Mesophotic azooxanthellate coral communities and submarine seascape during the early Pliocene in Manilva Basin (S Spain)

Abstract

Azooxanthellate corals are the most abundant macrofossils in the lower Pliocene deposits of the Manilva Basin (S Spain). In this paper, the cnidarian fossil assemblages have been studied in order to reconstruct the original communities and to depict the seascapes. Benthic foraminiferal assemblages associated with the corals have also been analysed to infer the palaeoenvironmental conditions in which they developed. Two sections have been studied. In the Canuto section, Coenosmilia fecunda dominates the cnidarian assemblage, followed by Asterosmilia cf. prolifera and Asterosmilia sp., which are all preserved as moulds and casts. Benthic foraminiferal assemblages indicate oligotrophic conditions and deposition from the middle platform to the upper slope. The Alamos section is characterized by Madrepora oculata, Dendrophyllia ramea, Asterosmilia cf. prolifera, Asterosmilia sp., Coenosmilia fecunda, and gorgonians of the Isididae family (most likely Keratoisis melitensis and/or Lepidisis longiflora), as well as a basal holdfast attributed to a member of either Primnoidae or the Chrysogorgiidae family. Here, corals preserve their original skeletons. Benthic foraminifers suggest deposition in oligotrophic conditions in mid–outer platform settings. Corals in the Canuto section formed autochthonous fossil assemblages, while in the Alamos section they were slightly displaced from their original growth positions to form parautochthonous fossil concentrations. The cnidarian community in the Canuto section was characterized by low-tier organisms either attached to hard substrates provided by skeletal remains (Coenosmilia fecunda) or inhabiting fine-grained bottoms (Asterosmilia spp.). In the Alamos section, Coenosmilia fecunda and Asterosmilia spp. occupied the lowest tier levels. The gorgonians, isidids and members of the Primnoidae or Chrysogorgiidae families, colonized both soft and hard substrates, dominating the next tier level. Finally, Madrepora oculata and Dendrophyllia ramea settled on submarine cliffs or on large blocks derived from substrate, inhabiting the highest position in the community. Large specimens of gorgonians could have also occupied this position.