Taphonomy and evolution of Lower Jurassic lithiotid bivalve accumulations in the Apennine Carbonate Platform (southern Italy)

• Published in: Palaeogeography, Palaeoclimatology, Palaeoecology
• Main Authors: Posenato, Renato, Bassi, Davide, Trecalli, Alberto, Parente, Mariano
• Format: Article in Journal/Newspaper
• Language: English
• Published: 2018
• Subjects: Carbonate platform; Global warming; Ocean acidification; Rock-forming bivalve; T-OAE; Oceanography; Ecology; Evolution; Behavior and Systematic; Earth-Surface Processe; Paleontology
• Online Access: http://hdl.handle.net/11392/2379245; https://doi.org/10.1016/j.palaeo.2017.10.017; https://www.sciencedirect.com/science/article/pii/S0031018217308738

Lower Jurassic Tethyan and Panthalassan marine shallow-water successions are characterized by aberrant lithiotid bivalves belonging to the Lithiotis Fauna. Their widespread occurrence, often in rock-forming abundance, represents a global biofacies, mostly restricted to the Pliensbachian–early Toarcian. Despite their wide occurrence and their prominent role as carbonate producers in shallow-water platforms, the biogeographic and stratigraphic distribution of this group of bivalves and their evolutionary history are obscure, mostly because they commonly have not been identified at the generic or specific level. In particular, their evolution and demise in relation to important global palaeoenvironmental perturbations, such as the Pliensbachian-Toarcian boundary event and the early Toarcian oceanic anoxic event are not yet known in detail. In the Apennine Carbonate Platform of southern Italy, the Lithiotis Member, in the upper part of the Lower Jurassic Palaeodasycladus Limestones Formation, is characterized by the abundant occurrence of lithiotid bivalves. They disappear abruptly in the lowermost beds of the overlying Oolitic-oncolitic Limestones Formation, at the onset of the early Toarcian Oceanic Anoxic Event. More than 60 lithiotid bivalve concentrations occur in a nearly 120 m-thick succession spectacularly exposed on freshly cut walls in a quarry west of Mercato San Severino (Salerno). Field observations on the taxonomic composition and fabric of the shell beds (packing, maximum shell size, degree of shell articulation and fragmentation) allowed to distinguish four taphofacies (A–D). Taphofacies A records the appearance and spreading of the lithiotids, with accumulations characterized mainly by small-sized and loosely packed shells. Taphofacies B records the acme of lithiotid bivalves, with densely packed accumulations of large shells. These two taphofacies yield prevailing articulated individuals, commonly in life position. Taphofacies C records a decrease of the shell packing and frequency of ...