Stratigraphic and structural investigations in the northern Heritage ...
Chirino-Gálvez, L.A. 1993. Cenozoic crabs from Chile. (Unpublished Master's thesis, Kent State University, Kent, Ohio.) Feldmann, R.M., and I.W. Keyes. 1992. Systematic and stratigraphic review with catalogue and locality index of the Mesozoic and Cenozoic decapod Crustacea of New Zealand. New Zealand Geological Survey Record. Lower Hut, New Zealand: Department of Scientific and Industrial Research, Geology and Geophysics. Feldmann, R.M, and R. Martins Neto. In press. Costacopluma nordestina n. sp. (Decapodal Retroplumidae) from the Maria Farinha
Formation (Paleocene) of Brazil. Journal of Paleontology. Feldmann, R.M., D. Tshudy, and M.R.A. Thomson. 1993. Late Cretaceous and Paleocene Decapod Crustaceans from James Ross
Basin, Antarctic Peninsula. Paleontological Society Memoir 28, 1-41. [Supplement to Journal of Paleontology, 67(1).] Weaver, C. 1927. The Roca Formation in Argentina. American Journal of Science, 15(5), 417-434. Zinsmeister, W.J., and R.M. Feldmann. 1984. Cenozoic high latitude heterochroneity of Southern Hemisphere marine faunas. Science, 224(4646), 281-283.
Stratigraphic and structural investigations in the northern Heritage Range, Ellsworth Mountains: Evidence for the Ross Orogeny? MARGARET N. REEs, Department of Geoscience, University of Nevada, Las Vegas, Nevada 89154 ERNEST M. DUEBENDORFER and DONALD J. THORSTENSON, Department of Geology, Northern Arizona University,
Flagstaff Arizona 86011
ur 1993-1994 field season in the northern Heritage Range O was the initiation of a 4-year project to collect stratigraphic, structural, geochronological, and geochemical data to evaluate currently conflicting models for the origin (Cambrian) of the Ellsworth-Whitmore Mountains terrane and the timing and kinematics of its accretion to East Antarctica. The Ellsworth Mountains, which are part of a California-sized terrane, are located between the Transantarctic Mountains of East Antarctica and the collage of amalgamated terranes of West Antarctica (figure 1). The approximately 13,000 meters (m) of Cambrian-through-Permian strata exposed in the Heritage Range appears to have paleogeographic and paleobiogeographic affinities to the paleo-Pacific margin of Gondwanaland (Webers and Sporli 1983, pp. 261-264; Craddock et al. 1986; Webers, Craddock, and Splettstoesser 1992, pp. 1-9), but the depositional and tectonic history of the terrane is equivocal. Our field party consisted of Margaret N. Rees (stratigrapher), Ernest M. Duebendorfer (structural geologist), Donald J. Thorstenson (graduate student), and Lucylle J. Smith (mountaineer). On 22 November 1993, an LC-130 aircraft with a VXE-6 crew put us into the field on the Balish Glacier (79 0 24'06"S 84 0 32'22"W) near the fuel cache left by a 1992-1993 U.S. party and near four 55-gallon drums of motorgas that were air dropped during a reconnaissance flight on 12 November 1993. Over the next 30 days, we used four snowmobiles and four Nansen sledges to transport gear and establish five temporary camps (figure 1). We met briefly with Mike Curtis (structural geologist) and Brian Hull (mountaineer) of the British Antarctic Survey. We were pulled out of the field on 24 December, leaving only the nearly buried drums from the 1992-1993 expedition. The northern Heritage Range is dominated by lower greenschist facies metasedimentary and metavolcanic rocks of the Cambrian Heritage Group and the Late Cambrian to
'e oessel
I,
(\J ç CD Li
C)f\ •: -79'30,.
1V CA
10 km
0 .,
Figure 1. Index map of field area in the northern Heritage Range, Ellsworth Mountains, Antarctica. Triangles are camp sites. Small filled circles are peaks. Dashed lines are snowmobile routes. Solid square is put-in site.
ANTARCTIC JOURNAL - REVIEW 1994 2
Devonian Crashsite Group (figure 2; Craddock et al. 1986; Webers et al. 1992, pp. 9-21; Sporli 1992, pp. 21-36) that record three phases of folding, the earliest of which had not been reported previously. Evidence for this deformational event includes • a west-northwest-striking, moderately north-dipping cleavage and mesoscopic folds in the Middle Cambrian Springer Peak Formation that are cut by the dominant north-northwest-striking cleavage; • the presence of rotated xenoliths of phyllite interpreted as fragments of the Springer Peak Formation within a Devonian stock (369±18 million years ago: rubidium/ strontium whole-rock isochron date, Vennum et al. 1992, pp. 295-324) that carries a later north-northwest-striking cleavage; and • the presence of strongly cleaved phyllite clasts within basal conglomerate beds of the Crashsite Group. Goldstrand et al. (1994) reported that the Crashsite Group disconformably overlies the middle Late Cambrian Minaret Formation and attributed the unconformity to the Ross Orogeny. The present data, however, can constrain the timing of the early phase of deformation only to postdeposition of the late Middle Cambrian Springer Peak Formation and predeposition of the Crashsite Group. The basal Crashsite is very poorly dated: the beds are certainly older than Devonian and may be as old as late Late Cambrian (Shergold and Webers 1992, pp. 125-168). Given present data, it is permissible to attribute the deformation reported here to the Ross Orogeny. The second deformational event, which produced the dominant structural trend in the northern Heritage Range, is defined by north-northwest-trending folds and an associated subvertical axial planar cleavage. This deformation has been attributed to the Triassic Ellsworth Orogeny (Craddock 1983, pp. 449-455). We have recognized two previously unreported east-vergent thrusts that are associated with this period of deformation: the Hurst Peak thrust and the Conglomerate Ridge shear zone. The latter fault dips moderately northwest and is marked by a 10- to 30-meter-wide cataclasic zone that records west-side-up, dextral movement. Large domains of east-dipping axial planar cleavage suggest opposite vergence for structures east of the Balish Glacier. Second-phase folds plunge variably to the northwest or southeast and may reflect post-D2 regional warping about approximately east-trending fold axes as suggested by Sporli and Craddock (1992, pp. 375-392). Our structural data and the recognition of an early Paleozoic phase of folding indicate that previously described stratigraphy in the Heritage Range (figure 2) needs to be refined. For example, the Drake Icefall area had been interpreted as a simple west-dipping homocline with a conformable stratigraphic succession (Craddock et al. 1986; Webers et al. 1992, pp. 9-21). Where we observed the Drake Icefall Formation, its base was highly sheared and the contact with the Union Glacier Formation appeared to be faulted. The contact of the "lower" and "middle units" also appeared to be faulted. The "lower unit" has yielded no fossils and carries
AL
PolarstarFm. Whiteout Conglomerate
-
g Mount Wyatt Earp Fm. Mount Uptak Fm.
•
o £ - - Howard Nunataks Fm. • IL IL
U
Minaret Fm. Frazier Ridge-Springer Peak-Liberty Hill Formation C 41 N - 0.
Conglomerate Ridge Fm.
• Drake Icefall Fm.
.D
E a 2
t Hyde Glacier Fm. I
p.
I.
I
Union Glacier Fm.
Figure 2. Generalized stratigraphic section for the Ellsworth Mountains (after Webers, Craddock, and Splettstoesser 1992, PP. 1-9; Webers et at. 1992, pp. 9-21). neither original sedimentary textures nor fabrics. Therefore, the stratigraphic position of this unit is uncertain. The "middle unit" is also strongly sheared and highly folded. It is composed predominantly of thin-bedded black limestone and calcareous shale, and our preliminary faunal data suggest a middle Cambrian age (Robison personal communication). The previously reported Middle Cambrian fauna from this unit (Jago and Webers 1992) came from one of the "pod-like, light-gray to black limestone lenses" (Webers et al. 1992, p. 15). We interpret the contact of these pod-like units with the thin-bedded limestone and shale succession as faults. Therefore, their stratigraphic position is uncertain, although at least one of them is Middle Cambrian in age (Jago and Webers 1992, pp. 101-124). The uppermost exposures of the "Drake Icefall Formation" is an argillite with sandstone succession that is indistinguishable from parts of the Spring Peak Formation. This upper unit is faulted against the "middle unit of the Drake Icefall Formation" on one side, and along its other margin, it is juxtaposed against the Conglomerate Ridge Formation by the Conglomerate Ridge tectonite zone. The age and stratigraphic position of this unit is unconstrained. Previously recorded west-dipping bedding attitudes within the Conglomerate Ridge Formation are attitudes of metamorphic cleavage; bedding attitudes dip gently east. Thus, in the Drake Icefall area, the stratigraphic relationships are still uncertain. Our structural and stratigraphic fieldwork revealed several features that are evidence for an early Paleozoic deformational event, possibly resulting from the Ross Orogeny. Ongo-
ANTARCTIC JOURNAL - REVIEW 1994 3
ing paleontologic, microstructural kinematic analysis, and argon-40/argon-39 and uranium! lead geochronologic investigations will constrain more closely the timing and kinematics of this deformational event. If deformation resulted from the Ross Orogeny as we suspect, then the structural history of the Ellsworth Mountains is much more similar to that of the Transantarctic Mountains than previously proposed. This research was supported by National Science Foundation grants OPP 92-20395 and OPP 93-12040.
Spettstoesser (Eds.), Geology and paleontology of the Ellsworth Mountains, West Antarctica (Memoir 170). Boulder, Colorado:
Geological Society of America. Sporli, K.B. 1992. Stratigraphy of the Crashsite Group, Ellsworth Mountains, West Antarctica. In G.F. Webers, C. Craddock, and J.F.
Spettstoesser (Eds.), Geology and paleontology of the Ellsworth Mountains, West Antarctica (Memoir 170). Boulder, Colorado:
Geological Society of America. Sporli, K.B., and C. Craddock. 1992. Structure of the Heritage Range, Ellsworth Mountains, West Antarctica. In G.F. Webers, C. Craddock, and J.F. Spettstoesser (Eds.), Geology and paleontology of the Ellsworth Mountains, WestAntarctica (Memoir 170). Boulder, Colorado: Geological Society of America. Vennum, W.R., P. Gizycki, V.V. Samsonov, A.G. Markovich, and R.J. Pankhurst. 1992. Igneous Petrology and Geochemistry of the southern Heritage Range, Ellsworth Mountains, West Antarctica. In G.F. Webers, C. Craddock, and J.F. Spettstoesser (Eds.), Geology
References Craddock, C. 1983. The East Antarctica-West Antarctic boundary between the ice shelves: A review. In R.L. Oliver, P.R. James, and J.B. Jago (Eds.), Antarctic earth science. New York: Cambridge University Press. Craddock, C., G.F. Webers, R.H. Rutford, K.B. Sporli, and J.J. Anderson. 1986. Geologic map of the Ellsworth Mountains, Antarctica. Geological Society ofAmerica, Map and Chart Series, MC-57. Goldstrand, P.M., P.G. Fitzgerald, T.F. Redfield, E. Stump, and C. Hobbs. 1994. Stratigraphic evidence for the Ross orogeny in the Ellsworth Mountains, West Antarctica: Implication for the evolution of the paleo-Pacific margin of Gondwana. Geology, 22(5), 427-430. Jago, J.B., and G.F. Webers. 1992. Middle Cambrian trilobites from the Ellsworth Mountains, West Antarctica. In G.F. Webers, C. Craddock, and J.F. Spettstoesser (Eds.), Geology and paleontology of the Ellsworth Mountains, WestAntarctjca (Memoir 170). Boulder, Colorado: Geological Society of America. Shergold, J.H., and G.F. Webers. 1992. Late Dresbachian (Idamean) and other trilobite faunas from the Heritage Range, Ellsworth Mountains, West Antarctica. In G.F. Webers, C. Craddock, and J.F.
and paleontology
of the Ellsworth Mountains, West Antarctica
(Memoir 170). Boulder, Colorado: Geological Society of America. Webers, G.F., R.L. Bauer, J.M. Anderson, W. Buggisch, R.W. Ojakangas, and K.B. Sporli. 1992. In G.F. Webers, C. Craddock, and J.F.
Spettstoesser (eds.), Geology and paleontology of the Ellsworth Mountains, West Antarctica (Memoir 170). Boulder, Colorado:
Geological Society of America. Webers, G.F., C. Craddock, and J.F. Splettstoesser. 1992. Geologic history of the Ellsworth Mountains, West Antarctica. In G.F. Webers, C. Craddock, and J.F. Splettstoesser (eds.), Geology and paleontology of the Ellsworth Mountains, West Antarctica (Memoir 170). Boulder, Colorado: Geological Society of America. Webers, G.F., and K.B. Sporli. 1983. Palaeontological and stratigraphic investigations in the Ellsworth Mountains, West Antarctica. In R.L. Oliver, P.R. James, and J.B. Jago (Eds.) Antarctic earth science. New York: Cambridge University Press, New York.
Geologic investigations in the Shackleton Range and Coats Land nunataks, Antarctica IAN W.D. DALZIEL, MARK A. HELPER, FREDERICK
E. HUTSON, and STEPHEN W. GRIMES, Department of Geological Sciences and Institute for Geophysics, University of Texas, Austin, Texas 78712
ecent global plate reconstructions for the Neoproterozoic R (Daiziel 1991; Hoffman 1991; Moores 1991) suggest that prior to the latest Precambrian to Cambrian amalgamation of Gondwana, the east antarctic craton was the core of an earlier supercontinent, Rondinia, whose break-up gave rise to North America. Our research tests this hypothesis by comparing the Precambrian geology of crustal provinces in North America and East Antarctica that the plate reconstructions suggest were once contiguous. The reconstructions start from the premise that two, distinct, Precambrian crustal provinces of the southwestern United States, the 1.8-1.6 billion-year-old Yavapai-Mazatzal and the 1.3-1.0 billion-year-old Grenville orogens, have equivalents in the Weddell Sea region of the east antarctic craton. Although previous work by British, German, and Russian geologists (cited below) has identified rocks of the former age range in the Shackleton Range and of the latter in nunataks along the Weddell Sea coast in Coats Land (Bertrab and Littlewood Nunataks), existing data are insufficient to test
the hypothesis thoroughly. To facilitate a more detailed comparison, we spent 6 weeks examining and sampling the rocks of these regions. A major goal of the work at both locations was the collection of well-characterized suites of samples suitable for petrologic, isotopic, and paleomagnetic study. Fieldwork during the 1993-1994 field season was conducted from an LC-130-placed tent camp on Recovery Glacier, approximately 3 kilometers south of Watts Needle in the Read Mountains of the Shackleton Range (figure). The field party consisted of Ian W.D. Dalziel, Mark A. Helper, Frederick E. Hutson, and Stephen W. Grimes and mountaineers Andy Harris and John Roberts. The camp was supported for 10 days early in the season by Twin Otter, which provided transport to the Coats Land nunataks and allowed 5 days of reconnaissance work in the Shackleton Range in areas remote from the camp. These included reconnaissance study and sampling of sites near the eastern end of the Pioneers Escarpment and the northern side of the Read Mountains, a site in the central Her-
ANTARCTIC JOURNAL - REVIEW 1994 4
Formation (Paleocene) of Brazil. Journal of Paleontology. Feldmann, R.M., D. Tshudy, and M.R.A. Thomson. 1993. Late Cretaceous and Paleocene Decapod Crustaceans from James Ross
Basin, Antarctic Peninsula. Paleontological Society Memoir 28, 1-41. [Supplement to Journal of Paleontology, 67(1).] Weaver, C. 1927. The Roca Formation in Argentina. American Journal of Science, 15(5), 417-434. Zinsmeister, W.J., and R.M. Feldmann. 1984. Cenozoic high latitude heterochroneity of Southern Hemisphere marine faunas. Science, 224(4646), 281-283.
Stratigraphic and structural investigations in the northern Heritage Range, Ellsworth Mountains: Evidence for the Ross Orogeny? MARGARET N. REEs, Department of Geoscience, University of Nevada, Las Vegas, Nevada 89154 ERNEST M. DUEBENDORFER and DONALD J. THORSTENSON, Department of Geology, Northern Arizona University,
Flagstaff Arizona 86011
ur 1993-1994 field season in the northern Heritage Range O was the initiation of a 4-year project to collect stratigraphic, structural, geochronological, and geochemical data to evaluate currently conflicting models for the origin (Cambrian) of the Ellsworth-Whitmore Mountains terrane and the timing and kinematics of its accretion to East Antarctica. The Ellsworth Mountains, which are part of a California-sized terrane, are located between the Transantarctic Mountains of East Antarctica and the collage of amalgamated terranes of West Antarctica (figure 1). The approximately 13,000 meters (m) of Cambrian-through-Permian strata exposed in the Heritage Range appears to have paleogeographic and paleobiogeographic affinities to the paleo-Pacific margin of Gondwanaland (Webers and Sporli 1983, pp. 261-264; Craddock et al. 1986; Webers, Craddock, and Splettstoesser 1992, pp. 1-9), but the depositional and tectonic history of the terrane is equivocal. Our field party consisted of Margaret N. Rees (stratigrapher), Ernest M. Duebendorfer (structural geologist), Donald J. Thorstenson (graduate student), and Lucylle J. Smith (mountaineer). On 22 November 1993, an LC-130 aircraft with a VXE-6 crew put us into the field on the Balish Glacier (79 0 24'06"S 84 0 32'22"W) near the fuel cache left by a 1992-1993 U.S. party and near four 55-gallon drums of motorgas that were air dropped during a reconnaissance flight on 12 November 1993. Over the next 30 days, we used four snowmobiles and four Nansen sledges to transport gear and establish five temporary camps (figure 1). We met briefly with Mike Curtis (structural geologist) and Brian Hull (mountaineer) of the British Antarctic Survey. We were pulled out of the field on 24 December, leaving only the nearly buried drums from the 1992-1993 expedition. The northern Heritage Range is dominated by lower greenschist facies metasedimentary and metavolcanic rocks of the Cambrian Heritage Group and the Late Cambrian to
'e oessel
I,
(\J ç CD Li
C)f\ •: -79'30,.
1V CA
10 km
0 .,
Figure 1. Index map of field area in the northern Heritage Range, Ellsworth Mountains, Antarctica. Triangles are camp sites. Small filled circles are peaks. Dashed lines are snowmobile routes. Solid square is put-in site.
ANTARCTIC JOURNAL - REVIEW 1994 2
Devonian Crashsite Group (figure 2; Craddock et al. 1986; Webers et al. 1992, pp. 9-21; Sporli 1992, pp. 21-36) that record three phases of folding, the earliest of which had not been reported previously. Evidence for this deformational event includes • a west-northwest-striking, moderately north-dipping cleavage and mesoscopic folds in the Middle Cambrian Springer Peak Formation that are cut by the dominant north-northwest-striking cleavage; • the presence of rotated xenoliths of phyllite interpreted as fragments of the Springer Peak Formation within a Devonian stock (369±18 million years ago: rubidium/ strontium whole-rock isochron date, Vennum et al. 1992, pp. 295-324) that carries a later north-northwest-striking cleavage; and • the presence of strongly cleaved phyllite clasts within basal conglomerate beds of the Crashsite Group. Goldstrand et al. (1994) reported that the Crashsite Group disconformably overlies the middle Late Cambrian Minaret Formation and attributed the unconformity to the Ross Orogeny. The present data, however, can constrain the timing of the early phase of deformation only to postdeposition of the late Middle Cambrian Springer Peak Formation and predeposition of the Crashsite Group. The basal Crashsite is very poorly dated: the beds are certainly older than Devonian and may be as old as late Late Cambrian (Shergold and Webers 1992, pp. 125-168). Given present data, it is permissible to attribute the deformation reported here to the Ross Orogeny. The second deformational event, which produced the dominant structural trend in the northern Heritage Range, is defined by north-northwest-trending folds and an associated subvertical axial planar cleavage. This deformation has been attributed to the Triassic Ellsworth Orogeny (Craddock 1983, pp. 449-455). We have recognized two previously unreported east-vergent thrusts that are associated with this period of deformation: the Hurst Peak thrust and the Conglomerate Ridge shear zone. The latter fault dips moderately northwest and is marked by a 10- to 30-meter-wide cataclasic zone that records west-side-up, dextral movement. Large domains of east-dipping axial planar cleavage suggest opposite vergence for structures east of the Balish Glacier. Second-phase folds plunge variably to the northwest or southeast and may reflect post-D2 regional warping about approximately east-trending fold axes as suggested by Sporli and Craddock (1992, pp. 375-392). Our structural data and the recognition of an early Paleozoic phase of folding indicate that previously described stratigraphy in the Heritage Range (figure 2) needs to be refined. For example, the Drake Icefall area had been interpreted as a simple west-dipping homocline with a conformable stratigraphic succession (Craddock et al. 1986; Webers et al. 1992, pp. 9-21). Where we observed the Drake Icefall Formation, its base was highly sheared and the contact with the Union Glacier Formation appeared to be faulted. The contact of the "lower" and "middle units" also appeared to be faulted. The "lower unit" has yielded no fossils and carries
AL
PolarstarFm. Whiteout Conglomerate
-
g Mount Wyatt Earp Fm. Mount Uptak Fm.
•
o £ - - Howard Nunataks Fm. • IL IL
U
Minaret Fm. Frazier Ridge-Springer Peak-Liberty Hill Formation C 41 N - 0.
Conglomerate Ridge Fm.
• Drake Icefall Fm.
.D
E a 2
t Hyde Glacier Fm. I
p.
I.
I
Union Glacier Fm.
Figure 2. Generalized stratigraphic section for the Ellsworth Mountains (after Webers, Craddock, and Splettstoesser 1992, PP. 1-9; Webers et at. 1992, pp. 9-21). neither original sedimentary textures nor fabrics. Therefore, the stratigraphic position of this unit is uncertain. The "middle unit" is also strongly sheared and highly folded. It is composed predominantly of thin-bedded black limestone and calcareous shale, and our preliminary faunal data suggest a middle Cambrian age (Robison personal communication). The previously reported Middle Cambrian fauna from this unit (Jago and Webers 1992) came from one of the "pod-like, light-gray to black limestone lenses" (Webers et al. 1992, p. 15). We interpret the contact of these pod-like units with the thin-bedded limestone and shale succession as faults. Therefore, their stratigraphic position is uncertain, although at least one of them is Middle Cambrian in age (Jago and Webers 1992, pp. 101-124). The uppermost exposures of the "Drake Icefall Formation" is an argillite with sandstone succession that is indistinguishable from parts of the Spring Peak Formation. This upper unit is faulted against the "middle unit of the Drake Icefall Formation" on one side, and along its other margin, it is juxtaposed against the Conglomerate Ridge Formation by the Conglomerate Ridge tectonite zone. The age and stratigraphic position of this unit is unconstrained. Previously recorded west-dipping bedding attitudes within the Conglomerate Ridge Formation are attitudes of metamorphic cleavage; bedding attitudes dip gently east. Thus, in the Drake Icefall area, the stratigraphic relationships are still uncertain. Our structural and stratigraphic fieldwork revealed several features that are evidence for an early Paleozoic deformational event, possibly resulting from the Ross Orogeny. Ongo-
ANTARCTIC JOURNAL - REVIEW 1994 3
ing paleontologic, microstructural kinematic analysis, and argon-40/argon-39 and uranium! lead geochronologic investigations will constrain more closely the timing and kinematics of this deformational event. If deformation resulted from the Ross Orogeny as we suspect, then the structural history of the Ellsworth Mountains is much more similar to that of the Transantarctic Mountains than previously proposed. This research was supported by National Science Foundation grants OPP 92-20395 and OPP 93-12040.
Spettstoesser (Eds.), Geology and paleontology of the Ellsworth Mountains, West Antarctica (Memoir 170). Boulder, Colorado:
Geological Society of America. Sporli, K.B. 1992. Stratigraphy of the Crashsite Group, Ellsworth Mountains, West Antarctica. In G.F. Webers, C. Craddock, and J.F.
Spettstoesser (Eds.), Geology and paleontology of the Ellsworth Mountains, West Antarctica (Memoir 170). Boulder, Colorado:
Geological Society of America. Sporli, K.B., and C. Craddock. 1992. Structure of the Heritage Range, Ellsworth Mountains, West Antarctica. In G.F. Webers, C. Craddock, and J.F. Spettstoesser (Eds.), Geology and paleontology of the Ellsworth Mountains, WestAntarctica (Memoir 170). Boulder, Colorado: Geological Society of America. Vennum, W.R., P. Gizycki, V.V. Samsonov, A.G. Markovich, and R.J. Pankhurst. 1992. Igneous Petrology and Geochemistry of the southern Heritage Range, Ellsworth Mountains, West Antarctica. In G.F. Webers, C. Craddock, and J.F. Spettstoesser (Eds.), Geology
References Craddock, C. 1983. The East Antarctica-West Antarctic boundary between the ice shelves: A review. In R.L. Oliver, P.R. James, and J.B. Jago (Eds.), Antarctic earth science. New York: Cambridge University Press. Craddock, C., G.F. Webers, R.H. Rutford, K.B. Sporli, and J.J. Anderson. 1986. Geologic map of the Ellsworth Mountains, Antarctica. Geological Society ofAmerica, Map and Chart Series, MC-57. Goldstrand, P.M., P.G. Fitzgerald, T.F. Redfield, E. Stump, and C. Hobbs. 1994. Stratigraphic evidence for the Ross orogeny in the Ellsworth Mountains, West Antarctica: Implication for the evolution of the paleo-Pacific margin of Gondwana. Geology, 22(5), 427-430. Jago, J.B., and G.F. Webers. 1992. Middle Cambrian trilobites from the Ellsworth Mountains, West Antarctica. In G.F. Webers, C. Craddock, and J.F. Spettstoesser (Eds.), Geology and paleontology of the Ellsworth Mountains, WestAntarctjca (Memoir 170). Boulder, Colorado: Geological Society of America. Shergold, J.H., and G.F. Webers. 1992. Late Dresbachian (Idamean) and other trilobite faunas from the Heritage Range, Ellsworth Mountains, West Antarctica. In G.F. Webers, C. Craddock, and J.F.
and paleontology
of the Ellsworth Mountains, West Antarctica
(Memoir 170). Boulder, Colorado: Geological Society of America. Webers, G.F., R.L. Bauer, J.M. Anderson, W. Buggisch, R.W. Ojakangas, and K.B. Sporli. 1992. In G.F. Webers, C. Craddock, and J.F.
Spettstoesser (eds.), Geology and paleontology of the Ellsworth Mountains, West Antarctica (Memoir 170). Boulder, Colorado:
Geological Society of America. Webers, G.F., C. Craddock, and J.F. Splettstoesser. 1992. Geologic history of the Ellsworth Mountains, West Antarctica. In G.F. Webers, C. Craddock, and J.F. Splettstoesser (eds.), Geology and paleontology of the Ellsworth Mountains, West Antarctica (Memoir 170). Boulder, Colorado: Geological Society of America. Webers, G.F., and K.B. Sporli. 1983. Palaeontological and stratigraphic investigations in the Ellsworth Mountains, West Antarctica. In R.L. Oliver, P.R. James, and J.B. Jago (Eds.) Antarctic earth science. New York: Cambridge University Press, New York.
Geologic investigations in the Shackleton Range and Coats Land nunataks, Antarctica IAN W.D. DALZIEL, MARK A. HELPER, FREDERICK
E. HUTSON, and STEPHEN W. GRIMES, Department of Geological Sciences and Institute for Geophysics, University of Texas, Austin, Texas 78712
ecent global plate reconstructions for the Neoproterozoic R (Daiziel 1991; Hoffman 1991; Moores 1991) suggest that prior to the latest Precambrian to Cambrian amalgamation of Gondwana, the east antarctic craton was the core of an earlier supercontinent, Rondinia, whose break-up gave rise to North America. Our research tests this hypothesis by comparing the Precambrian geology of crustal provinces in North America and East Antarctica that the plate reconstructions suggest were once contiguous. The reconstructions start from the premise that two, distinct, Precambrian crustal provinces of the southwestern United States, the 1.8-1.6 billion-year-old Yavapai-Mazatzal and the 1.3-1.0 billion-year-old Grenville orogens, have equivalents in the Weddell Sea region of the east antarctic craton. Although previous work by British, German, and Russian geologists (cited below) has identified rocks of the former age range in the Shackleton Range and of the latter in nunataks along the Weddell Sea coast in Coats Land (Bertrab and Littlewood Nunataks), existing data are insufficient to test
the hypothesis thoroughly. To facilitate a more detailed comparison, we spent 6 weeks examining and sampling the rocks of these regions. A major goal of the work at both locations was the collection of well-characterized suites of samples suitable for petrologic, isotopic, and paleomagnetic study. Fieldwork during the 1993-1994 field season was conducted from an LC-130-placed tent camp on Recovery Glacier, approximately 3 kilometers south of Watts Needle in the Read Mountains of the Shackleton Range (figure). The field party consisted of Ian W.D. Dalziel, Mark A. Helper, Frederick E. Hutson, and Stephen W. Grimes and mountaineers Andy Harris and John Roberts. The camp was supported for 10 days early in the season by Twin Otter, which provided transport to the Coats Land nunataks and allowed 5 days of reconnaissance work in the Shackleton Range in areas remote from the camp. These included reconnaissance study and sampling of sites near the eastern end of the Pioneers Escarpment and the northern side of the Read Mountains, a site in the central Her-
ANTARCTIC JOURNAL - REVIEW 1994 4
