Records of the Westem Australian Museum 18: 19-65 (1996), Early Cretaceous macrofloras of Western Australia Stephen McLoughlin School of Botany, The University of Melbourne, Parkville, Victoria 3052, Australia Abstract - Western Australian, Lower Cretaceous, macrofloras from the Broome Sandstone and Callawa Formation (Canning Basin), Nanutarra Formation and Birdrong Sandstone (Carnarvon Basin), Cronin Sandstone (Officer Basin), and Leederville and Bullsbrook Formations (Perth Basin) incorporate a range of lycophytes, ferns, pteridosperms, bennettitaleans, and conifers, The new monotypic genus Roebuckia is established for spatulate fern fronds (R, spatulata) of possible vittariacean alliance. Other newly established species include Phyllopteroides westralensis, Elatocladus ginginensis, and Carpolithes bullsbrookensis, Although the Western Australian fossil suites reveal some specific differences from other Australian late Mesozoic assemblages, several shared index taxa and the high proportion of bennettitaleans support correlation with the Victorian Neocomian Ptilophyllum-Pachypteris austropapillosa Zone (Zone B). Some Western Australian taxa are shared with Indian assemblages but fewer similarities exist with other Gondwanan Early Cretaceous floras, The representation of several hydrophilous fern, lycophyte, and pteridosperm groups together with growth indices from fossil woods implies a seasonal humid mesothermal climate for the Western Australian eratonic margin during the Neocomian-Barremian. Minor differences between the Western Australian assemblages are attributable to local depositional and preservational factors. INTRODUCTION assemblages of plant macrofossils from subsurface This paper reviews all Western Australian Cretaceous strata in Western Australia. Retallack Cretaceous plant fossils held in the collections of (1977, 1980) and McLoughlin (1993) have the Western Australian Museum and the illustrated differences in palaeosol development Department of Geology and Geophysics of the and the composition of plant fossil assemblages in University of Western Australia together with Australian Permian and Triassic strata according limited material held in the Australian Museum, to variations in local and regional depositional Sydney, As all specimens lack preserved organic settings. Such sedimentological and taphonomic matter, descriptions are based on gross controls also apply to the Cretaceous assemblages morphology, ornamentation, and venation offering an important tool for detailed patterns. This procedure necessarily places interpretation of non-marine sedimentary facies. limitations on the degree of discrimination between Additionally, permineralized, mollusc-bored, some taxa. However, the scarcity of previous driftwood preserved in Lower Cretaceous marine studies on the Western Australian fossil floras sediments has aided the definition of sequence invites this systematic appraisal in order to fill stratigraphic boundaries and systems tracts some major gaps in the knowledge of Australia's (McLoughlin et al. 1994). Palaeobotanical Cretaceous phytogeography. investigations of the diversity of plant groups The relative tectonic stability and deep­ together with anatomical indices such as growth weathering associated with much of the central ring variation are also useful for the categorization and western part of the Australian continent since of palaeoclimates and the identification of major the mid-Mesozoic has removed from outcrops food sources available to the large Cretaceous most of the organic material required for herbivorous dinosaurs. palynological studies. Apart from scarce vertebrate trackways (Colbert and Merrilees 1967; Long 1990), plant macrofossils are virtually the only fossil PREVIOUS STUDIES remains available in outcrop to date and Douglas (1969, 1973), Drinnan and Chambers palaeoenvironmentally categorize Western (1986) and McLoughlin et al. (1995) have provided Australian Cretaceous terrestrial strata. No studies the most detailed studies of Australian Cretaceous dealing with stratigraphic and petroleum fossil plants dealing with macrofloras from the exploration drilling have reported significant Gippsland, Otway and Eromanga Basins. Other 20 s. McLoughlin 113°E o 600 KILOMETRES Figure 1 Map of Western Australia showing Phanerozoic sedimentary basins and principal Cretaceous plant macrofossil localities (solid squares). significant contributions include those of Seward McLoughlin et al. (1994) detailed the anatomical (1904), Chapman (1908, 1909, 1914), Walkom (1918, character and palaeoenvironmental significance of 1919a), Medwell (1954a,b), Glaessner and Rao silicified and phosphatized woods from the (1955), and Dettmann et al. (1992). Although Birdrong Sandstone, Carnarvon Basin and several stratigraphic papers have provided lists of Backhouse et al. (1995) described lignitized but fossil plants recovered from Western Australian anatomically similar woods from the Barremian to Cretaceous strata (e.g., Brunnschweiler 1960; Cox earliest Aptian Nakina Formation of the Collie 1961; Playford et aI. 1976) many of these Basin. The Cretaceous palaeobotanical literature identifications are not supported by illustrations or from other Gondwanan continents (especially India descriptions and are commonly erroneous. A small and South America) is extensive. Therefore, assemblage described and illustrated by Walkom synonymy lists provided here deal only with (1944) from strata underlying the Molecap previously figured or described Western Greensand near Gingin is redescribed herein. Australian fossil plants. White (1961a) briefly described and illustrated plant remains recovered from the Canning Basin by Australian Bureau of Mineral Resources CRETACEOUS STRATIGRAPHY regional geological surveys. McLoughlin and Western Australian Cretaceous plant Guppy (1993), and McLoughlin and Hill (in press) macrofossils have been recovered from the Perth, provided preliminary revised lists of Western Carnarvon, Canning, and Officer Basins (Figure 1). Australian Cretaceous plant fossils from several Plant remains are best represented in Early sedimentary basins and briefly discussed some Cretaceous non-marine strata (Figure 2). Due to a palaeoclimatic implications of the floras. dearth of palynological studies and the absence of -------------------------------------------------- Early Cretaceous macrofloras 21 marine invertebrate biostratigraphic indices, the However, Feldtman (1963) reported that the plant­ ages of many of these rock units are only broadly bearing horizons occurred within the Strathalbyn constrained. Furthermore, lack of continuous Beds, a term which Playford et al. (1976) regarded outcrops in many areas hinders the mapping and as synonymous with the Leederville Formation. lithological correlation of plant-bearing strata and Wilde and Low (1978) also mapped outcrops in the has led to uncertainties over the application of vicinity of Walkom's plant beds (Cheriton Creek) lithostratigraphic names. For example, Playford et as part of the Leederville Formation. On the basis al. (1976) and Skwarko (1990) assigned Walkom's of lithology and stratigraphic position, the fossils (1944) Gingin fossil assemblage to the Yarragadee are here regarded as belonging to the marine to Formation (Middle Jurassic to Tithonian). continental Leederville Formation (Hauterivian- LOWER PERTH BASIN CARNARVON CANNING BASIN CRETACEOUS (Dandara~an BASIN (Anketell Shelf & STAGES Trough kGascoyne Broome Platform); ub-basin) OFFICER BASIN Osborne ALBIAN Formation Windalia Radiolarite 0 n ete s rezie 0 / ~ .-l «.-l (9 APTIAN iJ u Muderong Dandaragan Sh Sandstone Cl. ::J 0 0 0 .... Birdrong Sst .!.!!c .:::&.c <.!J =0 00 BARREMIAN c: '';= 0·- 0 m eel ..a«l .... "OEm .... -ClJE.... .0 mo "So c ...JLL COLL .... 0 eel m 0 ~ r-- HAUTERIVIAN s: m 0 E Z 0 c m South 0> 0 c m -.~ -0 -c « - c c -Perth 0 0 0 1i5 ~ Shale () .~ "0 1i5 E C "0 VALANGINIAN eel - 0 eel C 0 E LL (j) eel 0 <5 .... (j) 0 0 eel m 0 ~ LL ~ E c W .... ....eel eel 0 C Z ~ .... Cii ....0 0.... eel () CO () BERRIASIAN S Parmelia c Formation zeel Fossil leaves _ Permineralized wood 0 Figure 2 Stratigraphic correlation of Lower Cretaceous rock units in the Perth, Carnarvon, and Canning Basins, Western Australia (after Cockbain 1990; Hocking 1990; Middleton 1990) showing the distribution of plant macrofossi! assemblages. 22 s. McLoughlin Barremian): Figure 2. The Bullsbrook Formation, preserved in ferruginous shale and medium­ exposed 2 km east of Bullsbrook, is a fully grained quartzose sandstone apart from some continental lateral equivalent of the Leederville seeds, megaspores, and axes which are preserved Formation (Figure 2). as natural day or sandstone casts. Organic material The Neocomian-?Aptian shallow marine to was not preserved on any fossils but in some cases paralic Birdrong Sandstone is chiefly exposed latex and silicone casts yielded morphological along the Murchison River near Kalbarri, on the details not clearly evident on negative impressions. flanks of the Kennedy Ranges, and in the Giralia All specimens were illustrated under strong Anticline within the Carnarvon Basin (Hocking et unilateral light directed from the upper left unless al. 1987; McLoughlin et al. 1994). The upper part of otherwise stated. this unit is typically rich in fragmentary Fossil localities are as follows: permineralized gymnosperm wood showing Broome Sandstone - Gantheaume Point, Broome evidence of intensive molluscan borings. Other (material collected by W.H Butler, A. Dawson, Cretaceous