Successful online meeting of the Center

On Thursday, 19th November 2020, we organized a successful virtual meeting of the Center for Geosphere Dynamics with three lectures given by junior researchers: (1) Valéria Vaškaninová: Revival of our earliest ancestors by means of synchrotron tomography; (2) Jaroslav Hajná: Bohemian Massif records of Neoproterozoic to Lower Paleozoic geodynamic evolution of the northern Gondwanan margin and experimental modelling correlations and (3) Petr Tábořík: Hranice Abyss, the world’s deepest freshwater cave: a new evolutionary model.

Magmatic pulses during orogeny: when and how fast is magma added to the upper crust?

A new paper by Trubač et al. combines geochronologic data with a GIS-based spatial analysis of plutons in the Bohemian Massif, Variscan belt, to examine the magma fluxes and temporal pattern of plutonism during collisional orogeny. The collisional orogens differ from continental margin arcs, where the plutonic material is added in repeating cycles to the upper crust during protracted oceanic subduction. Instead, it was shown that the collisional plutonism reflects a secular thermotectonic evolution of the orogen, where magma sources change from mantle-dominated to intracrustal, paralleled by increasing significance of crustal recycling at the expense of crustal growth. The analysis also suggests that crustal thickening, commonly regarded as the main cause of plutonism in collisional orogens, may be of relatively lower significance than a late-stage mantle delamination.

Trubač J., Žák J., Kondrová L. (2020): Magmatic tempos in large hot orogens in comparison with continental margin arcs. Journal of Geology in press (DOI)

Measurements and calculations of evaporation rate from bare sandstone surfaces

Evaporation from porous rock plays an important role in weathering and biological processes. Despite its importance, evaporation from porous rocks has seen little scientific focus. We present a study on evaporation from bare sandstone, one of the most common rocks affected by weathering. A new method that measures the evaporation rate from the surfaces of sandstone samples under field microclimate was developed and tested. Also, a simple calculation of 1D evaporation rate from bare sandstone surfaces based on Fick’s law of diffusion is presented. The measurement was performed using sandstone cores in a humid continental climate and measured on a roughly monthly interval for about 1 year. For the calculations, a laboratory-measured water-vapour diffusion coefficient of the sandstone, in-situ seasonally measured vaporization plane depth (depth below the surface where liquid water evaporates), and values of air humidity and temperature were used. It was found that the most important factor controlling the evaporation rate was the vaporization plane depth, while seasonal and spatial changes of air humidity and temperature were of lesser importance. The calculated evaporation rate reasonably follows measured values with Pearson correlation coefficient r > 0.81. For its simplicity and the small number of parameters required, the proposed method has the potential to improve knowledge of weathering and living conditions of endolithic and epilithic organisms.

Slavík M., Bruthans J., Weiss T., Schweigstillová J. (2020): Measurements and calculations of seasonal evaporation rate from bare sandstone surfaces: Implications for rock weathering. Earth Surface Processes and Landforms 45, 2965-2981. (DOI)

Hranice Abyss, the Earth’s deepest freshwater cave, is twice as deep

Extremely deep freshwater filled cave systems are common in karst systems globally. The origin and evolution of such caves are usually attributed to hypogenic (bottom‐up) processes, in which acidic groundwater dissolves limestone from below. A combined geophysical survey was applied to improve a subsurface image of semi-buried karst morphology in the close vicinity of Hranice Abyss (HA). Based on the results of electromagnetic surveying (AMT method), suggesting a deep disintegration of the carbonate sequence, a new possible depth of ~0.9 km of HA was estimated. An alternative hypothesis, suggesting predominantly epigenic evolution (top-down process) of the HA evolution, was introduced. Furthermore, an applicability of individual geophysical methods and their combinations has been evaluated on the basis of an integrated interpretation of geophysical data. This research attracted attention of media abroad (Science Magazine, Newsweek, Science Alert) and in the Czech Republic (Seznam, ČT24).

Klanica R., Kadlec J., Tábořík P., Mrlina J., Valenta J., Kováčiková S., Hill G.J. (2020): Hypogenic versus epigenic origin of deep underwater caves illustrated by the Hranice Abyss (Czech Republic) – the world’s deepest freshwater cave. Journal of Geophysical Research: Earth Surface, 125, e2020JF005663. (DOI)

Fast screening of carotenoids in gypsum endoliths

We tested the potential of a portable Raman spectrometer RaPort (G) by EnSpectr with a 532-nm laser for use in field detection of biomarkers of endolithic colonization in gypsum. In this study, variously colored layers were found and screened separately on the outcrop under natural conditions in Sicily where such outcrops are widespread. In the recorded Raman spectra, stretching vibrations of carotenoids were observed— ν1 (C=C) around 1,513 cm-1, and ν2 (C‒C) around 1,154 cm-1, as well as the feature at around 1,005 cm-1. The exact identification of different carotenoids by a portable Raman spectrometer is limited. Nevertheless, the portable Raman spectrometer allowed fast and in situ detection of carotenoids of variously pigmented gypsum endolithic colonization. Application of miniature Raman instruments in the detection of biomarkers in situ conditions is important in the context of forthcoming astrobiological missions to Mars (Exomars and Mars 2020).

Němečková K., Jehlička J., Culka A. (2020): Fast screening of carotenoids of gypsum endoliths using portable Raman spectrometer (Messinian gypsum, Sicily). Journal of Raman Spectroscopy 51, 1127-1136. (DOI)

AutoSEM techniques applied to contaminated soils

Automated mineralogy has been used to quantitatively determine the contaminant partitioning in the soil particulates originating from heavily polluted mining/smelting sites. This method provides faster data acquisition, the full integration of the quantitative EDS data and better detection limits for the elements of interest. AutoSEM was found to be a useful tool for the determination of the modal phase distribution and element partitioning in the metal(loid)-bearing (As, Cu, Pb, Zn) soil particulates and will definitely find more applications in environmental soil sciences in the future.

Tuhý M., Hrstka T., Ettler V., Automated mineralogy for quantification and partitioning of metal(loid)s in particulates from mining/smelting-polluted soils. Environmental Pollution 266: 115118. (DOI) open-access

A new study in Science: the origin of our teeth is among the most primitive jawed fish

In the two extant jawed vertebrate groups, bony fish (and their descendants the land animals) and sharks, new teeth usually develop on the inner side of the old ones. Sharks have no bones and their teeth do not attach to the cartilaginous jaws, whereas in bony fish and land animals, the teeth are always attached to jaw bones. This diversity raises many questions about the origin of teeth. Until now, researchers have focused on fossils of a group of armoured fish,  the arthrodires, the only stem jawed vertebrates in which teeth were known. They struggled to understand how they could have evolved into the teeth of modern vertebrates, as arthrodire teeth are so different in position and mode of tooth addition.

A team of scientists from the Charles University, Uppsala University, the European synchrotron ESRF in Grenoble, Natural History Museum in London, and the National Museum in Prague (Valéria Vaškaninová as a lead author) turned to the acanthothoracids, an early fish group closely related to the common ancestor of jawed vertebrates. The very finest of them come from the Prague Basin, but due to their fragility they have never been investigated in detail. The researchers used synchrotron microtomography at the European synchrotron, the world’s brightest X-ray source, which allowed them to visualise the internal structure of the fossils in 3D, including unexpected well-preserved dentitions. Follow-up scans at higher resolution visualized the growth pattern and perfectly preserved cell spaces inside the dentine.

Like arthrodires, the acanthothoracid dentitions are attached to bones. This indicates that bony fish and land animals retain the ancestral condition, whereas sharks are specialized. In other ways, acanthothoracid dentitions are fundamentally different from those of arthrodires. Like sharks, bony fish and land animals, acanthothoracids only added new teeth on the inside. Even though acanthothoracids are among the most primitive of all jawed vertebrates, their teeth are far more like modern ones than arthrodire dentitions. Their jawbones resemble those of bony fish and seem to be directly ancestral to our own.

Vaškaninová V., Chen D., Tafforeau P., Johanson Z., Ekrt B., Blom, H., Ahlberg P.E. (2020): Marginal dentition and multiple dermal jawbones as the ancestral condition of jawed vertebrates. Science 369, 211-216. (DOI)

Handheld Raman spectrometer helps to identify sulfates in mining areas of Iberian Pyrite Belt

The São Domingos area (Corte do Pinto, Portugal) represents a large sulfide ore deposit in the Iberian Pyrite Belt that was mined primarily for copper and sulfur in the past. The deserted mine and mine wastes are the reason for the production of acid mining drainage, giving rise to abundant efflorescence and crusts of secondary sulfates. Metastable sulfates may temporary sink various pollutants, therefore a quick and reliable method is required for the in situ monitoring of their distribution directly in the field. In this work, we tested a handheld Raman spectrometer equipped with a 532 nm laser excitation for this task. Sulfate crusts and aggregates of the complex composition and various colors were analyzed using this particular spectrometer in the field. Additionally, the collected samples were also investigated through laboratory-based Raman spectroscopy and X-ray diffraction. A suite of hydrated Fe-, Cu-, Mg-, and Al-bearing sulfates and elemental sulfur was detected in the complex mixtures by the handheld instrument which was subsequently confirmed by the laboratory methods. The results show that handheld Raman spectrometers can often provide spectral data at a reasonable quality level fully complementary to laboratory-based methods. Therefore, such systems can be deployed for the monitoring of distribution of secondary sulfates and other minerals in post-mining areas.

Košek F., Culka A., Fornasini L., Vandenabeele P., Rousaki A., Mirao J., Bersani D., Candeias A., Jehlička J. (2020): Application of a handheld Raman spectrometer for the screening of colored secondary sulfates in abandoned mining areas – the case of São Domingos Mine (Iberian Pyrite Belt). Journal of Raman Spectroscopy 51, 1186-1199. (DOI)

Can we compare exceptionally preserved fossils to understand their evolution?

Exceptionally preserved fossils provide deep insight into early animal evolution. For example, the step by step evolution of morphological innovations that ultimately led to the origin of many recent animals was achieved using information from such exceptionally preserved fossils. Each of these sites with exceptional preservation – so-called Lagerstätten – is, however, a subject of specific fossilization bias. This means that at different fossil sites different information is lost during the fossilization process. To understand such information loss is especially important once we want to compare fossils from different sites and infer some general trends. Without knowing fossilization biases, we may end-up comparing apples and oranges. A new study by Saleh et al. (Lukáš Laibl as a co-author) tried to understand such biases. It compared three well known lower Paleozoic Lagerstätten – the Burgess Shale (ca. 505 million years old, Canada), the Chengjiang Biota (ca. 530 million years old, China) and the Fezouata Shale (ca. 479-478 million years old, Morocco). Interestingly, the Fezouata Shale is different from both Burgess and Changjiang. In Fezouata Shale, the soft parts of animals are most commonly associated with partially mineralized and sclerotized tissues. The digestive tract is, for example, preserved mostly in fossils with hard biomineralized exoskeletons (such as in trilobites and echinoderms). For the same reason, the entire soft animals are not preserved in Fezouata Shale. Indeed, most of the animals from Fezouata Shale were either biomineralized (trilobites, echinoderms, gastropods, brachiopods), sclerotized (many types of arthropods) or have had at least external cuticle (various “worms”). On the other hand, Burgess and Changjiang commonly preserve entirely soft animals and also show a higher diversity of different tissue types in particular fossil species. So to sum up, the answer to the question in the title is – yes, but with caution. We have to differentiate between fossilization absence and real absence. Many animals could have lived in the Fezouata Shale environment but were nor preserved because of the nature of the fossilization process. This is likely the case for early chordates that were entirely soft-bodied. On the other hand, the absence of penis worms (priapulids) in the Fezouata Shale is most probably a real aspect of the fauna, since these cuticle-bearing animals would “survive” the fossilization process.

Saleh F., Antcliffe J.B., Lefebvre B., Pitteta B., Laibl L., Peris F.P., Lustri L., Gueriau P., Daley A.C. (2020): Taphonomic bias in exceptionally preserved biotas. Earth and Planetary Science Letters 529, 115873 (DOI)

Zircon ages reveal dynamics of accretionary wedges

The detrital zircon geochronology has been increasingly used to analyze accretionary wedges over the past decade. A new study by Jiří Žák and others, stemming from collaboration of the Center with the Czech Academy of Sciences, explores the exciting potential of this method, with the key outcome being introduction of a new concept of the Age–Distance Curves (ADCs). The analysis of age variations across accretionary wedges may reveal a wealth of information on a variety of dynamic processes that occur above subduction zones: linear ADCs may track continuous accretion whereas variably sloping ADCs may reflect tectonic erosion, increase in the rate of deposition and accretion, or tectonic duplication; stepped ADCs may record the latter two processes, but also out-of-sequence thrusting while sawtooth ADCs may result from emplacement of older units within younger (olistoliths) or, vice versa, from tectonic underplating and exhumation. The new concept also outlined several issues that still remain poorly understood and would deserve attention in future research, for instance, quantifying temporal variations in the rates of accretion, estimating magmatic arc tempos, as well as rates of erosion and sediment supply from arc to trench.

Žák J., Svojtka M., Hajná J., Ackerman L. (2020): Detrital zircon geochronology and processes in accretionary wedges. Earth-Science Reviews 207, 103214 (DOI)