Biodiversity and terrestrial ecology of a mid-Cretaceous, high

Journal of the Geological Society, London, Vol. 158, 2001, pp. 709–724. Printed in Great Britain.

Biodiversity and terrestrial ecology of a mid-Cretaceous, high-latitude floodplain,Alexander Island, Antarctica

H. J. FALCON-LANG1,3, D. J. CANTRILL1 & G. J. NICHOLS2

1British Antarctic Survey, High Cross, Madingley Rd, Cambridge CB3 0ET, UK2Department of Geology, Royal Holloway, University of London, Egham, Surrey, TW20 0EX, UK

3Present address: Department of Earth Sciences, Dalhousie University, Halifax, Nova Scotia B3H 3J5, Canada(e-mail: [email protected])

Abstract: The biodiversity and terrestrial ecology of the Late Albian Triton Point Formation (Fossil Bluff

Group), Alexander Island, Antarctica is analysed to improve our understanding of polar biomes duringthe mid-Cretaceous thermal optimum. This formation was deposited on a high-latitude (75�S) floodplainand consists of two facies associations, a lower braided alluvial plain unit and an upper coastalmeander-belt unit. Analysis of fossil plants in well exposed palaeosols reveals the existence of spatiallycomplex plant communities. Braidplains supported patchy, low-density (91 trees/ha) stands of podocarpand taxodioid conifers on floodbasin substrates, and conifer–cycadophyte–fern–angiosperm thickets inriparian settings. Coastal meander-belts supported medium density (568 trees/ha) podocarp–araucarianconifer forests on mature floodbasin soils, and fern–angiosperm–ginkgo thickets in riparian settings.Growth-ring analysis indicates plants experienced stressful growing conditions on the braidplain charac-terized by high-frequency flood events, but more favourable growing conditions on the coastal plain.Additional vegetation disturbances were caused by arthropod–fungal attack, frost and wildfire. In termsof structure, composition, ecology and productivity these predominantly evergreen, broad-leafed coniferforests bear similarities to the extant temperate rainforests of New Zealand.

Keywords: Albian, Antarctica, polar regions, conifers, tree rings.

The recognition that polar regions were once covered by forestvegetation ranks as one of the most important palaeontologicaldiscoveries of the past 20 years (Axelrod 1984). The earliestpolar forests appeared in Late Permian times, and were com-posed of glossopterid trees which grew at palaeolatitudes of upto 80�S (Taylor et al. 1992). Forest vegetation remained estab-lished at both poles throughout the Mesozoic and Early Tertiarysurviving at palaeolatitudes as high as 85� (Spicer & Parrish1986), before finally contracting equatorward during the LateTertiary in response to global cooling (Spicer & Chapman 1990).An extraordinary feature of these forests was their ability totolerate extremes of light seasonality. Assuming that theobliquity of the Earth’s rotational axis has remained constantover geological time (Barron 1984), forests growing at 70� oflatitude would have experienced up to 70 days of unbrokendarkness each year, whilst those at 85� would have been deprivedof light for nearly 160 days per year (Read & Francis 1992).

The poleward limit of present-day forest vegetation is con-trolled by a combination of light seasonality, mean annualtemperature and annual temperature range (Woodward 1987).These factors constrain growing season length, rate of photo-synthesis and respiration, and seed germination potential, anddetermine whether the long-term positive carbon balancerequired for tree survival is achieved (Gower & Richards1990). In the Northern Hemisphere the tree-line ranges from59�N to 72�N whilst in the Southern Hemisphere forest veg-etation only extends to 55�S because no ice-free continentallandmasses exist in the high southern latitudes (Creber &Chaloner 1985; Read & Francis 1992). The massive polewardadvance in the tree-line envisaged for Late Palaeozoic–EarlyTertiary times has been attributed to the existence of asubstantially warmer polar environment with only small

permanent glaciers existing at altitude (Frakes & Francis 1988;Spicer & Parrish 1990).

Maximum global warmth occurred during the mid-Cretaceous (Albian–Turonian; 88–112 Ma) (Clarke & Jenkyns1999) and abundant polar forest localities have been describedfrom this time interval. Fossil forests dominated by taxodioidand pinoid conifers are known from northern Alaska (Spicer &Parrish 1986), Kamchatka and NE Russia (Herman & Spicer1996) at palaeolatitudes as high as 82�N. In the SouthernHemisphere, broad-leafed podocarp and araucarian coniferforests are known from SE Australia (Dettman et al. 1992),southern South America (Archangelsky 1963), New Zealand(Parrish et al. 1998) and Antarctica (Jefferson 1982) at palaeo-latitudes of up to 75�S. Forests were inhabited by a diverseterrestrial fauna which included small, large-eyed, large-brained dinosaurs which may have been adapted to the cool,dark winters or seasonally migrated with the sun-line (Parrishet al. 1987); birds, mammals, amphibians and arthropods werealso present (Rich et al. 1988).

None of these important Cretaceous fossil forest localitieshave yet received rigorous palaeoecological analysis. Little isknown of tree density and community structure, nor is theremuch data concerning ecophysiological response to climateand growing environment, and animal–plant interactions. Thisstudy presents new data concerning the biodiversity, palaeo-environments and palaeoecology of the classic fossil forests ofSE Alexander Island, Antarctic Peninsula (Jefferson 1982),which are the most southerly (palaeolatitude 75�S; Smithet al. 1994) and well-exposed Cretaceous polar forests so fardiscovered (Fig. 1a). These data are used to test and refinenumerical models of the Cretaceous polar environment (e.g.Otto-Bliesner & Upchurch 1997; Beerling 2000).

709

Study areaAlexander Island on the western side of the AntarcticPeninsula represents the uplifted fore-arc region of a mid-Palaeozoic to Tertiary calc-alkaline volcanic arc (McCarron &Larter 1998). The Fossil Bluff Group exposed in easternAlexander Island was deposited in a narrow (<60 km wide),elongate fore-arc basin, fault-bounded to the west by the ac-cretionary complex of the Le May Group and to the east by themagmatic arc (McCarron & Millar 1997). The fossil forestsdescribed in this paper occur in the Triton Point Formation ofthe Fossil Bluff Group, SE Alexander Island between 71�40�Sand 72�08�S (Moncrieff & Kelly 1993; Nichols & Cantrill 2001)(Fig. 1b) and have been assigned a Late Albian age on the basisof a bracketing molluscan fauna (105 Ma; Kelly & Moncrieff1992). This stratigraphic unit consists of a wedge-like package offluvial sedimentary rocks which thickens southward from 200 mat Triton Point to c. 950 m at Citadel Bastion, Titan Nunataksand Coal Nunatak, and has been divided into two facies associ-ations (Cantrill & Nichols 1996). The lower facies associationcrops out at all localities and is interpreted as the product of abraided alluvial plain environment. The overlying facies associ-ation is geographically restricted to the upper part of CoalNunatak, and has been interpreted as a coastal meander beltdeposit (Cantrill & Nichols 1996). In the course of recent strati-graphic revision by Nichols & Cantrill (2001) these two sedimen-tary packages have been formally assigned member status, thelower unit being named the Citadel Bastion Member (c. 820 mthick), and the upper unit named the Coal Nunatak Member(c. 130 m thick). Petrographic and palaeocurrent analysis indi-cates that most sediments were derived from the magmatic arcwith only minor input from the accretionary complex (Browne1996). Evidence from general circulation models, carbonaceouspalaeosols and fossil plants suggest that climate was temperatewith a high mean annual rainfall (Parrish et al. 1982, 1998;Spicer & Chapman 1990). KG. numbers mentioned in the fol-lowing text refer to British Antarctic Survey field stations in SEAlexander Island. Precise location details of these sites are givenin Figure 1b.

Floral biodiversityTaxonomic studies have shown than the vegetation of theTriton Point Formation was diverse compared with otherEarly Cretaceous floras; so far 42 form genera have beenrecorded containing approximately 69 species (Table 1).Conifers are the most abundant plant fossils, represented bysilicified woods and compressed foliage belonging to theAraucariaceae, Podocarpaceae and Taxodiaceae families(Falcon-Lang & Cantrill 2000; Cantrill & Falcon-Lang 2001).

��

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George VISound

George VISound

Coal NunatakCoal Nunatak

TitanNunataks

TitanNunataks

HyperionNunataksHyperionNunataks

PagodaRidgePagodaRidge

TritonPointTritonPoint

00 1010 2020

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71 50'S71 50'S

CitadelBastionCitadelBastion

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00 500500 10001000

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Fossil forestsFossil forests

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Alexander Island,AntarcticaAlexander Island,Antarctica

68 30'W68 30'W

KG. 2813KG. 2813KG. 4710KG. 4710KG. 4710KG. 4710

KG. 2821KG. 2821

KG. 4725KG. 4725

KG. 4737KG. 4737

KG. 4702 loose woodKG. 4702 loose wood

KG. 2814, 4740KG. 2814, 4740

KG. 2815KG. 2815

KG. 4741, 4745, 4746, 4747KG. 4741, 4745, 4746, 4747

KG. 2815KG. 2815

KG. 4688, 4697, 4699KG. 4688, 4697, 4699

KG. 1702KG. 1702

KG. 1704KG. 1704

KG. 2816, 4719KG. 2816, 4719KG. 2817KG. 2817

KG. 4657KG. 4657

KG. 4660KG. 4660

KG. 4717loose woodKG. 4717

loose wood

Fig. 1. (a) South Pole centred global palaeogeographic map (LateAlbian, 100 Ma). Light grey: open ocean, medium grey: continentalshelf, and dark grey: land (after Smith et al. 1994). Dotted linemarks polar circle at 66.6�S. Crossed circles mark mid-Cretaceouslocalities where podocarp–araucarian conifer woods and foliage aredominant. Data from Antarctic Peninsula (Francis 1986), SEAustralia (Frakes & Francis 1988), Keguelen Plateau (Francis &Coffin 1992), New Zealand (Parrish et al. 1998), South Africa(Bamford & Corbett 1994) and South America (Torres &Biro-Bagoczky 1986). Squares mark mid-Cretaceous localities withpodocarp–araucarian pollen close to the polar circle (Truswell 1990).(b) Inset: position of SE Alexander Island fossil forests on AntarcticPeninsula. Outcrop map of SE Alexander Island showing main fossilforest localities in the Triton Point Formation.

710 H. J. FALCON-LANG ET AL.

All the conifers were large trees except for one podocarpspecies which was probably a shrub (Cantrill & Falcon-Lang2001). However, although the conifers are abundant, theymake up only a small percentage of the total species diversityin the Triton Point Formation (c. 24%). The most diversecomponent of the flora are the ferns; the systematic taxonomyof this group is currently being revised by N. Nagalingum(Univ. Melbourne, Australia), but conservative estimates arethat as many as 26 species in 14 genera occur (c. 39% speciesdiversity). Some fern foliage can be allied to extant familiessuch as the Dipteridaceae, Gleicheniaceae, ?Lophosoriaceae,Matoniaceae, and Osmundaceae (Jefferson 1981, 1982;Cantrill 1995), whilst the majority of forms cannot at this stagebe attributed with confidence to family level (Cantrill 1996)(Table 1). Angiosperms are represented by a moderately diverseflora (c. 12% species diversity) consisting mainly of large arbor-escent plants and one or two small herbaceous forms (Cantrill &Nichols 1996). Other seed bearing plants include members of theBennettitales, Cycadales, Ginkgoales and Pentoxylales; collec-tively they make up only a minor component of the flora (c. 9%species diversity). Of the lower plants, lycopods and horse-tailsare rare whilst liverworts are abundant, particularly when com-

pared to Cretaceous floras from lower palaeolatitudes (Cantrill1997). Liverworts (c. 16% species diversity) include formsallied to the Marchantiales with minor representatives of theMetzgeriales. All these plant remains occur as assemblagesin particular sedimentary facies, indicating the existence ofspatially complex vegetation communities.

Facies and plant assemblages

Braided alluvial plain facies association (Citadel BastionMember)This member is characterized by erosive-based units of coarse-grained sandstone and gravel; they are laterally continuous forseveral kilometres and contain channelized incisions up to14.5 m deep and hundreds of metres wide. Channels are infilledby a basal layer of sandstone and conglomerate containingup to 3 m long conifer logs (93% Podocarpoxylon and 7%Taxiodioxylon, n=14, Table 2). Upper channel-fill units consistof 1–4.5 m thick sandstone packages that exhibit decimetre-scale trough cross-bedding or metre-scale low angle cross-stratification and contain Brachyphyllum and Ptilophyllum

Table 1. Floral biodiversity of Triton Point Formation

Hepatopsida (liverworts)Marchantiales

Marchantites (5 species)Hepaticites (3 species)Thallites (2 species)

Metzgeriales1 species

Lycopsida (lycopods)Selaginellales

1 speciesSphenopsida (horse-tails)

Equisetales1 species

Filicopsida (ferns)Dipteridaceae

Hausmania (1 species)Matoniaceae

Matonia (1 species)Osmundaceae

Cladophlebis (6 species)Phyllopteroides (2 species)

GleicheniaceaeGleichenites (1 species)

?LophosoriaceaeMicrophyllopteris (2 species)

Incertae sedisAculea (1 species)Adiantites (1 species)Alamatus (1 species)Sphenopteris (4 species)

(*In total, fern component comprises approximately14 genera and 26 species, many awaiting formal description).

ConiferopsidaConiferales (conifers)

AraucariaceaeAraucaria (2 species)Araucarites (2 species)Araucarioxylon (1 species)Araucariopitys (1 species)

PodocarpaceaePodocarpites (1 species)Podocarpoxylon (2 species)

TaxodiaceaeAthrotaxites (1 species)Taxodioxylon (1 species)

Incertae sedisBrachyphyllum (1 species)Elatocladus (2 species)Pagiophyllum (1 species)Podozamites (1 species)

Other minor gymnospermsBennettitales (extinct)

Ptilophyllum (2 species)Cycadales (cycads)

1 speciesGinkgoales (ginkgos)

Ginkgoites (1 species)*Pentoxylales (extinct)

Taeniopteris (3 species)Angiospermopsida(flowering plants)

Araliaephyllum (1 species)Dicotylophyllum (1 species)Ficophyllum (1 species)Gnafalea (2 species)Hydrocotylophyllum (1 species)Timothyia (1 species)

For details of systematic taxonomy see: liverworts (Cantrill 1997), ferns (Jefferson 1981; Cantrill 1995, 1997), conifers(Falcon-Lang & Cantrill 2000; Cantrill & Falcon-Lang 2001), and angiosperms (Cantrill & Nichols 1996). Other seed plantscurrently undescribed.*Systematic taxonomy of ferns currently being revised by N. Nagalingum (Univ. Melbourne, Australia), and Pentoxylales byJ. Howe (Univ. Leeds, UK).

CRETACEOUS HIGH-LATITUDE FLOODPLAIN, ANTARCTICA 711

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data

No

data

No

data

No

data

KG

.47

37.1

52(C

itad

elB

asti

on)

Pod

ocar

poxy

lon

sp.

2L

arge

drif

ted

log

ZS

No

data

No

data

No

data

No

data

Mea

n13

301.

66(1

.42)

3.66

0.42

(0.4

4)


Tab

le2.

Con

tinu

ed

Spec

imen

no.

(loc

alit

y)F

orm

genu

sof

coni

fer

woo

dT

ype

ofbo

tani

cal

mat

eria

lF

acie

sco

deN

o.of

grow

thri

ngs

Mea

nri

ngw

idth

(mm

)M

axim

umri

ngw

idth

(mm

)M

ean

sens

itiv

ity

(MS

)

Coa

stal

plai

nas

soci

atio

nK

G.

2814

.2(C

oal

Nun

atak

)P

odoc

arpo

xylo

nsp

.1

Lar

gedr

ifte

dlo

gZ

S29

1.15

2.15

0.31

2K

G.

2814

.252

(Coa

lN

unat

ak)

Pod

ocar

poxy

lon

sp.

2in

situ

tree

stum

pM

d37

0.56

1.10

0.28

0K

G.

2814

.253

(Coa

lN

unat

ak)

Pod

ocar

poxy

lon

sp.

2in

situ

tree

stum

pM

d6‡

1.35

‡1.

880.

289‡

KG

.28

14.2

54(C

oal

Nun

atak

)P

odoc

arpo

xylo

nsp

.2

insi

tutr

eest

ump

Md

451.

044.

800.

385

KG

.28

14.2

56(C

oal

Nun

atak

)P

odoc

arpo

xylo

nsp

.2

insi

tutr

eest

ump

Md

60†

1.68

†4.

080.

376†

KG

.28

14.2

57(C

oal

Nun

atak

)P

odoc

arpo

xylo

nsp

.1

insi

tutr

eest

ump

Md

5‡2.

75‡

3.05

0.09

4‡K

G.

2815

.52

(Coa

lN

unat

ak)

Pod

ocar

poxy

lon

sp.

1in

situ

tree

stum

pM

dN

oda

taN

oda

taN

oda

taN

oda

taK

G.

2815

.67

(Coa

lN

unat

ak)

Pod

ocar

poxy

lon

sp.

1in

situ

tree

stum

pM

dN

oda

taN

oda

taN

oda

taN

oda

taK

G.

2815

.70

(Coa

lN

unat

ak)

Pod

ocar

poxy

lon

sp.

1in

situ

tree

stum

pM

dN

oda

taN

oda

taN

oda

taN

oda

taK

G.2

815.

71(C

oal

Nun

atak

)P

odoc

arpo

xylo

nsp

.1

insi

tutr

eest

ump

Md

34*

1.16

*4.

24*

0.32

6*K

G.

2815

.77

(Coa

lN

unat

ak)

Pod

ocar

poxy

lon

sp.

1in

situ

tree

stum

pM

d5‡

4.09

‡4.

980.

175‡

KG

.46

69.1

(Coa

lN

unat

ak)

Ara

ucar

iopi

tys

Lar

gedr

ifte

dlo

gSx

lN

oda

taN

oda

taN

oda

taN

oda

taK

G.

4669

.2(C

oal

Nun

atak

)P

odoc

arpo

xylo

nsp

.1

Lar

gedr

ifte

dlo

gSx

lN

oda

taN

oda

taN

oda

taN

oda

taK

G.

4688

.44

(Coa

lN

unat

ak)

Pod

ocar

poxy

lon

sp.

1in

situ

tree

stum

pM

dN

oda

taN

oda

taN

oda

taN

oda

taK

G.

4699

.1(C

oal

Nun

atak

)A

rauc

ario

pity

sin

situ

tree

stum

pM

dN

oda

taN

oda

taN

oda

taN

oda

taK

G.

4699

.2(C

oal

Nun

atak

)P

odoc

arpo

xylo

nsp

.1

insi

tutr

eest

ump

Md

No

data

No

data

No

data

No

data

KG

.47

02.1

(Coa

lN

unat

ak)

Pod

ocar

poxy

lon

sp.

2W

ood

frag

men

tta

lus

No

data

No

data

No

data

No

data

KG

.47

02.4

(Coa

lN

unat

ak)

Ara

ucar

ioxy

lon

Woo

dfr

agm

ent

talu

s11

2.17

3.28

0.28

9K

G.

4702

.17

(Coa

lN

unat

ak)

Ara

ucar

iopi

tys

Woo

dfr

agm

ent

talu

s17

1.46

2.58

0.37

8K

G.

4702

.28

(Coa

lN

unat

ak)

Ara

ucar

iopi

tys

Woo

dfr

agm

ent

talu

s6‡

3.71

‡4.

300.

114‡

KG

.47

40.1

(Coa

lN

unat

ak)

Ara

ucar

iopi

tys

insi

tutr

eest

ump

Md

3‡12

.98‡

14.7

00.

155‡

KG

.47

40.3

(Coa

lN

unat

ak)

Ara

ucar

iopi

tys

insi

tutr

eest

ump

Md

4‡7.

42‡

10.9

50.

385‡

KG

.47

40.5

(Coa

lN

unat

ak)

Ara

ucar

iopi

tys

insi

tutr

eest

ump

Md

No

data

No

data

No

data

No

data

KG

.47

40.1

1(C

oal

Nun

atak

)A

rauc

ario

pity

sin

situ

tree

stum

pM

d28

2.95

5.78

0.29

8K

G.

4747

.133

(Coa

lN

unat

ak)

Pod

ocar

poxy

lon

sp.

2L

arge

drif

ted

log

Sxb

182.

644.

300.

376

KG

.47

47.1

38(C

oal

Nun

atak

)P

odoc

arpo

xylo

nsp

.2

Lar

gedr

ifte

dlo

gSx

b10

1.56

2.78

0.28

1M

ean

318

3.04

(1.7

9)4.

680.

28(0

.33)

Fac

ies

code

(aft

erN

icho

ls&

Can

trill

2001

);C

hann

elfil

lfa

cies

:Sm

g,m

ediu

m-

toco

arse

-gra

ined

sand

ston

e;Sx

b,cr

oss-

bedd

edsa

ndst

one.

Ove

rban

kfa

cies

:Sx

l,ri

pple

cros

s-la

min

ated

sand

ston

e;Z

S,th

innl

y-be

dded

sand

ston

ean

dsi

ltst

one;

MSf

,fin

esa

ndst

one

and

mud

ston

e;M

d,da

rkgr

eyor

blac

km

udst

one;

talu

s,lo

ose

woo

dfr

agm

ent

onta

lus

slop

e.*D

ata

take

nfr

omJe

ffer

son

(198

2).

†Com

posi

teda

tata

ken

from

mor

eth

anon

esa

mpl

e.‡L

ess

than

10ri

ngin

crem

ents

mea

sure

d.


foliage. At Titan Nunataks (KG. 4725) the rippled tops ofthe channel-fill units are patchily covered by Thallites mats(Cantrill 1997).

Interbedded with the large channel bodies lie an overbankfacies association which includes sheet sandstone beds (2–7 mthick) with flat, non-erosive bases. They are composed of0.2–2 m thick packages of medium- to coarse-grained sand-stone and siltstone that variously exhibit inverse-grading,trough cross-bedding, ripple cross-lamination or plane beddingwith primary current lineation. Adjacent to a channel body atKG. 2821 (Pagoda Ridge), immature palaeosols occur on topof a sheet sandstone unit and bear abundant Hausmania fernsin growth position, attached to the bed by stipes (Cantrill1995). In addition upright podocarp conifer trunks and stumpsoccur rooted in mature palaeosols beneath the sandstonesheets and extend up through the coarse-grained units to aheight of 7 m. Centroclinal cross-stratification is associatedwith many of these upright trunks.

Thinly bedded carbonaceous mudstone, siltstone, fine-grained sandstone units together with intermittent 1 m thickmedium-grained sandstone beds comprise only a small part ofthe Citadel Bastion Member, but contain numerous palaeosolhorizons. At Titan Nunataks (KG. 4718), an immaturepalaeosol is dominated by the shrubby angiosperm Gnafelea,together with ferns (Cladophlebis, Aculea), ginkgos, Bennetittes(Ptilophyllum), and rare conifers (Brachyphyllum). Anotherpalaeosol of greater maturity at KG. 4737 is dominated by thefoliage of Pentoxylales (Taeniopteris, up to 95% of plantremains) with rare fragments of ferns (Cladophlebis andHausmania), angiosperms (Araliaephyllum, Timothyia andDicotylophyllum), and occasional liverworts (Marchantites)(Cantrill & Nichols 1996; Cantrill 1997). A small number ofdrifted podocarp conifer trunks (100% Podocarpoxylon, n=4,Table 2) and araucarian and podocarp foliage occur in thesandstone beds between the palaeosols. At Offset Ridge (KG.4710) mature palaeosols occur in fine-grained units and bearconifer stumps in growth position; these are described furtherin a later section.

This facies association is interpreted as being deposited on abraided alluvial plain. Large channelized incisions were cut bybraided river channels c. 15 m deep and hundreds of metreswide; lower channel-fill units represent the coarse-grained lagdeposits, and upper cross-stratified channel fill units are inter-preted as the deposits of mid-channel bars (Nichols & Cantrill2001). Thick sheet sandstone units containing upright treesrepresent the product of single large-scale flood events thatdeposited coarse-grained sediment across the proximal inter-channel region, locally burying vegetation (Moncrieff 1989).Centroclinal stratification around some standing trees wasformed as the result of current scouring around the uprighttrunks (Underwood & Lambert 1974). Fine-grained unitsrepresent deposition from suspension on the floodplain distantfrom the braided channel, although the presence of numerousthin sandstone beds indicate that even this distal environmentwas subject to regular flooding (Jefferson 1981).

Meandering coastal plain facies association (CoalNunatak Member)This member is only exposed on Coal Nunatak. It containsmuch thicker successions of fine-grained units than the under-lying braidplain association and is characterized by gravelly tocoarse-grained, trough cross-bedded sandstone bodies with adistinct channelized geometry. Individual sandstone bodies are

lens-shaped with a width: depth ratio of <15:1 (sandstone rib-bons), and can only be laterally traced for a few tens of metres.Where channel margins are exposed they are inclined at alow-angle and within the channel bodies themselves mud drapedepsilon cross-stratification is locally present. Plant material inthe channels is usually highly macerated, but a few driftedconifer logs occur (100% Podocarpoxylon, n=3, Table 2).

Coarse-grained sheet sandstone units (0.1–2 m thick) adjacentto these channel bodies contain ripple cross-lamination, troughcross-bedding or plane bedding and possess non-erosive bases.At KG. 4697, one sheet sandstone unit passes laterally into achannelized sandstone ribbon, and contains allochthonous foli-age remains dominated by Cladophlebis (35%), Ginkgoites (32%)and Taeniopteris (9%), together with angiosperms (Hydrocotylo-phyllum) and conifers (Brachyphyllum) (Cantrill & Nichols1996). Elsewhere at KG. 4669, proximal deposits contain leafyconiferous branches of Araucaria and drifted conifer logs (50%Araucariopitys and 50% Podocarpoxylon, n=2). Other similarunits are covered by laterally extensive liverwort mats of March-antites type (KG. 4746; Cantrill 1997). The sheet sandstone unitsalso contain common palaeosols in regions distal to the channelbodies. The leaf litter of these palaeosols is typically dominatedby fern foliage (Aculea and Alamatus) with subordinate ginkgos,araucarian and podocarp conifers (Araucarites, Pagiophyllum,Podocarpites), and liverworts (KG. 4741 and KG. 4745;Cantrill & Nichols 1996; Cantrill 1997; Cantrill & Falcon-Lang2001).

Fine-grained sequences up to 30 m thick are common butpoorly exposed in the Coal Nunatak Member. These consist ofthinly bedded mudstone, siltstone and fine-grained, ripplecross-laminated sandstone. Palaeosols with well-developed leaflitter layers occur at multiple horizons and contain abundantsilicified conifer stumps in growth position; these are describedin greater detail below.

This facies association was deposited in a fluvial environ-ment, and sandstone ribbons exhibiting epsilon cross-stratification are interpreted as the lateral accretion deposits ofmeandering river channels (Nichols & Cantrill 2001). Theoccurrence of mud drapes in one channel body implies tidalinfluence, and suggests that the meander-belt developed in acoastal setting. Coarse-grained sheet sandstone units are inter-preted as channel levees, proximal flood deposits or crevassesplays (Nichols & Cantrill 2001). Fine-grained unitsrepresent the product of suspension deposition in distalinter-channel areas.

Mature palaeosols with rooted conifer stumpsAs noted above mature palaeosols occur in the distal flood-plains of both facies associations. Where fully developed theyconsist of a complex tripartite palaeo-weathered zone com-posed of an upper leaf litter layer (O horizon), a middle,medium brown, carbonaceous mudstone layer exhibitingclosely spaced vertical fractures (c. 8 cm thick; A horizon) anda lower bleached sandstone or siltstone layer (<60 cm thick;E/C horizon). Conifer stumps with basal diameters of 8–50 cmcommonly occur in growth position. Roots depart downwardfrom the stumps at angles of 35�–90� to the horizontal; they aremost abundant in the A horizon where they form a densemat, but also penetrate throughout the weathered E/C zone(Cantrill & Falcon-Lang 2001). Where they penetrate sandysoils rooting systems exhibit distinctive mycorrhizal nodulescharacteristic of podocarp conifers (cf. Cantrill & Douglas1988). Significant differences in the composition and spatial


arrangement of conifer stumps, and the composition of leaflitter layers exist between braidplain and coastal plain settings.

In the braided alluvial plain association, 13 palaeosolhorizons bearing conifer stumps and trunks have been ident-ified at Pagoda Ridge, with many others occurring at TritonPoint, Adonis Ridge, Offset Ridge and Phobos Ridge(Moncrieff 1989). At KG. 4710 on Offset Ridge, thirteenstumps occur over 1540 m2 of palaeosol exposure, where theyare grouped into clumps of four to five individuals with a meandensity of 91 stumps per hectare. All the stumps in thebraidplain association belong to podocarp conifers (100%Podocarpoxylon, n=16, Table 2), but nothing is known of theleaf litter composition of these mature palaeosols.

In contrast, the mature palaeosols of the coastal plainmeander-belt contain a much higher density of conifer stumpsin growth position. At KG. 2815 on Coal Nunatak 54 stumpsoccur on an exposed area of palaeosol, 25 m by 38 m (950 m2);this equates to a mean density of 568 stumps per hectare(Jefferson 1981). Furthermore coastal plain stumps have agreater compositional diversity than those of the braid-plain; both araucarian and podocarp conifers occur (29%Araucariopitys and 71% Podocarpoxylon, n=17, Table 2). AtKG. 4747 the litter layer of these palaeosols is dominated byconifers (46% Podozamites and 41% Elatocladus with rarePagiophyllum and Brachyphyllum) together with a minor com-ponent of ferns (Cladophlebis and Sphenopteris), angiosperms(Ficophyllum) and liverworts (Hepaticites).

The age of the palaeosols in both facies associations isindicated by growth ring counts in the largest of the coniferstumps; these show that many of the trees lived for more than100–200 years (Chapman 1994). In terms of general structureand composition, the palaeosols most closely resemble theleached podzolic soils of New Zealand which form on acidicvolcanic terrains colonized by podocarp–araucarian coniferforest under a humid, warm temperate climate (Wardle1991). Similar conditions were probably responsible for thedevelopment of the Triton Point Formation palaeosols.

Interpretation of plant community composition andstructure

Analysis of plant taxa distribution within the above palaeo-environmental context reveals the existence of spatially hetero-geneous plant communities in the Triton Point Formation(Fig. 2). In both floodplain settings, newly emergent sandsheets were first colonized by diverse and continuous liverwortmats, plants which may have played an important role ininitial sediment stabilization and soil formation. Both flood-plain settings were also characterized by a gradient of increas-ing vegetation complexity moving from frequently disturbedsandy riparian sites to more distal floodbasin localities whereflood disturbances were rarer and soils were of greater ma-turity. The size of the conifer stumps preserved in distalinter-channel areas indicate these were large trees with prob-able heights in the range 14–29 m (Falcon-Lang & Cantrill2000). However, beyond these initial similarities, significantdifferences in the vegetation ecology of the two floodplainsettings existed. This variability in ecosystem structure prob-ably resulted from differences in floodplain hydrology, ratherthan changing climate between the lower and the upper unit.Evidence from palaeosols indicate that climate was similarduring the deposition of both units, however, in terms ofhydrology there were much greater differences. The braidedalluvial plain setting consisted of mobile flood-prone channelbelts in which vegetation grew under considerable ecologicalstress, whilst the coastal plain was characterized by confinedmeander-belts where floods were less common and climaxvegetation could develop.

In the braided alluvial plain environment (Fig. 2a), im-mature, sandy, riparian soils appear to have locally supportedpatchy, monotypic communities of herbaceous Hausmaniaferns. However, the presence of abundant Podocarpoxylon andTaxodioxylon conifer logs and Ptilophyllum and Brachy-phyllum foliage within the braided channel deposits, togetherwith in situ podocarp stumps on near-channel sites implies that

Podocarp-araucarian climax forest(c. 568 trees per hectare)

Podocarp-araucarian climax forest(c. 568 trees per hectare) Fern thickets/conifer woodlandFern thickets/conifer woodland

Ginkgo-conifer scrubGinkgo-conifer scrub

MEANDER-BELTMEANDER-BELT

BRAIDPLAINBRAIDPLAIN

KG. 2821KG. 2821 KG. 4725KG. 4725KG. 4718KG. 4718KG. 4737KG. 4737KG. 4710KG. 4710

KG. 4697KG. 4697KG.4741KG.4741 KG. 4745KG. 4745KG. 4747KG. 4747KG. 2814KG. 2814

Cycadophyte-conifer scrubCycadophyte-conifer scrub

Gymnosperm-fern-angiosperm thicketsGymnosperm-fern-angiosperm thickets

Liverwort matsLiverwort mats

Broken podocarp woodland(c. 91 trees per hectare)

Broken podocarp woodland(c. 91 trees per hectare)

3030

1515

00

Ve

ge

tatio

nh

eig

ht

(m)

Veg

eta

tio

nh

eig

ht

(m)

3030

1515

00

Ve

ge

tatio

nh

eig

ht

(m)

Veg

eta

tio

nh

eig

ht(m

)

Locality:Locality:

Locality:Locality:

Bennettite

TaeniopteridTaeniopterid GingkoGingko

ArborescentangiospermArborescentangiosperm

HerbaceousangiospermHerbaceousangiosperm

FernFern LiverwortLiverwort

AraucarianconiferAraucarianconifer

PodocarpconiferPodocarpconifer

TaxodioidconiferTaxodioidconifer

KEY:KEY:

AA

BB

Fig. 2. Summary diagram of TritonPoint Formation ecosystems based onfacies analysis of plant assemblages, (a)braided alluvial plain facies associationand (b) coastal meander-belt association.


mature riparian vegetation was elsewhere composed of largepodocarp and taxodiod conifers interspersed with bennettitaleantrees. Rooting systems with mycorrhizal nodules suggest thesesandy soils were well-drained and nutrient-poor. Slightly furtherfrom channel influence, sandy soils supported a variety of two-tier plant communities. At one site, thickets of shrubby angio-sperms and ferns occurred between widely spaced ginkgos andBennettites. At another site vegetation was dominated by anoverstorey of Pentoxylales (Taeniopteris) interspersed with occa-sional angiosperms and conifers, and a diverse understoreyvegetation of ferns (Cladophlebis and Hausmania), rare angio-sperm shrubs (Timothyia and Dicotylophyllum) and liverworts(Marchantites). Podzolic soils in inter-channel areas were fre-quently subjected to flooding, preventing the development offorest climax vegetation on the distal parts of the braided allu-vial plain. Instead disturbed inter-channel sites supportedscattered low-density (91 trees/ha) clumps of large podocarpconifers as indicated by the distribution of rooted stumps; noth-ing is known of associated understorey plants.

In the coastal plain meander-belt environment (Fig. 2b),where river channels were more confined, extensive immaturesandy substrates covered by dense liverwort mats (Marchantites)were rarer. Vegetation on channel levees consisted of a podocarp–araucarian conifer canopy, a subcanopy of ginkgos and cycado-phytes and a monotypic fern understorey (Cladophlebis). Furtheraway from channel influence, sandy substrates were colonized bycontinuous fern-dominated thickets (Aculea and Alamatus) in-terspersed with shrubby podocarp conifers and scattered standsof ginkgos and araucarian conifers. Rare marchantiod liver-worts formed a ground layer (Cantrill 1996). Mature podzolicsoils in distal floodbasin regions where flood disturbance wasof low frequency, supported medium density (568 trees/ha)podocarp–araucarian climax forests, a similar tree density tothat seen in present-day New Zealand podocarp–araucarianrainforests (450–1400 trees/ha) (Duncan 1993). Understoreyvegetation was dominated by ferns (Cladophlebis and Sphenop-teris), with intermittent ginkgos, angiosperms (Ficophyllum) andliverworts (Hepaticites).

Growth rings in conifer woodsFurther insight into the dynamic nature of the Triton PointFormation ecosystems may be gained from an examination ofgrowth ring sequences in the silicified conifer stumps andtrunks. These represent a continuous record of what growingconditions were like in both facies associations over periods oftens to hundreds of years. In particular two growth ringparameters are useful in analysing growing conditions, meanring width and mean sensitivity (Creber 1977; Creber &Chaloner 1984).

The first parameter, mean ring width, is a measure of theannual productivity of the tree and therefore the favourabilityof the growing environment (e.g. climate, soil quality, degreeof leaf shading). The second parameter, mean sensitivity (MS),is a numerical expression of the year-to-year variability in ringwidth and is given by the formula:

where x is ring width, n is the number of rings in the sequenceanalysed, and t is the year number of each ring. Values ofmean sensitivity range from 0 where there is no year-to-yearvariability, to a maximum approaching 2 representing the

greatest possible variability. Under environmentally favour-able conditions, ring increments have a relatively constantyear-to-year width that reflects the genetic potential of the tree.If a ring sequence contains a high degree of width variabilitythen this implies that environmental conditions were suf-ficiently stressful to limit growth so that the genetic potentialwas not attained. An arbitrary MS value of 0.3 is used todistinguish ‘sensitive’ ring sequences with a high degree ofincremental width variability (MS>0.3) formed under stressfulconditions, from ‘complacent’ sequences with little incrementalvariability (MS<0.3) formed under favourable conditions(Fritts 1976).

Quantitative ring width and mean sensitivity dataThe ring width data-set presented here for the Triton PointFormation is the largest yet published for Mesozoic woods (cf.Jefferson 1982; Francis 1984, 1986; Keller & Hendrix 1997;Morgans et al. 1999); a total of 1648 ring increments weremeasured from undeformed wood samples with the aid of 6 cmby 3 cm thin sections, 1330 from 33 wood samples in thebraidplain association and 318 from 16 wood samples in thecoastal plain association (Table 2). An important feature tonote about the data-set, is that data from short ring sequences(n=<10) are usually characterized by relatively high ringwidths and relatively low mean sensitivities. This does notmean that these data are anomalous and should be excludedfrom the overall data-set on the basis of their statisticallyquestionable short ring sequences, because of the simple factthat wider growth ring increments will inevitably occur infewer number in a 6 cm by 3 cm thin section. However, inorder to emphasize this problematic feature of the data, themean ring width and mean sensitivity values for the whole ofeach two facies associations are expressed in two ways inTable 2 (in bold). The first figure is a simple arithmetic mean ofdata from each wood sample (SM) whilst in the second (inparenthesis) the mean is weighted in proportion to the numberof ring increments in each wood sample (WM).

Although there is a high degree of variability amongstindividual samples, there are clearly discernible differencesbetween the ring characteristics of the two facies associations(Table 2); growth rings are consistently wider (SM: 3.04 mm,WM: 1.79 mm) with a lower mean sensitivity (SM: 0.282, WM:0.326) in the coastal plain meander-belt association comparedwith those of the braidplain (ring width, SM: 1.66 mm, WM:1.42 mm; mean sensitivity, SM: 0.415, WM: 0.439) (Figs 3a–c,4 & 5). Mean maximum ring width is also wider in the coastalplain association (4.68 mm) compared with the braidplain(3.66 mm). Mean ring width for all trees in both faciesassociations is 1.92 mm (SM) or 1.49 mm (WM).

Qualitative growth ring dataA further qualitative feature of the Triton Point Formationgrowth rings is the occurrence in eight wood specimens of zonescomposed of extremely narrow growth rings (Figs 3a–b & 4b).These zones are typically less than 2 mm wide, and may occur atseveral randomly distributed sites with a single trunk cross-section. They are composed of rings which range from two cellsacross (the minimum identifiable growth ring) to about nine cellsacross, which equates to absolute ring widths in the order of0.05–0.26 mm. Single narrow rings are never observed, but theytypically occur grouped together into sequences of three tofourteen. The ring boundaries of these narrow growth rings arequalitatively different from those of the normal growth rings in


that they are usually subtly developed, being marked by late-wood cells of fewer number and larger diameter. In addition, thenarrow growth rings are locally symmetrical across the ringboundary, and do not persist around the whole trunk circumfer-ence. Furthermore individual tracheids within these anomalouswood zones often possess a rounded cross-sectional shape, suchthat they do not perfectly tessellate resulting in the occurrence ofabundant intercellular spaces. Good examples of the ‘narrowring’ phenomenon are restricted to seven podocarp wood speci-mens from the braided river facies association (particularly KG.4717.51 and KG. 4719.3), and one poorly developed examplefrom in the coastal plain facies association. These narrow ringsequences were excluded from the data used to calculate theabove MS values.

Environmental and ecological interpretationIn the mid-Cretaceous polar circle, climate possessed a distinctlyseasonal cycle characterized by warm, light summers and cool,dark winters (Read & Francis 1992), and the growth rings of theTriton Point Formation woods almost certainly reflect thisrhythm, with one ring forming annually (Francis 1986). Nar-rower growth rings with greater year-to-year variability in thebraided river association on Alexander Island imply that grow-ing conditions were more stressful than in the coastal plainmeander-belt environment. Two factors may have been import-ant in generating this pattern. First, mean sensitivity is generally

greater for trees growing in discontinuous woodlands comparedwith those in closed forests because the growing environment isgenerally more stable in the latter situation (Creber 1977). Maxi-mum conifer density on the Triton Point Formation braidplainwas only one sixth of that on the coastal plain, consequentlybraidplain trees were probably more exposed to adverse environ-mental impacts such as wind damage which may have resulted inmore irregular growth patterns (higher MS). However, if tree-spacing was the primary factor controlling the nature of thegrowth ring sequences, one might have expected the braidplaintrees to have formed wider rings than those of the meander-belt,because in the former situation there would have been lesscompetition for light and soil nutrients (Koga et al. 1997). In factthe opposite is the case, and rings are widest on the denselyforested meander-belt. A second possible factor responsible forthe observed growth ring patterns may have been the differinghydrological regimes of the two floodplains. Braided river sys-tems are much more prone to bank bursting and overbankflooding than meandering systems because energy conditions aremuch greater in the former (Reading 1996). The impact offlooding on vascular cambial growth is complex, and results inan initial short-term increase in growth rate followed by a longerterm decline (Kozlowski 1984), such that the growth rings offlooded trees may be only 60% of the width of unfloodedneighbours (Yamamato et al. 1987). The frequent inundation ofthe braidplain woodlands of Alexander Island would thereforehave given rise to a much more irregular tree growth rate and

Fig. 3. Conifer woods and barks. (a) Narrow, growth rings of variable width in Podocarpoxylon sp. 1 wood, KG. 4719.4, scale-bar is 1 mm,braided fluvial association (MS=0.44); some very narrow flood rings occur on left side (arrowed). (b) Flood rings in P. sp. 1, KG. 4719.4,scale-bar is 1 mm, braided association (MS=0.28); flood rings (arrowed). (c) Wide growth rings of regular width in P. sp. 2 wood, KG.2814.252, scale-bar is 1 mm, meandering fluvial association (MS=0.28). (d) Thick bark in P. sp. 2, KG. 4710.3, scale-bar is 3 mm, braidedassociation. (e) Root trace in bark of P. sp. 2, KG. 4710.3, scale-bar is 1 mm, braided association.


therefore higher mean sensitivity than on the meander-belt. Inaddition, the long-term suppression of growth due to floodingalso explains why the braidplain trees generally possess narrowerannual rings. Similar ring patterns are observed in modernfloodplain forests. For example, Martens (1993) showed thatSalix growing on flood-prone, in-channel benches possessednarrower rings with greater year-to-year variability than thosegrowing on adjacent, permanently drained levees and terraces.

Zones of very narrow rings in Triton Point Formationwoods provide additional information about growing con-ditions on the two floodplain systems. It is unlikely that thesevery narrow rings (0.05–0.26 mm) represent annual growthincrements because their subtle, discontinuous ring boundariesimply that they were formed by a short-term reduction incambial activity as opposed to a long-term cessation associatedwith the onset of winter. Instead we interpret them as intra-annual rings (‘false rings’ in the terminology of Fritts 1976).Several environmental disturbances may induce a short-termreduction in cambial activity during the growing season, andgive rise to multiple rings in each year’s growth increment;these include frost (Glock et al. 1960), drought (Ash 1983), fire(Dechamps 1984) and flooding (Young et al. 1993). In the mildand humid climatic setting envisaged for the Triton PointFormation, the only one of these disturbances which is likelyto have occurred regularly enough to produce the observedfalse ring sequences is flooding. This conclusion is supportedby the presence of rounded tracheids and intercellular spaces inthe podocarp woods. This anatomical feature has been associ-ated with greatly stimulated ethylene production in the sub-merged portions of conifer boles during floods (Yamamoto1992). The development of such intercellular spaces in floodedconifers is believed to improve oxygen diffusion rate into theroot system (Hook 1984). Woods containing flood-rings arealmost entirely restricted to the braidplain environment onAlexander Island, further supporting the hypothesis that veg-etation in this setting was prone to regular flooding. Up to 14adjacent flood rings in one wood sample implies that thisparticular tree was inundated many times during a singlegrowing season.

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Fig. 4. Examples of ring width sequences (a) braidplain wood withhigh mean sensitivity (MS), (b) braidplain wood with high MS andnarrows of very narrow flood rings (shaded), (c) coastalmeander-belt wood with moderate MS.

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Fig. 5. Growth ring data showing mean sensitivity versus ring width;black diamonds denote braidplain woods, white squares denotecoastal meander-belt woods.


Stumps with attached barks and adventitious roots

DescriptionThree tree stumps of Podocarpoxylon sp. 1 and sp. 2 rooted inpalaeosols in the braidplain facies association (KG. 4660.1,KG. 4710.2 and KG. 4710.3) exhibit extremely thick (up to43 mm wide) bark. The periderm is largely composed ofalternate layers of thin and thick walled cells arranged inapproximately radial files. Scattered thoughout the peridermare small diameter (0.3–3.0 mm) roots (Fig. 3d–e). The rootscomprise a central diarch or rarely triarch vascular bundlesurrounded by a prominent endodermis. Outside the endoder-mis are thin walled parenchymatous cells of the cortex. Inmany instances this cortical material is crushed particularlyaround the edges. Root traces pass vertically or slightlyradially through the bark towards the outside of the trunk.Rooting systems associated with the podocarp stumps andthose elsewhere in the braidplain unit are shallowly penetrative(typically <20–30 cm), horizontally orientated, and possessmycorrhizae (cf. Cantrill & Douglas 1988).

Ecological and environmental interpretationGrowth ring data indicates that the braidplain trees grew in aflood-prone environment. Further support for this interpret-ation is provided by the podocarp stumps with thick barkscontaining root traces. Some ecological studies interpret theoccurrence of thick bark as a fire adaptation, which acts toinsulate the vascular cambium from catastrophic heating(Burns 1993). However, fires appear to have been uncommonin the humid temperate ecosystems of Alexander Island (seebelow), and are unlikely to have been a sufficient ecologicalpressure to influence stem anatomy. Other studies suggest thatthe thick bark represents a response to flooding because itfacilitates greater aeration of the submerged portion of thetrunk (Hook 1984). For example, 150–230% increases in barkthickness have been reported in some conifers following flood-ing (Yamamoto & Kozlowski 1987; Yamamato et al. 1987).Some support for this is seen in entombed trunks whereindividual trees have been partially buried and the trunk formsan expanded bole at the top of the new sediment surface(Jefferson 1982, pl. 66, fig. 4). In flooded coniferous trees fromwestern Canada new roots developed at the top of the new soilsurface (Stone & Vasey 1968). Given the braidplain setting ofthe Triton Point Formation podocarp trunks, thick barks mayrepresent a flood adaptation. Rootlets within the podocarpbarks must have grown late in the tree’s life, and are inter-preted as being adventitious. Adventitious root growth isstimulated by flooding in many present-day conifers andappears to aid nutrient absorption from remaining aerated soilzones (Kozlowski 1984; Yamamoto 1992). In addition, theshallow, horizontally orientated nature of podocarp rootingsystems in the braidplain palaeosols provide yet further evi-dence that these conifer communities were flood-prone; suchroot gross-morphology is characteristic of periodically water-logged soils because roots preferentially grow in the mostaerated upper soil zone (Kozlowski 1984).

Tissue damage in conifer woods

DescriptionThree types of tissue damage occur in the conifer woods. First,traumatic parenchyma is present in <2% of the specimens. Onejuvenile specimen of Araucariopitys (KG. 4702.28) from thecoastal plain facies association, exhibited two discontinuous

rings of traumatic parenchyma which occurred within the firstthree growth increments (Fig. 6a–b). Wood immediately follow-ing these traumatic zones was characterized by cells with resin-ous contents. Chapman (1994) also noted similar traumaticparenchyma scattered throughout the innermost nine rings ofan unidentified conifer from the braidplain facies association.

Second, fungal material is common. For example, in 4% ofthe specimens studied large spindle-shaped cavities (up to 3 mmin diameter and up to 5 cm high) occur in the latewood (Fig.6d). They contain oval fungal organs (9–12 µm by 3–15 µm)comparable to modern basidospores or teliospores produced byBasidiomycetes, and aggregates of circular bodies which mayrepresent fruiting structures, along their inner margin.

Third, 7% of the wood samples contain large, complex,branching chambers several centimetres across (Fig. 6e). Theseare filled with abundant, closely packed, 1–3 mm long, oval,dark-coloured bodies containing highly digested xylem (frass),interpreted as arthropod coprolites (Fig. 6c). One slender stemof Podocarpoxylon sp. 2 (KG. 4717.43) contained two suchchambers. The first was emplaced following the growth ofthe eleventh ring increment (stem diameter at 13 mm); theformation of seven further ring increments were required toentirely cover this scar. The second chamber was emplacedfollowing the twentieth ring increment (stem diameter at24 mm) (Fig. 6f). This resulted in cambial damage over 17% ofthe stem circumference and even following the growth of afurther 42 ring increments this scar had not been entirelycovered. Growth ring width decreased markedly associatedwith each chamber emplacement event (mean ring width isonly 0.45 mm) (Fig. 7).

Ecological and environmental interpretationRings of traumatic tissue similar to those observed in theAraucariopitys specimen (KG. 4702.28) are common in somemodern conifer woods and usually represent cambial responseto canopy damage by fire (Dechamps 1984), frost (Glock et al.1960) or arthropod defoliation (Fritts 1976). Given the rarityof these traumatic features it is impossible to attribute themwith certainty to any of these causal agents. However, it isknown that frost rings are commonly formed immediatelyafter volcanic events, when temperatures drop unusuallylow (LaMarche & Hirschboek 1984). The forest bearing theAraucariopitys specimen is buried by a volcanic ash layer onCoal Nunatak and it is possible that the traumatic tissue mayrepresent a volcanically induced frost ring.

The presence of large spindle-shaped cavities in the latewoodwhich contain fungal bodies represent the seasonal attack ofconifers by fungi. In their gross-morphology these structuresare very similar to some white pocket rots (Blanchette 1992).Similar features have been seen in Permian and Triassic conifertrunks from Antarctica (Stubblefield & Taylor 1986) andNorth America (Creber & Ash 1990). The position of the whiterots within latewood component of the ring increment mayindicate that fungal attack occurred during the dusky lateautumn or dark winter when the trees’ defense mechanismwould have been particularly vulnerable.

Another biological disturbance to tree growth was the resultof arthropod attack. The emplacement of frass-filled chambersfollowing the production of the latewood, again suggests thatarthropod attack occurred to the trees’ dormant phase duringthe late autumn/winter months. The Podocarpoxylon sp. 2trunk described (KG. 4717.43) appears to have been badlydamaged by arthropod attack on two occasions, when the tree


was 11 and 20 years old. Attacks resulted in a marked decreasein growth rate and massive cambial damage from which thetree never fully recovered. A similar reduction in growth ringwidth has been observed in Douglas fir following arthropodattack; reduction in ring width was strongly correlated withdegree of canopy defoliation (Alfaro & Shepherd 1991).

Charcoal deposits

Abundance and taxonomic compositionAt some forest horizons plant material is anatomically pre-served as charcoal (fusain), the product of incomplete combus-tion in vegetation fires (Jones & Chaloner 1991). Charcoaloccurs in association with pale water-lain tuff layers, and ispresent in low abundance throughout the Triton PointFormation. In addition wood reflectance studies show rarebimodal peaks throughout the Fossil Bluff Group implyingthat both vitrinite and fusinite were present in measuredsamples (Doubleday 1994).

In one tuff sample (KG. 2818.1) collected from an overbanksequence within the meander-belt association, charcoal occursas an unsorted accumulation consisting of fragments rangingin size from 50 µm to 14 mm. Given the fragmented nature ofthe material only a small proportion was identifiable. Conifer-ous woods dominate the assemblage and include Araucariopi-tys and both Podocarpoxylon species in approximately equalproportion (Fig. 8a–b). Small leafless twigs (0.5 mm diameter)with parenchymatous piths were also common, and on thebasis of juvenile wood anatomy were probably derivedfrom podocarp conifers. Other probable coniferous remainsincluded young primary shoots, isolated diamond-shaped scaleleaves similar to those of Brachyphyllum or Pagiophyllum, andnumerous seed-coat fragments (Fig. 8c–d).

Interpretation of fire ecologyCharcoal abundance in Triton Point Formation is very lowwhen compared with the deposits of well-studied, denselyvegetated floodplains elsewhere in the geological record (e.g.

Fig. 6. Traumatic tissue in trunks. All transverse section. (a–b) Frost rings in young trunk of Araucariopitys, KG. 4702.28, (a) scale-bar is100 µm (b) scale-bar is 50 µm. (c) Oval arthropod coprolites in excavated chamber, Podocarpoxylon sp. 2, KG. 4717.43, scale-bar is 500 µm.(d) Fungal white rots concentrated in latewood region, P. sp. 2, KG. 4633.46, scale-bar is 2 mm. (e) Complex chamber filled with arthropodcoprolites, P. sp. 2, KG. 4717.43, scale-bar is 1 mm. (f) Cambial regrowth over wound caused by emplacement of arthropod chamber, P. sp. 2,KG. 4717.43, scale-bar is 2 mm.


Cope 1993; Falcon-Lang 1999, 2000). Charcoal has been rarelydocumented at other mid-Cretaceous southern high-latitudeforest sites, the only record being that of Francis & Coffin(1992) who described some Albian podocarp wood charcoalfrom the Kerguelan Plateau (ODP Site 750) at a palaeolatitudeof 56�S. The frequency with which fires occur in an ecosystemis closely related to the moisture content of the vegetationwhich is itself linked to atmospheric humidity (Uhl et al. 1988).In modern humid tropical and temperate rainforests highvegetation moisture content is maintained year-round andconsequently these ecosystems have very low fire-frequencieswith fire events spaced several hundred or thousand yearsapart (Veblen 1982; Sandford et al. 1985; Burns 1993).Independent evidence suggests that the Triton Point For-mation was probably deposited under a humid temperatepalaeoclimate (Parrish et al. 1982, 1998) and we interpret therarity of charcoal in this unit as indicating that fires were rareevents in the mid-Cretaceous polar biome. The association ofcharcoal with tuff layers implies that volcanism may haveinitiated some fires as occurs in the podocarp temperaterainforests on the flanks of Mount Taupo, New Zealand(Wilmshurst & McGlone 1996).

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Fig. 7. Ring width sequence in trunk attacked twice by wood-boringarthropods. Each injury caused large decrease in radial growth rate.R denotes the period during which the tree recovered from theinjury.

Fig. 8. Scanning electron micrographs of charcoal from coastal plain meander-belt facies association at KG. 2818.1. (a) Cross-section ofpodocarp conifer twig, scale-bar is 200 µm. (b) Radial view of Araucariopitys conifer wood, scale-bar is 20 µm. (c) Conifer seed coat, scale-bar is500 µm. (d) Conifer scale-leaf of Brachyphyllum- or Pagiophyllum-type, scale-bar is 500 µm.


DiscussionPalaeoecological synthesisA kaleidoscopic variety of intergrading conifer–fern-dominated plant communities existed on the floodplains ofAlexander Island, Antarctica during the Late Albian. Thesegrew under a seasonal climate characterized by cool, darkwinters and warm, light summers; and high year-round rainfall(Spicer & Chapman 1990). Vegetation dominated by lowdensity (91 trees/ha) stands of podocarp and taxodiod conifersgrew on mobile braided alluvial plains where it was subject toregular catastrophic flooding events. On coastal meander-beltsconditions were more stable and floods less frequent, so thatmedium density (568 trees/ha) araucarian–podocarp rain-forests were able to establish. This climax vegetation possesseda four-tier structure consisting of a c. 30 m high conifercanopy, a sub-canopy of tree ferns, ginkgos, Bennettitales,Pentoxylales and angiosperms, a herbaceous layer dominatedby ferns and minor angiosperms, and a liverwort ground layer.Almost all of the arborescent vegetation on both floodplaintypes possessed a broad-leafed evergreen canopy, althoughsome elements of the sub-canopy and herbaceous layerwere probably deciduous (Falcon-Lang & Cantrill 2001).Vegetation disturbances due to unusually hard frosts, wildfiresand attack by wood-boring arthropods and fungi periodicallyoccurred, but with very low frequency.

Comparison with warm temperate rainforests of NewZealandThe composition, structure and ecology of the AlexanderIsland vegetation bears some resemblance to the extantrainforests of New Zealand which grow under a humid(1500 mm a�1) and warm (MMST 16–22�C, MMWT 3–8�C)temperate climate (Wardle 1991). Like the vegetation de-scribed here from Alexander Island, these forests consist of apodocarp–araucarian conifer canopy (20–30 m high) and sev-eral understorey layers dominated by angiosperms, tree-ferns,palms, ferns, mosses and liverworts (Wardle 1991). The largestdifference between the Cretaceous forests and their puta-tive closest modern analogue is the greater abundance ofangiosperms in the latter (locally up to 52% of the woodyvegetation; Duncan 1993), a plant group which only evolvedand migrated to polar regions immediately prior to the depo-sition of the Triton Point Formation (Hill & Scriven 1995).Whilst angiosperm radiation has greatly modified the ecologyof the Southern Hemisphere temperate rainforests, a fewfeatures of these extant ecosystems provide important clues forinterpreting the terrestrial palaeoecology of Alexander Island.

For example, the araucarian and podocarp conifers ofNew Zealand exhibit a degree of ecological partitioning;araucarians prefer well-drained, ultra-infertile podzolic soils(Ecroyd 1982) whilst podocarps prefer flood-prone, semi-infertile alluvial substrates where periodic flooding plays animportant role in forest regeneration (Duncan 1993; Odgen &Stewart 1995). These present-day ecological preferences ex-plain the almost complete restriction of araucarian conifers tothe stable meander-belts of Alexander Island, and the domi-nance of podocarps on the disturbed flood-prone braidplains.

Furthermore, modern araucarian conifers are frost hardydown to �11�C and podocarps down to �23�C; below suchtemperatures frost rings are produced (Sakai & Larcher 1987).Assuming that Cretaceous conifers had similar thermal toler-ances, the rare occurrence of frost rings in araucarian woodsfrom Alexander Island imply that temperatures only occasion-

ally fell below the �11�C, whilst their absence in the podocarpwoods indicates that the �23�C threshold was never reached.

Mean growth ring width in extant New Zealand conifersand those of Cretaceous Alexander Island are also verysimilar. Mean annual ring widths for mature podocarps rangeup to 1 mm in South Island (42–46�S), and for araucariansand podocarps in North Island (35–42�S), up to 2.2 mm(Dunwiddie 1979; Ahmed & Ogden 1987; Norton et al. 1988).Annual ring widths in the order of 1–2.5 mm have also beenrecorded in araucarian conifers in warm temperate Chile (Burns1993). On Alexander Island conifers have a total mean ringwidth of 1.92 mm. However, these similarities in ring width donot necessarily imply that growing climate was the same onAlexander Island as it is in present-day warm temperate Chileand New Zealand. Studies by Downs (1962) rediscovered byG.T. Creber (Univ. London, pers. comm. 2000) have shown thatconifer seedlings grow at a very high rate under conditions ofpermanent sunlight, as would have existed during the summermonths on Alexander Island. Elevated growth rates under polarlight conditions may be caused by three factors. First, plants canmake use of the whole year’s 4380 hours of daylight (i.e.365�12 hours which every point on the planet receives annu-ally) which is delivered entirely during the warm summer grow-ing season. Second, growth inhibitors build up during darkperiods which need to be broken down in the subsequent lightperiod before growth can recommence; such growth inhibitorsdo not form during a regime of continuous daylight. Third,sucrose needed to translocate photosynthate from the leaves tothe trunk is only produced during daylight. During the darkperiods of lower latitude regions, vascular cambium activity isgreatly reduced because translocation slows. However, under thecontinuous light regime of the polar biome growth may occurcontinuously (G.T. Creber pers. comm. 2000). As a consequenceof this elevated growth rate under polar conditions, it is impos-sible to relate ring width directly to climatic favourability.

Nevertheless, ring width data may be used to calculate theannual productivity of the Alexander Island forests. Usingmean ring increment, mean stump diameter and forest densitydata, Creber & Francis (1999) estimated total wood pro-ductivity for the Alexander Island climax rainforest to be17.65 m3 ha�1 a�1 based on Jefferson’s (1981) data. Usingour revised data (presented above and based on additionalfieldwork), we estimate that the wood productivity of theAlexander Island forests was probably closer to 5.62–7.33 m3

ha�1 a�1. These values are similar to those of compositionallysimilar araucarian–podocarp stands in warm temperate NorthIsland, New Zealand, which have productivities in the order of4.5–7.5 m3 ha�1 a�1 (Wardle 1991).

Polar rainforests and mid-Cretaceous climate-vegetationmodelsWarm temperate broad-leafed, evergreen araucarian–podocarp rainforests similar to those of Alexander Islandappear to have dominated much of Gondwana above apalaeolatitude of 60�S (Fig. 1a; Spicer & Chapman 1990).Various attempts have been made to understand the climateand vegetation of this region using sophisticated numericalmodels. For example, Valdes et al. (1996) applied the UGAMPmodel to Smith et al.’s (1994) representation of mid-Cretaceous palaeogeography to analyse summer and wintersurface air temperatures. They estimated that SE AlexanderIsland, and much of coastal Antarctica, central Australia andNew Zealand was characterized a mild climate, with winter


temperatures of 0�C to �4�C and summer temperatures of20–24�C. These values are very similar to those estimated forSE Alexander in this paper on palaeobotanical grounds. Inanother study, Beerling (2000) modelled mid-Cretaceous(Albian) net primary productivity for the South Hemisphere.His model indicated that the whole of Antarctica, and sur-rounding high-latitude landmasses had a terrestrial net pri-mary productivity similar to modern Southern Hemispherewarm temperate evergreen forests. Calculations of productiv-ity above based on palaeobotanical data have verifiedBeerling’s (2000) model estimates, indicating that the SEAlexander Island forests had a similar productivity to those ofpresent warm temperate New Zealand.

Conclusions(1) Humid temperate rainforests grew on mid-Cretaceous(Late Albian), high-latitude (75�S) braided alluvial plains andcoastal meander-belts in SE Alexander Island, Antarctica, andcomprised a kaleidoscopic variety of inter-grading conifer–ferndominated communities.

(2) Floodplain hydrology exerted the greatest influence oncommunity structure. Only scattered woodlands and thicketsgrew on braidplains where flood disturbance was frequent,but on more stable meander-belts dense climax rainforestestablished.

(3) In terms of composition, structure, ecology and produc-tivity, vegetation resembled the warm temperate rainforests ofpresent-day New Zealand. The presence of warm temperateforests close to the mid-Cretaceous South Pole verifiesthe results of recent numerical computer models of mid-Cretaceous climates and biomes.

Fieldwork on Alexander Island by two of us (G.J.N. and D.J.C.) wassupported by the British Antarctic Survey, and was undertaken duringthe 1992–93 austral summer season. We thank Mike Tabecki andJeanette Ringman for preparing petrographic thin sections, ChrisGilbert and Pete Bucktrout for preparing photographic plates, andKen Robinson for assistance with Scanning Electron Microscopy. Thereviews of John Howell, Geoff Creber and Helen Morgans-Bell greatlyimproved this paper.

ReferencesA, M. & O, J. 1987. Population dynamics of the emergent conifer

Agathis australis (D.Don) Lindl. (Kauri) in New Zealand. I. Populationstructures and tree growth rates in mature stands. New Zealand Journal ofBotany, 25, 217–229.

A, R.I. & S, R.F. 1991. Tree-growth of interior Douglas-fir after oneyear’s defoliation by Douglas-fir tussock moth. Forest Science, 37, 959–964.

A, S. 1963. A new Mesozoic flora from Tico, Santa Cruz Province,Argentina. Bulletin of the British Museum (Natural History), Geology, 8,47–92.

A, J. 1983. Growth rings in Agathis robusta and Araucaria cunninghamii fromtropical Australia. Australian Journal of Botany, 31, 269–275.

A, D.I. 1984. An interpretation of Cretaceous and Tertiary biota in polarregions. Palaeogeography, Palaeoclimatology, Palaeoecology, 45, 105–147.

B, M.K. & C, I.B. 1994. Fossil wood of Cretaceous age from theNamaqualand continental shelf, South Africa. Palaeontologia africana, 31,83–95.

B, E.J. 1984. Climatic implications of the variable obliquity explanation ofCretaceous-Palaeogene high-latitude floras. Geology, 12, 595–598.

B, D.J. 2000. The influence of vegetation cover on soil organic matterpreservation in Antarctica during the Mesozoic. Geophysical ResearchLetters, 27, 253–256.

B, R. 1992. Anatomical responses of xylem to injury and invasion byfungi. In: B, R.A. & B, A.R. (eds) Defense mechanisms ofwoody plants against fungi. Springer, New York, 76–95.

B, J.R. 1996. Sandstone provenance and diagenesis of arc-related basins;James Ross Island and Alexander Island, Antarctica. PhD thesis. Universityof Exeter.

B, B.R. 1993. Fire-induced dynamics of Araucaria araucana-Nothofagusantarctica forest in the southern Andes. Journal of Biogeography, 20,669–685.

C, D.J. 1995. The occurrence of the fern Hausmannia Dunker(Dipteridaceae) in the Cretaceous of Alexander Island, Antarctica.Alcheringa, 19, 243–254.

C, D.J. 1996. Fern thickets from the Cretaceous of Alexander Island,Antarctica containing Alamatus bifarius Douglas and Aculea acicularis sp.nov. Cretaceous Research, 17, 169–182.

C, D.J. 1997. Hepatophytes from the Early Cretaceous of AlexanderIsland, Antarctica: systematics and palaeoecology. International Journal ofPlant Sciences, 158, 476–488.

C, D.J. & D, J.G. 1988. Mycorrhizal conifer roots from theLower Cretaceous of the Otway Basin, Victoria. Australian Journal ofBotany, 36, 257–272.

C, D.J. & F-L, H.J. 2001. Cretaceous (Late Albian)Coniferales of Alexander Island, Antarctica. 2: Foliage, reproductivestructures and roots. Review of Palaeobotany and Palynology, in press.

C, D.J. & N, G.J. 1996. Taxonomy and palaeoecology of EarlyCretaceous (Late Albian) angiosperm leaves from Alexander Island,Antarctica. Review of Palaeobotany and Palynology, 92, 1–28.

C, J.L. 1994. Distinguishing internal developmental characteristicsfrom external palaeoenvironmental effects in fossil wood. Review ofPalaeobotany and Palynology, 81, 19–32.

C, L.J. & J, H.C. 1999. New oxygen isotope evidence for long-termCretaceous climatic change in the Southern Hemisphere. Geology, 27,699–702.

C, M.J. 1993. A preliminary study of charcoalified plant fossils from theMiddle Jurassic Scalby Formation of North Yorkshire. Special Papers inPalaeontology, 49, 101–111.

C, G.T. 1977. Tree rings: a natural data-storage system. Biological Reviews,52, 349–383.

C, G.T. & A, S.R. 1990. Evidence of widespread fungal attack on UpperTriassic trees in the southwestern USA. Review of Palaeobotany andPalynology, 63, 189–195.

C, G.T. & C, W.G. 1984. Influence of environmental factors onthe wood structure of living and fossil trees. The Botanical Review, 50,357–448.

C, G.T. & C, W.G. 1985. Tree growth in the Mesozoic and earlyTertiary and the reconstruction of palaeoclimates. Palaeogeography,Palaeoclimatology, Palaeoecology, 52, 35–50.

C, G.T. & F, J.E. 1999. Fossil tree-analysis: palaeodendrology. In:J, T.P. & R, N.P. (eds) Fossil plants and spores: modern techniques.Geological Society, London, 245–250.

D, R. 1984. Evidence of bush fires during the Plio-Pliestocene in Africa(Omo and Sahabi) with aid of fossil woods. In: C, J.A. & VZ B, E.M. (eds) Paleoecology of Africa and the surroundingislands 16. Balkeema, Cape Town, 231–239.

D, M.E., M, R.E., D, J.G., B, D., F, C.,C, H.T., F, J.E., J, P., R, T., W, W., R, P.V.,P, N., K, A. & R, A. 1992. Australian Cretaceousterrestrial faunas and floras: biostratigraphic and biogeographicimplications. Cretaceous Research, 13, 207–262.

D, P.A.D. 1994. Structural and tectonic evolution of parts of theMesozoic fore-arc of Alexander Island, Antarctica. PhD Thesis. Universityof Leeds.

D, R.J. 1962. Photocontrol of growth and dormancy in woody plants. In:K, T.T. (ed.) Tree growth. Ronald Press, New York, 133–148.

D, R.P. 1993. Flood disturbance and the coexistence of species ina lowland podocarp forest, south Westland, New Zealand. Journal ofEcology, 81, 403–416.

D, P.W. 1979. Dendrochronological studies of indigenous NewZealand trees. New Zealand Journal of Botany, 17, 251–266.

E, C.E. 1982. Biological flora of New Zealand 8. Agathis australis (D.Don) Lindl. (Araucariaceae) Kauri. New Zealand Journal of Botany, 20,17–36.

F-L, H.J. 1999. Fire ecology of a Late Carboniferous floodplain,Joggins, Nova Scotia. Journal of the Geological Society, London, 156,137–148.

F-L, H.J. 2000. Fire ecology of the Carboniferous tropical zone.Palaeogeography, Palaeoclimatology, Palaeoecology, 164, 355–371.

F-L, H.J. & C, D.J. 2000. Cretaceous (Late Albian)Coniferales of Alexander Island, Antarctica. 1: Wood taxonomy, aquantitative approach. Review of Palaeobotany and Palynology, 111, 1–17.


F-L, H.J. & C, D.J. 2001. Leaf phenology of somemid-Cretaceous polar forests, Alexander Island, Antarctica. GeologicalMagazine, 138, 39–52.

F, L.A. & F, J.E. 1988. A guide to Phanerozoic cold polar climatesfrom high latitude ice-rafting in the Cretaceous. Nature, 333, 547–549.

F, J.E. 1984. The seasonal environment of the Purbeck (Upper Jurassic)fossil forests. Palaeogeography, Palaeoclimatology, Palaeoecology, 48,285–307.

F, J.E. 1986. Growth rings in Cretaceous and Tertiary wood fromAntarctica and their palaeoclimatic implications. Palaeontology, 29,665–684.

F, J.E. & C, M. 1992. Cretaceous fossil wood from the RaggattBasin, southern Kerguelen Plateau (Site 750). Proceeding of the OceanDrilling Program, Scientific Results, 120, 273–280.

F, H.C. 1976. Tree Rings and Climate. Academic Press, London.G, W.S., S, R.A. & A, S.R. 1960. Classification and

multiplicity of growth layers in the branches of trees. SmithsonianMiscellaneous Collections, 140. Publication No. 4421, Washington.

G, S.T. & R, J.H. 1990. Larches: deciduous conifers in anevergreen world. BioScience, 40, 819–826.

H, A.B. & S, R.A. 1996. Palaeobotanical evidence for a warmCretaceous Arctic Ocean. Nature, 380, 330–333.

H, R.S. & S, L.J. 1995. The angiosperm-dominated woody vegetation ofAntarctica: a review. Review of Palaeobotany and Palynology, 86, 175–198.

H, D.D. 1984. Adaptations to flooding with fresh water. In: K,T.T. (ed.) Flooding and plant growth. Academic Press, London, 265–293.

J, T.H. 1981. Palaeobotanical contributions to the geology of AlexanderIsland, Antarctica. PhD Thesis. University of Cambridge.

J, T.H. 1982. Fossil forests from the Lower Cretaceous of AlexanderIsland, Antarctica. Palaeontology, 25, 681–708.

J, T.P. & C, W.G. 1991. Fossil charcoal, its recognition andpalaeoatmospheric significance. Palaeogeography, Palaeoclimatology,Palaeoecology (Global Change Section), 97, 39–50.

K, S.R.A. & M, A.C.M. 1992. Marine molluscan constraints onthe age of Cretaceous fossil forests of Alexander Island, Antarctica.Geological Magazine, 129, 771–778.

K, A.M. & H, M.S. 1997. Paleoclimatologic analysis of a LateJurassic petrified forest, southeastern Mongolia. Palaios, 12, 282–291.

K, S., O, K., T, J. & F, T. 1997. Effect of thinning on thewood structure in annual growth rings of Japanese larch (Larix leptolepis).IAWA Journal, 18, 281–290.

K, T.T. 1984. Responses of woody plants to flooding. In: K,T.T. (ed.) Flooding and plant growth. Academic Press, London, 129–163.

LM, V.C. & H, K.K. 1984. Frost rings in trees as records ofmajor volcanic eruptions. Nature, 307, 121–126.

M, D.M. 1993. Hydrologic inferences from tree-ring studies on theHawkesbury River, Sydney, Australia. Geomorphology, 8, 147–164.

MC, J.J. & L, R.D. 1998. Late Cretaceous to early Tertiarysubduction history of the Antarctic Peninsula. Journal of the GeologicalSociety, London, 155, 255–268.

MC, J.J. & M, I.L. 1997. The age and stratigraphy of fore-arcmagmatism on Alexander Island, Antarctica. Geological Magazine, 134,507–522.

M, A.C.M. 1989. Field report of sedimentological studies in southeasternAlexander Island, Antarctica 1988/89. British Antarctic Survey FieldReport, AD6/2R/1988/G4.

M, A.C.M. & K, S.R.A. 1993. Lithostratigraphy of the uppermostFossil Bluff Group (Early Cretaceous) of Alexander Island, Antarctica:history of an Albian regression. Cretaceous Research, 14, 1–15.

M, H.S., H, S.P. & S, R.A. 1999. The seasonal climate of theEarly-Middle Jurassic, Cleveland Basin, England. Palaios, 14, 261–272.

N, G.J. & C, D.J. 2001. Fluvial sedimentology and revisedstratigraphy of the Triton Point Formation, Alexander Island, AntarcticPeninsula. Geological Magazine, 138, in press.

N, D.A., H, J.W. & B, A.E. 1988. The ecology of Dacrydiumcupressinum: a review. New Zealand Journal of Botany, 26, 37–62.

O, J. & S, G.H. 1995. Community dynamics of the New Zealandconifers. In: E, N.J. & H, R.S. (eds) Ecology of the SouthernConifers. Melbourne University Press, Australia, 81–119.

O-B, B.L. & U, G.R. 1997. Vegetation-induced warming ofhigh-latitude regions during the Late Cretaceous period. Nature, 385,804–807.

P, J.M., P, J.T., H, J.H. & S, R.A. 1987. LateCretaceous vertebrate fossils from the North Slope of Alaska andimplications for dinosaur ecology. Palaios, 2, 377–389.

P, J.T., D, I.L., K, E.M. & S, R.A. 1998. Palaeo-climatic significance of mid-Cretaceous floras from the Middle ClarenceValley, New Zealand. Palaios, 13, 149–159.

P, J.T., Z, A.M. & S, C.R. 1982. Rainfall patterns and thedistribution of coals and evaporites in the Mesozoic and Cenozoic.Palaeogeography, Palaeoclimatology, Palaeoecology, 40, 67–101.

R, J. & F, J. 1992. Responses of some Southern Hemisphere treespecies to a prolonged dark period and their implications for high-latitudeCretaceous and Tertiary floras. Palaeogeography, Palaeoclimatology,Palaeoecology, 99, 271–290.

R, H.G. 1996. Sedimentary Environments: Processes, facies andstratigraphy, 3rd Ed. Blackwell Science, Oxford.

R, P.V., R, T.H., W, B.E., ME M, M.J., D,C.B., G, R.T. & F, E.A. 1988. Evidence for low temperaturesand biological diversity in Cretaceous high latitudes of Australia. Science,242, 1403–1406.

S, A. & L, W. 1987. Frost survival in plants. Eco-studies 62.Springer-Verlag, Berlin, 221.

S, R.L., S, J., C, K.E., U, C. & H, R. 1985.Amazon rainforest fires. Science, 227, 53–55.

S, A.G., S, D.G. & F, B.M. 1994. Atlas of Mesozoic andCenozoic coastlines. Cambridge University Press, Cambridge.

S, R.A. & C, J.L. 1990. Climate change and the evolution ofhigh-latitude terrestrial vegetation and floras. Trends in Ecology andEvolution, 5, 279–284.

S, R.A. & P, J.T. 1986. Palaeobotanical evidence for cool northpolar climates in middle Cretaceous (Albian-Cenomanian) time. Geology,14, 703–706.

S, R.A. & P, J.T. 1990. Latest Cretaceous woods of the centralNorth Slope, Alaska. Palaeontology, 33, 225–242.

S, E.C. & V, R.B. 1968. Preservation of coast redwood on alluvial flats.Science, 159, 157–161.

S, S.P. & T, T.N. 1986. Wood decay in silicified gymnospermsfrom Antarctica. Botanical Gazette, 146, 116–125.

T, E.L., T, T.N. & C, N.R. 1992. The present is not the key tothe past: a polar forest from the Permian of Antarctica. Science, 257,1675–1677.

T, T. & B-B, Y.L. 1986. Xylotomy of fossil conifers from theQuiriquina Island, Chile. Comunicaciones, 37, 65–80.

T, E.M. 1990. Cretaceous and Tertiary vegetation of Antarctica: apalynological perspective. In: T, T.N. & T, E.L. (eds) AntarcticPalaeobiology: its role in the reconstruction of Gondwana. Springer,New York, 71–88.

U, C., K, J.B. & C, D.L. 1988. Fire in the VenezuelanAmazon 2: Environmental conditions necessary for forest fires in theevergreen rainforest of Venezuela. Oikis, 53, 176–184.

U, J.R. & L, W. 1974. Centroclinal cross strata, a distinctivesedimentary structure. Journal of Sedimentary Petrology, 44, 1111–1113.

V, P.J., S, B.W. & P, G.D. 1996. Evaluating concepts ofCretaceous equability. Palaeoclimates, 2, 139–158.

V, T.T. 1982. Regeneration patterns in Araucaria araucana forests in Chile.Journal of Biogeography, 9, 11–28.

W, P. 1991. Vegetation of New Zealand. Cambridge University Press,Cambridge.

W, J.M. & MG, M.S. 1996. Forest disturbance in the centralNorth Island, New Zealand, following the 1850 BP Taupo eruption. TheHolocene, 6, 399–411.

W, F.I. 1987. Climate and plant distribution. Cambridge UniversityPress, Cambridge.

Y, F. 1992. Effects of depth of flooding on growth and anatomy ofstems and knee roots of Taxodium distichum. IAWA Bulletin, 13, 93–104.

Y, F. & K, T.T. 1987. Effects of flooding, tilting of stems, andethrel application on growth, stem anatomy and ethylene production ofPinus densiflora seedlings. Journal of Experimental Botany, 38, 293–310.

Y, F., K, T.T. & W, K.E. 1987. Effect of floodingon growth, stem anatomy, and ethylene production of Pinus halepensisseedlings. Canadian Journal of Forestry Research, 17, 69–79.

Y, P.J., M, J.P., S, R.R. & D, F.P. 1993. False ringformation in Baldcypress (Taxodium distichum) saplings under two floodregimes. Wetlands, 13, 293–298.

Received 28 September 2000; revised typescript accepted 10 March 2001.Scientific editing by John Howell.


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Biodiversity and terrestrial ecology of a mid-Cretaceous, high