Palynological assemblages from the 2nd tectono-sedimentary cycle of the Southern Alps: New constraints for the onset of the Alpine cycle and regional-global inferences

Analysis of palynological assemblages from the Val Daone Conglomerate (VDC) Formation (central Southern Alps) provides significant new information on the age of this lithostratigraphic unit and, therefore, of the inception of the Permian tectono-stratigraphic cycle 2 (TSU2) in the Southern Alps. The VDC Formation represents a nearly 100-m thick, medium-grained fluviatile body which can be followed in western Trentino, from the NE part of the Permian Collio Basin to the west, up to the Val Rendena to the east. Palynomorphs from the VDC Formation are well- preserved in the Val di Scale (Val Rendena) section but poorly preserved in the Ronchi section (Val Daone). Comparisons between the results of the present study with data from the Tregiovo, Val Gardena Sandstone and Bellerophon formations of the Italian Southern Alps reveal a sequence of distinct associations that are stratigraphically and perhaps palaeoenvironmentally controlled. The stratigraphy of the palynomorph assemblage of the VDC is diagnostic of the late Capitanian-Wuchiapingian. Two different palynozones within the Val Daone Conglomerate PalynoZone - VDCPZ are established from the VDC Formation, the lower (VDCPZ1) from the Ronchi section, attributed to late Capitanian-early Wuchiapingian, and the upper (VDCPZ2) from the Val Rendena section, of Wuchiapingian age. These VDCPZs show close similarities with coeval associations recorded from other European areas. This is consistent with the stratigraphic position of the VDC Formation and allow us: 1) to assign the beginning of the Permian 2nd tectono-sedimentary cycle in this sector of the Southern Alps to the late Capitanian-early Wuchiapingian and 2) to suggest that the depositional hiatus caused by the intra-Permian tectonics straddled most of the Guadalupian and it is partly time-equivalent with the Pangaea gap. Moreover, the VDCPZ1 is one of the few low-latitude associations that are time-equivalent or slightly younger than the end-Guadalupian mass extinction, a major climate-driven event that significantly changed terrestrial faunas. • Two miospore biozones were established in the VDC Formation. • The magnitude of the gap between TSU1 and TSU2 in central Southern Alps is now estimated from 13 to 15 Ma. • The microflora “mixture” suggests a gradual floristic turnover from the Guadalupian to Lopingian time interval. • The resilience of land plants to the climatic change is associated with the end-Guadalupian extinction event.