T \ Anatomically preserved Glossopteris from the Beardmore ...
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Figure 2. Transverse section of Vertebraria showing decay pockets and disrupted growth rings. (x 30.)
The material examined in this study was collected during the 1969 - 1970 field season by the late James M. Schopf supported by the National Science Foundation (GA - 12315). The present research was supported by National Science Foundation grant DPP 82-13749. References Barrett, P.J. 1970. Paleocurrent analysis of the mainly fluviatile Permian and Triassic Beacon rocks, Beardmore Glacier area, Antarctica. Journal
Anatomically preserved Glossopteris from the Beardmore Glacier area of Antarctica K.B. PIGG and
T.N. TAYLOR
Department of Botany
and Institute of Polar Studies Ohio State University Columbus, Ohio 43210
The Glossopteridales represent an enigmatic group of pteridosperms that dominated the Permian flora of Gondwana. 8
Figure 3. A. Fungal hypha preserved in Araucarioxylon-type wood. (x 700.) B. Transverse section of wood showing wall appositions in tracheids of Araucarioxylon-type wood. (x 210.)
of Sedimentary Petrology, 40, 395 - 411. Blanchette, R.A. 1980-a. Wood decomposition by Phillinus (Fomes) pini: A scanning electron microscopy study. Canadian Journal of Botany, 58, 1496-1503. Blanchette, R. A. 1980-b. Wood decay: A submicroscopic view. Journal of Forestry, 78, 734 - 737. Otjen, L., and R.A. Blanchette. 1982. Patterns of decay caused by Inontus dryophilus (Aphyllophorales: Hymenochaetaceae), a whitepocket rot fungus of oaks. Canadian Journal of Botany, 60, 2770-2779. Schopf, J.M. 1970. Petrified peat from a Permian coal bed in Antarctica. Science, 169, 274 - 277.
Plants of this order were arborescent and had stems of the roots assignable to Vertebraria, a divers array of reproductive organs, and strap-shaped leaves with reticulate venation pattern. The leaves of these plants assigne to Glossopteris represent the major floristic component and ar known almost entirely from impression/compression spec imens. As such, they have provided little information about th biology and natural affinities of the plants. To date, the oni report of structurally preserved leaves of this general type i cludes the description of both fertile and vegetative foliage fro the Bowen Basin of Queensland (Gould and Delevoryas 1977. Numerous silicified specimens of Glossopteris have been ide tified in petrified peat collected from the Mount Augusta locality in the Beardmore Glacier area (Schopf 1970). This material provides a unique opportunity to investigate the anatomy and morphology of Glossopteris leaves and to compare the structurally preserved specimens with those taxa reported from the
Araucarioxylon-type,
ANTARCTIC JOURNAL
As presently understood, the genus Glossopteris is characterized by leaves that demonstrate considerable morphological variability. The silicified specimens from Mount Augusta are relatively small, measuring approximately 1.0 centimeter in maximum width and no more than 10.0 centimeters in length. The venation pattern is a unique reticulate type in which all of the veins appear to be the same size in surface view (figure 3). In addition, individual tracheids within the veins may branch or follow a sinuous course within the reticulum. The midrib consists of four or five larger veins that are parallel with the long axis of the leaf. In transverse section, each vein is characterized by a conspicuous bundle sheath (figure 2), up to two cell layers in thickness, with the individual cells often containing amor-
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Figure 1. Split surface of silicified specimen showing characteristic reticulate venation of Glossopteris leaf. (x 2.)
more commonly occurring impression/compression specimens. Specimens are analyzed by examining morphological features of the leaves that occur on split or weathered surfaces (figure 1) and subsequently preparing closely spaced, serial sections in order to examine histological features (figure 2).
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L
igure 2. Transverse section of Glossopteris leaf showing promient bundle sheaths containing disrupted vascular bundles. ( x 35.)
1485 REVIEW
Figure 3. Paradermal section of surface showing uniform size of reticulate veins. (x 9.)
phous materials. In some specimens, fibers may be associated with the bundle sheath. The vascular strand of each vein consists of primary, and a small amount of secondary, xylem. Phloem is not preserved and, in many specimens, the xylem is often distorted. Histologically, the ground tissue of the leaf consists of poorly differentiated mesophyll in which a palisade layer cannot be distinguished. Stomata occur on the lower epidermis. Upper epidermal cells have sinuous cell outlines, while those of the lower epidermis are straight. The' Mount Augusta Glossopteris foliage demonstrates marked histological differences when compared to the structurally preserved leaves from Bowen Basin. These differences include the absence of a palisade layer, thicker and more promi-
9
nent bundle sheath, lack of a distinctive hypodermis, and smaller amount of secondary xylem. These anatomical features provide for the first time the opportunity to compare details of Glossopteris leaves that differ in preservational mode. Such information greatly increases the value of foliage features as a useful biostratigraphic and evolutionary index. The material examined in this study was collected during the 1969 - 1970 field season by the late James M. Schopf supported by the National Science Foundation (GA - 12315). The present
Dating till by paleomagnetism: Allan Hills, southern Victoria Land E.M. CHERRY and H.C. NOLTIMIER Institute of Polar Studies
and
Department Geology and Mineralogy Ohio State University Columbus, Ohio 43210
A single oriented block sample of Sirius Formation till was collected for paleomagnetic analysis from Manhaul Bay in the Allan Hills by C. Faure and K.S. Taylor during the 1980 - 1981 austral summer. This till sample is poorly indurated and contains subangular to subrounded fragments of sandstone, shale, and coal derived from the local bedrock. The general composition and particle-size distribution is consistent with samples from the Allan Nunatak previously described by Mayewski (1973). The six specimen cores obtained from the block were subjected to alternating field (AF) demagnetization treatments up to 50 milliteslas in nine stages to determine the paleomagnetic directions and magnetic stability. Five particle-sized fractions were given a laboratory isothermal remanent magnetization (IRM) in fields up to 3.5 teslas to determine the type and distribution of ferromagnetic minerals. Five of the cores exhibit reversed polarity and one has normal polarity. The untreated natural remanent magnetization (NRM) of the reversed group clusters with a half angle cone of 95 percent confidence of a 95 = 19.5° and a precision parameter of k 16.4 (Fisher 1953). The individual specimen directions change by more than 15° after AF demagnetization to 50 milliteslas with an optimum distribution at the 40-millitesla stage with an a95 = 11.3° and k 47.2. The single core with normal polarity has been rejected on the basis of three criteria. First, the
10
research was supported by National Science Foundation grant DPP 82-13749. References
Gould, R.E., and T. Delevoryas. 1977. The biology of Glossopteris: Evidence from petrified seed-bearing and pollen-bearing organs. Alcheringa, 1, 387 - 399. Schopf, J.M. 1970. Petrified peat from a Permian coal bed in Antarctica. Science, 169, 274 - 277.
NRM moment
exceeds the reversed group's mean moment (2.70 10' emu/cc) by an order of magnitude and two standard deviations. In addition, this specimen fails two statistical tests, one for internal homogeneity (Harrison 1980) and another for directional concordance (McFadden 1982). The magnetization of this sample is interpreted to result from the incorporation of a strongly magnetized rock fragment with a random orientation. The AF demagnetization and IRM acquisition behaviors are indicative of stable, single domain magnetite as the primary remanence carrier. This magnetite is predominantly concentrated in the greater-than-63-micron size range. The magnetite in the coarser fractions will tend to be randomized during deposition. Thus, the magnetization of the reversed group is interpreted as a primary detrital remanent magnetization acquired at the time of deposition. Although these results are based on a single sample, the reversed primary detrital remanent magnetization places a restriction on the time of till deposition in the Allan Hills. The magnetization implies that this deposit has a minimum age of 0.69 million years (Matuyama Reversed Epoch) and excludes other normal polarity intervals of the late Cenozoic. This method of dating should be used with caution and additional sampling is required to further substantiate these results. This project was supported by National Science Foundation grant DPP 82-13511. X
References
Fisher, R.A. 1953. Dispersion on a sphere. Proceedings of the Royal Astronomical Society A217, 295 - 305. Harrison, C.G.A. 1980. Analysis of the magnetic vector in a single rock specimen. Geophysical Journal of the Royal Astronomical Society, 60, 489492. Mayewski, P.A. 1973. Glacial geology and Late Cenozoic history of the Transantarctic Mountains, Antarctica. (Unpublished doctoral dissertation, Ohio State University, Columbus, Ohio.) McFadden, P.L. 1982. Rejection of paleomagnetic observations. Eart and Planetary Science Letters, 61, 392 - 395.
ANTARCTIC JOURN
St
c.
\
-.
A
Figure 2. Transverse section of Vertebraria showing decay pockets and disrupted growth rings. (x 30.)
The material examined in this study was collected during the 1969 - 1970 field season by the late James M. Schopf supported by the National Science Foundation (GA - 12315). The present research was supported by National Science Foundation grant DPP 82-13749. References Barrett, P.J. 1970. Paleocurrent analysis of the mainly fluviatile Permian and Triassic Beacon rocks, Beardmore Glacier area, Antarctica. Journal
Anatomically preserved Glossopteris from the Beardmore Glacier area of Antarctica K.B. PIGG and
T.N. TAYLOR
Department of Botany
and Institute of Polar Studies Ohio State University Columbus, Ohio 43210
The Glossopteridales represent an enigmatic group of pteridosperms that dominated the Permian flora of Gondwana. 8
Figure 3. A. Fungal hypha preserved in Araucarioxylon-type wood. (x 700.) B. Transverse section of wood showing wall appositions in tracheids of Araucarioxylon-type wood. (x 210.)
of Sedimentary Petrology, 40, 395 - 411. Blanchette, R.A. 1980-a. Wood decomposition by Phillinus (Fomes) pini: A scanning electron microscopy study. Canadian Journal of Botany, 58, 1496-1503. Blanchette, R. A. 1980-b. Wood decay: A submicroscopic view. Journal of Forestry, 78, 734 - 737. Otjen, L., and R.A. Blanchette. 1982. Patterns of decay caused by Inontus dryophilus (Aphyllophorales: Hymenochaetaceae), a whitepocket rot fungus of oaks. Canadian Journal of Botany, 60, 2770-2779. Schopf, J.M. 1970. Petrified peat from a Permian coal bed in Antarctica. Science, 169, 274 - 277.
Plants of this order were arborescent and had stems of the roots assignable to Vertebraria, a divers array of reproductive organs, and strap-shaped leaves with reticulate venation pattern. The leaves of these plants assigne to Glossopteris represent the major floristic component and ar known almost entirely from impression/compression spec imens. As such, they have provided little information about th biology and natural affinities of the plants. To date, the oni report of structurally preserved leaves of this general type i cludes the description of both fertile and vegetative foliage fro the Bowen Basin of Queensland (Gould and Delevoryas 1977. Numerous silicified specimens of Glossopteris have been ide tified in petrified peat collected from the Mount Augusta locality in the Beardmore Glacier area (Schopf 1970). This material provides a unique opportunity to investigate the anatomy and morphology of Glossopteris leaves and to compare the structurally preserved specimens with those taxa reported from the
Araucarioxylon-type,
ANTARCTIC JOURNAL
As presently understood, the genus Glossopteris is characterized by leaves that demonstrate considerable morphological variability. The silicified specimens from Mount Augusta are relatively small, measuring approximately 1.0 centimeter in maximum width and no more than 10.0 centimeters in length. The venation pattern is a unique reticulate type in which all of the veins appear to be the same size in surface view (figure 3). In addition, individual tracheids within the veins may branch or follow a sinuous course within the reticulum. The midrib consists of four or five larger veins that are parallel with the long axis of the leaf. In transverse section, each vein is characterized by a conspicuous bundle sheath (figure 2), up to two cell layers in thickness, with the individual cells often containing amor-
4 W
•CLI •1
4
£
4
I s
Figure 1. Split surface of silicified specimen showing characteristic reticulate venation of Glossopteris leaf. (x 2.)
more commonly occurring impression/compression specimens. Specimens are analyzed by examining morphological features of the leaves that occur on split or weathered surfaces (figure 1) and subsequently preparing closely spaced, serial sections in order to examine histological features (figure 2).
- .
PF^lh
^r y
A
L
igure 2. Transverse section of Glossopteris leaf showing promient bundle sheaths containing disrupted vascular bundles. ( x 35.)
1485 REVIEW
Figure 3. Paradermal section of surface showing uniform size of reticulate veins. (x 9.)
phous materials. In some specimens, fibers may be associated with the bundle sheath. The vascular strand of each vein consists of primary, and a small amount of secondary, xylem. Phloem is not preserved and, in many specimens, the xylem is often distorted. Histologically, the ground tissue of the leaf consists of poorly differentiated mesophyll in which a palisade layer cannot be distinguished. Stomata occur on the lower epidermis. Upper epidermal cells have sinuous cell outlines, while those of the lower epidermis are straight. The' Mount Augusta Glossopteris foliage demonstrates marked histological differences when compared to the structurally preserved leaves from Bowen Basin. These differences include the absence of a palisade layer, thicker and more promi-
9
nent bundle sheath, lack of a distinctive hypodermis, and smaller amount of secondary xylem. These anatomical features provide for the first time the opportunity to compare details of Glossopteris leaves that differ in preservational mode. Such information greatly increases the value of foliage features as a useful biostratigraphic and evolutionary index. The material examined in this study was collected during the 1969 - 1970 field season by the late James M. Schopf supported by the National Science Foundation (GA - 12315). The present
Dating till by paleomagnetism: Allan Hills, southern Victoria Land E.M. CHERRY and H.C. NOLTIMIER Institute of Polar Studies
and
Department Geology and Mineralogy Ohio State University Columbus, Ohio 43210
A single oriented block sample of Sirius Formation till was collected for paleomagnetic analysis from Manhaul Bay in the Allan Hills by C. Faure and K.S. Taylor during the 1980 - 1981 austral summer. This till sample is poorly indurated and contains subangular to subrounded fragments of sandstone, shale, and coal derived from the local bedrock. The general composition and particle-size distribution is consistent with samples from the Allan Nunatak previously described by Mayewski (1973). The six specimen cores obtained from the block were subjected to alternating field (AF) demagnetization treatments up to 50 milliteslas in nine stages to determine the paleomagnetic directions and magnetic stability. Five particle-sized fractions were given a laboratory isothermal remanent magnetization (IRM) in fields up to 3.5 teslas to determine the type and distribution of ferromagnetic minerals. Five of the cores exhibit reversed polarity and one has normal polarity. The untreated natural remanent magnetization (NRM) of the reversed group clusters with a half angle cone of 95 percent confidence of a 95 = 19.5° and a precision parameter of k 16.4 (Fisher 1953). The individual specimen directions change by more than 15° after AF demagnetization to 50 milliteslas with an optimum distribution at the 40-millitesla stage with an a95 = 11.3° and k 47.2. The single core with normal polarity has been rejected on the basis of three criteria. First, the
10
research was supported by National Science Foundation grant DPP 82-13749. References
Gould, R.E., and T. Delevoryas. 1977. The biology of Glossopteris: Evidence from petrified seed-bearing and pollen-bearing organs. Alcheringa, 1, 387 - 399. Schopf, J.M. 1970. Petrified peat from a Permian coal bed in Antarctica. Science, 169, 274 - 277.
NRM moment
exceeds the reversed group's mean moment (2.70 10' emu/cc) by an order of magnitude and two standard deviations. In addition, this specimen fails two statistical tests, one for internal homogeneity (Harrison 1980) and another for directional concordance (McFadden 1982). The magnetization of this sample is interpreted to result from the incorporation of a strongly magnetized rock fragment with a random orientation. The AF demagnetization and IRM acquisition behaviors are indicative of stable, single domain magnetite as the primary remanence carrier. This magnetite is predominantly concentrated in the greater-than-63-micron size range. The magnetite in the coarser fractions will tend to be randomized during deposition. Thus, the magnetization of the reversed group is interpreted as a primary detrital remanent magnetization acquired at the time of deposition. Although these results are based on a single sample, the reversed primary detrital remanent magnetization places a restriction on the time of till deposition in the Allan Hills. The magnetization implies that this deposit has a minimum age of 0.69 million years (Matuyama Reversed Epoch) and excludes other normal polarity intervals of the late Cenozoic. This method of dating should be used with caution and additional sampling is required to further substantiate these results. This project was supported by National Science Foundation grant DPP 82-13511. X
References
Fisher, R.A. 1953. Dispersion on a sphere. Proceedings of the Royal Astronomical Society A217, 295 - 305. Harrison, C.G.A. 1980. Analysis of the magnetic vector in a single rock specimen. Geophysical Journal of the Royal Astronomical Society, 60, 489492. Mayewski, P.A. 1973. Glacial geology and Late Cenozoic history of the Transantarctic Mountains, Antarctica. (Unpublished doctoral dissertation, Ohio State University, Columbus, Ohio.) McFadden, P.L. 1982. Rejection of paleomagnetic observations. Eart and Planetary Science Letters, 61, 392 - 395.
ANTARCTIC JOURN
