Latest Cambrian–earliest Ordovician conodonts and microbrachiopods from northern Victoria Land, Antarctica: Handler Ridge revisited

Abstract Conodonts and microbrachiopods of latest Cambrian–earliest Ordovician age are documented from the Handler Formation of northern Victoria Land, Antarctica. Five spot samples from allochthonous limestone clasts collected during expeditions conducted by the Korean Polar Research Institute in 2013–2014 yielded the conodonts Cordylodus proavus , C. lindstromi , Hirsutodontus simplex , and Teridontus nakamurai , associated with four species of brachiopods (two indeterminate acrotretides, a zhanatellid lingulide, and a siphonotretide tentatively referred to Schizambon reticulatus ). The four conodont species are distinctive taxa occurring in the widely distributed Cordylodus lindstromi Biozone of the latest Cambrian and the Iapetognathus Biozone at the base of the Ordovician. The allochthonous limestone clasts in the Handler Formation were likely derived from now-lost carbonate shelves developed locally (in the Bowers Arc) or transported from further north. Fossil evidence from the Handler Formation indicates that the final episode of the Ross Orogeny that uplifted and deformed the Robertson Bay Group was no older than early Tremadocian (earliest Ordovician). Striking similarities in fossil content, ages and depositional settings between the limestone olistoliths in the Handler Formation and latest Cambrian–earliest Ordovician autochthonous and allochthonous carbonates of the post-Delamerian Orogen recognized in the Koonenberry Belt (Gnalta Shelf) in far western New South Wales support the depositional model considering the Robertson Bay Group as the synorogenic deposits of the Ross Orogeny.