Microstructures in Metasedimentary Rocks from the Neoproterozoic Bonahaven Formation, Scotland: Microconcretions, Impact Spherules, or Microfossils?

Microscopic spherules in relatively undeformed mudstones of the Neoproterozoic Bonahaven Formation, Islay, Scotland, are differentiated from their matrix by a sharp micron-scale, smoothly rounded boundary. These elongate spherules were earlier interpreted as hollow bodies filled penecontemporaneously by glauconite and subsequently metamorphosed to phengite, but their origin remains a matter of debate. Spherules observed in thin section are predominantly rounded (∼74%) but can exhibit a flat edge or protrusion at one end. In 11% of a sample population, two or more spherules are conjoined. X-ray diffraction indicates that spherule-bearing mudstones consist mainly of muscovite, with variable amounts of kaolin-group minerals and minor iron-chlorites. A range of physical origins for the spherules – including microconcretions or metamorphic microstructures; deposition from the sky as micrometeorites, microtektites/microkrystites, or accretionary volcanic ash particles; and detrital grains – is considered but rejected on distributional, morphological, and mineralogical evidence. Biological origins are considered most likely, especially protistan tests similar to the vase-shaped microfossils found in somewhat older Neoproterozoic rocks. If correct, this provides the first report of eukaryotic life in the Dalradian succession that passes critical tests for biogenicity and new evidence for testate microfossils in post-Sturtian but pre-Marinoan aged rocks.Earth and Planetary SciencesOrganismic and Evolutionary Biolog

Sulphate concentration in cave dripwater and speleothems:long-term trends and overview of its significance as proxy for environmental processes and climate changes

Sulphate concentrations in speleothems identify major volcanic eruptions, provide useful information on soil and aquifer dynamics and, in similar fashion to the 14C bomb peak, its Anthropocene peak can be used to date recent cave formations. However, the transmission of S from the atmosphere to cave dripwater and its incorporation in speleothems is subjected to biogeochemical cycling and accurate studies of each cave site are needed in order to assess how the S atmospheric signal is modified and eventually encoded in speleothems. This study investigates the role of biogeochemical cycling and aquifer hydrology by utilising published and new dripwater and speleothem data from Grotta di Ernesto (ER) in northern Italy. Here we provide the first long-term record of sulphate concentration in cave dripwater based on over 20 years of measurements. Fast drip site st-ER1 is characterised by a continuous decrease in SO4 concentration from a high of 7.5 ± 0.8 mg/l in 1993–1994 to a low of 2.2 ± 0.2 mg/l in 2013–2014, and replicates with a delay of ∼15 years the decline in the atmospheric SO2 emissions. The S-series of slow flow ER78 site is further delayed by ∼4.5 years in relation to the S retention in the aquifer matrix. The dripwater data are used to extend the previously published S record (1810–1998 AD) of stalagmite ER78 and reconstruct the anthropogenic S-peak: this displays a delay of ∼20 years with respect to the atmospheric S emission peak due to biogeochemical cycling and aquifer storage. However, sulphur recycling above the cave did not operate with the same degree of efficiency through time, which resulted in a variable time delay between S deposition and incorporation into the stalagmite. In the pre-Anthropocene era, and in particular during the cold Little Ice Age, biogeochemical cycling was far less efficient than today, and the fast transmission of the atmospheric signal allowed capture of S released during major volcanic eruptions by stalagmites

The Marinoan cap carbonate of Svalbard: Syngenetic marine dolomite with ¹⁷O-anomalous carbonate‐associated sulphate

Two cap carbonates overlying Cryogenian panglacial deposits are found in North- East Svalbard of which the younger (635 Ma) forms the base of the Ediacaran Period. It is represented by a transgressive succession in which laminated do-lostone, typically around 20 m thick (Member D1), is succeeded transitionally by a similar thickness of impure carbonates (Member D2). In Spitsbergen, there is evidence of microbially influenced sediment stabilisation and carbonate precipitation in the lower part of D1, whilst the upper part of D1 and D2 show centimetre- decimetre- scale graded units with undulatory lamination interpreted as evidence of storm activity. Carbonate originated as possible freshwater whitings, as well as microbial precipitates. Exhumed and eroded hardgrounds display replacive 10– 30 μm dolomite crystals with cathodoluminescence characteris-tics consistent with early diagenetic manganese and iron reduction. Regionally, carbon isotope values consistently decrease by around 2‰ from around −3‰ over 30 m of section which is both a temporal and a bathymetric signal, but not a global one. An exponential decline in carbonate production predicted by box models is fitted by a semi- quantitative sedimentation model. A mass- anomalous 17O depletion in carbonate- associated sulphate in dolomite, inherited from pre-cursor calcite, decreases from −0.6 to −0.3‰ in the basal 15 m of section and then approaches background values. The post- glacial anomalous 17O depletion in carbonate- associated sulphate and barite elsewhere has been interpreted in terms of ultra- high pCO2 at the onset of deglaciation. Such anomalies, with larger amplitude, have been reported in Svalbard from underlying lacustrine and tufa-ceous limestones representing a hyperarid glacial environment. The anomalous sulphate could be produced contemporarily, or the internally drained landscape may have continued to release 17O-anomalous sulphate as it was transgressed during cap carbonate deposition. The late Cryogenian to earliest Ediacaran record in Svalbard provides the most complete record of the basal 17O - depletion event in the world

The effect of visitors in a touristic cave and the resulting constraints on natural thermal conditions for palaeoclimate studies (Eagle Cave, central Spain)

Temperature in Eagle Cave, central Spain, was measured over a year to determine the effect of tourists on the natural environ­ment. The mean cave temperature was 15.6°C in 2009, witha seasonal amplitude of <0.4°C. Access of tourists to the cavern produces thermal anomalies of <0.15°C, whichare recovered overnight in most cases. During days withhighvisitor num­bers, cumulative thermal anomalies may persist from one day to the next, causing an increase of cave temperature for longer periods. However, this anthropogenic effect disappears soon after the number of tourists reduces, lasting less than a week in most cases. Cumulative thermal anomalies are <0.02°C dur­ing most of the year and <0.1°C in periods withlarge number of visitors. The anthropogenic effect on cave temperature is non-persistent and has a small magnitude in comparison withnatural oscillations. Thus, long-term absolute temperatures ob­tained from Eagle Cave are not affected by visitors. The input of thermal energy caused by tourists is absorbed as latent heat by the cave (causing evaporation), whichprevents the increase of baseline temperatures in the environment. A condensation process occurs over cave walls and speleothems. This is the re­sult of cooling the atmosphere during the thermal equilibra­tion withcave walls once visitors leave. Althoughcondensation is found in Eagle Cave, the magnitude of the process is not enoughto cause any significant condensation corrosion that could damage speleothems as a result of the tourist visits. The cave is in thermal equilibrium withsurface temperatures, and calibration studies will produce suitable results for palaeocli­mate studies despite being a tourist cavern.

Cortical thickness, surface area, and folding alterations in male youths with conduct disorder and varying levels of callous-unemotional traits.

PURPOSE: Previous studies have reported changes in gray matter volume in youths with conduct disorder (CD), although these differences are difficult to interpret as they may have been driven by alterations in cortical thickness, surface area (SA), or folding. The objective of this study was to use surface-based morphometry (SBM) methods to compare male youths with CD and age and sex-matched healthy controls (HCs) in cortical thickness, SA, and folding. We also tested for structural differences between the childhood-onset and adolescence-onset subtypes of CD and performed regression analyses to assess for relationships between CD symptoms and callous-unemotional (CU) traits and SBM-derived measures. METHODS: We acquired structural neuroimaging data from 20 HCs and 36 CD participants (18 with childhood-onset CD and 18 with adolescence-onset CD) and analyzed the data using FreeSurfer. RESULTS: Relative to HCs, youths with CD showed reduced cortical thickness in the superior temporal gyrus, reduced SA in the orbitofrontal cortex (OFC), and increased cortical folding in the insula. There were no significant differences between the childhood-onset and adolescence-onset CD subgroups in cortical thickness or SA, but several frontal and temporal regions showed increased cortical folding in childhood-onset relative to adolescence-onset CD participants. Both CD subgroups also showed increased cortical folding relative to HCs. CD symptoms were negatively correlated with OFC SA whereas CU traits were positively correlated with insula folding. CONCLUSIONS: Cortical thinning in the superior temporal gyrus may contribute to the social cognitive impairments displayed by youths with CD, whereas reduced OFC SA may lead to impairments in emotion regulation and reward processing in youths with CD. The increased cortical folding observed in the insula may reflect a maturational delay in this region and could mediate the link between CU traits and empathy deficits. Altered cortical folding was observed in childhood-onset and adolescence-onset forms of CD.This study was supported by Wellcome Trust project grant 083140 (Drs. Goodyer and Fairchild), Medical Research Council project code MC_US_A060_5PQ50 (Dr. Calder), and the Betty Behrens Research Fellowship at Clare Hall, Cambridge University (Dr. Passamonti). The authorswould like to thank the participants and their families for taking part in this study, as well as the Cambridge Youth Offending Service for their help with recruitment.This is the final version. It was first published by Elsevier at http://www.sciencedirect.com/science/article/pii/S2213158215000856

Methane in underground air in Gibraltar karst

AbstractLittle is known about the abundance and geochemical behaviour of gaseous methane in the unsaturated zone of karst terrains. The concentrations and δ13C of methane in background atmosphere, soil air and cave air collected at monthly intervals over a 4yr period are reported for St. Michaels Cave, Gibraltar, where the regional climate, surface and cave processes are well documented. Methane concentrations measured in Gibraltar soil are lower than the local background atmosphere average of 1868ppb and fall to <500ppb. The abundance–δ13C relationships in soil air methane lack strong seasonality and suggest mixing between atmosphere and a 12C depleted residue after methanotrophic oxidation. Methane abundances in cave air are also lower than the local background atmosphere average but show strong seasonality that is related to ventilation-controlled annual cycles shown by CO2. Cave air methane abundances are lowest in the CO2-rich air that outflows from cave entrances during the winter and show strong inverse relationship between CH4 abundance and δ13C which is diagnostic of methanotrophy within the cave and unsaturated zone. Anomalies in the soil and cave air seasonal patterns characterised by transient elevated CH4 mixing ratios with δ13C values lower than −47‰ suggests intermittent biogenic input. Dynamically ventilated Gibraltar caves may act as a net sink for atmospheric methane