Mawson Tillite, Victoria Land, East Antarctica: reinvestigation continued

SCOTT GLACIER

Everett, K. R., and R. E. Behling. 1970. Chemical and physical characteristics of Meserve Glacier morainal soils, Wright Valley, Antarctica: an index of relative age? In:

-

International Symposium on Antarctic Glaciological Exploration, Hanover, New Hampshire, 3-7 September 1968. International Association of Scientific Hydrology. Publication, 86. p. 459-460.

20O-

AMUND5EN GLACIER (A-A) DEVILS GLACIER lB-B)

3000. . .

ma

6p

1400

•. ...

1000

- -

600 200

tSHLETON GLACIER A I

3000

ro

FL

ma Indicates minimum level Data point ... High moraine surface Middle moraine surface - Present ice surface

Doumani, G. A., and V. H. Minshew. 1965. General geology of the Mount Weaver area, Queen Maud Mountains, Antarctica. Antarctic Research Series, 6: 127-139. Hollin, J . T. 1962. On the glacial history of Antarctica. Journal of Glaciology, 4(32): 173-195. Mercer, J . H. In press. Some observations on the glacial geology of the Beardmore Glacier area. In: R. J . Adie (ed.), Antarctic Geology and Geophysics. Oslo, Universitetsforlaget. Nichols, R. L. 1961. Multiple glaciation in the Wright Valley, McMurdo Sound, Antarctica. Tenth Pacific Science Congress. Abstracts of Papers Presented, p. 317. Oliver, R. L. 1964. Geologic observations at Plunket Point, Beardmore Glacier. In: R. J . Adie (ed.) Antarctic Geology. New York, John Wiley & Sons, Inc. p. 248-258. Wade, F. A., V. L. Yeats, J. R. Everett, D. W. Greenlee, K. E. LaPrade, and J . L. Shenk. 1965. Geology of the Central Queen Maud Range, Transantarctic Mountains, Antarctica. Texas Tech University. Antarctic Series, 65-1. 54 p.

600-

Figure 3. Profiles of middle and high moraines.

present ice, flowed in the same direction the present ice does. The broad expanse of depositional sites (Scott Glacier to the Coombs Hills) and the fabrics imply that the Sirius Formation was deposited by a continental-scale ice sheet. Moreover, to deposit a basal till the ice related to the Sirius Formation must have been not only of a continental scale but thick enough to permit basal melting. Further investigation of samples collected will help elucidate the environment of deposition of the Sirius Formation. This work was supported by National Science Foundation grant GV-26652. I acknowledge the aid of the helicopter crews of VXE-6 in transporting a 400-kilogram cavernously weathered granite boulder from Bull Pass (adjacent to Wright Valley) to McMurdo Station. The boulder was shipped to Boston's Museum of Science to be put on display as part of an exhibit of interesting rocks from around the world. References Barrett, P. J . 1969. Stratigraphy and petrology of the mainly fluviatile Permian and Triassic Beacon rocks, Beardmore Glacier area, Antarctica. Institute of Polar Studies. Report, 34. 132 p. Elliot, D. H., and D. A. Coates. 1971. Geological investigations in the Queen Maud Mountains. Antarctic Journal of the U.S., VI(4): 114-118.

106

Mawson Tillite, Victoria Land, East Antarctica: reinvestigation continued HAROLD W. BORNS, JR. and BRADFORD A. HALL

Department of Geological Sciences University of Maine at Orono HAROLD W. BALL

Division of Paleontology British Museum H. KELLEY BROOKS

Department of Geology University of Florida This program was a continuation of the program to reinvestigate the origin and age of the Mawson Tillite(?) begun in the 1968-1969 field season by H. W. Borns, Jr., and B. A. Hall. Our primary objective in the 1971-1972 season was to revisit a Jurassic pond deposit at Carapace Nunatak in the Transantarctic Mountains of south Victoria Land in a continuing effort to describe the fauna and flora and ascertain the paleoenvironment and age of this important Southern Hemisphere fossil locality (Borns and Hall, 1969; Hall and Borns, 1970). The party was placed on Carapace Nunatak by helicopters in late December and during the 10 days that followed quarried approximately 700 kilograms of ANTARCTIC JOURNAL

, --

k .t

N. &

Figure 1. Isepod, Carapace Nunatak pond deposit. Length: approximately 2.5 centimeters.

fossiliferous rock for shipment to the United States for study. Fossils known to be represented are conchostracans, notostrachans, isopods (fig. 1), ostracods, and syncarids (all fresh-water crustaceans), and these are associated with insects (fig. 2) and plants. The conchostracans and notostrachans are commonly associated with temporary pools and ponds, but the varied nature of many of the fossiliferous horizons in the Carapace deposit, their lateral extent, and the presence of the isopods and syncarids suggest the shallow margins of a more permanent lake. As yet no vertebrates have been found in association. A particularly interesting aspect of part of the fauna is that it appears to be anachronistic. On the basis of comparison with coeval volcanic beds, the pond deposits of Carapace Nunatak have been assigned a mean absolute age of 156 million years (Ballance and Watters, 1971, p. 521) near the base of the Upper Jurassic. This broadly accords with Townrow's (1967) assignation of a Middle Jurassic age for the plants. However, the conchostracans and notostrachans appear to have very close affinities with forms occurring together in the Upper Triassic Cave Sandstone of South Africa, and the isopods with a species from the Upper Trias of Australia. Apart from the apparent age differences, the geographical distribution of these forms also is noteworthy. With close helicopter support we visited sections of Battlements Nunatak and Allan and Coombs Hills, which were not visited in the 1968-1969 season. Additional volcanics for radiometric dating were collected, and the ubiquitous presence of stratification within the Mawson volcanic breccia was documented. This work was carried out under National Science Foundation grant GA-1148. July-August 1972

I A.

Figure 2. Insect and syncarid fragment, Carapace Nunatak pond deposit. Length of insect: approximately 1 .5 centimeters.

References Ballance, P. F., and W. A. Watters. 1971. The Mawson Diamictite and the Carapace Sandstone, formations of the Ferrar Group at Allan Hills and Carapace Nunatak, Vic-

toria Land, Antarctica. New Zealand Journal and Geophysics, 14: 512-527.

of

Geology

Borns, H. W., and B. A. Hall. 1969. Mawson "Tillite" in Antarctica: preliminary report of a volcanic deposit of Jurassic age. Science, 166 (3907): 870-872. Hall, B. A., and H. W. Borns, Jr. 1970. Jurassic geology of the Allan-Battlements-Carapace Nunataks area, Victoria Land (abs.). SCAR/IUGS Symposium, Oslo, Norway. Townrow, J . A. 1967. Fossil plants from Allan and Carapace Nunataks, and from the upper Mill and Shackleton Gla-

ciers, Antarctica. New Zealand Journal Geophysics, 10(2): 456-473.

of

Geology and

Basement geology of Mount Insel area, Victoria Valley, Antarctica A. G. SUBLETT, W. C. HAUCK, R. S. HOUSTON, and S. B. SMITHSON Department of Geology University of Wyoming During the 1971-1972 field season, we mapped basement rocks on the east flank of Mount Insel in Victoria Valley, where complex structural relationships are well exposed. Metamorphic basement rocks mapped are caicsilicate schist and gneiss, marble, and quartzo-feldspathic gneiss. Mineral assemblages containing garnet in the quartzo-feldspathic gneiss; sillimanite coexisting with K-feldspar, and lack of muscovite in pelitic schist place these rocks in the upper-amphibolite metamorphic facies. 107