Article: The Tremadoc graptolite sequence of Lancefield, Victoria
R. A. Cooper and I. R. Stewart
Biostratigraphy of the early Lancefieldian sequence of Lancefield, Victoria, is described. Lancefieldian zonal composition and nomenclature is revised: the earliest zone, La 1, here renamed the Zone of Dictyonema scitulum and Anisograptus, is comprised of D. scitulum Harris and Keble, D1 enigma sp. nov., Anisograptus compactus sp. nov., and A. delicatulus sp. nov. A newly discovered assemblage with Psigraptus and several species of Clonograptus has been found in overlying strata and is here given the new zonal designation, La 1.5, Psigraptus and Clonograptus. The following zone, La 2, Adelograptus victoriae and D. macgillivrayi, is unchanged from previous usage. All species are described and illustrated. D. campanulatum and Staurograptus diffissus are both regarded as dubious species. The genus Kiaerograptus is discussed and revised to include several biramous Tremadoc species; the genus, together with Anisograptus and Psigraptus are recorded for the first time in Australasia, and Staurograptus is deleted from the record.The La 1 Zone is correlated with the Matane horizon of Quebec and with the zones of S. tenuis and A. richardsoni of Yukon and inferred to be of early Tremadoc age. The La 1.5 Zone is correlated with the C. aureus Zone and basal part of the Kiaerograptus antiquus Zone of Yukon. The La 2 Zone is correlated with the K. antiquus Zone (upper part) of Yukon, with Zone 2 Adelograptus-Clonograptus of Texas, and is of late Tremadoc age.