First report of Hirnantian (Late Ordovician) palaeostomate bryozoans and associated biota of the northern Arabian Plate in southeastern Türkiye

The Halevikdere Formation of southern Türkiye yields an under-explored archive of Late Ordovician marine ecosystems. Our knowledge about Ordovician bryozoans in Türkiye is restricted due to the poor preservation of material. The first report of the Hirnantian high-latitude north Gondwanan bryozoans from southeastern Türkiye (Mardin-Derik area, Halevikdere Formation) is presented here. The Late Ordovician (Sandbian–Hirnantian) predominantly fine-grained succession of Derik is among the most remarkable Early Palaeozoic successions in southeastern Türkiye, but its precise geological age is poorly constrained. New bryozoan-rich sequence of glacio-marine related deposits contains indeterminate crinoids and brachiopods. Here we describe a new fauna of bryozoans from the ice-distal glaciomarine succession of the Halevikdere Formation, corresponding to the northern margin of the Arabian Plate. Three palaeostomate bryozoan species were identified: the esthonioporate Esthonioporata sp. indet., cryptostomes Graptodictya sp., and Ptilodictyina sp. indet. (aff. Proavella proava). In this study, a new trace fossil assemblage comprising several ichnotaxa is also documented from the upper part of the bryozoan-bearing sequence of the Hirnantian Halevikdere Formation. The identified bryozoans are related to the typical Ordovician taxa, but their presence in the assemblage, previously reported only from the Upper Ordovician of the Baltic region, is noticeable. These bryozoans and ichnofossils are typically associated with shallow marine environments, reflecting the conditions that prevailed during the time of their formation.