Mineral composition of the Sumer Formation sediments near the village of Sumer (Northwestern Bulgaria)

Previous analyses of the Sumer Formation sediments have been limited to samples up to 400 m deep near the village of Varbitsa. This study extends the investigation, exploring the mineral composition and carbonate content of the sediments near the village of Sumer. Samples were collected from two outcrops at the Montana-Vratsa Road junction (C-1) and the Shugavitsa river basin (C-2). Both outcrops revealed a quartz and calcite content of approximately 75–80%, with a significant variance in calcite levels: 11.4% at C-1 and 31.3% at C-2. Illite (4.5%) and kaolinite (2%), these clay minerals essential for the marls’ sorption properties, were only detected in C-1 samples. The C-2 outcrop exhibits a higher carbonate content (17.65%) compared to C-1 (10.85%). These findings mirror the mineral composition trends observed near Varbitsa, where the content of illite and kaolinite increases with depth. The results provide valuable data for future geochemical and geotechnical evaluations pertinent to the development of geological repositories.