Hydrothermal dedolomitisation of carbonate rocks of the Paleoproterozoic Zaonega Formation, NW Russia — Implications for the preservation of primary C isotope signals

This study was supported by Estonian Science Agency project PUT696 and PRG447, and Estonian Centre of Analytical Chemistry. K.P. and A.L. were supported by the Research Council of Norway through its Centres of Excellence funding scheme grant No. 223259.The Paleoproterozoic Zaonega Formation in Karelia, NW Russia, has played a key role in understanding the environmental conditions postdating the Great Oxidation and Lomagundi-Jatuli Events. Its carbonate- and organic-rich rocks (shungite) define the postulated Shunga Event representing an accumulation of very organic-rich sediments at c. 2 Ga and are central in ideas about changing ocean-atmosphere composition in the wake of those worldwide biogeochemical phenomena. Our work focussed on a key interval of carbonate rocks in the upper part of the Formation to: (i) obtain new high-resolution carbon, oxygen and strontium isotope data complemented by detailed petrography and mineralogical characterisation and (ii) expand upon previous studies by using our data to constrain geochemical modelling and show in greater detail how magmatic hydrothermal fluids induced dedolomitisation and altered geochemical signals. Our findings show that the δ13Ccarb of calcite-rich intervals are the most altered, with values between −16.9 to 0.6‰, whereas the dolomite-dominated parts retain the best-preserved (i.e. most original) values. Those define a trend of steadily increasing δ13Ccarb, from −6 to +0.5‰, which we interpret as a return to normal marine conditions and carbonate‑carbon values following the Lomagundi-Jatuli Event.PostprintPeer reviewe

Hydrothermal dedolomitisation of carbonate rocks of the Paleoproterozoic Zaonega Formation, NW Russia — Implications for the preservation of primary C isotope signals

The Paleoproterozoic Zaonega Formation in Karelia, NW Russia, has played a key role in understanding the environmental conditions postdating the Great Oxidation and Lomagundi-Jatuli Events. Its carbonate- and organic-rich rocks (shungite) define the postulated Shunga Event representing an accumulation of very organic-rich sediments at c. 2 Ga and are central in ideas about changing ocean-atmosphere composition in the wake of those worldwide biogeochemical phenomena. Our work focussed on a key interval of carbonate rocks in the upper part of the Formation to: (i) obtain new high-resolution carbon, oxygen and strontium isotope data complemented by detailed petrography and mineralogical characterisation and (ii) expand upon previous studies by using our data to constrain geochemical modelling and show in greater detail how magmatic hydrothermal fluids induced dedolomitisation and altered geochemical signals. Our findings show that the δ13Ccarb of calcite-rich intervals are the most altered, with values between −16.9 to 0.6‰, whereas the dolomite-dominated parts retain the best-preserved (i.e. most original) values. Those define a trend of steadily increasing δ13Ccarb, from −6 to +0.5‰, which we interpret as a return to normal marine conditions and carbonate‑carbon values following the Lomagundi-Jatuli Event

Minimally invasive direct coronary artery bypass surgery under high thoracic epidural.

This report describes the use of high-thoracic epidural anesthesia for a patient undergoing minimally invasive direct coronary artery bypass

Exploring Different Synthesis Parameters for the Preparation of Metal Nitrogen Carbon Type Oxygen Reduction Catalysts

The influence of various synthesis conditions of a metal nitrogen carbon M N C catalyst material on oxygen reduction reaction ORR kinetics is discussed. Seven M N C catalysts based on cobalt are obtained by changing various synthesis conditions, such as the mixing environment, pyrolysis gas, and post treatment. The ORR activity and stability measurements are performed using the classical three electrode configuration in a 0.1 M HClO4 solution. The most active and stable ORR catalyst proves to be the material obtained by mixing a cobalt salt, 2,2 bipyridine, and a high surface area silicon carbide derived carbon together in water and pyrolyzing the mixture in argon. In a fuel cell test, however, a maximum power density value of 135 mW cm amp; 8722;2 is achieved with the catalyst mixed together in a planetary ball mill at a low catalyst loading of 1.0 0.1 mg cm amp; 8722;2 and at a test cell temperature of 60 oC despite of the fact that preparing the catalyst via dry ball milling reduces the surface area of the material roughly 40 more than in the case of using a solution based method. Consequently, mixing the catalyst precursors together without any additional chemicals in a planetary ball mill instead of in a solution appears to be the most promising choic

The anti SARS-CoV-2 activity of nanofibrous filter materials activated with metal clusters

Nanofibrous filter materials were prepared by electrospinning a solution of 28 wt% poly(vinylidene fluoride) in N,N-dimethylacetamide with and without the addition of 2 wt% AgNO3, Cu(NO3)2·2.5H2O or ZnCl2. X-ray diffraction, scanning electron microscopy with energy dispersive X-ray spectroscopy, inductively coupled plasma mass spectroscopy, thermogravimetric analysis, contact angle measurement, nitrogen sorption, and mercury intrusion porosimetry methods were used for the characterization of physical structure as well as the chemical composition of the electrospun materials. Particle filtration efficiency and antiviral activity against the SARS-CoV-2 alpha variant were tested in order to estimate the suitability of the prepared electrospun filter materials for application as indoor air filtration systems with virucidal properties. All filter materials prepared with salts demonstrated very high particle filtration efficiency (≥98.0%). The best antiviral activity was demonstrated by a material containing Cu(NO3)2·2.5H2O in the spinning solution, which displayed the decrease in the number of infectious virions by three orders of magnitude after a contact time of 12 h. Materials with the addition of AgNO3 and ZnCl2 decreased the number of infectious virions after the same contact time by only ∼8 and ∼11 times, respectively

Two-billion-year-old evaporites capture Earth’s great oxidation

Major changes in atmospheric and ocean chemistry occurred in the Paleoproterozoic Era (2.5–1.6 billion years ago). Increasing oxidation dramatically changed Earth’s surface, but few quantitative constraints exist on this important transition. This study describes the sedimentology, mineralogy, and geochemistry of a two-billion-year-old and ~800 m-thick evaporite succession from the Onega Basin in Russian Karelia. The deposit consists of a basal unit dominated by halite (~100 m) followed by anhydrite-magnesite (~500 m) and dolomite-magnesite (~200 m) dominated units. The evaporite minerals provide a robust constraint that marine sulfate concentrations were at least 10 mmol/kg, representing an oxidant reservoir equivalent to over 20% of the modern ocean-atmosphere oxidizing capacity. These results show that substantial amounts of surface oxidant accumulated during this critical transition in Earth’s oxygenation