Permian Non-Marine Bivalves From the Collio and Guncina Formations (Southern Alps, Italy): Revised Biostratigraphy and Palaeobiogeography

Abstract

Non-marine bivalves are key fossils in Permian continental stratigraphy and palaeogeography. Although known since the end of 19th century, the occurrences from the continental basins of the Southern Alps have never been extensively studied. The non-marine bivalves from the Lower Permian Collio Formation (Brescian pre-Alps) are herein revised, and those from the Guncina Formation (Athesian District) are described for the first time. These two units yielded non-marine bivalves belonging to the genus Palaeomutela sensu lato, which is widespread in the Permian continental successions of eastern Euramerica. Three Palaeomutela morphotypes have been herein described: oval-subtriangular, subtrapezoidal and elongated. The latter includes several specimens herein assigned to Palaeomutela (Palaeanodonta) berrutii sp. nov. and dominates the Collio Formation association. The Guncina Formation yielded also the genus Redikorella, for the first time co-occurring on the same stratigraphic horizon of Palaeomutela, herein assigned to Palaeomutela (Palaeanodonta) guncinaensis sp. nov. To-date, it was generally accepted that the first members of the genera Palaeomutela and Redikorella occurred during the Ufimian (late Kungurian of the global scale) in the non-marine basins of the Cis-Ural Foredeep and of Angara, respectively. Such new finds in the early-middle Kungurian of southwestern Europe, well constrained by radioisotopic dating, suggest new global first appearance (First Appearance Datum) and a possible new center of origin of these genera. This fact raises new questions on biostratigraphy, palaeobiogeography and palaeoecology, which will require further research. If we assume that the genera Palaeomutela and Redikorella had only one center of origin, we need to hypothesise possible migration routes from SW Europe to the continental basins of Eastern Europe and Angara. Apparently, such migration could be better supported by a Pangaea B palaeogeographic configuration.

Radioisotopic U-pb Dating of the Kolchugino Group Basement (Kuznetsk Coal Basin, Siberia): Was the Change of Early-Middle Permian Floras Simultaneous at Different Latitudes in Angaraland?

“…Most interesting are the cosmopolitan Redikorella Silantiev, 1994 appearing for the first time in the Starokuznetsk Fm. This genus is abundant in the Solikamskian regional stage of the East European Platform and the Urals, in the Inta Fm of the Timan-Pechora Basin, and in the upper part of the Burguklian regional stage of the Tunguska Basin [27, ref. therein], and is recently found in the Guncina Fm of the Southern Alps [58]. In the upper part of the Starokuznetsk Fm, non-marine bivalves become smaller in size, their taxonomic diversity decreases.…”

“…Recent discoveries have broadened the understanding of the geographic radiation of Redikorella and Palaeomutela. These taxa are found in the Late Kungurian of the continental basins of the western Tethyan sector of the Variscides, suggesting that other areas may be the centre of origin for both genera [58].…”

U-Pb Dating of the Kolchugino Group Basement (Kuznetsk Coal Basin, Siberia): Was the Change in Early–Middle Permian Floras Simultaneous at Different Latitudes in Angaraland?

“…Recent discoveries have broadened the understanding of the geographic radiation of Redikorella and Palaeomutela. These taxa are found in the Late Kungurian in the continental basins of the western Tethyan sector of the Variscides, suggesting that other areas may be the centre of origin for both genera [50].…”

“…Most interesting are the cosmopolitan Redikorella Silantiev, 1994, appearing for the first time in the Starokuznetsk Fm. This genus is abundant in the Solikamskian regional stage of the East European Platform and the Urals, in the Inta Fm of the Timan-Pechora Basin and in the upper part of the Burguklian regional stage of the Tunguska Basin [26], and it has recently been found in the Guncina Fm of the Southern Alps [50]. In the upper part of the Starokuznetsk Fm, non-marine bivalves become smaller in size, and their taxonomic diversity decreases.…”