Coralline algae as depth indicators in the Sommières Basin (early Miocene, Southern France)

The aim of this work is to demonstrate the benefits of digital surface-quantification and species identification in the study of coralline algae. Within the well-constrained context of the Miocene Sommières Basin (Southern France), whose sedimentological and paleontological setting has been reconstructed by previous researches, the abundance of coralline algae is estimated through quantification of the area occupied by the different species, which are thoroughly described in order to make future taxonomic-revisions as easy as possible. Coralline distribution patterns are studied along a bathymetric gradient to assess the response of the major groups and of the different species to variations in water depth. Surface quantification highlights clear trends both at the species level and higher taxonomic ranks, showing that coralline algae can be a quite accurate instrument in paleoenvironmental reconstructions. Among the clearly identified species, Lithophyllum sp. A, Sporolithon sp. A, and Spongites fruticulosus prefer shallow-water; Mesophyllum roveretoi dominates at intermediate depth together with Lithothamnion ponzonense, while Phymatolithon sp. A occurs at the lower limit of the photic zone. The approach presented here can be applied to a variety of different contexts, providing a powerful instrument for the interpretation of coralline-algal associations.