Nullarbor Research Articles

Vegetation change, erosion risk and land management on the Nullarbor Plain, Australia

Arid karst landscapes that have been degraded by human activities provide a challenge for rehabilitation and an opportunity to test ideas about the stability and resilience of limestone ecosystems. The Nullarbor Plain is the largest arid karst area in Australia (220 000 km2) and is divided into extensive closed karstic depressions separated by low rocky ridges, while the dominant vegetation is chenopod shrubland. Since European settlement there has been considerable change in the vegetation, with significant reduction in shrub and grass cover over large areas of the plain. These changes are related to a state and transition model of vegetation dynamics which incorporates climatic variability, fire history and grazing pressure from sheep, kangaroos and rabbits. A partial sediment budget using 137Cs inventories reveals local and regional patterns of soil redistribution within this arid karst landscape. Rehabilitation of eroded soil in pastoral lands has been accomplished at several sites but is labour intensive and vulnerable to climatic fluctuations. Given the low stock numbers, limited number of people involved, and poor economic returns, it would be sensible to make pastoral activities on the Nullarbor secondary to conservation priorities. This would necessitate a change in land ethic to stewardship, with emphasis on rehabilitation and control of feral animals. Management of increased numbers of visitors to the caves and karst also requires that resource inventories and management plans for each area be drawn up and used.

Preliminary luminescence dates for archaeological sediments on the Nullarbor Plain, South Australia

Human occupation of the Nullarbor Plain in South Australia has been known to extend into the Pleistocene since a series of major archaeological excavations was begun in the 1950s and 1960s. An antiquity of more than 20,000 years BP for human presence in the region was established on the basis of 14 C chronologies at Koonalda Cave and Allen's Cave (also known as site N145). The oldest date reported for traces of human activity was -22,000 years BP (or -26,000 years BP after calibration) from Koonalda Cave. Here we present preliminary results of our luminescence dating investigations at Allen's Cave and Koonalda Cave, and also report some new 14 C age determinations on associated charcoal. The wind-blown quartzose sediments deposited in Allen's Cave were dated by optically-stimulated luminescence (OSL) and thermoluminescence (TL). A near-modern age was obtained for a near-surface sample and good agreement was obtained between the calibrated 14 C ages of a well-preserved -10,000 year-old hearth and the optical (OSL) and TL ages of the underlying sediments. An optical date of -40,000 years was obtained for the sediments immediately overlying the lowest artefacts at Allen's Cave, thereby extending the period of human occupation of the southern Nullarbor by 14,000 years. Optical dating was not successful at Koonalda Cave however, due to the probable intermittent storage and fluvial remobilisation of sediments en route to the cave floor in this deep karst system. An apparent optical age of -9000 years was obtained for alluvium deposited recently on the cave floor close to the Gallus Site, and substantial optical age overestimates were obtained for lacustrine sediments collected from the -20,000 years BP levels of the archaeological excavation. The validity of the 14 C age determinations made in the 1960s was confirmed using state-of-the-art 14 C methods to date two charcoal samples collected in 1991.

A taxonomic revision of the Cyclodomorphus branchialis species group (Squamata: Scincidae)

The Cyclodomorphus branchialis species group is defined on synapomorphies of scalation. Within this complex, five allopatric species, one with three subspecies, are recognised on morphological grounds: C. branchialis (Günther) of the lower west coast and hinterland, C. maximus (Storr) of the Kimberley, C. melanops melanops (Stirling and Zeitz) widespread in spinifex habitats of the arid north-west, and C. m. elongatus (Werner) widespread in spinifex habitats of the arid south and east of the continent, together with two new species, one from the lower west coast and the other from South Australia, and a new subspecies of C. melanops from chenopod habitats along the southern fringe of the Nullarbor Plain. The morphology, distribution, habitat preferences and reproduction of the seven taxa are described. All primary type specimens are illustrated. A key to the species and subspecies in the genus Cyclodomorphus is provided. Cyclodomorphus branchialis, considered on previous taxonomic opinion to be widespread in arid Australia, is restricted to a small area in Western Australia and is considered vulnerable.

Two Remarkable New Genera and Species of Troglobitic Carabidae (Coleoptera) from Nullarbor Caves

ABSTRACT Speozuphium poulteri gen. et sp.n. and Speothalpius grayi gen. et sp.n. are described from Weebubbie and Nurina Caves, respectively, in the West Australian division of the Nullarbor Plain and are placed in the carabid tribe Zuphiini. These species are remarkable for their high level of adaptation to the cave environment and they provide the first records of undoubtedly troglobitic Carabidae from mainland Australia.

Nullarbor 018: A new L6 chondrite from Australia

Abstract— A new meteorite find from the Nullarbor Plain in Australia was studied using optical, SEM, and electron microprobe techniques. The meteorite, Nullarbor 018, is an orthodox L6 chondrite that experienced minor‐to‐moderate alteration of metal during terrestrial weathering (grade A–B to B). During weathering, troilite was preferentially altered, and roughly 20% of the original complement of S in the meteorite was removed. Shock metamorphic effects corresponding to shock stage S4 (or shock facies d) are found, including the presence of some diaplectic feldspar (maskelynite). The meteorite is not obviously paired with other finds from the Nullarbor region, but the possibility that it is paired cannot be excluded.

Biogeography of Fire-Killed and Resprouting Banksia Species in South-Western Australia

Banksia includes 38 fire-killed (seeders) and 20 resprouting species, and two species with contrasting ecotypes, in south-western Australia. There may be up to 12 seeders per 50 × 50 km grid cell in the southern sandplains and 12 resprouters in the northern sandplains. The patterns of distribution of species across soil type and eight climatic attributes is similar for both life forms, except that greater numbers of resprouting species occur at higher rainfalls and where there is greater seasonal spread of rainfall. Most seeders occur on white sands and rocky substrates, and resprouters occur on yellow sands and the more fertile lateritic soils. Nutrient requirements for both life forms appear to be similar. Resprouters are more widespread than seeders which suggests that resprouters show greater environmental tolerances. The distribution of grid cells containing each life form across soil types and eight climatic attributes is similar and any differences in climatic profile for all species in each category are considered biologically insignificant. Both life forms in section Abietinae are well represented in the climatically distinct southern and northern sandplains indicating no climatic preferences within the lineage. There are no consistent trends in environmental attributes from fire-killed to resprouting ecotypes of B. ashbyi E.G.Baker and B. violacea C.A. Gardner. Multiple-partitioning classification of the floristic data produced 10 groups varying greatly in geography, species richness, and proportion and endemism of each life form. The Lesueur (northern) district has four endemic seeders, six endemic resprouters and a mean of 10 resprouters per cell. The East Eyre (southern) district has five endemic seeders, no endemic resprouters and one resprouter per cell. Both groups have a mean growing season of 5 months. The relative aridities and fluctuations of present and past (Quaternary and late Tertiary) climates are invoked to explain the much higher proportion of resprouters in the northern than southern sandplains and the absence of seeders in the most marginal cells. The absence of endemic species yet high proportion of resprouters (73%) in the extreme south-western corner of the region might be explained by elimination of seeders through frequent burning by Aborigines in the late Quaternary. The increase in the proportion of fire-killed species along the south coast from 23% to 100% at the edge of the Nullarbor Plain also requires an explanation.

Paleoecology of Cool-Water, Subtidal Cycles in Mid-Cenozoic Limestones, Eucla Platform, Southern Australia

The open-shelf, subtidal, bryozoan-rich Abrakurrie Limestone beneath the Nullarbor Plain (Eucla Platform) is cyclic at the meter-scale. Best developed cycles are asymmetric and comprise three distinct parts with a capping hardground. The basal part (A) is a thin, coarse, grainstone or rudstone that is rich in robust bryosoan and epifaunal echinoid fragments and pecten bivalves, reflecting growth and accumulation in generally high energy, hard bottom environments. The middle part (B), intepreted as a low-energy, sub-swellbase accumulation, is a burrowed to planar cross-laminated fine grainstone or packstone with a low diversity, delicate-branching bryozoan assemblage and little else except scattered infaunal echinoids and pectens. The upper part (C) is a burrowed, abundantly fossilferous (bryozoan, bivalve, echinoid) rudstone or floatstone. Upward increases in the numbers and diversity of Mg-calcite and aragonitic cheilostome bryozoans (especially erect rigid, flat robust branching and nodular/arborescent types), gastropods, infaunal bivalves, and infaunal echinoids points to a high-energy environment. Sediments at the top of C are variably cemented by inclusion-rich marine cement (now calcite) that formed a hardground which was subsequently physically and biologically eroded and stained by iron oxides during a period of non-deposition. Sediments from the next overlying cycle succeed cements in uppermost intergranular pores and fillmore » open crustacean burrows. Variably developed cyclicity is interpreted, on the basis of comparable Holocene cool-water shelf sediments, to reflect deposition in generally sub-photic environments that ranged from just below swell base (B) upwards towards the zone of wave abrasion (A and C). Hardgrounds (H) formed when the seafloor was within the zone of wave abrasion. Shallowing and deepening of these critical interfaces was controlled by fluctuating sea level and/or climatic change. 55 refs., 12 figs.« less

Denman 002: A new CV3 chondrite from South Australia

Abstract— Denman 002 is a new Australian carbonaceous chondrite. A single stone of 30 g was recovered in 1991 May near Fisher Station on the Trans Australian Railway, Nullarbor Plain, South Australia (30°36′S, 130°04′E). Texture, mineral and chemical composition indicate that it is a CV3 chondrite of oxidised subgroup with several similarities to Allende. It is composed of sharply defined chondrules, Ca‐Al rich inclusions up to 3.5 mm across, olivine aggregates and fine‐grained, nearly opaque matrix (40 vol%). Silicates are compositionally highly heterogeneous (olivine Fa: 0.2–45.6 mol%, PMD: 109.7). Denman 002 shows shock effects of stage SI and weathering of category A.

Surface hydrology and soil movement in an arid karst: the Nullarbor Plain, Australia

The Nullarbor Plain is the largest karst area in Australia (220,000 km2) and one of the largest in the world. Its climate is arid (Koppen BWk and BWh), and the surface relief is less than 10m. The landscape is divided into extensive closed karstic depressions separated by low rocky ridges, and the dominant vegetation is chenopod shrubland. The extent and severity of soil degradation has been assessed using remote sensing. GPS rectified images from 1972–1973, 1979, 1983, 1988, and 1991 have been compared for two sites on the Nullarbor. Over the 19 years the total extent of bare soil has reduced significantly, but some areas around water points have degraded and there is some disturbance due to fossorial wombats. Sheet-flow processes occur during intense rainfall events, which happen two or three times per decade. Runoff only occurs after the 10− or 50− year return frequency events, and at these times turbid water ponds in depressions and enters caves. Surface soil sorptivity and hydraulic conductivity differ markedly between ridges and depressions; the ridges are clearly zones of groundwater recharge, while ponding is evident in most depressions. Sorptivity is influenced by the extent and nature of ground cover and cryptogam crusts on the soil. The landscape has been divided into classes on the basis of vegetation type and percentage of foliage cover. In each class the activities of fallout radionuclides will be determined by high resolutionγ spectroscopy. Preliminary results suggest that in undisturbed sites little sediment movement has occurred over the time scale of cesium-137 (the last 35 years) but that the landscape has been well sorted over a much longer time scale. Future work will investigate disturbed sites to estimate relative soil loss during the pastoral period.

Synsedimentary Cemented Calcarenite Layers in Oligo-Miocene Cool-Water Shelf Limestones, Eucla Platform, Southern Australia

ABSTRACT The Abrakurrie Limestone is a bryozoan-rich, cool-water, open shelf unit of Oligocene--middle Miocene age beneath the Nullarbor Plain. The sediments have been in the meteoric diagenetic environment, never buried more than a few hundred meters, since middle Miocene time. The unit is composed of meter-scale subtidal cycles, each of which is capped by an erosion surface. The upper several centimeters of most cycles are well lithified, forming distinctive hard layers in otherwise friable carbonates. Intergranular cements in these layers are now isopachous rinds of low-magnesium calcite. Crystals are inclusion-rich, generally fibrous, and have a speckled cathodoluminescence signature. Cements in intergranular pores at the tops of cycles are overlain by interstitial marine sediment. The cem nts are interpreted to have been marine precipitates in the form of magnesium calcite originally containing from 8-12 mole % MgCO3 and having a 18O value of -1.0 ± 0.5 versus PDB. Stable carbon and oxygen isotope values in these interpreted marine hardgrounds are distinctly more positive than values from underlying soft sediments, reflecting alteration under lower water-rock ratio conditions due to reduced permeabilities. Covariance in stable isotope values from different localities suggests diagenesis in groundwaters of mixed composition. Fluid inclusions indicate neomorphism in fluids with salinities equal to or slightly greater than seawater. Alteration is envisaged to have taken place in a paleogroundwater system of variably mixed saline continental waters and seawater. Occurrence of similar to identical cemented layers and cements in coeval cool-water New Zealand shelf carbonates suggests that such cementation was a sporadic but widespread phenomenon on mid-Cenozoic platforms in this area. By inference, cool-water carbonates of all ages may contain units lithified on the seafloor by cements containing low to intermediate amounts of magnesium. Cool water is not an inhibitor to synsedimentary cementation.

Origin of a cool‐water, Oligo‐Miocene deep shelf limestone, Eucla Platform, southern Australia

ABSTRACTThe Abrakurrie Limestone is an areally extensive, bryozoan‐rich unit within the Eucla Platform, a Tertiary carbonate shelf which caps the central part of the southern Australian continental margin. The onshore portion, the topic of this study, has been exposed since middle Miocene time and lies beneath the Nullarbor Plain. The rocks are fine‐sand‐ to granule‐sized calcarenites, composed of bryozoans, bivalves, benthic foraminifera and echinoids with lesser numbers of brachiopods, solitary corals and serpulids. They conspicuously lack significant numbers of planktonic foraminifera and coralline algae. Most bryozoan remains are from delicate branching cyclostomes although delicate branching, robust branching, foliose, fenestrate, multilaminar encrusting and free‐living cheilostomes are variably abundant in specific units. The poorly lithified sequence is punctuated by well‐cemented layers with erosional tops, which are interpreted as hardgrounds.The limestone is interpreted as a cool‐water, deep shelf deposit which accumulated in water depths generally greater than 50 m on the inner part of the Eucla Platform. A model which involves deposition and cementation on a carbonate shelf swept by open ocean swells is proposed to explain the style of sedimentation. The shelf is envisaged as partitioned by the depth of the zone of wave abrasion. Sediments were produced throughout, but accumulated only below this depth. When the seafloor was above this depth it was an environment of cementation and erosion.The vertical sequence correlates in a general way with the global sea‐level model for the mid‐Cenozoic. While accumulation rates for southern Australian carbonates are similar to rates of cool‐water carbonate deposition elsewhere (c. 2.5 cm kyr‐1), the rate of Abrakurrie accumulation is much less, suggesting that significant time periods are represented by the hardgrounds.

Archaeology on the Anxious Coast

In recent years a significant amount of archaeological work has been carried out on the Nullarbor Plain. This adds to previous studies done in that region about two decades ago (Pretty 1977; Wright 1971) and includes excavations at Allens Cave, preliminary archaeological work at Ooldea, the description and recording of the Footprint Site at Bookabie, investigations into the distribution of flint at archaeological sites across the Plain, and mapping of the Wilson Bluff flint quarry (see Cane and Gara 1989; Gara and Cane 1988; Gara et al. 1988). An issue raised by this archaeological work relates to the nature of coastal occupation (Gara and Cane 1988). Bates (1912, 1918) and others (Greenway 1973; Tindale 1974) state that Aboriginal occupation within the larger Nullarbor environment concentrated on the coast. As a result one would expect to find midden sites similar to those found elsewhere in Australia. Yet this is not the case. There are no middens of the type found in eastern Australia recorded on the 300 km of the Nullarbor coastline. This raises questions about the nature of Aboriginal occupation in this semi-arid coastal area. Specifically, if occupation did focus on the coast why is there so little evidence of it? The unexpected absence of sites on the Nullarbor coastline promoted investigations further afield; in this case the Anxious Coast immediately to the east. Once again the large midden sites were absent. The archaeological sites found along this coastline were mostly small, containing thin surface scatters of deflated midden material. This demonstrated that Aboriginal people did live on this coast, but it suggested they were not using marine resources extensively. This raises an interesting question: Why were coastal resources under-exploited on the west coast of the Eyre Peninsula when elsewhere in Australia marine foods contributed significantly to Aboriginal economies? The answer to this question is the subject of a major study by Nicholson. At this stage we would like to draw attention to the archaeological character of the region and identify a series of interesting issues for future debate. To do this we will describe the results of an initial archaeological survey and provide a summary of the relevant ethnographic evidence. We will then examine how other scholars have interpreted Aboriginal subsistence and settlement of coastal areas, and in so doing raise the question: Why didn't the people of the Anxious Coast eat shellfish?

Tertiary coastal dunes of the Eucla Basin, Australia

On the northeast margin of the Nullarbor Plain in western South Australia, there is preserved an assemblage of coastal aeolian landforms that includes coastal dune, dune ridge and possible beach ridge. One of these landforms is the Ooldea Range, a 650 km long coastal dune that lies 25–300 km from the present coast. These landforms are believed to have formed at the end of the Eocene, after maximum marine transgression in the Eucla Basin. The Ooldea, Barton and Paling ranges formed in a tectonically stable region of topographically subdued terrain. Their orientation and position may be related in part to crustal fractures that were active during initial break-up of Australia and Antarctica. The large quantities of sand required for their construction were supplied to the coast by rivers which drained a hinterland of various suitable source rocks. Growth may have begun as chains of barrier islands, which amalgamated to form large coast-parallel dunes during progradation. These coastal dunes provide evidence about climate at and after the time of their formation. Their formation indicates an atmospheric circulation of at least moderate intensity and prevailing winds with a major westerly component. This occurred at a time when the climate is likely to have been temperate. If the interpretation of the dunes age is correct, they may be viewed as landforms bearing testimony to the global change in climate which occurred at the end of the Eocene. Their excellent preservation in the landscape today, some 34–37 million years after formation, is remarkable. Implied, is a degree of aridity for much of the remainder of the Cainozoic. This appears to have been more significant in the Nullarbor Plain region than in the southeastern part of Australia. Other factors responsible for their preservation are likely to include vegetation cover, the permeability of their quartz sands, subsequent history of sea level and hydrodynamics of the basin.

Pleistocene climatic change in Southern Australia and its effect on speleothem deposition in some Nullarbor caves

AbstractActivity ratios of 234U/238U, 230Th/234U, and 230Th/232Th have been determined for calcite, gypsum and halite speleothems from caves of the Nullarbor Plain, mostly in the area N and NW of Mundrabilla Station, for the purpose of U‐series dating. All calcite speleothems contain adequate amounts of uranium for dating, but some show an excess of 230Th. Stratigraphic relationships indicate that there were at least three phases of calcium carbonate deposition in the Nullarbor caves. The calcite samples, with one possible exception, have ages in excess of ca. 400000 yrs BP. This suggests that no significant amounts of calcium carbonate deposition have taken place during the last 400ka.At present, active deposition of speleothems is restricted almost entirely to gypsum and halite. The only gypsum speleothem dated was found to have a finite age of ca. 185 ka. Six dates on a small halite speleothem containing insect and arachnid remains indicate that it formed rapidly during Holocene time.

Potential wind erosion in Australia: A continental perspective

AbstractSeasonal and annual patterns of potential wind erosion in Australia are mapped. Potential erosion is estimated by applying Fryberger's sand drift potential concept to 3 p.m. wind data from 732 stations. Contour maps for January, April, July and October show monthly total drift potential, resultant drift potential, and drift directionality. Stream line maps show resultant drift direction. Annual resultant drift potential and drift direction are also mapped.Monthly total drift potential is maximal in October and minimal in April. Highest values occur on the coast, in the Nullarbor Plain, and in Tasmania; lowest values are scattered across the northern inland. Monthly resultant drift potential is similarly distributed. Monthly drift directionality is higher in the north.Monthly drift direction stream lines mainly express the general circulation of the atmosphere. Some local disturbances occur over ranges; others have cyclonic form. Annual resultant drift potential stream lines are broadly confluent and have anticyclonic curvature.These maps of potential wind erosion, linked to measures of erodibility, provide a basis for studying wind erosion hazard in Australia.

CAMEL DONGA METEORITE, A NEW EUCRITE FROM THE NULLARBOR PLAIN, WESTERN AUSTRALIA

Twelve stones, ranging up to 504 g (total weight 2.92 kg), of a very fresh eucrite have been collected from a 1 km2 area on the Nullarbor Plain in Western Australia. The location is approximately 75 km N6°E from Nurina Siding on the Trans‐Australian Railway; coordinates 30°19′S, 126°37′E. This eucrite consists almost entirely of pyroxene (mean composition Wo 16 Fs 49) and plagioclase (mean composition An 85) in approximate proportions 3: 2, with 2% almost pure Fe metal and accessory amounts of troilite, ilmenite, and an SiO2 phase. Gabbroic and doleritic clasts are present in a groundmass of comminuted pyroxene and plagioclase. The chemical composition (weight per cent) is: SiO2 49.53, TiO2 0.74, Al2O3 12.49, Cr2O3 0.33, FeO 16.07, MnO 0.56, MgO 6.31, CaO 10.41, Na2O 0.49, K2O 0.04, P2O5 < 0.01, H2O + < 0.1, H2O — 0.07, Fe metal 2.07, Ni < 0.01, Co < 0.01, FeS 0.19, C 0.03, sum 99.33.

Genesis of the Nullarbor Plain caves in southern Australia

Genesis of the Nullarbor Plain caves in southern Australia

SPECIATION IN THE GENUS CRINIA (ANURA: MYOBATRACHIDAE) IN SOUTHERN AUSTRALIA: A PHYLOGENETIC ANALYSIS OF ALLOZYME DATA SUPPORTING ENDEMIC SPECIATION IN SOUTHWESTERN AUSTRALIA.

Where there are several closely related species with sympatric distributions occurring in an isolated habitat, the cause is generally ascribed to multiple invasion (Mayr, 1963 p. 504). White (1978p. 115) has criticized the indiscriminate application of this principle in the Australian biota in the following way: such hypotheses are produced solely to satisfy the a priori postulate that speciation is only possible where populations are completely separated by major topographic barriers. Interpretations on the origin of the frog fauna of southwestern Australia have suffered in this regard, in that the region is topographically featureless (Prider, 1966) and isolated by desert from the rest of Australia while the frog species there have largely sympatric distributions. Thus it was postulated that frogs from southeastern Australia crossed the arid Nullarbor plain during several cycles of increased rainfall caused by Pleistocene glaciation. Speciation occurred after populations were separated each time the Nullarbor plain again became arid. The direction of invasion was determined on the basis of the number of species found in each area so that invasion proceeded from centres of low species number to areas which now have many species. Among the birds of southern Australia, for example, invasion is postulated to have gone from west to east (Keast, 1961). In the case of frogs, the proposed invasions were from east to west, and most authors have assumed that each southwestern species is most closely related to a southeastern species (e.g., Main et al., 1958; Martin, 1972; Littlejohn, 1981) and that several southwestern species may be related to one southeastern species. White (1978 p. 113) has challenged this interpretation, suggesting that the number of species in southwestern Australia is the result of endemic speciation, as such an hypothesis makes fewer assumptions. According to this interpretation, each southwestern species is most closely related to some other southwestern species. These alternative biogeographic hypotheses imply different phylogenies and these can be tested by an independent phylogenetic analysis. In the present study the alternative evolutionary scenarios were tested using seven species from the genus Crinia (six of these species were formerly in Ranidella [Blake, 1973] but were returned to Crinia by Heyer et al., 1982). The characters used were allozymes as most of these species are morphologically indistinguishable. Crinia is of especial interest as the first hypothesis invoking multiple invasion for the origin of frog species in southern Australia was formulated for this genus, before being extended to include not only Heleioporus and Neobatrachus (Main et al., 1958) but three other genera as well (Main, 1968).

FURTHER FINDS FROM THE MUNDRABILLA METEORITE SHOWER

Two new large iron meteorites, weighing 840 kg and 800 kg respectively, have been recovered from the Nullarbor Plain in the vicinity of the original Mundrabilla meteorite site, and are now at the Western Australian Museum in Perth. Numerous small knucklebone‐shaped irons were also found at Tookana Rock Hole in the vicinity of Eucla. X‐ray fluorescence spectrometry of these meteorites confirms that the additional finds are members of the Mundrabilla meteorite shower.

Geographical Variation in Cinclosoma Castanotum and its Historical Significance

SUMMARYFord, J. 1982. Geographical variation in Cinclosoma castanotum and its historical significance. Emu 81: 185–192.The Chestnut Quail-thrush Cinclosoma castanotum varies geographically in the amount of dorsal chestnut, the differences between extreme variants being very pronounced, specially in females. Quail-thrushes from southern Western Australia, the south-western side of the Nullarbor Plain and east of Spencer Gulf have the least amount of chestnut and those from near Shark Bay and the deserts north of the Nullarbor Plain, the greatest. Variation is strongly clinal in Western Australia, negligible in the central deserts, slightly clinal east of Spencer Gulf and apparently strongly stepped in north-western Eyre Peninsula. At the peak of the last ice age, when the climate was quite arid in southern Australia, the central deserts were extremely harsh and a wide coastal plain with mallee occurred in the Great Australian Bight, populations of quail-thrushes with little dorsal chestnut presumably ranged along the entire southern edge of the continent. As the present interglacial regime became established and the climate wetter, the species probably retracted from coastal areas and expanded from southern Western Australia into the Great Victoria Desert, recontacting the population on Eyre Peninsula, which had become isolated by Spencer Gulf and the Nullarbor Plain.