Relationships between fault-controlled subsidence and preservation of shallow-marine small-scale cycles: Example from the Lower Pliocene of the Crotone Basin (southern Italy)

The northern part of the Crotone Basin (southern Italy) was characterized by the activity of Pliocene growth faults bounding half-graben sub-basins. The thickest unit deposited during growth-fault activity is the lower Pliocene Belvedere Formation (up to 450 m thick), which shows a small-scale, highly regular rhythmic cyclicity. This sandstone unit was deposited in a shallow-marine environment, and its accumulation was mostly influenced by storm processes and locally by flows in tectonically confined areas. The meter-scale cycles are represented by rhythmic alternations between shell-rich intervals, characterized by storm structures or large-scale cross sets, and shell-poor sandy intervals that are commonly burrowed and poorly stratified. The better preserved cycles commonly show a fining-upward trend with minor progradation in their upper part, and may be bounded at the base by a shell lag. The deposition of large-scale cross sets is thought to be the consequence of the creation of fault scarps, which led to tectonic confinement in the half-graben basins. In the tectonically confined areas, tidal currents were enhanced and large subaqueous dunes migrated. The evidence suggests that the observed cyclicity was generated by sea-level and climatic variations that controlled the sediment input into the basin. The relationship between large-scale cross sets and tectonic confinement demonstrates that local extensional tectonics significantly influenced the sedimentation. The excellent preservation of the observed small-scale cycles is thought to be the consequence of deposition in the highly subsiding half-graben sub-basins. On the structural highs, this cyclicity is amalgamate and less appreciable. The data presented may be significant for a better understanding of the role of subsidence in preserving sedimentary successions in these growth-faulted settings.