Ophiolite derived material as parent rocks for Late Jurassic bauxite: evidence for Tithonian unroofing in the Northern Calcareous Alps (Eastern Alps, Austria)

Abstract In shallow-water limestones of the Plassen Formation in Tirolic nappe Northern Calcareous Alps, bauxite was formed on karstified and tilted platform margin grainstones to boundstones around ?Kimmeridgian/Tithonian boundary, or Early Tithonian as proven by Protopeneroplis striata Weynschenk, Labyrinthina mirabilis Salpingoporella pygmaea Gümbel. The established top obducted ophiolite stack. onset unroofing at Kimmeridgian/Tithonian boundary exposed ophiolites weathering, forming laterites, bauxites. weathered ophiolitic material shed tilted, emerged, platform, where accumulated. Continued subsidence led flooding, a transgressive carbonate sequence sealed XRD analysis yields composition mainly boehmite with hematite some berthierine, kaolinite, chromite. SEM verified magnetite, hematite, rutile, chromite, zircon, ferropseudobrookite, ilmenite, monazite, xenotime, garnet distributed pisoids within matrix. reach millimeter size partly show cores older, larger pisoids. chromites indicates an origin. Geochemical examination using major- trace elements points mafic andesitic basaltic parent contaminated highly fractionated rocks from island arc. bauxites confirms Middle Late Jurassic obduction. This followed uplift orogen onwards after period relative tectonic quiescence platforms during Kimmeridgian stack Neo-Tethys ophiolites.