Cambrian sedimentary basins recorded the initial break-up of northern Gondwana

 

 

 

 

 

Diachronous opening of the Rheic Ocean and separation of Avalonian–Cadomian terranes from Gondwana was a major, but still poorly understood paleogeographic event in the late Ediacaran to early Cambrian. A recent study from the Příbram–Jince basin in the Bohemian Massif revealed a significant provenance and paleocurrent changes in response to dextral transtension that enlarged the basin into a pull-apart structure, suggesting that strike-slip movements along the former Avalonian–Cadomian belt controlled the diachronous opening of the Rheic Ocean. Putting this piece of information into a plate-tectonic picture, it seems that an inherited suture in the Avalonian ribbon terrane facilitated complete rifting and rift–drift transition while the Cadomian terranes, including those now forming the Bohemian Massif, remained attached to Gondwana during this large-scale rifting event.

Syahputra R., Žák J., Nance R.D. (2021): Cambrian sedimentary basins of northern Gondwana as geodynamic markers of incipient opening of the Rheic Ocean. Gondwana Research 105, 492-513. (DOI)

Cobalt recovery from Zambian slags

Cobalt is one of the most important critical metals which could be potentially extracted from the old metallurgical slags in the Zambian Copperbelt. The slags from Luanshya, the oldest mining and smelting site in the Copperbelt, contain up to 5990 ppm Co (median: 2370 ppm). The detailed mineralogical investigation combined with the sulfuric acid leaching simulating hydrometallurgical recovery indicated that up to 67% of Co can be extracted from slag in a short period of time (24 h). However, despite the dramatic increase of Co prices on the global market, its recovery from the Luanshya slags appears to be non-economical due to the high costs of the mechanical and chemical processing of the slag materials. The paper is freely available via open access:

Ettler V., Mihaljevič M., Drahota P., Kříbek B., Nyambe I., Vaněk A., Penížek V., Sracek O., Natherová V. (2022): Cobalt-bearing copper slags from Luanshya (Zambian Copperbelt): Mineralogy, geochemistry, and potential recovery of critical metals. Journal of Geochemical Exploration 237, 106987. (DOI)

Do forest fires alter the Pb isotopic composition of topsoils?

We compared analogous healthy topsoils and ones burned by fires of different temperatures for their elemental and isotopic Pb content. The fires only affected the top 5 cm of the soil. We found that soils affected by low-temperature fires had increased Pb compared to healthy soils. The accumulation of Pb was not observed in the soils exposed to higher temperatures. The same results were found in ash. Lead isotopic ratios were affected by the fires. These increased in soils affected by higher temperatures but didn’t change with the low temperatures. We proposed that the temperature dependence is due to anthropogenic Pb (206Pb/207Pb < 1.16) volatilizing at lower temperatures than geogenic Pb (206Pb/207Pb > 1.19). This work suggests that it may be possible to determine the temperature of a forest fire from the Pb isotopic signatures of the burned materials.

Baieta R., Vieira A.M.D, Vaňková M., Mihaljevič M. (2022). Effects of forest fires on soil lead elemental contents and isotopic ratios. Geoderma 414, 115760. (DOI)

Raman spectroscopic search for scytonemin and gloeocapsin in endolithic colonizations in large gypsum crystals

New paper reports groundbreaking findings on the distribution of non-carotenoid pigments in gypsum endoliths. In the study, Raman microspectrometry was used for analysis of UV-protective pigments of dark-pigmented endolithic colonizations in gypsum outcrops from Sicily, Poland and Israel. Colonized samples were investigated using 445-, 532- and 780-nm excitation lasers. Scytonemin and gloeocapsin were detected at all studied sites. Major Raman signatures of scytonemin were detected at 1593, 1552, 1438 and 1173 cm−1. Gloeocapsin shows characteristic Raman bands similar to anthraquinone-based parietin of lichens: at 1665, 1575, 1378, 1310 and 465 cm−1. Scytonemin and gloeocapsin are highly specific for cyanobacteria and can be thus used as biomarkers for certain taxa of cyanobacteria in geobiological and astrobiological studies. Detection of such pigments by Raman spectroscopy combining three excitation wavelengths allows gathering more information about the composition of endolithic consortia in their natural habitats using fast and non-invasive methods.

Němečková K., Culka A., Němec I., Edwards H. G. M., Mareš J., Jehlička J. (2021): Raman spectroscopic search for scytonemin and gloeocapsin in endolithic colonizations in large gypsum crystals. Journal of Raman Spectroscopy 52, 2633. (DOI)

Accelerated disintegration of in situ disconnected portions of sandstone outcrops

The article presents a new look on sandstone weathering/recession characterized by rapid disintegration of portions of the rock massif which are no longer physically connected with the main rock mass, though still in situ. A set of field and laboratory measurements testing mechanical and hydraulic properties of the rock were applied to compare the disconnected portions with those of the surrounding rock mass. Also, physical weathering experiments were performed to characterize the effect of confinement on the breakdown rate of several sandstone samples. The surfaces of disconnection follow bedding planes, planar elements of other sedimentary structures, subhorizontal fractures and stress shadows on subvertical cliff faces. Weathered surfaces of the disconnected portions show noticeably impaired mechanical properties, a faster capillary water absorption and a higher surface moisture compared to the much less weathered surfaces of the surrounding rock mass. Physical experiments demonstrated that a confinement by the surrounding rock mass may considerably delay the loosening of rock during weathering. The much faster disintegration rates of the disconnected portions of rock compared to their surroundings are explained by the fact that they are not confined and have a larger surface area.The recession rates of sandstone surfaces with disconnected portions are highly variable both in space and time and their genesis is demonstrated by two suggested conceptual models.

Filippi M., Slavík M., Bruthans J., Weiss T., Řihošek J. (2021): Accelerated disintegration of in situ disconnected portions of sandstone outcrops. Geomorphology 391, 107897. (DOI)

Late Archean analogy to modern accretionary plate margins, an example from Superior Province, Canada

New paper recently published in Precambrian Research examines an illustrative example of a Late Archean granitic pluton emplaced along a major tectonic boundary in the Superior Province, northeastern Québec, Canada. To characterize the syn-magmatic strain patterns, we integrate structural and kinematic analysis with anisotropy of magnetic susceptibility (AMS) and numerical modeling of fabric development in response to strain increments. This dataset allowed us to set-up a general geological model that discusses the significance of pluton fabrics, interfering intrusive and tectonic strains, and finally also on evaluating various scenarios for the Late Archean assembly of the Superior Province.

Žák J., Tomek F., Svojtka M., Vacek F., Kachlík V., Ackerman L., Ježek J., Petronis, M.S. (2021): Distributed crustal shortening followed by transpressional shearing in the Superior Province, northeastern Canada: a Late Archean analogy to modern accretionary plate margins? Precambrian Research 362, 106322. (DOI)

Metal(loid)s remobilization from contaminated soils during experimental wildfires

The temperature-dependent releases of metal(loid)s (As, Cd, Cu, Pb, Zn) from biomass-rich savanna soils collected near a Cu smelter in Namibia have been studied under simulated wildfire conditions. For this purpose, new wildfire-simulating setups were introduced. Laboratory single-step combustion experiments (250–850 °C) and experiments with a continuous temperature increase and online ICP-OES detection (25–750 °C) were coupled with mineralogical investigations of the soils, ashes, and aerosols. The results indicate that metals are dominantly concentrating in the ash residue, and part of As is remobilized depending on temperature. Therefore, the active and abandoned mining and smelting sites, especially those highly enriched in As, should be protected against wildfires, which can be responsible for substantial As re-emissions.

Tuhý M., Ettler V., Rohovec J., Matoušková Š., Mihaljevič M., Kříbek B., Mapani B. (2021):  Metal(loid)s remobilization and mineralogical transformations in smelter-polluted savanna soils under simulated wildfire conditions. Journal of Environmental Management 293, 112899. (DOI)

Looking at a Pb–Zn mining/smelting site in Kabwe (Zambia) using tree rings

We used pine tree rings and soil geochemistry to expose the activity of a Pb-Zn smelter in Kabwe, Zambia. We found that local soils are extremely contaminated (up to 16000 mg/kg Pb; 14000 mg/kg Zn; 600 mg/kg Cu in the topsoil). Also, metal bearing particles share their Pb isotopic signature with smelting by-products, and more concerning, metals in tree biomass. We concluded that these metals enter the tree though the bark and leaves, not the roots, implying airborne contamination. Using Pb and C isotopes we mapped the dendrochronology of the tree and verified its susceptibility to changes in smelter production throughout the late 20th century.

Baieta R., Mihaljevič M., Ettler V., Vaněk A., Penížek V., Trubač J., Kříbek B., Ježek J., Svoboda M., Sracek O., Nyambe I. (2021): Depicting the historical pollution in a Pb–Zn mining/smelting site in Kabwe (Zambia) using tree rings. Journal of African Earth Sciences 181, 104246. (DOI)

Mobility of As in sulfidic gley soils during drought

We combined selective chemical extractions and S isotopes to examine the mobility of As and trace metals (Co, Cu, Ni) in two Czech wetland soils enriched in authigenic Fe-As sulfide minerals through the drying process. We found that As and trace metals released via oxidation of the sulfide phases (particularly Fe sulfides) were almost entirely sequestered by Fe(III) (oxyhydr)oxides, but concomitant acidification resulted in the pH-dependent release of the As(III) and trace metals. Although our results documented the relatively low As mobilization potential under relatively short droughts (several weeks), the preservation of the anoxic conditions must be regarded as a fundamental management strategy of these and other sulfidic wetlands enriched in As.

Drahota P., Peřestá M., Trubač J., Mihaljevič M., Vaněk A. (2021): Arsenic fractionation and mobility in sulfidic wetland soils during experimental drying. Chemosphere 277, 130306. (DOI)

Invasion to Carboniferous lakes makes horseshoe crabs look like babies

Today’s horseshoe crabs are often described as living fossils, mostly for their early appearance in the fossil record and their supposedly conservative morphologies. Nevertheless, after a careful investigation, one can find even peculiar species among this group of spider’s close relatives. Indeed, the recent marine representatives of horseshoe crabs (three genera, four species) are all members of one surviving clade called Limulidae. Deep in the past, during the Paleozoic and Mesozoic, some horseshoe crabs evolved into quite different morphologies and explored various environments. One group called Belinuridae comprises mostly late Paleozoic species that explored freshwater habitats. Lustri, Laibl and Bicknell, in their paper published recently in PeerJ (Lustri et al. 2021), redescribe small (about 3 cm long) and morphologically simple belinurid Prolimulus woodwardi. This species has been originally described by Antonín Frič, back in 1899, from the famous sapropelic coal of the Plzeň Basin. Based on numerous well-preserved specimens, the authors describe and clarify the species morphology, including such details as opercula and chelicerae. Phylogenetic analysis shows that Prolimulus is, together with some other morphologically similar genera, a member of highly paedomorphic (i.e., resembling juvenile stages of others closely related taxa) ingroup within Belinuridae. This discovery is further corroborated by morphometric results and by the fact that there are epibionts attached to some Prolimulus specimens. The presence of attaching organisms on the exoskeleton of Prolimulus suggests, that these small specimens are individuals that already stopped or significantly slowed the molting of their exoskeleton. In other words, they are adults that retain juvenile morphology. Such morphological and developmental plasticity, together with a successful exploration of freshwater habitats illustrates the horseshoe crab’s ability to adapt to various environmental conditions in the deep past.

Lustri L., Laibl L., Bicknell R. 2021. A revision of Prolimulus woodwardi Fritsch, 1899 with comparison to other highly paedomorphic belinurids. PeerJ 9, e10980. (DOI)