11
This article was downloaded by: [UQ Library] On: 02 November 2014, At: 09:13 Publisher: Taylor & Francis Informa Ltd Registered in England and Wales Registered Number: 1072954 Registered office: Mortimer House, 37-41 Mortimer Street, London W1T 3JH, UK Australian Journal of Earth Sciences: An International Geoscience Journal of the Geological Society of Australia Publication details, including instructions for authors and subscription information: http://www.tandfonline.com/loi/taje20 History of coastal dunes at Triangle Cliff, Fraser Island, Queensland W. T. Ward a & K. G. Grimes b a CSIRO Division of Soils , Cunningham Laboratory , 306 Carmody Rd, St Lucia, Qld, 4067, Australia b Geological Survey of Queensland , QMEC House, Mary St, Brisbane, Qld, 4000, Australia Published online: 01 Aug 2007. To cite this article: W. T. Ward & K. G. Grimes (1987) History of coastal dunes at Triangle Cliff, Fraser Island, Queensland, Australian Journal of Earth Sciences: An International Geoscience Journal of the Geological Society of Australia, 34:3, 325-333, DOI: 10.1080/08120098708729414 To link to this article: http://dx.doi.org/10.1080/08120098708729414 PLEASE SCROLL DOWN FOR ARTICLE Taylor & Francis makes every effort to ensure the accuracy of all the information (the “Content”) contained in the publications on our platform. However, Taylor & Francis, our agents, and our licensors make no representations or warranties whatsoever as to the accuracy, completeness, or suitability for any purpose of the Content. Any opinions and views expressed in this publication are the opinions and views of the authors, and are not the views of or endorsed by Taylor & Francis. The accuracy of the Content should not be relied upon and should be independently verified with primary sources of information. Taylor and Francis shall not be liable for any losses, actions, claims, proceedings, demands, costs, expenses, damages, and other liabilities whatsoever or howsoever caused arising directly or indirectly in connection with, in relation to or arising out of the use of the Content. This article may be used for research, teaching, and private study purposes. Any substantial or systematic reproduction, redistribution, reselling, loan, sub-licensing, systematic supply, or distribution in any form to anyone is expressly forbidden. Terms

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Page 1: History of coastal dunes at Triangle Cliff, Fraser Island, Queensland

This article was downloaded by: [UQ Library]On: 02 November 2014, At: 09:13Publisher: Taylor & FrancisInforma Ltd Registered in England and Wales Registered Number: 1072954 Registeredoffice: Mortimer House, 37-41 Mortimer Street, London W1T 3JH, UK

Australian Journal of Earth Sciences:An International Geoscience Journalof the Geological Society of AustraliaPublication details, including instructions for authors andsubscription information:http://www.tandfonline.com/loi/taje20

History of coastal dunes at TriangleCliff, Fraser Island, QueenslandW. T. Ward a & K. G. Grimes ba CSIRO Division of Soils , Cunningham Laboratory , 306Carmody Rd, St Lucia, Qld, 4067, Australiab Geological Survey of Queensland , QMEC House, Mary St,Brisbane, Qld, 4000, AustraliaPublished online: 01 Aug 2007.

To cite this article: W. T. Ward & K. G. Grimes (1987) History of coastal dunes at Triangle Cliff,Fraser Island, Queensland, Australian Journal of Earth Sciences: An International GeoscienceJournal of the Geological Society of Australia, 34:3, 325-333, DOI: 10.1080/08120098708729414

To link to this article: http://dx.doi.org/10.1080/08120098708729414

PLEASE SCROLL DOWN FOR ARTICLE

Taylor & Francis makes every effort to ensure the accuracy of all the information (the“Content”) contained in the publications on our platform. However, Taylor & Francis,our agents, and our licensors make no representations or warranties whatsoever as tothe accuracy, completeness, or suitability for any purpose of the Content. Any opinionsand views expressed in this publication are the opinions and views of the authors,and are not the views of or endorsed by Taylor & Francis. The accuracy of the Contentshould not be relied upon and should be independently verified with primary sourcesof information. Taylor and Francis shall not be liable for any losses, actions, claims,proceedings, demands, costs, expenses, damages, and other liabilities whatsoeveror howsoever caused arising directly or indirectly in connection with, in relation to orarising out of the use of the Content.

This article may be used for research, teaching, and private study purposes. Anysubstantial or systematic reproduction, redistribution, reselling, loan, sub-licensing,systematic supply, or distribution in any form to anyone is expressly forbidden. Terms

Page 2: History of coastal dunes at Triangle Cliff, Fraser Island, Queensland

& Conditions of access and use can be found at http://www.tandfonline.com/page/terms-and-conditions

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Page 3: History of coastal dunes at Triangle Cliff, Fraser Island, Queensland

Australian Journal of Earth Sciences (1987) 34, 325-333

History of coastal dunes at Triangle Cliff, Fraser Island, Queensland

W. T. Ward1 and K. G. Grimes2

1CSIRO Division of Soils, Cunningham Laboratory, 306 Carmody Rd, St Lucia, Qld 4067,Australia.

2Geological Survey of Queensland, QMEC House, Mary St, Brisbane, Qld 4000, Australia.

Triangle Cliff, at the western shore of Fraser Is., has been formed by marine erosion, mostly of parabolicdunes that were blown to their present position by southeast trade winds and fixed in place by vegetation.The section exposed at the shoreline shows that the blown sands (Triangle Cliff dune sand) lie on strandedforedunes (included with the Wathumba beach sand) developed when the present sea level was firstattained. At the eastern shore of Fraser Is., the Triangle Cliff dune sand was formed before the Wathumbabeach sand. It is inferred that the dune sands had begun to move before the sea attained its present level, butdid not reach the present position of Triangle Cliff until the middle Holocene. By this time conditions thatinitiated sand movement had possibly ceased to prevail.

Radiocarbon dates from material exposed in Triangle Cliffappear to be in reversed order of age but arecapable of simple explanation. The dated sediments are time-transgressive; however, the youngest carbondate is from material that may have intruded older deposits.

The new data allow a better placement of the Pleistocene-Holocene boundary in relation to the coastalsands. We recognize a maximum postglacial sea level of perhaps slightly more than + 1 m and a possibleminor fall in sea level at about 3400-4000 years BP.

Key words: dunes, coastal geomorphology, Quaternary, carbon dating, sea level, surficial geology.

INTRODUCTION

Queensland's coast is of particular interest toQuaternary geologists because of its exposure tothe southeast trade winds and its long history ofglacio-eustatic changes in level of the sea. Whenthe sea was high the coast was eroded by waveattack or, in some places, built forward by theaccretion of coastal strandplains. The coast wasalso affected periodically by wind erosion. Mostof the blown sands extend below the presentshoreline, showing that wind erosion coincidedmainly with low sea levels. At these timesextensive parabolic dune fields were formed.Today, all except a few of the youngest dunes arefixed in place by vegetation.

The unconsolidated sands are well exposed inspectacular cliffs at the ocean shore but thedeposits there have been mostly truncated bywind erosion; good sections showing therelations of the sand bodies are uncommon.Moreover, sections with datable material arerare. Triangle Cliff (Fig. 1), sheltered by FraserIs., has a special interest because it exposesseveral of the units of which the island iscomposed. Some of these units contain wood andcharcoal. The proper interpretation of the section

has, therefore, a large bearing on the under-standing of the coastal sediments.

In this paper we report new information andreconcile our previously divergent views con-cerning the interpretation of the section.

DESCRIPTION AND LOCAL SETTING OFTRIANGLE CLIFF

The coast with its immediate hinterland issketched in Fig. 2, and the section exposed at thebeach front in Triangle Cliff is shown in Fig. 3.The oldest ground is formed by ancient dunefields, which are shown by their soils andlandforms (Table 1) to be equivalent to theAwinya, Yankee Jack and Bowarrady dune sandsof Ward (1977a). An alluvial plain is presentbeside Bowal Creek. Behind the swamps atTowoi Creek (Fig. 2), the Awinya dune sand ispartly buried and the Bowarrady unit is formedby remoulded Yankee Jack dune sand. Aban-doned sea cliffs and a low barrier foredune marka former shoreline that truncates the dune sandunits. Proper identification of the soil of thestranded foredune where it lies behind TowoiCreek is prevented by high groundwater levels,

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326 W. T. WARD AND K. G. GRIMES

.Sandy Cape

Maryborough

GreatSandy

Strait

BullockPoint

SCALE30 km

-25"S

Hook Point\ > Inskip Point

Double IslandPoint

Fig. 1 Location map, Triangle Cliff and Fraser Is. Atsite H, near Hook Pt, the Wathumba beach sand liesseawards of the Triangle Cliff dune sand (see Fig. 4).W, Wathumba Inlet; SP (inset), Surfers Paradise. Thedistribution of the Triangle Cliffdune sand is indicatedby the stippled pattern.

but the strandplain farther south, by BowalCreek, is correlated with the Poyungan beachsand. North of Bowal Creek the beach sand isreplaced by alluvial sand that carries a deeplyleached humus podzol with 3-4 m of white sandover black sand cemented with organic matter, orhumate (Swanson & Palacas 1965). This soilprofile is similar to that found on the Poyunganbeach sand. It crops out at the modern coastwhere the black B horizon of the podzol is ex-posed as firm, humate-cemented sands beneaththe white leached zone of the soil in cliffs 5-6 mhigh. Fallen logs and in situ tree stumps, includ-ing satinay (Syncarpia hillii) and in places twigsand leaves, are preserved within the cementedhorizon and are picked out at the level of themodern beach by wave erosion of the enclosingsand. Radiocarbon dating (Grimes 1979;SUA-860) gave an age of > 39 300 years BP forwood from this buried forest. The alluviumenclosing the forest continues north for severalhundred metres and then passes beneath dunesand (Triangle Cliffdune sand). This is part of anextensive dune field that has blown in from thesoutheast to reach the shore at Hervey Bay.Triangle Cliff has formed where the dune sandsare truncated at the shore. The buried alluviumwith its deeply leached podzol soil is clearlyexposed at the foot of the cliff (Fig. 3) and easilyfollowed to the north, its level descending in thisdirection approaching Towoi Creek. From itsdistribution and the gentle slope of its surface weconclude that the entire deposit was formed as alow alluvial fan by Bowal Creek as the searetreated from the stranded cliff, and for con-venient naming we accept it as a facies of thePoyungan beach sand.

The buried surface of the sandy alluvium ismarked by its buried topsoil, which commonlycontains small, fragile fragments of charcoal. Inplaces the charcoal is oriented in lines as if itrepresented the roots of vegetation that oncegrew in the soil. A bulk sample (Ward 1977b;Grimes 1979, SUA-433) gave an age of 3880 ±105 years BP. At the northern end of the exposurethe buried topsoil passes beneath dark greyishbrown fine sand with clay, beginning 2 m abovethe usual high-water level of the modern beach.Ward (1977b) correlated this bed with theWoorim beach sand. Although this correlationwas accepted by Grimes (1979), we now considerit to be erroneous and distinguish the bed simply

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Page 5: History of coastal dunes at Triangle Cliff, Fraser Island, Queensland

HISTORY OF FRASER ISLAND DUNES, QLD 327

p' B w'

Fig. 2 Sketch of the composite landscape in the vicinity of Triangle Cliff, resulting from dune sand deposition andeustatic emergence, a, Awinya dune sand; a', post-Awinya alluvium; b, Bowarrady and Yankee Jack dune sands;p, Poyungan beach sand; p', Poyungan alluvium and sandrock with enclosed forest (exposed at beach); t, TriangleCliff dune sand; w, Wathumba beach sand; w', Wathumba alluvium; TC, Triangle Cliff; T, Towoi Creek; B, BowalCreek. The detailed stratigraphy of Triangle Cliff is given in Fig. 3.

as Bed T. Bed T impedes the flow of water per-colating down from the overlying sands and itsposition is marked by seeps for the entiredistance to Towoi Creek. As the bed is followednorthwards it descends to beach level, increasesin thickness (from less than 1 cm continuously to1 m), and incorporates an increasing proportionof organic matter. Abundant decayed wood and

peat is present in Bed T near Towoi Creek. Woodfrom an in situ stump (SUA-859) has been datedat 5690+120 years BP, and detached bark(SUA-858) enclosed in the peat at 4480 ± 115years BP (Grimes 1979). The age differencebetween the samples was attributed by Grimes tocontamination of the bark sample by modernrootlets and organic matter. The clays in Bed T

NE SW

5690±120r I ,4480^115

Bed T

Fig. 3 Sketch of the section exposed at the shore at Triangle Cliff. Vertical scale exaggerated 1:6. p', Poyunganalluvium and sandrock with enclosed forest (exposed at beach); w, Wathumba beach sand; w', Wathumba alluvium;t, Triangle ClifTdune sand; s, Station Hill dune sand; c, scree fixed by vegetation, with soils like those developed onthe Cape dune sand and Hook beach sand; m, Modern cliff-top dune; T, Towoi Creek; B, Bowal Creek. The carbondates show that the relationships of the Triangle unit, the Wathumba unit and Bed T are time-transgressive (seetext).

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328 W. T. WARD AND K. G. GRIMES

Table 1 Sequence of morphostratigraphic units on the southeast Queensland coast

Unit*

Modern beach and dune sandHook beach sandCape dune sandRooney Point beach sandStation Hill dune sandBool Creek beach sandTriangle Cliff dune sandWathumba beach sandGarawongera dune sandWoorim beach sandBribie beach sandBowarrady dune sandPoyungan beach sandYankee Jack dune sandUngowa beach sandAwinya dune sandCooloola dune sand

Dune forms

Blowouts (A-G)tForedunes (H-K)t

A, BHBHBHC

H, ICIJ

D, some EJ

D, EK

some F, GG

Common

soil§

11122334334343433

Depth of

bleachedsurface (m)

********

0.25-0.50.45-0.60.8-1.21.0-1.60.9-1.61.8-2.02.0-4.02.5-5>2.56.0-7.5>2.59.5-13>13

*In these names 'beach' includes the foredune that formed at the shore and 'dune' is used for parabolic dunes andother transgressing blown sands.

tA, sand dunes without vegetation; B, sharp-crested dunes bearing vegetation with an incompletely closedcanopy; C, strong dune relief without water-scoured channels; D, strong dune relief with water-scoured channels; E,subdued dune relief; F, degraded sands with very few subdued dune remnants; G, degraded sands without dunerelief. E, F, and G are all dissected by streams.

*H, fresh, sharp, narrow, parallel foredunes; I, narrow, parallel foredunes, somewhat smoothed, in places a singleridge; J, degraded, broad, parallel ridges; K, strongly degraded ridges to smooth sandplains without diagnosticforms.

§According to Soil Survey Staff (1975). Soils that exceed 2 m depth are not dealt with by this system and as aconsequence the soils formed on units older than Woorim beach sand cannot be classified. This arbitrary depth limithas no meaning in the present field, and we would not force its application to the natural situation. If it is ignored, thedeep soils can be classified as shown. 1, Quartzipsamment; 2, Spodic Quartzipsamment; 3, Orthod; 4, Humod.

**A bleached surface is not present.

suggest that it might have originated as amangrove swamp. Clays are uncommon in otherenvironments on Fraser Is., but in modern man-grove swamps they extend in still water to 0.5 mabove the mangrove level. The wood dated byGrimes was not identified, but other samplesfrom Bed T have been identified by the Queens-land Department of Forestry, with theSyncarpia/Tri.tfania group cf. Lophoslemonsuaveolens (swamp box, a freshwater species) andAvicennia marina var. australasica (grey man-grove). This suggests that Bed T is composed ofdeposits close to the upper tidal limit. The levelfrom which the wood was collected, close to thepresent day high water swash limit, is 0.5 mabove the present mangrove limit in WathumbaInlet and adjacent areas. As the bed rises 2 m

above the modern beach, a contemporary meansea level of ca. +1 m relative to the present issuggested. Fragments of pumice are present inplaces in Bed T, 30 cm below the top, at an eleva-tion close to the present swash limit near TowoiCreek. The pumice, in this quiet-water environ-ment, is an indicator of the level of high waterspring tides and appears to indicate a former sealevel comparable with that at present. However,because the enclosing peat has been compressedby the overlying sands, we infer that the shorelinewas somewhat higher than the modern one.

Bed T is overlain by brown and yellowishbrown aeolian sands, formed as a foredune.These sands carry humus podzols and podzolsoils typical of the Wathumba beach sand, andconsist of 0.8-1 m of grey sand resting sharply on

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Page 7: History of coastal dunes at Triangle Cliff, Fraser Island, Queensland

HISTORY OF FRASER ISLAND DUNES, QLD 329

dark brown sand that grades below 120 cm toyellowish brown sand. The Wathumba beachsand is more extensive than the underlying Bed Tand overlaps the leached white sands of thePoyungan alluvial facies farther south. Similarlyweathered sediments are also present onalluvium south of Bowal Creek (Fig. 2).

Age information is available for theWathumba beach sand at Bullock Pt, near InskipPt on the mainland south of Fraser Is. At thatsite, foredunes of the Wathumba beach sandoverlie shelly sands at depths of 20-30 m belowMSL. Shells from these sands give radiocarbondates of 6180 ± 180 years BP and 6360 ± 100years BP (Beta-2612,2611). When these dates arecompared with those determined from wood,some allowance must be made for errors result-ing from the incorporation in shells of 'dead'carbon. The size of this 'oceanic reservoir effect'is estimated to be approximately —450 years(Gillespie & Polach 1979; Bowman & Harvey1983). The 'corrected' ages for the shells, of 5730and 5910 years BP, are therefore close to thoseobtained for the wood and bark in Bed T.

At the northern end of Triangle Cliff soildeveloped on the Wathumba beach sand formsthe present ground surface (Fig. 3), and continuessouth to the middle section of the cliff, where itsposition is taken by soil formed on Triangle Cliffdune sand. At the point where the two units cometogether, 600 m south of Towoi Creek, thesection is obscured by modern sand blown on tothe cliff face, scree, and organic stains. For a fewmetres, the Wathumba beach sand appears topass below the Triangle Cliff dune sand. A pub-lished photograph (Grimes 1979) of this part ofthe cliff shows a buried soil (now termed Soil A)descending from the level of the last visible oc-currence of the soil on the Wathumba beachsand. This buried soil, between the letters 'a' and'b' in Grimes's (1979, fig. 3) photograph, is lessdeveloped than that on the Wathumba unit butcould represent it at an earlier stage of develop-ment. Soil A has a thin (5 cm) greyish brownsurface and grades into very pale brown sand atshallow depth. At its lowest point it is cut out,perhaps as a consequence of wind scour asso-ciated with the accumulation of the overlyingTriangle Cliff dune sand, but there is also anobscuring mass of slumped debris. We attemptedunsuccessfully to find Soil A here by augering.

South of the slump another buried soil (Soil B)is present 1.5-2 m above the surface of the deep

white-on-black soil formed on the Poyunganalluvium. This buried soil continues withoutsignificant change in elevation for a considerabledistance along the cliff face. Its topsoil is staineddark greyish brown by finely divided organicmatter, and the sand beneath is bleached palegrey for 10-20 cm before passing into very palebrown sand. Where foreset bedding is evident inthe sand beneath Soil B, the strike is mostlynortheast and east and the dip variously northand south. The sand above Soil B is Triangle Cliffdune sand. Carbonized plant debris lies in placeson the foreset bedding planes (dip 30-320°) nearthe base of the Triangle unit, 20-30 cm aboveSoil B. This material, which appears to be theresidue of leaves, twigs and ferns, has evidentlyaccumulated along with the enclosing sand. Aradiocarbon date of the sample gave 6740 ± 80radiocarbon years BP (Beta-3301). Triangle Cliffdune sand continues without interruption to thetop of the cliff. Minor cappings of sand blownfrom the bare cliff face form small cliff-topdunes, and a small patch of Station Hill dunesand (Table 1) is present at the foot of the cliff tothe south. The soil profile on the Triangle Cliffdune sand contains 1 m of grey and pale greysand above a variegated pale brown, brownishyellow and brown sandy B horizon which passes,below 1.8 m, to very pale brown sand.

Several patches of scrubby vegetation on theeroded face of Triangle Cliff, below its highestpoint, are associated with weakly developed soilswithout clearly defined leached A2 horizons, andare like those developed on the Cape and Hookunits (Table 1). This vegetated ground is unstableand is interrupted by slips as a consequence ofmarine erosion at the foot of the cliff. Thepresence of the vegetation and soil indicates thatthe cliff has been stable recently and has notalways been subject to wave attack.

PREVIOUS INTERPRETATIONS OF THESEQUENCE EXPOSED IN TRIANGLECLIFF

Ward (1977b) believed that all units at TriangleCliff except the cliff-top dunes and the smallpatch of Station Hill dune sand were Pleistocenein age (Table 2), and did not recognize soilsindicating the Cape and Hook units. Bed T wasinterpreted as a paludal correlative of Woorimbeach sand and implied a sea level about 1 m

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330 W. T. WARD AND K. G. GRIMES

Table 2 Previous age classifications of the morphostratigraphic units and the relationship with Bed T; the names ofdune sands are distinguished from beach sands by italics

WARD 1977a, b GRIMES 1979 PYE 1983 This paper

w

O

3o

ModernHookCapeRooney PointStation HillBool Creek

ModernHookCapeRooney PointStation HillBool CreekTriangle CliffWathumbaGarawongeraWoorim

ModernHookCapeRooney PointStation HillBool CreekTriangle CliffWathumbaGarawongeraWoorimBribieBowarrady

ModernHookCapeRooney PointtStation HilftBool Creek

<T< Bed T3 ;

/Wathumba

Triangle Cliff

W

wU

§

Triangle CliffWathumbaGarawongeraWoorimBribieBowarradyPoyunganYankee JackUngowaAwinyaCooloola

[Bribie]*[Bowarrady]Poyungan[Yankee Jack][Ungowa][Awinya][Cooloola]

PoyunganYankee JackUngowaAwinyaCooloola

GarawongeraWoorimBribieBowarradyPoyunganYankee JackUngowaAwinyaCooloola

T h e names in brackets are for units not discussed separately by Grimes (1979).tRooney Point beach sand and Station Hill dune sand were found to be contemporary in part by Ward (1982), who

suggested that the later phases of Station Hill dune sand overlapped the earlier phases of Rooney Point beachsand.

*Bed T was originally correlated with Woorim beach sand (Ward 1977b). This attribution is now rejected (seetext).

above that at present. The date of 3880 ± 105years BP for charcoal in buried topsoil of thePoyungan unit seemed to provide a limiting agefor Triangle Cliff dune sand at this point, but wasconsiderably younger than expected.

Grimes (1979) reported dates of 5690 years BPand 4480 years BP for Bed T and proposed thatall units except the Poyungan beach sand wereHolocene. As further support he cited a date of3440 ± 105 years BP (SUA-561) for shells said tocorrelate with Wathumba beach sand on BribieIs.

Pye (1983) accepted Grimes's (1979) views,and suggested that the Bowarrady dune sand andthe Bribie beach sand were also Holocene in age,

but gave no supporting evidence. The Poyunganbeach sand, Yankee Jack dune sand and Ungowabeach sand (Table 1) were all attributed to theLast Interglacial because the Ungowa unit hadthe same appearance and height above sea levelas the apparent Last Interglacial shoreline in NewSouth Wales.

Field observations made since 1979 havecaused us to reassess all of these views.

DISCUSSION

The question of the position of the Pleistocene-Holocene boundary relates particularly to the

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HISTORY OF FRASER ISLAND DUNES, QLD 331

Wathumba beach sand and the Triangle Cliffdune sand.

Ward (1977a, b) accepted the Woorim beachsand, Wathumba beach sand, and Triangle Cliffdune sand as Pleistocene because the TriangleCliff dune sand was associated with a low sealevel prior to the postglacial Bool Creek beachsand, and the Wathumba beach sand underlaythe Triangle Cliff dune sand at Wathumba Inlet(Fig. 1). It followed that Bed T was eithercontemporaneous with the Wathumba beachsand or represented an earlier high sea level. Ofthese options, an equivalence with the Woorimbeach sand was accepted because the Woorim sealevel had a similar elevation, as at Teewah (Wardet al 1977). The date of 3880 ± 105 years BP forthe soil on the Poyungan unit implied that theTriangle Cliff dune sand had developed throughthe postglacial transgression and into morerecent time.

Subsequently, ages provided by Grimes (1979)for Bed T demonstrated that the overlyingWathumba unit must be Holocene, and sug-gested that the Woorim unit, with which Bed Thad been identified (Ward 1977b), was also ofHolocene age. Although Grimes did not questionWard's identification of Bed T with the Woorimunit, we now agree that this correlation iserroneous.

We cannot reassign the Triangle Cliff dunesand entirely to the Holocene because, on the eastcoast of Fraser Is. (site H, Fig. 1), it lies behind theWathumba beach sand, which has been builtacross the wind-excavated blowouts of theTriangle Cliff unit (Fig. 4). At this locality theTriangle Cliff dune sand is obviously older thanthe Wathumba beach sand. The different fieldrelations on opposite sides of the island indicatethat the Triangle Cliff dune sand and theWathumba beach sand must be at least in partcontemporaneous. Thus, we explain the fieldobservations by supposing that the dune sandswere produced by sand-blowing at a time of low,possibly glacial, sea level; that they continued todevelop as the sea was rising; and were stillmoving at 6740 ± 80 years BP, near TriangleCliff, when the sea—as shown by the Wathumbabeach sand—had reached a level close to thepresent one. Triangle Cliff dune sand formed firstat the exposed eastern shore. When it arrived atthe present position of Triangle Cliff, theWathumba beach sand, which had been accum-ulating there, was partly buried (with Soils A and

Fig. 4 Relation of Wathumba beach sand (w) toTriangle ClifTdune sand (t) at site H, near Hook Pt (Fig.1). Contours simplified from a survey with contours at2 m intervals by Australian Survey Office; the 7.5 mcontour is interpolated, b, Bool Creek beach sand.

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332 W. T. WARD AND K. G. GRIMES

B) under the advancing dune sands. However,the Wathumba unit was not buried completely,and continued to form at the beach north ofTriangle Cliff. As it accumulated, the rising seaallowed the development of Bed T, which datesthis part of the Wathumba beach sand at ca. 5000years.

Because of its interstratification with theincoming sand, the date of 6740 ± 80 years BPfor organic detritus in foreset beds of the TriangleCliff dune sand shows the time of arrival of thesand at the present Hervey Bay shore moreprecisely than the younger date of 3880 ± 105years BP obtained from carbon in soil developedon the underlying Poyungan unit. We considerthat both dates are accurate, in spite of theirapparent reversed order. The younger date doesnot represent the vegetation growing on thePoyungan unit when it was overwhelmed by theTriangle Cliff dune sand, as appearances suggest(Grimes 1979), but represents the intruding rootsof vegetation which grew previously on theeroded face of Triangle Cliff and exploitednutrients contained in the buried soil. A similarsituation exists today with modern vegetationgrowing on the eroded cliff face.

The date of 3440 ± 105 years BP (=3890 +100 radiocarbon years BP, —450 years for thereservoir effect), cited for shells attributed to theWathumba beach sand by Grimes (1979) andPye (1983) at the northern limit of Bribie Is., isirrelevant, for no evidence supporting aconnection with the Wathumba beach sand isavailable and our field inspection of the site (in1981) found no evidence for any such con-nection. The dated shells occur in soft humate-cemented sand at 0.6 m below mean sea level. Asour observations at the coast show that humateforms first at groundwater level, its developmenthere implies a low water level; that is, a low sea,of perhaps —1.5 or — 2 m at about 3440 yearsBP.

postglacial rise. The date confirms that theTriangle Cliff dune sand was still being emplacedat 6740 years BP but it is for the downwind,advancing 'nose' of the blowing sands. It is notnecessarily implied, therefore, that the con-ditions which brought about sand movementstill prevailed because, once laid bare, sand willcontinue to move under the force of ordinarywinds until vegetation is able to give it effectiveprotection.

The presence of vegetation on Triangle Cliff at3880 ± 105 radiocarbon years BP is shown by thecarbon date for charcoal in the buried soil onPoyungan beach sand. This vegetation, and thepatches of soil on the present face of the cliff,show that the sea at times stood back fromTriangle Cliff. One of these intervals could wellcoincide with an apparent lower groundwaterlevel shown by humate and dating at Bribie Is.Both dated situations suggest that Holocene sealevel, soon after 3900 radiocarbon years BP, waslower than at present. Such a change in sea levelhas not hitherto been reported by other in-vestigators on the Queensland and New SouthWales coasts.

ACKNOWLEDGMENTS

Thanks are due to Myron Cause, QueenslandDepartment of Forestry, for identification ofwood from Bed T, and to A. W. Stephens,Geological Survey of Queensland, for adviceconcerning the interpretation of the radiocarbondate from Bribie Is. We also thank Peter Roy forhelpful comments on the manuscript and theNational Parks and Wildlife Service for per-mitting us to undertake this research in the GreatSandy National Park. G. M. Roberts, I. P. Little,and Russell Kelley assisted with field observa-tions. K. G. Grimes publishes with the per-mission of the Chief Government Geologist,Geological Survey of Queensland.

CONCLUSIONS

The Triangle Cliff dune sand is attributed eitherentirely to Early Holocene events, or partly toLate Pleistocene and partly to Holocene time. Itsformation continued to at least 6740 years BPand overlapped with the development of theWathumba beach sand, which formed as the seaapproached and met present sea level during its

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GILLESPIE R. & POLACH H. A. 1979. The suitability ofmarine shells for radiocarbon dating of Australianprehistory. Proceedings of the 9th InternationalRadiocarbon Conference, pp. 404-421. Universityof California Press, Los Angeles.

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HISTORY OF FRASER ISLAND DUNES, QLD 333

GRIMES K. G. 1979. Carbon-14 dates and the evolutionof Fraser Island. Queensland Government MiningJournal 80, 79-82.

PYE K. 1983. Formation and history of Queenslandcoastal dunes. Zeilschrift für GeomorphologieSupplementband 45, 175-204.

SOIL SURVEY STAFF 1975. Soil Taxonomy: a basicsystem of soil classification for making and in-terpreting soil surveys. US Department of Agri-culture, Handbook 436, 745 pp.

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WARD W. T. 1977a. Sand movement on Fraser Island:a response to changing climates. OccasionalPapers in Anthropology 8, 113-126. AnthropologyMuseum, University of Queensland.

WARD W. T. 1977b. Field excursion from OrchidBeach to Triangle Cliff and Lake Bowarrady. InDay R. W. ed. Field Conference 1977, Guidebook,pp. 65-71. Geological Society of Australia,Queensland Division, Brisbane.

WARD W. T., STEPHENS A. W. & MCINTYRE N. 1977.Brisbane's north coast and Fraser Island from theair. In Day R. W. ed. Field Conference 1977,Guidebook, pp. 14-30. Geological Society of Aus-tralia, Queensland Division, Brisbane.

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(Received 6 May 1986; accepted 24 September 1986)

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