tence of these and other new assemblages toward the south near the Shackleton Glacier, and we hope that proposed ver- tebrate paleontological field work in that area will take place within the next few years. This research was supported by National Science Foun- dation grant OPP 91-18620 and OPP 88-17023 and the Augus- tana Research Foundation. References Barrett, P.J., R.J. Baillie, and E.H. Colbert. 1968. Triassic amphibian from Antarctica. Science, 161(3840), 460-462. Colbert, E.H. 1982. Triassic vertebrates in the Transantarctic Moun- tains. In M.D. Turner and J.F. Splettstoesser (Eds.), Geology of the central Transantarctic Mountains (Antarctic Research Series, Vol. 36). Washington, D.C.: American Geophysical Union. Hammer, W.R. In press. New therapsids from the upper Fremouw Formation of Antarctica. Journal of Vertebrate Paleontology. Hammer, W.R. 1990. Triassic terrestrial vertebrate faunas of Antarcti- ca. In T.N. and E.L. Taylor (Eds.), Antarctic paleobiology: Its role in the reconstruction of Gondwanaland. New York: Springer-Verlag. Hammer, W.R. 1992. Jurassic dinosaurs from Antarctica: Another puzzling high latitude fauna. GSA 1992 Annual Meeting, Cincin- nati, Ohio, Abstracts (Vol. 193). Boulder, Colorado: Geological Society of America. Hammer, W.R., J.W. Collinson, and W.J. Ryan. 1990. A new Triassic vertebrate fauna from Antarctica and its depositional setting. Antarctic Science, 2(2), 163-169. Hammer, W.R., and J.W. Cosgriff. 1981. Myosaurus gracilis, an anomodont reptile from the Lower Triassic of Antarctic and South Africa. Journal of Paleontology, 55(2), 410-424. Hammer, W.R., and W.J. Hickerson. 1992. Comments on the fossil vertebrates from the Falla Formation Jurassic, Beardmore Glacier region, Antarctica. Antarctic Journal of the U.S., 27(5), 1. Hammer, W.R., and W.J. Hickerson. In preparation. A new crested therapod dinosaur from Antarctica. Hammer, W.R., W.J. Hickerson, J.R. Tamplin, and S. Krippner. 1991. Therapsids, temnospondyls, and dinosaurs from the Fremouw and Falla Formations, Beardmore Glacier region, Antarctica. Antarctic Journal of the U.S., 26(5), 19-20. Cambrian and possible Proterozoic strata in the Transantarctic Mountains, north of Leverett Glacier A.J. ROWELL, Museum of Invertebrate Paleontology and Department of Geology, University of Kansas, Lawrence, Kansas 66045 KEVIN R. EVANS and LAWRENCE W. MCKENNA, III, Department of Geology, University of Kansas, Lawrence, Kansas 66045 T he Pacific Ocean was initiated by rifting between a con- joined Antarctic /Australia continent and the western margin of Laurentia during Neoproterozoic time (Dalziel 1992). The antarctic sector of the paleo-Pacific margin approximately coincides with the present-day position of the Transantarctic Mountains, but timing of the rifting event that produced this margin is poorly constrained. In the Marsh Glacier-Skelton Glacier segment of Transantarctic Mountains the presence of oceanic crust and pillow basalts indicate that rifting had occurred by at least 700-800 million years (Borg et al. 1990; Rowell et al. 1993). Study of the Cambrian succession suggests that the margin was already an active one by early Cambrian time (Rowell, Rees, and Evans 1992; Goodge, Walk- er, and Hansen 1993). There are, however, essentially no data constraining breakup time elsewhere along the Pacific-facing margin of the continent. Furthermore, between Beardmore Glacier and the Pensacola Mountains, only reconnaissance- level information on the subsequent Cambrian stratigraphic and tectonic history exists. The principal objective of our 1992-1993 field season was to attempt to fill some of these gaps in our understanding and to provide needed informa- tion for the central part of Transantarctic Mountains in the Harold Byrd and Bender mountains, north of Leverett Glacier (figure 1). Specifically, our goal was to document the Protero- zoic and Cambrian geogical history of the region and collect samples for subsequent isotopic, geochemical, and paleonto- logical laboratory study. Two results of our fieldwork stand out as being notewor- thy. First, we recognized an Early Cambrian carbonate plat- form in an area where its existence was unexpected. Second, we consider some of the marbles and schists initially included in the upper part of the Middle Cambrian Leverett Formation to be significantly older, and possibly of Neoproterozoic age. With regard to our first point, the limestones forming the carbonate platform are moderately deformed micrites that carry an archaeocyath fauna (figure 2); we refer to these strata by the informal stratigraphic formational name of "Lime- stones of Mt. Mahan" (figure 1). The limestones are interbed- ded locally with epiclastic volcanic rocks and seemingly are overlain unconformably by a thick sequence of massive rhyo- lites to rhyodacites (figure 3) (shown informally on figure 1, as the "Volcanics of Mt. Fiedler"). Because the base of the lime- stones is concealed by ice, we do not know whether the car- bonate platform is perched on a volcanic edifice or whether it is a continuation of the Lower Cambrian platform known to border the Pacific-facing margin of the east antarctic craton (Rowell et al. 1992). Geochemical analysis of the associated volcanics may help to resolve the question. Our second point concerns Minshew's (1965, 1967a, 1967b), erection of the Leverett Formation for a sequence of volcanic rocks, siliciclastic strata, and associated limestone exposed in the southern part of Mount Webster. The forma- tion was considered to rest unconformably on Precambrian phyllites and schists (Minshew 1967a), although the boundary ANTARCTIC JOURNAL - REVIEW 1993 35
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tence of these and other new assemblages toward the southnear the Shackleton Glacier, and we hope that proposed ver-tebrate paleontological field work in that area will take placewithin the next few years.
This research was supported by National Science Foun-dation grant OPP 91-18620 and OPP 88-17023 and the Augus-tana Research Foundation.
Colbert, E.H. 1982. Triassic vertebrates in the Transantarctic Moun-tains. In M.D. Turner and J.F. Splettstoesser (Eds.), Geology of thecentral Transantarctic Mountains (Antarctic Research Series, Vol.36). Washington, D.C.: American Geophysical Union.
Hammer, W.R. In press. New therapsids from the upper FremouwFormation of Antarctica. Journal of Vertebrate Paleontology.
Hammer, W.R. 1990. Triassic terrestrial vertebrate faunas of Antarcti-
ca. In T.N. and E.L. Taylor (Eds.), Antarctic paleobiology: Its role inthe reconstruction of Gondwanaland. New York: Springer-Verlag.
Hammer, W.R. 1992. Jurassic dinosaurs from Antarctica: Anotherpuzzling high latitude fauna. GSA 1992 Annual Meeting, Cincin-nati, Ohio, Abstracts (Vol. 193). Boulder, Colorado: GeologicalSociety of America.
Hammer, W.R., J.W. Collinson, and W.J. Ryan. 1990. A new Triassicvertebrate fauna from Antarctica and its depositional setting.Antarctic Science, 2(2), 163-169.
Hammer, W.R., and J.W. Cosgriff. 1981. Myosaurus gracilis, ananomodont reptile from the Lower Triassic of Antarctic and SouthAfrica. Journal of Paleontology, 55(2), 410-424.
Hammer, W.R., and W.J. Hickerson. 1992. Comments on the fossilvertebrates from the Falla Formation Jurassic, Beardmore Glacierregion, Antarctica. Antarctic Journal of the U.S., 27(5), 1.
Hammer, W.R., and W.J. Hickerson. In preparation. A new crestedtherapod dinosaur from Antarctica.
Hammer, W.R., W.J. Hickerson, J.R. Tamplin, and S. Krippner. 1991.Therapsids, temnospondyls, and dinosaurs from the Fremouwand Falla Formations, Beardmore Glacier region, Antarctica.Antarctic Journal of the U.S., 26(5), 19-20.
Cambrian and possible Proterozoic strata in theTransantarctic Mountains, north of Leverett Glacier
A.J. ROWELL, Museum of Invertebrate Paleontology and Department of Geology, University of Kansas, Lawrence, Kansas 66045KEVIN R. EVANS and LAWRENCE W. MCKENNA, III, Department of Geology, University of Kansas, Lawrence, Kansas 66045
The Pacific Ocean was initiated by rifting between a con-joined Antarctic /Australia continent and the western
margin of Laurentia during Neoproterozoic time (Dalziel1992). The antarctic sector of the paleo-Pacific marginapproximately coincides with the present-day position of theTransantarctic Mountains, but timing of the rifting event thatproduced this margin is poorly constrained. In the MarshGlacier-Skelton Glacier segment of Transantarctic Mountainsthe presence of oceanic crust and pillow basalts indicate thatrifting had occurred by at least 700-800 million years (Borg etal. 1990; Rowell et al. 1993). Study of the Cambrian successionsuggests that the margin was already an active one by earlyCambrian time (Rowell, Rees, and Evans 1992; Goodge, Walk-er, and Hansen 1993). There are, however, essentially no dataconstraining breakup time elsewhere along the Pacific-facingmargin of the continent. Furthermore, between BeardmoreGlacier and the Pensacola Mountains, only reconnaissance-level information on the subsequent Cambrian stratigraphicand tectonic history exists. The principal objective of our1992-1993 field season was to attempt to fill some of thesegaps in our understanding and to provide needed informa-tion for the central part of Transantarctic Mountains in theHarold Byrd and Bender mountains, north of Leverett Glacier(figure 1). Specifically, our goal was to document the Protero-zoic and Cambrian geogical history of the region and collectsamples for subsequent isotopic, geochemical, and paleonto-logical laboratory study.
Two results of our fieldwork stand out as being notewor-thy. First, we recognized an Early Cambrian carbonate plat-form in an area where its existence was unexpected. Second,we consider some of the marbles and schists initially includedin the upper part of the Middle Cambrian Leverett Formationto be significantly older, and possibly of Neoproterozoic age.
With regard to our first point, the limestones forming thecarbonate platform are moderately deformed micrites thatcarry an archaeocyath fauna (figure 2); we refer to these strataby the informal stratigraphic formational name of "Lime-stones of Mt. Mahan" (figure 1). The limestones are interbed-ded locally with epiclastic volcanic rocks and seemingly areoverlain unconformably by a thick sequence of massive rhyo-lites to rhyodacites (figure 3) (shown informally on figure 1, asthe "Volcanics of Mt. Fiedler"). Because the base of the lime-stones is concealed by ice, we do not know whether the car-bonate platform is perched on a volcanic edifice or whether itis a continuation of the Lower Cambrian platform known toborder the Pacific-facing margin of the east antarctic craton(Rowell et al. 1992). Geochemical analysis of the associatedvolcanics may help to resolve the question.
Our second point concerns Minshew's (1965, 1967a,1967b), erection of the Leverett Formation for a sequence ofvolcanic rocks, siliciclastic strata, and associated limestoneexposed in the southern part of Mount Webster. The forma-tion was considered to rest unconformably on Precambrianphyllites and schists (Minshew 1967a), although the boundary
ANTARCTIC JOURNAL - REVIEW 199335
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stern haroldByrd
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d MountainankeCressey Pk. s gr
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Levereti Formation (Members A-E), m C
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Figure 1. Reconnaissance geologic map of parts of the Harold Byrd—Bender mountains area. Inset indexmap of Antarctica showing position of field area in the Harold Byrd Mountains and other locationsmentioned in the text. B-Beardmore Glacier; M-Marsh Glacier; P-Pensacola Mountains; S-SkeltonGlacier. Outline oosition of the Transantaretic Mountains shown b y mountain symbols bounding fh
constrain their age. As dis-cussed below, other aspects ofthe study await results of labo-ratory work on the 700 kilo-grams of samples that werereturned to the University ofKansas.
We observed that thegranitoids of the Berry Peaksand the northern part ofMount Mahan, which werefirst mapped by Stump (Stumpet al. 1978; Heintz 1980), areseparated from outcrops of the"Cressey schists and marbles"by a major shear zone (figure1). Borg (1983) noted thataspects of the geochemicalcomposition of these grani-toids are anomalous withrespect to other granites crop-ping out to the south and west.He suggested that they mighthave had a different origin.The relationship between theBerry Peaks granitoid and theleucocratic unfoliated grani-toids intruded into the schistsand gneisses of the FalloneNunataks, which crop outwestward along the regional
margin of the east antarctic craton. --, strike, is unknown. We hope to
is not exposed (Minshew 1967b). Minshew informally dividedthe Leverett Formation into seven members: members Athrough G arranged from the base to the top. Thin-beddedlimestone beds of member E yielded a poorly preserved trilo-bite fauna of probable Middle Cambrian age (Palmer andGatehouse 1972). We, like the only other party to have workedin the area (Lowry 1980), failed to find additional MiddleCambrian trilobites, although we recognized thin-beddedlimestones that were probably part of member E. As Minshew(1967b) noted, the thick marbles of member F are conspicu-ous because of their white color and massive appearance. Wemapped these marbles, however, as tectonically separatedfrom strata of member E by a fault; we consider them as olderthan members A through E of the Leverett Formation. Stumpet al. (1978) recognized that these marbles cropped out in theline of hills extending between Mount Mahan and MountManke; we show them as an informal stratigraphic unit in fig-ure 1, "Cressey schists and marbles." Their age is problematicand they could be either Early Cambrian or Neoproterozoic.Details of lithologic succession and higher level of deforma-tion and metamorphism suggest to us that these beds are notcorrelative with the Lower Cambrian "Limestone of Mt.Mahan," but more probably are older. Isotopic analysis ofsome samples from the "Cressey schists and marbles" may
address these questions anddate the intrusions by isotopic
and geochemical study. Comparable investigations of theextensive series of granitoid samples that we collected fromthe western Harold Byrd Mountains and Mount Webster willenable these results to be seen in the context of the igneous
I
. -. . -..,.••,•I.'
-..
Figure 2. Negative print from thin section of archaeocyaths from"Limestones of Mt. Mahan," x 2.5.
ANTARCTIC JOURNAL - REVIEW 1993
36
and tectonic history of the larger area, as well as provideinsight into the nature and composition of the lower crust.
Our field party consisted of A.J. Rowell, Kevin R. Evans,and Lawrence W. McKenna, III, as well as Glenn Ruckhaus, anenvironmental geologist who acted as our field safety special-ist. We air-dropped eight 55-gallon barrels of MOGAS fuel onour reconnaissance flight of 20 November and were subse-quently put in the field by LC-130 aircraft on 26 November.Our landing site, about 3 kilometers north of Cressey Peak at85027'S 143 008'W, served as our main depot; we were pickedup from this location on 4 January 1993.
We thank the LC-130 crews of the U.S. Navy VXE-6squadron for assistance in completion of our fieldwork, ourcolleagues with Antarctic Support Associates and the NationalScience Foundation for their help and logistical support, andGlen Ruckhaus for his many contributions to our field party.We are particularly indebted to Ed Stump, who made avail-able his maps of the field area together with copies of twounpublished master's theses. His generosity allowed ourfieldwork to be accomplished much more effectively. Thiswork was supported by National Science Foundation grantOPP 91-17444 to the University of Kansas.
References
Borg, S.G. 1983. Petrology and geochemistry of the Queen MaudBatholith, central Transantarctic Mountains, with implications forthe Ross Orogeny. In Oliver, R.L., P.R. James, and J.B. Jago (Eds.)Antarctic earth science. Canberra: Australian Academy of Science.
Borg, S.G., D.J. DePaolo, and B.M. Smith. 1990. Isotopic structure andtectonics of the central Transantarctic Mountains. Journal of Geo-physical Research, 95(B5), 6647-6667.
Dalziel, I.A.W. 1992. Antarctica: A tale of two supercontinents. AnnualReview of Earth and Planetary Science, 20, 501-526.
Goodge, J.W., N.W. Walker, and V.L. Hansen. 1993. Neoproterozoic-Cambrian basement-involved orogenesis within the antarcticmargin of Gondwana. Geology, 21(l),37-40.
Heintz, G.M. 1980. Structural geology of the Leverett Glacier area,Antarctica. (Unpublished Master of Science thesis, Arizona StateUniversity.)
Lowry, P.H. 1980. The stratigraphy and petrography of the CambrianLeverett Formation, Antarctica. (Unpublished Master of Sciencethesis, Arizona State University.)
Minshew, V.H. 1965. Potassium-argon age from a granite at MountWilbur, Queen Maud Range, Antarctica. Science, 150(3697),741-743.
Figure 3. View of the most westerly of the north-south trendingridges of Mount Mahan, looking west. Dark colored "Volcanics ofMt. Fiedler" resting unconformably above the Lower Cambrian"Limestones of Mt. Mahan." Poorly preserved archaeocyaths arepresent at many limestone outcrops along the skyline ridge.
Minshew, V.H. 1967a. Petrologic investigations in the area of the ScottGlacier—Wisconsin Range. Antarctic Journal of the U.S., 2(4),109-110.
Minshew, V.H. 1967b. Geology of the Scott Glacier and WisconsinRange areas, central Transantarctic Mountains, Antarcica.(Unpublished Ph.D. dissertation, Ohio State University.)
Palmer, A.R., and C.G. Gatehouse. 1972. Early and Middle Cambriantrilobites from Antarctica. (U.S. Geological Survey, professionalpaper, 456-D.) Washington, D.C.: U.S. Government PrintingOffice.
Rees, M.N., B.R. Pratt, and A.J. Rowell. 1989. Early Cambrian reefs,reef complexes, and associated lithofacies of the Shackleton Lime-stone, Transantarctic Mountains. Sedimentology, 36(2), 341-361.
Rowell, A.J., M.N. Rees, E.M. Duebendorfer, E.T. Wallin, W.R. VanSchmus, and E.I. Smith. 1993. An active Neoproterozoic margin:Evidence from the Skelton Glacier area, Transantarctic Moun-tains. Journal of the Geological Society, London, 150(4), 677-682.
Rowell, A.J., M.N. Rees, and K.R. Evans. 1992. Evidence of major Mid-dle Cambrian deformation in the Ross Orogen, Antarctica. Geolo-gy, 20(l),31-34.
Stump, E., P.H. Lowry, G.M. Heintz-Stocker, and P.V. Colbert. 1978.Geological investigations in the Leverett Glacier area. AntarcticJournal of the U.S., 13(4), 3-4.
