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TRIASSIC PLANTS OF EASTERN AUSTRALIA

Locality Wivenhoe Hill

The Wivenhoe Hill flora (Middle Triassic)

Fossil plants are preserved in a road cutting on the western side of Wivenhoe Hill, near Esk, about 50 km northwest of Brisbane , southeast Queensland , Australia. The plants are preserved primarily as manganese- and iron-stained impressions, although some stem casts of shenophytes are also present. The fossils occur in the Esk Formation, within the Esk Trough — a narrow, NNW-SSE, graben-like structure that has also been interpreted as a relictual southerly extension of the BowenBasin foreland basin complex (Campbell et al. 1998). The Esk Trough contains three principal units: the Esk Formation, Bryden Beds and Neara Volcanics. The relationships of these units within the basin are obscure due to poor and discontinuous exposures. The Esk Formation is dated as Anisian—Ladinian (Middle Triassic: roughly 246—229 Ma) based on their fossil spore-pollen content (de Jersey 1975) and a radiometric date of 236—242±5 Ma from lavas in the overlying and partly interdigitating Neara Volcanics (Webb 1982a).

 
The Wivenhoe Hill site is one of several localities in the Esk area yielding Middle Triassic plant fossils. Some of these are now submerged beneath Wivenhoe Dam but episodically become accessible after prolonged droughts. These floras, although rich and relatively well-represented in museums, have not been studied intensively. A few papers have provided relatively brief surveys of individual sites or more focused studies of selected taxa. Amongst these, the more important include the studies of Walkom (1924, 1928), Hill et al. (1965), Webb (1982b, 1983 2001) and Rigby (1977). The Esk Formation flora is probably equivalent in age to the well-studied flora of the Nymboida Coal Measures in northern New South Wales. The flora is dominated by corystosperm (Dicroidium) leaves, but a broad range of other gymnosperm, fern and sphenophyte taxa are also represented.

 
The Swedish Museum of Natural History hosts 267 specimens from Wivenhoe Hill collected in 1982 by Stephen McLoughlin. Most of the specimens represent leaf fossils but a few reproductive structures are also present. The collection includes one of the oldest Australian records of insect oviposition trace fossils on a leaf.

Reference

Campbell, L.M., Holcombe, R.J. & Fielding, C.R. 1998. The internal structure and sedimentology of the Esk Trough, southeast Queensland. Australian geological Convention Townsville, July 1998. Abstract.

De Jersey ,N.J. 1975. Miospore zones in the Lower Mesozoic of southeastern Queensland. In Gondwana Geology.Campbell , K.S.W., ed.,AustralianUniversityPress, Canberra, 159—172.

Hill, D., Playford, G. & Woods, J.T. (eds), 1965. Triassic fossils of Queensland.QueenslandPalaeontographical Society: Brisbane.

Rigby, J.F. 1977. New collections of Triassic plants from the Esk Formation, southeast Queensland. Queensland Government Mining Journal 78, 320—325.

Webb, J.A. 1982a. Triassic radiometric dates from eastern Australia. In Numerical Dating in Stratigraphy. Odin, G.S., ed., John Wiley, New York, 515-521.

Webb, J.A. 1982b. Triassic species of Dictyophyllum from eastern Australia. AIcheringa 6, 79—91.

Webb, J.A. 1983. A new plant genus, possibly a marattialean fern, from the Middle Triassic of eastern Australia. Association of Australasian Palaeontologists Memoir 1, 363—371.

Webb, J.A. 2001. A new marattialean fern from the Middle Triassic of eastern Australia. Proceedings of the Linnean Society of New South Wales 123, 215—224.

Walkom, A.B. 1928. Fossil plants from the Esk district of Queensland. Proceedings of the Linnean Society of New South Wales 53, 458—468.

Walkom, A.B. 1924. On fossil plants fromBellevue , near Esk. Memoirs of the QueenslandMuseum 8, 77—92.

Map of Australia showing the distribution of Triassic sedimentary basins including the Esk Trough. Click for larger image.