Miocene Wood from the Latrobe Valley Coal Measures, Victoria

Miocene wood from the LaTrobe Valley coal measures, Victoria,. Australia DAVID R. GREENWOOD GREENWOOD, DAVID R., 30.9.2005. Miocene wood from the LaTrobe Valley coal measures, Victoria, Australia. Alcheringa 29, 351-363. ISSN 0311 5518. An initial study of a collection of fossil conifer wood is reported from the late early Miocene Yallourn Clays, an interseam unit intergrading into the base of the early to middle Miocene Yallourn seam of the LaTrobe Valley, Victoria in southeastern Australia. The fossil wood shares characteristics with the modern genera Dacrycarpus and Dacrydium. On the basis of contiguous, uniseriate tracheid pitting and 1-2 podocarpoid cross field pits, it is placed in the form genus Podocarpoxylon, and the new species P. latrobensis. The wood is compared with extant Podocarpaceae and other Australian fossil woods. Its ring anatomy is consistent with low temperature or rainfall seasonality in the early Miocene. David R. Greenwood [[email protected]], Sustainability Group, Victoria University, St Albans campus, PO Box 14428, Melbourne City MC, VIC 8001, Australia; received 18.7.2003; revised 6.1.2005. Current address; Environmental Science, Brandon University, 270-18th Street, Brandon, MB, Canada, R7A 6A9. Key words: Miocene, wood, Podocarpaceae, coal, LaTrobe Valley, Australia MIOCENE vegetation in Australia is primarily Australia (Taylor et al. 1990), a wood character known from fossil pollen and the macrofossil that is consistent with deciduous forests record of leaves or reproductive organs. Bishop (Greenwood 2001). The paucity of systematic & Bamber (1985), Leisman (1986), and Bamford & analysis of Australian Cenozoic wood is McLoughlin (2000), are the sole recent systematic perplexing given the abundance of material readily accounts of Australian Cenozoic fossil wood, available and the attention given to systematic although early and more recent Australian analysis of modern taxa of Australian forest trees workers noted the presence and quality of (e.g. Dadswell & Eckersley 1935, 1940, Dadswell preservation of Cenozoic fossil wood in the 1972, Ilic 1991, see also Greguss 1955). In their brown coals of the LaTrobe Valley of Victoria account of the Australian fossil record for and in South Australia, and in other sediments in conifers, Hill & Scriven (1998) did not cite any these States and also in New South Wales, fossil wood taxa. including silicified wood (Chapman 1918, Nobes The brown coal deposits of the LaTrobe 1922, Howchin 1923, Chapman 1926, Barnard 1927, Valley of South Gippsland in Victoria (38° 05’S, Patton 1928, 1958; Gill 1952, Douglas 1983, Taylor 146° 05’E; Fig. 1) have been palaeobotanically et al. 1990). Sahni (1920) described two investigated since early last century (Chapman angiosperm species from Paleogene sediments 1925a, 1925b; Deane 1925, Greenwood et al. 2000, near Brisbane in Queensland, and Rozefelds & Holdgate 2003). They were also the subject of Baar (1991) have described termite frass in numerous investigations by Cookson and her co- Cenozoic wood from Queensland. Fossil wood workers (Cookson 1947, 1950, 1953; Cookson & with well-defined uniform growth rings has been Duigan 1950, 1951; Cookson & Pike 1953a, 1953b; reported from high palaeolatitudes sites in Pike 1953), and others (e.g. Willis & Gill 1965), Paleocene floras from the Southern Highlands of culminating in Duigan’s (1965) description of the 0311/5518/2005/02351-13 $3.00 © AAP Miocene palaeovegetation. Numerous palyno- 352 DAVID R. GREENWOOD ALCHERINGA Fig. 1. Location map showing site of the Morwell Open Cut brown coal mine and the Latrobe Valley, and other localities where Cenozoic fossil wood has been described from southeastern Australia (1 Moorlands, 2 Lachlan River, 3 Monaro Plains / Southern Highlands, 4 Yallourn mine, 5 Morwell mine, 6 Jungle Creek). Inset A, sketch map showing Early Miocene palaeolatitude of the study area, modified from a map provided by S.J. Gallagher. Inset B, detail of the LaTrobe Valley showing fossil collection site (5). logical studies (Luly et al. 1980, Sluiter & Kershaw al. 1995, Kershaw 1996), and the macrofossil work 1982, 1996; Kershaw et al. 1991, 1994; Sluiter et of Blackburn (1980, 1985) and Blackburn & Sluiter ALCHERINGA MIOCENE WOOD FROM VICTORIA 353 Fig. 2. Annotated lithological log of site of fossil wood collection (April, 1981) from a vertical exposure of the Yallourn Clays in the Morwell Open Cut Mine. Bulk samples macerated from the 1-5 m interval yielded leafy shoots of Dacrycarpus latrobensis and other Podocarpaceae. Fossil wood samples were collected at ‘A’ from one in situ log. (1994) provided insight into the palaeoecology noted above, surprisingly little has been of the middle Miocene Yallourn Coal seam and published on the fossil wood from the LaTrobe the early Miocene Morwell coal vegetation. As Valley brown coals and associated sediments 354 DAVID R. GREENWOOD ALCHERINGA (e.g. Patton 1958), and the palaeobotany of the 1994; Greenwood et al. 2000, Greenwood & interseam sediments in general, despite an Christophel 2005). apparent abundance of material (Greenwood et The topmost fine silty clays were al. 2000). This report is an initial attempt to redress progressively more carbonaceous upsection and this situation. graded into a thin exposure of the overlying Yallourn Coal seam. Blackburn & Sluiter (1994) considered the Yallourn Clays intergradational Geological setting with the Yallourn Coal seam. Palynological The LaTrobe Valley of southeastern Australia is analysis of samples from the upper 2 m of the a major area of brown coal extraction (Hocking section containing the fossil wood yielded 10.8- 1972, Holdgate & Clarke 2000, Holdgate 2003). 33.0% Nothofagidites (6.3-20.8% subgen. Three open cut mines in the vicinity of the towns Brassospora & 0.5-12.5% subgen. Lophozonia), of Morwell and Traralgon (Fig. 1) provide access 7.0-23.5% Myrtaceae (incl. 0-0.3% Eucalyptus to extensive lateral and vertical stratigraphic simplex & 4.5-17.0% Syzygium complex), 0-3.5% sequences of both the brown coal seams and the Proteaceae, and 10-32.5% conifer pollen (incl. 7.0- inter- and intraseam clays, sands and gravels. 28.8% Podocarpaceae) (I.R.K. Sluiter, pers. comm. Major interseam clastic sediments are laterally 1981 in Greenwood 1981; see also Blackburn & extensive, and generally extend across the whole Sluiter 1994). This assemblage is typical for early basin (Holdgate 2003, Holdgate et al. 1995). The Miocene sediments in southeastern Australia, and Yallourn Clays constitute an interseam clastic unit is indicative of a mixed Nothofagus-Syzygium- between the Morwell 1A Coal Seam (M1A), and conifer closed forest, although sclerophyllous the Yallourn Coal Seam. According to Luly et al. forest may also have been present based on the (1980), the Yallourn Clays are basal to the low counts of Eucalyptus simplex pollen. Triporopollenites bellus Zone of Stover and Occasional large pieces of conifer wood were Partridge (1973), and are thus middle Miocene. encountered in the topmost unit, including in However, more recent stratigraphic analyses situ stumps with associated Dacrycarpus place the Yallourn Clays (Interseam Influence latrobensis leafy shoots (Blackburn & Sluiter Zone 12 [IIZ 12]) as spanning the boundary of 1994). One sample of this wood is dealt with the Upper Proteacidites tuberculatus and systematically here. Triporopollenites bellus Zones, and thus late early Miocene (Holdgate & Sluiter 1991, Blackburn & Sluiter 1994, Holdgate et al. 1995, Materials and methods Holdgate 2003; Holdgate & Gallagher 2003). Histology of the fossil material was analysed The fossil material described herein was using standard histological sectioning collected by the author and David T. Blackburn techniques with wood pretreated in 80% ethanol in April 1981 from an exposure of the Yallourn prior to sectioning. Transverse, radial and Clays in the north-west corner of the Morwell tangential sections were made using a sledge Open Cut Coal Mine operated by the then State microtome and the sections placed in an alcohol Electricity Commission of Victoria (see also dehydration series (80%, 90% and 100% ethanol), Blackburn & Sluiter 1994, p. 350). A 10 m vertical remaining in each bath for at least 5 minutes. The sequence overlying the Morwell 1A seam was dehydrated sections were immersed in xylene for sampled through basal coarse white sands 5-10 minutes and mounted in xam neutral interbedded with carbonaceous seams, mounting medium on glass microscope slides, gradually replaced by very fine silty clays barren and photographed using black and white film at of leaf fossils (Fig. 2). Analysis of macrofossils 50 ASA in the former Botany Department, extracted from the lower 5 m of this sequence University of Adelaide. Terminology of wood (Fig. 2) is reported elsewhere (Greenwood 1981, histology follows Greguss (1955), but using the ALCHERINGA MIOCENE WOOD FROM VICTORIA 355 pit descriptions and types from Philippe (1995). Data on modern wood anatomy are principally based on Greguss (1955), but using the systematic treatment of the Podocarpaceae from Page (1988). The fossil wood xylotomy slides are lodged in the University of Adelaide Palaeobotany Collection, Department of Environmental Biology. The original fossil wood specimens were destroyed in a fire at the University of Adelaide’s Thebarton campus facility in 1998. Systematic palaeobotany Phylum CONIFEROPHYTA Order CONIFERALES Family PODOCARPACEAE Podocarpoxylon Gothan, 1908 Type species. Podocarpoxylon juniperoides Gothan, 1908. Podocarpoxylon

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