Palaeobiology of Pliocene-Pleistocene shallow-water biocalcarenites (Northern Apennines, Italy) and their relationship with coeval sapropels

Abstract

© The Author(s), 2020. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Cau, S., Roveri, M., & Taviani, M. Palaeobiology of Pliocene-Pleistocene shallow-water biocalcarenites (Northern Apennines, Italy) and their relationship with coeval sapropels. Bollettino Della Societa Paleontologica Italiana, 59(1), (2020): 25-40, doi:10.4435/BSPI.2020.04.The interplay between carbonate and siliciclastic sediment production in shallow marine environments may result in the development of mixed depositional systems showing a cyclical arrangement of sedimentary facies. The palaeoenvironmental record associated with these cyclical facies changes is not always univocally correlated with eustatic oscillations, suggesting that other forcing processes have played an additional role. The Castell’Arquato Basin (CAB: Pliocene-Pleistocene, Northern Apennines, Italy) offers the opportunity to integrate the study of small and large-scale stratigraphic architectures with that of shell beds in shelf to deep-water successions. The analysis of diversity trends allows a first insight into the structure of CAB benthic communities associated with minor and major biocalcarenites. Biofacies types are identified through a multivariate analysis of a large quantitative database including shells of all molluscs, serpulids and brachiopods. The study shows that these bio-detrital deposits and their bracketing marine mudstones developed at inner-shelf settings and that taphonomic feedback played an important role in the stratigraphic distribution of biofacies. Benthic communities from shelly bottoms depend on the winnowing of fines by bottom currents, a factor that is not related to water depth in a simple manner. Heterogeneity of the seafloor is associated to high-diversity of communities of topset strata of major biocalcarenites. Communities living in siliciclastic bottoms depend on factors that are largely depth-dependant. The study confirms the correlation of major biocalcarenite cycles with coeval deep-water sapropels, supporting the hypothesis of a more effective role of high-amplitude climatic changes driven by orbital forcing. This affects the source-to-sink dynamics of the whole basin and the biological structuring processes of shelfal depositional settings and related ecosystems.Thanks to Stefano Dominici (Museo di Storia Naturale, Università di Firenze) for his review and editorial handling. Ronald Nalin (Loma Linda University, California, USA) and an anonymous reviewer are acknowledged for their constructive comments and suggestions that improved an early version of the paper. We thank Alessandro Freschi, Gianluca Raineri (Riserva Geologica del Piacenziano e dello Stirone) and Carlo Francou (Museo Geopaleontologico “G. Cortesi”, Castell’Arquato) for their assistance with sample collection. This is ISMAR CNR, Bologna, scientific contribution n. 1950