Present-day and fossil rhodolith pavements compared: Their potential for analysing shallow-water carbonate deposits

Abstract

Coralline red algae represent the main biogenic components in most shallow-water carbonate successions from the Eocene to the Recent. They contribute significantly to sediment production on open platforms. Carbonate sediments formed by unattached coralline algae include rhodolith pavements (RPs) which represent dense accumulations of rhodoliths, as well as maërl which is composed of rhodoliths, coralline algal branches and their detritus. Recent RPs sampled off Sesoko-jima (Okinawa-jima, southern Japan) occur at depths of 50–70 m on a submarine terrace. The taxonomic coralline composition is dominated by melobesioids associated with minor amounts of mastophoroids and sporolithaceans. The rhodoliths are characterised by various nuclei, an encrusting inner arrangement, encrusting to warty outer growth-forms and sub-spheroidal shapes. Bioerosion, encrustation and abrasion are the most prevalent taphonomic features. Possible fossil counterparts were identified in Chattian and Priabonian RPs from middle-ramp depositional systems from the Venetian area, north-east Italy. A direct comparison between Recent and fossil RPs is possible by contrasting the constituent rhodolith characteristics including taxonomic composition, nature of the nucleus, inner arrangement, outer growth-forms, size and shape as well as taphonomic signatures. This allows factors controlling rhodolith formation and growth in RPs to be compared especially with respect to hydrodynamic regimes and substrate type.