pleistocene glaciation of the king valley, western...

QUATERNARY RESEARCH 36, 135-156 (1991)

Pleistocene Glaciation of the King Valley, Western Tasmania, Australia

SEAN J. FITZSIMONS’

Department of Geography and Oceanography, Australian Defence Force Academy, University of New South Wales, Campbell, ACT 2601, Australia

AND

ERIC A. COLHOUN

Department of Geography, University of Newcastle, Newcastle, NSW 2308, Australia

Received October 16. 1989

Analysis of the geomorphology, geology, and palynology of deposits in the King Valley permits the identification of four glaciations and two interglaciations and has led to a revision of the Pleistocene stratigraphy of the West Coast Range. The oldest late-Cenozoic deposits in the valley appear to predate glaciation, contain extinct pollen types, and are probably of late-Tertiary age. Overlying deposits of the Linda Glaciation show intense chemical weathering and have a reversed detrital remanent magnetization indicating deposition before 730,000 yr B.P. The highly weathered tills are conformably overlain by organic deposits of the Regency Interglaciation which show a transition from montane scrub rainforest to lowland temperate rainforest. Deposits formed during the later Moore Glaciation record advances of the King Glacier and glaciers from the West Coast Range. A pollen-bearing fluvial deposit records an interstade during this glaciation. On the basis of weathering rinds, amino acid dating, and palaeomagnetism the deposits are estimated to have formed between 730,000 and 390,000 yr B.P. The Moore Glaciation deposits are overlain by sediments of the Henty Glaciation which are believed to predate 130,000 yr B.P. These deposits record multiple advances of the King Glacier and the development of a large lake during an interstade. Deposits of the subsequent Pieman Interglaciation consist of organic line sands and silts that record a lowland scrub rainforest. Deposits of the last (Margaret) glaciation are restricted to small areas in the northern part of the valley. Although the most recent ice advance culminated after 19,000 yr B.P., evidence of older deposits of the Margaret Glaciation suggests that an early last-glaciation ice advance may have occurred. When combined with earlier studies, the recent work in the King Valley has provided one of the more complete records of Pleistocene glaciation in the Southern Hemisphere. Comparison of the deposits with the record of glaciation in southern South America and Westland, New Zealand, suggests some similarities exist between pre-last- glaciation events and indicates that glacial events in Southern Hemisphere middle latitude areas were synchronous during the last glaciation. 6 1991 University of Washington.

INTRODUCTION

During the Pleistocene, the King Valley was occupied by the principal southern outlet glacier from the central West Coast Range which is the type area of glaciation in Tasmania (Kiernan, 1983; Colhoun, 1985).

’ Present address: Department of Geography, Uni- versity of Otago, P.O. Box 56. Dunedin, New Zealand.

This valley provides one of the more de- tailed records of glaciation of an outlet valley system in the Southern Hemisphere. Development of the area for hydroelectric power provided the opportunity for a de- tailed study of the glacial and interglacial stratigraphy which promised to yield new and important information on the complex Quarternary history of the West Coast Range. The objectives of the study were to describe the character and extent of the

13s 0033-5894/91 $3.00 Copyright 0 1991 by the Unwersity of Washington. All tights of reproduction in any form reserved.

136 FITZSIMONS AND COLHOUN

Pleistocene deposits, to establish the num- Because all the mountains are below 1817 ber and periods of glaciation, to reevaluate m and the latitude is relatively low, Tasma- the existing Pleistocene stratigraphy, and to nia is considered to have been a marginal compare the glacial events with those environment for the development of gla- known in other Southern Hemisphere mid- tiers during the Pleistocene. During the last dle latitude areas. glaciation the extent of ice was limited to

the formation of small ice caps, and valley STUDY AREA and cirque glaciers. Ice volumes were con-

siderably greater during early and middle Tasmania lies between 40” and 44”s and Pleistocene glaciations.

is separated from mainland Australia by The King Valley is a structurally con- Bass Strait (Fig. 1). At present there are no trolled north-south trending valley in a geo- permanent snow or ice fields in Tasmania. logically complex area that consists of

FIG. 1. Map showing the topography and drainage system of the King Valley. The shaded area is land over 400 m and the dotted line is the southern limit of Jurassic dolerite clasts in Quatemary sediments. The dolerite is derived from a sill that caps the Eldon Range and Mt. Sedgwick.

TASMANIAN GLACIATIONS 137

faulted, folded, and mineralized Precam- brian to Jurassic rocks (Corbett et al., 1977). The area is dominated by the West Coast Range which is interrupted by the Comstock and Linda valleys and the King River Gorge (Fig. 1). The valley experi- ences a humid, maritime climate with a mean annual rainfall of 2Om3000 mm, and has a mean annual temperature of 10.9”C. The natural vegetation is temperate rainforest dominated by Nothofagus cunninghamii. However, because of the combined effects of poor drainage, extensive burning of the vegetation during exploration, and logging activities in the area, the vegetation has been strongly altered (Kirkpatrick, 1977). Today the floor of the valley is mainly covered with eparidaceous heathland, sedgeland, and wet scrub.

THE GLACIAL SYSTEM

Ice flowed into the King Valley from an ice cap on the Tyndall Plateau and from cirques that formed on the northern part of the West Coast Range and on the Eldon Range (Fig. 2). During the greatest ice advances, the King Glacier split into four distributary lobes that flowed south down the King Valley, east and south in the Nelson Valley, and west up both the Comstock and Linda valleys.

The distributary system regulated the extent of ice in the largest lobe that flowed south down the King Valley. The volume of ice in the main lobe was controlled by the altitudes of the Comstock, Linda, and Nel- son drainage divides. When ice flowed up the valleys and/or breached the divides, the volume of ice available to flow down the King Valley decreased. The self-regulating system caused many of the ice advances of the central lobe to attain similar extents even though the advances involved very different ice volumes (Fig. 2).

In addition to the main ice center, several small glaciers developed on the southern part of the West Coast Range (Fig. 2). Ice from Mt. Owen coalesced with ice in the

King Valley during the larger advances. Ice from two cirque glaciers on Mt. Jukes flowed onto the floor of the valley, though study of the deposits did not reveal whether they met the southward-flowing ice of the King Glacier.

STRATIGRAPHY

Mapping and Stratigraphic Classification

Although the study of glaciation in Tas- mania has a long history (Banks et al., 1987; Colhoun, 1985), systematic mapping and stratigraphic classification of deposits has been lacking. Most mapping has been done by students of the Department of Geogra- phy, University of Tasmania (Sansom, 1978; Kiernan, 1980; Augustinus, 1982). The studies lack a consistent approach to mapping and classification, but they pro- vide a background with which the present study can be compared.

The recent mapping of the King Valley permits a more rigorous approach to stratigraphic classification that supplants and extends the existing designations. Because the sequence is discontinuous, it was not possible to adhere strictly to the “Interna- tional Stratigraphic Guide” (Hedberg, 1976). However, where possible the mapping and classification methods follow the guide in the definition of lithostratigraphic, morphostratigraphic, and biostratigraphic units. Each unit has a type section and has been given a local geographic name (Table 1). The physical characteristics of the units are summarized in Table 2.

Dating Methods

Subdivision of the glacial sequence of the King Valley is based upon the recognition of distinct morphologic, lithologic, and bi- ologic units. Once the sequence was defined, it was tested and refined by the use of weathering rind thickness on Jurassic dolerite, 14C dating, experimental amino acid dating of wood, and determination of the detrital remanent magnetization of la-

FITZSIMONS AND COLHOUN

Thureau advance

Henly Glaciation

0 L + Ice flow direction e Cableway advance

FIG. 2. Quatemary ice limits in the King Valley during (a) the early Pleistocene Linda Glaciation, (b) the middle Pleistocene Moore Glaciation, (c) the middle Pleistocene Henty Glaciation, and (d) the late Pleistocene Margaret Glaciation. Solid lines are mapped ice limits and dashed lines are inferred ice limits.

custrine sediments. Although the use of deposits (Fitzsimons, 1988). Age estimates weathering rinds is of considerable value as derived from the weathering data are re- a dating technique, the method has some problems that are related to the antiquity

garded as minimum ages because they are

and complex postdepositional history of the based on an assumed linear weathering rate. Although field and laboratory studies


TABLE 1. FORMATIONS AND CLIMATIC STAGES OF THE KING VALLEY

Glaciationkterglaciation

Linda Glaciation Regency Interglaciation” Moore Glaciation”

Henty Glaciation

Pieman Interglaciation” Margaret Glaciation

Lithostratigraphic unit Interpretation

Thureaub Stadial Regency Interglacial Huxley Stadial Baxter Interstadial Pyramid Stadial Mooreb Stadial Cableway Stadial Nelson Interstadial Davidb Stadial Bull Rivulet Stadial Smelter Interglacial Chamouni Stadial Danteb Stadial

a New glaciation/interglaciation. b Type formations of glaciations.

of chemical weathering elsewhere suggest that the rate of weathering is a square-root function of time (Colman, 1981), in practice a square-root function tends to overesti- mate age because several factors, including erosion, burial, and changing water tables, slow down weathering over long periods of time (Fitzsimons, 1988). Linear weathering rates were used in order to avoid overesti- mates of age.

Preglacial Deposits

The oldest unconsolidated sediments known in the King Valley catchment are locally derived nonglacial sediments exposed 1 km northeast of Gormanston in the Linda Valley (Fig. 1). Although their age is not accurately known, the sediments underlie deposits of the Linda Glaciation and may be of late Tertiary age. The section shows a series of locally derived fluvial sands and gravels overlying a palaeosol with in situ tree stumps (Kiernan, 1980; Fitzsimons, 1988). Pollen from the palaeosol contains Tertiary floral relicts including Nothofagus brassii type pollen which is now extinct in Tasmania (Kieman, 1980). Although earlier studies have suggested that the pollen was derived from older deposits and the gravels were of glacial origin

(Kiernan, 1980; Colhoun, 1985), reinterpre- tation of the lithology, geometry, and pollen suggests that the entire sequence pre- dates glacial lake sediments of the Thureau Formation (Fitzsimons, 1988).

Several contradictory 14C dates of wood from the palaeosol indicate there are problems in the interpretation of the age of the deposit (Colhoun, 1985). Amino acid dating of wood from the palaeosol was attempted but the samples were too degraded to be useful for dating (B. J. Pillans, personal communication, 1987). Although the radiocarbon dating problem is not completely resolved, it appears that the age of the wood is beyond the range of radiocarbon dating.

An indication of age of the deposit can be gained by comparing the pollen from the palaeosol with pollen assemblages from Oligocene, Pliocene, and early Pleistocene deposits. The Oligocene deposits contain 47% Nothofagus brassii type pollen, the Pliocene deposits contain only trace values, none occurs in Quaternary interglacial pollen deposits (Hill and Macphail, 1983, 1985; Fitzsimons, et al., 199Oa), and the palaeosol contains 13% (Kiernan, 1980). If the re- duction in number of extinct rainforest taxa in Tasmania is largely a function of time, as it seems to be, the nonglacial sediments are at least of Pliocene age.

TABL

E 2.

PH

YSIC

ALCH

ARAC

TERI

STIC

SOFT

HEG

LACI

ALAN

DREL

ATED

FO

RMAT

IONS

Form

atio

n Lo

catio

n of

ty

pe s

ectio

n

Thur

eau

Reg

ency

Hux

ley

Baxt

er

Pyra

mid

Moo

re

East

ern

edge

of

Thur

eau

Hills

2 km

NW

of

the

King

-Gov

erno

r co

nflu

ence

R

ight

ba

nk

of

Baxt

er

Riv

ulet

Rig

ht

bank

of

Baxt

er

Riv

ulet

R

ight

ba

nk o

f Ba

xter

R

ivul

et

200m

Softh

e Ki

ng-G

over

nor

conf

luen

ce

Dis

tribu

tion

Surfa

ce

form

Rem

nant

s in

the

Ki

ng

Valle

y,

larg

e m

orai

nes

in

the

Lind

a Va

lley

Erod

ed

mor

aine

s or

bu

ried

Onl

y kn

own

at

one

loca

tion

Burie

d

Sout

h of

the

Gov

erno

r R

iver

Smal

l te

rrace

re

mna

nt

Onl

y kn

own

at

one

loca

tion

Sout

h of

the

G

over

nor

Riv

er

Sout

h of

the

G

over

nor

Riv

er

Burie

d

Smal

l te

rrace

re

mna

nts

and

ice-

cont

act

ridge

s

Burie

d

Lith

olog

y

Wea

ther

ing

rinds

on

Ju

rass

ic

dole

rite

clas

ts i

n til

ls

Age

(mea

n an

d ra

nge)

Pa

laeo

mag

netis

m

fyr

B.P.

)

Lacu

strin

e se

dim

ents

. ic

e-ra

fted

tills

, til

ls,

and

outw

ash

grav

els.

C

ompo

sitio

n in

dica

tes

deriv

atio

n fro

m

the

Eldo

n Ra

nge

Drif

ted

wood

, le

aves

, an

d pe

at

x =

44.1

mm

20

-75

mm

No

dole

rite

2 2 E N

ot

mea

sure

d >7

3o,o

oo

E VI

Rev

erse

d >7

30,0

00

ca.

910,

000

Out

wash

gr

avel

. C

ompo

sitio

n in

dica

tes

deriv

atio

n fro

m

the

Wes

t C

oast

Ra

nge

Org

anic-

rich

sand

.

Out

wash

gr

avel

an

d bo

ulde

ry

till.

Com

posit

ion

indi

cate

s de

rivat

ion

from

th

e W

est

Coa

st

Rang

e C

oars

e,

ice-p

roxim

al,

outw

ash

grav

el.

Com

posit

ion

indi

cate

s de

rivat

ion

from

th

e El

don

Rang

e

No

dole

rite

Not

m

easu

red

73o,

ooo-

39

0,oo

o

8 E

No

dole

rite

Nor

mal

73

o,oo

o-

390,

ooo

No

dole

rite

Not

m

easu

red

73o,

ooO

- 39

0,oo

o

x =

15.8

mm

10

-25

mm

N

ot

mea

sure

d 73

o,oo

o-

390,

ooo

Cab

lew

ay

Nel

son

Dav

id

Bull

Riv

ulet

Smel

ter

Cham

ouni

Dan

te

400

m N

of

the

King

-Gov

erno

r co

nflu

ence

Sout

h of

the

Thur

eau

Hills

3 km

N o

f th

e So

uth

of th

e Ki

ng-N

elso

n Ly

e11

conf

luen

ce

Hig

hway

3

km N

of

the

Sout

h of

the

King

-Nel

son

Lye1

1 co

nflu

ence

H

ighw

ay

5 km

NE

of M

t. O

wen

3km

EofM

t. Ju

kes

2 km

S o

f Da

nte-

King

co

nflu

ence

Smal

l ar

ea

2 km

so

uth

of th

e Ly

e11

Hig

hway

O

nly

know

n at

on

e lo

catio

n La

rge

terra

ces

north

of

Lye

11

Hig

hway

1 km

NE

of

Dant

e-Ki

ng

conf

luen

ce

Lim

itedt

o th

e C

omst

ock

Valle

y

Erod

ed

outw

ash

surfa

ce a

nd

low

hum

moc

ks

Burie

d

Larg

e en

d m

orai

ne

and

outw

ash

surfa

ce

Smal

l m

orai

ne

and

outw

ash

surfa

ce

Burie

d

Out

wash

te

rrace

s

Smal

l ou

twas

h fa

n

Out

wash

gr

avel

, til

l, an

d ic

e-co

ntac

t st

ratif

ied

sedi

men

ts.

Der

ived

fro

m t

he

Eldo

n Ra

nge

Rhy

thm

ical

ly

lam

inat

ed

silt

and

mud

O

utwa

sh

grav

el,

lodg

men

t til

l, an

d bo

ulde

ry

till.

Der

ived

fro

m t

he

Eldo

n Ra

nge

Boul

dery

til

l. D

eriv

ed

from

the

Eld

on

Rang

e

Drif

ted

leav

es a

nd

peat

Lam

inat

ed

silts

, ou

twas

h gr

avel

, an

d lo

dgm

ent

till.

Der

ived

fro

m

the

Tynd

all

Plat

eau

Out

wash

gr

avel

, sa

nd,

and

till.

Der

ived

fro

m

the

Tynd

all

Plat

eau

x =

6.9

mm

2.

9-13

m

m

Not

m

easu

red

>13o

,ooo

No

dole

rite

x =

11.2

mm

5-

16

mm

Not

m

easu

red

No

dole

rite

x =

1.5

mm

0.

s2.8

m

m

x =

1.5

mm

0.

9-2.

7 m

m

Nor

mal

Nor

mal

>13o

,ooo

>13o

,ooo

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m

easu

red

>13o

,ooo

2

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m

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>13o

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%

E N

ot

mea

sure

d >4

8,00

0 9 b 2

Not

m

easu

red

>18,

800

$ CA


Linda Glaciation

Deposits of the Linda Glaciation are the most extensive glacial deposits in western Tasmania and have been mapped as the Thureau Formation in the study area. Sed- iments of the Thureau Formation are exposed in five principal areas: in the lower King Valley near the Governor River confluence, adjacent to the Thureau Hills, and in the Linda, Nelson, and Queen valleys. The most extensive sediments accumulated in ice-contact lakes in the Linda and Nelson valleys which were beyond the limits of later advances (Fig. 2). Most other deposits have been eroded by subsequent ice advances and many are buried by younger deposits.

The type section of the Thureau Forma- tion is exposed on the eastern slopes of the Thureau Hills (Fig. 1) and has been described by Fitzsimons et al. (1990a). It consists of highly weathered till and sediment flows overlain by laminated silt and slope deposits (Fig. 3). Postdepositional deformation structures suggest that the sediments were initially deposited in a supraglacial po-

sition on melting ice. The till and sediment flows are intensely chemically weathered, have thick iron pans, and weathering rinds on Jurassic dolerite clasts are 20-75 mm thick.

The overlying laminated silt has a reversed detrital remanent magnetization, as do other Thureau Formation sediments in the Linda Valley (M. Pollington, personal communication, 1986). Reversely magnetized silts at the type section appear to pass downward into normally magnetized sandy silts, although the field relationships between the silt and sandy silt are not clear (Fitzsimons, 1988).

During the Thureau advance ice ex- tended 19 km down the King Valley to the entrance of the King River Gorge (Fig. 2a). At this time the glacier was at least 400 m thick near the Thureau Hills. Although no depositional morphology is preserved where the glacier terminated, the absence of Jurassic dolerite and Permian erratics south of the limit shown in Figure 1 dem- onstrates that the King Glacier did not flow south of the Andrew Divide. Although some Thureau deposits are marginally

Slope deposits

Laminated silt

Sediment flow

Sand

Sediment flows

Meltout till

FIG. 3. Type section of the Thureau Formation showing intense chemical weathering of Jurassic dolerite boulders.


above the altitude of the divide at the head Regency Interglaciation of the Linda Valley, the unmodified fluvial topography and lack of deposits on the Regency interglacial sediments consist of other side of the divide suggest that the ice an organic deposit that contains 0.8 m of was restricted to the Linda Valley. drifted wood and leaves, and organic silty

The age of the Thureau Formation is dif- sand that overlies highly weathered out- ficult to estimate. The reversed magnetiza- wash gravel and till of the Thureau Forma- tion of the formation implies that the sedi- tion (Fitzsimons et al., 1990a; Fig. 5). ments predate the Brunhes/Matuyama re- Pollen analysis and examination of plant versa1 (730,000 yr B.P.). The change from macrofossils of the Regency Formation reversed to normal magnetization could shows an interglacial flora rich in Lagaro- represent the Jaramillo or Olduvai events strobos franklinii, Nothofagus cunning- which occurred between 0.89 and 0.95, and hamii, and Phyllocladus aspleniifolius. The 1.62 and I.83 myr B.P., respectively. In the high percentage of tree and shrub pollen absence of more precise dating, the and the very small amount of grass and herb Thureau Formation has been tentatively pollen throughout the deposit indicate that placed at the Jaramillo Event in the the river which deposited the sediment was Matuyama Chron (Fig. 4).

Olduvai event

transporting detritus from a forested source

0 - Dante advance Chamouni advance 1 MARGARET GLACIATION

WBa Smelter Formation 1 PIEMAN INTERGLACIATION

$“,u,;i,“i;;le,‘n;vance ] HENTY GLACIATION

I 1 ‘Cableway advance

0.4 -

0.8 -

1.2 -

1.6 -

2.0 - 1

Pyramid/Moore advance MOORE GwClATlON

‘Huxley advance 1

Regency Formation 1 REGENCY lNTERGLAC!ATlON

Thureau advance 1 LINDA GLACIATION

?

Pleistocene I

Pliocene

FIG. 4. Inferred chronology of glacial events in the King Valley.

144

80 cm outwash gravel

L I I I 1 I

0 20 40 60 80 100

%

FIG. 5. Type section of the Regency Formation and summary pollen diagram from Fitzsimons et al.

i- !I \I

David Formation outwash gravel

FITZSIMONS AND COLHOUN

Regency Formation organic deposits

Thureau Formation

(1990a).

at all times (Fig. 5). The presence of aquatic and subalpine taxa in the lower part of pollen zone RY2 suggest the deposit formed on a low-lying plain with standing water (Fig. 5; Fitzsimons et al., 1990a). The abundance of the treeferns Cyathea and Dicksonia in zone RYl suggests that the climate was at least as warm as the Holocene climatic optimum, when the relative abundance of treeferns in the King Valley was considerably lower.

Two of the most interesting taxa recorded are the extinct species (for Tasma- nia) Quintinia psilatispora and Gothanipol- lis perplexus. Today Q. psilatispora is a subtropical wet-forest taxon and G. perplexus is a wet-forest parasite. Quintinia has not previously been recorded from Tas- mania in deposits of Pleistocene age, although since the Regency deposit was ana- lyzed it has been recorded in late Pleisto- cene deposits (Colhoun and van de Geer, 1988). Together the records suggest that Quintinia may have survived in Tasmania until after glaciation had commenced.

Based on the pollen data and the inferred vegetation assemblages, the climate was wet at all times and a cool-temperate rainforest developed.

Incorporation of highly weathered clasts in the lower part of the organic deposit and the geometry of the sections suggest that the Regency Formation may be conformable on the Thureau Formation. This infer- ence is supported by the pollen analysis which suggests that initial deposition occurred on a recently deglaciated landscape. If the deposits are conformable on the Thureau Formation sediments, they may predate 730,000 yr B.P. However, an amino acid analysis of wood from the deposits suggests that deposition of at least part of the sediment occurred during oxygen isotope stage 8 (B. J. Pillans, personal communication, 1987). The apparent conflict between the amino acid results, which suggest a young age, and the field evidence, which suggests an age close to that of the Thureau Formation, has not been resolved. At present the evidence is insufficient to

TASMANIAN

justify changing the preferred stratigraphic succession. The Regency Formation is therefore regarded here as an early Pleisto- cene interglacial deposit that postdates the Linda Glaciation (Fig. 4).

Moore Glaciation

Deposits of the Moore Glaciation are most clearly exposed at two sites where outwash gravels from the Mt. Jukes cirque glaciers rest on the Thureau Formation deposits and are overlain by outwash gravel

GLACIATIONS 145

coarse gravel that forms remnants of a high- level outwash surface. The sediments are not very extensive and are difficult to dis- tinguish from other glacigenic sediments derived from Mt. Jukes except where they are separated by silty sand of the Baxter Formation. Because the sediments consist of locally derived siliceous cobbles and do not contain Jurassic dolerite, they are only slightly weathered.

The Baxter Formation consists of 1.2 m of organic silty sand that overlies the Hux- ley Formation (Fig. 6). Pollen analysis of

of the Cableway Formation which dates to the silty sand shows an herbaceous assem- the Henty Glaciation (Fig. 6). blage with an alpine component that indi-

The oldest Moore outwash gravels, the cates a cool, nonforested, interstadial cli- Huxley Formation, have a distinctive li- mate (Fitzsimons et al., 1990b; Fig. 6). thology and were deposited by the northern The pollen evidence indicates that during cirque glacier that developed on Mt. Jukes zone BRI the vegetation was either an open (Fig. 2b). The formation consists of >4 m of Casuarina woodland with an abundance of

BR 1

Cableway Formation outwash gravel

Moore Formation lag gravel

Pyramid Formation outwash gravel

Baxter Formation organic sands

Huxley Formation outwash gravel

Thureau Formation till

Ordovician limestone

1

020 40 60 80 100

FIG. 6. A section at Baxter Rivulet showing the deposits of the Linda, Moore and Henty glaciations and summary pollen diagram from Fitzsimons et a/. (199Ob). The Cableway Formation was deposited during the Henty Glaciation; the Moore, Pyramid, Baxter and Huxley formations were deposited during the Moore Glaciation; and the Thureau Formation was deposited during the Linda Glaciation.


Microstrobos and Epacridaceae shrubs or a wet shrub-heathland in which Casuarina was abundant. It was neither a forested nor a predominantly herbaceous vegetation. The vegetation became more open during zone BR2 as the average proportion of woody taxa was reduced from 86.4 to 60% and herbaceous taxa, particularly Grami- neae and Compositae, increased from 13.6 to 40%. The change suggests either that the understory of the woodland became grassy or that a mosaic of scrubland-herbland- heathland vegetation was developed.

The two major temperate rainforest taxa Nothofagus cunninghamii and Phyllocla- dus aspleniifolius never exceed 8% collec- tively, and generally do not exceed 4% (Fitzsimons et al., 1990b). If temperate rainforest was present, these values would almost certainly exceed 25%. The preferred interpretation is that the vegetation was a wet Casuarina heath which became either a herbland-heath mosaic(?) or a mix of herb and heath species.

The organic sediments of the Baxter For- mation have a normal detrital remanent magnetization (M. Pollington, personal communication, 1987). An amino acid analysis of wood from the Baxter Formation suggests a minimum age equivalent to oxygen isotope stage 10 (B. J. Pillans, personal communication, 1987).

Outwash gravel that overlies the Baxter Formation is a member of the Pyramid For- mation which was deposited by an advance of the Mt. Jukes Glacier. The type section of the Pyramid Formation is at Baxter Riv- ulet where it is represented by 4 m of coarse, iron-stained gravel composed en- tirely of siliceous rocks derived from the West Coast Range (Fig. 6).

Tills of the Huxley and Pyramid formations are rarely exposed and difficult to identify because glacial comminution of the highly resistant source rocks of the West Coast Range produces little silt and clay. However, the occurrence of stratified ice- contact sediments that form low, isolated hills suggests that ice from Mt. Jukes

flowed about 2 km across the floor of the King Valley toward the Governor River.

Outwash of the Pyramid Formation also extends southward to the Andrew Divide (Fig. 1) where up to 5 m of gravel rests on weathered Ordovician limestone. The absence of glacial landforms, till, and large boulders in the area suggests that ice from the Mt. Jukes Glacier did not cross the divide.

The Moore Formation overlies the Pyra- mid Formation and is distinguished from the Pyramid gravels by the presence of Ju- rassic dolerite and Permian erratic clasts (Table 2). Most deposits of the Moore For- mation are buried by younger outwash gravels. The formation is only known from four exposures in the area between the Governor River and the southern limit of Jurassic dolerite erratics (Fig. 1).

At the type section, 500 m east of Baxter Rivulet, the Moore Formation consists of 4.5 m of poorly bedded outwash gravel that is iron-stained, has multiple iron pans, contains boulders up to 0.7 m in diameter, and is overlain by outwash gravel of the Cable- way Formation. Moore gravel is easily dis- tinguishable from the Cableway gravel on the basis of the degree of weathering of Ju- rassic dolerite clasts. Samples of the Moore gravels have weathering rinds with mean values of 14.3 2 2.9 and 17.3 + 2.5 mm compared to means of 5.3 ? 1.4 and 5.1 ? 1.5 mm for samples from the Cableway Formation.

At the Baxter Rivulet section the Moore Formation is reduced to 1.6 m of coarse gravel with clasts up to 0.7 m in diameter (Fig. 6). Although the extent of the Moore advance is not accurately known, the presence of very large clasts in the deposits suggest that the glacier terminated close to the Baxter Rivulet section (Fig. 2b).

The Baxter Rivulet section also shows that outwash deposits from the King and Mt. Jukes glacier systems overlapped, though it is not known whether the glaciers were ever in contact. The Pyramid and Moore formations are considered to have


been deposited during the same stade by ice advancing from different source areas. Be- cause the Mt. Jukes Glacier was considerably smaller and closer to the site than the King Glacier, the sediment flux from Mt. Jukes arrived before, and was buried by, the later-arriving sediments from the King Glacier.

The age of the Moore Formation can be estimated by comparing the thickness of weathering rinds with those of the Cable- way Formation where the two formations are in contact. At these sites where the weathering rinds are directly comparable, the Cableway Formation has mean weathering rind thicknesses of 5.2 mm and the Moore Formation has mean a value of 15.8 mm. The differences suggest that the Moore Formation is at least three times older than the Cableway Formation. Given a minimum age for the Cableway Forma- tion of 130,000 yr, a minimum estimated age for the Moore Formation is 390,000 yr. This estimated age is a minimum because linear weathering rates are assumed and because burial of sediments can significantly decrease weathering rates (Colman, 1981).

The distinct lithological composition and field relationships between the Moore For- mation and the underlying Pyramid Forma- tion suggest that they were deposited during the same stade but from different ice sources (viz, the King Glacier and the Mt. Jukes Glacier). While there are no dates for the Pyramid Formation, it is regarded as being marginally older than the Moore For- mation.

The Baxter interstadial sediments have a normal detrital remanent magnetization which indicates that they belong in the Brunhes Chron, and an amino acid age suggests deposition during oxygen isotope stage 10 (B. J. Pillans, personal communication, 1987). The amino acid age and the detrital remanent magnetization of the deposit are in agreement with age estimates for the Moore Formation derived from the weathering-rind data. Taken together the dating suggests the Moore Glaciation is

middle Pleistocene and dates to between 730,000 and 390,000 yr B.P. Although no age estimates for the Huxley Formation are possible, it is thought to be only slightly older than the Baxter Formation.

Henty Glaciation

Deposits of the Henty Glaciation are the most extensive glacial deposits in the King Valley. They form large outwash surfaces and moraine belts south of the Lye11 High- way (Fig. 1). The oldest deposits are those of the newly defined Cableway Formation. The type section of the Cableway Forma- tion is a 23-m-high roadside exposure near the lower King River bridge and consists of 18 m of poorly sorted outwash gravel and till overlain by 5 m of locally derived slope deposits. The deposits are moderately weathered. Mean weathering-rind thicknesses on Jurassic dolerite clasts range from 4.7 to 9.8 mm in outwash gravel and from 7.6 to 14.8 mm in till. Till exposed near the type section, together with low ridges of ice-contact stratified sediments, indicate that the extent of ice was similar to that attained during the preceding Linda and Moore glaciations (Fig. 2).

The Cableway Formation is succeeded stratigraphically by the newly defined Nel- son Formation which consists of 44 m of laminated silts that are known from a few riverbank outcrops and drill holes (Fig. 7). The type section is from a drill core taken 2 km northeast of the northern edge of the Thureau Hills. (Fig. 7). The position of the silts suggest that a dam formed in the lower part of the valley after the Cableway advance. The dam probably formed behind a moraine about 2 km north of the King- Governor confluence where the valley has steep sides and is only 350 m wide.

The Nelson Formation consists of pale- green laminated silts with multiple sublam- inae < 1 mm thick and occasional dark gray mud laminae up to 40 mm thick (Fig. 7). They have a normal detrital remanent magnetization (M. Pollington, personal communication, 1987). The sediments are remark-


Till

Outwash gravel

Till

Lodgment till

Poorly sorted gravel and till

1

60

80

Nelson Formation

(laminated silts)

Cableway Formation (outwash gravel)

Siluro-Devonian (siltstone)

-David Formation

FIG. 7. Lithological log of sections and drill holes through the David Formation end moraine showing the Cableway, Nelson, and David formations. All sediments were deposited during the Henty Glaciation.

ably uniform throughout the 44 m and have laminated sediments suggests that they ac- no other primary or secondary structures cumulated in an ice-distal lake fed by melt- except within 2 m of the contact with the water from a remote glacier. The length of overlying till where the silts shows intense the episode of lake deposition can be esti- deformation. Absence of ice-rafted clasts mated assuming sedimentation rates similar and the uniformly fine-grained nature of the to postglacial, proglacial lakes in New


Zealand which seem to be an appropriate analogue. Pickrill and Irwin (1983) cal- culated the sedimentation rate in Lake Tekapo as 1.0 ? 0.1 cm/yr. Using this rate, the 44 m of silts known from the David-type section could have accumulated over a period of 4400 2 440 yr.

While the climatic conditions during deposition are uncertain, the sediments clearly represent a significant period of time during which ice was not present in this part of the valley. Although the formation cannot represent an interstade like the Baxter Interstade, the silts represent a significant temporal break in glacigenic deposition and they lie between the deposits of two ice advances. On these grounds alone, the deposit can be regarded as an interstade that is recognized on a lithostratigraphic basis.

The eroded surface of the Nelson silts are overlain by the David Formation (new). The type section of the David Formation is the same drill core that forms the type section of the Nelson Formation (Fig. 7). Ex- cavations and drill holes show that the formation consists of 29 m of interbedded till and outwash that form a steep aggradation surface and a large moraine that extends in an arc across the valley floor. The till and outwash gravel are moderately weathered, and average weathering-rind thicknesses of Jurassic dolerite clasts range from 2 to 8.8 mm in outwash gravel and 8.1 to 15.6 mm in till.

During the David advance, the glacier ex- tended to the middle part of the King Valley (Fig. 2d) where it formed a prominent end moraine. Although deformation and erosion of the underlying silts south of the moraine suggest that ice flowed beyond the end moraine, there is no depositional evidence to indicate where it terminated. In the lower King Valley two logs buried in David outwash gravel have 14C ages of 32,800 +400/-700 yr B.P. (SUA 2392) and 39,300 + 800/-700 yr B.P. (SUA 2393). These samples are probably beyond the range of radiocarbon dating and were con-

taminated by modern carbon from humic acids that are highly mobile in such humid environments (Colhoun, 1986).

Four kilometers north of the David For- mation end moraine a small moraine rem- nant that consists of poorly sorted glaci- genie gravel forms the newly defined Bull Rivulet Formation. The type section of the formation is a shallow pit in the crest of the moraine 3 km northeast of Mt. Owen. Al- though the duration of the period separating the David and Bull Rivulet formations cannot be assessed, their proximity and similar altitudes suggest the latter may represent a minor ice advance or a stable period during a general recession following the David ad- Vance.

The estimated age of the Bull Rivulet Formation is dependent on its close geographic relationship, and inferred temporal relationship, to the David Formation. It therefore is considered to be of Henty age. However, lack of exposure limits knowl- edge of the characteristics of the deposits, so the Bull Rivulet Formation may prove to be considerably younger.

Although there is no reliable radiometric date for the David Formation, the age of the sediments can be assessed by comparing the weathering rinds with those of the dated Dante Formation. The mean weathering- rind thickness of the David Formation is 11.2 mm, which is about seven times that of the Dante Formation (1.5 mm). Assuming a linear weathering rate and given the age of the Dante Formation (18,800 yr), the weathering-rind thicknesses suggest that the David Formation is at least 130,000 yr old (Fig. 4).

The Cableway Formation is assigned to the Henty Glaciation based on the inferred short interval between the Cableway and David formations. The period of time represented by the 44 m of NeIson lake sediments is estimated as representing about 4400 yr, assuming sedimentation rates similar to those of postglacial, proglacial lakes in New Zealand. Because the top of the lake sediments is eroded, this estimate is


probably conservative and indicates that the Cableway Formation is at least 4,000 yr older than the David Formation. This estimate suggests that the deposits are not younger than the last interglaciation, but are not extremely old. Taken together, the age estimates and the geomorphic evidence suggest that the Henty Glaciation is the penultimate glaciation and equivalent to oxygen isotope stage 6.

Pieman Interglaciation

The newly defined Smelter Formation in the King Valley is assigned to the Pieman Interglaciation. The Smelter Formation consists of 1.65 m of organic fine sand and organic silt with abundant plant remains (Fig. 8). The type section of the formation is exposed near Smelter Creek where it is un- derlain by coarse outwash gravel derived

from Mt. Jukes and overlain by late Pleis- tocene sand and Holocene peat (Fig. 8).

Pollen analysis of the organic silts and sands shows a flora rich in Casuarina, Phyllocladus aspleniifolius, Lagarostrobos franklinii, and Leptospermum. The pollen assemblage is very similar to the Holocene record for the lowland parts of western Tas- mania. The absence of taxa that are normally found at higher altitudes today suggests that the vegetation was a lowland scrub-rainforest (Fig.8; Colhoun and van de Geer, 1988). An amino acid analysis of wood from the base of the deposit suggests a minimum age equivalent to oxygen isotope stage 5 (B. J. Pillans, personal communication, 1987). Although the Smelter Formation cannot be directly related to the deposits of the King Glacier, they are regarded as being of the last interglacial age and are correlated with the Pieman Inter-

Fibrous peat -Holocene

Medium sands -last glaciation

Smelter Formation Organic fine sand over organic silt -last interglaciation

Coarse gravel derived from Mt.Jukes -penultimate glaciation or older

1.65 c I

0 20 40 60 80 %O

FIG. 8. Type section of the Smelter Formation and summary pollen diagram from Colhoun and van de Geer (1988).


glaciation (Colhoun, 1980) of the northern part of the West Coast Range.

Margaret Glaciation

Deposits of the Margaret Glaciation are limited to the upper part of the valley near Dante Rivulet (Fig. 1). Prior to this study the last glaciation was thought to be relatively simple, with one advance, represented by the Dante Formation (Table I), that occurred about 18,000 yr ago (Kiernan, 1983; Fig 2d). However, recognition of glacial sediments outside the limits of the Dante advance that have weathering characteristics similar to those of the Dante Formation suggests the possibility of an early advance of the last glaciation.

The deposits of the suspected early last- glaciation event are mapped as the Cha- mouni Formation which forms extensive terrace inset into older glacial deposits north of the Lye11 Highway. The type section of the formation is a road cut that ex- poses 3 m of fissile lodgment till on the edge of the terrace. The till is slightly weathered, with weathering rinds on Jurassic dolerite clasts averaging 1.5 mm, compared to 7.8 mm for the youngest till of the Henty Gla- ciation and 1.5 mm for tills younger than 19,000 yr. An exposure in the terrace 800 m south of the type section shows 4 m of gray

230

i

laminated silts that grade upward into sands and well-sorted pebble gravel (Fig. 9). The sequence records changing depositional conditions at the onset of the Chamouni advance. The distinctive gray laminated silts underlie all subsequently deposited sediments in the upper King Valley. Although the stratigraphic relations are unclear, the silts may represent the upper part of a la- custrine sequence that formed during the last interglaciation. The evidence is equiv- ocal and the relationships require further investigation. A pollen count from the sediments from which the wood was taken indicates that the environment was not forested and probably had an alpine to subalpine vegetation.

Drifted wood and leaves incorporated within the upper part of the silts, where they are unconformably overlain by postglacial gravels, were dated 48,700 +2900/ -2100 yr B.P. (SUA 2599; Fig. 9). The age indicates that the Chamouni advance pre- dates the limit of radiocarbon dating.

The Dante Formation, which was initially described by Kiernan (1980), consists of the distal part of an outwash fan from Dante Rivulet (Fig. 1). A section of the fan shows outwash gravels of unknown age overlain by organic silts, sands, and outwash gravels of the Dante Formation (Fig.

Chamouni Formation terrace

E 220

laminated silt

4 g a 210

wood & leaves

VE=30X 200 I I

0 1 2

Distance (km)

FIG. 9. Cross section showing the Chamouni Formation outwash gravel overlying laminated silts 1 km north of the Lye11 Highway.


E 2 t 4 E

170 yr B.P

18 800 + 5.50 yr B.P.

(ANU 2533)

Fibrous peat - Holocene

Sik.,sands B gravels

Silts with wood fragments

Sandy gravel

Laminated silt Organic soil profile

Coarse gravel

- Dante Formation

I Chamouni Formation 21 180 f 370 and 20 100 + 100 yr B (SUA 2154 and WA 2155)

FIG. 10. Type section of the Dante Formation exposed 1 km northeast of the confluence of Dante Rivulet and the King River. Based on Kieman (1980) and Gibson et al. (1987) with modifications from a new exposure of the section.

10). A palaeosol developed on the outwash that it postdates 18,800 yr B.P. The exis- gravel is overlain by sediments of the Dante tence of slightly weathered tills of the last advance. Wood, 10 cm from the base of the glaciation (Chamouni Formation) outside Dante outwash, was dated 18,800 f 550 yr the limits of glacigenic sediments of the B.P. (ANU 2533). Pollen from the palaeo- Dante Formation demonstrate that the lat- sol records an alpine herbfield-bog mosaic ter does not necessarily record the maxi- and contains a macrofossil of the alpine mum extent of ice during the last glaciation. cushion plant Donatia novae-zelandiae There are three possible interpretations of (Gibson et al., 1987). The Donatia was the stratigraphy: (1) the Chamouni Forma- dated 21,180 + 370 yr B.P. (SUA 2154) and tion is slightly older than the Dante Forma- drifted twigs stratigraphically below the tion; (2) the Chamouni Formation repre- Donatia were dated 20,100 + 470 yr B.P. sents an ice advance early in the last glaci- (SUA 2155). A further date from 2.5 m ation; and (3) Chamouni Formation was above the base of the Dante Formation out- deposited before the last glaciation began. wash gravel of 19,000 f 170 yr B.P. (SUA The second interpretation is favored. The 2856) suggests the gravel accumulated rap- other interpretations are regarded as less idly. Although Kiernan (1980) and Gibson likely because the minimum age of 48,700 et al. (1987) describe the lower outwash yr B.P. suggests that the formation is con- gravel as drift of the Comstock Glaciation siderably older than the Dante deposits. (= Henty Glaciation), it is probably part of Furthermore, deposits of the Henty Glaci- the Chamouni Formation and belongs to ation are considerably more weathered. In the Margaret Glaciation. the absence of reliable dating, the problem

The age of the Dante Formation has been can not yet be resolved. determined by 14C dating which suggests The transition from the Margaret Glacia-


tion to postglacial conditions appears to have been abrupt and is placed at about 13,000 yr B.P. A 14C date of 13,010 + 130 yr B.P. (SUA 2723) from a sediment-filled sinkhole, as well as pollen analysis, shows that temperate rainforest was developing by 13,000 yr B.P. This is confirmed by the presence of tree trunks in postglacial gravels in the upper King Valley that date to 12,250 2 90 yr B.P. (SUA 2415), showing that large trees were in the King Valley at this time.

COMPARISON WITH MIDDLE-LATITUDE GLACIAL EVENTS

IN THE SOUTHERN HEMISPHERE

The record of Pleistocene glaciation in the King Valley is one of the more complete records of glaciation in the Southern Hemi- sphere and is therefore of significance for hemispheric comparisons of glacial events. Western Tasmania, Chile, and Westland, New Zealand are at similar latitudes, and have similar west-coast maritime climates and a similar topography, although the altitude of the West Coast Range of Tasmania is considerably lower than the Andes and the Southern Alps. Because the environments are similar, close similarities in responses of glaciers and vegetation to climatic change are to be expected, at least during the Late Pleistocene.

Intrahemispheric correlations of glacial events that lie beyond the range of radiocarbon dating are hampered because of different preservation of deposits and because the three areas experienced very different uplift rates. Different preservation of deposits is dependent on postdepositional erosion which can result in absence of parts of the depositional record of glaciation. Up- lift rates of mountains can have an impact on the record of glaciation because glaciation in the Southern Hemisphere middle latitudes is dependent on the presence of mountain barriers that form the accumula- tion areas for glaciers. The formation and uplift of mountain barriers can therefore be a trigger to glaciation that is partly indepen-

dent of climatic change. In New Zealand, lack of evidence for glaciation between 2.1 and 0.35 myr has been attributed to the re- cency of uplift of the Southern Alps (Bo- wen, 1978) and to the role of uplift in caus- ing erosion of evidence of glaciation (Sug- gate, 1985b). Consequently, glacial events in one area may have no counterparts in the other (Mercer, 1983). For these reasons, Tasmania, which was tectonically stable during the Quatemary, may prove to be a useful reference point in trans-Pacific correlations.

The magnitude of glaciation in South America and Tasmania is broadly similar, with the greatest ice advances occurring in the early Pleistocene and a succession of ice advances of decreasing magnitude in the middle and late Pleistocene. Although the greatest Patagonian glaciation (Mercer, 1983) and the Linda Glaciation may be similar in age, lack of reliable dating of the Tas- manian sequence precludes correlation. It is intriguing to note that the greatest glacial events in Tasmania and South America that occurred in the early Pleistocene are appar- ently not recorded in New Zealand where there is no confirmed record of glaciation between 2.1 myr and 350,000 yr B.P. (Sug- gate, 1985b).

The Regency interglacial deposit is the oldest known interglacial unit known in Tasmania and records the presence of temperate rainforest that suggests a climate at least as warm, if not warmer, than the Ho- locene climatic optimum. No correlative deposits are known from South America or New Zealand.

The importance of the Moore glacial deposits to the glacial stratigraphy of Tasma- nia is that they record a multiphase glaciation that appears to have occurred between 730,000 and 390,000 yr B.P., and an interstadial pollen flora preserved between glacial deposits. Although the age of the Moore Glaciation is not well constrained, there are no confirmed comparable deposits in southern South America or New Zealand.


The minimum age estimate of 130,000 yr B.P. for the Henty Glaciation suggests it represents the penultimate glaciation that occurred during oxygen isotope stage 6. The two main phases of the Henty Glacia- tion, the Cableway and David advances, may represent the two cold spikes of the oxygen isotope record seen in the ocean sediment record and the Antarctic ice sheet (Shackleton and Opdyke, 1973; Jouzel et al., 1987). In Westland, the Waimea Glaci- ation (Suggate, 1965, 1985a, 1985b) also appears to be the penultimate glaciation, although lack of reliable dating of both events precludes correlation at this time. Although Colhoun (1985) suggested that the Santa Maria, Rio Lice, and Caracol drifts of Chile (Porter, 1981) are possible correlates of the Henty Glaciation, the older two of these Chilean drifts are likely to antedate isotope stage 6, based on their extreme degree of weathering (S. C. Porter, personal communication, 1990). However, lack of age estimates on the Chilean drifts means that firm correlations with glacial deposits in New Zealand or Tasmania are not possible at present.

The pollen assemblage at Smelter Creek represents the development of cool temperate rainforest during the Pieman Interglaci- ation. Amino acid analysis of wood from the sediments suggests deposition during isotope stage 5, and the stratigraphic position also suggests that the deposit represents the last interglacial stage. On this basis, the Pieman Interglaciation seems to be a correlate of the Oturi Interglaciation, now the Kaihinu Interglaciation (Suggate, 1985a) of north Westland.

The stratigraphic position and the 14C date of 48,700 + 2900/ - 2100 yr B.P. (SUA 2599) from the Chamouni Formation suggest it represents an ice advance early in the last glaciation and may have occurred during oxygen isotope stage 4. In Chile, Porter (1981) described the Llanquihue I drift as the outermost moraine arc of the last glaciation. Although the age of the Llanquihue I

deposits has yet to be resolved, i4C ages indicate that the deposits may have formed during an ice advance between 30,000 and 19,000 yr B.P. or at a time beyond the limits of conventional radiocarbon dating (Stuiver et al., 1975; Porter, 1981). In north West- land, Suggate (1985a) suggests that the Loopline Formation (Loopline 1 of Suggate (1965)) represents an early advance of the last glaciation. The Chamouni Formation of the King Valley may correlate with the Llanquihue I drift of Chile and Loopline Formation of north Westland. Although the ages of all three events are not yet well constrained, our interpretation of the Cha- mouni Formation lends support to other evidence of an early advance of the last glaciation and to suggestions that glaciers were largest during the last glaciation at a time close to or beyond the limits of radiocarbon dating (van der Hammen et al., 1981; Mercer, 1983).

Radiocarbon dates and the stratigraphic position of the Dante Formation suggest deposition during the peak of oxygen isotope stage 2. On the basis of 14C dates, correlations between events late in the last glaciation in Tasmania, New Zealand, and South America have been suggested by Colhoun (1985). The i4C dates of 18,800 ? 550 yr B.P. (ANU 2533) and 19,000 + 170 yr B.P. (SUA 2856) for the Dante Formation (Fig. 10) suggest correlation with the Larrikins Formation of Suggate (1985a), (Loopline 2 Formation of Suggate, 1965), and the Llan- quihue II drift of central Chile (Porter, 1981).

Mercer (1983) pointed to a further corre- spondence in glacial behavior in New Zealand and southern South America where ice advances occurred between 14,500 and 14,000 yr B.P. In southern South America, Mercer (1976) and Porter (1981) infer a readvance of ice between 15,000 and 13,000 yr B.P. from the sedi- mentary record of water-level fluctuations of Lago Llanguihue. In north Westland, a small readvance occurred between 14,500


and 14,000 yr B.P. (Suggate, 1965; Suggate and Moat-, 1970). In contrast, there is no geological or palynological evidence in the King Valley, or elsewhere in Tasmania, for a readvance after the last glacial maximum (ca. 18,000 yr B.P.). Radiocarbon dates of logs in postglacial gravel and bogs suggest rapid deglaciation after 13,000 yr B .P. and the absence of ice in the upper King Valley by 12,350 yr B.P. Pollen evidence from a bog at the contluence of the King and Gov- ernor rivers (Fig. 1) records an abrupt change from alpine heathland, Microstro- bos scrub, and heath at 13,000 yr B.P. to Eucalyptus subalpine woodland, succeeded by Phyllocladus-Nothofagus rainforest after 12,500 yr B.P. (E. A. Colhoun et al., unpublished data). Although the rainforest degenerated into scrub rainforest after 11,000 yr B.P., there is no evidence of cool- ing after the last glacial maximum. While evidence for a readvance after the last glacial maximum may yet be found in Tasmania, it appears that the climatic threshold for the development and mainte- nance of glacier ice was crossed by 12,000 yr B.P.

Comparison of Quaternary glacial events in Tasmania, New Zealand, and South America shows that responses to climatic change in the Southern Hemisphere middle latitudes were broadly synchronous during the last glaciation. The Dante, Larrikins, and Llanquihue II ice advances also appear to correlate with the greatest expansions of the Northern Hemisphere ice sheets during the last glacial maximum. However, evidence from the Southern Hemisphere of a more extensive ice advance during the early part of the last glaciation contrasts with evidence from the Northern Hemi- sphere where the ice sheets reached their maximum extent after 18,000 yr B.P. (Den- ton and Hughes, 1981). Comparison of pre- late Pleistocene events are hampered by lack of reliable dates for the deposits. Until the dating of deposits in all three middle- latitude Southern Hemisphere areas is im-

proved, correlations of glacial events will remain speculative.

ACKNOWLEDGMENTS

This work is largely based on a Ph.D. thesis com- pleted by S.J.F. in the Department of Geography, Uni- versity of Tasmania. The work was supported by an Australian Research Grants Committee grant, the Hy- droelectric Commission of Tasmania and the Univer- sity of Tasmania. The work has benefited from the assistance and support of several people including Dr. G. van de Geer (pollen analysis), Mr. M. J. Pollington (palaeomagnetism), Dr. B. J. Pillans (amino acid anal- yses), Dr. R. S. Hill (plant macrofossils) and Dr. F. J. Baynes. Eileen Hampson typed the text and Paul Bal- lard drew the diagrams. We are grateful to Dr. R. P. Suggate and Dr. S. C. Porter for their critical com- ments on the manuscript.

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