Coralline algal assemblages in upper Neogene reef and temperate carbonates in Southern Spain

Abstract

Reef and temperate carbonate units alternate in the upper Miocene–Pliocene stratigraphic record of Betic basins palaeogeographically connected to the Mediterranean. Shallow-water coralline algal assemblages in temperate units differ in taxonomic composition from those in reef carbonate units. The difference attains the subfamily level since the temperate lithofacies are characterised by assemblages dominated by lithophylloids ( Lithophyllum), whereas mastophoroids ( Spongites and Neogoniolithon) predominate in the reef units. The proportion of lithophylloids, however, can be high in samples from shallow-reef palaeoenvironments. The distinction is less marked in deeper platform deposits since melobesioids ( Lithothamnion, Mesophyllum and Phymatolithon) are the major elements in the assemblages from both reef and temperate units. Sporolithon, the only representative of the family Sporolithaceae, is frequent in reef-slope deposits but very rare in temperate lithofacies. The change in coralline algal assemblages from temperate to subtropical/tropical units is probably the result of the palaeophytogeography of the coralline red algae during the Late Neogene along climatic belts. Shallow-water floras were dominated by lithophylloids in cooler periods, during which the western Mediterranean was within the temperate belt, as in the present-day situation. In warmer episodes, subtropical/tropical conditions enveloped the region and the tropical coralline floras, in which mastophoroids predominate, together with reef corals and green algae inhabited the Betic basins. Similar, less pronounced, phytogeographic patterns can be roughly recognised in modern oceans. Fossil coralline algal assemblages can, therefore help to identify the palaeoclimatic context of sedimentation of the rocks in which they are recorded. They constitute a palaeontological tool supplemental to lithofacies and other fossil indicators for characterising such contexts in Cenozoic platform deposits.