western australia's permian plants

THE

FOSSIL

COLLECTOR

September 1992 - Page 25

WESTERN AUSTRALIA'S PERMIAN PLANTS SteTe Mcloughlin, Department of Geology, University of Western Australia, Nedlands, W. A" Australia, 6009. Abs tract: Permian floral assemblages from the Collie Basin, Irwin River Coal Measures (Perth Basin ) , Carnarvon Basin and Canning Basin of Western Australia are brief ly described and i llustrated .

ThE' remains o f Permian ( ca. 290-245 Myo) plants constituted the raw material for the bulk of Australia's vast black coal reserves. In Western Australia, o pencut mines at Collie supply coal which generates a large proportion of the state 1 s electrical energy needs. Lesser reserves of coal i n the northern Perth and Canning Basin s have not, a s yet, been economically viable for extraction. I n addition, partial breakdown of fossilised terrestrial plants and marine algae may have significantly contributed to the generation of the state's liquid and gaseous hydrocarbon reserves. Permian plant macrofossils in Western Australia are most readily accessible at Collie in the state 1 s southwest a nd along the Irwin River approximately 350 km north of Perth. Once exposed, fossils from these areas can deteriorate quickly d ue to cracking and the crystallisation of salts and sulphates with drying. Some protection can be offered by the application of a thin coat of varnish although this sometimes makes the fossils less photogenic.

Institutional collections The Geology Department of the University of Western Australia has the la rgest collections of Permian plant fossils from W.A. Several thousand specimens have been collected in the past two years as part of a revision of the fossil floras by the author. The Western Australian Museum has a small but significant collec tion including specimens of several rare sphenophyte and lycophyte species. The Geological Survey of Western Australia possesses a small collection consisting mostly of glossopterid leaves from the Col l ie coal mi nes. The Bureau of Mineral Resources in Canberra holds most of the Canning Basin Perm i an plant collections . The University of Newcastle holds a range of Perth and Collie Basin specimens described by Rigby (1966) .

Collie Basin The best fossil-bearing exposures in the Collie district are within the operating opencut coal mines. However, the mines are strictly off-limits to collectors owing to safety hazards in the work area.

Page 26 - September 1992

THE

FOSSIL

COLLECTOR

WESTERN AUSTRALIA ' S PERMIAN PLANTS (Cont. ) Access is also prohi bited to t he ove rbur den heaps as th e dump slopes are of ten unstab le and are in close proximity to the operating mines . Some old mines i n the di s tri c t (e . g . Stoc kton and Black Diamond Pits) are no .... abandoned and have filled .... ith ....ater prov iding local ....atersport rec rea t ion areas . Over bur den dumps around t hes e a bandoned mines st i ll occas i ona lly yield ....ellprese rved fossil plants . The Permi an flo r as preserved at Coll ie

Figures 1-5. Vertebra ria indi ca Ro yle (a glossopter id root i mp r ession) . J. 1 ; Collie Coal Me~sures (hg.I) . Glossopte r is sp ., J. 1; Collie Coal Measures (fig . 2). Sama ropsfs sp. (probable glossopterid seed), J. 2. 5; Irwin River Coal Measures (fig.3 ) . Eretlllonia sp . (scale of glossopterid male fr uit)' x 1; Irwin River Coal Measures (£1g.4). ?Cangamopteris obovata (Carruthers) White , x 1 ; Collie Coal Measures (fig.5) .

THE

FOSSIl.

COl.l.ECTOR


are of low di versi ty a nd no more than abou t six s pecies are like ly to be fou nd a t an yone sit e. The Co llie fl oras de veloped in high lat i t ude s dur i ng the Ear l y Permian ( 290-260 My» shortly after t he re treat of one or more major i ce sheets that had co vered much of Gondwana about 290 mi ll ion years ago. The dominant fossils (as 1n virtually ever y te rre s trial assemblage of this age across th e southern hemi sphe r e) are the spatula- s haped , net-vei ned, gloss opterid leaves . Two gene ra . . .ithin this group are recognised at Col l ie: Glossopteris - with a prominent ce ntral midrib in the leaf ( Fig . 2) ; and Gangamopteris . . . hic h lacks such a midrib (Fig . S) . In reality the dist inction i s sometimes rather arbitrary as the "midribs" of (;losso pte ris leaves are constructed of tightl y a gg regated in terco nnec t ed ve i ns other . . . ise identica l to the reticulate vei ns fou nd on the outer parts of the Glossopteris leaf a nd throughout the leaf in Ga ngamopteris. Both genera undoubted ly belonged to the same natural alliance. Several species of both ge nera are repr esented at Collie and their c lassification is c urr e ntly under rev iew by the author. Because glossopterid s we r e deCiduous, different parts of the plants . . . ere often foss i lised sepa ratel y . As a result many differen t names have been app l ied to the various fossilised orga ns of this group e.g., Glossopteris and Gangamopteris leaves; Vertebra ria roots ( Fig. 1); Samaropsis seeds ( Fig. 3 ); Ot tokaria , Dictyopte r idi um, etc .fema le fruits (Fig. 6 ) ; Eretmonia male fr uits ( scale leaves: Fig . 4); Arberiella - po llen sacs; Protohaploxipinus - po ll en ; a nd Araucarioxylon wood. A second group of leaves fo und at Collie is assigned to Cordaites (sometimes called Noeggerathiopsi s: Fig . 7). These leaves show a similar spatulate shape t o GlOSSOPteris but lack cross-connec t i ons between the veins . Fru i t ing bodies have not yet been found di rectl y connec t ed to sout he rn hemis phere Cordaites l eaves so t heir rela t ionships with very similar norther n hemisphere forms of t hi s age remain uncertain. The gond wa nan Cordaites may indeed have cl osest affinities with the glossop terids a nd be only dis t antl y related t o the northern Cordaites . Both glossopterids and cor daitaleans . . .ere probably substantia l woody trees reac hi ng 30 m in height based on t he presence of abundant large coalifi e d woody fragments within the coal measures. Silicified wood appears to be absent from the Co llie Coal Measures o . . . ing to unfavourable sediment chemistry at the t ime of deposition. The glossopterids probab l y fo rmed exte ns ive l ow-d iversity forests on broad swam py l owlands somewha t ak i n t o t he moder n co nifer fo rests of the Wes t Si ber i an Plai n . The co rdai talea ns are not s o abu ndan t l y preserved as the glossopte r ids and ma y have preferred better-drained habitats

Pag!! 28 - September 1992

THE

FOSSIL CO LLECTOR

WESTERN AUSTRALIA ' S PERMIAN PLANTS (Cont. ) norma ll y further away from s ites of sediment deposition. He rba ceous pLants are rare at Collie and ferns appear to be enti rely absent. Small lycopod axes with spinose leaves (Fig . B) or undividual needle- shaped leaves ( Fig.9 ) from larger shr ubt o tree-si zed lyco pods are found spo r adically. Sphenophyte fo l iage is represented by a single species (Raniganjia minima Rigby. 1966 ) showing regular whorls o f delicate t ransverse ly striate fused leaves arranged around a slender join ted axis (Fig . 15). The dear th of de licate herbaceous fossils , the abundance of coalified wood fragments , the structura l character of the Co llie Basi n, an d t he dominance of coarse-gr ained channel s a ndstones within t he Co llie Coal Measures s uggest t hat the sediments were deposited in an alluvial plain setting within a f a ult-bounded valley .

Irwin River (Perth Basin) The pl a nt fossils o f the Irwin River distric t are of roughly the s ame age as t hose at Collie. The best deposits occur within Coa l Seam Park, an environme ntal reserve at the junction of the North and South Irwin Rivers. Excavati on of fresh material should be avoided W"ithin the reserve but the split ting of loose surface siltstone blocks may sometimes reveal exquisite plant impressions . The Irwi n River Coal Meas ur es we r e probably deposited in lower delta plain environments and the unit is both underlain and ove rlai n by ma rine sediment s. This coastal de positional se tti ng probably experienced a more equable climate , consequently t he f oss il flora s are more diverse here than at Collie . Glossopterids again dominate the fossil as's emblages but Cor daites appea r s to be absen t ( r eflecti ng its prefe r ence for mo r e upland habitats) . A single delicate fer n species [Neomariopteris lobifolia (Morris) Maithy 1974] occurs at several intervals within the coal measures . Lycopods are relat ively rare and mostly herbaceous (Rigby, 1966). Sphenophytes are common and diverse especial ly towards the top of the fo rmation and are represented by the ge nera Sphen ophyllum (Figs . 11, 12) , Lelstotheca (Fig . 10) , Paracalamites (Fig . 13 ), ?Phyllotheca, and Go ndwa nophyton (Fi g . 14 ) . The last genus r epresents a r e lativel y new fi nd within Australia (it having bee n previously described f r om I ndia) , however, all the known s pecimens are somewhat fragmentary and the fan-shaped dichotomo us-ve ined leaves of this plant may indicate affini ties

THE FOSSIL COLLECTOR

September 1992 - Pase 29

Yisurea 6-8. 10ttokaria sp . ( glossopterid fecale fruit ) , I 4; Irwin Ril'er Coal l'Ieasurea (ftg . 6). Cordaitea .patulata (Dana) Ri8by, Kahesh wad & Schopf, I 1: Collie Coal l1easurea (fia . 7). s..U lycopod a!lb, 13; Irvin lil'e r Coal Hea.sures (fia.8) .

Page 30 - September 1992

THE

FOSSIL COLLECTOR

WESTERN AUSTRALIA'S PERMIAN PLANTS (Cont . ) with the Ginkgoales rather than the Sphenophyta . Most of the sphenophytes at Irwin River are delicate slender-stemmed herbaceous species which probably possessed a scrambling habit and filled niches in the understory of glossopterid woodlands or perhaps occupied more exposed samphi r e'=H Ke-posrtions on the Permian delta flats. Carnarvon Basin Most of the Permian sequence in the Carnarvon Basin (stretching from Kalbarri in the south to Karratha in the north) is represented

Figures 9-15. Detached leaf from a large lycopod, x I; Collie Coal Measures (fig.9). lanceolata McLoughlin, x 1.5; Irwin River Coal Measures (fig.l0). rhodesii Rigby, x 1.5; Ir .... in River Coal Measures 1). McLoughlin, x 1; Irwin River Coal Measures (fig. a sphenophyte axis, x 1 j Irwin River Coal dayrnondii Ri gby, x 1.5; Irwin River Coal Measures (fig.14). x I.S; Collie Coal Measures (fig .IS ) .

THE

FOSSIL

COLLECTOR


by marine sediments. Al though these deposits are often rich in shelly fossils, few plant remains have been recovered from this region. Teichert 0942, 1943) identified isolated glossopterid leaves from the shallow marine Callytharra Formation and silicified and limonitized wood occurs in several units (Hocking, 1990). White (1959) and White & Condon (1959) described lycopod log impressions ft:om the Harr is Sandstone which may be of latest Carboniferous or earliest Permi an age.

Canning Basin Although well-preserv~d Permian plant fossils, including silicified wood, occur in the Canning Basin they are confined to exposures in the remote northern and eastern parts of the basin wi thin the Great Sandy Desert. They are preserved in the Poole Sandstone (Early Permian) and Condren Sandstone and Hardman Formation (both Late Permian). White (961) identified several species of glossopterid leaves, seeds, and roots together with Cordaites and possible sphenophyte remains collected during Bureau of Mineral Resources regional geological surveys, The identifications of some of these taxa have been revised by Rigby et a1. (1988) and Rigby (in press). Future fieldwork is planned by the author to more thoroughly investigate these fossil assemblages.

References Hocking, R. M., 1990. Carnarvon Basin. In, Geology and Mineral Resources of Western Australia: Western Australian Geological Surrey , Memoir 3: 77-119. Maithy, P. K., 1974. A revision of the Lower Gondwana Sphenopteris from India. PalaeoOotanist 21(1): 70- 80. Rigby, J. F ., 1966a. The Lower Gondwana floras of the Perth and Collie Basins , Western Australia . Palaeontographica lISB : 113-152. Rigby, J. F., in press. Permian flora . Geological SurTer of Western Australia, Bulletin 135. Rigby, J . F. Chandra, S . , & Surange , K. R., 1988. Glossopterid plant remains in the Permian of Western Australia . Association of Australasian Palaeontologists, Memoir 5: 73-78. Teichert, C., 1942. Gangamopteris in the marine Permian of Western Australia. Geology Magazine 79: 321-327. Teichert, C., 1943. The distribution of Gangamopteris in the Permian of Wester n Australia. Australian Journal of Science 6(3): 79-80. White, M. E., 1959. Botanical report on 8 lepidodendroid log from the Harris Sandstone, Carnarvon Basin, Western Australia. Bureau Hilleral Resources, Geology and Geophysics, Australia, Report 38: 53-54. White, M. E., 1961. Plant fossils from the Canning Basin , Western Australia. Appendix 6, In Veevers, J. J. & Wells, A. T . The Geology of the Canning Basin, Western Australia. Bureau of Hineral Resources, Geologr and Geophysics, Australia, Bulletin 50: 291-320. White, M. E. & Condon, M. A., 1959. A species of Lepidodendron from the basal Lyons Group Carnarvon Basin, Western Aus tralia. Bureau of Mineral Resources, Geologr and Geophysics, Australia, Report 38: 55-54.