Preservation of calcareous fossils of Late Quaternary fauna in sedimentary fills of sandstone caves in the Elbe River Canyon

Sandstone caves are usually an unfavourable environment for the preservation of gastropod shells and vertebrate bones in Quaternary sediments. The cause of unfavourable taphonomic conditions in sedimentary fills is most often low pH, which leads to the dissolution of fossils. However, there are exceptions to this rule. Here we report on the discovery of Quaternary sediments rich in calcareous fossils that we have made in Otto Mörtzsch Cave (Labské pískovce Protected Landscape Area, Czechia). This site is one of the deepest crevice-type caves (−40 m) in the Elbe River Canyon, the largest European sandstone canyon located at the border between Czechia and Germany (Fig. 1). The good preservation of the gastropod shells and vertebrate bones found (Fig. 2) is probably due to the presence of secondary carbonates (speleothems) on the cave walls and their erosion and deposition together with the fossils (Figs 2, 3, 4). The original source of calcium carbonate was likely loess, which was deposited above the cave during the Last Pleniglacial and later degraded. Radiocarbon (14C) dating results (Table 1) show that the natural archive represented by the sedimentary sequence studied reflects environmental changes in the Elbe River Canyon during the Early and Middle Holocene (Northgrippian and Greenlandian), when the sandstone landscape was not yet strongly affected by natural acidification. The acidification process later caused decalcification and oligotrophication of soils and a subsequent decline in acid- sensitive fauna and flora. This fact is also evidenced by the gastropod fauna we found, dominated by species associated with mixed forest environment (Fig. 2), and by dated charcoal from oak (Quercus) and hazel (Corylus) trees (Table 1). Results of 14C dating further indicate that Otto Mörtzsch Cave was formed at the beginning of the Holocene at the latest. The natural archive in Otto Mörtzsch Cave is unique, and further research may significantly deepen our knowledge of the Holocene environmental history of the Labské pískovce (Elbe Sandstones) Protected Landscape Area and the nearby České Švýcarsko (Bohemian Switzerland) National Park.