Vestiges of atoll-like formations in the Lower Cretaceous of the Mecsek Mountains, Hungary

Abstract

Macro- and microfossils and microfacies of a few Lower Cretaceous sections in the Mecsek Mountains have been studied. Twenty five species of corals are reported for the time first from the Hungarian Cretaceous. Fossils derived from the carbonate platform are often found together with those of pelagic origin and monomictic volcanoclastics, indicating a special sedimentary environment. Based on this study the following model is proposed for the Early Cretaceous geological history of the Mecsek Mountains: instead of overall uplift and erosion giant basalt volcanoes grew above sea level until the Valanginian, whilst bathyal conditions were preserved between them. The volcanoes were bordered by gravel beaches, then sandy and silty lagoons, and the edge, of submarine slopes were crowned by atoll-type build-ups. Fossils and rocks of different environments were transported down the slopes of the volcanoes and mixed. As a result of widespread erosion during the Late Cretaceous or Palaeogene only the basal parts of a few volcanoes are preserved.