ELSEVIER
REVIEW
OF
PALAEOBOTANY
AND
PALYNOLOGY
Review of Palaeobotanyand Palynolo-ey8l ( 1994) 83-97
The paleoecologyof high-latitude Eoceneswamp forestsfrom
Axel Heiberg Islatrd,Canadian High Arctic
David R. Greenwood *, JamesF. Basinger
Depurttrtent o./ Geologit'ul Sc'ience,s,
Urtiversitt' o.f'Su.skutchewun,
Sask. 57N 0W0, Canudu
(Received March 9, 1993,revisedand acceptedJune 23, 1993)
Abstract
A record of high-latitude(79'55'N)Eocene polar vegetationis preservedon Axel Heiberg Island, Canadian High
Arctic. in megafloras in an alternating sequenceof swamp-coal, fluvio-lacustrine shale and channel-sandlithofacies
of the upper coal member of the Buchanan Lake Formation. Some exposuresof the swamp facies contain significant
fossil forests representedby autochthonous assemblagesof mummified in-situ tree stumps and forest-floor leaf-litter
mats. Exposed trunks within a single coal layer represent multiple stands of trees killed and buried at the different
times over 500 2000 yr. Stratigraphic examination of peat and coal megafossilfloristics of the "level M' fossil forest
at the centimetre-scaledemonstrates small-scalechanges in forest composition and swamp hydrology horizontally,
and temporal variation vertically within this layer. A mosaic of taxodiaceousswamp (Metesequoradominant with or
without Glyptostrobu.s).a mixed coniferous community. and Alruslfern bog appears to have produced both the leaf
mats and the in-situ stumps. with the taxodiaceousswamp the dominant peat-accumulatingphase. Taxodiaceous
layers are interpreted as areas of standing water which may have experienced seasonal water-level fluctuations.
Alnu.slfern (with or without other broadleaved angiosperms) communities reflect areas of slightly higher peat and
hence locally lower water tables, but may also reflect successionalprocesses.The areal extent and position of these
different hydrologically-controlled plant communities appearsto have changedthroughout the interval of accumulation
of the peat layer examined.
l. Introduction
Abundant Cretaceousand Tertiary megafloras
at high latitudestestily to the presenceof extensive
forestsin areaswhich today support only tundra.
These megaflorashave attracted attention due to
interestin both the ecosystemsthey reflect,and in
polar climatesduring periodsof Earth history with
warmer global temperaturesthan the present(e.g.
Jefferson,1982:Wolfe, 1985; Francis, 1986, l99l:
Spicer, 1990; Crame, 1992). In particular, some
commentators have suggestedthat environments
* Pre.santuddre.ss'.
Paleobiolo_eyDepartment, MRC NHB l2l.
S m i t h s o n i a nI n s t i t u t i o n . W a s h i n - e t o nD
, C 2 0 5 6 0 .U S A .
0034-6667'94.$7.00A 1994 ElsevierScienceB.V. All rishts reserved
. s s D / 0 0 3 4- 6 6 6 7 ( 9 3 ) E 0 0 8 5 - J
of past warm periods, such as the Late Cretaceous
and the Eocene,may offer insight into potential
present global climatic change (Spicer and
Corfield, 1992:Wing and Greenwood, 1993).
Arctic and Antarctic megafloras of Cretaceous
and Tertiary agerepresentterrestrial plant communities adapted to a yearly cycle of light and dark,
possibly representingprecusorsof modern deciduous broadleaved temperate and boreal forests
(Wolfe, 1980,1987:Spicer,1990).However, many
Tertiary megafloras from Arctic areas are either
poorly described or provide limited information
on the ecology of polar forest ecosystems.Detailed
analysisof the dynamics and character of Tertiary
vegetation,including that from the Arctic, is most
( 1994) 83 97
Pul.t'nolog.t'81
D.R. Graantrotxl,J.F. Bu:;ingc'rlRclic,rl
o./Pulueohotuu.t'utul
readily accomplishedthrough careful integration
of taphonomic and phytosociologicalinformation.
In-situ accumulations of plant megafossils,such
"fossil forests",provide
as found in
an opportunity
for high-resolution studies and, when combined
with information from a variety of contemporaneous biofacies, allow reconstruction of local and
intraregional vegetational mosaics (Christophel
et a l .. 1987; T aggar t , 1 9 8 8 ; G re e n w o o d , l 9 9 l ;
Wing and DiMichele, 1992).
A re c or d of high- l a ti tu d e (7 9 ' 5 5 ' N ) Eo c e n e
polar vegetation is preserved on Axel Heiberg
Isl a n d ( F ig. I ) , in t h e C a n a d i a n H i g h Arc ti c
Arch i p e lago ( B as inge r, l 9 9 l ; Ma c l n ty re , l 9 9 l ;
Greenwood and Basinger, 1993). The Axel
HeibergEocenemegaflorasincludeboth allochtho"fossil forest"
nous lacustrineand autochthonous
facies ( Fig. 2 ) which exhibit clear floristic differencesreflectingthe complexity of the local vegetati o n a l m os aic ( B as ing e r, l 9 9 l ). T h e d i s tri b u ti o n
of stumps. both horizontally and vertically within
the fossil forests of Axel Heiberg, indicates that
the exposedtrunks within a singlecoal layer likely
representmultiple generationsof trees(Greenwood
an d Ba s inger ,1993) .
Modern taxodiaceous[fu-vodiuntclistit'hunt(L.)
Richard] and tropical angiospermousswamp forests exhibit successionalchangesin speciescomposition and dominance associatedwith changing
local water tablesand nutrient levels( Davis, 1946:
Sp a ckm anet al. , 1969 :Mo o re , 1 9 8 7 ;M o o re a n d
Hilbert. 1992). Temporal and spatial variation in
the floristic characterof swamp forestsis reflected
in the plant fossilsand petrographiccharacter of
th e p e a t s( S pac k m ane t a l ., 1 9 6 9 ,Ma c C a b e , 1 9 8 4 ;
M o o r e , 1 9 8 6 . 1 9 8 7 :C o l l i n s o n a n d S c o t t , 1 9 8 7 ) ;
however,decayand post-depositionalpetrographic
changeswill also influence the representationof
sw a mp s pec iesas ( m e g a )fo s s i l s(C l y mo , 1 9 8 3 ;
Moore. 1989;Moore and Hilbert, 1992).
Autochthonous forest-floor leaf mats permit
more detailedexamination of the paleoecologyof
the Axel Heiberg fossil forests.Studiesof modern
suggestthat leaf
autochthonousplant assemblages
material will reflect both the spatial arrangement
and the productivity of the standing forest
(C h a n e y . 1924: F er gu s o n , 1 9 8 5 ; B u rn h a m e t a l .,
Axel
Heiberg
Fossil
O Forest
Locality
Fig. l. Location of Eocene megafloral sites of the Buchanan
Lake Formation. Axel Heiberg Island: geographical locale of
Axel Heiberg Island: area of interest on Axel Heiberg Island:
"Fossil
Ridge" area of fossil forests
and the location of
( a u t o c h t h o n o u sl e a f m a t s * ) a n d m u d s t o n e l o c a l i t i e s( U S 2 l 0
and USl88).
1992: Greenwood, 1992; Wing and DiMichele,
1992). Individual "fossil forest" organic layers
have been labelled with a letter code ( Francis and
McMi l l an, 1987;Franci s, l 99l ). B asi nger( l 99l )
noted that some taxa, particularly angiosperm
"pockets" within
seeds and fruits, occurred in
"level
(
M'. Greenwood and
Francis' l99l )
"level
Basinger(1994) found that floristicsof the
M" organic layer varied laterally at the kilometrescale,and that lithology within the level M and N
Pulynolo$ 81 ( 1994) 83-97
D.R. Greentrood,J.F. BusingerlRcvicwo./Puluaobotutt.r'und
Fig. 2. Sketch map of outcrop of level N organic layer and
o v e r l y i n - ep a l e o s o l( w h e r e p r e s e n t )s h o w i n g s a m p l e p o i n t s a n d
adjacent stumps (numbered) for the floristic analysis.Base
map from data compiled by Sweda et al. (in prep.); map
c o m p u t e r - e e n e r a t e db y C . L . G r e e n w o o d . S t u m p s ( O ) n o t
to scale.
organic layersvaried vertically and horizontally at
the centimetre- to metre-scale.Significant clay
partings within the organic layers appeared to
reflect a complex record of hydrological changes
in the swamp forest community. Stratigraphic
sequences
over fine time scales(< 1000yr) and the
representationof biota are likely to be incomplete
( Sadler, l98l ; Sadler and Dingus, 1982:'Taggart,
1 9 8 8 ) .I n t his r epor t, th e a u to c h th o n o u sl e a f-l i tte r
layer associatedwith the fossil forest of level //
( Fra n c is ,l99l ) is ex a m i n e di n d e ta i l .T h i s a n a l y s is
providesevidenceof forestdynamicsof this Eocene
polar forest community.
85
"level M' in Francis'
Basinger, 1993) is labelled
nomenclature ( Francis and McMillan, 1987:
Francis, l99l ) and this procedureis followed here.
Field work in l99l at the Axel Heiberg Island
Fossil Forests examined lithic variation at the
centimetre- to metre-scale within level .|y', and
floristic variation laterally within level M at the
kilometre-scale(Greenwood and Basinger,1993).
Each tree stump within level N was individually
numbered in a detailed survey ( T. Sweda, S.
Kojima [Nagoya Univ.] and K. Hyashi [Ehime
Univ.] unpubl. data) and these tree numbers are
used here as points of referencefor later reports.
A reconnaissanceof the level l/ exposureidentified
a number of areas to examine demography and
local succession(Fig. 2). Sevensiteswere selected
for detailed analysis of floristic variation with
depth on the basis of: ( I ) good surface preservation of megafossils,(2) proximity to tree stumps
selected for dendrological identification (Sweda
et al., unpubl.), and (3) apparent local succession,
basedon root systemstratigraphy and the presence
of severaltree stump size classesat the local site.
The first site represents one of several vertical
sections (trenches A-l ) through level 1/ discussed
in an earlier report (Greenwood and Basinger,
"trench
1993), labelled here
G". The remaining
sites represent surface trenches cut down into the
horizontally exposed leaf mat of the level 1/
organic layer.
2. Location of study and methodology
Eocenemegaflorason Axel Heiberg Island crop
out in an alternating sequenceof swamp-coal,
fluvio-lacustrineshaleand channel-sandlithofacies
of the upper coal member of the Buchanan Lake
Fo rm at ion ( Ric k etts , l 9 9 l ). E x p o s u re s o f th e
"fossil ridge" locale
swamp faciesat the so-called
( Fig. 2 ) contain significant fossil forests repreof mummisentedby autochthonousassemblages
fied in-situ tree stumps and forest-floor leaf-litter
ma ts ( F r anc is , 19 8 6 , l 9 9 l ; Ba s i n g e r, l 9 9 l ;
Greenwoodand Basinger,1993).[n earlier reports
the leaf-litter layers, or coal layers, have been
labelledwith a letter code designatingstratigraphic
position. The fossil forest and associatedleaf-litter
or organic layer discussedin this report and previo u s s t udies ( F r an c i s " l 9 9 l : G re e n w o o d a n d
2.1 Site l: verticalsec'tionat trench G
A vertical section had been cut through the level
.N organic layer (:litter mat), from the basal clay
that underlies all of level 1/, through a complete
organic layer, to the capping paleosol(Greenwood
and Basinger,1993).Analysisof this, and adjacent
sections,in the l99l field seasonhad identified a
complex centimetre-scalelithic stratigraphy with
significant laterally discontinuous clay partings.
Floristic variation with depth at I cm intervalsfor
the trench G complete section was examined by
Greenwood and Basinger( 1993) and those results
are repeatedin more detail here. The methodology
of sampling for this site and the other sites is
explainedbelow.
D. R. Greanrrood,J.F. Bu.siug<,rlRat'iatof' Pulucobotutt.t'tuul Pulytnlog.r 8l ( 1994) 83 97
2 . 2 S i r e s2 - 7
Several areas (sites 2-7 ) near particular tree
stumps were identified for detailed analysis
( Fig. 2). Each site was selectedto provide information on areas where stump positions and sizes
indicated potential changesin local floristics over
the combined lifespanof the stumps presentat the
site, particularly where multiple generations of
treeswere indicated.A number of samplingpoints
were identified at each site. Megafossils(needles,
shoots, cones, etc.) were sampled at I cm depth
intervalsin vertical sequenceat each point, extending from the exposed surlace of the litter mat to
the basal clay (where accessible).Samples were
removedas stratigraphicallycontiguoussquaresof
leaf mat approximately l0 x l0 cm. A semiquantitative measure of relative abundance was
made for each I cm interval by visual assessment
of all identifiablemegafossiltaxa in each sample.
Taxa representedby both sterile and reproductive
material were scoredas one taxon and abundance
assessedbased on the summed amount of both
organ classes,although the presenceor absence
and grossabundanceof reproductivematerial was
recorded.Unfortunately, at somesitesrecognisable
megafossilswere only encountered at the surlace
and so data are not available.Quantitative analyses of the level N vertical sectionswere based on
a 5 point abundance scale (whole or equivalent
recognisableorgans) used in Quaternary megafos, 9 8 6 , p . 6 0 8 ).
si l studies ( G r os s e- Bra u c k ma n n 1
The scale(slightly modified) is given below:
* : only a few pieces ( I -2 specimens)of tissue
remains(e.g.angiospermleaf pieces),representing <-1"/uof material; fruits, cones or seedsof
the taxon generallynot present.
I :l-3"1, of material, or 3-5 fruits, conesor seeds
of the same taxon.
2:4-10"1' of material; 5-14 fruits, conesor seeds.
J : I 0-25"/uof material; > 14 fruits, conesor seeds.
4 :2 5 -50' 1, of m at er i a l .
5: ) 50"1,of material.
The mudstonemegaflorascrop out in a separate
area from the fossil forests. Multiple sites along
an unnamedriver to the ENE of FossilRidge have
been collected over several seasons ( Basinger,
l 9 9 l ; B as inger and L e P a g e , u n p u b l . d a ta ).
Collection was from scree and was semiquantitative in that material of common taxa was
selectively collected and curated and can be
expected to be under-represented.Two of these
si tes,U S l 88 and U S 2l 0, are exami nedhere.
The channel sands, associatedwith both the
fossil forest outcrop and the mudstone outcrop,
are sparsely fossiliferous, but locally restricted
outcrop may contain small megafossil-richlenses.
Floras from this facies are examined qualitatively.
3. Results
3.I Sv'ctntp
Jtrcies (organic layers assot'iatedwitlt
"Jbs.silJbrests"
)
Level N organic layer, where complete, is typically 40-60 cm in thickness. Over the area where
"fossil forest"
the
stumps are exposed, multiple
sample points in level N indicated the depth of
section was much less ( 5-22 cm; Figs. 3-7) than
measured for the section at trench G (47 cm),
indicating that a truncated sequencehas been
preserved over this area. The thinner section of
organic layer from level l/ around the fossil stumps
may reflect deflation of the organic layer due to
post-exposureaeolian erosion,or more likely represents spatially variable rates of accumulation
(Sadler, l98l; Sadler and Dingus, 1982: Clymo,
1 9 8 4 ;C o h e n , 1 9 8 5 ) .
The principal megafossil taxa were scored for
each sample (and are listed as generic names),
although the presence of rare taxa were noted.
Conifers dominate the level N leaf mat, and systematic work on Pinaceae (e.9. LePage and
Basinger,1991,1992)and the presenceof attached
reproductive material for many of the taxa generally indicates the presence of modern genera
( Basinger, l99l ); however, some taxodiaceous
material would appear to representa speciesfrom
an undescribednew genus,and so is listed here as
"
undescribedTaxodiaceae".
Site I (vertical set'tiortat trenc'hG)
The results for this section were reported by
Greenwood and Basinger 11993; see fig. 12
D.R. Greertrrood,J.F. BusirtgcrlRevicn'o./
Pulueobotun.t'uncl
( 1994) 83 97
Pul.t'nolog.t'81
therein). The following detailed observations
were made:
( I ) t he dom inanc e(i .e . s c o reo f 5 o n th e a b u ndance scale) of Metasecluoictthroughout most of
th e s ec t ion( ex c eptw h e reb a rre n ),b u t n o t a t l 7 -1 8
and 9-7 cm depth;
( 2 ) the trend for Alnus to be richer lower in the
section, particularly between 20-6 cm depth, and
always richer or even dominant when Metasecluoiet
i s n o t dom inant ;
(3 ) most of the other taxa scoredin the analysis,
(GI.t'pto,stt'obu.t,
P,seudolurir, undescribed Taxodiaceae, and O:;nttmclu)are restricted to the lower
part of the section;
(4) some taxa (e.g.undescribedTaxodiaceaeand
O:;tutmclu)are quite sporadic in occurrence in
vertical section (a pattern repeated in horizontal
transects),or may be either richest towards the
base of the section (Glvpto.strohus)
or the middle
of the section (Pseucloluri.r).
Site2 ( tree 96 anclenvirons)
Seven sampling points (A-G) were identified
for analysis at this site. Sample points B and C
were adjacent to tree 93; points A, D and E to
tree 94: and sample points G and F were adjacent
to trees98 and 97. Samplepoints F, E and C were
found to be only fossiliferousat the surface and
so no data charts are provided for these sample
p o i n t s .T he r em aini n gs a m p l ep o i n ts (A, B, E a n d
G ) yielded megafossilsover depths varying from
4 to 22 cm from the exposed litter-mat surface
( Fig. 3a-d ). Glvptostrobuswas the most common
taxon at the surface lor sample points B and E,
whereas Metusecluoiuwas dominant at the surlace
o f sa m plepoint G ( F i g .3 d ). Pi n u ,rw a s d o mi n a n t
at the surlace of point A. Metu:;ecluoict
decreased
in abundanceor becameabsentwith depth in three
o f th e s ec t ionsex am i n e da t s i te B (F i g .3 a ,c ,d ) ,
although Metersequora
seedcones were found at F
a n d 8 c m at point G .
In three of the sections( Fig. 3b-d ) angiosperm
remains were most abundant over short intervals
in the lower part of the sections,just above clay
partings barren of plant remains. Angiosperm
seedswere encounteredat D, F and 8 cm depth at
point G. In contrast to points B, E and G, angiosperms were moderately abundant in the upper
part of the secti on at poi nt A (Fi g.3a). The
megafossil taxa ?Chamaet'yparis and Pseudolarix
were not recorded in any of the sectionssampled
at site 2. Pinus and the undescribed Taxodiaceae
taxon were only recorded at points A and B,
respectively(Fig. 3a,b). A previously unrecorded
bipinnate fern was encounteredat point E at 3 cm.
Site3 (trees14-17)
Three samplepoints (A-C) were identifiednear
trees l4 and l7 at site 3. Only two of thesepoints
( B and C ) yielded recognisablemegafossilsbelow
the litter-mat surlace and so data charts are
only presented for these sections ( Fig. 4a,b).
Angiosperms were dominant at the surface
(0-l cm) of all three sample points. Metusecluoicr
was a subdominant over this interval, although
seed cones were found at I cm at both points B
and C. Angiosperm leaf remains and Metasecluoicr
decreasedsharplyin abundancewith depth in these
sections. At points B and C Glyptostrobushad a
minor abundancepeak in the middle of the sections
(2cm depth in both cases).No other conifer taxa
were encounteredat any of the samplepoints and
no fern remains were recorded.
Site4 (tree74)
Three points (A-C) were sampled near tree 74
at site 4. The sectionsanalysed varied in depth
from 5 cm (poi nts B and C ) to 8 cm (poi nt A ).
Metusecluoiowas the dominant taxon in each secti on over much of the verti cali nterval(Fi g.5a-c),
reaching 100"1,of material at the baseof the section
at point A. Significant floristic differences were
recorded at some depths in the section A. The leaf
litter in the sectionat point B ( Fig. 5b ) was almost
completely composed of Metusequoiafoliage, with
only trace amounts of Osmunda,the undescribed
Taxodiaceaetaxon and Glyptostrobusrecorded at
the I cm level. Moderate amounts of angiosperm
leaf material was found at the I cm level in the
section at point C, and significant amounts of
Glyptostrobusat 3 cm (Fig. 5c).
The top 3 cm of leaf litter in the sectionat point
A was quite rich, recording the following taxa:
Glyptostrobus,
Metasequoia,
undescribed
Taxodiaceae, Osnunda, other unidentified ferns,
and angiosperms(including a small leaf type; see
88
D.R. Grautttttttl. J.F. BusirtgcrRclic,rl of Puluuthoturt.t'ttttcl
ktl.r'nolog.t'81( 1994)83 97
(b)
(a)
c)
()
at
Cg
5.
4.
3
2
1
c)
o
Osmunda
ang,tosperms
PseuZlolarix
unk Taxodiaceae
Pinus
Glyptostrobus
Metasequioa
Cd
E
I
4
3
2
Osmunda
angrosperrns
Pseudolarix
unk Taxodiaceae
cl
Pinus
Glyptostrobus
Metasequioa
depth
(cm)
depth
(cm)
(d)
(c)
5l
c)
()
Cd
\t
.o
Cg
(l)
4)
3.
2.
I
0
tzt-I
o
cd
r5
I
CU
32.
I
0
Y,rfi##,itu'
, pixrfrt axoataceae
Glyptostrobus
depth(cm)
Osmunda
angiosperms
unkTaxbdiaceae
Glyptostrobus
Metasequioa
/
depth(cm)
F i g . 3 . R e - l a t i r ca b u n d a n c co l ' p r i n c i p a l t a x a w i t h d e p t h i n v e r t i c a ls e c t i o nl b r p o i n t s r " l e a trr e e 9 6 . ( a ) S e c t i o na t p o i n t A . ( b ) S e c t i o n
a t p o i n t B . ( c ) S e c t i o na t p o i n t E . ( d ) S e c t i o n a t p o i n t G . B a r r e ni n t e r v a l s( i . e . n o t a x a s c o r e d )c o r r e s p o n dt o c l a y p a r t i n g s[ A p p l i c s
t o a l l s c - c t i o n(sF i g s . 3 7 ) l
si te 7 des c r ipt ion) .A s i g n i fi c a n tb a rre n i n te rv a l
occurred at 4 cm in the point A section. above
wh i ch (at 3 c m ) a m in o r p e a k i n a n g i o s p e rma n d
was
O,vtttmduremains was recorded. Gl.rpto.;trohu.s
donrinant and Metu.secluoiupresent in lesser
a mo u nt sin t he t op 2 c m o f th e p o i n t A s e c ti o n .A
significant surface exposure at this site (near A
a n d C ) was par t ic ula rl yri c h (6 0 7 0 " /ui)n l e a f a n d
cone material of the undescribed Taxodiaceae
(10"1,).
taxor"rin associationwith Gl_r'pto.strobu.s
Site J ( trce 4l uul environs)
Three samplepoints (A C ) were identifiednear
tre e 4 l at s it e 5. T he s e c ti o n sa n a l y s e d(F i g . 6 a -c )
varied in depth from 3 cm ( point A ) to 5 cm
(poi nts B and C ). S ampl epoi nts A and B w ere I
and 2.5 m from tree 4l B respecti vel y(i n a l i ne
trendi ng E N E ), and poi nt C w as 0.5 m from tree
4l A (W S W ). Metusecl uoi uw as the domi nant
taxon over much of the section lor points B and
Y umateri alat 3 cm
C (Fi g. 6b,c),representi ng95' of
was less
depth at point B; however, Metusequoicr
abundant at the surface ( I -2 cm) than lower in
the secti on ( 3-5 cm). A t poi nt A ( Fi g. 6a)
Metu,sequolrrwas most abundant at the surface
( I cm), becomi ngl essabundantw i th depth (2 cm)
was abundant
and absent at 3 cm. Gll,plostnrbu.r
at point A becoming dominant at 3 cm. but was
D.R. Greentroorl,J.F. BusingarlRt,r'iol of Pulueobotun.t'tnd Pul.t'nolog.t'81( 1994) 83 97
(a)
';l
q)
()
cd
3!
tr
2l,
0
€
-o
GI
Osmunda
anflosperms
PseuZlolarix
unkTmodiaceae
Chamaecyparis
Glyptostrobus
Metasequioa
depth
(cm)
(b)
;l
(l)
()
e,
'oc€
I
cd
32.
1
0
Osmunda
angiosperms
PseuTlolarix
unk Tuodiaceae
Chamaecyparis
Glyptostrobus
Metasequioa
depth
(c-)
r
4
Fig. 4. Relative abundance of principal taxa with depth in
v e r t i c a ls e c t i o nl o r p o i n t s n e a r t r e e s l 4 1 7 . ( a ) S e c t i o na t p o i n t
A . ( b ) S e c t i o na t p o i n t B .
lower in abundance in the section at point C
becoming much less abundant with depth below
2 cm. Glvptostrobus was present as only a trace
through most of the section at point B. Material
removed during excavation of a trench leading
from tree 4lB to 4lC was rich in Glyptostrobus
(*)and
(5) with trace amounts of ?Chantaec'yltaris
small amounts of Pseudolarix( 1). The upper 3 cm
of the section at point C was quite diverse,with
the all but one of the scored taxa present at
different depths. Angiosperm leaveswere recorded
89
over most of both of the sectionsat points B and
C; however, angiospermswere recorded only as a
trace between 2 and 4 cm at point B, but at
moderate amounts at I cm at point B and over 2
to 4 cm in the point C section. ?Cltctmctec'yparis
was recordedin trace amounts at points B and C,
exceptingat 2 cm at point C.
Site6 ( tree 62)
A pit was dug 60 cm southeastof the centre of
the large stump of tree 62. Despite the appearance
of abundant megafossilson the surface,only trash
(unrecognisablemegafossilremains) was encountered throughout a 6 cm section examined from
this pit. The top 3 cm contained abundant fine
roots suggestingthat this area was an active soil
humic horizon. A trace amount of Glyptostrobus
leafy twigs was found in this material. Between3
and 6 cm the leaf-mat was also trash. but at this
depth trace amounts of well degradedangiosperm
leaveswere found.
S i re7 (tree2l )
Five sample points (A E ) were identified near
tree2l at site 7. Only the sectionsat samplepoints
A. B. D and E were fossiliferousbelow the littermat surlaceand so data charts are only presented
for thesepoints (Fig. 7a-d). The sectionsanalysed
varied in depth from 5-7 cm ( points A, D and E )
to l 2cm (poi nt B ). S i gni fi cantbarren i nterval s
(clay partings)were presentat 3-4 and 6-7 cm in
the point D section(Fig. 7c), at 4 cm in the point
E s e c t i o n( F i g . 7 d ) , a n d a t 7 a n d l l c m d e p t h i n
the point B section( Fig. 7b ). Preservationof plant
megafossilswas generally poor for much of secti on D .
Metusequoiqwas dominant for the whole section
at point E (Fig. 7d ), and all but the top 2 cm
(0-l cm) of the secti onat poi nt A (Fi g. 7a), w i th
a peak abundanceof 80-90"1,of materialat 3-4 cm
depth at point A. Three intervalswithin the point
B section were dominated by Metasequoia: 3-4,
9- 10, and I 2 cm depth ( Fig. 7b). Metusecluoioseed
conesw ere found at 3,8 and 9-l 0cm at poi nt B .
Significant other occurrenceswere a Glltptostrobus
spike at l-2 cm in the point E section,an undescribedTaxodiaceaetaxon spike at l-2 cm (and a
lesser spike at 6 cm) in the point B section, an
D.R. Greunroocl.J.F. Bu:;ingarlRavien'o/Pulueohotcut.vcuul
Pulynolog.t'81( 1994) 83-97
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7
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32,
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depth(c-)
{',ortff;f,/fl,
rseuaolartx
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Metasequioa
depth(c-)
(c)
a)
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ct
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I
cl
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4.
3.
2,
I
0
W'
^ynK laxocltaceae
cnamaecyDarts
Glvptostrobits
Metasequioa
#f
z
J
depth (cm)
4
t 5
F i g . 5 . R e l a t i v ea b u n d a n c eo f p r i n c i p a l t a x a w i t h d e p t h i n v e r t i c a ls e c t i o nf o r p o i n t s n e a r t r e e 7 4 . ( a ) S e c t i o na t p o i n t A . ( b ) S e c t i o n
a t p o i n t B . ( c ) S e c t i o na t p o i n t C .
angiospermspike at the surface(0 cm) of the point
A section (and significant abundance scores
between I 3 cm), and an angiospermspike above
a barren clay parting at 2 cm in the point D
section.Angiosperm leaveswere also abundant at
5 cm in the point B sectionwith lesserspikesat 9
a n d 1 2c m dept h in t h i s s e c ti o n(F i g . 7 b ); i n e a c h
case 0- I cm above clay partings. The most
common angiospermleaf-type(at all points at site
7 ) was a small leaf (non-Betulaceae) about
I x 2 cm, however,angiospermdiversity was quite
high in some sections(especiallyat point B) with
at least 4 types seen, including Betulaceaeand
?Juglandaceae,
and a narrow leaf (undescribed)at
5 cm at point E. The conifer taxa, Chunuect'paris
and Pseudolarix were not encountered in anv of
the site 7 sections.
megafloras
3.2 Mudstone und c'lrunnel-scrndstone
Detailed examinationand systematicanalysisof
the megaflorasof the channelsandsand mudstones
are not presented here. However, generalisations
can be drawn from a morphotype analysis and
initial generic survey of the main mudstone-facies
sites,and particularly USl88. These sitesprovide
some insight into diversity and the floristic character of the interfluvial vegetation that was contemporaneous with the taxodiaceous swamps
representedin the "fossil forests" and associated
9l
D. R. Grecnyoocl,J.F. Bu.singer,tRevictol' Puktaobotutt.runtl Pul.t'nolo$ 8l ( 1994) 83 97
(a)
(b)
q)
o
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'1,
-o
cl
4.
3
2
I
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o
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Osrnunda
' pfttflhloYo'r^'
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Chamaecyparis
Glyptostrobus
Metasequioa
-
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I
43.
2'
I
0
t 2
depth
(cm)
Osmunda
anQtosDerms
PseuVolhrix
unk Taxodiaceae
Chamaecyparis
Glyptostroliis
Metasequioa
a
depth(cm)
(c)
(l)
C)
Cd
€
p
Cg
4)
3.
2,
I
0
l- Oqrnunda
^angp,spe.rms
rseuaotartx
unk Tuodiaceae
Chamaecvparis
Glyptostroiis
Metasequioa
J
depth(cm)
4
5
F i g . 6 . R e l a t i v ea b u n d a n c eo f p r i n c i p a l t a x a w i t h d e p t h i n v e r t i c a ls e c t i o nf o r p o i n t s n e a r t r e e 4 1 . ( a ) S e c t i o na t p o i n t A . ( b ) S e c t i o n
a t p o i n t B . ( c ) S e c t i o na t p o i n t C .
organic layers.Sporadic occurrencesof megafossils
( principally coniferous seedcones, but also some
angiosperm fruits and seeds;Basinger, l99l) in
the channel sands allows some understandingof
additional plant communities in the regional
mosaic.
Basinger( l99l ) noted the dominanceof angiosperms in the mudstone megafloras,compared to
"fossil forest" organic layers,
the coniferous
particularly platanoids, Ulmaceae (cf. Zelkova),
Betulaceae (Alnus, Betulu), and Juglandaceae.
Coniferous foliage (especially Metasequoiu) and
cones were collected at all sites, but were never
common in the mudstonefloras.Somebroadleaved
taxa have quite localisedstratigraphicand spatial
occurrences,being collected at only I or 2 mudstone sites, but not from the same sites in subsequent seasons.For example, leavesof Ginkgo have
been collected at only one site, and putative leaves
of a quercoid ( Fagaceae) taxon were collected
lrom site USl88 during two separateseasons,but
not during intervening collecting seasonsat the
same site.
Very little mudstone outcrop has been sampled
at the Fossil Ridge as its integrity is destroyed by
frost action within the thin active layer overlying
permafrost. However, ironstone nodules found
"cones"
in the paleosols rarely contain Alnus
( Basinger, l99l ) and leaf impressionsof platanoids
and betulaceousleaves.Minor clay-partingswithin
92
D.R. Gracttrrood,J.F. BusirtgcriRo'icrlof Pulueoltottut.t'ttnd
Pulynolog.t'81( 1994) 83-97
(a)
c)
O
cd
p
cg
(b)
()
()
il
.dc6
32.
1,
0
s(s
Pg!#i\l?fiy'
'd
2l,
0
unk Taxodiaceae
Chamaecvparis
Glyptostrobus
Metasequioa
-
depth(cm)
(d)
c)
()
o
Cg
p
CC
I
32.
1
0
'ocd
Osmunda
P!!r'si3f8fi{'
ry
v
^rnK tcrxoaaceae
C:namaecypans
Glvptostrobis
Methiequioa
7
'
2 3 ;
r
depth (cm)
6
.o
CE
4.
3
2
1
q/
l 2 ?r >+. . y
LnamaecvDar$
Glvptostrob'us
Mefrisequioa
5 6 7
n
t
Osmunda
p3\fr'fif"fi{'
W
y AnK IAxoaraceae
depth(cm)
F i g . 7 . R e l a t i v ea b u n d a n c eo f p r i n c i p a l t a x a w i t h d e p t h i n v e r t i c a ls e c t i o nf o r p o i n t s n e a r t r e e 2 1 . ( a ) S e c t i o na t p o i n t A . ( b ) S e c t i o n
a t p o i n t B . ( c ) S e c t i o na t p o i n t C . ( d ) S e c t i o n a t p o i n t D .
organic layers may be dominated by angiosperm
leaves.These occurrencesrepresenttaxa encountered in the mudstone floras.
In th e US l88 f lor ul e th e d o mi n a n ts (> 4 0 " 1 , o f
collectedmaterial, > 50 70'1,of outcrop) in succesive collections(i.e. samplescollectedin different
years at the same site) were Betulaceae(cf. Betulu)
or aff. Quercus( Fagaceae),with smaller amounts
of Ulmaceae (cf. Zelkover),magnolids (2 species)
and Cercidophvllutn-complexleaves.Minor though
commonly present broadleaved elements in the
surveyed site collections included: Ginkgo,
Juglandaceae, aff.
Plutunites and
other
Platanaceae, other hamaleliids, and Alnus
(Betulaceae). Other stratigraphically equivalent
si te si n t he s am e out c ro p a s U S l 8 8 w e re ri c h i n
either Cercidopltyllum-complex leaves, or platanoi ds and other hamal el i i ds (e.g. U S 2l 0).
Modern forest litter studies have demonstrated
that leaves from canopy trees numerically dominate litter, and hence fossil leaf assemblages
( Burnham, 1989; Burnham et al., 1992:
Greenwood, 1992): it is likely therefore that these
megafloras are reflecting forests dominated by
Betulaceae-Quercoideaeand Cercidophyllum-complex producing canopy trees respectively. Local
areas were of moderate to low diversity (typically
10-12 speciesin 100-200leaf samples),but site to
site variation in speciespresenceindicatesa varied
and moderately diverse broadleaved-angiosperm
forest community. Whether the site to site variation reflectscontemporaneousvariation in species
93
D.R. Greenrroocl,J.F. Busingerf Revietro/'Pulueoboturtt uncl Pull'nolog.v8l ( 1994) 83-97
membershipdue to microsite differences,or successional variation associatedwith the shifting positi o n o f t he r iv er c han n e l s(e .g . S a l o e t a l ., 1 9 8 6 ),
is not clear.
Based on NLR analogy, these broadleaved forests were predominantly if not exclusivelycomposed of deciduous plants. Foliar physiognomy
supports this interpretation. The mudstone leaf
floras are composed exclusively of leaves with a
length to width ratio ( L:W ) close to l: I ( L/W
1.0), and toothed, lobed or partly lobed forms
were common in these floras, as were leaveswith
their widest point in the lower third of the leaf.
Litter collected under tropical to temperate evergreen broadleaved rainforests is dominated by
si mp l e ent ir e leav e s th a t h a v e a L :W> 3 :l
(LlW> 3.0) and with the widestpoint in the middle
third of the leaf (Greenwood, 1992:Table I ). Litter
collectedunder dominantly deciduousbroadleaved
cool temperate and boreal forests is dominated by
toothed leaveswhere the L: I,tr/is close to l:1, with
the widest point in the lower third of the leaf, and
lobed and partly lobed leavesare common, as seen
for the mudstone megafloras (Table l). Several
studies have indicated that L:W reflectsaspectsof
climate (Hall and Swaine, 1981;Christophel and
Greenwood, 1988;\4/olfe, 1990, 1993:Greenwood.
1992:Gregory and Chase, 1992). Our unpublished
data (e.g. Table I ) suggestthat Tertiary leaf meg-
afloras dominated by leaveswith a L:W close to
l:l are reflecting deciduous broadleaved forests.
The channel sands associated with both the
mudstone floras and the organic layers at Fossil
Ridge are only sparselyfossiliferous.Scarcecones
and rare foliage of Pseudolarix, Picea, Pinus, other
taxa within the Pinaceae, Taxodiaceae and
Cupressaceae,and rare Carya seedsare the main
recognisablemegafossils( Basinger, l99l; LePage
and Basinger, 1991, 1992). Logs of various sizes
also are encountered and rarely in-situ stumps
have been found on stabilised point bars. A few
exposuresof the channel sands at the Fossil Ridge
site are richly fossiliferous over very short horizontal and vertical areas of outcrop, representing
channel lags. Some of the cones and angiosperm
seedsfrom thesechannel sands representtaxa also
"fossil forest" organic layers, but
found in the
LePageand Basinger(1992) reported that different
speciesof Picea are found in the channel sands
and the organic layers (forest floor/swamp facies),
respectively.
Channel-sand megafloras generally preserve
riparian vegetation (Wing and DiMichele, 1992).
However, based on our observationsof a number
of sites,including areas distal and proximal to the
conglomerate wedges of the alluvial fan-meander
belt complex defined by Ricketts ( l99l ), it appears
likely to us that the coniferous megafossilscharac-
Table I
Summary of mudstone facies megaflora (2 successivecollections from the USl88 florule); modern litter samples for comparlson:
Aspen Parkland ( Boreal broad-leaved deciduous forest, Namekus Lake, Sask.). Maple-oak-poplar-beech Deciduous Forest
(Kingsmere and Pink Lakes, Gatineau National Park. Quebec), Notophyllous Broad-leaved Evergreen Forest (Washpool National
Park. New South Wales), and Paratropical Tropical Rainforest (Mulgrave River. NE Queensland)
Site
Specimens
Morphotypes
LIW^
(Zr
spp. entireb
u s l 8 8( 1 9 9 0 )
u s l 8 8( 1 9 9 r )
I15
63
l3
l0
1.6
t.4
16.7
10.0
Namekus Lake
r00
9
1.4
0
Kingsmere Lake
Pink Lake
r06
64
ll
8
1.5
1.3
0
0
Washpool National Park"
200
7
3.9
t4.3
Mul-eraveRiver"
200
20
4.7
95.0
"Mean of all leaf specimensin sample.
bSimple percent (i.e. leaf specieswith both entire and non-entire specimensscored as non-entire).
"Sub-samplesfrom original data set of Greenwood (1992. tables xt and xvtl).
D.R. Grecrttrood,J.F. Bu.singarlRcvicvo/ Puluaohotun.t'tuul
Pul.t'nolog.t'8l( 1994) 83-97
teristicof the channel sandsof the BuchananLake
Formation also representsthe upland ( headwater)
vesetationof this area in the Eocene.
4. Discussion
The leaf-litter mats (organic layers) of the
Geodetic Hills "fossil forests", Axel Heiberg
Island. representa substantial record of Eocene
near-polarforestgrowth. Greenwoodand Basinger
( 1993) examinedtwo of theseorganic layers,levels
M and ,^/. and concluded that variation in the
floristic character of the level M peat layer over
the kilometre-scalereflected a Metasecluoiu-dominated swamp forest, but that vertical variation at
within a 47 cm sectionthrough
the centimetre-scale
level N implied a seriesof complex shifts between
severalfloristic associationsreflecting responsesto
local hydrological conditions. Greenwood and
Basinger( 1993) calculatedthat the organic layer
of level // represents500-1000 and probably as
much as 2000yr of accumulationof plant megadetritus, and that multiple standsof the swamp forest
are juxtaposed. Patterns of presenceand absence
and abundancebetweensiteson the level N littermat, and variation at depth within the forest-floor
litter of this Eocenepolar forest,have beeninvestigated in more detail here.
Modern autochthonous accumulations of leaf
litter in deciduous hardwood forests reflect the
canopy biomass and spatial distribution of the
standinglorest ( Burnham et al., 1992).It is reasonable to assumethereforethat the observedpatterns
of vertical and horizontal floristics for the "fossil
forest" similarly will reflect forest structure and
floristics. However, the study presentedhere suggeststhat the incompletenessof the litter mat in
vertical sequence from point to point, either
through erosion andlor changes in depositional-hydrological character(from peat accumulation
to clay), or in-situ decay and compaction within
organic layers, contributes much to the observed
patterns of floristics (e.g. Spackman et al., 1969:
Sadler and Dingus, 1982: MacCabe, 1984;
Moore, 1987).
Metu.sequoiu
was commonly the dominant mega-
f,ossil taxon over at least part of any vertical
sequencethrough level 1/, and typically over most
of the vertical leaf-mat accumulation. Angiosperm
leaf remains were common at all level l/ sites
examined,but usually as either trace amounts or
at different stratigraphic levels from the main
Metusecluoicr
abundancepeaks. In some instances,
angiosperm rich layers were associatedwith the
top of clay partings (e.g. Figs. 3b-d, 7c,d); clay
partings correspond to barren depth intervals.
Conifer taxa other than Metusecluoiawere sporadic
in occurrence between sites, within sites, and at
depth within individual sections. In particular,
Gll,ptostrobuswas presentat all sites,but either as
a rare or uncommon component of the leaf-mat,
or narrowly restrictedwithin the analysedsections.
Glyptostrobus was usually absent or in low
amounts where Metasequoia was abundant or
dominant. The conifers Pseudolarix, ?Chamaecyparis, Pinus and the undescribed Taxodiaceae
taxon were only present at a few sites, and were
quite restricted stratigraphically at each site where
they were present. These taxa were typically present in low amounts when co-occurring,and more
typically one of these conifers was present as the
dominant in place of Metasequoia, or as the
co-dominant either with Metasecluoiaor lesscommonly, with a secondtaxon.
Sadler and Dingus ( 1982) cautioned that short
stratigraphic sequencesare highly likely to be
incomplete,particularly where significantlithological changes occur cyclically within the sequence
(such as the shift from peat/coal to clay observed
in level //). The stratigraphically restricted nature
of the litter accumulation of the non-Metasecluoiadominated plant associations(i.e. l-3 cm depth),
however, suggests that these communities were
short-lived within the period of accumulation of
the whole level N litter-mat (12-60 cm). Common
members of these associations were: ?Chamaec'ypuris, Pseudolarix, Pinus, various angiosperms
(including but not restricted to Alnus and other
Betulaceae) and the undescribed Taxodiaceae
taxon. The limited lateral detectionof theseassociations also implies that they occupied only small
areas (2-5 m radius). This may suggestthat they
reflectedgap-phaseprocesses(regenerationafter a
D.R. Greenrrood.J.F. Busingarf Ret'iet of'Pulueobotuny untl Pul)'nolog.v81 1 1994) 83-97
canopy tree [: Metusecluolc]dies). The angiosperm
occurrencesand some of the diverseconifer associations also may reflect larger scalesuccessionafter
local flooding, as evidenced by the presence of
significantpeaks in abundanceof some taxa (such
as Alnus) stratigraphicallyhigher than significant
clay partings.
The analysispresentedabove providesan initial
look at a high latitude Eocene forest landscape,
and provides some insight into local floristic
changesover short time frames within a swampforest community. These plant communities have
no exact modern analogue as today no forests
occur at equivalent high latitudes. The diverse
regional mosaic of angiosperm-dominatedfloodplain forests, and taxodiaceous swamp forests,
mosaicsof Betulaceae,and
with their successional
conifers, is in direct
pinaceousand cupressaceous
contrast to the modern tundra environment of
theseareas.
5. Conclusions
The following conclusionswere reached:
(l) Metosequoicr
is the dominant contributor to
litter accumulationover the time span represented
by the most complete sections examined
( 1000-2000yr) and is therefore the main canopy
dominant of these Eocene polar swamp forests;
angiospermsmay be presentas either a trace or in
si g n if ic antam ount s .A l n u s i s c o mmo n l y th e ma i n
angiospermtaxon, although severalas yet unidentified angiospermtaxa may be common over short
vertical intervals.
(2 ) Lithic variation with depth at differentpoints
over the level N layer suggeststhat short-term
changesin local swamp hydrology, perhapsrepresentingminor flooding events,occurred at different
points at different times during peat accumulation
(Greenwood and Basinger, 1993); the association
of some episodesof floristic changeat depth with
the clay partings implies recovery or successional
processesoccurred within these forests.
( 3 ) The short interval ( I -3 cm depth) and short
distance(2-5 m) changesin floristics in the level
// leaf mat impliescyclesof changeat small scales.
95
(4) Glvptostrobusis uncommon, but where it is
present in significant quantities, Metasecluoiais
usually not dominant and angiospermsare either
absent or present in low quantities; other taxa,
particularly conifers such as Chunuec'yparis,
Pseudolurix and an undescribed Taxodiaceae
taxon, are present only sporadically.Where present,theseother conifer taxa may co-occur,or one
conifer taxon may be dominant.
(5) The sequenceof presenceand absenceof,
floristic associations in vertical sections through
level 1/, is different at each point examined. This
suggests that some parts of level 1/ reflect an
incomplete or truncated record of the floristic
history, but also that the plant community varied
in composition horizontally.
A mosaic of taxodiaceous (Metusecluoia*
Glyptostrobus)swamp forest, mixed conifer forests,
and Alnu.r (* other broadleaved angiospermsand
Osmunclufotherferns) bog, appears to have produced both the leaf-matsand the in-situ stumps,
with the Metusecluoiaswamp the dominant peataccumulating phase.Taxodiaceouslayers are interpreted as areas of standing water which may have
experienced seasonal water-level fluctuations.
Alnuslfern communities reflect areas of slightly
higher peat and hence locally lower water tables,
or may reflectareasof early successionafter disturbance. The areal extent and position of these
differenthydrologicallycontrolled plant communities appears to have changed throughout the
interval of accumulation of the peat layer
examined.
Detailedreconstructionof the paleoenvironment
reflectedin the mudstone and channel-sandsfacies
is unwarranted at this stage;however,the mudstone-facies megafloras examined in this present
report (U S l 88 and U S 2l 0; seeal so B asi nger,l 99l )
reveal temporal and spatial variation in dominance
and composition of the floodplain forests of this
area of the Arctic in the middle Eocene.
Broadleaved deciduous forests containing a moderately diverseassemblageof Betulaceae(cf. Betulct
and Alnus), Fagaceae (aff. Quercus), Ulmaceae
(cf. Zelkovu), Juglandaceae,Ginkgo, platanoids'
other
and
Cerc'idopltyllunt-complex plants
broadleavedplants with modern NLR's that are
D.R. Greernroocl,J.F. BusingerlReviex'o/'Pulueobotcul'und Palvnolo7),81 ( 1994) S3-97
deciduous appear to reflect successionalor microsite variation within this floodplain environment.
Acknowledgements
We thank E. Mclver and B. LePage(Sask.), L.
Savard ( Laval ), T. Sweda and S. Kojima
(Nagoya), and K. Hyashi (Ehime), for field assistance during the 1992 field season, and C.
Greenwoodand C. Nelson for assistance
preparing
and analysing mudstone-flora and modern leaflitter samples. This research was made possible
through field support from the Polar Continental
Shelf Project, and Natural
Sciences and
EngineeringResearchCouncil (Canada)Operating
Gra n t N o. O G P 0001 3 3 4to J F B , a n d w a s c o mpleted while DRG was a NSERC International
Postdoctoral Fellow at the University of
Saskatchewan.DRG also acknowledgesthe provision of support and facilities during manuscript
preparation while a Smithsonian Postdoctoral
Fellow at the National Museum of Natural
History. We thank also W. DiMichele, B. LePage
and E. Mclver for their comments on the
manuscript.
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