Irwin River Coal Measures
Specimen:
| Catalogue ID | Taxa | Element |
|---|---|---|
| S087432 | Glossopteris sp. | leaf |
Four principal coal seams are exposed in the North Branch of the Irwin River. Several test drives were opened into these seams during the late 19th century and again in the 1940s but seam splits, discontinuities and relatively high ash and sulfur contents discouraged further exploration until the 1980s. Even though this more recent exploration identified larger resources to the south, no exploitation of the coals has been undertaken due to the discontinuous nature of the coal seams and uneconomic seam thicknesses and coal quality (Le Blanc Smith & Mory 1995).
Invertebrate burrows are locally common, but the unit is better known for its abundant, but typically low diversity fossil flora incorporating species of Glossopteris, Vertebraria, Gangamopteris, Sphenophyllum, Neomariopteris, Liknopetalon, Paracalamites, Lelstotheca and Gondwanophyton (Rigby 1966, McLoughlin 1992, Adendorff et al. 2003). The floras contain a greater proportion of herbaceous plants than the coeval Glossopteris-dominated floras of the coal measures in the Collie Basin south of Perth. Floristic differences are likely due to the deltaic versus fluvial plain depositional settings of these respective assemblages.
Plant fossils are most visible in the shale bed immediately above the fourth (highest) coal
seam in the North Branch of the Irwin River (within the Coal seam Conservation Park, northeast of Mingenew). Private collecting is no longer permissible in the park, but extensive historical collections of fossils from this locality are held by the Western Australian Museum and the University of Western Australia. The NRM holds just a single specimen of Glossopteris from the Irwin River Coal Measures, collected by R. Fairbridge from Carynginia Gully in 1948.
References
Le Blanc Smith, G. & Mory, A.J., 1995. Geology and Permian coal resources of the Irwin Terrace,Perth Basin, Western Australia : Western Australia Geological Survey Report 44, 1-60.
McLoughlin, S. 1991. Locality 3.IrwinRiver , CoalSeamPark. In, Haig, D.W. (Ed.) Guide to pre-symposium excursion A3: northernPerthand southern CarnarvonBasin. 11th International Symposium on Ostracoda, Warrnambool, 1991. pp. 13-22.
McLoughlin, S. 1992. Permian sphenophytes from the Collie and Perth Basins ,Western Australia. Review of Palaeobotany and Palynology 75, 153-182.
McLoughlin, S. 1993. Plant fossil distributions in some Australian Permian non-marine sediments. Sedimentary Geology 85, 601-619.
McWhae, J.R.H., Playford, P.E., Linder, A.W., Glenister, B.F. & Balme, B.E., 1958. The stratigraphy of Western Australia. Journal of the Geological Society of Australia 4(2), 1-161.
Mory, A.J., Haig, D.W., McLoughlin, S. & Hocking, R.M. 2005. Geology of the northern Perth Basin ,Western Australia. A field guide. Geological Survey of Western Australia Record 2005/9, 71 pp.
Rigby, J.F. 1966. The Lower Gondwana floras of thePerthand Collie Basins, Western Australia. Palaeontographica 118B, 113-152.
Segroves, K.L., 1971. The sequence of palynological assemblages in the Permian of the Perth Basin, Western Australia. Proceedings and Papers of the Second International Gondwana Symposium, Johannesburg, South Africa, 1970, 511-529.
Fig. 1. Outcrop of the fourth (uppermost) coal seam of the Irwin River Coal Measures in the Coalseam Conservation Park, northern Perth Basin. The coal is overlain by grey–white fossiliferous shales, which are in turn unconformably overlain by a river terrace of Cenozoic red ferricrete.