Facies analysis of a Upper Cretaceous high-energy rudist dominated carbonate ramp (Matese Mts., central-southern Italy): subtidal and peritidal cycles

Upper Cretaceous shallow-water limestones rich in rudists have been studied in the Matese Mountains. They show the preponderance of skeletal components (molluscs and benthic foraminifers) and the lack of non-skeletal grains. The most prominent sediments of the studied stratigraphic interval are rudist-dominated fine- to coarse-grained lithologies. Most of the Senonian successions are characterized by massive neritic limestones rich in molluscs (mostly rudists and subordinate gastropods) and a few corals. The sediments were generated in situ on shelves where rudist bivalves were the primary sediment producers. These sediments were actively moved by storms, waves and swells. The finer fractions were probably winnowed out and deposited in deeper water. Well-bedded dolomitized mudstones/wackestones, microbial laminites and benthic foraminifer wackestones characterize some successions where they rhythmically alternate and testify to deposition in tidal-flat environments. The lithofacies, faunal and taphonomic characters and the sedimentary structures are typical of a ramp-like open shelf with local peritidal deposition. The vertical lithofacies organization consists of numerous decimeter-to-meter-scale shallowing-upward subtidal and peritidal cycles. A complete transition from peritidal to subtidal cycles has been recognized and documented. The peritidal cycles are usually bounded by desiccation surfaces and/or dolomitized crusts followed by shallow-subtidal to peritidal facies of the next cycle. The subtidal cycles are typified by rudist floatstones passing to large-scale cross-bedded bioclastic packstones/grainstones. Current and storm structures are distinctive features; in shallower-water environments the effects of submarine erosion prevail; hardgrounds commonly developed and the resulting cycles are usually truncated. The formation of the peritidal cycles appears to have been controlled by accommodation space in response to fluctuations in relative sea-level. The formation of the subtidal cycles was determined by sedimentation rates in response to fluctuations in the zones of fair-weather and storm-wave reworking, in turn controlled by relative sea-level. This indicates that sediment production and supply were important controlling factors in the cycle formation during the early Senonian stratigraphic interval. The recognition of similar depositional styles in other early Senonian successions cropping out in the southern Apennines suggests that this type of sedimentation is a recurring attribute of the Upper Cretaceous open shelves.