Stratigraphic Framework and Lower Palaeozoic Land Plant Evolution in the Cellon Section (carnic Alps, Austria)

The Cellon Section is widely regarded as one of the most iconic Silurian reference sections worldwide and serves as a fundamental benchmark for numerous Ordovician, Silurian and Devonian studies. It represents the type locality for five major lithostratigraphic units: the Uqua, Plöcken, Kok, Cardiola and Alticola formations. Eighteen conodont zones have been identified throughout the succession. The entire Ordovician interval at Cellon corresponds to the Amorphognathus ordovicicus Zone, while fifteen additional conodont zones have been documented across the Silurian, from the upper Llandovery through the end of the Pridoli. However, some upper Llandovery and Wenlock intervals associated with black shale layers are absent from the record. Two further biozones have been recognized in the lower Lochkovian. During the early Palaeozoic, the Carnic Alps belonged to the Galatian terranes, which detached from northern Gondwana in the Early Ordovician and migrated northward at a rate exceeding that of the main supercontinent. The biostratigraphic dating of the Cellon section based on conodonts provides a valuable framework for palynological investigations, particularly those based on cryptospores, trilete spores and acritarchs, offering new perspectives on the terrestrialization process, its timing and its palaeoenvironmental implications across the end Ordovician mass extinction and throughout the Silurian on the northern Gondwana margin. The studied interval comprises, in ascending order, the Valbertad Formation (Katian), the Uqua Formation (Katian), the Plöcken Formation (Hirnantian), the Kok Formation (Aeronian to lower Ludfordian) and the Cardiola Formation (Ludfordian). Eight well‑preserved palynozones, containing diverse miospore and acritarch assemblages, have been defined and rigorously calibrated against the conodont biostratigraphy. Notably, vascular‑plant‑producing trilete spores are documented for the first time in the Katian–Hirnantian interval of this palaeogeographic region. These results shed new light on the resilience of early land plants during the end‑Ordovician glaciation, refine the chronostratigraphic framework of Ordovician–Silurian palynozones through conodont correlation, and reveal strong compositional similarities with both Laurussian and Gondwanan assemblages highlighting the low diversity typical of early evolving terrestrial vegetation.