Hierarchy of high-frequency orbital cycles in Cretaceous carbonate platform strata

Lower Cretaceous (Valanginian-Hauterivian) carbonate platform strata, which are well exposed in the Matese Mountains of the southern Apennines (Italy), have been analyzed on a microstratigraphic (cm) scale to exemplify the high-frequency cyclic nature of the Mesozoic shallow water sedimentation in southern Italy. Based on the vertical organization of lithofacies and their early diagenetic signature 46 metre-scale cycles are recognized. These elementary cycles are hierarchically organized into groups (bundles and superbundles). The elementary cycles are prevalently formed by subtidal deposits and show emersion-related features at the top, suggesting repeated sea-level fluctuations. The number of elementary cycles compared to time, as constrained by biostratigraphy, and their grouping into sets, implying higher-order complexity in the environmental oscillation, suggest an orbital control on sedimentation. Spectral analysis of recurrent thickness in stratal features defines and quantifies the cyclicity, which is characterized by lithofacies thickness periodicities of 1271, 391, 159, 124, and 69 cm. Linear correlation of the relative ratio set (RRS) of these periodicities with the corresponding RRS of the orbital perturbation periodicities shows that 1271 and 391 cm fit the 404,220 and 94,890 year cycles of Early Cretaceous orbital eccentricity; 159 and 124 cm fit the 49,010 and 38,030 year cycles of the Earth's axial obliquity, whereas 69 cm corresponds to the precession periodicity. Thus the San Lorenzello section required not less than 1.6 Ma to form, at an average rate of ≊26 mm/ka. Each ≊400 ka cycle can be viewed as a depositional sequence in which sequence boundaries, maximum flooding surfaces and system tract equivalents have been recognized. The microstratigraphic approach is very promising for understanding the fine structure of climate-related environmental fluctuation recorded by the >3000 m thick carbonate platform successions of the southern Apennines, over a time span of about 150 Ma (Upper Triassic-Upper Cretaceous), and for deriving a more precise chronostratigraphy for global correlation.