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Permian polar forests: deciduousness and environmentalvariationE. L . GULBRANSON,1 ,* J . L . ISBELL,1 E . L . TAYLOR,2 , 3 P . E . RYBERG,2 , 3 T . N. TAYLOR2 , 3
AND P. P. FLAIG4
1Department of Geosciences, University of Wisconsin-Milwaukee, Milwaukee, WI, USA2Department of Ecology and Evolutionary Biology, Natural History Museum and Biodiversity Institute, University of Kansas,
Lawrence, KA, USA3Division of Paleobotany, Natural History Museum and Biodiversity Institute, University of Kansas, Lawrence, KS, USA4Bureau of Economic Geology, University of Texas-Austin, Austin, TX, USA
ABSTRACT
Forests are expected to expand into northern polar latitudes in the next century. However, the impact of
forests at high latitudes on climate and terrestrial biogeochemical cycling is poorly understood because such
forests cannot be studied in the modern. This study presents forestry and geochemical analyses of three
in situ fossil forests from Late Permian strata of Antarctica, which grew at polar latitudes. Stem size mea-
surements and stump spacing measurements indicate significant differences in forest density and canopy
structure that are related to the local depositional setting. For forests closest to fluvial systems, tree density
appears to decrease as the forests mature, which is the opposite trend of self-thinning observed in modern
forests. We speculate that a combination of tree mortality and high disturbance created low-density mature
forests without understory vegetation near Late Permian river systems. Stable carbon isotopes measured
from permineralized wood in these forests demonstrate two important points: (i) recently developed tech-
niques of high-resolution carbon isotope studies of wood and mummified wood can be applied to permin-
eralized wood, for which much of the original organic matter has been lost and (ii) that the fossil trees
maintained a deciduous habit at polar latitudes during the Late Permian. The combination of paleobotani-
cal, sedimentologic, and paleoforestry techniques provides an unrivaled examination of the function of
polar forests in deep time; and the carbon isotope geochemistry supplements this work with subannual
records of carbon fixation that allows for the quantitative analysis of deciduous versus evergreen habits
and environmental parameters, for example, relative humidity.
Received 22 February 2012; accepted 2 July 2012
Corresponding author: E. L. Gulbranson; Tel.: 530-601-1927; Fax: 414-229-4561; e-mail: [email protected]
*Present address: Department of Geology and Geophysics, University of Hawaii, Honolulu, HI, USA
INTRODUCTION
Well-preserved fossils of the extinct plant Glossopteris and
other plants from Antarctica demonstrate that the conti-
nent was vegetated in the late Paleozoic (e.g., Seward,
1914; Schopf, 1970; Francis et al., 1993; Taylor, 1996).
Apparent polar wander paths indicate that Antarctica was
near the South Pole during the Permian (Powell & Li,
1994; Lawver et al., 2008; Domeier et al., 2011; Isbell
et al., 2012), implying that Glossopteris and other flora
grew and thrived near or above the South Polar Circle.
Tree ring studies of permineralized Glossopteris wood in
Upper Permian strata of Antarctica reveal that tree rings
are dominated by earlywood with very minimal amounts of
latewood (1–3 cells wide), suggesting that the unique pho-
toperiod of the polar latitudes promoted rapid cessation of
photosynthesis at the onset of winter (Ryberg & Taylor,
2007; Taylor & Ryberg, 2007). The occurrence of leaf-rich
sedimentary layers has been used to invoke a seasonally
deciduous habit for Glossopteris (Plumstead, 1958; Retal-
lack, 1980; Taylor et al., 1992). Pigg & Taylor (1993)
observed that Glossopteris leaf compressions vary little in
leaf size and suggest that this may reflect periodic leaf drop
owing to environmental stresses similar to the habit of
© 2012 Blackwell Publishing Ltd 479
Geobiology (2012), 10, 479–495 DOI: 10.1111/j.1472-4669.2012.00338.x
evergreen trees and that more evidence is required to link
these leaf compression layers with seasonal conditions that
would indicate a deciduous habit for Glossopteris. Evergreen
trees and deciduous trees, however, exhibit distinct pat-
terns in carbon isotope ratios within tree rings (Schubert
& Jahren, 2011). Carbon isotope ratios in tree rings of
evergreen trees display symmetrical variation while decidu-
ous trees display pronounced asymmetrical carbon isotope
ratio variation within tree rings. These distinct patterns
open the possibility that high-resolution carbon isotope
analysis of fossil wood can determine a deciduous or ever-
green habit for fossil trees. This study provides additional
evidence from variations of carbon isotope ratios in per-
mineralized wood that confirm a seasonally deciduous
habit for Glossopteris and provides a promising avenue for
further work in quantifying the environmental effects on
plant growth at polar latitudes at unprecedented temporal
resolution. Extracting an isotopic signature over the life
history of several plants in an ecosystem is critically impor-
tant in quantitatively reconstructing past climates, as isoto-
pic variation in plant material provides a record of a first-
order response of the plant, via stomatal conductance and
photosynthetic rate, to the environment (Farquhar et al.,
1982, 1989; Leavitt & Long, 1991; Diefendorf et al.,
2010; Kohn, 2010). As forested polar regions have no
modern analogue (Taylor et al., 1992; Creber & Francis,
1999) they can only be studied from deep time case stud-
ies (e.g., Francis, 1990; Falcon-Lang et al., 2001; Falcon-
Lang, 2004; Jahren, 2007; Williams et al., 2008) or by
simulating environmental parameters unique to the polar
regions in growth chambers (e.g., Royer et al., 2005).
Therefore, quantification of plant–environment interactions
from deep time examples and experimentation with extant
plants via growth chambers will aid in understanding bio-
geochemical cycling and climate feedbacks of high-latitude
environments colonized by plants.
Paleoenvironmental reconstructions have suggested that
the Antarctic forests occupied a riparian niche in the Perm-
ian (Cuneo et al., 1993; Isbell and MacDonald, 1991)
implying that the associated soils maintained at least peri-
odic wetness and dryness. The complex morphology of
Glossopteris roots, known as Vertebraria, has led to the
concept that morphologic variation in Vertebraria was an
adaptation for growth in a semi-aquatic environment
(Gould, 1975). Sheldon (2006) compared Permian and
Triassic paleosols (cf. Krull & Retallack, 2000) and inferred
a change in soil horizonation through time not related to
landscape position, but rather related to the duration of
soil formation and specific environmental conditions of the
region. This indicates that depositional environment played
an important role in determining the type of soil in an
area, and subsequently helped control the plants adapted
to grow in these soils. This study presents paleosol descrip-
tions and interpretations from three locations hosting
in situ fossil forests to compare paleosol composition and
maturity with forest succession and structure.
This study aims to describe (i) the soils and sedimentol-
ogy of three Late Permian polar forests, (ii) the variation
of forests with paleolandscape position, and (iii) the poten-
tial to use stable carbon isotopes in permineralized wood
at subannual resolution to further study the environment
of polar forests and perhaps plant physiology at polar lati-
tudes. This work is the first comparison of multiple con-
temporaneous Permian fossil forests at polar latitudes and
provides an integration of paleobotany, sedimentology,
and isotope geochemistry to study carbon cycling in deep
time terrestrial environments at unprecedented temporal
resolution. Two recently discovered fossil forests are
described here for the first time from localities on Graphite
Peak (85.05251ºS, 172.34792ºE) and near Wahl Glacier
(84.09500ºS, 165.33167ºE), and we compare these forests
with a previously studied fossil forest on Mt. Achernar
(84.17824ºS, 160.90057ºE) supplemented with geochemi-
cal analysis of Glossopteris wood from Mt. Sirius and
Mt. Achernar (Fig. 1).
BACKGROUND
Late Permian paleogeographic reconstructions place the
Transantarctic Mountain region between 70 and 80ºS(approximately 75ºS for the study area), which is well
within the South Polar Circle (Powell & Li, 1994; Torsvik
& Cocks, 2004; Lawver et al., 2008; Domeier et al.,
2011). The stratigraphy presented here is part of the Vic-
toria Group of the Beacon Supergroup, which is earliest
Permian to Triassic in age (Kyle & Schopf, 1982; Barrett
et al., 1986; Collinson et al., 1994; Isbell et al., 2001).
The fossil forests studied herein are found in the upper
member of the Buckley Formation (Fig. 2), which is dated
to the Late Permian on the basis of palynology (Kyle &
Schopf, 1982; Farabee et al., 1990, 1991) and from detri-
tal zircons that exhibit an abundance of zircons of Late
Permian age (Elliot & Fanning, 2008). The oldest sedi-
mentary rocks in the studied depositional basin are earliest
Permian (i.e., Asselian/Sakmarian, Kyle & Schopf, 1982),
indicating that the Transantarctic Basin was actively subsid-
ing at least by the Carboniferous-Permian boundary
(approximately 299 Ma, Gradstein et al., 2004).
Fossil forests in the Permian of Antarctica are exclusive
to the Late Permian Buckley Formation and its strati-
graphic equivalents (Doumani & Minshew, 1965; Cuneo
et al., 1993; Francis et al., 1993). A published description
is only available for the forest on Mt. Achernar, whereas
Permian fossil forests are known to exist in the central
Transantarctic Mountains at Wahl Glacier, Lamping Peak,
McIntyre Promontory, and Mt. Picciotto in the upper
Buckley Formation near the Beardmore and Shackleton
glaciers; and Mt. Weaver in the Queen Maud Mountains
© 2012 Blackwell Publishing Ltd
480 E. L. GULBRANSON et al.
near the Robert Scott Glacier. The fossil forest in the
upper Buckley Formation at Mt. Achernar (Figs 1 and 2)
is notable in that the preserved tree stumps have diameters
of 9–18 cm with no more than 15 rings per trunk, imply-
ing that this was a stand of saplings or juvenile trees (Tay-
lor et al., 1992). Fossil leaf mats and permineralized peat
from the upper Buckley in the study area suggest that
these polar forests were low diversity and probably did not
have an understory flora (Cuneo et al., 1993). However,
the Mt. Achernar in situ fossil forest does contain evidence
of understory vegetation comprised of herbaceous lycops-
ids, preserved as compression/impression fossils, whereas
the permineralized tree stumps of the forest are attributed
to the Glossopteris seed plant (Schwendemann et al., 2010).
Despite the fact that Glossopteris trees grew at polar lati-
tudes, Taylor et al. (1992) found no evidence of frost rings
in the fossil forest at Mt. Achernar.
The upper Buckley Formation is primarily composed of
volcaniclastic sedimentary rocks with terrestrial facies of flu-
vial and lacustrine affinity (Isbell et al., 1997; Isbell and
MacDonald, 1998), but coal also occurs within this part of
the formation and it is notable that coal is absent in Ant-
arctica between the top of the Buckley Formation and the
upper portion of the overlying Triassic Fremouw
Formation (Retallack et al., 1996). The Buckley Formation
has local variations in grain size (Barrett et al., 1986; Isbell
et al., 1997). Some regions are predominantly sand rich,
but coeval stratigraphic intervals in other areas are com-
posed of thinner sandstone beds interbedded with thicker
beds of shale and silty sandstone containing either carbona-
ceous plant detritus or non-carbonaceous plant compres-
sions (Briggs et al., 2010).
Glacial deposits of the late Paleozoic ice age do not
occur in Antarctica after (i.e., younger than) the Early
Permian (Isbell et al., 2003, 2008, 2012); however, glacia-
tion is interpreted to have existed at lower paleolatitudes in
eastern Australia until the Late Permian (Fielding et al.,
2008). Therefore, it is likely that the Late Permian time
interval in which these forests developed represents a tran-
sitional climate period from the icehouse(s) of the late
Paleozoic to the greenhouse state of the Mesozoic.
METHODS
Measured stratigraphic sections (Fig. 2) were made at
Graphite Peak, Wahl Glacier, and Mt. Achernar noting
sedimentary structures, sediment composition, and fossils.
Three permineralized stumps and root material were
RO
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Skaar Ridge
Mt. AchernarGordon Valley
Mt. Falla
Fremouw Peak
Lamping peak
Mt. Sirius
Wahl Glacier
Keltie Glacier
5 S
Graphite Peak
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ange
Permian fossil forest locality studied herein
Permian sections studied in 2010-2011
Triassic sections studied in 2010-2011
Law Glacier
P o l a r P l a t e a u
Permian fossil forest locality with Triassic strata
Permian and Triassic sections studied in 2010-2011
LatePermian
paleoflow
300 Ma
275 Ma
250Ma
polar wander (Domeier et al., 2011)
EastAntarctica
Africa
India
Australia
S.Amer.
studyarea
300Mapola
rcirc
le
C
B
A
Fig. 1 Map of the study area within Antarctica. (A) Present-day map of the study area, gray areas represent exposed rock of the Transantarctic Mountains.
Symbols denote studied locations during the 2010–2011 austral summer season; star symbols represent fossil forest localities studied herein. Large arrow
denotes general Late Permian paleoflow direction compiled from paleocurrent measurements throughout the Beardmore Glacier region. (B) Map of Antarctica
showing position of study area on the continent. (C) Paleogeographic reconstruction showing the position of the study area (star) relative to the rest of
Gondwana (gray areas). The most recent paleo-polar wander path for the studied time interval (Domeier et al., 2011; Isbell et al., 2012) is shown for
reference.
© 2012 Blackwell Publishing Ltd
Permian polar forests 481
sampled for stable isotope analysis at Graphite Peak, taking
care to preserve as much of the fossil in place. Six stumps
were collected from Wahl Glacier, and four stumps were
collected from Mt. Achernar for stable isotope analysis.
Existing samples are housed in the Department of Geology
and Geophysics, University of Hawaii, but will be perma-
nently deposited in the Paleobotanical Collections, Natural
History Museum, University of Kansas (Taylor et al.,
1992) under accession numbers 17169 A, B top and bot-
tom, and C for the Mt. Achernar specimen, and accession
number 17170 for the Mt. Sirius specimen. Leaf compres-
sions and the surrounding sedimentary rocks were also
sampled for geochemical and petrographic analysis.
We analyzed fossil forests at Graphite Peak and Wahl
Glacier localities by measuring the spacing between trees
and inferring tree height from the stem diameter (Table 1)
0
10
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30
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70
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90
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110
93
203T
hic
knes
s (m
)
Triassic Fremouw Fm.
Upper Permian upper Buckley Fm.
fossil forest
Trough cross-bedding
Current ripple lamination
Horizontal bedding
Coal
In situ stumps
Leaf compression
Explanation
co.md.f.vf.sil.cl/coalGrain Size
heig
ht fr
om b
ase
of s
ectio
n (m
)
0
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240Triassic Fremouw Fm.
Upper Permianupper Buckley Fm.
0
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50 m
co.md.f.vf.sil.cl/coalGrain Size co.md.f.vf.sil.cl/coal
Grain Size
GRAPHITE PEAK
WAHL GLACIERMOUNT ACHERNAR
Fig. 2 Stratigraphic columns at Graphite Peak, Wahl Glacier, and Mount Achernar. Only the thickness that contains the fossil forest and the contact between
the upper Buckley and Frewmouw fms. are shown. Grain size on the x-axis increases from left to right.
© 2012 Blackwell Publishing Ltd
482 E. L. GULBRANSON et al.
to understand the canopy structure. Carbon isotopes are
measured from permineralized wood at 1.5–2-mm intervals
in the direction of wood growth (i.e., radially), to infer the
annual or seasonal uptake of CO2 from the Late Permian
atmosphere. The carbon isotope measurements are likely
indicative of seasonal carbon fixation because the sampling
intervals are much thinner than the tree ring widths, which
range from 4 to 11 mm. Sampling tree rings at higher res-
olution (e.g., 0.1-mm intervals) was completed to observe
whether the carbon isotope pattern of a tree ring changes
with increased sampling density.
Tree height estimates were determined using the transfer
functions of Niklas (1994) for woody species that correlate
stem diameter to tree height (Table 1). We calculated the
95% confidence interval for the original data set of Niklas
(1994), which indicates that stem diameters must differ
between 6 and 10 cm to produce statistically significant
tree height estimates (Fig. S1). Forestry analysis of the Mt.
Achernar fossil forest has been previously completed. This
manuscript presents new field measurements of tree posi-
tions for Graphite Peak and Wahl Glacier to quantify tree
density and basal area using the point-centered quarter
method (Cottam & Curtis, 1956; Cuneo et al., 2003).
The point-centered quarter method is designed to estimate
the mean area of plants by measuring the distances of
plants to arbitrary sampling points along a transect. Each
sampling point is divided into four quadrants and the dis-
tance between the sampling point to the closest tree in
each quadrant is used as an individual sample and the aver-
age distances of all the samples is equal toffiffiffiffiffi
Mp
, where M
is the mean area of plants (Cottam & Curtis, 1956).
Samples of tree rings were cut from permineralized
wood with a tile saw equipped with a wafer blade at the
University of Wisconsin-Milwaukee. The tree ring samples
were split in half along the tangential plane such that the
two halves represent one half that is predominantly early-
wood and one half that has earlywood and a portion of
latewood. The halved tree rings were crushed in an agate
mortar to pass through a 40-lm sieve and combusted off-
line for carbon isotope ratio measurement on a Thermo
Finnigan MAT 253 (and a Finnigan MAT 252 for small
volumes) in dual inlet mode at the Huffington Department
of Earth Sciences, Southern Methodist University. XRD
analysis of homogenized powders of the sample did not
indicate the presence of carbonate minerals, and carbonate
minerals were not observed in thin section, and therefore,
contamination from inorganic carbon sources is unlikely.
Samples were combusted in sealed Vycor tubes at 900 °Cfor two hours followed by a linear decrease in temperature
to 650 °C at 1 °C min�1, temperature was held at 650 °Cfor two hours followed by cooling to 25 °C overnight.
Carbon dioxide produced during the combustion of the
sample was cryogenically purified from water vapor, SOx,
and non-condensable gasses. Reaction with 0.5 g native
Cu was complete for the majority of samples, and there-
fore, the cryogenic distillation procedure was modified to
separate CO2 from the large quantities of SOx possibly
remaining in the Vycor tubes. A mixture of liquid nitrogen
(LN) and n-pentane (�131 °C) was made in place of the
usual dry ice methanol/ethanol slush (�72 °C) to facilitate
the separation of CO2 from SOx by lowering the tempera-
ture closer to the freezing point of sulfur oxides. The gas
was passed through a LN trap and non-condensable gasses
were evacuated. The LN trap was quickly replaced with the
LN-n-pentane trap to maintain temperatures close to
liquid nitrogen temperature during the switch. CO2
evolved rapidly from the LN-n-pentane trap and was
allowed to be collected in a second LN trap. The amount
of purified CO2 gas was measured manometrically
and transferred to borosilicate tubes for isotope ratio
measurement.
The results of the offline combustion and dual inlet iso-
tope ratio measurements indicated that sampling at higher
spatial resolution (i.e. 0.1-mm sample intervals within tree
rings) might be possible. In advance of this higher-resolu-
tion sampling strategy we analyzed replicate samples from
the dual inlet data set via an elemental analyzer (EA)
interfaced to an isotope ratio mass spectrometer in contin-
uous flow mode at the Stable Isotope Facility at the Uni-
versity of California-Davis to assess reproducibility
between these very different analytical procedures. Sec-
ondary reference materials (nylon d13C = �27.81&, peach
leaves d13C = �26.12&, and bovine liver
d13C = �21.69&), which are calibrated against primary
reference materials, were analyzed within each batch run
to correct and normalize the measured values from the
sample. All materials resulted in precision better than
0.1& (1r). A quality assurance standard (USGS-41 Glu-
tamic Acid, d13C = +37.626&) was run within each batch
and had a standard deviation (1r) <0.3& over the course
of the experiment with an average d13C value of
+37.62&.
Table 1 Permineralized stump diameters at Graphite Peak
Stump
Stem
diameter
(cm)
Tree
height
(m)*
Basal
area
(m2)† Latitude (ºS) Longitude (ºE)
1 60 31 0.28 85.05251 172.34792
2 32 23 0.080 85.05251 172.34798
3 43 26 0.15 85.05260 172.34724
4 28 21 0.062 85.05262 172.34709
5 30 22 0.071 85.05279 172.34688
*Tree height inferred from transfer function: Log(y) = 1.59 + 0.39 Log (x)
� 0.18[Log(x)]2, where y is tree height in meters, and x is stem diameter in
meters (Niklas, 1994).†Basal area (BA) calculated as BA = dbh2 9 7.854
(10�5), where dbh is diameter-at-breast-height in centimeters.Total basal
area [m2 ha�1] is calculated by summing all of the basal areas of trees in a
stand and dividing by the area of the studied.
© 2012 Blackwell Publishing Ltd
Permian polar forests 483
To sample permineralized wood at a spatial resolution of
approximately 0.1 mm thickness we milled samples by
hand with a rotary tool equipped with a diamond bit and
monitored depth of sampling with calipers. Sampled sec-
tions of permineralized wood (0.050–1.0 mm thick) from
the upper Buckley Formation at Mt. Sirius were prepared
for analysis via elemental analyzer-continuous flow isotope
ratio mass spectrometry (EA-CFIRMS) at the laboratory of
Dr. A. Hope Jahren at the University of Hawaii-Manoa.
The sampling strategy is designed to make ultra-thin sam-
ples of permineralized wood sequentially along the direc-
tion of wood growth and has the potential to directly
sample latewood, which is commonly a few cells thick
(0.01–0.2 mm thick) in these samples (Ryberg & Taylor,
2007; Taylor & Ryberg, 2007). For the determination of
evergreen habit versus deciduous habit from stable isotope
trends in tree rings it is important to isolate latewood from
earlywood to conclusively determine whether a wood sam-
ple has an asymmetric carbon isotope profile in the tree
ring (deciduous habit) or a symmetrical carbon isotope
profile (evergreen habit). Samples are ground away from
the permineralized wood sample, massed, and sealed in a
tin capsule for EA-CFIRMS analysis thereby permitting rel-
atively rapid collection of isotope data from multiple sam-
ples within a single tree ring and for several rings. This
method can be envisioned as an improvement over the
more analytically precise dual inlet measurements in that a
greater portion of the total isotopic signal can be extracted
from a tree ring (Schubert & Jahren, 2011).
RESULTS
Graphite peak
During the 2010–2011 austral summer season in Antarc-
tica we discovered a Permian in situ fossil forest at Graph-
ite Peak near the Keltie Glacier (Fig. 1), which occurs 99
m below the contact of the upper Buckley and the Triassic
Fremouw fms (Fig. 2). The stumps are found upright with
intact roots in a approximately 50 cm thick, thinly bedded
(<1 cm thick), light gray siltstone (Fig. 3A–C) that con-
tains carbonaceous Glossopteris leaf compressions on bed-
ding planes. The compressions preserve leaf morphology
with both the blade and attached petiole in many speci-
mens. The siltstone, interpreted as a paleosol, is laterally
continuous for >100 m and is overlain by 6.5–7 m of par-
tially covered siltstone capped by a conspicuous, partially
silicified coal seam. Root structures were excavated from
A B
C
E
D
F
Fig. 3 Field photographs of permineralized
stumps. (A–B) Drawing overlay and
photograph of permineralized stump 1 from
Graphite Peak showing upright position, intact
roots, and two sedimentary units ‘i’ and ‘ii’.
Unit i is an organic-rich siltstone into which
the roots penetrate, unit ii corresponds to the
siltstone with leaf compression fossils that the
stump is set within and covered by. (C)
Upright permineralized stump 3 at Graphite
Peak; tree rings can be observed in the
transverse plane (top surface). (D) Upright
permineralized stump 2 at Graphite Peak.
Note that the only the high-relief feature is
permineralized wood; the depression is infilled
with blocky gray siltstone. (E) Upright
permineralized stump at Wahl Glacier. (F)
Upright stump at Wahl Glacier with attached
root trending away from the stump toward
the bottom of the image.
© 2012 Blackwell Publishing Ltd
484 E. L. GULBRANSON et al.
the in situ stumps and these roots were traced tens of cen-
timeters into the thinly bedded gray siltstone (Fig. 3A,B),
tapering downwards. In cross section the roots are com-
pletely permineralized but lack the diagnostic lacunae of
many Vertebraria roots, although this may be due to their
proximity to the root-shoot transition zone (Neish et al.,
1993; McLoughlin et al., 1997, 2005; Decombeix et al.,
2009). Vertebraria was also observed in float in the overly-
ing beds. In total, six in situ stumps were observed in the
exposed bedding plane; five stumps were completely per-
mineralized and one was permineralized only in the outer-
most portions of the stump, whereas the innermost
portions were filled with gray, blocky, siltstone (Fig. 3D).
Sandstones that crop out above and below the fossil for-
est layer are laterally extensive across the outcrop having a
sheet-like geometry. The sandstones are fine- to medium-
grained, with a subangular to subround texture; the com-
position is dominated by lithic fragments, although mud-
stone clasts and quartzite clasts are observed at the base of
sandstone beds, and the sandstones truncate underlying
strata at the centimeter-scale. Trough cross-bedding and
ripple laminations are observed within the sandstone beds.
Interpretation of Graphite Peak Stratigraphy
The sandstone lithofacies at Graphite Peak above and
below the fossil forest layer represent fluvial channel and
floodplain (splays, mires, lakes) deposits of low-sinuosity
streams (Fig. 2). Paleoflow directions for fluvial sandstones
at Graphite Peak are oriented toward the South Pole and
represent transverse flow relative to axial drainage patterns
directed toward South Victoria Land (Collinson et al.,
1994; Isbell et al., 1997; Fig. 1). Sandstones at Graphite
Peak contain mudstone rip-up clasts and quartzite pebbles
near the sandstone base, indicating erosion of underlying
strata during the entrenchment of the channel system. The
fine-grained texture and weak horizontal bedding of the
fossil forest layer suggests a low energy environment of
deposition. These sedimentary rocks are likely floodplain
deposits formed from the continued aggradation of sedi-
ment after an avulsion episode (Smith et al., 1989). This
interpretation is consistent with the low degree of pedo-
genic modification of these sedimentary rocks inferred
from the lack of field-based indications of soil formation
(e.g., horizonation, reddening, clay accumulation, redoxi-
morphic features), where pedogenesis is punctuated by the
continued addition of sediment (Kraus & Aslan, 1993).
Wahl glacier
During the 2003–2004 austral summer season we (J.L. Is-
bell) discovered the remains of a fossil forest in the upper
Buckley Formation at Wahl Glacier, near Walcott Neve
(Knepprath, 2006; Fig. 1). The discovery of the Wahl
Glacier and Graphite Peak forests brings the total number
of in situ fossil forest localities in the Beardmore Glacier
region to four, with the other two being the Permian
forest at Mt. Achernar (Taylor et al., 1992) and a Triassic
forest in the Fremouw Formation at Gordon Valley
(Cuneo et al., 2003). The fossil forest at Wahl Glacier is
approximately 100 m below the contact between the Buck-
ley and Fremouw formations (Fig. 2). Thirteen permineral-
ized stumps are found upright with intact root systems
that penetrate underlying sedimentary rocks (Fig. 3E,F).
The root systems trend horizontally away from the stumps.
The sedimentary rocks surrounding the permineralized
stumps are divided into a lower siltstone that contains the
root systems and an overlying sandstone that covers most
or all of the stumps. The lower siltstone is gray with a
white patina, thinly bedded, and contains leaf compres-
sions. The overlying sandstone is brown, fine- to medium-
grained and medium-bedded, and contains crude
cross-stratification; the basal contact of the sandstone trun-
cates underlying siltstone. The stratigraphic succession of
the upper Buckley Formation at Wahl Glacier has a general
fining upward trend in grain size, and the fossil forest
layer, including the sandstone surrounding the stumps, is
bounded by organic-rich shale.
Interpretation of Wahl Glacier stratigraphy
The sedimentary strata surrounding the fossil forest at
Wahl Glacier, like Graphite Peak, contain both thick and
thin lithic sandstones with sheet-like geometries that
contain trough cross-bedding, organic-rich shales, thin
laminated siltstones, and coal. Therefore, these sandstones
are interpreted as low-sinuosity channel, splay, lake, and
mire fluvial deposits. The mean paleocurrent vector of
these sandstones indicates an oblique direction (i.e., trans-
verse flow) relative to the basin axis, with a general orienta-
tion toward South Victoria Land. The fossil forest layer,
however, is found rooted within a thinly bedded, gray silt-
stone that is in contact with crudely laminated sandstones.
The environment of deposition at Wahl Glacier for the fos-
sil forest layer is likely a channel margin or forested levee/
splay complex of a low-sinuosity fluvial system, suggesting
a closer proximity to the fluvial system than the Graphite
Peak stumps that are surrounded by finer-grained and
thinly bedded strata representing a relatively distal portion
of a splay complex (cf., Smith et al., 1989).
Mount Achernar
We studied two Permian fossil forest levels at Mt. Achernar
in the vicinity of the Law Glacier (Fig. 1). The overlying
Fremouw Fm. does not crop out at this locality; however,
comparison with surrounding locations suggests that this
section of upper Buckley occurs approximately 50 m below
© 2012 Blackwell Publishing Ltd
Permian polar forests 485
the upper Buckley Fm. and Fremouw Fm. contact (Fig. 2).
The basal 3 m of this section consists of a massive white
siltstone and fine root haloes that branch downwards but
diverge horizontally at approximately 1 cm depth. The silt-
stone has sharp upper and lower boundaries and interbed-
ded white siltstone beds with crude bedding that contain
Glossopteris leaf compressions and carbonaceous woody tis-
sue. The preservation of the fossil plant material is variable
with some fossils preserving only vein skeletons and other
beds preserving most of the blade attached to the petiole.
Glossopteris reproductive structures are present in some of
the beds as well (Ryberg et al., 2011).
Overlying these units is approximately 1 m of coal inter-
bedded with medium- to thin-bedded (5 cm to <1 cm)
white siltstone with abundant plant debris on bedding
planes. The coal contains woody tissue and leaf fragments.
Greenish brown mudstone clasts occur within the white
siltstone. Overlying the coal and siltstone is approximately
1 m of medium-bedded, interbedded siltstone with a white
patina, blue-gray interior, and rare ripple laminations. Fos-
sil leaf fragments are abundant on some bedding planes.
Two truncation surfaces were noted that cut through the
underlying siltstone; these have a lenticular geometry and
are roughly 1.5 m wide with bedding that onlaps onto the
truncation surface. The upper 2 m of the section contains
the two beds hosting the in situ tree stumps and roots
(Fig. 4A,B).
Interpretation of Mount Achernar stratigraphy
Mt. Achernar contains evidence of subaerial exposure in
the form of rooted siltstones interpreted as weakly devel-
oped paleosols (Protosols) and coals (Histosols). Unlike
Graphite Peak (Fig. 5A,B), however, the environment of
deposition at Mt. Achernar is interpreted as being lower
energy on the basis of an abundance of fine-grained sedi-
mentary rocks near the fossil forest beds (Fig. 5C,D).
Channelization of some siltstone beds indicates water
movement and transport of material (Fig. 5D), and the
horizontal bedding with abundant plant remains implies a
subaqueous environment with low energy (e.g., rare ripple
laminations) or perhaps standing water allowing for sus-
pension settling of material. Interbedding of splays, coal,
and siltstone suggest deposition along the margins of a
shallow lake. These environments are consistent with a
shallow lacustrine system or wetland with fluvial input of
sediment. Therefore, the lower energy lacustrine, marginal
lacustrine, mire, and splay environments interpreted at Mt.
A B
Fig. 4 (A) Upright permineralized stump at
Mt. Achernar in white siltstone. (B)
Permineralized root (arrow) at Mt. Achernar
trending subhorizontally in siltstone.
A B
C D
Fig. 5 Field photographs of fossil forest sites.
(A) upper Buckley Fm. and upper Buckley/
Fremouw fms. contact at the Graphite Peak
locality. Fossil forest location indicated by solid
black line, dashed where inferred laterally. (B)
Sedimentary units (i, ii) that contains the fossil
forest at Graphite Peak, note the preservation
of bedding throughout. See explanation in
Fig. 3. (C) upper Buckley Fm. at Mt.
Achernar. Fossil forest is marked (light gray
bench) as is the measured section. (D) Bedded
and laminated siltstone lithofacies at Mt.
Achernar. Fossil forest layers are in the white
colored units at the top of the photograph.
Note the small cut-and-fill structure in the
center of the photograph.
© 2012 Blackwell Publishing Ltd
486 E. L. GULBRANSON et al.
Achernar are likely part of a mosaic of landscapes that were
laterally equivalent to low-sinuosity channel and floodplain
fluvial deposits at Wahl Glacier and elsewhere in the Beard-
more Glacier region (Isbell et al., 1997).
Paleoforestry
The permineralized stumps at Graphite Peak have diame-
ters that range from 28 to 60 cm (Fig. S1), which corre-
spond to tree heights that range from 21 to 31 m
(Table 1). The mean distance between trees in the Graph-
ite Peak forest is 20.8 m (Fig. S3A), which corresponds to
a density of 23 individuals ha�1 using the method of Cot-
tam & Curtis (1956). Moreover, these measurements were
made on upright stems found with attached roots that
penetrate siltstone (Figs 3, 4 & 6), and we interpret these
fossil wood samples as being in situ. Stem diameter mea-
surements for the fossil forest at Mt. Achernar are pub-
lished as a range of 9–18 cm (Fig. S3B, Taylor et al.,
1992) for fifteen permineralized stumps, and correspond
A
B C
D E
Fig. 6 Fossil forest photographs. (A) Two
upright permineralized stumps from Graphite
Peak (stumps 4 and 5) found within light gray
siltstone (unit ‘i’ of Figs 3 & 5). (B) Upright
stump at Graphite Peak (stump 1) showing
two intact roots trending down into organic-
rich siltstone (unit ‘ii’ of Figs 3 and 5). (C)
Glossopteris leaf impressions indicated by
ovals, and the reproductive structure
Plumsteadia (Taylor et al., 2007) indicated by
the squares on a bedding plane from Mt.
Achernar. (D) Upright stump from Wahl
Glacier fossil forest with at least two attached
roots. Brown sandstones covers most stumps
and exhibits an erosional contact with the
underlying siltstone. (E) Glossopteris leaf
impression from Graphite Peak.
© 2012 Blackwell Publishing Ltd
Permian polar forests 487
to tree heights ranging from 10 to 16 m, respectively (Fig.
S1).
Permineralized stumps at Wahl Glacier have a mean
diameter of 25.6 cm (Fig. S1), which corresponds to a
mean tree height of 19.2 m. The mean distance between
trees at Wahl Glacier is 6.2 m and corresponds to a tree
density of 263 individuals ha�1 (Fig. S3C), which reflects
an average obtained by using the point-centered quarter
method and by dividing the number of stumps by the
area of the exposed surface (Knepprath, 2006). It is
noteworthy that several permineralized stumps at Wahl
Glacier contain secondary mineralization of sulfur-bearing
minerals, such as pyrite or chalcopyrite, near the pith
of the stump, whereas Graphite Peak permineralized
wood appears to be homogeneous with respect to
mineralization.
Geochemistry
Preliminary geochemical analyses were made on a permin-
eralized Glossopteris stump from Mt. Achernar. XRD
analysis of powdered and mixed permineralized wood from
Mt. Achernar indicates that quartz is the only mineral pres-
ent in the sample. Offline combustion and cryogenic sepa-
ration of CO2 allowed for high-precision measurements of
the carbon yield of the samples (Fig. S2A,B). A range of 3
–23 mg of sample was combusted and corresponds linearly
to a range of CO2 quantities of between 9 and 31 lmol,
respectively (Table 2). Thus, the average weight percent of
carbon in a bulk sample of this permineralized wood is 2%
(±0.4% 1 SD).
Stable carbon isotope ratios were measured within
growth rings of permineralized wood to assess whether or
not seasonal variation observed in extant plants (e.g., Fran-
cey & Farquhar, 1982; Leavitt & Long, 1991; Helle &
Schleser, 2004; Schubert & Jahren, 2011) occurs in the
fossil plants and whether the variation in carbon isotope
ratios can elucidate whether Glossopteris maintained a
deciduous or evergreen habit. For the Mt. Achernar sam-
ple, measured d13C values range from �21.4& to
�24.9& (Table 2), with an average d13C value of �23.2&(±0.9& 1SD). Carbon isotope ratios vary within tree rings
with the beginning of a ring having the most positive d13Cvalue and the later portion of the ring having the most
negative d13C value (Fig. 7). This pattern repeated for the
majority of rings analyzed, with exception of the exterior
of the sample that showed a pronounced enrichment in13C relative to samples from the interior of the specimen.
In this outer part of the stump, the beginning of the rings
had a fairly consistent d13C value of approximately
�22.6&, whereas the values for the later portion of the
rings varied from �24& to �25&. Thus, d13C values vary
by 1–2& within tree rings in the permineralized wood
specimen from Mt. Achernar.
Replicate samples from Mt. Achernar analyzed via
EA-CFIRMS, a technique that will efficiently accommodate
an increase in the number of samples analyzed, were sys-
tematically more positive than the samples analyzed via
dual inlet by approximately 0.2& (Fig. S2C). The system-
atic and small offset between the dual inlet and elemental
analyzer methods indicates that the samples analyzed via
EA-CFIRMS will likely preserve the same isotopic signals
identified with dual inlet measurements.
Ultra-thin sections (<0.1 mm thick) of permineralized
wood from an Araucarioxylon specimen collected in the
uppermost Buckley Fm. at Mt. Sirius (Fig. 1) were ana-
lyzed for carbon isotope ratios via EA-CFIRMS to test
whether a deciduous or evergreen habit can be inferred
from high-resolution isotope geochemistry of fossil wood
(Fig. 8). Modern deciduous and evergreen trees display
pronounced differences in intra-ring carbon isotope ratios,
where deciduous trees show an asymmetric, three-phase
trend with more negative values in latewood, increasing
through the ring boundary an into the earlywood of a sub-
sequent tree ring (Helle & Schleser, 2004). On the other
hand, evergreen trees display a symmetric carbon isotope
trend throughout a tree ring, with more positive values in
the earlywood (Schubert & Jahren, 2011). The results
show clear isotopic variation within tree rings (Fig. 8). The
d13C values are more negative than the Mt. Achernar
Table 2 Carbon yield and d13C from Mt. Achernar
Sample*,†Mass
(mg)
Carbon yield
(lmol�C)d13C
(& VPDB)
2p 17.5 30.7 �22.7
2c 5.1 10.5 �23.9
3p 6 11.8 �23.7
3c 16.1 23.8 �22.6
4p 14.8 22.4 �22.9
4c-1 7.3 10.9 �23.7
4c-2 5.7 9 �24
5p 13.5 21.1 �22.6
5c 4.6 6.04 �24.9
6p-1 18.2 22.8 �22.8
6p-2 11 12.6 �23.3
6c-1 9.8 18 �23.3
6c-2 11.2 16.5 �23
7p-1 2.6 5.9 �24.9
7p-2 26.8 37.6 �22.44
7p-3 25.9 33.2 �22.5
7c 17.3 23.8 �22.6
8p 3.7 9.1 �23.9
8c 20.5 27.7 �22.5
9p 13.9 18.8 �22.3
9c 23 31.3 �21.4
*Samples are referenced by ring number ‘2’ and whether they are early-
wood dominated ‘p’ or a mixture of earlywood and latewood ‘c’. Replicate
analyses are indicated by the number, for example, 7p-2 is the second rep-
licate analysis of sample 7p.†University of Kansas accession number for the
sample is 17169B top and bottom, the sample is from Mt. Achernar, upper
Buckley Formation, Antarctica.
© 2012 Blackwell Publishing Ltd
488 E. L. GULBRANSON et al.
stump, by up to 2&, and the magnitude of d13C value var-
iation within a tree ring is approximately 1& (Table 3).
Moreover, an important trend is observed between the two
tree rings in the Mt. Sirius sample. d13C values are most
positive in the initial wood of the tree ring and then
become progressively more negative throughout the tree
ring, exhibiting a change toward more positive values near
the earlywood/latewood boundary, which continues into
the next tree ring. This three-phase variation in carbon sta-
ble isotopes is similar to stable isotope variation observed
in extant deciduous trees (Helle & Schleser, 2004). As
demonstrated by Schubert & Jahren (2011), an increase in
the number of samples per tree ring will yield an increase
in the amount of seasonal signal recorded in stable isotope
variations. Therefore, the sampling approach used on the
Mt. Sirius specimen is clearly more advantageous than the
approach used for the Mt. Achernar specimen as 60–80%
of the total isotopic signal was recovered from the tree
rings in the Mt. Sirius sample. However, potentially impor-
tant differences in d13C values and the range of d13C val-
ues within tree rings between the two localities are
apparent despite the differences in sampling strategy and
isotope analysis.
DISCUSSION
Fossil forests in the upper Buckley Formation at Graphite
Peak and Wahl Glacier occur at similar lithostratigraphic
positions approximately 100 m below the contact between
A
B
Fig. 7 Mt. Achernar wood and carbon isotope values. (A) Transverse sec-
tion of permineralized wood from Mt. Achernar used for isotope ratio mea-
surements. (B) Tree ring d13C values, gray shading indicates where two
samples were taken from the same ring, other values likely represent one
d13C value for the entire ring. Arrows point to region in the stump that the
data points correspond to. Dashed vertical lines denote tree ring bound-
aries. Note peculiar increase in d13C values toward the exterior of the sam-
ple (to the right).
A B
Fig. 8 Carbon isotope ratios for the permineralized wood specimen from Mt. Sirius. (A) Individual data points (circles) were used to calculate a 3-point run-
ning average (black line). Photograph (inset) of the section of permineralized wood used for sampling. Sample widths are indicated by the widths of the alter-
nating black and gray bars, with 10 samples for rings 1 and 2, sample numbers are shown for ring 1 for reference. Note that sample widths <0.1 mm
(Table 3) are difficult to show clearly. (B) Idealized carbon isotope trends within tree rings for a deciduous tree and an evergreen tree generalized from a glo-
bal compilation of high-resolution isotope records of modern wood (modified from Schubert & Jahren, 2011). The Mt. Sirius sample displays carbon isotope
trends that are more similar to a tree of a deciduous habit, having a three-phase carbon isotope trend, than an evergreen habit that has a prominent positive
d13C value peak yet similar d13C values at the beginning and end of a growth ring.
© 2012 Blackwell Publishing Ltd
Permian polar forests 489
the Buckley and Fremouw formations. The fossil forest at
Mt. Achernar occurs within the upper Buckley Formation;
however, the Fremouw Formation does not crop out at
this locality, and so it is not possible to definitively corre-
late the fossil forest at Mt. Achernar with Graphite Peak
and Wahl Glacier other than to assign it a Late Permian
age on the basis of palynology (Farabee et al., 1990,
1991). In the following discussion, we interpret the nature
of the forests at each locality in regard to the environment
of deposition. The preliminary stable carbon isotope data
will be discussed in terms of the potential for recovering
high-resolution geochemical archives from these fossil
plants.
Retallack & Krull (1999) interpreted broad areas of Ant-
arctic landscapes in the Permian as densely forested, a
monotonous extension of vegetation observed from sedi-
mentary deposits of fluvial-floodplain affinity. Such general-
izations are problematic as the preservation of plant fossils
is biased toward riparian environments and without direct
observation from other environments, it is impossible to
describe the vegetative habit and ecology without incurring
significant errors in paleoclimate/paleoforestry reconstruc-
tion (Demko et al., 1998). The occurrence of only Glossop-
teris leaves (Fig. 6C,E) in the Graphite Peak fossil forests
implies that the stand was low diversity, which is consistent
with Late Permian fossil forests elsewhere in Antarctica
(Cuneo et al., 1993). In addition, no other fossil macrofl-
ora was observed in the fossil forest and this suggests the
absence of understory vegetation at Graphite Peak in con-
trast to the Mt. Achernar in situ forest that does contain a
herbaceous lycopsid understory (Schwendemann et al.,
2010). The field measurements of spacing between trees
indicates that the preserved trees at Graphite Peak and
Wahl Glacier are widely spaced relative to the fossil forest
at Mt. Achernar and were likely more mature trees relative
to Mt. Achernar (Fig. S3; Fig. 9A). There is overlap
between tree height estimates at the fossil forest localities,
however, taking into account the 95% confidence interval
for the regression equation used to estimate tree height
(Fig. 1), which suggests that the mean height of the fossil
forest at Wahl Glacier was likely intermediate in a grada-
tion between taller trees at Graphite Peak and shorter more
juvenile trees at Mt. Achernar.
At least three wood morphogenera have been described
from the study region: Araucarioxylon, Kaokoxylon, and
Australoxylon (Pigg & Taylor, 1993; Taylor & Ryberg,
2007; Decombeix et al., 2010, 2012); therefore, it is pos-
sible that tree height differences are related to species dif-
ferences in the region. As each wood morphogenera has
been found among Glossopteris leaf fossils, however, it is
difficult to assess the impact of these different wood mor-
phogenera on the paleoecology of the forests. Alterna-
tively, the variation of tree height and tree density likely
reflects some combination of forest maturity, environmen-
tal stresses, and/or disturbance. It is possible that forest
maturity, disturbance and environmental stress may be
linked to landscape position as pronounced variation in
tree density and plant diversity are observed in extant
plants on a variety of landscapes (Fig. 9B,C; Gregory et al.,
1991; Viereck et al., 1993; He & Duncan, 2000).
Both Wahl Glacier and Graphite Peak fossil forests occur
in similar depositional environments, proximal to low-sinu-
osity stream systems, whereas the fossil forest at Mt. Acher-
nar occurs in a lower energy environment further away
from large drainage systems in the Transantarctic basin.
Stark differences in basal area and tree density further sug-
gest an environmental control on forest development
(Fig. 9A), where low basal area and low tree density corre-
sponds to levee/splay complexes at Wahl Glacier and
Graphite Peak, and much higher basal area and tree density
are estimated for lacustrine and distal floodplain environ-
ments at Mt. Achernar and a suite of stumps from Lamping
Peak (Figs 1, 9A, Knepprath, 2006). This trend of decreas-
ing tree density and increasing tree maturity is known as
‘self-thinning’ (Cao et al., 2000; Falcon-Lang, 2004) and
is observed in modern landscapes as forests age away from
Table 3 Carbon isotopic data of fossil wood from Mt. Sirius
Sample*,†Position
(mm)
Mass
(mg)
Carbon yield
(lg C)
d13C
(VPDB)
Ring 1
1 0.500 1.82 90 �24.73
2 1.00 1.66 41 �24.90
3 1.50 1.51 17 �24.95
4 1.60 1.67 26 �25.56
5 2.55 1.49 18 �25.48
6 2.59 1.65 16 �25.25
7 2.60 1.89 21 �25.16
8 3.25 1.59 10 �24.93
9 3.35 1.82 12 �25.15
10 3.70 1.42 16 �25.14
Ring 2
1 3.80 1.83 10 �24.71
2 3.85 1.67 11 �25.08
3 3.90 1.66 10 �24.82
4 4.25 1.55 11 �25.10
5 4.40 1.22 8 �24.27
6 4.60 1.79 13 �24.86
7 4.65 1.37 9 �24.71
8 4.75 1.09 27 �24.75
9 5.00 1.22 11 �25.31
10 5.05 1.7 14 �25.07
11 5.23 1.31 35 �25.34
12 5.55 1.22 32 �24.84
13 5.70 1.36 14 �25.42
14 5.83 1.51 23 �25.03
Ring 3
1 6.23 1.85 10 �25.42
*Numbers correspond to samples within a tree ring; thus, for ring 1,
there are 10 samples individually analyzed for carbon isotope composition.
†University of Kansas accession number is 17170, the sample is from Mt.
Sirius, upper Buckley Formation, Antarctica.
© 2012 Blackwell Publishing Ltd
490 E. L. GULBRANSON et al.
zones of high and persistent disturbance (i.e., streams). A
common progression of diversity and tree densities in the
Pacific northwest trend from bare alluvium to mixed shrubs
and thin alders of high density (approximately
100 000 ind. Ha�1) on terraces adjacent to active stream
channels, whereas the oldest landscapes (>700 years) of
bogs or mires occupied by black spruce with densities rang-
ing from 500 to 2000 ind. Ha�1 (Fig. 9B,C, Viereck et al.,
1993). The observed self-thinning in the Permian, how-
ever, is opposite of the modern, where Permian tree matu-
rity increases (and density decreases) closer to the area of
high potential disturbance and is similar to younger high-
latitude fossil forests of Cretaceous age in the Antarctic
peninsula region (Falcon-Lang et al., 2001; Falcon-Lang,
2004). This trend is possibly related to intense competition
for resources in a persistently disturbed (e.g., flooding)
environment that was unsuitable for understory vegetation
in the region. Moreover, as trees age, tree mortality can be
induced by intense competition for light, water, and nutri-
ents (Cao et al., 2000; Falcon-Lang, 2004). Forest canopy
structure is an important determining factor in resource
competition and future work to assess the growth form of
glossopterid trees at different latitudinal gradients, as well
as the ecology of different late Permian wood morphogen-
era in Antarctica, may elucidate competition for light as
opposed to nutrients or water.
The sedimentary rocks that host in situ fossil forests at
Graphite Peak, Mt. Achernar, and Wahl Glacier are inter-
preted as paleosols as they meet the principle criterion for
soil, which is to support plant life (Soil Survey Staff,
2010). The paleosols at each locality are gray to whitish
gray (Figs 3B–F; 4A,B; 6B,D), contain some degree of
bedding or sedimentary fabric, including leaf compressions
on bedding planes, and have a silt texture. These paleosols
lack field-based indicators indicative of seasonal changes
in moisture content (Kraus & Aslan, 1993), that is,
60
40
20
0
80
100
0 500 1000 1500 2000 2500 3000
GP
WG
LP
LP MA
Levee/splayDistal floodplain/
lacustrine
Tree Density (trees ha–1)
Bas
al A
rea
(m2
ha–
1 )
Bas
al A
rea
(m2
ha–
1 )
A
Curio Bay
Gordon Valley
Axel Heiberg
Decreasing tree density
Increasing forest maturity/age
Mt. AchernarWahl Gl./Graphite Pk.
C
D Lamping Pk.
60
40
20
80
100
6543210Log10 Tree Density (trees ha–1)
B
Distal
Splay
Modernfloodplain
position
Dis
tal
Spla
y
river
Braided streamLake
Shr
ubs
Ald
erW
hite
sp
ruce
Bla
cksp
ruce
Bog
Late Permian forests
Decreasing tree density
Increasing forest maturity/age
Perm
ian
flood
plai
npo
sitio
n
Glossopterids
Lycopsids
Modern boreal forests
Fig. 9 Paleoforestry calculations and modern comparison. (A) Basal area and tree density estimates for Permian fossil forests (green circles): Graphite Peak
(GP), Wahl Glacier (WG), Lamping Peak (LP), and Mount Achernar (MA). Lamping Peak estimates are from Knepprath (2006). Additional polar forest locali-
ties are displayed by the blue square symbols: Gordon Valley (Middle Triassic, Cuneo et al., 2003), Curio Bay (Middle Jurassic, Pole, 1999), and Axel Heiberg
Island (Eocene, Francis, 1991; Basinger et al., 1994; Greenwood & Basinger, 1994). (B) Basal area and tree density measurements for a modern boreal forest.
Data from Viereck et al. (1993). Blue square symbols correspond to early succession forest near a river. Red circles correspond to mature forest on terraces
and within bogs. Gray symbols indicate the Late Permian forestry data for reference. (C) Illustration of ‘self-thinning’ within a modern boreal forest (modified
from Viereck et al., 1993) where tree density decreases from left to right and forest maturity increases from left to right. (D) Interpretation of Late Permian
paleoenvironments and forest structure at Wahl Glacier, Graphite Peak, Lamping Peak, and Mt. Achernar. Self-thinning is interpreted to be the exact opposite
trend from the modern, that is, toward areas of high disturbance in the Late Permian.
© 2012 Blackwell Publishing Ltd
Permian polar forests 491
redoximorphic coloration, sequestration of redox-sensitive
elements such as Fe and Mn, and differentiation of clay-
sized material into argillic horizons (sensu Alfisols, Verti-
sols). Rather the studied paleosols are reflective of nearly
perennial saturation by freshwater (i.e., immature and
poorly drained). The occurrence of well-preserved, abscised
leaves in the sediment directly adjacent to permineralized
stumps in growth position further confirms prolonged
water saturation as this situation produces an increase in
acidity and contributes to the preservation of leaf litter rel-
ative to exposure at the soil-air interface (Gastaldo &
Staub, 1999). A persistent and high water table is inferred
from the gray to whitish gray color and lack of mottling as
seasonal aeration would promote the oxidation and trans-
port of Fe- and Mn-bearing compounds resulting in redox-
imorphic features (Vepraskas, 1994).
Applying modern soil classification (Soil Survey Staff,
2010) to the paleosols studied herein results in their classi-
fication as Aquents, Aqu-Aquic those forming under
perennial water saturation, and ents-Entisols, poorly devel-
oped soils on young or unstable landscapes. The term
aquic is problematic in paleosol taxonomy as it is inher-
ently interpretative, because we cannot know for certain
whether water saturation was perennial or seasonal. There-
fore, our interpretations are guided by the range of afore-
mentioned observations on soil color, mineralogy, root
morphology, and tree ring analysis. The paleosol classifica-
tion system of Mack et al. (1993) is adapted for use in
geologic materials where these paleosols (Aquents) are clas-
sified as Protosols on the basis of poor (i.e., absent) horiz-
onation. The modern equivalents of Protosols (Entisols
and Inceptisols) dominate the global landscape and occur
across all climate regimes, slopes, vegetation types, land
surface ages, and hydrology. Based on the aforementioned
criteria, we interpret these paleosols as being saturated with
liquid water for several months of the year, if not perenni-
ally. Freezing conditions were apparently short-lived given
the absence of frost rings in Mt. Achernar tree stumps
(Taylor et al., 1992); therefore, despite the polar latitude
of these fossil forests, perennial water saturation was a
plausible condition.
The isotope geochemistry of permineralized wood from
Mt. Achernar indicates that carbon isotopic records at sub-
annual resolution can be extracted from permineralized
wood (Fig. 7). However, the data we collected from the
sample from Mt. Sirius (Fig. 8) are the oldest subannual
carbon isotope study of tree growth rings, with the next
oldest samples being the ‘sub fossil’ wood of Eocene age
in the Canadian Arctic (Jahren, 2007; Jahren & Sternberg,
2008; Schubert et al., 2012), underscoring the need for
high-resolution studies such as this for other time periods
in the Phanerozoic. The results for the Mt. Achernar and
Mt. Sirius samples provide evidence for a deciduous habit
for Glossopteris trees. Measured d13C values within tree
growth rings show markedly different trends between trees
with a deciduous versus evergreen habit (Fig. 8B; Schubert
& Jahren, 2011). The permineralized stump from
Mt. Achernar contains d13C patterns that are consistent
with a deciduous habit (Fig. 7); however, the low sampling
density (i.e., two data points per ring) does not permit
trends to be established to rigorously support such a con-
clusion. On the other hand, because of the higher sam-
pling density, the permineralized wood from Mt. Sirius
displays a three-phase d13C trend within individual growth
rings that is consistent with a deciduous habit (Fig. 8);
however, the isotope geochemistry does not indicate
whether this habit was advantageous at polar latitudes. Ro-
yer et al. (2005) indicate that deciduousness under a polar
light regime (i.e., months of continuous light and months
of continuous darkness in one year) and cold winters
results in a reorganization of carbon fixation strategies
when compared to evergreen trees. While these results may
seem to cast doubt on an elemental cycling competitive
edge of deciduous trees over evergreen trees at polar lati-
tudes, the fact that deciduous trees existed at polar lati-
tudes is a fact that is as yet not fully understood. Perhaps,
the explanation lies in the dominance of deciduous plants
at polar latitudes during past times of global warmth, for
example, the Late Permian-Triassic of Antarctica and the
Late Cretaceous of Alaska.
CONCLUSIONS
A field- and laboratory-based study of Late Permian in situ
fossil forests of the central Transantarctic Mountains pro-
vides the first integrated geochemical, sedimentologic,
paleopedologic, and paleobotanical analysis of this unique
polar ecosystem. The analysis of paleosols and contempora-
neous sedimentary rocks indicates that the fossil forests
grew in two different paleoenvironments, a low energy
environment adjacent to axial drainage systems of the
Transantarctic basin, and two higher energy environments
proximal to low-sinuosity fluvial systems. Tree height, tree
density, and basal area differ markedly between the inferred
distal floodplain environment and levee or splay environ-
ments; however, tree density and basal area are similar for
localities in the same inferred paleoenvironment. We inter-
pret this tree density trend as ‘self-thinning’. A comparison
with modern forests indicates that the observed Late Perm-
ian self-thinning is opposite of the modern, which suggests
that the unique ecology of Late Permian polar forests pro-
moted the loss of understory vegetation in regions of high
disturbance (e.g., fluvial systems).
Carbon isotope ratios of permineralized wood presented
herein are, to our knowledge, the first high-resolution data
set of this kind from material older than the Cenozoic.
The stable isotope geochemistry indicates that intra-tree
ring measurement of carbon isotope ratios is possible even
© 2012 Blackwell Publishing Ltd
492 E. L. GULBRANSON et al.
in permineralized samples. Such detail can provide impor-
tant insights into the habit of arborescent plants and implies
that additional environmental variables, such as water stress,
could be quantified from such ancient ecosystems.
ACKNOWLEDGMENTS
We are especially grateful to Drs. Neil Tabor and A. Hope
Jahren for assistance and generosity in the use of their lab-
oratory facilities; and Mr. Bill Hagopian and Dr. Scott Me-
yers for assistance with stable isotope ratio measurements.
Danielle Sieger is thanked for her assistance with the mea-
sured section at Mt. Achernar. We thank Brian Staite for
his help with logistics, mountaineering, and for sharing
with neophyte Antarctic researchers his >2 decades of
experience working on ‘the ice.’ Fixed wing transport was
provided by the 62nd and 446th Airlift Wing of the U.S.
Air Force, stationed at Joint Base Lewis-McChord, WA,
the 109th Airlift Wing of the New York Air National
Guard, and Kenn Borek Air Ltd. This work was supported
by funding from NSF grants ANT-0943935 and ANT-
0944532 to the University of Wisconsin-Milwaukee, and
ANT-0943934 to the University of Kansas.
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SUPPORTING INFORMATION
Additional Supporting Information may be found in the
online version of this article:
Fig. S1 Results of tree height estimate using the Niklas (1994) regression
calculation (red line); 95% confidence interval for the regression is indicated
by the dashed lines.
Fig. S2 Carbon isotope values for fossil stumps.
Fig. S3 Permineralized stump positions along three transects.
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