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The Đurđevac Sands: First dating results and preliminary paleogeographical reconstruction

“Abrupt climate changes–Evidence from Quaternary sedimentary sequences in Croatia” is a four-year research project that is funded by the Croatian Science Foundation and started on April 1st 2021. A fundamental and multidisciplinary approach is producing meaningful data on past abrupt climate changes (CC). Interpretation of these data helps to create the basis both for comparison of paleo- and modern climate changes and for predicting their dynamics in the future. The specific geological, pedological, geomorphological and climatic diversity of Croatia enables us to study in high-resolution the parallel development of abrupt CC during the Late Pleistocene and Holocene. Four investigated locations are only 300 km apart: loess/palaeosoil sequences and dunes in the Pannonian area (continental climate) on the one hand, and fluvioglacial sediments and karst lacustrine sediments in the Dinaric area (Mediterranean climate) on the other hand. The Đurđevac Sands form a unique terrestrial dune landscape that covers Late Pleistocene loess deposits and Holocene river Drava fluvial and associated marshy deposits. Based on the superposition principle, in the Guidebook of the geological map for the Đurđevac sheet 1:100.000, the Đurđevac Sands are Holocene in age. Samples were taken in an abandoned sand quarry, Draganci, in the town of Kalinovac. The quarry is carved out into what seems to have been a massive (hummocky) dune, bordering a partially degraded large-scale parabolic dune created by northern winds. Samples were taken after clearing the excavation wall, turning it partially into a staircase. Within the dunes sets, two palaeosoils were discovered. Preserved bioturbations confirm that the palaeosoils are found in situ. Several analytic methods were applied to characterise soils and sediments, together with their age and paleoenvironmental significance: radiocarbon and optically stimulated luminescence dating, digital elevation model, geoelectrical, pedological, sedimentological, modal and grain-size analyses. According to the grain-size measurements, the sand fraction dominates in all analysed samples, mostly between 95 and 100 %. Medium and fine sand grains represent equally the sand fraction. Therefore, most of the samples are classified as sand, or less frequently as fine sand. The dunes are composed of high spherical sand grains with quartz dominating in the light mineral fraction. The heavy mineral fraction contributes with 22-46%, and garnet is dominating. Recent radiocarbon dating results of charcoal suggests that the older palaeosoil (14 659 ± 498 cal yr BP) developed at the beginning (peak), and the younger palaeosoil (13 566 ± 229 cal yr BP) developed in the middle part of the Bølling–Allerød warming (BA). They represent an abrupt interstadial period, roughly between 14.7 and 12.9 ka BP, just before the Younger Dryas cooling, the final stadial of the Pleistocene. Optically stimulated luminescence (OSL) dating was applied to verify those recent findings using the aeolian sands covered by and covering the palaeosoils. The two lowermost samples below the palaeosoils yield OSL ages of around 14.5 ka, while the uppermost sample above the upper palaeosoil has an age of around 8 ka. It thus seems that at this site, aeolian activity has been registered during the period just before the BA warming, and later in the Holocene, but not during the Younger Dryas. A detailed sampling campaign with additional analyses is foreseen, together with digital elevation surveys, in order to refine the palaeoenvironmental history of the Đurđevac Sands.

Abrupt climate changes, Quaternary, dune, Đurđevački Pijeci, Croatia

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