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Evidence of high sea level during isotope stage 5c in Queensland, Australia
QUATERNARY
RESEARCH
Evidence
24, 103- 114 (1985)
of High Sea Level during Isotope Stage 5c in Queensland, Australia
J. W. PICKETT,* C. H. THOMPSON,? R. A. KELLEY,$ AND D. ROMAN§ *Geological Survey of New South Wales, Geological and Mining Museum, 36 George Street, Sydney, Neti South Wales 2000, KSIRO Division of Soils* 306 Carmody Road, and #Department qf Geology, University of Queensland, Chancellor’s Place, St Lucia, Queensland 4067, #Isotope Division, Australian Atomic Energy Research Establishment, Private Mail Bag, Sutherland, New South Wale.7 2232, Australia
Received April 11, 1984 Thirty-nine species of scleractinian corals have been recovered from under a high dune on the western (mainland) side of North Stradbroke Island, eastern Australia. The corals are associated with thin intertidal sediments and their good condition implies burial in situ and preservation in a saturated zone. Most IikeIy this occurred as the coast prograded and a large dune advanced into the littoral zone, burying intertidal sediments and coral. The species assemblage indicates a she]tered environment but one open to the ocean without wide fluctuations in salinity. Three species yielded a mean z30Th/Z34Uage of 105,000 yr B.P. which is significantly younger than the nearest Pleistocene corals at Evans Head, New South Wales. The corals provide evidence of a sea stand near present sea level during isotope Stage 5c, which is considerably higher than previously suggested for this period. Their good condition implies that the overlying parabolic dune is of comparable age and formed during that high stand of sea level. Also, the isotope age provides a maximum period for the development of giant podzols in the podzoi chronosequences on coastal dunes in southern Queensland. 0 1985 University of Washington.
INTRODUCTION
North Stradbroke Island is situated on the subtropical coast of eastern Australia at about 2T south latitude. It is a large sand island that extends along the Queensland coast for some 37 km, reaches a maximum width of 12 km in its northern part, and forms the southeastern boundary of Moreton Bay (Fig. 1). In composition and development it is similar to several other sandmasses along the eastern coast (Bird, 1973; Thompson, 1983). Most of the exposed island consists of quartz sands deposited in a series of overlapping dune systems. These now commonly reach elevations of 80-100 m and rise to a maximum of 228 m at Mt. Hardgrave in the northcentral part of the island. Most of the dunes have a northwesterly trend, indicating dune building by onshore winds from mainly the southeast. Drillings, associated with hydrological investigations (Laycock, 1975), show that dune sands and other sediments
extend to depths of 90 m below sea level under parts of the island. In early 1982, dredging for heavy minerals in the northwestern part of the island produced an assemblage of scleractinian corals, marine shells, and some wood fragments (Brisbane (1: 100,000) grid reference 441658, Figs. 1 and 2). Coral beds had been intercepted by drilling between + 2 and - 6 m and samples were brought up by a floating suction dredge operating in an artificial pond with water level at about mean sea level. Samples of 39 species of corals, representing 2.5 genera, 62 species of mollusts (J, Stanisic 1983, personal communication), and wood fragments from 4 mangrove genera and one freshwater swamp tree were recovered from the dredge screen. Isotope ratios have been determined fat samples from three of the coral species by 230Th/234U dating and yielded a mean isotope age of 105,000 yr B.P. In this paper, the coral assemblage is compared with IO3 0033-S894/8.5 $3.00 Copyright 6 1985 by the Umversity of Wishington Ail rights of reproduction in any form reserved.
104
PICKETT 1
I.40
1
I50
0
ItJO0
Newcastle
Embaymer
0
soo km t
0
,
c?
Moreton
Island
North
Stradbroke Island
0
L.!LJ
20 kr
u
153’E ,
1
28O s
FIG. 1. Map of eastern Australia and Moreton Bay, Queensland showing location of North Stradbroke Island site.
modern corals nearby, its isotope age in relation to other Australian Pleistocene corals is examined, and the geological and pedological importance of the find is discussed. SITE STRATIGRAPHY Stratigraphic
Relationships
Most of the sedimentary column above the buried coral consists of unconsolidated
ET AL.
dune sands (unit A of Fig. 3) which now form a sinuous, north-south-trending ridge. Crest elevations vary from 70 to 1IO m, and a maximum thickness of approximately 107 m of dune sands occurs adjacent to the coral site. The dune sands are well sorted and are generally less than 500 km in diameter, with a modal size between 180 and 212 pm. They consist almost entirely of quartz but also contain small amounts of K-feldspar and up to 2% heavy minerals, mainly ilmenite, rutile, and zircon. Crossbedding showing eolian foreset and topset beds is evident in the mine pit. The dune has been severely modified by water erosion since eohan activity ceased. Even so, giant podzols, with both thick bleached AZ and pipey B horizons (Thompson, 1983), that formed in the upper 15-25 m of dune sands persist on the dune crest. Truncated profiles with yellowishbrown sands near the surface are evident on the western slopes where water erosion has been greatest, The soils grade with depth into unweathered yellowish-brown sands which continue unchanged to 3-6 m above the present water table where browner sands are recorded by the mine drill logs. These appear to be dune sands stained by groundwater during seasonal oscillations. The browner dune sands rest on brown and off-white sandy sediments of variable thickness which in places overlie the coral beds within a depth of 6 m. The contacts between the dune sands, the mixed brown and off-white sediments, and the coral beds were below the surface of the dredge pond and could not be observed. Diving in the dredge pond by one of us (R.A.K.) established that the corals are incorporated in gray and olive muds. Diving also led to recovery of wood and bark samples from submerged logs released from the contact zone by dredging. Four of these have been identified at the Queensland Herbarium as mangrove genera (Xyfocurpus vel. aff. grunaturn), Ceriops sp., Rhizophora sp., Avicenniu sp.) and another as swamp tea-tree
LAST
INTERGLACIAL
SEA LEVEL
105
FIG. 2. Airphoto of northwestern North Stradbroke Island, showing coral locality and mined area (Reproduced with permission of Department of Lands, Queensland.1
vel. aff. quinquerzervia) (R. M. Dowling, 1983 personal communication). The mining drill logs record coral at six sites along a single traverse (Fig. 4) and make no mention of coral under the adjacent dune sands to -30 m, except for one hole about 1000 m to the south (Fig. 2) in which coral was reported at approximately -3 m. At the sample locality (Fig. 4), coral beds were encountered in five adjacent drill (Melakuca
holes and recovered by dredging from a zone between + 2 and - 6 m in relation to present sea level. The upper surface of the coral beds rises to the east and this slope probably represents the environmental gradient; maximum thickness recorded by drilling is 6 m. Corals were not recorded in drill traverses 200 m to the north or south and their extent in these directions is not available from dredging, because the water
106
PICKETT
ET AL.
Pleistocene Ho@ene
dunes
sediments. plain
surface -Pleistocene clays, during low sea level @ = transgressive w
= depositional
muds
and
sands
progradatIon
-
with
rising
sea
progradation
FIG. 3. Schematic geologic cross section of eastern Moreton Bay and western North Stradbroke Island.
level in the dredge pond was raised by 5 m when difficulties were experienced with the heavy coral masses. Small pieces of three different materials associated with the corals were recovered by the dredge; these include weakly consolidated, bedded yellowish-brown sand, black peaty sand containing pieces of mangrove wood and seagrass (Zmtera sp.), and grayish and olive sandy muds attached to coral and shells. These sediments are interpreted as beach, intertidal, and subtidal faties, respectively. The mixed brownish and white sands recorded in the drill logs probably represent a mixing (during drilling) of these sediments with white sand similar to that recorded below the coral beds. Data from the drill holes (Fig. 4) indicate that the muddy horizon is underlain by white fineto medium-grained sands. Pieces from two lithologies brought up by the dredge appear to belong to this unit. One is an off-white, weakly consolidated sand with yellowishbrown color variation in the bedding and the other is a white, weakly consolidated sand with prominent dark bands of heavy minerals. Both are considered alluvial sediments derived from the degraded old dune to the east (unit B). These are the only samples that have been obtained below the coral although the drill logs record white sands for a further 20 m and show that they continue east toward the old, degraded
dune (unit B). Some of the deeper white sand could be continuous with this unit. Znterpretation
of Stratigraphy
The morphology of the dune and its foreset bedding planes indicate deposition along the advancing front of a large parabolic dune or group of parabolic dunes that coalesced as they advanced across the island and terminated along its western margin. Such dunes were probably initiated along the eastern coast by sand blown inland by onshore winds but incorporated additional sand from the underlying dunes through deflation as they advanced. It appears that the corals initially colonized marine shells lying on the weakly consolidated white sands in the subtidal zone. Mangroves were associated with muddy, sandy sediments of the adjacent intertidal zone to the east and there was a small sandy beach backed by large sand dunes from which freshwater springs entered the intertidal zone. The tea-tree (Melufeucu vel. aff. quinquenerviu) and the buttress mangrove (Xylocurpus vel. aff. grun&urn) both indicate the presence of fresh water. M. quinquenervia today occurs on North Stradbroke Island above the tidal zone on low sandy banks underlain by fresh water and around swamp margins. Xylocarpus granatum is no longer found in
LAST
INTERGLACIAL
SEA
LEVEL
I07
Moreton Bay, its most southerly known occurrence being some 200 km north along the western (inland) side of Frazer Island, where freshwater springs from the dunes enter the intertidal zone (R. M. Dowhng. 1983, personal communication). The thickness and structure of the dune sands overlying intertidal sediments with mangrove fragments, and the slope of the coral surface to the west imply burial by the large dune as it advanced westward into the littoral zone. Apparently the coral community was overwhelmed and buried by the muddy intertidal sediments prograding ahead of the advancing dune and all three units are therefore of similar age. A substantial time gap between the deposition of the intertidal sediments and dune sands is unlikely because no evidence has been found of subaerial weathering in either intertidal sediments or coral. Many of the corals show little evidence of chemical, physical, or biological degradation; their good condition, range in size, and number of species present imply burial in situ and subsequent protection from subaerial weathering or oxidation. The intertidal sediments that enclose the corals are thin and unlikely to protect them for any lengthy period. However, burial by 100 m of dune sand as the shore prograded would ensure protection and maintain saturation in the finer-textured coral beds during lower sea levels. The evidence of strong degradation of the dune by water erosion together with the great depth of soil development indicates that the dune is an old feature preceding the last glaciation (Thompson, 1983). Further, the preservation of a giant pdzol on the crest of such a high exposed feature indicates that it carried vegetation for a very long period preceding the last glaciation; otherwise the podzol would have been destroyed by wind erosion. This in turn implies a climate conducive to vegetation and one able to maintain a saturation zone in the coral beds during low sea levels.
108
PICKETT
THE CORAL ASSEMBLAGE
ET
AL.
TABLE PLEISTOCENE
Composition
Thirty-nine species of scleractinian coral, referable to 25 genera, have been recorded from the locality (Table 1). Some of the colonies reach substantial dimensions (e.g., fragments of a colony of Symphyilia cf. recta indicate that it had a height greater than 29 cm, which is a considerable size for this species and implies prolonged conditions suitable for growth). From visual accounts of coral recovery during the mining operation, Acropora and Porites seem to have been the dominant genera. In addition to massive colonies, such as those of Goniastrea, Symphyllia, and Porites, there are foliose forms (Pavona, Coscinaraea, Pachyseris, Montipora), multibranched Acropora and Lobophyllia, and solitary, freeliving fungiids. Environment
The corals are enclosed in muddy sediment. There is no evidence of cemented reef rock, and the associated sediments are unconsolidated. The small samples of weakly coherent sand brought up by the dredge may represent the initial colonizing surface. These are interpreted as alluvium derived from the old dune system to the east which would have sheltered the coral locality to some extent. Twenty of the species identified from the fossil deposit are not recorded among the 119 species in a recent census of corals at Flinders Reef which is in an oceanic situation at the entrance to Moreton Bay, some 50 km to the north (J. E. N. Veron, 1983, personal communication). These 20 are mostly associated with quiet conditions. The assemblage of Acropora species is also characteristic of quiet waters (C. Wallace, 1983, personal communication). The colonies of Cyphastrea have a “cauliflower” surface, typical of living specimens from Moreton Bay. Other indicators of quiet waters are the fungiids, Pachyseris rugosa (Veron and Pichon, 1979, p. 81),
I.
CORAL
SPECIES IDENTIFIED
CORAL
DEPOSIT
FROM THE
ON NORTH
ISLAND, COMPARED WITH THOSE (COLUMN A) AND IN MORETON
STRADBROKE
AT FLINDERS BAY (COLUMN A
Pocillopora damicornis Seriatopora hystrix Acropora formosa Acropora millepora Acropora aspera Acropora valida Acropora cf. longicyathus Acropora microphthalma Acropora cf. cuneata Acropora cf. robusta Astraeopora sp. Montipora sp. A Montipora sp. B Pavona varians Pavona decussata Pachyseris rugosa Coscinaraea columna Heliofungia actiniformis Fungia fungites Herpolitha limax Goniopora sp. Porites sp. Favia cf. pallida Favia sp. Favites halicora Favites bennettae Goniastrea australensis Goniastrea aspera Platygyra sp. Leptastrea purpurea Oulophyllia crispa Hydnophora exesa Cyphastrea serailia Galaxea fascicularis Lobophyllia corymbosa Lobophyllia hemprichii Symphyllia cf. recta Symphyllia cf. valenciennesi Turbinaria radicalis Millepora sp.
REEF B) B
+ + i+
0 0 4
+
+
0 0
0
0
0
0
0
i+
+ +
+ +
+
+
Note. + = species present; o = genus represented by (anjother species.
Goniastrea aspera (Veron et al., 1977, p. 84), and Leptastrea purpurea which, through encrusting habit, even size of corallites, and general lack of calical variation, is simiIar to quiet water forms described by Veron et al. (1977).
LAST
INTERGLACIAL
SEA
109
LEVEL
Many of the forms in the fossil assem- given the southerly latitude of the fossil loblage of corals are indicative of conditions cality, these tolerances were probably reduced . far less restrictive than those of Moreton The corals are regarded as in situ because Bay at present, and the overlap with the of (a) the large size of some species, (b) the modern assemblage in Moreton Bay is remarkably slight. Of the 25 species recorded good condition of fragile species and of delthere (Lovell, 1975). only 5 are certainly icate structures such as protruding Acropora calyces, and (c) the presence of mud common to both assemblages, although there may be as many as 8 because some with the corals which indicates that they forms (Goniopora, Favia, Platygyra) could are not supratidal storm deposits. Corals only be identified to genus. On the other associated with muddy sediments are alhand, comparison with the fauna1 list from ways found in sheltered situations (Veron Flinders Reef indicates 12 forms common, and Pichon, 1976, 1979, 1982; Veron et al.+ 1977), and the paleogeographical situation and a further 7 potentially common, to both assemblages. The environment of Flinders on the leeward side of proto-Stradbroke IsReef is unsheltered; the greater apparent land would have sheltered this community. similarity of the fossil assemblage with that Then, as in modern Moreton Bay, the of Flinders Reef rather than Moreton Bay corals inhabited a slope from shallower to gradient). is possibly due to warmer s&ace waters at deeper water (environmental the time and also to a partly sheltered geo- This is reflected in the maximum range of graphical situation, but one that was open +2 to -6 m from which the corals were to the ocean and sufficiently free from sa- recovered. However, the depth to the top linity fluctuations to allow an abundant and of the corals cannot be given with absolute varied coral assemblage to thrive. It seems precision because the sampling interval in that the conditions were similar to those the mining drill holes was 3 m. Neverthethat led to the development of a rich assem- less, this does allow an absolute minimum blage at Evans Head, New South Wales height of 0 m for the intersection of the Using the modern an(Pickett, 1981). The sheltered situation of upper coral s&ace. both these deposits also appears to be alog of habitat conditions in Moreton Bay partly responsible for their preservation. and assuming a tidal regime of 2 1 m, then paleo-sea level relative to modern sea level must have been between + I and + 3 m. Water Depth Several of the taxa in the fossil assemblage are unable to survive in an intertidal situation, although most forms are common subtidally. Using data from Veron and Pichon (1976, 1979, 1982) and Veron et al. (1977), it is possible to obtain an indication of the proportion of species tolerant to tidal exposure. Such data are available for 23 of the species listed in Table 1. Of these, 1 I are specifically mentioned as occurring in the intertidal zone (Pocilfopora damicornis, Pavona decussata, Fungia fungites, Favia cf. pallida, Favites halicora, Goniastrea aspera, Platygyra sp., Leptastrea purpurea, Cyphastrea serailia, Galaxea fascicularis, Syrnphyllia cf. recta), although,
AGE
OF THE
CORALS
Samples from three of the corals, Porites sp., Syrnphyllia cf. recta, and Goniastrea aspera, were selected for analysis. All proved to have a high degree of purity. Analysis by X-ray diffraction (Slansky, 1982) indicated that none contained detectable calcite. Under the microscope the skeletons appear pristine; the finest growth increments of delicate structures, such as dissepiments, are still observable. This is in accord with the undamaged nature of many of the coralla at the site, and the fact that the corals were probably not exposed to either marine or aerial influences from the
110
PICKETT
time of their burial until their recovery by the dredge. Zsotupe Analysis
Analytical details of the three coral samples are presented in Table 2. The method used has been described previously (Roman, 1980). Ages were calculated using the formula of Kaufman and Broecker (1965). The levels of 232Th recorded were negligible over the counting time. The spread of ages is small, encompassing some 7000 yr. By comparison, the spread of ages of seven specimens of coral from five localities within the Gundurimba Clay of the Richmond River Valley, New South Wales, covers 17,000 yr (Marshall and Thorn, 1976; Drury and Roman, 1983). Taken together, the ages for the North
TABLE
2. AGES DETERMINED
FOR CORAL
ET AL.
Stradbroke Island corals are significantly younger (average 105,000 yr) than those from Evans Head (average 118,600 yr), and both of these are younger than the age for the most southerly Pleistocene locality, Newcastle Embayment, New South Wales (average 142,500 yr). Correlation
with Deep-Sea-Core
Stages
Drury and Roman (1983) have correlated the deposits at the Evans Head locality with isotope substage 5e of Shackleton (1969), and with reef VIIb of Bloom et af. (1974), which is indicated by their similar isotope ages. The age determined for the North Stradbroke Island locality is similar to that of the next youngest peak in Figure 5 of Bloom et al. (1974) and may correlate with substage 5c.
SAMPLES
FROM NORTH
STRADBROKE
ISLAND
QMFl2385 Porites sp.
4.05
2.24 2 0.09 (1985 2 45)*
2.39 2 0.07 (2116 e 46)*
1.07 2 0.03
0.06 2 0.01
QMF 12400
4.70
1.92 2 0.09 (1303 k 36)*
2.15 2 0.13 (1455 * 39)*
1.12 2 0.04
ND
3.92
2.27 2 0.09 (1737 ? 42)*
2.47 ? 0.11 (1890 k 45)*
1.09 k 0.04
ND
Symphyllia cf. rectu
QMFl2401 Goniastrea aspera
Sample
z30Thp34U
QMFl2385 Porites sp.
1.46 2 0.05
0.61 k 0.03
QMFl2400
1.37 2 0.03
0.64 2 0.04
1.55 k 0.05
0.63 2 0.03
Symphyilia
As (yr ELFt)
DNA 5 6%
Expt
2.9
3.00 2 0.12
108,000 +11,000/ - 10,000
2.5
2.57 iz 0.12
~W~~~ +- 6,000/ g$()o
3.0
3.04 2 0.12
cf. recta QMFl2401 Goniastrea aspera
Note,
* = total counts used in ratio calculations.
ND indicates that 232Th is below detectable levels.
LAST INTERGLACIAL
FIG. 5. Maximum altitudes of sea level for the last interglaciation based on scleractinian coral occurrences in eastern Australia. A = North Stradbroke Island; B = Evans Head: C = Newcastle Embayment.
The ranges in isotope ages at each of the various localities are fairly limited, except for some samples from the Gundurimba Clay, and there is no overlap in the determined values; the range for the Evans Head locality (using dates on corals alone and excluding other localities within the Gundurimba Clay) is 112,000 to 127,000 yr B.P., for Newcastle Embayment 142,000 to 143,000 yr B.P., and for the present locality 101,000 to 108,000 yr B.P. As a control between different laboratories and analysts, Roman (1980) has also analyzed samples from the Evans Head locality, with a result similar to that reported by Marshall and Thorn ( 1976). For these reasons, and because the ages determined correlate well with other assessments of the high sea-level stands of isotope stages 5c and 5e, the possibility that the coral deposit at Evans Head and that on North Stradbroke Island belong to the same isotope stage is unlikely. SIGNIFICANCE TO GEOLOGY AND PEDOLOGY Sea Levels of the Last Inter-glaciation The eastern coast of Australia is an area of remarkable tectonic stability. No study thus far has disclosed any evidence for isostatic movements since the Tertiary (Oilier, 1982: Jones and Veevers, 1982; Searle, 1983). Most Quaternary researchers agree that only eustatic influences have affected eastern Australian coastal development during the Quaternary period.
SEA LEVEL
Ill
The two older Pleistocene coral localities, Evans Head and Newcastle Embayment, both indicate a sea level of + 4 to + 6 m (Marshall and Thorn, 1976; Pickett, 1981), which is in accord with the maximum height of sea level recorded for isotope stage 5e in other places (e.g., Bloom et a/. , 1974, Fig. 5; Chappell, 1983, Fig. 1). Regional movement affecting deposits of isotope stage 5c would, in all probability, have also affected the older 5e deposits at Evans Head, 180 km distant. This does not appear to be the case, so that the relative heights indicated by the two deposits remain the same. The heights for former sea levels indicated by all three coral localities are considered to have been unaffected by isostatic movement. Evidence from the Pleistocene coral assemblage on North Stradbroke Island indicates that the highest point reached by the corals is possibly +2 m and certainly not less than 0 m (present sea level): this probably corresponds to the former low tide level. Assuming that the tidal regime was not greatly different from that of the present, and because no effects due to isostatic movements have been established. mean sea level at 105,000 yr B.P. (stage 5c) was at least + 1 m and possibly as high as +3 m. The relative heights for sea levels during isotope stages 5c and 5e as calculated by Bloom et ul. (1974) differ by almost 20 m, or by at least 15 m according to Chappell (1983, Fig. 1). This is in contrast to the heights implied by the eastern Australian occurrences (Fig. 5, points A and B), which indicate a difference of only 2 m for the same peaks. Whereas the sea level indicated by the Evans Head locality (stage 5e) is in accord with that determined by Bloom et al. (1974) for both New Guinea and Barbados, the level of + 1 to +3 m at North Stradbroke Island is significantly greater than the height of - 16 m established for the younger peak (stage 5~) by Bloom et t~i. (1974) or Chappell (1983). There has been remarkable coincidence
112
PICKETT
between oxygen-isotope paleotemperature curves, derived by Emiliani (1961) and modified by Shackleton and Opdyke (1973), and Pleistocene sea levels deduced from reef terraces in both the Atlantic (Broecker et ul., 1968) and Pacilic oceans (Bloom et al., 1974; Chappell, 1974; Chappell and Veeh, 1978). For the last interglaciation, this is reflected in the relative heights of the peaks for isotope stages 5a, 5c, and 5e, during which the highest peaks for both sea level and temperature are associated with stage Se. The pattern of sea-level fluctuation summarized by Bloom et ul. (1974, Fig. 5) includes two peaks, both included in stage 5e by Drury and Roman (1983), the older one (140,000 yr BP.; ca. -5 m) being lower than the younger (124,000 yr B .P. ; ca. + 5 m). As can be seen from Figure 5, the eastern Australian localities indicate that these maxima were both higher than present sea level. Considering the coral assemblages alone, the depth at Evans Head is much better documented than that at Newcastle Embayment (point C on Fig. 5), because only two species are known from the latter locality, neither of which gives any critical indication of the water depth. Consequently, the sea level indicated at point C merely represents a minimum figure and the actual sea level may have been higher than for point B. Thus, as the subdivision of stage 5 (Shackleton, 1969) does not distinguish between the two peaks of stage 5e, the highest sea level remains associated with that subdivision. A recent compilation of New Guinea data (Chappell, 1983) has produced a sea-level curve which diverges from the paleotemperature envelope of Shackleton and Opdyke (1973) for the interval 150,000-30,000 yr B.P. and implies a sea level of approximately - 30 m at 140,000 yr B,P., in contrast to the levels indicated by the corals of the Newcastle Embayment. No evidence of sea levels associated with isotope stage 5e has yet been recognized on North Stradbroke Island; presumably it has either been obscured by dune building or obliterated by erosion.
ET AL.
Dune Building
and Sea Levels
Dune sands make up most of North Stradbroke Island above sea level. Several dune systems, deposited episodically during the Quaternary, have been recognized (Thompson and Ward, 197.5; Ward, 1978) and may be correlated with dune systems on similar large sand masses along the coast (Ward et ul., 1977; Thompson, 1981; 1983). Along the eastern coast of Australia, there is good evidence, supported by radiocarbon dates, that the three youngest parabolic dune systems are Holocene features deposited since the sea reached approximately its present level, some 6000 yr ago (Thorn, 1965; Bird, 1973; Thorn et al., 1978). Also, large parabolic dunes are still forming at several localities along the Queensland coast, e.g., Cooloola, Fraser Island, and Shoalwater Bay, during the present marine transgression. Environmental conditions during the deposition of similar Pleistocene dune systems are less certain, and Ward (1977) has associated the main periods of Pleistocene dune building on Fraser Island with the lower seas of glacial periods. However, the evidence, at the coral site on North Stradbroke Island, of rapid burial of the littoral environment by dune sands and the preservation of corals in a saturated zone point to dune building at the time of coral growth during that marine transgression. Other evidence, such as the prevalence of similarly orientated Holocene and Pleistocene parabolic dunes, absence of arid dune forms, and preservation of giant podzols, show that these dunes (including that overlying the coral) have been continuously vegetated since deposition. This finding implies that the climate here during the last glaciation did not deteriorate beyond that necessary to sustain vegetation. It seems that dune building along the Australian subtropical coast was not necessarily associated with low sea levels or very arid conditions. Development
of Giant Podzols
The soils on the dune overlying the corals vary locally from rudimentary podzols
LAST INTERGLACIAL
about 1 m thick on the actively eroding western slopes to giant forms on the crest where profiles with pipey 3 horizons up to 10 m thick and overall depths exceeding 25 m persist. Irregularities in the boundaries between the AZ and Bhir horizons of @Z&S on coastal dunes in Australia become increasingly evident as the age of soil development exceeds 4500 yr (Thompson and Bowman, in press). Pipey B horizons with columns of bleached AZ sand encased in precipitated organic and sesquioxide compounds and penetrating the Bhir for several meters are characteristic of soil development in the Pieistocene dune systems 4 and .5 in the podzol chronosequence on coastal dunes at Cooloola to the north (Thompson, 1981, 1983). Such phenomena indicate long periods of weathering: a mean isotope age of 105,000 yr BP. is therefore important as a measure of the maximum time needed for their development. ACKNOWLEDGMENTS We gratefully acknowledge the ready cooperation of many colleagues and associates. and particularly thank the QueensIand Museum for permission to date coral samples. Associated Minerals Consolidated Ltd. for access to the site and samples from the dredge screen. Consolidated Rutile Ltd. for drill logs, Dr. J. E. N. Veron of the Australian Institute of Marine Science for the unpublished census of corals at Fhnders Reef, Dr. C. Wallace, Department of Biology, James Cook University, for identification of Acroporu species, and Mr. D. J. Ross, CSIRO Division of Soils, for drafting figures. J. W. Pickett publishes with permission of the Secretary, New South Wales Department of Mineral Resources.
REFERENCES Bird, E. C. F. (lY73t. Australian Coastal barriers. /n “Barrier Islands” (M. L. Swartz. Ed.), pp. 4lO426. Dowden, Hutchinson & Ross, Stroudsburg. Bloom. A. L.. Broecker. W. S.. Chappell, J. M. A.. Matthews, R. K., and Mesolella, K. J. (JY74). Quaternary sea-level fluctuations on a tectonic coast: New Z30Th/Z34U dates from the Huon Peninsula, New Guinea. Quuternury Research 4, 185-205. Broecker, W. S., Thurber, D. L., Goddard, J., Ku, T. L.% Matthews, R. K., and Mesolella, K. J. (1968). Milankovitch hypothesis supported by precise dating of coral reefs and deep sea sediments. Science (Washingtwz, D.C.) 159, 2Y7-300. Chappell, J. M. A. (1974). Geology of coral terraces, Huon Peninsula, New Guinea: A study of Quater-
SEA LEVEL
II3
nary tectonic movements and sea level changes. Geoiogicu/ Society of America Bu//etitz 85, 553570. Chappeh. J. M. A. (lY83t. A revised sea-level record for the last 300.000 years from Papua New Guinea. Seurch 14, YY- 101. Chappell, J. M. A., and Veeh. H. (lY78). Late Quaternary tectonic movements and sea level change\ at Timor and Atauro Islands. Geo/ogicu/ Society ol America Bulletin 89, 356-368. Drury, L. W.. and Roman, D. (lY83). Chronological correlation of interglacial sediments of the Richmond River Valley. New South Wales. In *‘Archaeometry. an Australian perspective.’ (W. Ambrose and P. Duerden, Eds.). pp. 2YO-2Y6. Australian National University. Canberra (imprint tY82J. Emiliani. C. (lY61). Cenozoic climatic changes as indicated by the stratigraphy and chronology of deep sea cores of the Globigerina facies. Armu/~s qf’ th AJew3York Acudemy qf Science 95, S21-536. Jones, J. G.. and Veevers. J. J. tlY82). A Cainozoic history of Austrahd’s southeast highlands. Geo/ogicai Society of Austruliu Journui 29, 1- 12. Kaufman, A.. and Broecker. W. S. (lY65t. Comparison of ?‘“Th and 14C ages for carbonate material from Lakes Lahontin and Bonneville. Jowmd 0.f Geophy.sicu/ Reseurch IO, 403Y-4054. Laycock. J. W. (lY75t. *‘North Stradbroke Island-Hydrogeological Report.” Department of Mines Re port No. 88. Geological Survey Queensland. Lovell, E. R. (iY75). ‘.The Reef Building Corals (Cotlenterata: Scleractiniat of Moreton Bay, Queen\land: Their Distribution and Ecology.” Unpublished M.Sc. thesis. University of Queensland. Marshall, J. F., and Thorn, B. G. (lY76~. The sea level in the last interglacial. Nuture (London) 263, IX-* 121. Olher, C. D. (lY82). The Great Escarpment of eastern Australia: Tectonic and geomorphic significance. Geologicui Society qf Austruliu Jourmd 29. 13-23. Pickett. J. W. (1981 t. A late Pleistocene coral fauna from Evans Head. N.S.W. A/cheringu 5, 71-83. Roman, D. (lY80). The electrodeposition of thorium in natural materials for alpha spectrometry. ,~~z~~~?~~/ ofRudioana/ytiru/ Chemist? 60, 317-322. Searle, D. W. t lY83). Late Quaternary regional controls on the development of the Great Barrier Reek Geophysical evidence. BMR Jowrud qf ,A//.\tru/iou Geology & Geophysic.s 8, 267. Shackleton. N. J. tlY6Yt. The last interglacial in the marine and terrestrial records. f’roceeding.x qf the Royal Society of London Serie.s B 174, 135- 154. Shackleton, N. J., and Opdyke, N. D. t lY73). Oxygen isotope and paleomagnetic stratigraphy of equatorial Pacific core V28-238: Oxygen isotope temperdturc~ and ice volumes on a l@’ yr and lob yr scale. r&lrfernczv Resetwch 3. 3Y. Slanksy. E. (lY82). .-Mineral Composition of Cot-al Skeletons from North Strddbroke Island. Queens-
114
PICKETT
land,” Mineralogical Report 82/17 (in mimeo). Geological Survey of N.S. W. Thorn, B. Ci. (1965). Late Quaternary coastal morphology of the Port Stephens-Myall Lakes area, New South Wales. Royal Society of New Sourh Wales
Journal
and
Proceedings
98, 23-36.
Thorn, B. G., Polach, H. A., and Bowman, G. M. (1978). “Holocene Age Structure of Coastal Sand Barriers in New South Wales, Australia.” Royal Military College, Canberra. Thompson, C. H. (1981). Podzol chronosequence of coastal dunes of eastern Australia. Nature (London) 291, 59-61. Thompson, C. H. (1983). Development and weathering of large parabolic dune systems along the subtropical coast of eastern Australia. Zeitschrtyt fur Geomorphologie
Supplementband
45,
205-225.
Thompson, C. H., and Bowman, G. M. (in press). Subaerial denudation and weathering of vegetated coastal dunes in eastern Australia. Zn “Coastal Geomorphology in Australia” (B. G. Thorn, Ed.). Academic Press, Sydney/New York. Thompson, C. H., and Ward, W. T. (1975). Soil landscapes of North Stradbroke Island. Proceedings of the Royal Society of Queensland 86, 9-14. Veron, J. E. N., and Pichon, M. (1976). Scleractinia of eastern Australia. Part I. Families Thamnasteriidae, Astrocoeniidae, Pocilloporidae. Australian Znstitute of Marine Science Monograph Series 1.
ET AL. Veron, J. E. N., and Pichon, M. (1979). Scleractinia of eastern Australia. Part III. Families Agariciidae, Siderastreidae, Fungiidae, Oculinidae, Meruhnidae, Mussidae, Pectiniidae, Caryophyllidae, Dendrophylliidae. Australian Znsititute of Marine Science h4onograph
Series
4.
Veron, J. E. N., and Pichon, M. (1982). Scleractinia of eastern Australia. Part IV. Family Poritidae. Australian Series
Znsititute S.
of Marine
Science
Monograph
Veron, J. E. N., Pichon, M., and Wijsman-Best, M. (1977). Scleractinia of eastern Australia. Part II. Families Faviidae, Trachyphylhidae. Australian Znstitute
of Marine
Science
Monograph
Series
3.
Ward, W. T. (1977). Sand movement on Fraser Island: A response to changing climates. University of Queensland
Department
of Anthropology
Papers
8,
113-121. Ward, W. T. (1978). Notes on the origin of Stradbroke IsIand. University of Queensland Department of Geology
Papers
8, 91-104.
Ward, W. T., Stephens, A. W., and McIntyre, N. (1977). Brisbane’s north coast and Fraser Island from the air. Zn ” 1977 Field Conference, Lady Elliott Island-Fraser Island-Gayndah-Biggenden” (R. W. Day, Ed.). pp. 14-30. GeoIogical Society of Australia, Queensland Division, Brisbane.
RESEARCH
Evidence
24, 103- 114 (1985)
of High Sea Level during Isotope Stage 5c in Queensland, Australia
J. W. PICKETT,* C. H. THOMPSON,? R. A. KELLEY,$ AND D. ROMAN§ *Geological Survey of New South Wales, Geological and Mining Museum, 36 George Street, Sydney, Neti South Wales 2000, KSIRO Division of Soils* 306 Carmody Road, and #Department qf Geology, University of Queensland, Chancellor’s Place, St Lucia, Queensland 4067, #Isotope Division, Australian Atomic Energy Research Establishment, Private Mail Bag, Sutherland, New South Wale.7 2232, Australia
Received April 11, 1984 Thirty-nine species of scleractinian corals have been recovered from under a high dune on the western (mainland) side of North Stradbroke Island, eastern Australia. The corals are associated with thin intertidal sediments and their good condition implies burial in situ and preservation in a saturated zone. Most IikeIy this occurred as the coast prograded and a large dune advanced into the littoral zone, burying intertidal sediments and coral. The species assemblage indicates a she]tered environment but one open to the ocean without wide fluctuations in salinity. Three species yielded a mean z30Th/Z34Uage of 105,000 yr B.P. which is significantly younger than the nearest Pleistocene corals at Evans Head, New South Wales. The corals provide evidence of a sea stand near present sea level during isotope Stage 5c, which is considerably higher than previously suggested for this period. Their good condition implies that the overlying parabolic dune is of comparable age and formed during that high stand of sea level. Also, the isotope age provides a maximum period for the development of giant podzols in the podzoi chronosequences on coastal dunes in southern Queensland. 0 1985 University of Washington.
INTRODUCTION
North Stradbroke Island is situated on the subtropical coast of eastern Australia at about 2T south latitude. It is a large sand island that extends along the Queensland coast for some 37 km, reaches a maximum width of 12 km in its northern part, and forms the southeastern boundary of Moreton Bay (Fig. 1). In composition and development it is similar to several other sandmasses along the eastern coast (Bird, 1973; Thompson, 1983). Most of the exposed island consists of quartz sands deposited in a series of overlapping dune systems. These now commonly reach elevations of 80-100 m and rise to a maximum of 228 m at Mt. Hardgrave in the northcentral part of the island. Most of the dunes have a northwesterly trend, indicating dune building by onshore winds from mainly the southeast. Drillings, associated with hydrological investigations (Laycock, 1975), show that dune sands and other sediments
extend to depths of 90 m below sea level under parts of the island. In early 1982, dredging for heavy minerals in the northwestern part of the island produced an assemblage of scleractinian corals, marine shells, and some wood fragments (Brisbane (1: 100,000) grid reference 441658, Figs. 1 and 2). Coral beds had been intercepted by drilling between + 2 and - 6 m and samples were brought up by a floating suction dredge operating in an artificial pond with water level at about mean sea level. Samples of 39 species of corals, representing 2.5 genera, 62 species of mollusts (J, Stanisic 1983, personal communication), and wood fragments from 4 mangrove genera and one freshwater swamp tree were recovered from the dredge screen. Isotope ratios have been determined fat samples from three of the coral species by 230Th/234U dating and yielded a mean isotope age of 105,000 yr B.P. In this paper, the coral assemblage is compared with IO3 0033-S894/8.5 $3.00 Copyright 6 1985 by the Umversity of Wishington Ail rights of reproduction in any form reserved.
104
PICKETT 1
I.40
1
I50
0
ItJO0
Newcastle
Embaymer
0
soo km t
0
,
c?
Moreton
Island
North
Stradbroke Island
0
L.!LJ
20 kr
u
153’E ,
1
28O s
FIG. 1. Map of eastern Australia and Moreton Bay, Queensland showing location of North Stradbroke Island site.
modern corals nearby, its isotope age in relation to other Australian Pleistocene corals is examined, and the geological and pedological importance of the find is discussed. SITE STRATIGRAPHY Stratigraphic
Relationships
Most of the sedimentary column above the buried coral consists of unconsolidated
ET AL.
dune sands (unit A of Fig. 3) which now form a sinuous, north-south-trending ridge. Crest elevations vary from 70 to 1IO m, and a maximum thickness of approximately 107 m of dune sands occurs adjacent to the coral site. The dune sands are well sorted and are generally less than 500 km in diameter, with a modal size between 180 and 212 pm. They consist almost entirely of quartz but also contain small amounts of K-feldspar and up to 2% heavy minerals, mainly ilmenite, rutile, and zircon. Crossbedding showing eolian foreset and topset beds is evident in the mine pit. The dune has been severely modified by water erosion since eohan activity ceased. Even so, giant podzols, with both thick bleached AZ and pipey B horizons (Thompson, 1983), that formed in the upper 15-25 m of dune sands persist on the dune crest. Truncated profiles with yellowishbrown sands near the surface are evident on the western slopes where water erosion has been greatest, The soils grade with depth into unweathered yellowish-brown sands which continue unchanged to 3-6 m above the present water table where browner sands are recorded by the mine drill logs. These appear to be dune sands stained by groundwater during seasonal oscillations. The browner dune sands rest on brown and off-white sandy sediments of variable thickness which in places overlie the coral beds within a depth of 6 m. The contacts between the dune sands, the mixed brown and off-white sediments, and the coral beds were below the surface of the dredge pond and could not be observed. Diving in the dredge pond by one of us (R.A.K.) established that the corals are incorporated in gray and olive muds. Diving also led to recovery of wood and bark samples from submerged logs released from the contact zone by dredging. Four of these have been identified at the Queensland Herbarium as mangrove genera (Xyfocurpus vel. aff. grunaturn), Ceriops sp., Rhizophora sp., Avicenniu sp.) and another as swamp tea-tree
LAST
INTERGLACIAL
SEA LEVEL
105
FIG. 2. Airphoto of northwestern North Stradbroke Island, showing coral locality and mined area (Reproduced with permission of Department of Lands, Queensland.1
vel. aff. quinquerzervia) (R. M. Dowling, 1983 personal communication). The mining drill logs record coral at six sites along a single traverse (Fig. 4) and make no mention of coral under the adjacent dune sands to -30 m, except for one hole about 1000 m to the south (Fig. 2) in which coral was reported at approximately -3 m. At the sample locality (Fig. 4), coral beds were encountered in five adjacent drill (Melakuca
holes and recovered by dredging from a zone between + 2 and - 6 m in relation to present sea level. The upper surface of the coral beds rises to the east and this slope probably represents the environmental gradient; maximum thickness recorded by drilling is 6 m. Corals were not recorded in drill traverses 200 m to the north or south and their extent in these directions is not available from dredging, because the water
106
PICKETT
ET AL.
Pleistocene Ho@ene
dunes
sediments. plain
surface -Pleistocene clays, during low sea level @ = transgressive w
= depositional
muds
and
sands
progradatIon
-
with
rising
sea
progradation
FIG. 3. Schematic geologic cross section of eastern Moreton Bay and western North Stradbroke Island.
level in the dredge pond was raised by 5 m when difficulties were experienced with the heavy coral masses. Small pieces of three different materials associated with the corals were recovered by the dredge; these include weakly consolidated, bedded yellowish-brown sand, black peaty sand containing pieces of mangrove wood and seagrass (Zmtera sp.), and grayish and olive sandy muds attached to coral and shells. These sediments are interpreted as beach, intertidal, and subtidal faties, respectively. The mixed brownish and white sands recorded in the drill logs probably represent a mixing (during drilling) of these sediments with white sand similar to that recorded below the coral beds. Data from the drill holes (Fig. 4) indicate that the muddy horizon is underlain by white fineto medium-grained sands. Pieces from two lithologies brought up by the dredge appear to belong to this unit. One is an off-white, weakly consolidated sand with yellowishbrown color variation in the bedding and the other is a white, weakly consolidated sand with prominent dark bands of heavy minerals. Both are considered alluvial sediments derived from the degraded old dune to the east (unit B). These are the only samples that have been obtained below the coral although the drill logs record white sands for a further 20 m and show that they continue east toward the old, degraded
dune (unit B). Some of the deeper white sand could be continuous with this unit. Znterpretation
of Stratigraphy
The morphology of the dune and its foreset bedding planes indicate deposition along the advancing front of a large parabolic dune or group of parabolic dunes that coalesced as they advanced across the island and terminated along its western margin. Such dunes were probably initiated along the eastern coast by sand blown inland by onshore winds but incorporated additional sand from the underlying dunes through deflation as they advanced. It appears that the corals initially colonized marine shells lying on the weakly consolidated white sands in the subtidal zone. Mangroves were associated with muddy, sandy sediments of the adjacent intertidal zone to the east and there was a small sandy beach backed by large sand dunes from which freshwater springs entered the intertidal zone. The tea-tree (Melufeucu vel. aff. quinquenerviu) and the buttress mangrove (Xylocurpus vel. aff. grun&urn) both indicate the presence of fresh water. M. quinquenervia today occurs on North Stradbroke Island above the tidal zone on low sandy banks underlain by fresh water and around swamp margins. Xylocarpus granatum is no longer found in
LAST
INTERGLACIAL
SEA
LEVEL
I07
Moreton Bay, its most southerly known occurrence being some 200 km north along the western (inland) side of Frazer Island, where freshwater springs from the dunes enter the intertidal zone (R. M. Dowhng. 1983, personal communication). The thickness and structure of the dune sands overlying intertidal sediments with mangrove fragments, and the slope of the coral surface to the west imply burial by the large dune as it advanced westward into the littoral zone. Apparently the coral community was overwhelmed and buried by the muddy intertidal sediments prograding ahead of the advancing dune and all three units are therefore of similar age. A substantial time gap between the deposition of the intertidal sediments and dune sands is unlikely because no evidence has been found of subaerial weathering in either intertidal sediments or coral. Many of the corals show little evidence of chemical, physical, or biological degradation; their good condition, range in size, and number of species present imply burial in situ and subsequent protection from subaerial weathering or oxidation. The intertidal sediments that enclose the corals are thin and unlikely to protect them for any lengthy period. However, burial by 100 m of dune sand as the shore prograded would ensure protection and maintain saturation in the finer-textured coral beds during lower sea levels. The evidence of strong degradation of the dune by water erosion together with the great depth of soil development indicates that the dune is an old feature preceding the last glaciation (Thompson, 1983). Further, the preservation of a giant pdzol on the crest of such a high exposed feature indicates that it carried vegetation for a very long period preceding the last glaciation; otherwise the podzol would have been destroyed by wind erosion. This in turn implies a climate conducive to vegetation and one able to maintain a saturation zone in the coral beds during low sea levels.
108
PICKETT
THE CORAL ASSEMBLAGE
ET
AL.
TABLE PLEISTOCENE
Composition
Thirty-nine species of scleractinian coral, referable to 25 genera, have been recorded from the locality (Table 1). Some of the colonies reach substantial dimensions (e.g., fragments of a colony of Symphyilia cf. recta indicate that it had a height greater than 29 cm, which is a considerable size for this species and implies prolonged conditions suitable for growth). From visual accounts of coral recovery during the mining operation, Acropora and Porites seem to have been the dominant genera. In addition to massive colonies, such as those of Goniastrea, Symphyllia, and Porites, there are foliose forms (Pavona, Coscinaraea, Pachyseris, Montipora), multibranched Acropora and Lobophyllia, and solitary, freeliving fungiids. Environment
The corals are enclosed in muddy sediment. There is no evidence of cemented reef rock, and the associated sediments are unconsolidated. The small samples of weakly coherent sand brought up by the dredge may represent the initial colonizing surface. These are interpreted as alluvium derived from the old dune system to the east which would have sheltered the coral locality to some extent. Twenty of the species identified from the fossil deposit are not recorded among the 119 species in a recent census of corals at Flinders Reef which is in an oceanic situation at the entrance to Moreton Bay, some 50 km to the north (J. E. N. Veron, 1983, personal communication). These 20 are mostly associated with quiet conditions. The assemblage of Acropora species is also characteristic of quiet waters (C. Wallace, 1983, personal communication). The colonies of Cyphastrea have a “cauliflower” surface, typical of living specimens from Moreton Bay. Other indicators of quiet waters are the fungiids, Pachyseris rugosa (Veron and Pichon, 1979, p. 81),
I.
CORAL
SPECIES IDENTIFIED
CORAL
DEPOSIT
FROM THE
ON NORTH
ISLAND, COMPARED WITH THOSE (COLUMN A) AND IN MORETON
STRADBROKE
AT FLINDERS BAY (COLUMN A
Pocillopora damicornis Seriatopora hystrix Acropora formosa Acropora millepora Acropora aspera Acropora valida Acropora cf. longicyathus Acropora microphthalma Acropora cf. cuneata Acropora cf. robusta Astraeopora sp. Montipora sp. A Montipora sp. B Pavona varians Pavona decussata Pachyseris rugosa Coscinaraea columna Heliofungia actiniformis Fungia fungites Herpolitha limax Goniopora sp. Porites sp. Favia cf. pallida Favia sp. Favites halicora Favites bennettae Goniastrea australensis Goniastrea aspera Platygyra sp. Leptastrea purpurea Oulophyllia crispa Hydnophora exesa Cyphastrea serailia Galaxea fascicularis Lobophyllia corymbosa Lobophyllia hemprichii Symphyllia cf. recta Symphyllia cf. valenciennesi Turbinaria radicalis Millepora sp.
REEF B) B
+ + i+
0 0 4
+
+
0 0
0
0
0
0
0
i+
+ +
+ +
+
+
Note. + = species present; o = genus represented by (anjother species.
Goniastrea aspera (Veron et al., 1977, p. 84), and Leptastrea purpurea which, through encrusting habit, even size of corallites, and general lack of calical variation, is simiIar to quiet water forms described by Veron et al. (1977).
LAST
INTERGLACIAL
SEA
109
LEVEL
Many of the forms in the fossil assem- given the southerly latitude of the fossil loblage of corals are indicative of conditions cality, these tolerances were probably reduced . far less restrictive than those of Moreton The corals are regarded as in situ because Bay at present, and the overlap with the of (a) the large size of some species, (b) the modern assemblage in Moreton Bay is remarkably slight. Of the 25 species recorded good condition of fragile species and of delthere (Lovell, 1975). only 5 are certainly icate structures such as protruding Acropora calyces, and (c) the presence of mud common to both assemblages, although there may be as many as 8 because some with the corals which indicates that they forms (Goniopora, Favia, Platygyra) could are not supratidal storm deposits. Corals only be identified to genus. On the other associated with muddy sediments are alhand, comparison with the fauna1 list from ways found in sheltered situations (Veron Flinders Reef indicates 12 forms common, and Pichon, 1976, 1979, 1982; Veron et al.+ 1977), and the paleogeographical situation and a further 7 potentially common, to both assemblages. The environment of Flinders on the leeward side of proto-Stradbroke IsReef is unsheltered; the greater apparent land would have sheltered this community. similarity of the fossil assemblage with that Then, as in modern Moreton Bay, the of Flinders Reef rather than Moreton Bay corals inhabited a slope from shallower to gradient). is possibly due to warmer s&ace waters at deeper water (environmental the time and also to a partly sheltered geo- This is reflected in the maximum range of graphical situation, but one that was open +2 to -6 m from which the corals were to the ocean and sufficiently free from sa- recovered. However, the depth to the top linity fluctuations to allow an abundant and of the corals cannot be given with absolute varied coral assemblage to thrive. It seems precision because the sampling interval in that the conditions were similar to those the mining drill holes was 3 m. Neverthethat led to the development of a rich assem- less, this does allow an absolute minimum blage at Evans Head, New South Wales height of 0 m for the intersection of the Using the modern an(Pickett, 1981). The sheltered situation of upper coral s&ace. both these deposits also appears to be alog of habitat conditions in Moreton Bay partly responsible for their preservation. and assuming a tidal regime of 2 1 m, then paleo-sea level relative to modern sea level must have been between + I and + 3 m. Water Depth Several of the taxa in the fossil assemblage are unable to survive in an intertidal situation, although most forms are common subtidally. Using data from Veron and Pichon (1976, 1979, 1982) and Veron et al. (1977), it is possible to obtain an indication of the proportion of species tolerant to tidal exposure. Such data are available for 23 of the species listed in Table 1. Of these, 1 I are specifically mentioned as occurring in the intertidal zone (Pocilfopora damicornis, Pavona decussata, Fungia fungites, Favia cf. pallida, Favites halicora, Goniastrea aspera, Platygyra sp., Leptastrea purpurea, Cyphastrea serailia, Galaxea fascicularis, Syrnphyllia cf. recta), although,
AGE
OF THE
CORALS
Samples from three of the corals, Porites sp., Syrnphyllia cf. recta, and Goniastrea aspera, were selected for analysis. All proved to have a high degree of purity. Analysis by X-ray diffraction (Slansky, 1982) indicated that none contained detectable calcite. Under the microscope the skeletons appear pristine; the finest growth increments of delicate structures, such as dissepiments, are still observable. This is in accord with the undamaged nature of many of the coralla at the site, and the fact that the corals were probably not exposed to either marine or aerial influences from the
110
PICKETT
time of their burial until their recovery by the dredge. Zsotupe Analysis
Analytical details of the three coral samples are presented in Table 2. The method used has been described previously (Roman, 1980). Ages were calculated using the formula of Kaufman and Broecker (1965). The levels of 232Th recorded were negligible over the counting time. The spread of ages is small, encompassing some 7000 yr. By comparison, the spread of ages of seven specimens of coral from five localities within the Gundurimba Clay of the Richmond River Valley, New South Wales, covers 17,000 yr (Marshall and Thorn, 1976; Drury and Roman, 1983). Taken together, the ages for the North
TABLE
2. AGES DETERMINED
FOR CORAL
ET AL.
Stradbroke Island corals are significantly younger (average 105,000 yr) than those from Evans Head (average 118,600 yr), and both of these are younger than the age for the most southerly Pleistocene locality, Newcastle Embayment, New South Wales (average 142,500 yr). Correlation
with Deep-Sea-Core
Stages
Drury and Roman (1983) have correlated the deposits at the Evans Head locality with isotope substage 5e of Shackleton (1969), and with reef VIIb of Bloom et af. (1974), which is indicated by their similar isotope ages. The age determined for the North Stradbroke Island locality is similar to that of the next youngest peak in Figure 5 of Bloom et al. (1974) and may correlate with substage 5c.
SAMPLES
FROM NORTH
STRADBROKE
ISLAND
QMFl2385 Porites sp.
4.05
2.24 2 0.09 (1985 2 45)*
2.39 2 0.07 (2116 e 46)*
1.07 2 0.03
0.06 2 0.01
QMF 12400
4.70
1.92 2 0.09 (1303 k 36)*
2.15 2 0.13 (1455 * 39)*
1.12 2 0.04
ND
3.92
2.27 2 0.09 (1737 ? 42)*
2.47 ? 0.11 (1890 k 45)*
1.09 k 0.04
ND
Symphyllia cf. rectu
QMFl2401 Goniastrea aspera
Sample
z30Thp34U
QMFl2385 Porites sp.
1.46 2 0.05
0.61 k 0.03
QMFl2400
1.37 2 0.03
0.64 2 0.04
1.55 k 0.05
0.63 2 0.03
Symphyilia
As (yr ELFt)
DNA 5 6%
Expt
2.9
3.00 2 0.12
108,000 +11,000/ - 10,000
2.5
2.57 iz 0.12
~W~~~ +- 6,000/ g$()o
3.0
3.04 2 0.12
cf. recta QMFl2401 Goniastrea aspera
Note,
* = total counts used in ratio calculations.
ND indicates that 232Th is below detectable levels.
LAST INTERGLACIAL
FIG. 5. Maximum altitudes of sea level for the last interglaciation based on scleractinian coral occurrences in eastern Australia. A = North Stradbroke Island; B = Evans Head: C = Newcastle Embayment.
The ranges in isotope ages at each of the various localities are fairly limited, except for some samples from the Gundurimba Clay, and there is no overlap in the determined values; the range for the Evans Head locality (using dates on corals alone and excluding other localities within the Gundurimba Clay) is 112,000 to 127,000 yr B.P., for Newcastle Embayment 142,000 to 143,000 yr B.P., and for the present locality 101,000 to 108,000 yr B.P. As a control between different laboratories and analysts, Roman (1980) has also analyzed samples from the Evans Head locality, with a result similar to that reported by Marshall and Thorn ( 1976). For these reasons, and because the ages determined correlate well with other assessments of the high sea-level stands of isotope stages 5c and 5e, the possibility that the coral deposit at Evans Head and that on North Stradbroke Island belong to the same isotope stage is unlikely. SIGNIFICANCE TO GEOLOGY AND PEDOLOGY Sea Levels of the Last Inter-glaciation The eastern coast of Australia is an area of remarkable tectonic stability. No study thus far has disclosed any evidence for isostatic movements since the Tertiary (Oilier, 1982: Jones and Veevers, 1982; Searle, 1983). Most Quaternary researchers agree that only eustatic influences have affected eastern Australian coastal development during the Quaternary period.
SEA LEVEL
Ill
The two older Pleistocene coral localities, Evans Head and Newcastle Embayment, both indicate a sea level of + 4 to + 6 m (Marshall and Thorn, 1976; Pickett, 1981), which is in accord with the maximum height of sea level recorded for isotope stage 5e in other places (e.g., Bloom et a/. , 1974, Fig. 5; Chappell, 1983, Fig. 1). Regional movement affecting deposits of isotope stage 5c would, in all probability, have also affected the older 5e deposits at Evans Head, 180 km distant. This does not appear to be the case, so that the relative heights indicated by the two deposits remain the same. The heights for former sea levels indicated by all three coral localities are considered to have been unaffected by isostatic movement. Evidence from the Pleistocene coral assemblage on North Stradbroke Island indicates that the highest point reached by the corals is possibly +2 m and certainly not less than 0 m (present sea level): this probably corresponds to the former low tide level. Assuming that the tidal regime was not greatly different from that of the present, and because no effects due to isostatic movements have been established. mean sea level at 105,000 yr B.P. (stage 5c) was at least + 1 m and possibly as high as +3 m. The relative heights for sea levels during isotope stages 5c and 5e as calculated by Bloom et ul. (1974) differ by almost 20 m, or by at least 15 m according to Chappell (1983, Fig. 1). This is in contrast to the heights implied by the eastern Australian occurrences (Fig. 5, points A and B), which indicate a difference of only 2 m for the same peaks. Whereas the sea level indicated by the Evans Head locality (stage 5e) is in accord with that determined by Bloom et al. (1974) for both New Guinea and Barbados, the level of + 1 to +3 m at North Stradbroke Island is significantly greater than the height of - 16 m established for the younger peak (stage 5~) by Bloom et t~i. (1974) or Chappell (1983). There has been remarkable coincidence
112
PICKETT
between oxygen-isotope paleotemperature curves, derived by Emiliani (1961) and modified by Shackleton and Opdyke (1973), and Pleistocene sea levels deduced from reef terraces in both the Atlantic (Broecker et ul., 1968) and Pacilic oceans (Bloom et al., 1974; Chappell, 1974; Chappell and Veeh, 1978). For the last interglaciation, this is reflected in the relative heights of the peaks for isotope stages 5a, 5c, and 5e, during which the highest peaks for both sea level and temperature are associated with stage Se. The pattern of sea-level fluctuation summarized by Bloom et ul. (1974, Fig. 5) includes two peaks, both included in stage 5e by Drury and Roman (1983), the older one (140,000 yr BP.; ca. -5 m) being lower than the younger (124,000 yr B .P. ; ca. + 5 m). As can be seen from Figure 5, the eastern Australian localities indicate that these maxima were both higher than present sea level. Considering the coral assemblages alone, the depth at Evans Head is much better documented than that at Newcastle Embayment (point C on Fig. 5), because only two species are known from the latter locality, neither of which gives any critical indication of the water depth. Consequently, the sea level indicated at point C merely represents a minimum figure and the actual sea level may have been higher than for point B. Thus, as the subdivision of stage 5 (Shackleton, 1969) does not distinguish between the two peaks of stage 5e, the highest sea level remains associated with that subdivision. A recent compilation of New Guinea data (Chappell, 1983) has produced a sea-level curve which diverges from the paleotemperature envelope of Shackleton and Opdyke (1973) for the interval 150,000-30,000 yr B.P. and implies a sea level of approximately - 30 m at 140,000 yr B,P., in contrast to the levels indicated by the corals of the Newcastle Embayment. No evidence of sea levels associated with isotope stage 5e has yet been recognized on North Stradbroke Island; presumably it has either been obscured by dune building or obliterated by erosion.
ET AL.
Dune Building
and Sea Levels
Dune sands make up most of North Stradbroke Island above sea level. Several dune systems, deposited episodically during the Quaternary, have been recognized (Thompson and Ward, 197.5; Ward, 1978) and may be correlated with dune systems on similar large sand masses along the coast (Ward et ul., 1977; Thompson, 1981; 1983). Along the eastern coast of Australia, there is good evidence, supported by radiocarbon dates, that the three youngest parabolic dune systems are Holocene features deposited since the sea reached approximately its present level, some 6000 yr ago (Thorn, 1965; Bird, 1973; Thorn et al., 1978). Also, large parabolic dunes are still forming at several localities along the Queensland coast, e.g., Cooloola, Fraser Island, and Shoalwater Bay, during the present marine transgression. Environmental conditions during the deposition of similar Pleistocene dune systems are less certain, and Ward (1977) has associated the main periods of Pleistocene dune building on Fraser Island with the lower seas of glacial periods. However, the evidence, at the coral site on North Stradbroke Island, of rapid burial of the littoral environment by dune sands and the preservation of corals in a saturated zone point to dune building at the time of coral growth during that marine transgression. Other evidence, such as the prevalence of similarly orientated Holocene and Pleistocene parabolic dunes, absence of arid dune forms, and preservation of giant podzols, show that these dunes (including that overlying the coral) have been continuously vegetated since deposition. This finding implies that the climate here during the last glaciation did not deteriorate beyond that necessary to sustain vegetation. It seems that dune building along the Australian subtropical coast was not necessarily associated with low sea levels or very arid conditions. Development
of Giant Podzols
The soils on the dune overlying the corals vary locally from rudimentary podzols
LAST INTERGLACIAL
about 1 m thick on the actively eroding western slopes to giant forms on the crest where profiles with pipey 3 horizons up to 10 m thick and overall depths exceeding 25 m persist. Irregularities in the boundaries between the AZ and Bhir horizons of @Z&S on coastal dunes in Australia become increasingly evident as the age of soil development exceeds 4500 yr (Thompson and Bowman, in press). Pipey B horizons with columns of bleached AZ sand encased in precipitated organic and sesquioxide compounds and penetrating the Bhir for several meters are characteristic of soil development in the Pieistocene dune systems 4 and .5 in the podzol chronosequence on coastal dunes at Cooloola to the north (Thompson, 1981, 1983). Such phenomena indicate long periods of weathering: a mean isotope age of 105,000 yr BP. is therefore important as a measure of the maximum time needed for their development. ACKNOWLEDGMENTS We gratefully acknowledge the ready cooperation of many colleagues and associates. and particularly thank the QueensIand Museum for permission to date coral samples. Associated Minerals Consolidated Ltd. for access to the site and samples from the dredge screen. Consolidated Rutile Ltd. for drill logs, Dr. J. E. N. Veron of the Australian Institute of Marine Science for the unpublished census of corals at Fhnders Reef, Dr. C. Wallace, Department of Biology, James Cook University, for identification of Acroporu species, and Mr. D. J. Ross, CSIRO Division of Soils, for drafting figures. J. W. Pickett publishes with permission of the Secretary, New South Wales Department of Mineral Resources.
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nary tectonic movements and sea level changes. Geoiogicu/ Society of America Bu//etitz 85, 553570. Chappeh. J. M. A. (lY83t. A revised sea-level record for the last 300.000 years from Papua New Guinea. Seurch 14, YY- 101. Chappell, J. M. A., and Veeh. H. (lY78). Late Quaternary tectonic movements and sea level change\ at Timor and Atauro Islands. Geo/ogicu/ Society ol America Bulletin 89, 356-368. Drury, L. W.. and Roman, D. (lY83). Chronological correlation of interglacial sediments of the Richmond River Valley. New South Wales. In *‘Archaeometry. an Australian perspective.’ (W. Ambrose and P. Duerden, Eds.). pp. 2YO-2Y6. Australian National University. Canberra (imprint tY82J. Emiliani. C. (lY61). Cenozoic climatic changes as indicated by the stratigraphy and chronology of deep sea cores of the Globigerina facies. Armu/~s qf’ th AJew3York Acudemy qf Science 95, S21-536. Jones, J. G.. and Veevers. J. J. tlY82). A Cainozoic history of Austrahd’s southeast highlands. Geo/ogicai Society of Austruliu Journui 29, 1- 12. Kaufman, A.. and Broecker. W. S. (lY65t. Comparison of ?‘“Th and 14C ages for carbonate material from Lakes Lahontin and Bonneville. Jowmd 0.f Geophy.sicu/ Reseurch IO, 403Y-4054. Laycock. J. W. (lY75t. *‘North Stradbroke Island-Hydrogeological Report.” Department of Mines Re port No. 88. Geological Survey Queensland. Lovell, E. R. (iY75). ‘.The Reef Building Corals (Cotlenterata: Scleractiniat of Moreton Bay, Queen\land: Their Distribution and Ecology.” Unpublished M.Sc. thesis. University of Queensland. Marshall, J. F., and Thorn, B. G. (lY76~. The sea level in the last interglacial. Nuture (London) 263, IX-* 121. Olher, C. D. (lY82). The Great Escarpment of eastern Australia: Tectonic and geomorphic significance. Geologicui Society qf Austruliu Jourmd 29. 13-23. Pickett. J. W. (1981 t. A late Pleistocene coral fauna from Evans Head. N.S.W. A/cheringu 5, 71-83. Roman, D. (lY80). The electrodeposition of thorium in natural materials for alpha spectrometry. ,~~z~~~?~~/ ofRudioana/ytiru/ Chemist? 60, 317-322. Searle, D. W. t lY83). Late Quaternary regional controls on the development of the Great Barrier Reek Geophysical evidence. BMR Jowrud qf ,A//.\tru/iou Geology & Geophysic.s 8, 267. Shackleton. N. J. tlY6Yt. The last interglacial in the marine and terrestrial records. f’roceeding.x qf the Royal Society of London Serie.s B 174, 135- 154. Shackleton, N. J., and Opdyke, N. D. t lY73). Oxygen isotope and paleomagnetic stratigraphy of equatorial Pacific core V28-238: Oxygen isotope temperdturc~ and ice volumes on a l@’ yr and lob yr scale. r&lrfernczv Resetwch 3. 3Y. Slanksy. E. (lY82). .-Mineral Composition of Cot-al Skeletons from North Strddbroke Island. Queens-
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