Algal diversity during the onset of the Late Paleozoic Ice Age in low-latitude basins of the Western Palaeotethys

A study of calcareous algae from the late Vise ' an to Serpukhovian interval in basins from the western margin of Palaeotethys (basins located currently in Western Europe and Northern Africa) shows varied responses in terms of palaeoecological diversity, specimen abundance, genus richness and taxonomic distinctness for the lowlatitude basins. Algal associations are more similar in cratonic areas, although many local diversity peaks correspond to ecological/environmental factors. Terranes with Laurussian affinities contain the most unusual abundances and seem to be the most affected by palaeogeographic reorganization and local tectonics. Algae from the palaeo-equatorial zone show more dramatic changes than those in the southerly tropics. The varied results suggest that it is not suitable to extrapolate a particular diversity result from a single region to global conditions, since many factors have influenced the regional assemblages.The main taxonomic turnover of most fossil groups occurred from the uppermost Serpukhovian, linked to a severe cooling phase inferred by delta 18O data from brachiopods. It coincides with the post-glacial phase C1 defined in eastern Australian basins. Most ecological changes occurred from the early Serpukhovian, predating the glacial phase C1 and coinciding with the Main Eustatic Signal. Far-field proxies used to define the onset of icehouse intervals in the LPIA are inconsistent and are located several million years before the main biota changes. This questions the definition of the onset of sustained icehouse glaciation at different levels of the low palaeolatitude Vise ' an, without the resulting modifications in the warm-water biota.