Tracing multiple resedimentation on an isolated karstified plateau: The bauxite-bearing Miocene red clay of the Southern Bakony Mountains, Hungary

The Vöröstó (= Red Lake) Formation, located in the Southern Bakony Mountains and the Balaton Highlands (Hungary), is a red, clayey continental assemblage containing hard, up to fist-sized bauxite pebbles, occurring in a large apparent stratigraphic gap between underlying karstified Triassic carbonates and mid' Miocene to Quaternary cover. The origin and the exact stratigraphic position of the assemblage have been controversial for a long time. In this study, petrographic observations on the bauxite pebbles revealed common features with Cretaceous bauxite deposits known in the region, whereas heavy mineral composition of the red clay matrix is similar to those known from the Eocene bauxite horizon of the region. Single grain zircon U-Pb ages obtained from the bauxite pebbles and their red clayey matrix show similar late Archean to Jurassic age components. Additionally, Cenozoic U-Pb ages are well represented in the mostly euhedral zircon crystals separated from the red clays, whereas this volcanogenic contribution completely missing from the bauxite pebbles. SEM morphology and related EDX chemical analysis of clay minerals indicate polygenetic, detrital origin for the red clays. The main source material of the bauxite bearing Vöröstó Formation is most probably local Cretaceous and Eocene bauxite deposits exposed during the middle-late Miocene. These tropical weathering products were partly decomposed and degraded, but dilution by siliciclastic contribution is negligible. We suggest a transport mechanism dominated by local redeposition of mostly pelitic and allitic material through seasonal muddy debris flows within a karstic landscape.