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Dinas Powys, United Kingdom

Caracciolo L.,Chemostrat Ltd | Orlando A.,CNR Institute of Geosciences and Earth Resources | Marchev P.,Bulgarian Academy of Science | Critelli S.,University of Calabria | And 3 more authors.
Sedimentary Geology | Year: 2016

Detrital heavy mineral and bulk rock geochemistry and a review of sandstone petrographic data have been used to investigate the post-collisional effusive magmatism that followed the closure of the Vardar Ocean and the generation of volcanic sediments in a complex and compositionally variable volcanic region. Available petrographic data gives evidence of contributions from three key source areas corresponding to the three main tectonic units: the structurally lower Gneiss-Migmatite Complex (Byala Reka-Kechros and Kesebir-Kardamos domes) and the upper Variegated (Kimi) Complex, both fringed by the low-to-medium-grade Mesozoic rocks of the Circum-Rhodope Belt. Besides the deposition of siliciclastic material, volcanic contributions from both, intermediate and acid products represent an important source of sediment in the area. Despite dominant intermediate to acid volcanic products, volcanic lithic fragments in sandstones (microlithic, lathwork and brown vitric textures) indicate main inputs from intermediate and basic-intermediate products generating questions on the interpretation of volcanic detritus in reconstruction of provenance. Detrital amphibole and pyroxene chemistry is used to characterise the supply of volcanic material as well as the dispersal mechanisms and understand the role played by each of the volcanic centers present in the area in the infill of the north-western Thrace basin. Amphibole chemistry reveals high compositional heterogeneity according to both compositional variability of the numerous volcanic centres active at the time of deposition and presence of metamorphic amphibole. 4Al and AlT apfu values indicate that most of the amphiboles from the NERZ are not of volcanic origin and their presence can only be attributed to the numerous amphibolite facies metamorphic rocks abundantly documented in the area. Detrital amphibole compositions from the ZKVS indicate major contributions from the Iran Tepe and Zvedzel volcanoes. Analysed detrital clinopyroxenes from the NERZ are mostly diopside-augite, with no hedenbergite or Fe-augite detected. The 4Al/6Al ratio is comparable with compositions of volcanic pyroxenes from the Momchilgrad-Arda (ZKVS) region and products from the pre-caldera phase of the Borovitza. © 2016 Elsevier B.V. Source

rodon J.,Polish Academy of Sciences | Szulc J.,Jagiellonian University | Anczkiewicz A.,Polish Academy of Sciences | Jewula K.,Polish Academy of Sciences | And 3 more authors.
Clay Minerals | Year: 2014

Mudstones and claystones from the southern marginal area of the European Upper Triassic, midcontinental Keuper basin (Silesia, southern Poland) were investigated using XRD, organic and inorganic geochemistry, SEM, K-Ar of illite-smectite, AFT, and stable isotopes of O and C in carbonates in order to unravel the consequent phases of the geological history of these rocks, known for abundant fossils of land vertebrates, and in particular to evaluate the diagenetic overprint on the mineral composition. The detected and quantified mineral assemblage consists of quartz, calcite, dolomite, Ca-dolomite, illite, mixed-layer illite-smectite, and kaolinite as major components, plus feldspars, hematite, pyrite, chlorite, anatase, siderite, goethite as minor components. Palygorskite, gypsum, jarosite and apatite were identified in places. The K-Ar dates document a post-sedimentary thermal event, 164 Ma or younger, which resulted in partial illitization of smectite and kaolinite. The maximum palaeotemperatures were estimated from illite-smectite as ~125°C. Apatite fission track data support this conclusion, indicating a 200-160 Ma age range of the maximum temperatures close to 120°C, followed by a prolonged period of elevated temperatures. These conclusions agree well with the available data on the Mesozoic thermal event, which yielded Pb-Zn deposits in the area. Organic maturity indicators suggest the maximum palaeotemperatures <110°C. Palygorskite was identified as authigenic by crystal morphology (TEM), and calcite by its accumulation in soil layers and by its isotopic composition evolving with time, in accordance with the sedimentary and/or climatic changes. Dolomite isotopic composition indicates more saline (concentrated) waters. Palygorskite signals a rapid local change of sedimentary conditions, correlated with algal blooms. This assemblage of authigenic minerals indicates an arid climate and the location at the transition from a distal alluvial fan to mudflat. Fe-rich smectite, kaolinite, and hematite were products of chemical weathering on the surrounding lands and are therefore mostly detrital components of the investigated rocks. Kaolinite crystal morphology and ordering indicates a short transport distance. Hematite also crystallized in situ, in the soil horizons. A large variation in kaolinite/2:1 minerals ratio reflects hydraulic sorting, except of the Rhaetian, where it probably signals a climatic change, i.e. a shift in the weathering pattern towards kaolinite, correlated with the disappearance of hematite. Quartz, 2M1 illite, and minor feldspars and Mg-chlorite were interpreted as detrital minerals. The documented sedimentation pattern indicates that in more central parts of the Keuper playa system, where an intense authigenesis of the trioctahedral clays (chlorite, swelling chlorite, corrensite, sepiolite) took place, illite and smectite were the dominant detrital clay minerals. Cr/Nb and Cr/Ti ratios were found as the best chemostratigraphic tools, allowing for the correlation of all investigated profiles. A stable decrease of these ratios up the investigated sedimentary sequence is interpreted as reflecting changes in the provenance pattern from more basic to more acidic rocks. © 2014 Mineralogical Society. Source

Porter S.J.,University of British Columbia | Porter S.J.,Durham University | Porter S.J.,Chemostrat Ltd | Smith P.L.,University of British Columbia | And 4 more authors.
Earth and Planetary Science Letters | Year: 2014

Recognising variations in the carbon isotope compositions of marine organic-rich sedimentary rocks can provide insight into changes in ocean chemistry throughout geological time. Further, identification of global excursions in the carbon isotope record has proved to be valuable as a chronostratigraphic correlation tool. This investigation presents new high-resolution organic carbon isotope data (δCorg13) for marine sediments from 2 regions in North America (Last Creek, British Columbia, Canada and Five Card Draw, Nevada, USA). The carbon isotope profiles demonstrate that there were significant differences between the carbon reservoirs at Five Card Draw and Last Creek, notably in the upper part of the Leslei Zone. The δCorg13 values show a gradual positive CIE (~2‰) at Last Creek in the upper part of the Leslei Zone. This corresponds to a coeval positive CIE of similar duration in Dorset, UK (upper Turneri Zo≠ Jenkyns and Weedon, 2013), suggesting that this may be a global marine carbon isotope signature, and likely reflects a widespread increase in primary productivity during the Early Sinemurian. In addition, a brief negative CIE is observed in the uppermost Lower Sinemurian at Last Creek. This negative excursion is not recorded in the Dorset section, suggesting localised upwelling of 12C-rich bottom-waters at Last Creek. Further, the signals identified at Last Creek are not present in coeval sections at Five Card Draw, thus highlighting a significant difference between these localities. Osmium (Os) isotope data (initial 187Os/188Os values) provide a quantitative determination of the contrasting depositional environments of Five Card Draw and Last Creek (at least partially restricted with high levels of continental inundation and open-ocean, respectively). This demonstrates that basinal restriction may act as a major factor that controls isotopic stratigraphic signatures, thus preventing the identification of global or widespread regional excursions. © 2014. Source

Nyhuis C.J.,University of Cologne | Riley D.,Chemostrat Ltd | Kalasinska A.,Origin Analytical Ltd.
Geologie en Mijnbouw/Netherlands Journal of Geosciences | Year: 2016

Sedimentological data acquired by thin section petrography is a rich source of information to better understand and interpret depositional environments that are dominated by fine-grained deposits. This study provides an evaluation of the sedimentological and geochemical changes recorded over Upper Viséan to Lower Namurian successions preserved in a core section from a well drilled in the southern part of the Netherlands. Facies analysis and the recognition of microfacies associations allow detailed interpretations of depositional environments. Interpretation of additional geochemical data acquired by portable X-ray fluorescence analyses has resulted in a chemostratigraphic zonation for the core section. The zonation reflects stratigraphic changes in the mineralogy of the sedimentary successions. Integration of the microfacies associations and the chemostratigraphic zonation has led to the identification of three so-called depositional zones, which show the development of depositional settings from Late Viséan to Early Namurian times. Depositional Zone 1 consists of fine-grained turbiditic limestones and mudstones deposited in a distal carbonate ramp setting during Latest Viséan times. The overlying Depositional Zone 2 corresponds to the Geverik Member (Lower Namurian) and is particularly heterogeneous in geochemical and lithological terms: the zone reflects a complex interplay between different parameters such as sediment source, transport mechanisms and oxygen content that are assumed to be governed by fluctuating sea levels and changing depositional environments (from basinal to shallow marine settings). Sandy lenticular mudstones are predominant in the lower part of Depositional Zone 2 and show that sedimentation was via erosive bedload, whilst the common fossiliferous mudstones present within the upper part of the same zone yield evidence for increased endobenthic activity in dysoxic conditions. The successions assigned to Depositional Zone 3 ( = Epen Formation - Namurian) are the products of cyclic sedimentation of a terrestrial sourced delta. Copyright © Netherlands Journal of Geosciences Foundation 2015. Source

Marynowski L.,University of Silesia | Zaton M.,University of Silesia | Rakocinski M.,University of Silesia | Filipiak P.,University of Silesia | And 2 more authors.
Palaeogeography, Palaeoclimatology, Palaeoecology | Year: 2012

Presented for the first time in this paper are the results of a detailed multi-proxy investigation conducted on the Hangenberg Black Shale (HBS) from the Polish part of the Laurussian Shelf, which provide details about the environmental conditions in existence during deposition of the shale and the role played by anoxic conditions in the mass extinction events that occurred at the end of the Devonian times. Inorganic and organic redox indicators indicate that bottom water redox conditions changed periodically from being mainly anoxic/euxinic to oxic or being partially depleted in oxygen. U/Th values above 1.25, Ni/Co values above 7 and V/(V. +. Ni) values above 0.8 recorded from the lower part of the HBS all point to anoxic/euxinic conditions being present, as do high total organic carbon contents (TOC) above 10% and degree of pyritisation (DOP) values around 0.75%. However, the presence of benthic fauna over the lower part of the HBS attests to opportunistic colonisation of the seafloor during oxic episodes. Evidence for similar episodes has also been recognised over the middle part of the HBS, e.g., U/Th values below 1.25, Ni/Co values below 4, V/(V. +. Ni) values below 0.8, TOC values of 3% to 5.5% and DOP values of 0.4% to 0.75%, plus the common occurrence of benthic fauna. Anoxic conditions returned during the deposition of the upper part of the HSB, though they were not as well developed as when the lower part of the shale was laid down.Of interest is the presence of small pyrite framboids and isorenieratene biomarkers in all the analysed samples, which suggest that euxinic conditions persisted in the photic zone of the water column. A twenty centimetre thick layer of volcanogenic deposits (tuffites) is present in the middle part of the HBS, the geochemical characteristics of which are typical of ocean floor basalts. The occurrence of volcanogenic material below and within the HBS, together with an absence of calcium carbonate over its upper part, the presence of abundant tetrads just above the black shale and a drastic decrease in faunal frequency in the upper part of the HBS imply that volcanism may have caused oceanic acidification (or hypercapnia) that in turn potentially may have influenced the Hangenberg mass extinction event. © 2012 Elsevier B.V. Source

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