Middle Pleistocene glacial outwash in poljes of the Dinaric karst

Poljes are distinctive features of Mediterranean karst landscapes, but their Pleistocene sedimentary fills have not been widely investigated. Most previous research has focused on their formation and hydrology. Many Mediterranean poljes are situated downstream of high mountains that were glaciated during the cold stages of the Pleistocene, so that meltwater streams delivered glacially derived sediment into these basins. This study examines the Pleistocene alluvial records in karst poljes surrounding Mount Orjen in western Montenegro and explores their wider significance. There is a record of at least four glaciations preserved on Mount Orjen—two from the Middle Pleistocene (marine isotope stages [MIS] 12 and 6) and two from the last cold stage (MIS 5d-2), including the Younger Dryas. Detailed sedimentological analysis and uranium-series dating indicate that the Orjen poljes were filled with thick deposits of coarse- and fine-grained alluvium prior to 350 ka, during the major glacial phase of MIS 12. During the cold stages that followed MIS 12, ice was less extensive and limited to the Orjen plateau, and there is little evidence of outwash deposition during these later glaciations. Surface runoff and sediment supply were greatly reduced after MIS 12 and largely channeled into the subterranean karst network. The poljes around Orjen contain some of the best-preserved records of Middle Pleistocene glacial outwash in the Mediterranean, representing an important legacy of an extensive Middle Pleistocene glaciation for which wider impacts have not been fully appreciated.