The Loess “Cave” Near the Village of Surduk - an Unusual Pseudokarst Landform in the Loess of Vojvodina, Serbia

Loess “caves” (piping caverns, wells, tunnels) exposed in loess cliffs are rare pseudokarst landforms that can be regarded as morphological equivalents to collapse dolines or sinkholes formed in classical karst terrains. This study presents the results of an investigation into a loess cave exposed in a loess cliff on the right bank of the Danube River near the village of Surduk in the Vojvodina region, Serbia. This study provides a first detailed morphologic description of this young pseudokarstic landform formed by piping erosion, probably partly supported with carbonate dissolution. The loess “cave” has a height of approximately 12 m and average diameter of around 3.5 m. In the middle of the cave ceiling there is a window. Observations indicate that over the last several years, the morphological characteristics of the landform have been stable. The main aim of this study is to provide a better understanding of the evolution of the piping process in the thick loess-paleosol sequences in the Vojvodina region, northern Serbia. A key role in the genesis of this landform was the short distance between an initial loess doline and a cliff exposing loess sediments, providing the possibility for the lateral removal of loess material. The presence of Robinia pseudoakacia trees around the initial depression modulated the evolution of the doline and provides support for the loess cavern roof. The nature of the dynamic erosional processes on the steep cliffs of the soft loess sediment indicates a very limited lifetime of this pseudokarstic landform

Loess as a Quaternary paleoenvironmental indicator

Loess (aeolian silt) is widespread in Eurasia and the Americas. Paleowind direction and wind strength can be reconstructed from spatial and temporal trends of loess thickness and particle size. Fossil land snails in loess can reveal much about past climate and vegetation. Loess is aeolian sediment that is dominated by silt-sized particles. Unlike either coarser dune sand or finer-grained, long-rangetransported dust, loess is relatively poorly sorted, reflecting a combination of transport processes, including saltation, low suspension, and high suspension. Loess can be readily identified in the field; deposits range in thickness from a few centimeters to many tens of meters, and are found over large areas of Eurasia, South and North America (Fig. 1), and smaller areas of New Zealand, Australia, Africa and the Middle East. Loess covers approximately 10% of the Earth’s land surface and is therefore one of the most important terrestrial archives of paleoenvironmental change during the Quaternary. In many regions, loess sections consist of deposits of mostly unaltered sediment with intercalated paleosols. Paleosols represent periods of landscape stability when loess deposition ceased altogether, or at least slowed significantly. Loess can be dated directly using luminescence, radiocarbon, and amino acid geochronology methods

Organic Cation Substitution in Hybrid Perovskite CH₃NH₃PbI₃ with Hydroxylammonium (NH₃OH⁺): A First-Principles Study

The exceptional success of hybrid perovskite materials in the next generation of photovoltaics has attracted the interest of scientists across many fields in photophysics. Structural and optoelectronic properties are of main importance when searching for potential compounds beyond photovoltaics or as top-cell absorbers. In this article, we theoretically study the thermodynamic stability and electronic properties of organic cation substituted MAPbI₃ with hydroxylammonium ions. Results from structural relaxations are compared to predictions from Goldschmidt tolerance factors. Our findings evidence that size effects and the initial orientation of the central cation result in strongly alternated octahedral distortions and markedly different optoelectronic properties. The latter becomes noticeable mainly due to band gap variations and significant frontier orbital splitting, which is observed in the case of relativistic calculations and seems to highly depend on the inorganic network deformation