Characterization and mapping of MIS‐2 thermal contraction crack polygons in Western Transdanubia, Hungary

Abstract

The Pannonian Basin was located in the southernmost, disputed limit of permafrost during the Last Glacial Maximum (LGM). In the western part of the basin, over an area of 1,200 km2, more than 150 sites with polygonal patterned ground were surveyed, and 72 sediment samples from forms identified as relict sand wedges were collected. Ten optically stimulated luminescence ages were obtained from the infills, while morphometric analyses were also carried out on satellite images. Our study revealed that the polygonal networks developed in several phases, from 15.01 ± 1.68 to 23.0 ± 1.7 ka. The polygons have an average diameter of 13–23 m and are mainly present on flat surfaces, intruding into the gravelly, alluvial host of the paleo‐Rába. Statistical analyses highlighted the short transportation period of the sandy infill and multiple sediment provenances. This study adds further data to assess the presence of permafrost or deep seasonal frost and to the interpretation of the LGM in the central European periglacial domain.

Optically‐Stimulated‐Luminescence Ages and Paleo‐Environmental Implications of Relict Frost Wedges in North–Central Bohemia, Czech Republic

“…The pairwise OSL ages tended to be randomly distributed within the individual frost wedges (Table 3; Figure 2), which is consistent with other studies (e.g., [22,41,46,48]). This may be due either to spatially uneven cracking and infilling, possible secondary mixing with materials brought in later, or uncertainties in the OSL ages.…”

“…However, wedge activity peaked at 16.1 ± 1.3 ka under cold-climate conditions of Heinrich Stadial 1/Greenland Stadial 2.1a (Figure 3). The development of the frost wedges at Uhersko was consistent with the timing of indirectly dated frost wedges in the southern Bohemia, Czech Republic, which probably originated after 18.7 ± 1.9 ka [64], as well as with an extensive formation of frost wedges and other kinds of patterned ground in other central and western European lowlands, such as Belgium [35], France [22], Hungary [40,41], Poland [44,[46][47][48], and the United Kingdom [110], which may have been even stronger than during LGM (Figure 4). This mismatch may, however, be due to a relatively small number of samples and/or sampling sites in the Czech Republic.…”

“…These cryogenic cave carbonates may therefore relate to short episodes of permafrost degradation caused by rapid and pronounced climate warming during pre-LGM interstadials (Figure 3) between 38.1 ± 0.6 ka and 26.0 ± 1.5 ka [115,116]. Because the frost wedges in lowlands as well as the periglacial features in uplands of the Czech Republic were active Denmark [32,37], France [22,39,105,106], Germany [32], Hungary [40,41], the Netherlands [32,43], Poland [32, [44][45][46][47][48][49], Sweden [107], and the United Kingdom [32,51]. Means and standard deviations for the OSL ages (rectangles) are based on the central age model [95], while those for the 14 C ages (triangles) are based on the IntCal20 calibration curve [108] and the OxCal 4.4 software [109].…”

“…Numerical ages (mostly optically-stimulated-luminescence [OSL], thermoluminescence, or radiocarbon [ 14 C]) are only available for a tiny fraction of the identified frost wedges, with the majority of wedges being chronologically constrained by their stratigraphic position (e.g., [31][32][33][34]) or not at all due to unknown sedimentary situation or high financial costs for numerical dating. The most extensive direct numerical datings of relict frost wedges have been carried out mainly in the last two decades in connection with advances in modern geochronological methods, especially in Belgium [35,36], Denmark ( [37,38]), France [22,39], Hungary [40][41][42], the Netherlands [36,43], Germany [36], Poland ( [36,[44][45][46][47][48][49][50]), and the United Kingdom [51]. Generally, these studies have shown that frost wedges developed throughout the last glacial period [22].…”