The study is focused on the provenance and transport environment of autochthonous fluvial sediments from the bottom parts of the Kolkina Dupka Cave (Ponor Mountain). The transport depends on the fluctuation and dynamics of underground water flow. There is evidence for different sources according to the diversity of lithic grains and fossil fragments. The fluvial sediments originate from erosion and redeposition of Triassic sedimentary rocks.
Yordanka Donkova (Sat,) studied this question.