Crystallographic orientations of structural elements in skeletons of Syringoporicae (tabulate corals, Carboniferous): Implications for biomineralization processes in Palaeozoic corals

he crystallographic orientation of structural elements in skeletons of representatives of Carboniferous Syringoporicae (Auloporida) has been analysed by scanning electron microscopy (SEM), petrographic microscopy and electron backscatter diffraction (EBSD) on specimens from the Iberian Peninsula. The skeletons of the tabulate corals of the Syringoporicae consist of biogenic calcite crystals, and their microstructure is composed of lamellae, fibres and granules, or of a combination of these. Independent of the microstructure, the c-axis is oriented towards the lumen, quasi-perpendicular to the growth direction of the skeleton (perpendicular to the morphological axis lamellae, parallel to fibres). Most phaceloid taxa have a turbostratic distribution, as a biogenic response to prevent the cleavage of crystals. Cerioid and some phaceloid corals, whose microstructure is conditioned by wall elements, do not exhibit turbostratic distribution. Wall elements are determined by the biology of each taxon. Holacanth septal spines are composed of fibres arranged in a cone-shape structure, sometimes clamped to the external part of the corallite and show a complex crystallography. Monacanth septal spines are spindle shaped and composed of bundles of fibres. Tabulae are composed of lamellae. Their development and crystallographic orientation depends on the position of the epithelium in each case. Shared walls are formed by a combination of the walls of two independent corallites with a median lamina, composed of granules; these have a crystallographic orientation between that of the two corallites. The growth of the microstructure is derived by a coordinated stepping mode of growth, similar to other groups of organisms such as molluscs and scleractinians. The nucleation and formation of packages of co-oriented microcrystals suggest a growth mode similar to mineral bridges with a competitive growth mode between each crystal. The growth pattern of corallites suggests that the growth direction is divided into two main components: a horizontal growth direction towards the lumen and a vertical direction towards the top

Estudio preliminar de las mineralizaciones de Vanadatos de Uranio asociadas a dientes y huesos fósiles: Implicaciones genéticas y geoquímicas

Depto. de Mineralogía y PetrologíaFac. de Ciencias GeológicasTRUEpu

Corals from Asturian substage in Cantabrian Mountains: A review

The subdivision of the Pennsylvanian divided the Namurian, Westphalian and Stephanian regional stages in substages named with letters. During the second half of the 20th Century, some of these substages were more properly defined. Westphalian A, B and C were defined as Langsettian, Duckmantian and Bolsovian. The Stephanian A was renamed as Barruelian and the transition between Westphalian and Stephanian as Cantabrian. The Westphalian D, defined in continental strata from Saar-Lorraine, was proposed to be substituted by the Asturian substage with the stratotype in the Cantabrian Mountains. An extensive documentation with assemblages and stratigraphic distribution of plants, fusulinids, brachiopods, corals, molluscs and ostracods was presented. But a formal definition of the stratotype was never proposed. The Asturian substage in the Cantabrian Mountains comprises both marine and terrestrial strata rich in fossils and allows easy correlations with other areas. Recent studies have improved the stratigraphic data and the knowledge on the coral assemblages, mainly in the eastern area of Asturias and Palencia. The entire coral assemblage from Asturian substage in the Cantabrian Mountains is composed of 48 named species and 20 species described in open nomenclature. The short stratigraphic range of many of them may be the basis for the characterization of the Asturian stage with corals. Although some species are endemic in the Cantabrian Mountains, there are some species that are also present in other regions of the Palaeotethys. At the generic level there are significant similarities that should be the basis for wider correlations with North America and East Asia

Middle to Late Mississippian and Early Pennsylvanian foraminiferal zonal scheme of South China—a case study from the Youjiang Basin: biostratigraphical and palaeobiogeographical implications

Ten foraminiferal zones are proposed in the Youjiang Basin (South China): Pojarkovella, Pojarkovella nibelis-Endothyranopsis compressa, Cribrospira panderi-Eostaffella ikensis, Climacammina, Janischewskina delicata, Eostaffellina decurta, Bradyina cribrostomata, Eostaffellina actuosa-Eostaffellina protvaensis, Plectostaffella and Pseudostaffella antiqua zones. These zones span the interval from the middle Viséan to the late Serpukhovian in a continuous succession, and above, a final zone characteristic of the Severokeltmian Substage in the middle part of the early Bashkirian. These zones are compared with other foraminiferal zones described from China, particularly with those from South China and allow to uniformize the foraminiferal stratigraphical records in the region, and to standardize the foraminiferal zones defined in those regions. The stratigraphical range of some taxa is still debated, but the Viséan-Serpukhovian and the lower-upper Serpukhovian boundaries are well constrained by well-known cosmopolitan taxa. Foraminifers during the lower Middle Mississippian (middle Viséan to the earliest late Viséan) are more similar to the foraminiferal assemblages described from Western Europe, whereas from the upper Middle to Late Mississippian (i.e. latest Viséan-Serpukhovian) are more similar to those in the Russian Platform, and thus, the use of the Russian zonal scheme and biostratigraphy is more practical than to use the biozones defined in Western Europe

Coral assemblages of the Serpukhovian–Bashkirian transition from Adarouch (Morocco)

The Carboniferous outcrops from Adarouch (central Morocco) are composed of siliciclastic and carbonate rocks, and the latter have yielded abundant fossils. The upper part of the marine succession in the Idmarrach Formation and its laterally equivalent Tirhela Formation belong to the Bashkirian. More recent investigations of poorly preserved coral assemblages from the upper part of Idmarrach 2 section and the upper part of the Tirhela Formation are here described. The assemblage from the upper Idmarrach Formation comprises several typical Mississippian taxa, such as Aulophyllum fungites, Dibunophyllum bipartitum, Koninckophyllum interruptum, Siphonodendron scaleberense and Lithostrotion decipiens, and some highly evolved forms previously undescribed of Mississippian genera such as Haplolasma sp., Arachnolasma sp., Siphonodendron sp., Diphyphyllum sp., Solenodendron sp., Clisiophyllum sp. and a new species Corwenia tirhelensis sp. nov. In addition, an undetermined petalaxid has been also recorded. Similarly, the assemblage from near the top of the Tirhela Formation yielded some species regarded usually as Mississippian, such as Palaeosmilia murchisoni and Lithostrotion decipiens. We also identified the long-ranging tabulate Syringopora sp., Corwenia tirhelensis sp. nov., and a single species of the fasciculate rugosan, Siphonodendron tindoufense, previously described from Bashkirian rocks in the Tindouf Basin (southern Morocco). The presence of the latter taxon in both the Idmarrach and Tirhela sections implies a communication between the Adarouch region and the Saharan basins. The occurrence of S. tindoufense at the approximately same stratigraphic level in Tindouf, Taoudenni, Reggan-Ahnet and Adarouch, demonstrates its important regional stratigraphic value in North Africa

A new early Visean coral assemblage from Azrou-Khenifra Basin, central Morocco and palaeobiogeographic implications

A new early Visean coral assemblage has been recorded from turbidite facies in the southern part of the Azrou-Khenifra Basin, northwest of Khenifra, central Morocco. The newly discovered Ba Moussa West (BMW) coral fauna includes Siphonophyllia khenifrense sp. nov., Sychnoelasma urbanowitschi, Cravenia lamellata, Cravenia tela, Cravenia rhytoides, Turnacipora megastoma and Pleurosiphonella crustosa. The early Visean age of the coral assemblage is supported by foraminiferal and conodont data, with the recognition of the basal Visean MFZ9 Zone. This confirms that the first transgression in the Azrou-Khenifra Basin was during the earliest Visean. The allochthonous coral assemblage was recovered from coarse-grained proximal limestone debris flow and turbidite beds within a fault-bounded unit, lying to the west of a thrust syncline containing upper Visean limestones. No evidence exists of the former early Visean shallow-water platform from which the corals were derived. All other in situ platform carbonate rocks around the southern margin of the Azrou-Khenifra Basin are probably of late Visean (Asbian–Brigantian) age. The early Visean Ba Moussa West coral fauna can be compared with that at Tafilalt in eastern Morocco, as well as in other Saharian basins of Algeria. Many of the genera and species in the Ba Moussa West assemblage are identical to those in NW Europe, with which it must have had marine connections. The new rugose species described, Siphonophyllia khenifrense, is probably endemic to North Africa. Its ecological niche in NW Europe was occupied by S. cylindrica or S. aff. garwoodi

Diagenetic and Biological Overprints in Geochemical Signatures of the Gigantoproductus Tertiary Layer (Brachiopoda): Assessing the Paleoclimatic Interpretation

Variations in the geochemical signatures of fossil brachiopod shells may be due to diagenesis and/or biological processes (i.e., ‘vital effects’). It is critical to characterise them in order to identify reliable shell areas suitable for paleoclimate studies. This investigation contributes to an in-depth understanding of geochemical variations in Gigantoproductus sp. shells (SW Spain, Serpukhovian age), throwing light onto the Late Paleozoic Ice Age interpretation. Microstructural, crystallographic, cathodoluminescence and geochemical (minor and trace elements, δ18O, δ13C, and strontium isotopes) characterisations have been performed on the tertiary layer of the ventral valve, to assess the preservation state. Poorly preserved areas exhibit microstructural and geochemical changes such as recrystallisation, fracturing and higher Mn and Fe enrichment. Moreover, these areas have a higher dispersion of ⁸⁶Sr, ⁸⁷Sr, δ18O and δ13C than well-preserved areas. Three structural regions have been identified in well-preserved areas of the ventral valve by differences in valve curvature and thickness, such as the umbonal and thick and thin regions. These regions have different proportions of Mg, S, Na, δ18O, and δ13C, which are interpreted as ‘vital effects’ and probably related to growth-rate differences during shell growth. The Gigantoproductus tertiary layer seems the most suitable for paleoclimate studies, because it retains the original microstructure and geochemical composition

Uranium-bearing minerals characterization with laboratory reflectance spectroscopy: study of Córcoles fossil site, Guadalajara

En la naturaleza, el ion uranilo se asocia comúnmente a arseniatos, fosfatos y vanadatos; uno de los orígenes secundarios más frecuentes del uranio está asociado a fosfatos cálcicos biogénicos. En este estudio se han caracterizado minerales de uranio con espectroscopia de reflectancia VNIR-SWIR de laboratorio (400-2500 nm). Entre las muestras estudiadas se han incluido los minerales secundarios de uranio: metatorbernita, metautunita y metauranocircita, así como fosfatos cálcicos (biogénicos e inorgánicos) y fósiles coexistentes con mineralizaciones de metatyuyamunita encontrados en el yacimiento de vertebrados del Mioceno inferior de Córcoles (Cuenca del Tajo, Guadalajara, España). Este yacimiento representa un ejemplo de la formación de minerales secundarios de uranio de tipo fosfatos. Su origen es el resultado de la interacción de los fósiles con aguas subterráneas u otros fluidos mineralizadores portadores de uranilo (UO2 2+) durante la diagénesis. Los minerales con uranilo muestran rasgos de absorción a 1100, 1330 y 1672 nm atribuidos a los aniones uranilo. Dada la escasa información preexistente, la caracterización de los minerales que contienen uranio aporta valiosa información con gran potencial para ser aplicada en teledetección. Los datos obtenidos pueden ser de utilidad en la exploración, caracterización y/o protección de los yacimientos de uranio.Uranyl ion is commonly associated with arsenates, phosphates and vanadates; one of the most frequent secondary origins of uranium is associated with biogenic calcium phosphates (bones and teeth) in nature. In this study different uranium minerals have been characterized with laboratory VNIR-SWIR reflectance spectroscopy (400-2500 nm). The samples studied included the secondary uranium minerals: metatorbernite, metautunite and metauranocyrcite. Calcium phosphates (biogenic and inorganic) and fossil remains coexisting with metatyuyamunite mineralization found in the Lower Miocene fossil vertebrate deposit of Córcoles (Tajo Basin, Guadalajara, Spain) have also been studied. This deposit represents a remarkable example of the formation of secondary uranium minerals of the phosphate type. Its origin is the result of the interaction of fossils with groundwater or other uranyl (UO2 2+) bearing mineralizing fluids during diagenesis. The uranyl-bearing minerals show absorption features at 1100, 1330 and 1672 nm attributed to uranyl anions. The characterization of uranium-bearing minerals provides valuable information with great potential for application in remote sensing, given the scarcity of pre-existing information. The obtained data can be useful in the exploration, characterization and/or protection of uranium deposits.Depto. de Geodinámica, Estratigrafía y PaleontologíaDepto. de Mineralogía y PetrologíaFac. de Ciencias GeológicasTRUEMinisterio de Ciencia e InnovaciónAgencia Estatal de Investigación/Proyectosa Unión Europeapu

Contrasting reef patterns during the evolution of the carboniferous azrou-khenifra basin (Moroccan Meseta)

Five types of reefs are described from the northern and southern parts of the Azrou-Khenifra Basin generated by the interactions of microbes and coral communities. The type 1 microbial reefs grew in both shallow- and deep-water settings, with a strong control by glacioeustasy. Type 2 microbial reefs developed in more tranquil periods, associated with common intermounds, and where only a single major regressive-transgressive sequence is recognised. Type 3 microbial reefs developed in constant deeper water conditions, generated by higher rates of subsidence in the basin, and creating an overall deepening-upward sequence. Type 4 microbial reefs recognised in the northern part of the basin have no clear counterparts in southern outcrops, but they are likely the capping strata observed in the latter area. Rugose corals allow to define a Type 5 reef, unrelated to microbial facies, and are recorded in oolitic-bioclastic backshoals or quiet inner platform settings. The presence of similar reefs in both the northern and southern parts of the basin demonstrates that conditions were not as different as previously proposed, and a lithostratigraphical, environmental uniformity occurs, which permits the analysis of different subsidence rates and glacioeustastic influence. In the Azrou-Khenifra Basin, the reefs, as well as other regional features, suggest that the basin, overall, evolved from an extensional tectonic regime during the early Brigantian into a complex extensional or compressional regime during the early Serpukhovian, passing into a predominantly compressional phase during the late Serpukhovian in a polyphase tectonic inversion during the onset of the Variscan Orogeny in the region