Reconstruction of a Late Cisuralian (Early Permian) floodplain lake environment: Palaeontology and sedimentology of the Tregiovo Basin (Trentino-Alto Adige, Northern Italy)

The Late Cisuralian is known as a time of increasing aridity, compared to the Late Pennsylvanian-Early Cisuralian. Although several studies highlighted this trend at low latitudes of Western Pangaea, little is known from Central Pangaea environments. The discovery of new fossiliferous horizons in the Late Cisuralian Tregiovo Formation (Northern Italy), allowed a new palaeoenvironmental study based on facies analysis, ichnology, palaeobotany, plant-insect interaction and palynology. Three facies associations were identified (A-C), and correspond to floodplain lake, ephemeral lacustrine and distal alluvial fan environments, respectively. The tetrapod ichnoassociation is more diverse than previously known, including abundant diapsid and non-diapsid reptile tracks and rarer temnospondyl amphibian tracks. Plant fossils are characterized by a predominance of hinterland taxa (conifers), hygrophytic plants are present as well. The sporomorph association is dominated by miospores of Cordaitales, Voltziales, and Peltaspermales while trilete lycopsid and fern miospores are rare which corresponds well with the macroflora. Invertebrate trace fossils and feeding traces on plant fossils are described for the first time from the Tregiovo Basin suggesting transitional, low energy environments, and a relatively low level of herbivory, respectively. This study evidences the development in the Tregiovo Basin of a wet-and-dry (probably seasonal) climate, which became drier between facies associations A-B. This environment constitutes an important reference since few data are known to infer the Late Cisuralian climatic conditions of Central Pangaea.