Diagenetic haematite and sulfate assemblages in Valles Marineris

Previous orbital mapping of crystalline gray haematite, ferric oxides, and sulfates has shown an association of this mineralogy with light-toned, layered deposits on the floor of Valles Marineris, in chaos terrains in the canyon’s outflow channels, and in Meridiani Planum. The exact nature of the relationship between ferric oxides and sulfates within Valles Marineris is uncertain. The Observatoire pour la Mineralogie, l’Eau, les Glaces et l’Activite (OMEGA) spectrometer initially identified sulfate and ferric oxides in the layered deposits of Valles Marineris. The Thermal Emission Spectrometer (TES) has also mapped coarse (gray) haematite in or at the base of these deposits. We use Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) spectra and Context Camera (CTX) and High Resolution Imaging Science Experiment (HiRISE) imagery from the Mars Reconnaissance Orbiter (MRO) to explore the mineralogy and morphology of the large layered deposit in central Capri Chasma, part of the Valles Marineris canyon system that has large, clear exposures of sulfate and haematite. We find kieserite (MgSO₄·H₂O) and ferric oxide (often crystalline red haematite) in the lower bedrock exposures and a polyhydrated sulfate without ferric oxides in the upper bedrock. This stratigraphy is duplicated in many other basinal chasmata, suggesting a common genesis. We propose the haematite and monohydrated sulfate formed by diagenetic alteration of a sulfate-rich sedimentary deposit, where the upper polyhydrated sulfate-rich, haematite-poor layers either were not buried sufficiently to convert to a monohydrated sulfate or were part of a later depositional phase. Based on the similarities between the Valles Marineris assemblages and the sulfate and haematite-rich deposits of Meridiani Planum, we hypothesize a common evaporite and diagenetic formation process for the Meridiani Planum sediments and the sulfate-bearing basinal Interior Layered Deposits.     

Contrasting the geochemistry of oxic sediments across ecosystems: a synthesis

The geochemistry of oxic sediments was contrasted across a range of Canadian aquatic ecosystems; 7 freshwater lakes, (3 circumneutral and 4 acidic), 15 peatlands (5 mineral-rich, 5 moderately-poor and 5 mineral-poor), 9 wetlands (3 oligosaline, 3 mesosaline and 3 euryhaline), an estuary (deposited and suspended sediments) and an intertidal region. Sediments were characterized by a simultaneous extraction that separated sediments into easily reducible (ER) metal (oxyhydroxides of Mn and easily reducible amorphous oxyhydroxides of Fe) and reducible (R) metal (more crystalline forms of oxyhydroxides of Fe), organic matter, and, the concentrations and partitioning of Zn, Cu and Cd associated with these 3 sediment components. Ecosystems were distinct with respect to ER Fe and organic matter [canonical variate analysis (CVA)] with 53% of among system variation in geochemistry attributed to these 2 components. Sediments of peatlands and wetlands contained greater amounts of organic matter whereas sediments of lakes, intertidal and estuarine deposited and suspended sediments were characterized by greater amounts of ER Fe. A further 21% of among system variation could be ascribed to organically bound Fe that was greater in acidic lakes and mineral-rich peatlands as compared to other systems. Concentration and partitioning of Cd within sediments was regionally dependent with 41% of among system variation (CVA) attributed to differences in ER Cd and R Cd. Cadmium from peatlands and lakes located in Ontario was recovered from all 3 sediment components whereas sediment from wetlands, the estuary and the intertidal regions of British Columbia (BC) contained no organically bound Cd with amounts recovered occurring mostly as ER Cd. Lakes and peatlands located in Ontario contained 3–5-fold total Cd as compared to ecosystems located in BC. A further 21% of among ecosystem variation was attributed to Zn partitioning. Zinc in peatland and wetland sediments occurred as R Zn as compared to lake and estuarine deposited sediments where Zn was recovered both as ER and R Zn. Total Zn was also 3–5-fold greater in sediments of systems in Ontario as compared to those sampled in BC. Concentration and partitioning of Cu was similar across all systems with Cu recovered from the organic component of sediment. The geochemistry of surficial oxic sediments with respect to ER Mn, R Fe and organic matter and the geochemical associations among these sediment components is ecosystem and region dependent. For assessing impacts of metals on sediment dwelling biota the geochemical characteristics of the system under study should first be defined.     

Seasonal δ13CDIC sourcing and geochemical flux in telogenetic epikarst of south-central Kentucky

Telogenetic epikarst carbon sourcing and transport processes and their associated hydrogeochemical responses are complex and dynamic. Carbon dioxide (CO₂) transport rates in the epikarst zone are often driven by hydrogeochemical responses, which influence carbonate dissolution and conduit formation. This study examines the influence of land use on carbon sourcing and carbonate dissolution kinetics through a comparative analysis of separate, but similar, epikarst systems in south-central Kentucky. The use of high-resolution hydrogeochemical data from multiple data loggers and isotope analysis from collected water samples reflects the processes within these epikarst aquifers, which are estimated to contribute significantly to bedrock dissolution. Results indicate that, in an agricultural setting, long-term variability and dissolution is governed by seasonal production of CO₂ . In a more urbanized, shallower epikarst system, land cover may affect CO₂ transport between the soil and underlying bedrock. This concentration of CO₂ potentially contributes to ongoing dissolution and conduit development, irrespective of seasonality. The observed responses in telogenetic epikarst systems seem to be more similar to eogenetic settings, which is suggested to be driven by CO₂ transport occurring independent of high matrix porosity. The results of this study indicate site-specific responses with respect to both geochemical and δ¹³C_DIC changes on a seasonal scale, despite regional geologic similarities. The results indicate that further comparative analyses between rural and urban landscapes in other karst settings is needed to delineate the impact of land use and seasonality on dissolution and carbon sourcing during karst formation processes. © 2019 John Wiley & Sons, Ltd.     

Conflict in Common: Heritage-making in Cape York

The outstanding natural and cultural values of Cape York have been acknowledged for decades, but those decades have been characterised by deep conflict. Non-government organisation intervention in local politics has seen a forceful push for nominating some or all of the Cape York Peninsula as a World Heritage Site. We illuminate the authorised heritage discourse at work in heritage-making, and highlight contested issues of ownership, governance, authenticity, and value. These themes contribute to the possibility of marginalising the voices of local people who wish to contribute to heritage-making in Cape York. Politics infuses all aspects of heritage-making in Cape York, and the specific experiences on Cape York reflect larger political processes occurring in World Heritage discourse. The paper draws on interviews undertaken in May and June 2012.     

Mineralogical controls on element dispersion in regolith over two mineralised shear zones near the Peak, Cobar, New South Wales

Effective exploration for polymetallic ore deposits in the Cobar region is hampered by incomplete knowledge of the mineralogical controls on element dispersion in the different regolith-landform settings throughout the area. A detailed mineralogical and geochemical study of regolith profiles over two major mineralised shear zones in a strongly weathered but dominantly erosional setting has delineated the important host minerals for a range of base metal cations. Iron oxides/oxyhydroxides, particularly goethite and to a much lesser extent hematite, are major hosts for Pb, Cu, and Zn as substituted/adsorbed cations and as constituents of associated or intergrown minerals, probably including members of the jarosite–alunite group. Correlations between elements and major regolith minerals suggest that goethite is also a host phase for As, Bi and Sb. Minor manganese minerals, including lithiophorite and cryptomelane group minerals, also host base metals in appreciable amounts. No clear association was found between gold and any particular secondary mineral. It is likely that gold is present largely as elemental gold particles associated with a range of minerals.Sampling strategies for geochemical exploration in variably leached and stripped regolith in the Cobar area should take into account the relative abundance of goethite and manganese oxides/oxyhydroxides within the profiles and overlying lag. Goethite would appear to be the preferred sampling medium for base metals. Highly ferruginous lag has a high proportion of hematite with variable maghemite and very low manganese oxide contents. Most of the base metal content in this surface material is strongly bound to the crystalline oxides/oxyhydroxides. More work is required to understand the effects of surface transformation of goethite to hematite and maghemite on the mobility and distribution of base metal cations in soil and ferruginous lags.     

Archaeological age constraints from extrusion ages of obsidian: Examples from the Middle Awash,Ethiopia

Extrusion ages of archaeological obsidian, especially as determined by the ⁴⁰Ar/³⁹Ar method, can provide reliable maximum ages for tool manufacture. In at least one case in the Middle Awash of Ethiopia, freshly extruded obsidian was used for tool making, resulting in useful maximum ages for site occupation. Hydration resulting in mobility of K and/or Ar in glass, and recoil artifacts produced by neutron irradiation, fatally affect most glass shards from volcanic ashes. The much lower surface area to volume ratio of most archaeological obsidian, however, indicates that the affected areas can be manually removed prior to analysis and the recoil and hydration problems can be easily overcome. A more important issue in dating obsidian is that of possible mass-dependent kinetic isotope fractionation during or subsequent to quenching of volcanic glasses. This is evidenced in some cases by sub-atmospheric initial ⁴⁰Ar/³⁶Ar ratios, and more generally in sub-atmospheric ³⁸Ar/³⁶Ar. Resulting bias can be avoided through the use of isochron ages, which do not entail the assumption of an initial value of ⁴⁰Ar/³⁶Ar as is required for plateau ages. Since step heating of glasses often yields limited variability in ⁴⁰Ar:³⁹Ar:³⁶Ar (and therefore little spread on isochrons), another approach is to use an average value for initial ⁴⁰Ar/³⁶Ar, with concomitantly larger uncertainty than is associated with atmospheric ⁴⁰Ar/³⁶Ar, when calculating a plateau age. The ³⁸Ar/³⁶Ar of an un-irradiated subset of our samples validates the inference of kinetic fractionation, and potentially provides a basis for determining initial ⁴⁰Ar/³⁶Ar in samples that fail to yield isochrons, but only in samples lacking magmatic excess ⁴⁰Ar. These approaches allow us to reliably apply the ⁴⁰Ar/³⁹Ar method to volcanic glasses, which has resulted in maximum ages for archaeological sites that are not amenable to traditional geochronological methods. ⁴⁰Ar/³⁹Ar geochronology can also provide information on the geological provenance of the raw material used for tool making, especially when combined with geochemical data.     

An example of fingerprint detection of greenhouse climate change

As an example of the technique of fingerprint detection of greenhouse climate change, a multivariate signal or fingerprint of the enhanced greenhouse effect is defined using the zonal mean atmospheric temperature change as a function of height and latitude between equilibrium climate model simulations with control and doubled CO₂ concentrations. This signal is compared with observed atmospheric temperature variations over the period 1963 to 1988 from radiosonde-based global analyses. There is a significant increase of this greenhouse signal in the observational data over this period.These results must be treated with caution. Upper air data are available for a short period only, possibly too short to be able to resolve any real greenhouse climate change. The greenhouse fingerprint used in this study may not be unique to the enhanced greenhouse effect and may be due to other forcing mechanisms. However, it is shown that the patterns of atmospheric temperature change associated with uniform global increases of sea surface temperature, with El NinoSouthern Oscillation events and with decreases of stratospheric ozone concentrations individually are different from the greenhouse fingerprint used here.     

西秦岭凤太矿集区丝毛岭金矿床地质地球化学特征

西秦岭凤太矿集区丝毛岭金矿床位于八卦庙造山型金矿床西侧5km左右,是一个新探明的剪切带型金矿。其成矿作用过程可分为早期石英-绢云母-硫化物阶段、中期多金属-硫化物阶段和晚期碳酸盐阶段。对早、中期的石英流体包裹体测试结果表明,丝毛岭金矿床成矿流体以富CO2、中温、低盐度为特征,总体上属于中温低盐度CO2-H2O体系,流体包裹体类型的多样性是流体不混溶性的产物。从早阶段到主成矿阶段成矿流体的温度、压力和盐度均有降低,硫逸度增高,有利于金的沉淀富集。H、O、S、C同位素研究结果,以及与八卦庙金矿床的对比分析表明,二者的成矿流体具有相似性和同源性,都是以深部来源为主的多源流体。由于丝毛岭金矿床产出的层位高于八卦庙金矿床,其成矿环境相对开放。     

“Twenty years is yesterday”: Science, multinational mining, and the political ecology of trust in New Caledonia

To date, the scholarly literature has insufficiently investigated the micropolitical ecology of trust, the ways that different interests and expectations within a community can differentially mediate trust relationships between members of that community and an exogenous institution. This study explores the complexities of, and intra-community disagreements about, Kanak villagers’ decisions about whether to trust information provided by, or seemingly in support of, a multinational mining project in southern New Caledonia (South Pacific). An indigenous protest group challenged the company’s claims that the construction and operation of a refinery would have no harmful effects on local ecosystems. The company construed this opposition as stemming from fear based in ignorance, to which the solution lay in the provision of technical information. However, villagers disagreed as to whether this information was reliable. Meanwhile, many project employees joined the protest group. I argue that this seeming irony may be explained by examining the role of affiliation - defined here as a sense of solidarity with a group, and the desire to maintain that relationship - in establishing trust. Culturally-informed expectations of long-term social relationships and the reciprocal power these entailed, and concerns about long-term economic security, played a large role in determining which affiliations people chose to privilege, which in turn influenced which “scientific” information they chose to trust. Ultimately, I argue for the usefulness of a deeper understanding of relationships between trust, affiliation, and expectations of long-term social and economic relations in analyzing lay persons’ evaluations of science.