czech Republic.     

Anatomically preserved plants in siderite concretions in the shale split of the Foord Seam: mineralogy, geochemistry, genesis (Upper Carboniferous, Canada)

A shale split in the well-studied Foord Seam (Upper Carboniferous), Stellarton Basin, Nova Scotia, provides a rare opportunity to study little known siderite concretions with anatomically preserved plants from a limnic basin. Siderite concretions occur throughout the split, commonly as sheet-like, inter-connected lepidodendrid logs, or less frequently as spherical masses; they are typically vuggy. A sample of 14 stratigraphically oriented concretions in the split shows that primary siderite varies from 45% to 80% (wt.%) due to selective replacement by 5% to 40% ferroan dolomite or ankerite in plant tissues. These two minerals show large Mg/Fe and Mg/Ca variability and are Fezoned. Clay content ranges from trace to 20%, and quartz from 5% to 10%. Partial cell-wall destruction by erosion and changeable oxic/anoxic conditions, prior to siderite permineralization, resulted in preservation mainly of the more resistant plant tissues. On average, carbon from siderite is isotopically heavier (+4.8±1.9 0/00) than that from ‘dolomite' (−7.2±1.1 0/00). The distribution of and the positive correlation between δ¹³C and δ¹⁸O probably reflects the two fractionation processes associated with methanogenesis and ‘dolomitization', respectively, in the genetic history of the siderite concretions in the split. Siderite concretions formed diagenetically early from bicarbonate under reducing conditions in a slightly alkaline freshwater environment that precluded calcite deposition.     

Depositional record of an avulsive fluvial system controlled by peat compaction (Neogene, Most Basin, Czech Republic)

This paper illustrates the response of a fluvial depositional system to the interplay between peat compaction and clastic sediment supply, at a range of spatial and temporal scales, as documented by extensive exposures in an open-cast mine in the Most Basin, part of the Oligo-Miocene Ohře Rift (Eger Graben) basin system in the Czech Republic. The Most Basin is characterized by the occurrence of a number of phenomena resulting from syn- and post-depositional interactions between clastic sedimentary systems and the underlying accumulation of organic material that was the precursor of the main lignite seam of up to 45 m thickness. The studied strata are interpreted as deposits of an avulsive, mixed-load fluvial system. The large-scale depositional architecture documents an existence of at least five stratal packages up to 1500 m wide and up to several tens of metres thick, representing a record of long-term evolution of a clastic floodplain bordered by accumulating peat. Within each of the packages, several small-scale channel-belts were documented. Individual packages are separated by carbonaceous mudstones indicating a period of reduced clastic input and interpreted as due to avulsion of the fluvial channels out of the floodplain limit. Two main, mutually linked, processes controlled the evolution of the studied fluvial system: (i) syndepositional compaction of the underlying peat and (ii) avulsions of the channels away from the original floodplain, resulting in formation of a new floodplain. The processes which caused the channels of the Hrabák fluvial system to reach the avulsion threshold were: (i) decrease of rate of creation of accommodation leading to increased sinuosity and thus to a decreased channel slope, and (ii) cross-floodplain tilting of the channel belt caused by differential compaction of underlying organic-rich substratum.