Aeromagnetic surveys of the Ross Island and Taylor ...
Aeromagnetic surveys of the Ross Island and Taylor Glacier quadrangles
isolated remanents of the Ferrar dolerites. The sills of the Ferrar dolerites have sufficient susceptibility contrast with the Beacon sandstones (Bull et al., 1962) to produce these magnetic intensity values. The region near the coast appears relatively free of any anomalous magnetic field; however, steep magnetic peaks of 1,000 gammas, which correlate with the location of the Dailey Islands, also are associated with a broad magnetic high decreasing in value in the direction of Ross Island. This broad anomaly appears to be centered over the Dailey Islands and extends in the northeast-southwest direction about 14 kilometers. The broad high indicates a deep magnetic source rock capped by the volcanic cones of the Dailey Islands. The magnetic variation near Ross Island is typical of the data observed over the island and is related to a southwestward extension of the Ross volcanics. This is an incomplete analysis, and until the data have been corrected and a magnetic contour map of the region constructed, only a qualitative interpretation can be stated. Thanks are due to the officers and men of Antarctic Development Squadron Six who flew for us and to the many others, including the photographic section, who aided us in making this a successful program. This work was supported by National Science Foundation contract C-642.
GERALD E. MONTGOMERY
Department of Geology Northern Illinois University An aeromagnetic survey of the dry valley area was flown during the 1971-1972 field season as part of the Dry Valley Drilling Project (McGinnis et al., 1972). Approximately 50 percent of the 12,000 kilometers of flight line has been completed. Flight lines were oriented east-west with 2-kilometer spacing and were flown at 300 meters above the ground surface. Shaded areas on the map (fig. 1) indicate the completed section of the study. Magnetic profiles flown in 1962 along the axes of Wright and Taylor Valleys (Robinson, 1964) indicated there were no magnetic anomalies exceeding 20 gammas. Data from the present survey bear out those findings, but, as shown in fig. 2, magnetic anomalies having amplitudes of 1,200 gammas are present in the uplands surrounding the dry valleys. Depths to the magnetic source for the two anomalies near the plateau were calculated to be within 300 meters of the surface. The anomalies are believed to be produced by
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References Bull, C., E. Irving, and I. Willis. 1962. Further palaeomagnetic results from south Victoria Land, Antarctica.
Royal Astronomical Society. Geophysical Journal, 6(3):
320-336. McGinnis, L. D., T. Toni, and P. Webb. 1972. Dry Valley Drilling Project. Antarctic Journal of the U.S., VII(3) 53-56. Robinson, E. E. 1964. Correlation of magnetic anomalies with bedrock geology in the McMurdo Sound area, Antarctica. Journal of Geophysical Research, 69(20): 4319– 43 26.
Seismic refraction and electrical resistivity investigations in the dry valleys CLIFFORD C. CLARK
Department of Geology Northern Illinois University Geophysical field work in the ice-free valleys of Victoria Land, Antarci;ica, during the 1971-1972 austral summer included both electrical depth sounding July-August 1972
and seismic refraction profiling. This ground exploration was conducted as part of the Dry Valley Drilling Project (McGinnis et al., 1972). Geophysical studies were conducted to establish geologic control at borehole sites where drilling would provide relevant information concerning the history of the dry valleys. For a detailed description of electrical equipment and methods, see McGinnis and Jensen (1971). An SIE portable, 12-channel seismograph with an internal nickelcadmium power supply was used for the 12 seismic stations of 366-meter geophone spread. Some of the numerous lakes in the dry valleys are suspected to be connected hydrologically to the subsurface. In an area where the mean annual air temperature is —20° to — 25°C. (Horowitz et al., 1972), permafrost would be expected to restrict completely the transfer of surface and subsurface water. Electrical and seismic measurements indicate that the occurrence of "confining" permafrost (McGinnis and Jensen, 1971) varies but is predictable. Temperatures at the bottom of some of these lakes are unexplicably high, and in some cases permafrost beneath the lakes is absent. Drilling near these lakes will give us important information concerning the hydrology of the area. 91
