Siderite Nodules Research Articles

Types and Genesis of Siderite in the Coal-Bearing Beds of the Late Permian Xuanwei Formation in Eastern Yunnan, China

The Late Permian strata of the Xuanwei Formation in the eastern Yunnan region exhibit extensive diverse morphological features within siderite deposits. These variations in siderite deposits suggest potential differences in their formation processes. In this study, fieldwork and comprehensive indoor studies revealed four distinct forms of siderite deposits: stratiform-laminated, lens-like nodule, sandstone cementation, and fracture filling. The stratiform-laminated siderite, varying in color from bluish-grey to dark grey, is composed of uniformly sized microcrystalline to fine-grained siderite along with detrital matter, displaying precise layering and banding structures that suggest direct deposition from cyclic iron-rich seawater under reducing conditions. Lens-like-nodule siderite, which appears grey-yellow, is composed of mud microcrystalline siderite, medium to coarse-grained pseudo-ooids, and glauconite. It shows conformable distribution characteristics resulting from the diagenetic differentiation of iron-rich sediments under reducing conditions during the diagenetic and early diagenetic periods. Siderite as sandstone cementation exhibits a yellow-brown color and consists of dispersed colloidal siderite and cemented siderite clumps that fill intergranular pores of detrital particles. It precipitated under reducing conditions within those intergranular pores. Siderite filling fractures typically appear as vein-like or network-like structures intersecting bedding at large angles. They exhibit grain structures with significant variations in size. These siderite deposits exhibit exceptional purity and result from siderite dissolution during sedimentary periods, followed by reprecipitation within regional extensional fractures during the diagenetic phase. The primary occurrence of siderite deposits in the study area is within coal-bearing strata, as revealed by the integration of sedimentary profiles and sedimentary facies analysis. The coal-bearing strata, influenced by the Emeishan large igneous province, underwent iron enrichment during and after volcanic eruptions while developing a reducing environment, which was facilitated by abundant vegetation. Consequently, geological processes led to siderite layers, lens-like siderite nodules, and siderite cementation. The Yanshan orogeny induced extensive high-angle fracture development in epigenetic coal-bearing strata, facilitating fluid circulation and the redistribution of soluble siderite. This geological activity resulted in the formation of vein-like structures composed of siderite.

Genetic mechanism of Carboniferous-Permian coal measures siderite nodules in an epicontinental sea basin—An example from the Zibo area in North China

Siderite is a mineral resource and a climate sensitive mineral. Siderite nodule layers are widely developed in coal measures within the marine-ontinental transitional facies of North China epicontinental sea basin, yet their formation environment and genetic mechanism are poorly understood. In this paper, taking the siderite nodule layers in the coal measures of the Late Paleozoic Taiyuan Formation in Zibo area of North China as an example, the formation environment and genetic mechanism of siderite nodules in the transitional facies of the epicontinental sea basin are studied through detailed petrological, sedimentological and geochemical analysis. It is found that the siderite nodules in the research area were formed in a tidal flat-lagoon environment. The siderite nodules are formed in the synsedimentary stage, the original information of chemical composition and characteristics of the nodules being largely retained. Most of the carbon in the siderite nodules originates from inorganic carbon from marine carbonate rocks, with the remainder originating from inorganic carbon formed by dissimilatory iron reducing bacteria (DIR) degrading organic matter. Meanwhile, most of the iron in the siderite nodules originates from hydrothermal fluids, and the remainder from terrigenous sediments. The content of iron input from hydrothermal fluids and terrestrial sediment represents a trade-off relationship. The two genetic mechanisms of the siderite nodules are as follows: 1) Chemical genetic mechanism: The siderite nodules are mainly formed by the combination of low-valence iron (Fe2+) and inorganic carbon in seawater through reduction with iron input from hydrothermal fluids as the main source. 2) Biochemical genetic mechanism: Some is formed by the combination of low-valence iron (Fe2+) and inorganic carbon with high-valence iron (Fe3+) as an oxidant to degrade the organic matter and convert organic carbon into inorganic carbon through DIR. On this basis, a genetic model of the Late Paleozoic coal measures siderite nodules in the epicontinental sea basin is established.

Integrated detection and investigation of bad borehole section in the Wolfcamp Formation in the Midland Basin using machine learning, petrophysics, and core characterization

The quality of formation evaluation and reservoir estimates depends a lot on the quality of open hole logs, which is intricately tied to the borehole geometry and stand-offs. Bad borehole sections cause interesting patterns on wireline logs that can result in multiple interpretations. We have conducted an automated identification of bad borehole sections (>50 ft [15 m] thick) in multiple wells in the Wolfcamp Formation in the Midland Basin of the United States and investigated the causalities behind the unstable borehole section. The wells impacted by bad hole conditions appear to be within a particular region of the northern Midland Basin, and the bad hole condition impacts a specific zone in the Wolfcamp D. We consider well logs as multivariate time series (or depth series), where they share interdependencies to a large extent. We use this concept and unsupervised multivariate time series clustering to automatically identify bad borehole sections. Our proposed workflow simultaneously clusters the wireline logs, resulting in a large labeled regional-scale data set that can be further used for log quality assurance, processing, and petrophysical modeling. More importantly, we investigate the reasons behind the borehole washout, integrating sedimentology and geochemical data. Thick borehole washout sections are related to the presence of a significant amount of clay (>73 wt%, a mixture of smectite and illite) in the Wolfcamp D. The results also indicate that the manual editing of wireline logs and even supervised machine learning-based log reconstruction (commonly known as a missing log prediction problem) can lead to erroneous and inconsistent interpretation of subsurface characteristics. Such exercise can be meaningless if derived models are not validated with the ground truth (preserved subsurface rocks). Geologic feature: Clay-rich unstable borehole section Log appearance: Large-to-small caliper response associated with erratic density and neutron porosity logs Features with similar appearance: Gypsum, siderite nodules, and tool failure Formation: Wolfcamp Formation Age: Wolfcampian Location: Northern Midland Basin, Texas, USA Well data: Obtained from the IHS Analysis tools: Unsupervised machine learning, core description, geochemistry, and petrophysical inversion modeling

Gold in Irish Coal: Palaeo-Concentration from Metalliferous Groundwaters

Gold grains, up to 40 μm in size and containing variable percentages of admixed platinum, have been identified in coals from the Leinster Coalfield, Castlecomer, SE Ireland, for the first time. Gold mineralisation occurs in sideritic nodules in coals and in association with pyrite and anomalous selenium content. Mineralisation here may have reflected very high heat flow in foreland basins north of the emerging Variscan orogenic front, responsible for gold occurrence in the South Wales Coalfield. At Castlecomer, gold (–platinum) is attributed to precipitation with replacive pyrite and selenium from groundwaters at redox interfaces, such as siderite nodules. Pyrite in the cores of the nodules indicates fluid ingress. The underlying Caledonian basement bedrock is mineralised by gold, and thus likely provided a source for gold. The combination of the gold occurrences in coal in Castlecomer and in South Wales, proximal to the Variscan orogenic front, suggests that these coals along the front could comprise an exploration target for low-temperature concentrations of precious metals.

Reservoir Characterization of the Pennsylvanian (Desmoinesian) Lower Bartlesville Sandstone in Big Sandy and Clinesmith Fields, Southeast Kansas

Big Sandy and Clinesmith oil fields are located about five miles apart along the boundary between Woodson and Wilson counties in southeast Kansas. They are located on the Pennsylvanian Cherokee Platform and were discovered almost 60 years apart in 1923 and 1982 respectively. Both fields produce from Desmoinesian lower Bartlesville sandstone reservoirs at shallow depths (1,100 to 1,200 ft) from reservoirs that have been interpreted as “shoestring sandstones.” However, if Big Sandy is restricted just to the area of Section 23 and the southeast quarter of Section 22, T26S, R14E where it offers the best wireline log control, the two fields have different orientations. Big Sandy has a southwest/northeast trend almost perpendicular to Clinesmith Field, which trends from north-northwest to southward. Big Sandy Field has a more elliptical shape with a length-to-width ratio of 3:1, vs. 10:1 for the very linear Clinesmith Field. Another major difference between the two fields is that the gamma-ray logs in and along the Clinesmith reservoir trend generally have a fairly well-defined fining-upward trend characteristic of a fluvial channel system. Big Sandy logs, in contrast, show much more variability from well to well. Petrographically the two fields have characteristics that are both consistent and strikingly different. Both reservoirs have a consistent very-fine to fine sand grain size with fair to well-sorted grains. Both also have texturally immature grains that are angular to subrounded with nearly identical compositions of abundant quartz, and associated plagioclase, biotite, muscovite, plant debris, and metamorphic rock fragments. Thus, the Bartlesville Sandstone in both fields had the same nearby sediment source terrain comprised mainly of granites and metamorphic rocks. Each field also produces mainly from primary interparticle porosity in sandstones with loosely packed grains where total porosity locally exceeds 20%. A difference is that, although both fields contain common shale clasts, those in Big Sandy Field tend to be much larger and occur with common siderite (iron carbonate) nodules. Siderite is rare in Clinesmith Field although a few small nodules occur in the associated floodplain shales, along with carbonaceous partings. Also present in Big Sandy’s reservoir are other iron-bearing minerals such as glauconite, pyrite, and chlorite, although all of these are far less common than the siderite. Such an abundance of iron-rich minerals can occur in marginal marine environments such as estuaries where a reducing diagenetic environment forms just below the sediment/water interface. In contrast, well-oxygenated fluvial systems generally contain any iron in highly oxidized forms such as hematite and limonite. From these observations, it appears that Big Sandy’s reservoir interval was deposited in an estuarine (coastal marine) setting with diverse localized depositional environments whereas the Clinesmith reservoir represents a nearly straight, south-flowing fluvial channel and adjacent floodplain, with no marine influence on deposition.

Bacteriomorph Structures in Nodules, a Characteristic of Euxinic Conditions of Nodule Formation

Electron microscopic, spectroscopic, and geochemical study of Middle Ordovician shamosite, Wenlockian calcite, and Lower Carboniferous siderite nodules revealed the presence of organic matter and traces of microbial organisms involved in the formation of iron oxides and hydroxides and mineralized microbial films. The structure and composition of the films show high similarity to mineralized glycocalyx, which is a product of bacterial metabolism. Diversity of the framboidal micropyrite and bacteriomorph structures in size and shape indicates the formation of nodules under anoxic bottom conditions and abundance of sulfate-reducing, iron-reducing, and iron-oxidizing bacteria. The presence of authigenic minerals in the nodules, which is atypical for sedimentary rocks, suggests the influence of bottom gas–fluid seeps and, therefore, local hydrosulfuric contamination, fluctuations in salinity, and intensive development of bacterial communities.

Elemental affinity for siderite found in a Japanese paddy subsoil

ABSTRACTSiderite (FeCO3), a type of carbonate mineral, is very occasionally recognized as a nodule in anoxic soils and sediments. During siderite formation, elements are expected to be accumulated or excluded between siderite and bulk soil. Therefore, we verified the affinity of 40 elements for siderite found in the gley horizon of a smectite-rich paddy field in northeastern Japan from the elemental concentration of the soil and the siderite dissolved in 2.88 mol L−1 hydrochloric acid (10% HCl). The concentration ratio of the target element of the soil to the siderite was expressed by the product of the dimensionless R0 value and ratio of titanium (Ti) concentration of the soil to the siderite (Csiderite /Csoil) = R0 (Tisiderite /Tisoil). The affinity of each element for the siderite was analyzed by comparing the R0 values. In comparison with Ti used as the reference element, P, Cr, Co and Mo were accumulated (R0 > 1.0), and alkali metals, such as Li, Na and K, and chalcophile elements, such as Cu, Zn, Cd and Pb, tended to be equal or excluded from the siderite (R0 ≦1.0). Of the group 2 elements, Ca, Sr and Ba were accumulated, while Mg was excluded. The affinity of Mn for siderite exceeded that of Fe as the main component of the siderite, which reflects the fact that siderite was formed in a fresh water condition. The siderite size did not influence the elemental affinity. Observation of micromorphology using a scanning electron microscope showed that the siderite nodules were aggregations of siderite particles and clays, suggesting that the siderite grew by taking in clay around it. The rare earth element (REE) distribution pattern showed a tendency not to increase linearly but to increase with forming a concave curve at the intervals of the four elements with the increase of atomic number (i.e. tetrad effects). Although these findings are from the lower horizons of anoxic soils, the elemental affinity for siderite of this study is useful in order to elucidate the complex elemental dynamics in the anoxic environment.

Genesis of siderite nodules from the lower carboniferous terrigenous sequence in the Subpolar Urals

The paper presents the lithological, mineralogical, and geochemical characteristics of the composition, structure, and organic matter of siderite nodules and host mudstones in the Lower Carboniferous (Tournaisian–Visean) siderite-bearing sequence exposed along the Kozhym River on the western slope of the Subpolar Urals. The obtained results revealed that organic matter in the mudstones is dominated by C16 and C18 n-alkanes, suggesting a significant microbial activity in the sedimentation environment. The formation of nodules was promoted by the activity of diverse bacterial communities, the abundance of which was related to processes of methanogenesis in bottom sediments owing to gaseous fluid seepages that promote the saturation of sediments with methane and the flourishment of bacterial colonies. Such processes in a marine basin led to the local freshening or some salinization of water and the development of euxinic setting and specific bacteria. Consequently, siderite nodules therein are marked by bacteriomorphic textures and specific authigenic mineralization (framboidal pyrite, sphalerite, galena, sulfoselenides, and tellurides). Bacteria utilized the substrate of the redeposited weathered crust, resulting in a large-scale formation of the nodular siderite.

Characteristics of Early Earth’s Critical Zone Based on Middle—Late Devonian Paleosol Properties (Voronezh High, Russia)

AbstractLand colonization with vascular plants during the late Silurian—early Devonian and then arborescence during the Pragian—Givetian caused the development of new soil types. These true-rooted soils increased the rate of pedogenesis on a global scale. Since that time, soil has become a key component of the biosphere and has given rise to profound development of the Earth’s Critical Zone (CZ). Case studies of Devonian CZs have helped to record the transformation from Precambrian—Lower Paleozoic ‘proto-CZs,’ which had insufficient proto-soil cover, to modern soils with true-rooted pedosphere. Devonian (Givetian—Frasnian) paleosols from the Voronezh region of Russia are combined into pedocomplexes which occupied the top, slope, and bottom positions of a pronounced paleo-relief. Paleosols were developed from terrigenous argillites and volcanigenic-sedimentary deposits. Each pedocomplex consisted of four or more paleosols with different degrees of development and profile preservation. Paleosols exhibited several common characteristics including production and translocation of clay, ferruginization and the presence of siderite nodules, enhanced MnO/Al2O3 and (Fe2O{3}+MnO)/Al2O3 values, and in situ roots and root-system traces. The latter are siderite/goethite substituted. Stable isotope analysis of siderite shows δ13C values of between -6.1 and -13.7% indicating that CO2 had originated from C3 plants. The main mineral component of clay fractions in automorphic paleosols (top and slope of the paleorelief) is kaolinite. The important feature of these paleosols is the red-stained hematite-rich layer in their bases. These horizons developed at different depths and with different thicknesses, and marked the paleo-groundwater tables of each sub-CZ. Evidence of the imprints of vegetation is seen in the abundant in situ roots, plant fragments, and spores of rhyniophytes, lycopsids, progymnosperms, cladoxylalean ferns, and phytoleims of algae-like vascular plants. The near-equatorial location and the overall characteristics of paleosols studied suggest that the aforementioned horizons were formed in a tropically warm and humid climate. The paleo-ecological environments which accompanied pedogenesis were probably controlled by tectonic activity and volcanism.

Exceptional preservation of Upper Carboniferous (lower Westphalian) fossils from Edlington, Doncaster, South Yorkshire, UK

A new fossil‐bearing, Upper Carboniferous (lower Westphalian) locality in Doncaster, South Yorkshire, UK, is reported and an account of the fossils is presented. The diverse flora and fauna consists of plants, bivalves, arthropods (primarily xiphosurans), tentaculitids (microconchids), fish scales, shark egg capsules and coprolites. Fossils are preserved in siderite nodules and shales, and display excellent preservation and detail. Previous collecting of Carboniferous fossils in the Doncaster area has been minimal. The discovery of this locality addresses this deficit and is of further importance as such localities in the UK are diminishing in number with the cessation of coal‐mining and the reclamation of mine dumps, further demonstrating the importance and recognition of the Edlington site. Copyright © 2014 John Wiley & Sons, Ltd.

The Montceau-les-Mines Lagerstätte (Late Carboniferous, France)

The Montceau-les-Mines Lagerstätte (Late Stephanian, Late Carboniferous) is located northeast of the French Massif Central. Situated at equatorial latitudes during the Pennsylvanian, this Lagerstätte, probably a freshwater environment, preserves a rich and diverse flora (lycopsids, sphenopsids, ferns, pteridosperms, and cordaites) and fauna (bivalves, annelids, crustaceans, myriapods, insects, chelicerates, myxinoids, actinopterygians, sarcopterygians and tetrapods). These exceptionally preserved fossils can be found either flattened in shales or three-dimensionally preserved in sideritic nodules. The fossils from the nodules are exceptional for at least two reasons: the absence of major disarticulation of their body structure and the preservation of soft parts and extremely fragile cuticular structures. Such preservation was made possible by the combination of several factors: rapid burial in fine anoxic mud, early siderite precipitation (inducing the nodule formation) and phosphatization of cuticles and soft-bodied features.

Synthèse sur la flore des nodules du Lagerstätte de Montceau-les-Mines (Carbonifère supérieur, France)

The flora from the Montceau-les-Mines Lagerstätte (Late Pennsylvanian, Stephanian, France) is preserved in small sideritic nodules and was studied in three locations in the (1) Saint-Louis, (2) Saint-François, and (3) Sainte-Hélène opencast mines. Qualitative and quantitative analyses of plant diversity and floristic composition in about 7000 nodules indicate substantial variations in the floral composition of these opencast mines. More than 50 taxa are recognized and belong to groups typical of the Late Carboniferous flora (lycopsids, sphenopsids, tree ferns, and pteridosperms). Arborescent sphenopsids and tree ferns were the major components at Saint-Louis, whereas the flora from Saint-François consisted mainly of pteridosperms; the one from Sainte-Hélène has a more balanced composition. Taphonomic and sedimentological data show that the flora contained in the nodules was hypoautochthonous to parautochthonous. The Montceau Basin displayed a mosaic of paleoenvironments (e.g., deltaic lacustrine, paludal to fluvial) which favored colonization by plants and animals.

Upper Carboniferous seed fern (Pteridospermophyta) pollen organs from Silesia (Poland) and related evolution considerations

Extinct seed ferns (Pteridospermophyta) fill a key position in the evolutionary tree of seed plants. Their reproductive structures enable to recognition of the interrelationship within seed ferns and other seed plants descending from them. Seed fern reproductive structures from Poland are very rarely found and very poorly known, especially the pollen organs to which this paper is dedicated. A new genus and species <em>Silesiatheca formosa</em><em> </em>Pacyna & Zdebska, gen. et sp. nov. of lyginopteridalean aggregated synangia was recognized based on specimens preserved within sideritic nodules from Sosnowiec. The genus <em>Codonotheca </em>is recognized from European Carboniferous for the first time. The least evolutionarily advanced species of <em>Codonotheca</em><em> </em>− <em>Codonotheca</em><em> silesiaca</em><em> </em>Pacyna & Zdebska sp. nov., is described based on specimens with weakly expressed radial symmetry and slight fusion of the sporangia. this species matches the hitherto hypothetical simplest species of <em>Codonotheca </em>very well, constituting the initial form for all the more compound pollen organs of Medullosales. For the first time in the European Carboniferous the North American species <em>Aulacotheca campbellii </em>(White, 1900) Halle, 1933 is recognized. A new emended diagnosis for the typical species <em>Boulayatheca fertilis </em>(Kidston, 1914) Taylor & Kurmann, 1985 is proposed, based on specimens from Poland. Two new species of genus <em>Boulayatheca </em>Taylor & Kurmann, 1985 are recognized. <em>Boulayatheca ciliata </em>Pacyna & Zdebska, sp. nov. with a synangium surface covered with hairs (a feature hitherto unknown in the <em>Boulayatheca </em>genus) and <em>Boulayatheca saganii </em>Pacyna & Zdebska, sp. nov<em>. </em>with a markedly elongated synangium. Occurrence of <em>Whittleseya </em>Newberry, 1853a emend. Halle, 1933 typical species <em>− Whittleseya elegans </em>Newberry, 1853a was confirmed in Lower Silesia based on new specimens. Some specimens referred to earlier in the literature as <em>W. elegans </em>were ascribed here to the new species <em>W. silesiaca</em><em> </em>Pacyna & Zdebska, sp. nov<em>.</em>, which differs from typical species in synangium shape and sporangia clustering into groups. The new species <em>Whittleseya campanulata </em>Pacyna & Zdebska, sp. nov<em>. </em>has a large synangium and sporangia clustering into groups. Heterogeneity within the genus <em>Whittleseya </em>is recognized, where some species, including those new described here, probably formed compound synangia. The aggregated synangia of Medullosales are recognized in thecompression state of preservation for the first time they are the base for establishing a new genus and species <em>Kotasotheca annaeadamii </em>Pacyna & Zdebska, gen. et sp. nov. The genus <em>Dolerotheca</em><em> </em>Halle, 1933 was recognized in the Polish Carboniferous for the first time and a new species <em>Dolerotheca migierii</em><em> </em>Pacyna & Zdebska, sp. nov. was described. T.N. Taylor’s model of evolution of medullosalean pollen organs was confirmed, and the new taxa described were included within it.

Combined methodologies for three-dimensional reconstruction of fossil plants preserved in siderite nodules: Stephanospermum braidwoodensis nov. sp. (Medullosales) from the Mazon Creek lagerstätte

A new species of Medullosan ovule from the Mazon Creek Carboniferous lagerstätte is documented using a novel combination of non-invasive X-Ray Micro-Tomography (XMT) and orientated precision sectioning based on the XMT results. 3-D reconstruction of the ovule has correlated geometries of different layers with tissue characteristics gathered from wafered sections, with the methodological combination presenting a virtual reconstruction of the specimen and also enabling positioning of serial sections of the holotype in pre-determined positions. Stephanospermum braidwoodensis sp. nov. has four longitudinally orientated sarcotestal wings, two to each side of the major plane that demonstrate 180° rotational (bilateral) symmetry, while the sclerotesta has three prominent longitudinal commissural ribs and the pollen chamber has three small ribs and triangular nucellar beak, both demonstrating radial (threefold) symmetry. This demonstration of both radial and bilateral symmetries in different tissues emphasises the complexities of inferring systematic affinities of fossil seeds from symmetry alone. We consider S. braidwoodensis to be closely related to the co-occurring S. konopeonus Drinnan et al., and postulate that it was born on a fertile truss similar to that of the latter species. Finally implications of our findings for the utility of these methods in identifying additional species from the Mazon Creek biota are discussed, and the advantages and disadvantages of different methods of nodule preparation are considered. We conclude that additional species are likely to be recognised from the Mazon Creek flora by application of the same methodologies used in this investigation.

High-resolution three-dimensional imaging of coal using microfocus X-ray computed tomography, with special reference to modes of mineral occurrence

Samples of coal from the Sydney and Bowen Basins of eastern Australia have been imaged at high resolution using a large-field, 3D microfocus X-ray computed tomography (μCT) system, with special but not exclusive attention to evaluating the modes of occurrence of the mineral matter within the coal. The samples imaged were 110mm, 25mm, 19mm, 10mm, and 4mm in size, yielding voxel dimensions of 54, 30, 12, 6, and 3μm respectively. Data collection was carried out using a helical stage, providing images with >20002voxels in the horizontal (X–Y) plane and up to 3500voxels high. Three-dimensional image blocks derived from the scans were examined as cross-sections along orthogonal planes and as perspective images, manipulated to be viewed from any angle. Imaging after saturating the coal with X-ray attenuating brine was also carried out to highlight the distribution of connected micro-pores and cleats, and improve the detail of features seen within the samples.Features evaluated within the coals included the size and three-dimensional distribution of siderite nodules, and different types of mineral infillings in petrifactions of maceral components. Individual macerals could also be identified within the coal, based partly on X-ray density and partly on the associated porosity and structure. In some cases high-resolution images enabled the nature of individual plant particles to be identified within the coal samples. Mineral-filled cleats and open fractures were also evaluated, including the origin of radiating fracture patterns around siderite nodules in vitrinite. In some cases several generations of cleat and/or fractures could be distinguished, and the sequence of their formation and infilling was interpreted.Complementary analyses of the mineral matter in the samples were carried out using X-ray diffraction, as well as examination of polished sections by optical microscopy examination. Images obtained from the μCT scans were also registered against SEM–EDX and QemSCAN images of polished sections prepared from the same samples after scanning, providing a more definitive basis for identifying the different components and for integrating μCT data with results from other petrographic and electron microscope studies.

Outcrop versus core and geophysical log interpretation of mid-Cretaceous paleosols from the Dakota Formation of Kansas

Paleosols of the mid-Cretaceous (late Albian to early Cenomanian) Dakota Formation in Kansas and Nebraska are well exposed in road, river and clay pit exposures, but show systematic overprinting by modern weathering. Examination of deep drill cores reveals that modern weathering effects include (1) oxidation of pyrite to jarosite, (2) reaction of jarosite and calcite to clear selenite, and (3) oxidation of sphaerosiderite and siderite nodules to hematite. Surface oxidation in this region extends no deeper than 2m from the surface. Hematite nodules and coatings of leaves are found in core only at one stratigraphic horizon, which was not as appears in outcrop, a laterite. Transformed matrix density and photoelectric absorption logs of cores reveal that kaolinite clays are most abundant within deeply weathered paleosols (Sayela pedotype) at this stratigraphic level, near the Albian–Cenomanian boundary, when angiosperm forests were especially diverse and lived in a subtropical humid climate. Other paleosols of the early Cenomanian were less deeply weathered, and fossil plants of this age included temperate humid angiosperm mangal and swamp woodland, but conifer-dominated floodplain forests. This short-lived mid-Cretaceous warm–wet spike has also been recognized in other paleosols of Minnesota, Utah, Nevada, and New Mexico, and coincides with marine black shale of the Breitstroffer event, midcontinental marine transgression, a sequence-stratigraphic boundary, and a marked increase in early angiosperm diversity.

Morphology and systematics of anthracomartidae (Arachnida: Trigonotarbida)

Abstract: X‐ray microtomography (XMT) was applied to three species of the extinct arachnid order Trigonotarbida, hosted in siderite nodules from the late Carboniferous British Middle Coal Measures. All three, Cryptomartus hindi (Pocock, 1911), Cleptomartus plautus (Petrunkevitch, 1949) and Maiocercus celticus (Pocock, 1902), belong to the family Anthracomartidae. As well as providing interactive three‐dimensional visualisations of their likely appearance in life, XMT study has resolved new morphological detail, yielding key data about the likely stance and habitus of these early arachnids. Similarities in the form of the carapace, eyes and coxosternal region between anthracomartids and the Devonian genus PalaeocharinusHirst, 1923 are highlighted. Analogies in limb disposition are drawn between anthracomartids and modern crab spiders (Araneae: Thomisidae), which exhibit sit‐and‐wait style predatory behaviour. Anthracomartids are relatively common fossils at many Coal Measures localities. Although they appear to exhibit limited morphological variation, numerous genera and species have been proposed in the literature, often distinguished from each other on rather trivial characters. From our reconstruction of well‐preserved examples, we have resolved a number of common features likely to be present in a typical anthracomartid. Comparisons to this model suggest that the characters on which many anthracomartid genera are distinguished may be artefacts of preservation. We hence treat PromygaleFrič, 1901, BrachylycosaFrič, 1904, PerneriaFrič, 1904, CoryphomartusPetrunkevitch, 1945, CryptomartusPetrunkevitch, 1945, PleomartusPetrunkevitch, 1945, CleptomartusPetrunkevitch, 1949 and OomartusPetrunkevitch, 1953 as junior synonyms of the type genus of the family, AnthracomartusKarsch, 1882. Only the genera BrachypygeWoodward, 1878 and MaiocercusPocock, 1911 are additionally retained. Within Anthracomartus, Cleptomartus planusPetrunkevitch, 1949, Cryptomartus meyeriGuthörl, 1964, Cleptomartus hangardiGuthörl, 1965 and Cryptomartus rebskeiBrauckmann, 1984 are treated as junior synonyms of A. hindiPocock, 1911 (all syn. nov.). Cleptomartus plautusPetrunkevitch, 1949 and Anthracomartus denuitiPruvost, 1922 are treated as junior synonyms of A. priestiPocock, 1911 (both syn. nov.).

Generation of siderite nodules an indicator of the oxygen-poor marine environments in the Middle-Upper Yezo Groups, Hokkaido, Japan

Generation of siderite nodules an indicator of the oxygen-poor marine environments in the Middle-Upper Yezo Groups, Hokkaido, Japan

First non-calcified dasycladalean alga from the Carboniferous

A non-calcified dasycladalean alga is described from the Mississippian of Scotland. This occurrence constitutes the first Carboniferous record of non-calcified dasyclads. The fossils are preserved as carbonaceous remains within siderite nodules. Preservation of their delicate structure suggests that the algae were preserved in situ or experienced minimal transport from life habitat. Associated fauna include small adult shells of the bivalve Naiadites obesus, palaeoniscid fish and a distinctive tooth of the shark Ageleodus pectinatus. The presence of these algae provides further evidence that some of the Strathclyde Group sediments of the Midland Valley of Scotland were deposited in relatively shallow water marine conditions.

The affinities of the Carboniferous whip spider Graeophonus anglicus Pocock, 1911 (Arachnida: Amblypygi)

ABSTRACTThe Late Carboniferous whip spiderGraeophonus anglicusPocock, 1911 (Arachnida: Amblypygi), is redescribed on the basis of the holotype and nine other specimens all preserved in sideritic nodules from the British Middle Coal Measures of Coseley, Staffordshire, UK. This species is clearly basal with respect to most living whip spiders, expressing numerous plesiomorphic character states and can be referred to both the suborder Paleoamblypygi and the ‘living fossil’ family Paracharontidae (with one Recent species), the latter based on an explict character of dorsal spination on the pedipalp femur. This suggests that crown-group Amblypygi originated by at least the mid-Palaeozoic.