Facies-succession and architecture of the third-order sequences and their stratigraphic framework of the Devonian in Yunnan-Guizhou-Guangxi area, South China

AbstractThe Caledonian orogeny at the end of the Silurian resulted in great changes in the palaeogeography in the Yunnan-Guizhou-Guangxi area of South China; the continental area of the Early Paleozoic evolved into the extensive Dian-Qian-Gui Sea in the Late Paleozoic. Early in the Devonian, as a result of a major transgression, seawater encroached gradually from the south to the north and clastic facies were deposited. Carbonate deposition was then established in the Yunnan-Guizhou-Guangxi area, with a palaeogeography marked by attached platforms, isolated platforms and narrow basins. As a result of the Ziyun movement towards the end of the Devonian, the Upper Devonian strata are regressive and thin out from the open-sea to the land areas. A study of the nature and distribution of sedimentary facies in space and time recognises 13 third-order sequences in the Devonian strata in Yunnan-Guizhou-Guangxi area, and these form two second-order sequences. The strata of the Lower Devonian comprise 5 third-order sequences (SQ1 to SQ5), which are dominated by transgressive clastics. 4 third-order sequences (SQ6 to SQ9) in the Middle Devonian are characterized by alternations of transgressive clastics and highstand carbonates. In the Upper Devonian, carbonates constitute 4 third-order sequences (SQ10 to SQ13), which are generally marked by the transgressive limestones and highstand dolomites. On the basis of earlier biostratigraphic studies, sea-level changes represented by the third-order sequences with their different facies successions are explored, and the sequence stratigraphic framework is established. Therefore, the Devonian strata in the study area provide an example for further understanding of depositional trends within the sequence-stratigraphic framework

A Palaeoproterozoic dolomite (Vempalle Formation, Cuddapah Basin, India) showing Phanerozoic-type dolomitisation

© 2019 The Palaeoproterozoic Vempalle Formation of the Cuddapah Basin, India, significantly adds to our understanding of the evolution of Precambrian marine carbonate systems and the redox state of the Earth's early oceans. A facies-microfacies-diagenetic-geochemical examination of samples from a ∼1000-m long exposure in a freshly-cut canal section shows that 10–15% of precursor limestone is still preserved in the Vempalle Formation in the form of remnant patches of calcimicrite and ooids with calcite spar cement. The ooids, preserving primary radial and concentric fabrics and radial fractures, are considered to have been originally precipitated as calcite, which may have been low-Mg. In places the preserved calcite spar, that is partially replaced by fabric-destructive dolomite, shows Type I calcite twin lamellae. Petrographic observations demonstrate that Vempalle Formation dolomite formed through very early precipitation, which in stromatolites preserved microbial filaments, as well as through fabric-destructive dolomitization during shallow to moderate burial. Vempalle Formation dolomite is characterized by micritic dolomite crystals which suggest rapid early dolomitization of lime mud and micritic calcite from a supersaturated Mg-Ca-rich solution, probably near-surface or during shallow burial. Depletion of Na and Sr contents of Vempalle Formation dolomite along with negative δ18O values indicate dolomite recrystallisation during burial and further replacement. Dolomite δ13C values of −0.5 to 2‰ are likely inherited original marine values. Geochemical proxies (trace elements and rare earths) imply that Cuddapah Basin seawater and dolomitizing fluids were anoxic and ferruginous but not euxinic. Geochemical analyses also indicate that the burial diagenetic fluids evolved from Eu-enriched seawater that probably resulted from continental rifting around 1.9–2.0 Ga. This probable ocean chemistry is in contrast with the anoxic, ferruginous and extremely high Mg/Ca “dolomite oceans” that prevailed during Proterozoic time. The Vempalle dolomite shows more similarities with dolomitised Phanerozoic platform carbonates than typical Precambrian dolomite with its well-preserved textures and burial dolospar cements

Shale-gas potential of the Mid-Carboniferous Bowland-Hodder Unit in the Cleveland Basin (Yorkshire), Central Britain

The shale-gas potential of mid-Carboniferous mudrocks in the Bowland-Hodder unit in the Cleveland Basin (Yorkshire, northern England) was investigated through the analysis of a cored section from the uppermost part of the unit in the Malton-4 well using a multidisciplinary approach. Black shales are interbedded with bioturbated and bedded sandstones, representing basinal-offshore to prodelta – delta-front lithofacies. The total organic carbon (TOC) content of the shales ranges from 0.37 to 2.45 wt %. Rock-Eval pyrolysis data indicate that the organic matter is mainly composed of Type III kerogen with an admixture of Type II kerogen. Tmax (436–454°C), 20S/(20S+20R) C29 sterane ratios, and vitrinite reflectance values indicate that organic matter is in the mid- to late- mature (oil) stage with respect to hydrocarbon generation. Sedimentological and geochemical redox proxies suggest that the black shales were deposited in periodically oxic-dysoxic and anoxic bottom waters with episodic oxic conditions, explaining the relatively low TOC values. The Rock-Eval parameters indicate that the analysed mudrocks have a limited shale-gas potential. However, burial and thermal history modelling, and VRr data from other wells in the region, indicate that where they are more deeply-buried, the Bowland-Hodder shales will be within the gas window with VRr > 1.1 % at depths in excess of 2000 m. Therefore although no direct evidence for a high shale-gas potential in the Cleveland Basin has been found, this cannot be precluded at greater depths especially if deeper horizons are more organic rich

Nearshore euxinia in the photic zone of an ancient sea:Part II – The bigger picture and implications for understanding ocean anoxia

Biomarker, palaeontological and isotopic evidence suggests that the Late Permian carbonate seas, i.e. the Northern (NPB) and Southern (SPB) Permian basins of northern Pangea, were characterized by significant spatial and temporal variations in the palaeowater-column redox state. This is particularly the case with regard to the deposition of the Lopingian Zechstein cycle 2 carbonate rocks. A shelf to basin reconstruction of environmental conditions was achieved by analysing nearly 400 core samples from 49 wells. This allowed an evaluation of the spatial variations in facies and broad oceanographic conditions at the basin scale. Specifically, in the lower slope and shallow-basin facies of the northern margin of the SPB (present-day northern Poland and eastern Germany), highly variable concentrations of the green sulphur bacterial biomarkers chlorobactane and isorenieratane (and their likely degradation products, C15 to C31 2,3,6-aryl isoprenoids, indicative of photic zone euxinia) and homohopane indices (indicative of anoxia), combined with the presence of a benthic fauna and bioturbation, indicate a variable but occasionally anoxic/euxinic water column. Locally in lagoonal facies in the northern and southern margin of the SPB, euxinic conditions also developed but these were likely associated with localised conditions or benthic production in association with microbialites. The presence of gammacerane in the eastern SPB (south-eastern Germany and eastern Poland) suggests elevated salinities there, compatible with the restricted configuration of the basin. However, a lack of these signatures in basinal settings of the eastern SPB indicates that strongly reducing conditions were restricted to the lower slope and shallow-basin locations and restricted lagoons, and were not developed in the basin centre. Moreover, this anoxia/euxinia in marginal settings is restricted to the north-eastern part of the SPB. The south-eastern part of the SPB (SE Poland), in contrast, is devoid of evidence for PZE. The southern margin of the SPB is also characterized by generally oxic-suboxic conditions, with local anoxia limited to more restricted embayments, and elevated salinities limited to restricted oxic-anoxic lagoons. In the western SPB (NE England and adjacent offshore) and the NPB (Outer Moray Firth, offshore Scotland) the water columns were oxic-suboxic. Overall, it appears that high but episodic primary bioproductivity of organic matter was concentrated on (or even limited to) the lower slopes of the SPB's north-eastern margin and the restricted lagoons and shallow basin of its southern margin, leading to the formation of source rocks for petroleum in these areas. In addition, the temporal and geographical restriction of anoxia appears to have prevented the accumulation of large and more widespread quantities of organic matter; in fact TOC contents exhibit a poor correlation with ecological and anoxia indicators. Crucially, this work confirms that the strong evidence for PZE observed in shelf and lower slope/shallow-basin facies of the north-eastern SPB need not be associated with widespread, basin-scale anoxia; this conclusion has implications for organic matter burial, carbon cycling and biotic crises during other times in Earth history

Bio-precipitation of calcium and magnesium ions through extracellular and intracellular process induced by bacillus licheniformis SRB2

Removal of calcium and magnesium ions through biomineralization induced by bacteria has been proven to be an effective and environmentally friendly method to improve water quality, but the process and mechanism are far from fully understood. In this study, a newly isolated probiotic Bacillus licheniformis SRB2 (GenBank: KM884945.1) was used to induce the bio-precipitation of calcium and magnesium at various Mg/Ca molar ratios (0, 6, 8, 10, and 12) in medium with 30 g L−1 sodium chloride. Due to the increasing pH and HCO3− and CO32− concentrations caused by NH3 and carbonic anhydrase, about 98% Ca2+ and 50% Mg2+ were precipitated in 12 days. The pathways of bio-precipitation include extracellular and intracellular processes. Biominerals with more negative δ13C values (−16‰ to −18‰) were formed including calcite, vaterite, monohydrocalcite, and nesquehonite with preferred orientation. The nucleation on extracellular polymeric substances was controlled by the negatively charged amino acids and organic functional groups. The intracellular amorphous inclusions containing calcium and magnesium also contributed to the bio-precipitation. This study reveals the process and mechanism of microbial desalination for the removal of calcium and magnesium, and provides some references to explain the formation of the nesquehonite and other carbonate minerals in a natural and ancient earth surface environment

'To live and die [for] Dixie': Irish civilians and the Confederate States of America

Around 20,000 Irishmen served in the Confederate army in the Civil War. As a result, they left behind, in various Southern towns and cities, large numbers of friends, family, and community leaders. As with native-born Confederates, Irish civilian support was crucial to Irish participation in the Confederate military effort. Also, Irish civilians served in various supporting roles: in factories and hospitals, on railroads and diplomatic missions, and as boosters for the cause. They also, however, suffered in bombardments, sieges, and the blockade. Usually poorer than their native neighbours, they could not afford to become 'refugees' and move away from the centres of conflict. This essay, based on research from manuscript collections, contemporary newspapers, British Consular records, and Federal military records, will examine the role of Irish civilians in the Confederacy, and assess the role this activity had on their integration into Southern communities. It will also look at Irish civilians in the defeat of the Confederacy, particularly when they came under Union occupation. Initial research shows that Irish civilians were not as upset as other whites in the South about Union victory. They welcomed a return to normalcy, and often 'collaborated' with Union authorities. Also, Irish desertion rates in the Confederate army were particularly high, and I will attempt to gauge whether Irish civilians played a role in this. All of the research in this paper will thus be put in the context of the Drew Gilpin Faust/Gary Gallagher debate on the influence of the Confederate homefront on military performance. By studying the Irish civilian experience one can assess how strong the Confederate national experiment was. Was it a nation without a nationalism