Geological significance of middle Cambrian trilobites from near Melba Flats, western Tasmania

Abstract

In western Tasmania, near Melba Flats, a basalt within the Serpentine Hill Complex is overlain unconformably by Dundas Group sediments (Hodge Slate). About 32 m above the unconformity, a siltstone contains agnostoid and polymerid trilobites that indicate correlation with the middle Cambrian Ptychagnostus punctuosus Zone (Drumian Stage of unnamed Epoch 3 of the Cambrian). This provides an upper limit of about 505.2–504.5 Ma to the emplacement of ultramafic allochthons in western Tasmania. Other fossils present include dendroids, inarticulate brachiopods, hyolithids, helcionellids and sponges. The widespread agnostoid trilobite Ptychagnostus affinis (Brøgger 1878) and the holocephalinid trilobites Meneviella and Holocephalina are recorded for the first time in Tasmania.

Key Words:

• Cambrian
• Dundas Group
• Tasmania
• trilobites
• ultramafic allochthons

Acknowledgements

Subsequent to the initial collections made by Rubenach and Jago, further work was supported by ARC grants to JBJ. The assistance of Max Banks (University of Tasmania) and the present and former curators Sue Cameron, Penny Williamson, Kathy Stait, Fernando Della Pasqua and Isabella von Lichtan of the Department of Earth Sciences, University of Tasmania is gratefully acknowledged. Ron Berry (University of Tasmania) is thanked for providing constructive comments. Keith Corbett and Ken McNamara provided constructive reviews of the original manuscript. The Director, Mineral Resources Tasmania, gave permission to use the map in Figure 1.