Alteration of abyssal peridotites is a major sink in the W geochemical cycle

Arc lavas and the continental crust exhibit a selective enrichment of W relative to similarly incompatible elements, indicating that subduction zone environments are a tectonic setting where W is mobilized from the subducting slab. Here we present evidence that ultramafic portions of altered oceanic lithosphere are a major sink for W and evaluate how its W budget needs to be included in constraining the global geochemical cycle of W. We report high precision W, HFSE and U-Th data obtained by isotope dilution for altered basement formed at super-slow spreading rates along the Mid-Atlantic Ridge drilled during ODP Leg 209 (between 14 degrees N and 16 degrees N). The oceanic basement consists of abyssal peridotites and associated gabbroic rocks exhumed in a magma starved setting. Hydrothermal alteration styles covered in the sample set are serpentinization, talc alteration, and low-T seawater alteration. The drilled rock portions are among the most depleted in HFSE that have ever been studied. Tungsten concentrations range from 4 ppb in the least altered harzburgites to 500 ppb in strongly serpentinized dunites. Locally, W is significantly enriched relative to U, Th and Ta by factors of up to 100 compared to canonical mantle values, much higher than in mafic portions of altered oceanic crust such as hole 1256D (up to 10). The samples from ODP Leg 209 show strong W enrichment during progressive serpentinization (holes 1268A, 1270 and 1271) and during late-stage oxidative seawater alteration (hole 1270D and 1272A). In contrast, silica metasomatism associated with talc alteration (hole 1268A) is associated with selective W depletion relative to Th and Ta. Trace element modelling indicates that hydrothermal enrichment of W by redistribution is a more likely source than seawater-derived W. Collectively, our data show that altered ultramafic rocks likely constitute an important geochemical reservoir in the global geochemical cycle of W contributing to the enrichment of W found in arc lavas and to the recycling of W into the Earth's mantle. (C) 2022 Elsevier Ltd. All rights reserved

Environmental change in the Early Permian of NE Svalbard : from a warm-water carbonate platform (Gipshuken Formation) to a temperate, mixed siliciclastic-carbonate ramp (Kapp Starostin Formation)

A detailed facies study of Early Permian strata within NE Svalbard reveals a fundamental change of the depositional setting, from a restricted-marine, warm-water carbonate platform to an open-marine, temperate-water, mixed siliciclastic-carbonate ramp. The uppermost strata of the Gipshuken Formation (Templet and Sørfonna members; Sakmarian–early Artinskian?) consist of microbialites (algal mats), mudstones, bioclastic/peloidal limestones, carbonate breccias and Microcodium facies reflecting peritidal platform areas and supratidal sabkhas. A mixed heterozoan/reduced photozoan assemblage indicates temperate-water conditions within neighboring deeper, open-marine mid-platform areas, while warm-water conditions still prevailed within inner platform zones. In contrast, the lowermost strata of the overlying Kapp Starostin Formation (Vøringen Member; late Artinskian?–Kungurian) show a fully heterozoan biotic assemblage reflecting temperate water conditions within open-marine, storm-dominated, nearshore to transitional offshore areas of a mixed carbonate-siliciclastic ramp. The Vøringen Member comprises three facies associations, which form a shallowing-upward sequence subsequent to an initial transgression. The sediments reflect bryozoan bioherms in most distal areas, followed by stacked tempestites of sandy brachiopodal shell banks and Skolithos piperocks, grading into broad sand flats in most proximal areas of the inner ramp. The above environmental change is regarded as a regional event taken place across the entire shelf along the northern margin of Pangea and is attributed to paleoclimatic, paleoceanographic, as well as paleogeographic changes, possibly related to the overall northwards drift of the supercontinent. An abrupt increase in terrigenous input coinciding with this change is ascribed to the uplift of a new local source area, probably to the north or east of the investigation area

A peroxidase from Lepista irina cleaves beta,beta-carotene to flavor compounds

Extracellular liquid of the edible fungus Lepista irina was found to effectively degrade beta,beta-carotene. beta-Ionone, beta-cyclocitral, dihydroactinidiolide, and 2-hydroxy-2,6,6-trimethylcyclohexanone were formed as volatile breakdown products of beta,beta-carotene with myceliumfree culture supernatants, whereas beta-apo 10'-carotenal was identified as nonvolatile degradation product. The key enzyme catalyzing the oxidative cleavage of beta,beta-carotene was purified with an overall yield of 63% and a purification factor of 43. Biochemical characterization showed a molecular mass of 50.5 kDa and an isoelectric point of 3.75. Fastest beta,beta carotene degradation occurred at 34degreesC and pH values between 3.5 and 4. Degenerate oligonucleotides were derived from Nterminal and internal amino acid sequences. By means of PCRbased cDNAlibrary screening a 1284 bp cDNA was identified which showed great overall similarity to Pleurotus eryngii polyvalent peroxidases. The obtained sequence contains an open reading frame of 1083 nucleotides, encoding a polypeptide of 361 amino acids. A 30 amino acid signal peptide was identified upstream of the Nterminal sequence of the mature enzyme. The L. irina versatile peroxidase represents the first microbial enzyme capable of carotenoid degradation that has been characterized on a molecular level, proving the participation of extracellular enzymes of white rot fungi in biotic carotenoid degradation processes