Orbitally forced cyclical changes in the quantity of calcareous and siliceous microfossils in an Upper Jurassic to Lower Cretaceous pelagic basin succession, Bakony Mountains, Hungary



Rhythmic changes were observed in the quantity of radiolarians and calpionellids preserved in an Upper Jurassic to Lower Cretaceous deep water succession in the Bakony Mountains of Hungary. Statistical analysis revealed that for short periods (order of 100 kyr) the correlation of the two planktonic groups is negative. Over longer time intervals definite trends are recognized, which can be explained by the combined effect of facies transition, evolution of the calpionellids and rhythmic environmental (climatic) changes. Spectral analysis and time span calculations indicate that orbital forcing in the Milankovitch frequency band influenced the observed changes.