Petrography and geochemistry of Carboniferous coal seams in the Donets Basin (Ukraine): implications for paleoecology

The Carboniferous succession in the Donets Basin hosts about 130 seams, each with a thickness over 0.45 m. Nine economically important seams from the (south)western Donets Basin are studied using organic petrographical, inorganic geochemical, and organic geochemical techniques. The main aim of the study is the reconstruction of peat facies of Serpukhovian (Mississippian) and Moscovian (Middle Pennsylvanian) coals.Formation of major coal seams commenced during Serpukhovian times. Early Serpukhovian coal accumulated in a relatively narrow shore-zone and is rich in inertinite and liptinite. Very low ash yields, low to moderate sulphur contents, and upward increasing inertinite contents suggest coal deposition in raised mires.Moscovian coal has a significantly wider lateral extension and is generally rich in vitrinite. Coal properties vary widely in response to different peat facies. Low-sulphur, low-ash k₇ coal was formed in a raised mire or in a low-lying mire without detrital input. l₁ and l₃ seams containing several fluvial partings were formed in low-lying mires. Both seams are more than 2 m thick. Seams m₂ and m₃ contain high-sulphur coal, a consequence of deposition in a peat with marine influence. In contrast, syngenetic sulphur content is low in the m₅^{1 upper} seam, which was formed in a lacustrine setting. The late Moscovian n₁ seam, up to 2.4 m thick, accumulated in a swamp with a vegetation rich in bryophytes and pteridophytes. The properties of the n₁ seam are transitional between those of Serpukhovian and other Moscovian seams. Differences in maceral composition between Serpukhovian and Moscovian coals probably reflect changes in climate and vegetation type.Tuff layers are observed in the l₁, l₃, and m₃ seams. The l₃ and m₃ seams contain abundant authigenic quartz. Trace element contents are high in many seams. As contents are especially high in seams c₁₀², k₇, l₃ and m₃. Ash in the l₃ seam contains up to 8000 ppm As. Co is enriched near the base of several seams. Maxima up to 2400 ppm occur in the ash of the k₇ and l₃ seams. Cd contents in ash are frequently as high as 30 or 40 ppm.     

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A red algal bloom in the aftermath of the Marinoan Snowball Earth

Organic matter from the cap dolostones overlying the Marinoan‐age glacigenic diamictites of the Araras Group, Amazon craton, has been studied to reconstruct the post‐glacial ecosystem. Molecular fossils indicate that the post‐Marinoan ecosystem was marked by an apparent decline in marine algal diversity. The proliferation of red algae may be explained by environmental changes, such as a massive nutrient input accompanying continental weathering after the ice thaw and a dimer light penetrating sea water due to the drowning of the platform. In addition, the presence of green sulphur bacteria indicates that sea water was stratified with an anoxic (possibly euxinic, i.e. sulphidic) layer at the water–sediment interface. Sulphur cycling probably occurred at the redox boundary as suggested by the recognition of active sulphate reduction. This observation supports a microbially induced model for the formation of the cap dolostones.     

Modelling diatom responses to climate induced fluctuations in the moisture balance in continental Antarctic lakes

The water chemistry of lake systems on the edge of the Antarctic continent responds quickly to changes in the moisture balance. This is expressed as increasing salinity and decreasing lake water level during dry periods, and the opposite during wet periods. The diatom composition of the lakes also changes with these fluctuations in salinity and lake water depth. This is important, as their siliceous remains become incorporated into lake sediments and can provide long-term records of past salinity using transfer functions. In order to develop transfer functions, diatoms and water chemistry data were inter-calibrated from five different East Antarctic oases, namely the Larsemann Hills, the Bølingen Islands, the Vestfold Hills, the Rauer Islands and the Windmill Islands. Results indicate that salinity is the most important environmental variable explaining the variance in the diatom flora in East Antarctic lakes. In oligo- saline lakes the variance is mainly explained by lake water depth. This dataset was used to construct a weighted averaging transfer function for salinity in order to infer historical changes in the moisture balance. This model has a jack-knifed r² of 0.83 and a RMSEP of 0.31. The disadvantage of this transfer function is that salinity changes in oligo-saline lakes are reconstructed inaccurately due to the edge effect and due to the low species turnover along the salinity gradient at its lower end. In order to infer changes in the moisture balance in these lakes, a second transfer function using weighted averaging partial least squares (with two components) for depth was constructed. This model has a jack-knifed r² of 0.76 and a RMSEP of 0.22. Both transfer functions can be used to infer climate driven changes in the moisture balance in lake sediment cores from oligo-, hypo-, meso- and hyper-saline lakes in East Antarctic oases between 102–75°E. The transfer function for lake water depth is promising to track trends in the moisture balance of small freshwater lakes, where changes in shallow and deep-water sediments are readily reflected in changing diatom composition.     

Recent rapid salinity rise in three East Antarctic lakes

Research in East Antarctica has shown several recent environmental changes that may be linked to human impacts on climate. In order to detect the influence and context of these changes on coastal aquatic ecosystems we examined lake sediment cores from three lakes in the Windmill Islands, East Antarctica; Beall Lake, Holl Lake and ȁ8Lake Mȁ9. Cores were sectioned at␣2.5 mm intervals. Their diatom species composition was examined to detect changes in lake salinity using a diatom-salinity transfer function, and their algal pigment content was examined to detect photoautotrophic community responses to environmental change. Results showed that Holl Lake originated in a depression exposed by Holocene recession of the continental ice sheet and that Beall Lake and Lake M originated as isolated marine basins formed by changes in relative sea level. A general late Holocene trend of declining lake salinity was evident in all three lakes, interrupted by one short-term high salinity event in Beall Lake. This is consistent with a long-term positive moisture balance. This general decline in salinity has been followed by a remarkable recent rapid increase in salinity in all three lakes in the last few decades. We speculate that this rapid increase in salinity might be linked to changes taking place in the region including feedbacks resulting from decreasing sea ice extent as recorded in the nearby Law Dome ice core, and positive feedbacks in the catchments whereby reduced snow cover has led to decreased albedo, which in turn has caused increased evaporation and sublimation. Collectively these changes have shifted the lakes across a threshold from positive to negative moisture balance. A minor, but not rapid shift in the abundance of diatom pigments relative to pigments from green algae and cyanobacteria was also detected suggesting that some changes in photoautotrophic community composition have occurred. Measurements of modern nutrient levels are also higher than would be expected in Beall Lake and Holl Lake, given the extremely low sediment accumulation rates. This may be associated with a c. 300% increase in the population of Adélie penguins in the Windmill Islands recorded since the 1950s, or may a first signs of a rapid increase in catchment development and associated lake productivity as experienced in Antarctic and Arctic lakes subject to recent rapid regional warming. The most marked feature of the records is the rapid increase in salinity in all three lakes in␣the last few decades, which has occurred in lakes both with and without resident penguin populations.Dominic A. Hodgson and Donna Roberts contributed equally to this work     

Ecological primordialism: the human–environment nexus in Soqotra

This article depicts the initial human–environmental relations that prevailed during the pre-modern period of Soqotra’s history prior to its incorporation into a state-led modernization process and its subsequent enclosure within a United Nations-designed conservation zoning plan and ecotourism economy. The term ecological primordialism is coined to highlight the primacy of the environment as the enabling and constraining context for the constitution of the Soqotran community. It entails a symbiotic relationship between an ecosystem and a human social system, which structured the contingent relations between the raw materials for livelihood making and community formation: people, resources and space. The article elucidates how Soqotrans managed this mostly constraining human–environment nexus through a series of adaptive practices: their taxonomic appropriation and practical domestication of the island’s environmental resources; their transformation of the landscape into a domain of livelihood; their organization of dispersed settlements into a socio-political unit; their demarcation of the island into geographical zones of cultural differentiation; and their establishment of mutual aid institutions that simultaneously regulated resource use while integrating all islanders into relations of social kinship. The article concludes with a cautionary tale about the use of anachronistic human–environment relations as the basis of conservation policy.     

Planktonic diatom communities in temperate South-Central Chilean lakes with a focus on Asterionella formosa and the genus Aulacoseira

Journal of Paleolimnology - Paleolimnological records from temperate South-Central Chilean lakes revealed a recent and marked increase in the relative abundances of the key-planktonic diatom...     

Anhydrite–gypsum transition in the argillites of flooded salt workings in eastern France

This study aims at understanding the physico-chemical interactions between the saturated brine and the rocks enclosing the underground salt workings in Lorraine (eastern France). These anhydrite-rich and argillaceous rocks were characterized in terms of mineralogy, micro-texture and connected porosity. Then, the two main lithofacies, massive anhydrite and anhydrite-rich argillite, were immersed in brine during more than 1 year. During this batch experiment, the argillites were affected by macroscopic splitting, contrarily to the massive anhydrite. Micro-texture and brine chemical analyses clearly show the swelling due to the hydration of anhydrite into gypsum inside the argillites, whereas hydration occurs superficially on the massive anhydrite, due to its very low permeability. Anhydrite–gypsum transformation is promoted by the presence of dissolved strontium and potassium in saturated brine. The low activity of water in saturated brine does not allow the clay fraction to swell significantly during the experiment. Thus, the expansion resulting from the hydration of anhydrite into gypsum might be responsible of the splitting of argillite in a saturated brine environment. The superficial anhydrite hydration on massive anhydrite can be explained by the low amount of connected porosity (less than 1%).