New age constraints for the Perdasdefogu Basin, Italy: implications for vertebrate paleobiogeography during the early Permian

Abstract

This study reports new sedimentological, paleontological and geochronological data from the Perdasdefogu Basin, Sardinia, Italy. Sedimentological investigations showed that the basin hosted a permanent lake, initially infilled by epiclastic and volcaniclastic material, then by carbonates, and finally covered by thick felsic volcanic series. Lacustrine sediments yielded various fossils including plant and temnospondyl amphibian remains. Geochronological investigations, performed by U-Pb analyses on zircon, indicate that the Perdasdefogu Basin was being infilled during the early Permian, between 297.9 ± 0.9/3.1 and 295.7 ± 0.7/3.0 Ma (without/with systematic uncertainties propagated, respectively), and covered shortly after, at 295.9 ± 1.1/3.1 Ma, by volcanic series. These age constraints show that the temnospondyls of the Perdasdefogu Basin, located in the southern side of the Variscan belt, were coeval to those of lower Permian basins located in the northern side of the belt. This demonstrates a rather large areal distribution for these fossil amphibians, which encompassed the northern, inner and southern parts of the Variscan belt. This in turn implies probable hydrographic connections that allowed for vertebrate migration between basins located across the belt. While hydrographic networks represent an obvious dispersal mechanism for ichthyofaunas, geochronological and paleontological data from the Perdasdefogu Basin suggest that this dispersal mechanism also holds for tetrapods, at least for aquatic and semi-aquatic groups. The reorganization of hydrographic networks due to the combined effects of climate change and Variscan tectonics could then have represented a driving mechanism for the migration of tetrapods in central Pangea during the late Carboniferous and early Permian.