Hooked and tubular coralline algae indicate seagrass beds associated to Mediterranean Messinian reefs (Poniente Basin, Almerيa, SE Spain)

Abundant hooked and tubular crustose coralline algae (CCA) record early Messinian (Late Miocene) seagrass beds on the northern margin of the Poniente Basin in southeastern Spain. Hooked and tubular shapes in CCA result from their epiphytic growth over seagrass leaves and stems. The lower Messinian deposits consist of a thin retrograding subunit overlain by sigmoidal bed packages that prograded to the southwest at least 650 m from the basin margin. Seagrass deposits mainly occur as bivalve/CCA packstone to rudstone and CCA floatstone, seawards of a conglomerate facies belt in the retrograding subunit and downslope of coral reefs and serpulid packstone to rudstone in the prograding sigmoidal beds. Fragments of contorted foliose CCA (“algal flakes”), some hooked or tubular, are common components in the seagrass deposits. They mainly belong to an unidentified species of Mesophyllum. Like their present-day counterparts, the epiphytic CCA grew attached to seagrass by the initial parts of their thalli and displayed unattached projections or open frameworks of contorted foliose plants. In a few cases, hooked CCA occur attached to Halimeda plates. Small benthic foraminiferal assemblages are further evidence of macrophyte vegetation. Hooked contorted foliose CCA can be a helpful tool for the identification of ancient seagrass beds, especially in Mediterranean Neogene and Quaternary deposits, in which foraminiferal taxa fully indicative of seagrass ecosystems are scarce.