The Ordovician-Silurian boundary at Darraweit Guim, central Victoria

Abstract

The graptolite-bearing sequence across the Ordovician-Silurian boundary at Darraweit Guim, central Victoria is subdivided into four biostratigraphic units: the Dicellograptus ornatus-Climacograptus latus Zone, Climacograptus? extraordinarius Zone, Glyptograptus? persculptus Zone and Parakidograptus acuminatus Zone. Diagnostic graptolites of the upper three zones are described, and the trilobite D. (Dalmanitina) darraweitensis Campbell, characteristic of the C? extraordinarius Zone, is revised and assigned to the genus Songxites Lin within the subfamily Mucronaspidinae. Detailed correlation of the Darraweit Guim sequence with the Ordovician-Silurian boundary sequences of Dob's Linn (Scotland), Mirny Creek (northeastern Siberia), Chu-Ili Range (Kazakhstan), the Yangtze Gorge region (Hubei) and the northern Cordillera (Canada) is made on the basis of short-lived, cosmopolitan graptolite species. The relevant rock units at Darraweit Guim are defined for the first time.