Devonian fish remains, biostratigraphy and unconformities, Narromine 1:250 000 map sheet area, central New South Wales (Lachlan Fold Belt)

Abstract

A fossil fish assemblage associated with marine invertebrates from the Coonardoo Sandstone (Wallingalair Group) at Boor Hill (eastern limb of Tullamore Syncline) contains phyllolepid and bothriolepid placoderms of probable Late Devonian age. An angular unconformity with the overlying Hervey Group indicates erosion and folding during the Middle – Late Devonian, and evidently younger than the main Tabberabberan orogenic event. Invertebrate remains demonstrate a Late Devonian marine interval, not previously recognised as far west as the Tullamore Syncline, and assumed to represent the global maximum sea-level in the late Frasnian immediately preceding the Frasnian – Famennian extinction event. A phyllolepid placoderm plate from a sedimentary interbed of the Dulladerry Volcanics in the Hervey Syncline compares with abundant phyllolepid material from the Merriganowry Shale Member of the Dulladerry Volcanics near Cowra, and similar occurrences in the Comerong Volcanics and Boyd Volcanic Complex in southeastern New South Wales. Biostratigraphic data suggest a late Middle Devonian (Givetian) age for the Merriganowry Shale Member of the Dulladerry Volcanics, which appears conformable beneath the Upper Devonian Hervey Group.

Key words:

• Devonian
• fish
• Hervey Group
• Lachlan Fold Belt
• marine transgressions
• unconformities

Acknowledgements

Lawrence Sherwin, John Pickett and Carole Burrow assisted with fieldwork in 1994, and advised on various fossil age determinations, and Lawrence Sherwin provided manuscripts in press. H. M. (Mike) Doyle assisted with specimen preparation. Pam O'Sullivan provided the Tomingley specimen for study, with the assistance of Bill Platts and Noreen Morris, who provided locality details. Dave Wallace, Doone Wyborn, Lawrence Sherwin and Ollie Raymond contributed to field mapping of the Hervey Group for the new edition of the Forbes map sheet (1995 – 96). Alex Ritchie (Australian Museum, Sydney) and John Long (Museum Victoria, Melbourne) provided unpublished information and casts of phyllolepid material for comparison. Ian Percival provided data on old specimens in the Geological Survey of New South Wales palaeontological collection. I thank Australian National University (ANU) colleagues Dick Barwick for advice on illustrations, Peter Jones and Chris Klootwijk for commenting on a draft of the manuscript and journal reviewers John Long and Fons VandenBerg. This research is a contribution to IGCP Project 491, and is supported by ARC Discovery Grant DP0558499. R. Arculus is thanked for provision of facilities in the Department of Earth & Marine Sciences, ANU.