Occurrence and significance of smectite in the Pliensbachian (Lower Jurassic) at Lókút (Bakony Mts., Hungary)

Abstract Although the Mesozoic rocks of Transdanubian Range have been subject a multitude different studies, mineralogical research is largely underrepresented. The clay mineralogy Lower Jurassic (especially Pliensbachian and Toarcian) strata was broadly investigated earlier; however, systematic high-resolution studies remain scarce. Here we present study focusing on Upper Lókút-Hosszúárok section, located near Eplény Manganese Ore Field. We identified dioctahedral smectite, randomly interstratified illite/smectite, illite as 10 Å phyllosilicate, quartz cristobalite. Based our new results propose that smectite formed by aging Mg or Fe hydroxide-silica precipitates. cristobalite were presumably from siliceous tests radiolarians, whose abundance controlled local upwelling system. occurrence in Lókút outcrop shows similarities with Úrkút smectites known both Toarcian strata, which implies similar processes sedimentation during well black (gray) shale-hosted ore accumulation basins.