The Messinian fishes of Capo di Fiume (Palena, Abruzzo): Stratigraphy, taphonomy and paleoecology

The Messinian laminated diatomites exposed in the Capo di Fiume stratigraphic section, near the town of Palena, along the slopes of Mt. Porrara in the Abruzzo Apennines, contain well-preserved articulated fish skeletal remains, often associated with plants. A large collection of fossils from this section was accumulated and donated by Erminio Di Carlo to the Museo Geopaleontologico dell’Alto Aventino, Palena, Italy. Herein, we present the stratigraphy of the Capo di Fiume section and a preliminary biosedimentological study of the fossiliferous laminated diatomites. A taphonomic and paleoecological analysis of the fish remains deriving from the oldest diatomite interval of the succession is also included. The sedimentary succession documents the transition from continental to paralic to coastal to open marine conditions, suggesting the existence of a rather narrow shelf connecting coastal and basinal areas. The deposition of the diatomite laminae took place through different biological mechanisms, most notably the so-called “fall dump”, which involved the formation of flocs (mucilaginous aggregates) that included diatom assemblages dominated by Coscinodiscus spp. and Thalassionema nitzschioides. The macrofossil assemblage of the diatomites and the biosedimentological study of the laminated fossiliferous diatomites have provided new data regarding the paleoenvironmental and paleophysiographic setting and the ecological relationships. The diatom content of the fossiliferous (biogenic) laminae as well as the structure and composition of the fish assemblage clearly indicate a depositional marine environment with depths of up to several tens of meters. The fish assemblage is largely dominated by the round herring Spratelloides lemoinei, which represented the trophic nucleus of the original fish community. This and other clupeid species and certain “adventitious visitors” occupied the upper portion of the water column. The “adventitious visitors” are represented by mesopelagic diel vertical migrants (Diaphus edwardsi, Lestidiops sphekodes, Maurolicus cf. muelleri, Myctophum columnae, Paralepis albyi), which were probably attracted in the Capo di Fiume paleobiotope by abundant planktonic organisms as well as by shoals of Spratelloides lemoinei. The lower portion of the water column and the seafloor were well aerated and occupied by a diverse community of demersal fish taxa, especially sparids. The rapid deposition of diatom mats, abundantly represented in the fossiliferous intervals, may have resulted in the swift entombment of fish carcasses, whose fossilization was promoted even under relatively well-oxygenated bottom conditions.