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Weaver, C. 1927. The Roca Formation in Argentina. American Journalof Science, 15(5), 417-434.

Zinsmeister, W.J., and R.M. Feldmann. 1984. Cenozoic high latitudeheterochroneity of Southern Hemisphere marine faunas. Science,224(4646), 281-283.

Stratigraphic and structural investigations in the northernHeritage 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

Our 1993-1994 field season in the northern Heritage Rangewas the initiation of a 4-year project to collect strati-

graphic, structural, geochronological, and geochemical datato evaluate currently conflicting models for the origin (Cam-brian) of the Ellsworth-Whitmore Mountains terrane and thetiming and kinematics of its accretion to East Antarctica. TheEllsworth Mountains, which are part of a California-sized ter-rane, are located between the Transantarctic Mountains ofEast Antarctica and the collage of amalgamated terranes ofWest Antarctica (figure 1). The approximately 13,000 meters(m) of Cambrian-through-Permian strata exposed in the Her-itage Range appears to have paleogeographic and paleobio-geographic affinities to the paleo-Pacific margin of Gond-wanaland (Webers and Sporli 1983, pp. 261-264; Craddock etal. 1986; Webers, Craddock, and Splettstoesser 1992, pp. 1-9),but the depositional and tectonic history of the terrane isequivocal.

Our field party consisted of Margaret N. Rees (stratigra-pher), Ernest M. Duebendorfer (structural geologist), DonaldJ. Thorstenson (graduate student), and Lucylle J. Smith(mountaineer). On 22 November 1993, an LC-130 aircraft witha 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 a1992-1993 U.S. party and near four 55-gallon drums of motor-gas that were air dropped during a reconnaissance flight on12 November 1993. Over the next 30 days, we used four snow-mobiles and four Nansen sledges to transport gear and estab-lish five temporary camps (figure 1). We met briefly with MikeCurtis (structural geologist) and Brian Hull (mountaineer) ofthe British Antarctic Survey. We were pulled out of the fieldon 24 December, leaving only the nearly buried drums fromthe 1992-1993 expedition.

The northern Heritage Range is dominated by lowergreenschist facies metasedimentary and metavolcanic rocksof the Cambrian Heritage Group and the Late Cambrian to

'eoessel

I,

(\J çCD

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 filledcircles are peaks. Dashed lines are snowmobile routes. Solid squareis put-in site.

ANTARCTIC JOURNAL - REVIEW 19942

Devonian Crashsite Group (figure 2; Craddock et al. 1986;Webers et al. 1992, pp. 9-21; Sporli 1992, pp. 21-36) thatrecord three phases of folding, the earliest of which had notbeen reported previously. Evidence for this deformationalevent includes• a west-northwest-striking, moderately north-dipping

cleavage and mesoscopic folds in the Middle CambrianSpringer Peak Formation that are cut by the dominantnorth-northwest-striking cleavage;

• the presence of rotated xenoliths of phyllite interpreted asfragments of the Springer Peak Formation within a Devon-ian stock (369±18 million years ago: rubidium/ strontiumwhole-rock isochron date, Vennum et al. 1992, pp.295-324) that carries a later north-northwest-strikingcleavage; and

• the presence of strongly cleaved phyllite clasts within basalconglomerate beds of the Crashsite Group.

Goldstrand et al. (1994) reported that the Crashsite Groupdisconformably overlies the middle Late Cambrian MinaretFormation and attributed the unconformity to the RossOrogeny. The present data, however, can constrain the tim-ing of the early phase of deformation only to postdepositionof the late Middle Cambrian Springer Peak Formation andpredeposition of the Crashsite Group. The basal Crashsite isvery poorly dated: the beds are certainly older than Devonianand may be as old as late Late Cambrian (Shergold andWebers 1992, pp. 125-168). Given present data, it is permissi-ble to attribute the deformation reported here to the RossOrogeny.

The second deformational event, which produced thedominant structural trend in the northern Heritage Range, isdefined by north-northwest-trending folds and an associatedsubvertical axial planar cleavage. This deformation has beenattributed to the Triassic Ellsworth Orogeny (Craddock 1983,pp. 449-455). We have recognized two previously unreportedeast-vergent thrusts that are associated with this period ofdeformation: the Hurst Peak thrust and the ConglomerateRidge shear zone. The latter fault dips moderately northwestand is marked by a 10- to 30-meter-wide cataclasic zone thatrecords west-side-up, dextral movement. Large domains ofeast-dipping axial planar cleavage suggest opposite vergencefor structures east of the Balish Glacier. Second-phase foldsplunge variably to the northwest or southeast and may reflectpost-D2 regional warping about approximately east-trendingfold axes as suggested by Sporli and Craddock (1992, pp.375-392).

Our structural data and the recognition of an early Paleo-zoic phase of folding indicate that previously describedstratigraphy in the Heritage Range (figure 2) needs to berefined. For example, the Drake Icefall area had been inter-preted as a simple west-dipping homocline with a con-formable stratigraphic succession (Craddock et al. 1986;Webers et al. 1992, pp. 9-21). Where we observed the DrakeIcefall Formation, its base was highly sheared and the contactwith the Union Glacier Formation appeared to be faulted. Thecontact of the "lower" and "middle units" also appeared to befaulted. The "lower unit" has yielded no fossils and carries

AL PolarstarFm.

Whiteout Conglomerate-

gMount Wyatt Earp Fm.

Mount Uptak Fm.•o£--Howard Nunataks Fm.

IL• UIL

Minaret Fm.

Frazier Ridge-Springer Peak-Liberty HillFormation

C41N-0. Conglomerate Ridge Fm..DE•Drake Icefall Fm.a 2

tHyde Glacier Fm.I

p.I.I

Union Glacier Fm.

Figure 2. Generalized stratigraphic section for the Ellsworth Moun-tains (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 "mid-dle unit" is also strongly sheared and highly folded. It is com-posed predominantly of thin-bedded black limestone andcalcareous shale, and our preliminary faunal data suggest amiddle Cambrian age (Robison personal communication).The previously reported Middle Cambrian fauna from thisunit (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 thethin-bedded limestone and shale succession as faults. There-fore, their stratigraphic position is uncertain, although at leastone of them is Middle Cambrian in age (Jago and Webers1992, pp. 101-124). The uppermost exposures of the "DrakeIcefall Formation" is an argillite with sandstone successionthat is indistinguishable from parts of the Spring Peak Forma-tion. This upper unit is faulted against the "middle unit of theDrake Icefall Formation" on one side, and along its othermargin, it is juxtaposed against the Conglomerate Ridge For-mation by the Conglomerate Ridge tectonite zone. The ageand stratigraphic position of this unit is unconstrained. Previ-ously recorded west-dipping bedding attitudes within theConglomerate Ridge Formation are attitudes of metamorphiccleavage; bedding attitudes dip gently east. Thus, in the DrakeIcefall area, the stratigraphic relationships are still uncertain.

Our structural and stratigraphic fieldwork revealed sev-eral features that are evidence for an early Paleozoic deforma-tional event, possibly resulting from the Ross Orogeny. Ongo-

ANTARCTIC JOURNAL - REVIEW 1994

3

ing paleontologic, microstructural kinematic analysis, andargon-40/argon-39 and uranium! lead geochronologic inves-tigations will constrain more closely the timing and kinemat-ics of this deformational event. If deformation resulted fromthe Ross Orogeny as we suspect, then the structural history ofthe Ellsworth Mountains is much more similar to that of theTransantarctic Mountains than previously proposed.

This research was supported by National Science Foun-dation grants OPP 92-20395 and OPP 93-12040.

References

Craddock, C. 1983. The East Antarctica-West Antarctic boundarybetween the ice shelves: A review. In R.L. Oliver, P.R. James, andJ.B. Jago (Eds.), Antarctic earth science. New York: Cambridge Uni-versity Press.

Craddock, C., G.F. Webers, R.H. Rutford, K.B. Sporli, and J.J. Ander-son. 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 theEllsworth Mountains, West Antarctica: Implication for the evolutionof the paleo-Pacific margin of Gondwana. Geology, 22(5), 427-430.

Jago, J.B., and G.F. Webers. 1992. Middle Cambrian trilobites from theEllsworth Mountains, West Antarctica. In G.F. Webers, C. Crad-dock, and J.F. Spettstoesser (Eds.), Geology and paleontology of theEllsworth Mountains, WestAntarctjca (Memoir 170). Boulder, Col-orado: Geological Society of America.

Shergold, J.H., and G.F. Webers. 1992. Late Dresbachian (Idamean)and other trilobite faunas from the Heritage Range, EllsworthMountains, West Antarctica. In G.F. Webers, C. Craddock, and J.F.

Spettstoesser (Eds.), Geology and paleontology of the EllsworthMountains, West Antarctica (Memoir 170). Boulder, Colorado:Geological Society of America.

Sporli, K.B. 1992. Stratigraphy of the Crashsite Group, EllsworthMountains, West Antarctica. In G.F. Webers, C. Craddock, and J.F.Spettstoesser (Eds.), Geology and paleontology of the EllsworthMountains, 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. Crad-dock, and J.F. Spettstoesser (Eds.), Geology and paleontology of theEllsworth Mountains, WestAntarctica (Memoir 170). Boulder, Col-orado: 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 thesouthern Heritage Range, Ellsworth Mountains, West Antarctica.In G.F. Webers, C. Craddock, and J.F. Spettstoesser (Eds.), Geologyand 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. Ojakan-gas, and K.B. Sporli. 1992. In G.F. Webers, C. Craddock, and J.F.Spettstoesser (eds.), Geology and paleontology of the EllsworthMountains, West Antarctica (Memoir 170). Boulder, Colorado:Geological Society of America.

Webers, G.F., C. Craddock, and J.F. Splettstoesser. 1992. Geologic his-tory of the Ellsworth Mountains, West Antarctica. In G.F. Webers,C. Craddock, and J.F. Splettstoesser (eds.), Geology and paleontol-ogy of the Ellsworth Mountains, West Antarctica (Memoir 170).Boulder, Colorado: Geological Society of America.

Webers, G.F., and K.B. Sporli. 1983. Palaeontological and stratigraphicinvestigations in the Ellsworth Mountains, West Antarctica. In R.L.Oliver, P.R. James, and J.B. Jago (Eds.) Antarctic earth science. NewYork: Cambridge University Press, New York.

Geologic investigations in the Shackleton Range and CoatsLand nunataks, Antarctica

IAN W.D. DALZIEL, MARK A. HELPER, FREDERICK E. HUTSON, and STEPHEN W. GRIMES, Department of Geological Sciencesand Institute for Geophysics, University of Texas, Austin, Texas 78712

Recent global plate reconstructions for the Neoproterozoic(Daiziel 1991; Hoffman 1991; Moores 1991) suggest that

prior to the latest Precambrian to Cambrian amalgamation ofGondwana, the east antarctic craton was the core of an earliersupercontinent, Rondinia, whose break-up gave rise to NorthAmerica. Our research tests this hypothesis by comparing thePrecambrian geology of crustal provinces in North Americaand East Antarctica that the plate reconstructions suggestwere once contiguous. The reconstructions start from thepremise that two, distinct, Precambrian crustal provinces ofthe southwestern United States, the 1.8-1.6 billion-year-oldYavapai-Mazatzal and the 1.3-1.0 billion-year-old Grenvilleorogens, have equivalents in the Weddell Sea region of the eastantarctic craton. Although previous work by British, German,and Russian geologists (cited below) has identified rocks of theformer age range in the Shackleton Range and of the latter innunataks along the Weddell Sea coast in Coats Land (Bertraband Littlewood Nunataks), existing data are insufficient to test

the hypothesis thoroughly. To facilitate a more detailed com-parison, we spent 6 weeks examining and sampling the rocksof these regions. A major goal of the work at both locations wasthe collection of well-characterized suites of samples suitablefor petrologic, isotopic, and paleomagnetic study.

Fieldwork during the 1993-1994 field season was con-ducted from an LC-130-placed tent camp on Recovery Glac-ier, approximately 3 kilometers south of Watts Needle in theRead Mountains of the Shackleton Range (figure). The fieldparty consisted of Ian W.D. Dalziel, Mark A. Helper, FrederickE. Hutson, and Stephen W. Grimes and mountaineers AndyHarris and John Roberts. The camp was supported for 10 daysearly in the season by Twin Otter, which provided transport tothe Coats Land nunataks and allowed 5 days of reconnais-sance work in the Shackleton Range in areas remote from thecamp. These included reconnaissance study and sampling ofsites near the eastern end of the Pioneers Escarpment and thenorthern side of the Read Mountains, a site in the central Her-

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