Permian and Triassic fossil forests from the central ...
Permian and Triassic fossil forests from the central Transantarctic Mountains EDITH L. TAYLOR, RUBEN CUNEO, and THOMAS N. TAYLOR Byrd Polar Resca rcli Ct'i
ltL'r
and Department of Plant Bill Ohio State University Colu uiliu (lluo 4321(1-12°
During the 1990-1991 lick! cason, [vo lossil lorests were studied and wood specimens collected in the vicinity of tim Beardmore Glacier. Both forests include silica permineralizotions of trunks preserved in growth position; the stands were analyzed using the point-quarter centered method. The Permian forest occurs on Mount Achernar, near the Law Glacier (84°22'23"S 164°37'56"E) and is within the Upper Buckley Formation. The site is about 20 x 12 meters in size and includes 15 rooted stumps. These range from 9 to 18 centimeters in diameter; the tallest specimen is approximately 20 centimeters in height, possibly reaching 5-6 meters in life. The stumps are separated 1.95 meters on average (1 tree per 3.8 square meters), suggesting a very dense forest. An analysis of ring structure in the Mount Achernar wood reveals that distinct growth rings are present. These are narrow (generally 4.5 millimeters wide), although occasional, very much larger rings (about 11.4 millimeters) are present. The rings consist primarily of earlywood with a small proportion of latewood. A maximum of 7 growth rings have been counted in one specimen, indicating a short life span for the entire stand. The bedding plane that includes the trunks is dominated (56 percent) by a Glossopteris leaf-litter; Vertebraria roots are also present. It is probable that the trunks and compression fossils were produced from the same type of plant. These plants were growing on floodplains with well-developed soils and were part of a braided fluvial system. The second forest occurs in the upper Gordon Valley, near Mount Falla (84°11'10"S 164°54'28"E). This site is within the upper part of the Fremouw Formation and is believed to be Middle Triassic in age. There are many more rooted stumps preserved at this site (approximately 100 on two levels) than at the Permian site. The forest covers an area of approximately 128 x 30.5 meters. The trees are also larger than those at Mount Achernar, ranging from 13 to 61 centimeters in diameter (figure). The tallest trunk is about 60 centimeters high and probably exceeded 20 meters in life. The stumps are separated 6.23 meters on average (1 tree per 38 square meters or 258 trees per hectare), forming part of a relatively open, mature forest. Each tree covered 0.075 square meters per hectare 19.31 square meters total trunk cover per hectare. A Dicroidium leaf-litter, probably produced by the same plants as the stumps, covers 50 percent of the bedding plane in which the trunks occur. This forest grew on the levee of a braided river system where the soils were sandy and not very well-developed. Slighty smaller growth rings suggest a more mature forest than at the Permian site (largest trunk = 86 rings). Growth rings are currently being 1991 REVIEW
Silicified Triassic tree trunk in growth position in the upper Gordon Valley, central Transantarctic Mountains. Distance from ground level to top of trunk is approximately 1 meter.
analyzed utilizing standard dendrochronology techniques (Cook and Kairiukstis 1990, also outlined in Jefferson 1982). Although growth rings in fossil wood have been described from other sites in Antarctica (e.g. Francis 1986; Taylor 1989, pp. 109-113), there has been only one other report of a fossil forest preserved in growth position (Jefferson 1982). This material occurred on Livingston Island in Lower Cretaceous rocks. The ring structure exhibited by the in situ wood from the central Transantarctic Mountains is typical of that described from high latitudes today, as well as fossil material collected from high paleolatitudes (e.g., Spicer and Parrish 1990). It is also comparable to that from other sites in the Transantarctic Mountains (e.g., wood from the permineralized peat deposits on Skaar Ridge (Permian) and Fremouw Peak (Triassic)) (Taylor 1989), as well as with Jefferson's data from Alexander Island. The importance of trees preserved in growth position is that not only can the ring structure be analyzed using standard dendrochronology techniques (e.g., Cook and Kairiukstis 1990), but forest density can also be calculated, as Jefferson (1982) illustrated on Livingston Island (Antarctic Peninsula). This density provides data on the productivity of the forests (Creber 1990, pp. 37-41) which can be compared with that known from other forests, both living and fossil. 23
This work was supported in part by National Science Foundation grant DPP 88-15976.
References Cook, E.R., and L.A. Kairiukstis (Eds.). 1990. Methods of dendrochronology. Dordrecht: Kluwer Academic Publications. Creber, G.T. 1990. The south polar forest ecosystem. In T.N. Taylor and E.L. Taylor (Ed.), Antarctic paleobiology: Its role in the reconstruction of
Gondwana. New York: Springer-Verlag.
Studies of granitic and metamorphic rocks, Horlick and Whitmore mountains area S.G. BORG, D.J. DEPAOLO, E.E. DALEY, and K.W.W. SIMS Berkeley Center for Isotope Geochemistry Department of Geology and Geophysics University of California Berkeley, California 94720
This paper reports on field work on the granitic and metamorphic basement rocks of the Transantarctic Mountains during the 1990-1991 austral summer. It supplements previous reports in Antarctic Journal (see Borg and DePaolo 1990). Geologic mapping and sampling of granitic and metamorphic rocks were carried out in the Horlick Mountains (including the Wisconsin Range, the Ohio Range, Long Hills, Metavolcanic Mountain, and Minna Spur) and the Whitmore Mountains during the 1990-1991 austral summer. This was accomplished with a combination of Twin Otter support and ground traverses. In early December, a tent camp, including several fuel drums for Twin Otter operations, was placed by LC-130 about 4 kilometers north of Metavolcanic Mountain on the east side of the upper Reedy Glacier (figure) for later occupancy. The field party and geologic field equipment were staged at the Corridor Aerogeophysics of the Southeastern Ross Transect Zone (CASERTZ) camp (figure) for Twin Otter operations. An additional fuel cache was established in the northwestern Horlick Mountains by the Twin Otter crew prior to beginning science support. The Twin Otter was used in a close-support role for reconnaissance geologic mapping and sampling directly from the CASERTZ camp. Although the CASERTZ camp was approximately 1 hour flight time from the nearest outcrop, it provided access to a large segment of the Transantarctic Mountains, from the upper Reedy Glacier to the Whitmore Mountains. In a close-support role, the Twin Otter proved to be ideal for our purposes, providing a large operational area with the ability to land within walking distance of outcrops. About 1,600 kilograms of rock was collected representing all the basement lithologies (79 samples from 46 localities). Our work follows up on reconnaissance studies done in the Horlick Mountains by J. Murtaugh and G. Faure in the late 24
Francis, J. 1986. Growth rings in Cretaceous Tertiary wood from Antarctica and their palaeoclimatic implications. Palaeontology, 29(4), 665684.
Jefferson, T.H. 1982. Fossil forests from the Lower Cretaceous of Alexander Island, Antarctica. Palaeontology, 25(4), 681-708. Spicer, R.A., and J.T. Parrish. 1990. Latest Cretaceous wood of the central North Slope, Alaska. Palaeontology, 33, 225-242. Taylor, E.L. 1989. Tree-ring structure in woody axes from the central Transantarctic Mountains, Antarctica. In Proceedings of the International Symposium on Antarctic Research. (Hangzhou, P.R. China, May 1989.) Tianjin: China Ocean Press.
1960's (Murtaugh 1969; Faure, Murtaugh, and Montigny 1968). Our goal is to characterize the crystalline basement rocks in terms of their neodymium, strontium, and oxygen isotopic compositions and to delineate crustal provinces (see Borg and DePaolo 1990; Borg, DePaolo, and Smith 1990). The basement in the Horlick Mountains region is composed of granitic and metamorphic rocks (see Murtaugh 1969). The metamorphic rocks include both metasedimentary and metaigneous lithologies. At Spear Nunatak in the upper Reedy Glacier area, the metasedimentary rocks are represented by complexly folded amphibolite-grade banded gneisses and schists. This unit is lithologically similar to the Miller Formation in the upper Nimrod Glacier region. In the lower Reedy Glacier area, metasedimentary rocks are represented by greenschist facies graywacke-shale sequences, probably equivalent to the LaGorce Formation. Metaigneous rocks are represented by dacitic porphyritic volcanic rocks, probably Wyatt Formation, exposed at Metavolcanic Mountain, in the Mims Spur region, and in the Long Hills. Granitic rocks that have intruded these metamorphic rocks range from granite to granodiorite and include deformed and undeformed lithologies. The deformed lithologies are associated with well-developed shear zones, and there is no compelling field evidence to suggest that any of these granites are significantly older than the undeformed lithologies. All of the granites in the Horlick Mountains are probably associated with the Cambro-Ordovician Ross Orogeny. Analytical work is underway to characterize the granites and metamorphic units. This will allow us to trace basement provinces delineated in the Nimrod-Shackleton Glaciers region toward the southeast in the Transantarctic Mountains. We would like to thank National Science Foundation Polar Operations, Kenn Borek Air Ltd., VXE-6, and Antarctic Support Associates, Inc., for their efforts in support of our field work. Special thanks go to Henry Perk, Jim Pearce, and Doug Gaunt of Kenn Borek Air Ltd., and to Kevin Killilea (manager of the CASERTZ camp) and Rick Campbell (field party liaison) of Antarctic Support Associates. This research was supported by National Science Foundation grant DPP 88-16925.
References Borg, 5G., and D.J. DePaolo. 1990. Crustal basement provinces of the Transantarctic Mountains, Ross Sea sector. Antarctic Journal of the U.S., 25(5), 29-31.
Borg, 5G., D.J. DePaolo, and B.M. Smith. 1990. Isotopic structure and tectonics of the central Transantarctic Mountains. Journal of Geophysical Research, 95(135), 6647-6667.
ANTARCTIC JOURNAL
ltL'r
and Department of Plant Bill Ohio State University Colu uiliu (lluo 4321(1-12°
During the 1990-1991 lick! cason, [vo lossil lorests were studied and wood specimens collected in the vicinity of tim Beardmore Glacier. Both forests include silica permineralizotions of trunks preserved in growth position; the stands were analyzed using the point-quarter centered method. The Permian forest occurs on Mount Achernar, near the Law Glacier (84°22'23"S 164°37'56"E) and is within the Upper Buckley Formation. The site is about 20 x 12 meters in size and includes 15 rooted stumps. These range from 9 to 18 centimeters in diameter; the tallest specimen is approximately 20 centimeters in height, possibly reaching 5-6 meters in life. The stumps are separated 1.95 meters on average (1 tree per 3.8 square meters), suggesting a very dense forest. An analysis of ring structure in the Mount Achernar wood reveals that distinct growth rings are present. These are narrow (generally 4.5 millimeters wide), although occasional, very much larger rings (about 11.4 millimeters) are present. The rings consist primarily of earlywood with a small proportion of latewood. A maximum of 7 growth rings have been counted in one specimen, indicating a short life span for the entire stand. The bedding plane that includes the trunks is dominated (56 percent) by a Glossopteris leaf-litter; Vertebraria roots are also present. It is probable that the trunks and compression fossils were produced from the same type of plant. These plants were growing on floodplains with well-developed soils and were part of a braided fluvial system. The second forest occurs in the upper Gordon Valley, near Mount Falla (84°11'10"S 164°54'28"E). This site is within the upper part of the Fremouw Formation and is believed to be Middle Triassic in age. There are many more rooted stumps preserved at this site (approximately 100 on two levels) than at the Permian site. The forest covers an area of approximately 128 x 30.5 meters. The trees are also larger than those at Mount Achernar, ranging from 13 to 61 centimeters in diameter (figure). The tallest trunk is about 60 centimeters high and probably exceeded 20 meters in life. The stumps are separated 6.23 meters on average (1 tree per 38 square meters or 258 trees per hectare), forming part of a relatively open, mature forest. Each tree covered 0.075 square meters per hectare 19.31 square meters total trunk cover per hectare. A Dicroidium leaf-litter, probably produced by the same plants as the stumps, covers 50 percent of the bedding plane in which the trunks occur. This forest grew on the levee of a braided river system where the soils were sandy and not very well-developed. Slighty smaller growth rings suggest a more mature forest than at the Permian site (largest trunk = 86 rings). Growth rings are currently being 1991 REVIEW
Silicified Triassic tree trunk in growth position in the upper Gordon Valley, central Transantarctic Mountains. Distance from ground level to top of trunk is approximately 1 meter.
analyzed utilizing standard dendrochronology techniques (Cook and Kairiukstis 1990, also outlined in Jefferson 1982). Although growth rings in fossil wood have been described from other sites in Antarctica (e.g. Francis 1986; Taylor 1989, pp. 109-113), there has been only one other report of a fossil forest preserved in growth position (Jefferson 1982). This material occurred on Livingston Island in Lower Cretaceous rocks. The ring structure exhibited by the in situ wood from the central Transantarctic Mountains is typical of that described from high latitudes today, as well as fossil material collected from high paleolatitudes (e.g., Spicer and Parrish 1990). It is also comparable to that from other sites in the Transantarctic Mountains (e.g., wood from the permineralized peat deposits on Skaar Ridge (Permian) and Fremouw Peak (Triassic)) (Taylor 1989), as well as with Jefferson's data from Alexander Island. The importance of trees preserved in growth position is that not only can the ring structure be analyzed using standard dendrochronology techniques (e.g., Cook and Kairiukstis 1990), but forest density can also be calculated, as Jefferson (1982) illustrated on Livingston Island (Antarctic Peninsula). This density provides data on the productivity of the forests (Creber 1990, pp. 37-41) which can be compared with that known from other forests, both living and fossil. 23
This work was supported in part by National Science Foundation grant DPP 88-15976.
References Cook, E.R., and L.A. Kairiukstis (Eds.). 1990. Methods of dendrochronology. Dordrecht: Kluwer Academic Publications. Creber, G.T. 1990. The south polar forest ecosystem. In T.N. Taylor and E.L. Taylor (Ed.), Antarctic paleobiology: Its role in the reconstruction of
Gondwana. New York: Springer-Verlag.
Studies of granitic and metamorphic rocks, Horlick and Whitmore mountains area S.G. BORG, D.J. DEPAOLO, E.E. DALEY, and K.W.W. SIMS Berkeley Center for Isotope Geochemistry Department of Geology and Geophysics University of California Berkeley, California 94720
This paper reports on field work on the granitic and metamorphic basement rocks of the Transantarctic Mountains during the 1990-1991 austral summer. It supplements previous reports in Antarctic Journal (see Borg and DePaolo 1990). Geologic mapping and sampling of granitic and metamorphic rocks were carried out in the Horlick Mountains (including the Wisconsin Range, the Ohio Range, Long Hills, Metavolcanic Mountain, and Minna Spur) and the Whitmore Mountains during the 1990-1991 austral summer. This was accomplished with a combination of Twin Otter support and ground traverses. In early December, a tent camp, including several fuel drums for Twin Otter operations, was placed by LC-130 about 4 kilometers north of Metavolcanic Mountain on the east side of the upper Reedy Glacier (figure) for later occupancy. The field party and geologic field equipment were staged at the Corridor Aerogeophysics of the Southeastern Ross Transect Zone (CASERTZ) camp (figure) for Twin Otter operations. An additional fuel cache was established in the northwestern Horlick Mountains by the Twin Otter crew prior to beginning science support. The Twin Otter was used in a close-support role for reconnaissance geologic mapping and sampling directly from the CASERTZ camp. Although the CASERTZ camp was approximately 1 hour flight time from the nearest outcrop, it provided access to a large segment of the Transantarctic Mountains, from the upper Reedy Glacier to the Whitmore Mountains. In a close-support role, the Twin Otter proved to be ideal for our purposes, providing a large operational area with the ability to land within walking distance of outcrops. About 1,600 kilograms of rock was collected representing all the basement lithologies (79 samples from 46 localities). Our work follows up on reconnaissance studies done in the Horlick Mountains by J. Murtaugh and G. Faure in the late 24
Francis, J. 1986. Growth rings in Cretaceous Tertiary wood from Antarctica and their palaeoclimatic implications. Palaeontology, 29(4), 665684.
Jefferson, T.H. 1982. Fossil forests from the Lower Cretaceous of Alexander Island, Antarctica. Palaeontology, 25(4), 681-708. Spicer, R.A., and J.T. Parrish. 1990. Latest Cretaceous wood of the central North Slope, Alaska. Palaeontology, 33, 225-242. Taylor, E.L. 1989. Tree-ring structure in woody axes from the central Transantarctic Mountains, Antarctica. In Proceedings of the International Symposium on Antarctic Research. (Hangzhou, P.R. China, May 1989.) Tianjin: China Ocean Press.
1960's (Murtaugh 1969; Faure, Murtaugh, and Montigny 1968). Our goal is to characterize the crystalline basement rocks in terms of their neodymium, strontium, and oxygen isotopic compositions and to delineate crustal provinces (see Borg and DePaolo 1990; Borg, DePaolo, and Smith 1990). The basement in the Horlick Mountains region is composed of granitic and metamorphic rocks (see Murtaugh 1969). The metamorphic rocks include both metasedimentary and metaigneous lithologies. At Spear Nunatak in the upper Reedy Glacier area, the metasedimentary rocks are represented by complexly folded amphibolite-grade banded gneisses and schists. This unit is lithologically similar to the Miller Formation in the upper Nimrod Glacier region. In the lower Reedy Glacier area, metasedimentary rocks are represented by greenschist facies graywacke-shale sequences, probably equivalent to the LaGorce Formation. Metaigneous rocks are represented by dacitic porphyritic volcanic rocks, probably Wyatt Formation, exposed at Metavolcanic Mountain, in the Mims Spur region, and in the Long Hills. Granitic rocks that have intruded these metamorphic rocks range from granite to granodiorite and include deformed and undeformed lithologies. The deformed lithologies are associated with well-developed shear zones, and there is no compelling field evidence to suggest that any of these granites are significantly older than the undeformed lithologies. All of the granites in the Horlick Mountains are probably associated with the Cambro-Ordovician Ross Orogeny. Analytical work is underway to characterize the granites and metamorphic units. This will allow us to trace basement provinces delineated in the Nimrod-Shackleton Glaciers region toward the southeast in the Transantarctic Mountains. We would like to thank National Science Foundation Polar Operations, Kenn Borek Air Ltd., VXE-6, and Antarctic Support Associates, Inc., for their efforts in support of our field work. Special thanks go to Henry Perk, Jim Pearce, and Doug Gaunt of Kenn Borek Air Ltd., and to Kevin Killilea (manager of the CASERTZ camp) and Rick Campbell (field party liaison) of Antarctic Support Associates. This research was supported by National Science Foundation grant DPP 88-16925.
References Borg, 5G., and D.J. DePaolo. 1990. Crustal basement provinces of the Transantarctic Mountains, Ross Sea sector. Antarctic Journal of the U.S., 25(5), 29-31.
Borg, 5G., D.J. DePaolo, and B.M. Smith. 1990. Isotopic structure and tectonics of the central Transantarctic Mountains. Journal of Geophysical Research, 95(135), 6647-6667.
ANTARCTIC JOURNAL
