Csernye revisited: New ammonite finds and ostracods from the Lower Jurassic Pliensbachian/Toarcian boundary beds in Bakonycsernye, Transdanubian Hungary

Recently a new exposure near the classic outcrops at Bakonycsernye made possible to make a closer study on the Pliensbachian/Toarcian boundary beds. Careful sampling and the reinvestigation of formerly collected but unpublished material (ammonites and microfossils) evidenced that in the new section the hiatus between the Pliensbachian massive red limestone and the Toarcian claymarl is much shorter than suggested before, on the basis of previous exposures. The earliest Toarcian ammonite in the new section is Paltarpites cf. paltus of the Paltus Subzone, while the earliest Toarcian ammonites in the classic Csernye section indicated the Falciferum Zone. The ammonite fauna shows no abrupt change at the chronostratigraphic boundary: most of the represented morphological lineages are continuous across, while the ostracod fauna, having been represented by benthonic forms, reacted heavily to the limestone to claymarl facies change at the boundary: the former sublittoral elements are replaced by deper-water forms in the Toarcian. To document these circumstances and changes, the most important ammonites and ostracods from the new section and from the boundary beds of the classic Csernye section are figured and stratigraphically evaluated