Permian Polar Forests: Deciduousness and Environmental Variation E

Geobiology (2012), 10, 479–495 DOI: 10.1111/j.1472-4669.2012.00338.x

Permian polar forests: deciduousness and environmental variation E. L. GULBRANSON,1,*J.L.ISBELL,1 E. L. TAYLOR,2,3 P. E. RYBERG,2,3 T. N. TAYLOR2,3 ANDP.P.FLAIG4 1Department of Geosciences, University of Wisconsin-Milwaukee, Milwaukee, WI, USA 2Department of Ecology and Evolutionary Biology, Natural History Museum and Biodiversity Institute, University of Kansas, Lawrence, KA, USA 3Division of Paleobotany, Natural History Museum and Biodiversity Institute, University of Kansas, Lawrence, KS, USA 4Bureau 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 measurements 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 techniques of high-resolution carbon isotope studies of wood and mummified wood can be applied to permineralized 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 paleobotanical, 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

Upper Permian strata of Antarctica reveal that tree rings INTRODUCTION are dominated by earlywood with very minimal amounts of Well-preserved fossils of the extinct plant Glossopteris and latewood (1–3 cells wide), suggesting that the unique pho- other plants from Antarctica demonstrate that the conti- toperiod of the polar latitudes promoted rapid cessation of nent was vegetated in the late Paleozoic (e.g., Seward, photosynthesis at the onset of winter (Ryberg & Taylor, 1914; Schopf, 1970; Francis et al., 1993; Taylor, 1996). 2007; Taylor & Ryberg, 2007). The occurrence of leaf-rich Apparent polar wander paths indicate that Antarctica was sedimentary layers has been used to invoke a seasonally near the South Pole during the Permian (Powell & Li, deciduous habit for Glossopteris (Plumstead, 1958; Retal- 1994; Lawver et al., 2008; Domeier et al., 2011; Isbell lack, 1980; Taylor et al., 1992). Pigg & Taylor (1993) et al., 2012), implying that Glossopteris and other ﬂora observed that Glossopteris leaf compressions vary little in grew and thrived near or above the South Polar Circle. leaf size and suggest that this may reﬂect periodic leaf drop Tree ring studies of permineralized Glossopteris wood in owing to environmental stresses similar to the habit of

© 2012 Blackwell Publishing Ltd 479 480 E. L. GULBRANSON et al. evergreen trees and that more evidence is required to link in situ fossil forests to compare paleosol composition and these leaf compression layers with seasonal conditions that maturity with forest succession and structure. would indicate a deciduous habit for Glossopteris. Evergreen This study aims to describe (i) the soils and sedimentol- trees and deciduous trees, however, exhibit distinct pat- ogy of three Late Permian polar forests, (ii) the variation terns in carbon isotope ratios within tree rings (Schubert of forests with paleolandscape position, and (iii) the poten- & Jahren, 2011). Carbon isotope ratios in tree rings of tial to use stable carbon isotopes in permineralized wood evergreen trees display symmetrical variation while decidu- at subannual resolution to further study the environment ous trees display pronounced asymmetrical carbon isotope of polar forests and perhaps plant physiology at polar lati- ratio variation within tree rings. These distinct patterns tudes. This work is the first comparison of multiple con- open the possibility that high-resolution carbon isotope temporaneous Permian fossil forests at polar latitudes and analysis of fossil wood can determine a deciduous or ever- provides an integration of paleobotany, sedimentology, green habit for fossil trees. This study provides additional and isotope geochemistry to study carbon cycling in deep evidence from variations of carbon isotope ratios in per- time terrestrial environments at unprecedented temporal mineralized wood that confirm a seasonally deciduous resolution. Two recently discovered fossil forests are habit for Glossopteris and provides a promising avenue for described here for the first time from localities on Graphite further work in quantifying the environmental effects on Peak (85.05251ºS, 172.34792ºE) and near Wahl Glacier plant growth at polar latitudes at unprecedented temporal (84.09500ºS, 165.33167ºE), and we compare these forests resolution. Extracting an isotopic signature over the life with a previously studied fossil forest on Mt. Achernar history of several plants in an ecosystem is critically impor- (84.17824ºS, 160.90057ºE) supplemented with geochemi- tant in quantitatively reconstructing past climates, as isoto- cal analysis of Glossopteris wood from Mt. Sirius and pic variation in plant material provides a record of a first- Mt. Achernar (Fig. 1). order response of the plant, via stomatal conductance and photosynthetic rate, to the environment (Farquhar et al., BACKGROUND 1982, 1989; Leavitt & Long, 1991; Diefendorf et al., 2010; Kohn, 2010). As forested polar regions have no Late Permian paleogeographic reconstructions place the modern analogue (Taylor et al., 1992; Creber & Francis, Transantarctic Mountain region between 70 and 80ºS 1999) they can only be studied from deep time case stud- (approximately 75ºS for the study area), which is well ies (e.g., Francis, 1990; Falcon-Lang et al., 2001; Falcon- within the South Polar Circle (Powell & Li, 1994; Torsvik Lang, 2004; Jahren, 2007; Williams et al., 2008) or by & Cocks, 2004; Lawver et al., 2008; Domeier et al., simulating environmental parameters unique to the polar 2011). The stratigraphy presented here is part of the Vic- regions in growth chambers (e.g., Royer et al., 2005). toria Group of the Beacon Supergroup, which is earliest Therefore, quantification of plant–environment interactions Permian to Triassic in age (Kyle & Schopf, 1982; Barrett from deep time examples and experimentation with extant et al., 1986; Collinson et al., 1994; Isbell et al., 2001). plants via growth chambers will aid in understanding bio- The fossil forests studied herein are found in the upper geochemical cycling and climate feedbacks of high-latitude member of the Buckley Formation (Fig. 2), which is dated environments colonized by plants. to the Late Permian on the basis of palynology (Kyle & Paleoenvironmental reconstructions have suggested that Schopf, 1982; Farabee et al., 1990, 1991) and from detri- the Antarctic forests occupied a riparian niche in the Perm- tal zircons that exhibit an abundance of zircons of Late ian (Cuńeo et al., 1993; Isbell and MacDonald, 1991) Permian age (Elliot & Fanning, 2008). The oldest sedi- implying that the associated soils maintained at least peri- mentary rocks in the studied depositional basin are earliest odic wetness and dryness. The complex morphology of Permian (i.e., Asselian/Sakmarian, Kyle & Schopf, 1982), Glossopteris roots, known as Vertebraria, has led to the indicating that the Transantarctic Basin was actively subsid- concept that morphologic variation in Vertebraria was an ing at least by the Carboniferous-Permian boundary adaptation for growth in a semi-aquatic environment (approximately 299 Ma, Gradstein et al., 2004). (Gould, 1975). Sheldon (2006) compared Permian and Fossil forests in the Permian of Antarctica are exclusive Triassic paleosols (cf. Krull & Retallack, 2000) and inferred to the Late Permian Buckley Formation and its strati- a change in soil horizonation through time not related to graphic equivalents (Doumani & Minshew, 1965; Cuńeo landscape position, but rather related to the duration of et al., 1993; Francis et al., 1993). A published description soil formation and specific environmental conditions of the is only available for the forest on Mt. Achernar, whereas region. This indicates that depositional environment played Permian fossil forests are known to exist in the central an important role in determining the type of soil in an Transantarctic Mountains at Wahl Glacier, Lamping Peak, area, and subsequently helped control the plants adapted McIntyre Promontory, and Mt. Picciotto in the upper to grow in these soils. This study presents paleosol descrip- Buckley Formation near the Beardmore and Shackleton tions and interpretations from three locations hosting glaciers; and Mt. Weaver in the Queen Maud Mountains

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Permian fossil forest locality studied herein Permian fossil forest locality with Triassic strata Permian sections studied in 2010-2011 Permian and Triassic sections studied in 2010-2011 Triassic sections studied in 2010-2011

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 restof 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. near the Robert Scott Glacier. The fossil forest in the Formation (Retallack et al., 1996). The Buckley Formation upper Buckley Formation at Mt. Achernar (Figs 1 and 2) has local variations in grain size (Barrett et al., 1986; Isbell is notable in that the preserved tree stumps have diameters et al., 1997). Some regions are predominantly sand rich, of 9–18 cm with no more than 15 rings per trunk, imply- but coeval stratigraphic intervals in other areas are com- ing that this was a stand of saplings or juvenile trees (Tay- posed of thinner sandstone beds interbedded with thicker lor et al., 1992). Fossil leaf mats and permineralized peat beds of shale and silty sandstone containing either carbona- from the upper Buckley in the study area suggest that ceous plant detritus or non-carbonaceous plant compres- these polar forests were low diversity and probably did not sions (Briggs et al., 2010). have an understory flora (Cuńeo et al., 1993). However, Glacial deposits of the late Paleozoic ice age do not the Mt. Achernar in situ fossil forest does contain evidence occur in Antarctica after (i.e., younger than) the Early of understory vegetation comprised of herbaceous lycops- Permian (Isbell et al., 2003, 2008, 2012); however, glacia- ids, preserved as compression/impression fossils, whereas tion is interpreted to have existed at lower paleolatitudes in the permineralized tree stumps of the forest are attributed eastern Australia until the Late Permian (Fielding et al., to the Glossopteris seed plant (Schwendemann et al., 2010). 2008). Therefore, it is likely that the Late Permian time Despite the fact that Glossopteris trees grew at polar lati- interval in which these forests developed represents a tran- tudes, Taylor et al. (1992) found no evidence of frost rings sitional climate period from the icehouse(s) of the late in the fossil forest at Mt. Achernar. Paleozoic to the greenhouse state of the Mesozoic. The upper Buckley Formation is primarily composed of volcaniclastic sedimentary rocks with terrestrial facies of flu- METHODS vial and lacustrine affinity (Isbell et al., 1997; Isbell and MacDonald, 1998), but coal also occurs within this part of Measured stratigraphic sections (Fig. 2) were made at the formation and it is notable that coal is absent in Ant- Graphite Peak, Wahl Glacier, and Mt. Achernar noting arctica between the top of the Buckley Formation and the sedimentary structures, sediment composition, and fossils. upper portion of the overlying Triassic Fremouw Three permineralized stumps and root material were

110 240 Triassic Fremouw Fm. Triassic Fremouw Fm.

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100 Upper Permian Upper Permian upper Buckley Fm. upper Buckley Fm. 100 Explanation 90 Trough cross-bedding 90 Current ripple lamination 80

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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.

sampled for stable isotope analysis at Graphite Peak, taking 1992) under accession numbers 17169 A, B top and bot- care to preserve as much of the fossil in place. Six stumps tom, and C for the Mt. Achernar specimen, and accession were collected from Wahl Glacier, and four stumps were number 17170 for the Mt. Sirius specimen. Leaf compres- collected from Mt. Achernar for stable isotope analysis. sions and the surrounding sedimentary rocks were also Existing samples are housed in the Department of Geology sampled for geochemical and petrographic analysis. and Geophysics, University of Hawaii, but will be perma- We analyzed fossil forests at Graphite Peak and Wahl nently deposited in the Paleobotanical Collections, Natural Glacier localities by measuring the spacing between trees History Museum, University of Kansas (Taylor et al., and inferring tree height from the stem diameter (Table 1)

Table 1 Permineralized stump diameters at Graphite Peak mortar to pass through a 40-lm sieve and combusted off-

Stem Tree Basal line for carbon isotope ratio measurement on a Thermo diameter height area Finnigan MAT 253 (and a Finnigan MAT 252 for small † Stump (cm) (m)* (m2) Latitude (ºS) Longitude (ºE) volumes) in dual inlet mode at the Hufﬁngton Department

1 60 31 0.28 85.05251 172.34792 of Earth Sciences, Southern Methodist University. XRD 2 32 23 0.080 85.05251 172.34798 analysis of homogenized powders of the sample did not 3 43 26 0.15 85.05260 172.34724 indicate the presence of carbonate minerals, and carbonate 4 28 21 0.062 85.05262 172.34709 minerals were not observed in thin section, and therefore, 5 30 22 0.071 85.05279 172.34688 contamination from inorganic carbon sources is unlikely. *Tree height inferred from transfer function: Log(y) = 1.59 + 0.39 Log (x) Samples were combusted in sealed Vycor tubes at 900 °C 0.18[Log(x)]2, where y is tree height in meters, and x is stem diameter in for two hours followed by a linear decrease in temperature meters (Niklas, 1994).†Basal area (BA) calculated as BA = dbh2 9 7.854 ° ° 1 ° to 650 Cat1 C min , temperature was held at 650 C (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 for two hours followed by cooling to 25 C overnight. stand and dividing by the area of the studied. 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 to understand the canopy structure. Carbon isotopes are Cu was complete for the majority of samples, and there- measured from permineralized wood at 1.5–2-mm intervals fore, the cryogenic distillation procedure was modified to in the direction of wood growth (i.e., radially), to infer the separate CO2 from the large quantities of SOx possibly annual or seasonal uptake of CO2 from the Late Permian remaining in the Vycor tubes. A mixture of liquid nitrogen atmosphere. The carbon isotope measurements are likely (LN) and n-pentane (131 °C) was made in place of the indicative of seasonal carbon fixation because the sampling usual dry ice methanol/ethanol slush (72 °C) to facilitate intervals are much thinner than the tree ring widths, which the separation of CO2 from SOx by lowering the tempera- range from 4 to 11 mm. Sampling tree rings at higher res- ture closer to the freezing point of sulfur oxides. The gas olution (e.g., 0.1-mm intervals) was completed to observe was passed through a LN trap and non-condensable gasses whether the carbon isotope pattern of a tree ring changes were evacuated. The LN trap was quickly replaced with the with increased sampling density. LN-n-pentane trap to maintain temperatures close to

Tree height estimates were determined using the transfer liquid nitrogen temperature during the switch. CO2 functions of Niklas (1994) for woody species that correlate evolved rapidly from the LN-n-pentane trap and was stem diameter to tree height (Table 1). We calculated the allowed to be collected in a second LN trap. The amount

95% confidence interval for the original data set of Niklas of purified CO2 gas was measured manometrically (1994), which indicates that stem diameters must differ and transferred to borosilicate tubes for isotope ratio between 6 and 10 cm to produce statistically significant measurement. tree height estimates (Fig. S1). Forestry analysis of the Mt. The results of the offline combustion and dual inlet iso- Achernar fossil forest has been previously completed. This tope ratio measurements indicated that sampling at higher manuscript presents new field measurements of tree posi- spatial resolution (i.e. 0.1-mm sample intervals within tree tions for Graphite Peak and Wahl Glacier to quantify tree rings) might be possible. In advance of this higher-resolu- density and basal area using the point-centered quarter tion sampling strategy we analyzed replicate samples from method (Cottam & Curtis, 1956; Cuńeo et al., 2003). the dual inlet data set via an elemental analyzer (EA) The point-centered quarter method is designed to estimate interfaced to an isotope ratio mass spectrometer in contin- the mean area of plants by measuring the distances of uous flow mode at the Stable Isotope Facility at the Uni- plants to arbitrary sampling points along a transect. Each versity of California-Davis to assess reproducibility sampling point is divided into four quadrants and the dis- between these very different analytical procedures. Sec- tance between the sampling point to the closest tree in ondary reference materials (nylon d13C = 27.81&, peach 13 each quadrant is used as an individual samplep andffiffiffiffiffi the aver- leaves d C = 26.12&, and bovine liver age distances of all the samples is equal to M , where M d13C = 21.69&), which are calibrated against primary is the mean area of plants (Cottam & Curtis, 1956). reference materials, were analyzed within each batch run Samples of tree rings were cut from permineralized to correct and normalize the measured values from the wood with a tile saw equipped with a wafer blade at the sample. All materials resulted in precision better than University of Wisconsin-Milwaukee. The tree ring samples 0.1& (1r). A quality assurance standard (USGS-41 Glu- were split in half along the tangential plane such that the tamic Acid, d13C =+37.626&) was run within each batch two halves represent one half that is predominantly early- and had a standard deviation (1r) <0.3& over the course wood and one half that has earlywood and a portion of of the experiment with an average d13C value of latewood. The halved tree rings were crushed in an agate +37.62&.

To sample permineralized wood at a spatial resolution of ples within a single tree ring and for several rings. This approximately 0.1 mm thickness we milled samples by method can be envisioned as an improvement over the hand with a rotary tool equipped with a diamond bit and more analytically precise dual inlet measurements in that a monitored depth of sampling with calipers. Sampled sec- greater portion of the total isotopic signal can be extracted tions of permineralized wood (0.050–1.0 mm thick) from from a tree ring (Schubert & Jahren, 2011). the upper Buckley Formation at Mt. Sirius were prepared for analysis via elemental analyzer-continuous flow isotope RESULTS ratio mass spectrometry (EA-CFIRMS) at the laboratory of Dr. A. Hope Jahren at the University of Hawaii-Manoa. Graphite peak The sampling strategy is designed to make ultra-thin samples of permineralized wood sequentially along the direc- During the 2010–2011 austral summer season in Antarc- tion of wood growth and has the potential to directly tica we discovered a Permian in situ fossil forest at Graph- sample latewood, which is commonly a few cells thick ite Peak near the Keltie Glacier (Fig. 1), which occurs 99 (0.01–0.2 mm thick) in these samples (Ryberg & Taylor, m below the contact of the upper Buckley and the Triassic 2007; Taylor & Ryberg, 2007). For the determination of Fremouw fms (Fig. 2). The stumps are found upright with evergreen habit versus deciduous habit from stable isotope intact roots in a approximately 50 cm thick, thinly bedded trends in tree rings it is important to isolate latewood from (<1 cm thick), light gray siltstone (Fig. 3A–C) that con- earlywood to conclusively determine whether a wood sam- tains carbonaceous Glossopteris leaf compressions on bed- ple has an asymmetric carbon isotope profile in the tree ding planes. The compressions preserve leaf morphology ring (deciduous habit) or a symmetrical carbon isotope with both the blade and attached petiole in many speci- profile (evergreen habit). Samples are ground away from mens. The siltstone, interpreted as a paleosol, is laterally the permineralized wood sample, massed, and sealed in a continuous for >100 m and is overlain by 6.5–7 m of par- tin capsule for EA-CFIRMS analysis thereby permitting rel- tially covered siltstone capped by a conspicuous, partially atively rapid collection of isotope data from multiple sam- silicified coal seam. Root structures were excavated from

A B

C D

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 E F 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 Permian polar forests 485 the in situ stumps and these roots were traced tens of cen- Glacier and Graphite Peak forests brings the total number timeters into the thinly bedded gray siltstone (Fig. 3A,B), of in situ fossil forest localities in the Beardmore Glacier tapering downwards. In cross section the roots are com- region to four, with the other two being the Permian pletely permineralized but lack the diagnostic lacunae of forest at Mt. Achernar (Taylor et al., 1992) and a Triassic many Vertebraria roots, although this may be due to their forest in the Fremouw Formation at Gordon Valley proximity to the root-shoot transition zone (Neish et al., (Cuńeo et al., 2003). The fossil forest at Wahl Glacier is 1993; McLoughlin et al., 1997, 2005; Decombeix et al., approximately 100 m below the contact between the Buck- 2009). Vertebraria was also observed in float in the overly- ley and Fremouw formations (Fig. 2). Thirteen permineral- ing beds. In total, six in situ stumps were observed in the ized stumps are found upright with intact root systems exposed bedding plane; five stumps were completely per- that penetrate underlying sedimentary rocks (Fig. 3E,F). mineralized and one was permineralized only in the outer- The root systems trend horizontally away from the stumps. most portions of the stump, whereas the innermost The sedimentary rocks surrounding the permineralized portions were filled with gray, blocky, siltstone (Fig. 3D). stumps are divided into a lower siltstone that contains the Sandstones that crop out above and below the fossil for- root systems and an overlying sandstone that covers most est layer are laterally extensive across the outcrop having a or all of the stumps. The lower siltstone is gray with a sheet-like geometry. The sandstones are fine- to medium- white patina, thinly bedded, and contains leaf compres- grained, with a subangular to subround texture; the com- sions. The overlying sandstone is brown, fine- to medium- position is dominated by lithic fragments, although mud- grained and medium-bedded, and contains crude stone clasts and quartzite clasts are observed at the base of cross-stratification; the basal contact of the sandstone trun- sandstone beds, and the sandstones truncate underlying cates underlying siltstone. The stratigraphic succession of strata at the centimeter-scale. Trough cross-bedding and the upper Buckley Formation at Wahl Glacier has a general ripple laminations are observed within the sandstone beds. 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 Graphite Peak Stratigraphy The sandstone lithofacies at Graphite Peak above and Interpretation of Wahl Glacier stratigraphy below the fossil forest layer represent fluvial channel and floodplain (splays, mires, lakes) deposits of low-sinuosity The sedimentary strata surrounding the fossil forest at streams (Fig. 2). Paleoflow directions for fluvial sandstones Wahl Glacier, like Graphite Peak, contain both thick and at Graphite Peak are oriented toward the South Pole and thin lithic sandstones with sheet-like geometries that represent transverse flow relative to axial drainage patterns contain trough cross-bedding, organic-rich shales, thin directed toward South Victoria Land (Collinson et al., laminated siltstones, and coal. Therefore, these sandstones 1994; Isbell et al., 1997; Fig. 1). Sandstones at Graphite are interpreted as low-sinuosity channel, splay, lake, and Peak contain mudstone rip-up clasts and quartzite pebbles mire fluvial deposits. The mean paleocurrent vector of near the sandstone base, indicating erosion of underlying these sandstones indicates an oblique direction (i.e., trans- strata during the entrenchment of the channel system. The verse flow) relative to the basin axis, with a general orienta- fine-grained texture and weak horizontal bedding of the tion toward South Victoria Land. The fossil forest layer, fossil forest layer suggests a low energy environment of however, is found rooted within a thinly bedded, gray silt- deposition. These sedimentary rocks are likely floodplain stone that is in contact with crudely laminated sandstones. deposits formed from the continued aggradation of sedi- The environment of deposition at Wahl Glacier for the fos- ment after an avulsion episode (Smith et al., 1989). This sil forest layer is likely a channel margin or forested levee/ interpretation is consistent with the low degree of pedo- splay complex of a low-sinuosity fluvial system, suggesting genic modification of these sedimentary rocks inferred a closer proximity to the fluvial system than the Graphite from the lack of field-based indications of soil formation Peak stumps that are surrounded by finer-grained and (e.g., horizonation, reddening, clay accumulation, redoxi- thinly bedded strata representing a relatively distal portion morphic features), where pedogenesis is punctuated by the of a splay complex (cf., Smith et al., 1989). continued addition of sediment (Kraus & Aslan, 1993). Mount Achernar Wahl glacier We studied two Permian fossil forest levels at Mt. Achernar During the 2003–2004 austral summer season we (J.L. Is- in the vicinity of the Law Glacier (Fig. 1). The overlying bell) discovered the remains of a fossil forest in the upper Fremouw Fm. does not crop out at this locality; however, Buckley Formation at Wahl Glacier, near Walcott Ne´ve´ comparison with surrounding locations suggests that this (Knepprath, 2006; Fig. 1). The discovery of the Wahl section of upper Buckley occurs approximately 50 m below

© 2012 Blackwell Publishing Ltd 486 E. L. GULBRANSON et al. the upper Buckley Fm. and Fremouw Fm. contact (Fig. 2). truncation surface. The upper 2 m of the section contains The basal 3 m of this section consists of a massive white the two beds hosting the in situ tree stumps and roots siltstone and fine root haloes that branch downwards but (Fig. 4A,B). diverge horizontally at approximately 1 cm depth. The siltstone has sharp upper and lower boundaries and interbed- Interpretation of Mount Achernar stratigraphy ded white siltstone beds with crude bedding that contain Glossopteris leaf compressions and carbonaceous woody tis- Mt. Achernar contains evidence of subaerial exposure in sue. The preservation of the fossil plant material is variable the form of rooted siltstones interpreted as weakly devel- with some fossils preserving only vein skeletons and other oped paleosols (Protosols) and coals (Histosols). Unlike beds preserving most of the blade attached to the petiole. Graphite Peak (Fig. 5A,B), however, the environment of Glossopteris reproductive structures are present in some of deposition at Mt. Achernar is interpreted as being lower the beds as well (Ryberg et al., 2011). energy on the basis of an abundance of fine-grained sedi- Overlying these units is approximately 1 m of coal inter- mentary rocks near the fossil forest beds (Fig. 5C,D). bedded with medium- to thin-bedded (5 cm to <1 cm) Channelization of some siltstone beds indicates water white siltstone with abundant plant debris on bedding movement and transport of material (Fig. 5D), and the planes. The coal contains woody tissue and leaf fragments. horizontal bedding with abundant plant remains implies a Greenish brown mudstone clasts occur within the white subaqueous environment with low energy (e.g., rare ripple siltstone. Overlying the coal and siltstone is approximately laminations) or perhaps standing water allowing for sus- 1 m of medium-bedded, interbedded siltstone with a white pension settling of material. Interbedding of splays, coal, patina, blue-gray interior, and rare ripple laminations. Fos- and siltstone suggest deposition along the margins of a sil leaf fragments are abundant on some bedding planes. shallow lake. These environments are consistent with a Two truncation surfaces were noted that cut through the shallow lacustrine system or wetland with fluvial input of underlying siltstone; these have a lenticular geometry and sediment. Therefore, the lower energy lacustrine, marginal are roughly 1.5 m wide with bedding that onlaps onto the lacustrine, mire, and splay environments interpreted at Mt.

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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

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 C D 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.

Fig. 6 Fossil forest photographs. (A) Two upright permineralized stumps from Graphite D E 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.

Achernar are likely part of a mosaic of landscapes that were (Table 1). The mean distance between trees in the Graph- laterally equivalent to low-sinuosity channel and floodplain ite Peak forest is 20.8 m (Fig. S3A), which corresponds to fluvial deposits at Wahl Glacier and elsewhere in the Beard- a density of 23 individuals ha 1 using the method of Cot- more Glacier region (Isbell et al., 1997). 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 Paleoforestry fossil wood samples as being in situ. Stem diameter mea- The permineralized stumps at Graphite Peak have diame- surements for the fossil forest at Mt. Achernar are pub- ters that range from 28 to 60 cm (Fig. S1), which corre- lished as a range of 9–18 cm (Fig. S3B, Taylor et al., spond to tree heights that range from 21 to 31 m 1992) for fifteen permineralized stumps, and correspond

S1). Mass Carbon yield d13C † Permineralized stumps at Wahl Glacier have a mean Sample*, (mg) (lmolC) (& VPDB) diameter of 25.6 cm (Fig. S1), which corresponds to a 2p 17.5 30.7 22.7 mean tree height of 19.2 m. The mean distance between 2c 5.1 10.5 23.9 trees at Wahl Glacier is 6.2 m and corresponds to a tree 3p 6 11.8 23.7 density of 263 individuals ha 1 (Fig. S3C), which reflects 3c 16.1 23.8 22.6 an average obtained by using the point-centered quarter 4p 14.8 22.4 22.9 method and by dividing the number of stumps by the 4c-1 7.3 10.9 23.7 4c-2 5.7 9 24 area of the exposed surface (Knepprath, 2006). It is 5p 13.5 21.1 22.6 noteworthy that several permineralized stumps at Wahl 5c 4.6 6.04 24.9 Glacier contain secondary mineralization of sulfur-bearing 6p-1 18.2 22.8 22.8 minerals, such as pyrite or chalcopyrite, near the pith 6p-2 11 12.6 23.3 of the stump, whereas Graphite Peak permineralized 6c-1 9.8 18 23.3 6c-2 11.2 16.5 23 wood appears to be homogeneous with respect to 7p-1 2.6 5.9 24.9 mineralization. 7p-2 26.8 37.6 22.44 7p-3 25.9 33.2 22.5 7c 17.3 23.8 22.6 Geochemistry 8p 3.7 9.1 23.9 8c 20.5 27.7 22.5 Preliminary geochemical analyses were made on a permin- 9p 13.9 18.8 22.3 eralized Glossopteris stump from Mt. Achernar. XRD 9c 23 31.3 21.4 analysis of powdered and mixed permineralized wood from *Samples are referenced by ring number ‘2’ and whether they are early- Mt. Achernar indicates that quartz is the only mineral pres- wood dominated ‘p’ or a mixture of earlywood and latewood ‘c’. Replicate ent in the sample. Offline combustion and cryogenic sepa- analyses are indicated by the number, for example, 7p-2 is the second rep- † ration of CO2 allowed for high-precision measurements of licate analysis of sample 7p. University of Kansas accession number for the the carbon yield of the samples (Fig. S2A,B). A range of 3 sample is 17169B top and bottom, the sample is from Mt. Achernar, upper –23 mg of sample was combusted and corresponds linearly Buckley Formation, Antarctica. to a range of CO2 quantities of between 9 and 31 lmol, respectively (Table 2). Thus, the average weight percent of Replicate samples from Mt. Achernar analyzed via carbon in a bulk sample of this permineralized wood is 2% EA-CFIRMS, a technique that will efficiently accommodate (±0.4% 1 SD). an increase in the number of samples analyzed, were sys- Stable carbon isotope ratios were measured within tematically more positive than the samples analyzed via growth rings of permineralized wood to assess whether or dual inlet by approximately 0.2& (Fig. S2C). The system- not seasonal variation observed in extant plants (e.g., Fran- atic and small offset between the dual inlet and elemental cey & Farquhar, 1982; Leavitt & Long, 1991; Helle & analyzer methods indicates that the samples analyzed via Schleser, 2004; Schubert & Jahren, 2011) occurs in the EA-CFIRMS will likely preserve the same isotopic signals fossil plants and whether the variation in carbon isotope identified with dual inlet measurements. ratios can elucidate whether Glossopteris maintained a Ultra-thin sections (<0.1 mm thick) of permineralized deciduous or evergreen habit. For the Mt. Achernar sam- wood from an Araucarioxylon specimen collected in the ple, measured d13C values range from 21.4& to uppermost Buckley Fm. at Mt. Sirius (Fig. 1) were ana- 24.9& (Table 2), with an average d13C value of 23.2& lyzed for carbon isotope ratios via EA-CFIRMS to test (±0.9& 1SD). Carbon isotope ratios vary within tree rings whether a deciduous or evergreen habit can be inferred with the beginning of a ring having the most positive d13C from high-resolution isotope geochemistry of fossil wood value and the later portion of the ring having the most (Fig. 8). Modern deciduous and evergreen trees display negative d13C value (Fig. 7). This pattern repeated for the pronounced differences in intra-ring carbon isotope ratios, majority of rings analyzed, with exception of the exterior where deciduous trees show an asymmetric, three-phase of the sample that showed a pronounced enrichment in trend with more negative values in latewood, increasing 13C relative to samples from the interior of the specimen. through the ring boundary an into the earlywood of a sub- In this outer part of the stump, the beginning of the rings sequent tree ring (Helle & Schleser, 2004). On the other had a fairly consistent d13C value of approximately hand, evergreen trees display a symmetric carbon isotope 22.6&, whereas the values for the later portion of the trend throughout a tree ring, with more positive values in rings varied from 24& to 25&. Thus, d13C values vary the earlywood (Schubert & Jahren, 2011). The results by 1–2& within tree rings in the permineralized wood show clear isotopic variation within tree rings (Fig. 8). The specimen from Mt. Achernar. d13C values are more negative than the Mt. Achernar

A stump, by up to 2&, and the magnitude of d13C value variation 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 B the earlywood/latewood boundary, which continues into the next tree ring. This three-phase variation in carbon stable 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 important differences in d13C values and the range of d13C values within tree rings between the two localities are apparent despite the differences in sampling strategy and

Fig. 7 Mt. Achernar wood and carbon isotope values. (A) Transverse sec- isotope analysis. tion of permineralized wood from Mt. Achernar used for isotope ratio measurements. (B) Tree ring d13C values, gray shading indicates where two samples were taken from the same ring, other values likely represent one DISCUSSION d13C value for the entire ring. Arrows point to region in the stump that the Fossil forests in the upper Buckley Formation at Graphite data points correspond to. Dashed vertical lines denote tree ring boundaries. Note peculiar increase in d13C values toward the exterior of the sam- Peak and Wahl Glacier occur at similar lithostratigraphic ple (to the right). positions approximately 100 m below the contact between

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 global 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.

Table 3 Carbon isotopic data of fossil wood from Mt. Sirius tion (Demko et al., 1998). The occurrence of only Glossop-

Position Mass Carbon yield d13C teris leaves (Fig. 6C,E) in the Graphite Peak fossil forests † Sample*, (mm) (mg) (lgC) (VPDB) implies that the stand was low diversity, which is consistent with Late Permian fossil forests elsewhere in Antarctica Ring 1 1 0.500 1.82 90 24.73 (Cuńeo et al., 1993). In addition, no other fossil macrofl- 2 1.00 1.66 41 24.90 ora was observed in the fossil forest and this suggests the 3 1.50 1.51 17 24.95 absence of understory vegetation at Graphite Peak in con- 4 1.60 1.67 26 25.56 trast to the Mt. Achernar in situ forest that does contain a 5 2.55 1.49 18 25.48 herbaceous lycopsid understory (Schwendemann et al., 6 2.59 1.65 16 25.25 7 2.60 1.89 21 25.16 2010). The field measurements of spacing between trees 8 3.25 1.59 10 24.93 indicates that the preserved trees at Graphite Peak and 9 3.35 1.82 12 25.15 Wahl Glacier are widely spaced relative to the fossil forest 10 3.70 1.42 16 25.14 at Mt. Achernar and were likely more mature trees relative Ring 2 to Mt. Achernar (Fig. S3; Fig. 9A). There is overlap 1 3.80 1.83 10 24.71 2 3.85 1.67 11 25.08 between tree height estimates at the fossil forest localities, 3 3.90 1.66 10 24.82 however, taking into account the 95% confidence interval 4 4.25 1.55 11 25.10 for the regression equation used to estimate tree height 5 4.40 1.22 8 24.27 (Fig. 1), which suggests that the mean height of the fossil 6 4.60 1.79 13 24.86 forest at Wahl Glacier was likely intermediate in a grada- 7 4.65 1.37 9 24.71 8 4.75 1.09 27 24.75 tion between taller trees at Graphite Peak and shorter more 9 5.00 1.22 11 25.31 juvenile trees at Mt. Achernar. 10 5.05 1.7 14 25.07 At least three wood morphogenera have been described 11 5.23 1.31 35 25.34 from the study region: Araucarioxylon, Kaokoxylon, and 12 5.55 1.22 32 24.84 Australoxylon (Pigg & Taylor, 1993; Taylor & Ryberg, 13 5.70 1.36 14 25.42 14 5.83 1.51 23 25.03 2007; Decombeix et al., 2010, 2012); therefore, it is pos- Ring 3 sible that tree height differences are related to species dif- 1 6.23 1.85 10 25.42 ferences in the region. As each wood morphogenera has

*Numbers correspond to samples within a tree ring; thus, for ring 1, been found among Glossopteris leaf fossils, however, it is there are 10 samples individually analyzed for carbon isotope composition. difficult to assess the impact of these different wood mor- †University of Kansas accession number is 17170, the sample is from Mt. phogenera on the paleoecology of the forests. Alterna- Sirius, upper Buckley Formation, Antarctica. tively, the variation of tree height and tree density likely reflects some combination of forest maturity, environmen- the Buckley and Fremouw formations. The fossil forest at tal stresses, and/or disturbance. It is possible that forest Mt. Achernar occurs within the upper Buckley Formation; maturity, disturbance and environmental stress may be however, the Fremouw Formation does not crop out at linked to landscape position as pronounced variation in this locality, and so it is not possible to definitively corre- tree density and plant diversity are observed in extant late the fossil forest at Mt. Achernar with Graphite Peak plants on a variety of landscapes (Fig. 9B,C; Gregory et al., and Wahl Glacier other than to assign it a Late Permian 1991; Viereck et al., 1993; He & Duncan, 2000). age on the basis of palynology (Farabee et al., 1990, Both Wahl Glacier and Graphite Peak fossil forests occur 1991). In the following discussion, we interpret the nature in similar depositional environments, proximal to low-sinu- of the forests at each locality in regard to the environment osity stream systems, whereas the fossil forest at Mt. Acher- of deposition. The preliminary stable carbon isotope data nar occurs in a lower energy environment further away will be discussed in terms of the potential for recovering from large drainage systems in the Transantarctic basin. high-resolution geochemical archives from these fossil Stark differences in basal area and tree density further sug- plants. gest an environmental control on forest development Retallack & Krull (1999) interpreted broad areas of Ant- (Fig. 9A), where low basal area and low tree density corre- arctic landscapes in the Permian as densely forested, a sponds to levee/splay complexes at Wahl Glacier and monotonous extension of vegetation observed from sedi- Graphite Peak, and much higher basal area and tree density mentary deposits of fluvial-floodplain affinity. Such general- are estimated for lacustrine and distal floodplain environ- izations are problematic as the preservation of plant fossils ments at Mt. Achernar and a suite of stumps from Lamping is biased toward riparian environments and without direct Peak (Figs 1, 9A, Knepprath, 2006). This trend of decreas- observation from other environments, it is impossible to ing tree density and increasing tree maturity is known as describe the vegetative habit and ecology without incurring ‘self-thinning’ (Cao et al., 2000; Falcon-Lang, 2004) and significant errors in paleoclimate/paleoforestry reconstruc- is observed in modern landscapes as forests age away from

100 100 A LP B ) ) Axel Heiberg 80 –1

–1 80 LP MA ha ha Modern 2 2 60 60 floodplain Distal Distal position Distal floodplain/ Permian 40 Levee/splay 40 floodplainposition lacustrine Splay Gordon Valley 20 WG 20 Splay Basal Area (m Basal Area (m GP Curio Bay 0 0 500 1000 1500 2000 2500 3000 0 1 2 3 4 5 6 –1 Tree Density (trees ha–1) Log10 Tree Density (trees ha )

C Increasing forest maturity/age Modern boreal forests Black Alder

White Bog spruce spruce Shrubs

river Decreasing tree density

D Wahl Gl./Graphite Pk. Lamping Pk. Mt. Achernar Glossopterids Lycopsids Lake Braided stream Late Permian forests

Increasing forest maturity/age

Decreasing tree density

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 localities are displayed by the blue square symbols: Gordon Valley (Middle Triassic, Cu´ neo 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. zones of high and persistent disturbance (i.e., streams). A induced by intense competition for light, water, and nutri- common progression of diversity and tree densities in the ents (Cao et al., 2000; Falcon-Lang, 2004). Forest canopy Pacific northwest trend from bare alluvium to mixed shrubs structure is an important determining factor in resource and thin alders of high density (approximately competition and future work to assess the growth form of 100 000 ind. Ha 1) on terraces adjacent to active stream glossopterid trees at different latitudinal gradients, as well channels, whereas the oldest landscapes (>700 years) of as the ecology of different late Permian wood morphogen- bogs or mires occupied by black spruce with densities rang- era in Antarctica, may elucidate competition for light as ing from 500 to 2000 ind. Ha 1 (Fig. 9B,C, Viereck et al., opposed to nutrients or water. 1993). The observed self-thinning in the Permian, how- The sedimentary rocks that host in situ fossil forests at ever, is opposite of the modern, where Permian tree matu- Graphite Peak, Mt. Achernar, and Wahl Glacier are inter- rity increases (and density decreases) closer to the area of preted as paleosols as they meet the principle criterion for high potential disturbance and is similar to younger high- soil, which is to support plant life (Soil Survey Staff, latitude fossil forests of Cretaceous age in the Antarctic 2010). The paleosols at each locality are gray to whitish peninsula region (Falcon-Lang et al., 2001; Falcon-Lang, gray (Figs 3B–F; 4A,B; 6B,D), contain some degree of 2004). This trend is possibly related to intense competition bedding or sedimentary fabric, including leaf compressions for resources in a persistently disturbed (e.g., flooding) on bedding planes, and have a silt texture. These paleosols environment that was unsuitable for understory vegetation lack field-based indicators indicative of seasonal changes in the region. Moreover, as trees age, tree mortality can be in moisture content (Kraus & Aslan, 1993), that is,

© 2012 Blackwell Publishing Ltd 492 E. L. GULBRANSON et al. redoximorphic coloration, sequestration of redox-sensitive growth rings show markedly different trends between trees elements such as Fe and Mn, and differentiation of clay- with a deciduous versus evergreen habit (Fig. 8B; Schubert sized material into argillic horizons (sensu Alfisols, Verti- & Jahren, 2011). The permineralized stump from sols). Rather the studied paleosols are reflective of nearly Mt. Achernar contains d13C patterns that are consistent perennial saturation by freshwater (i.e., immature and with a deciduous habit (Fig. 7); however, the low sampling poorly drained). The occurrence of well-preserved, abscised density (i.e., two data points per ring) does not permit leaves in the sediment directly adjacent to permineralized trends to be established to rigorously support such a con- stumps in growth position further confirms prolonged clusion. On the other hand, because of the higher sam- water saturation as this situation produces an increase in pling density, the permineralized wood from Mt. Sirius acidity and contributes to the preservation of leaf litter rel- displays a three-phase d13C trend within individual growth ative to exposure at the soil-air interface (Gastaldo & rings that is consistent with a deciduous habit (Fig. 8); Staub, 1999). A persistent and high water table is inferred however, the isotope geochemistry does not indicate from the gray to whitish gray color and lack of mottling as whether this habit was advantageous at polar latitudes. Ro- seasonal aeration would promote the oxidation and trans- yer et al. (2005) indicate that deciduousness under a polar port of Fe- and Mn-bearing compounds resulting in redox- light regime (i.e., months of continuous light and months imorphic features (Vepraskas, 1994). of continuous darkness in one year) and cold winters Applying modern soil classification (Soil Survey Staff, results in a reorganization of carbon fixation strategies 2010) to the paleosols studied herein results in their classi- when compared to evergreen trees. While these results may fication as Aquents, Aqu-Aquic those forming under seem to cast doubt on an elemental cycling competitive perennial water saturation, and ents-Entisols, poorly devel- edge of deciduous trees over evergreen trees at polar lati- oped soils on young or unstable landscapes. The term tudes, the fact that deciduous trees existed at polar lati- aquic is problematic in paleosol taxonomy as it is inher- tudes is a fact that is as yet not fully understood. Perhaps, ently interpretative, because we cannot know for certain the explanation lies in the dominance of deciduous plants whether water saturation was perennial or seasonal. There- at polar latitudes during past times of global warmth, for fore, our interpretations are guided by the range of afore- example, the Late Permian-Triassic of Antarctica and the mentioned observations on soil color, mineralogy, root Late Cretaceous of Alaska. morphology, and tree ring analysis. The paleosol classification system of Mack et al. (1993) is adapted for use in CONCLUSIONS geologic materials where these paleosols (Aquents) are clas- sified as Protosols on the basis of poor (i.e., absent) horiz- A field- and laboratory-based study of Late Permian in situ onation. The modern equivalents of Protosols (Entisols fossil forests of the central Transantarctic Mountains pro- and Inceptisols) dominate the global landscape and occur vides the first integrated geochemical, sedimentologic, across all climate regimes, slopes, vegetation types, land paleopedologic, and paleobotanical analysis of this unique surface ages, and hydrology. Based on the aforementioned polar ecosystem. The analysis of paleosols and contempora- criteria, we interpret these paleosols as being saturated with neous sedimentary rocks indicates that the fossil forests liquid water for several months of the year, if not perenni- grew in two different paleoenvironments, a low energy ally. Freezing conditions were apparently short-lived given environment adjacent to axial drainage systems of the the absence of frost rings in Mt. Achernar tree stumps Transantarctic basin, and two higher energy environments (Taylor et al., 1992); therefore, despite the polar latitude proximal to low-sinuosity fluvial systems. Tree height, tree of these fossil forests, perennial water saturation was a density, and basal area differ markedly between the inferred plausible condition. distal floodplain environment and levee or splay environ- The isotope geochemistry of permineralized wood from ments; however, tree density and basal area are similar for Mt. Achernar indicates that carbon isotopic records at sub- localities in the same inferred paleoenvironment. We inter- annual resolution can be extracted from permineralized pret this tree density trend as ‘self-thinning’. A comparison wood (Fig. 7). However, the data we collected from the with modern forests indicates that the observed Late Perm- sample from Mt. Sirius (Fig. 8) are the oldest subannual ian self-thinning is opposite of the modern, which suggests carbon isotope study of tree growth rings, with the next that the unique ecology of Late Permian polar forests pro- oldest samples being the ‘sub fossil’ wood of Eocene age moted the loss of understory vegetation in regions of high in the Canadian Arctic (Jahren, 2007; Jahren & Sternberg, disturbance (e.g., fluvial systems). 2008; Schubert et al., 2012), underscoring the need for Carbon isotope ratios of permineralized wood presented high-resolution studies such as this for other time periods herein are, to our knowledge, the first high-resolution data in the Phanerozoic. The results for the Mt. Achernar and set of this kind from material older than the Cenozoic. Mt. Sirius samples provide evidence for a deciduous habit The stable isotope geochemistry indicates that intra-tree for Glossopteris trees. Measured d13C values within tree ring measurement of carbon isotope ratios is possible even

© 2012 Blackwell Publishing Ltd Permian polar forests 493 in permineralized samples. Such detail can provide impor- Carboniferous-Permian, Buenos Aires, Argentina, Stratigraphy tant insights into the habit of arborescent plants and implies and Geology, 2,13–40. ´ that additional environmental variables, such as water stress, Cuneo NR, Taylor EL, Taylor TN, Krings M (2003) In situ fossil forest from the upper Fremouw Formation (Triassic) of could be quantified from such ancient ecosystems. Antarctica: paleoenvironmental setting and paleoclimate analysis. Palaeogeography, Palaeoclimatology, Palaeoecology, 197, 239– 261. ACKNOWLEDGMENTS Decombeix A-L, Taylor EL, Taylor TN (2009) Secondary growth We are especially grateful to Drs. Neil Tabor and A. Hope in Vertebraria roots from the Late Permian of Antarctica: a change in developmental timing. International Journal of Plant Jahren for assistance and generosity in the use of their lab- Sciences 170, 644–656. oratory facilities; and Mr. Bill Hagopian and Dr. Scott Me- Decombeix A-L, Taylor EL, Taylor TN (2010) Epicormic shoots yers for assistance with stable isotope ratio measurements. in a Permian gymnosperm from Antarctica. International Danielle Sieger is thanked for her assistance with the mea- Journal of Plant Science, 171, 772–782. sured section at Mt. Achernar. We thank Brian Staite for Decombeix A-L, Taylor EL, Taylor TN (2012) Gymnosperm trees from the Permian of Antarctica: an anatomically preserved trunk his help with logistics, mountaineering, and for sharing of Kaokoxylon sp. Comptes Rendus Palevol, 11,21–29. with neophyte Antarctic researchers his >2 decades of Demko TM, Dubiel RF, Parrish JT (1998) Plant taphonomy in experience working on ‘the ice.’ Fixed wing transport was incised valleys: implications for interpreting paleoclimate from provided by the 62nd and 446th Airlift Wing of the U.S. fossil plants. Geology, 26, 1119–1122. Air Force, stationed at Joint Base Lewis-McChord, WA, Diefendorf AF, Mueller KE, Wing SL, Koch PL, Freeman KH (2010) Global patterns in leaf 13C discrimination and the 109th Airlift Wing of the New York Air National implications for studies of past and future climate. Proceedings of Guard, and Kenn Borek Air Ltd. This work was supported the National Academy of Sciences of the United States of by funding from NSF grants ANT-0943935 and ANT- America, 107, 5738–5743. 0944532 to the University of Wisconsin-Milwaukee, and Domeier M, Van Der Voo R, Tohver E, Tomezzoli RN, Vizan H, ANT-0943934 to the University of Kansas. 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