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

Abstract

Azooxanthellate corals are the most abundant fossils 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 cnidarian 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. The Canuto section is dominated by moulds and casts of Coenosmilia fecunda followed by Asterosmilia cf. prolifera and Asterosmilia sp. Benthic foraminiferal assemblages indicate oligotrophic conditions and deposition from the middle platform to the upper slope. The Álamos section is characterized by Madrepora oculata, Dendrophyllia ramea, Asterosmilia cf. prolifera, Asterosmilia sp., Coenosmilia fecunda, and gorgonians of the family Isididae (most likely Keratoisis melitensis and/or Lepidisis longiflora) as well as a basal holdfast attributed to a member of the families Primnoidae or Chrysogorgiidae. 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 Álamos section they were slightly displaced from their original growth positions to form parautochthonous fossil concentrations. The cnidarian community in the Canuto section was characterised by low-tier organisms attached to hard substrates provided by skeletal remains (Coenosmilia fecunda) or dispersed in the soft substrate provided by the marls and silts (Asterosmilia spp). In the Álamos section, Coenosmilia fecunda and Asterosmilia spp occupied the lowest tier levels. The gorgonians, isidids and members of the family Primnoidae or Chrysogorgiidae, 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.