Coralline red algal assemblage from the Middle Pliocene shallow-water temperate carbonates of the Monte Cetona (Northern Apennines, Italy)

摘要

During the Pliocene and Pleistocene, the Monte Cetona (Northern Apennines, central Italy) was part of an elongated island. The Middle Pliocene deposits around the Monte Cetona are represented by shallow-water marine carbonates rich in coralline red algae and bryozoans. These skeletal carbonates, characterising a coralline algal-dominated factory, were analysed in terms of microfacies, taxonomy, and growth-forms of coralline red algal assemblage. Three microfacies were distinguished on the basis of component distribution and fabric analysis: coralline algal rudstones, coralline algal floatstones, and bioclastic packstones. Skeletal components are commonly abraded, bioeroded, and encrusted. The shallow-water skeletal carbonates are strongly bioturbated and any primary sedimentary structure is obliterated. The distribution of the coralline growth-forms suggests a decreasing hydrodynamic gradient from the coralline algal rudstone, through the coralline algal floatstone to the bioclastic packstone microfacies. The coralline algal flora consists of eight species representing the subfamilies Lithophylloideae, Mastophoroideae and Melobesioideae. The assemblage is dominated by lithophylloids. Other biogenic components are bryozoans, barnacles, echinoderms, and benthic foraminifera. These coralline algal assemblages were deposited just above the fair-weather wave base and indicate a shallow-marine temperate water setting for the eastern Tyrrhenian Sea during the Mid Pliocene.