The study aims to reconstruct the crystalline parent rock assemblages of the Eocene Strihovce Formation (Krynica Unit) and Mrazovce Member (Raca Unit) deposits, based on the heavy mineral suites, their corrosive features, geochemistry of garnet and tourmaline, zircon cathodoluminescence (CL) images, and exotic pebble composition. Both units are an integral part of the Magura Nappe belonging to the Flysch Belt (Outer Western Carpathians). Corrosion signs observable on heavy minerals point to different burial conditions and/or diverse sources. The compositions of the detrital garnets and tourmalines as well as the CL study of zircons indicate their origin in gneisses, mica schists, amphibolites, and granites in the source area. According to observed petrographic and mineralogical characteristics, palaeoflow data and palaeogeographical situation during the Eocene may show that the Tisza Mega-Unit crystalline complexes including a segment of the flysch substratum could represent the lateral (southern) input of detritus for the Krynica Unit. The Raca Unit might have been fed from the northern source formed by the unpreserved Silesian Ridge. The Marmarosh Massif (coupled with the Fore-Marmarosh Suture Zone) is promoted to be a longitudinal source.