Testing an indirect palaeo-seagrass indicator: Benthic foraminifera from the Lower Pleistocene Posidonia meadow of Fauglia (Tuscany, Italy)

Well-preserved remains of a Posidonia oceanica meadow have been found in a Lower Pleistocene (Calabrian) succession cropping out near Fauglia (Tuscany, Italy). This paper analyses and describes the benthic foraminiferal community associated with this well-preserved Pleistocene P. oceanica meadow, with the purpose of testing the usefulness of foraminifera as an Indirect Palaeo-Seagrass Indicator (IPSI), providing both qualitative and quantitative parameters to recognize other meadow-related environments where fossil remains of seagrasses are not preserved. Despite being influenced by some diagenetic processes that might have affected the foraminiferal assemblage, the Fauglia succession represents a suitable setting for testing benthic foraminifera as IPSI in a temperate environment. Considering this limitation, together with other ecological constraints such as seawater temperature, this study provides evidence of the high potential of benthic foraminifera as IPSI. Several parameters such as the modified Foraminifera Index (FI'), the long vs. short life-span index (ILS), and the presence of permanently attached, encrusting foraminifera were tested. New indexes were also developed, namely the K/R ratio, consisting of the ratio between keeled Elphidium and the sum of rounded elphidiids (e.g., Elphidium translucens, Cribroelphidium, Porosononion) and Haynesina, and the K/REXT ratio, consisting of the ratio between keeled Elphidium and the sum of rounded elphidiids, Haynesina and other related genera that display a rounded periphery (i.e., Astrononion, Melonis, Nonion, Nonionella, Valvulineria). All these indexes were examined, suggesting their potential use for recognizing seagrass-related palaeoenvironments. The K/REXT ratio (and K/R) in association with the presence of permanently attached foraminifera revealed to be the most reliable palaeoseagrass indicators, suggesting that this combination could be very useful also in other case studies where diagenesis altered the foraminiferal association.

Automated summary

This study examines well-preserved Pleistocene Posidonia oceanica remains and tests the feasibility of using benthic foraminifera as Indirect Palaeo-Seagrass Indicators (IPSI). The study finds that the K/REXT ratio and the presence of permanently attached foraminifera are the most reliable indicators of ancient seagrass.