Magnetostratigraphy and Sedimentology of Late Cenozoic
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Specific targets, especially those related to the sediments approximately 3 kilometers long and is coincident in orienta- that lie immediately above the Kukri erosion surface, were tion with the old landing strip at Marble Point. It terminates examined in detail. Several areas were found where sedimen- on the northwest against the Wilson Piedmont Glacier and on tary beds in the lower Beacon Group showed elevated uranium the southeast at the shore of Arnold Cove. Figure 1 shows the concentrations. These apparently are associated with shale location of the flightpath A-B and the general geology of the zones. Also, the Ross Island volcanics are anomalously high area. Figure 2 shows the relative surface count rate in counts in a number of localities. Our survey revealed that almost all per second and the geologic profile of the flightpath. Figure 3 of the exposed rocks in a large area at the south end of the indicates the variation in counts per second in the individual Royal Society Range have higher than normal uranium levels. channels of the gamma-ray spectrometer at an elevation of 15 The radiometric survey continued from 20 November to 23 meters above the ground. These channels measure the con- December 1980 and included one reconnaissance flight with centration of potassium-40 and the radioactive equilibrium an LC-130 aircraft. The airplane was flown at 100 meters above- concentrations of uranium and thorium. ground to permit the scanning of exposed rocks in the Darwin This project is a continuing joint research effort of the Uni- Mountains and Brown Hills adjacent to the Darwin Glacier in versity of Kansas and the West German Federal Institute of the Transantarctic Mountains. Although the detector volume Geosciences and Resources. This research was supported in of 8,390 cubic centimeters cannot be considered adequate for part by National Science Foundation grant DPP 77-21504. the high forward speed of this fixed-wing aircraft, we found that it was possible to obtain very useful information about References ratios of uranium/thorium and uranium/potassium. This experiment suggests that remote areas of the continent could Zeller, E. J., and Dreschhoff, C. A. M. 1980. Uranium resource eval- be reached and surveyed for evaluation of uranium resource uation in Antarctica. In Uranium evaluation and mining techniques. potential by the use of aircraft similar to the LC-130. Vienna: International Atomic Energy Agency. The second objective of this field season was the establish- Zeller, E. J., Dreschhoff, G. A. M., Crisler, K., and Tessensohn, F. In ment of a new calibrated flightpath to permit the standardiza- press. Resource and radioactivity survey in South Victoria Land, tion of the airborne counting apparatus. This flightpath is Antarctica. Geoscience. sampling of the core for paleomagnetic and sedimentologic Magnetostratigraphy and analysis, and examination and sampling of apparently correl- sedimentology of late Cenozoic ative strata exposed along stream courses near the margins of the valley (figure). Preliminary results of the field and labo- glaciogenic deposits, ratory work are summarized in a report we are preparing for eastern Taylor Valley open file. Photographic and lithologic logs of the core are given in that report. Frozen, ice-cemented cores from two holes (ETV- 1, drilled to a depth of 4 meters, and ETV-2, drilled to a depth DONALD P. ELSTON and STEPHEN L. BRESSLER of 45 meters) are in the freezer at the antarctic core storage facility at Florida State University, Tallahassee. U.S. Geological Survey Flagstaff, Arizona 86001 The object of the study was to investigate the nature, age, and distribution of deposits underlying a veneer of drift that PAUL H. ROBINSON accumulated during incursion of the Ross Sea ice in late Pleis- tocene time (Ross Sea I drift of Denton, Armstrong, and Stuiver Ministry of Works and Development 1971, reported to be about 15,000 years old). A field recon- Christchurch, New Zealand naissance in 1979 had led to the inference that comparatively fine-grained deposits, perhaps aggregating some tens of meters in thickness, underlay the Ross Sea drift in the valley A joint U.S.-New Zealand stratigraphic, paleomagnetic, and floor, particularly near a north to south-trending ridgeline that sedimentologic study was undertaken in late Cenozoic glaci- forms a transverse divide about 100 meters above sea level ogenic deposits in eastern Taylor Valley. Fieldwork, which (figure). Ross Sea drift that caps this ridge locally contains was carried out from 18 November to 5 December 1980, solitary corals and bivalves. These fossils weather out of soft involved Winkie core drilling in the valley floor, logging and siltstone clasts apparently transported from the Ross Sea dur- ing the last incursion of the ice. This ridge thus has been informally called Coral Ridge. This report is preliminary and has not been reviewed for conformity with U.S. Geological Survey editorial standards and stratigraphic The youngest deposits in the area are comparatively well- nomenclature. sorted sand that overlaps Ross Sea drift along and adjacent to 1981 REVIEW 39 COMMOIWealth Stream L$8 Ross O Sea I- drift I HARBOR COMMONWEALTH Li iY "CcrI Ridge GLACIER sand o base of exposure - New Harbor sand I -77°35 / New Harbor / sand Coral. - ETV-i- - ( ) 6 Explanation Ross Sea ETV1,,E 1 \\25 . silt and / fine sandDV DP7I l• fine to 1 2 Meters medium sand - 30 0 coarse sand Coral ••• and conglomerate Ridge - j ws I Ross Sea 20 16 sand - / - drift - O diomictite CL5 100 9 1.0Coral451:4 Kilometers Ridge £ bench mark 0 sand Index map and generalized stratigraphic sections of cores and outcrops in eastern Taylor Valley. Abbreviations: DVDP, Dry Valley Drilling Project; ETV, Eastern Taylor Valley; cws, Commonwealth Stream; ws, Wales Stream. Depths or thicknesses are In meters. Wales Stream and its delta at New Harbor. DVDP-8 and -10 are quence of a single depositional episode. This sand body is collared in this "New Harbor sand" unit on a bench about 2 informally called the "Coral Ridge sand." meters above sea level. A carbon-14 ( 14C) age of 5,800 years The Coral Ridge sand is dominantly medium- to coarse- was obtained on an in situ bivalve shell encountered 25 meters grained and is rather well sorted, lacks clay and silt, and deep in the core (Stuiver, Denton, and Borns 1976), presum- exhibits common fluviatile cross-stratification. Small pebbles ably near the base of this deposit. are rare. Deposition appears to have occurred in a fluviatile or The Ross Sea drift appears to consist of two units where it perhaps a fluvio-marine deltaic environment, above and pre- is exposed along Commonwealth Stream (figure). A silty, com- sumably very near sea level. The sand body accumulated fol- monly well-sorted, fine-grained lower unit about 5-13 meters lowing deposition of coarse diamictons and interbedded sand thick (unit a, figure) is overlain by a generally coarser, poorly in a fjord that once occupied the site of Taylor Valley. The sorted deposit that contains boulder-size detritus and locally source of the sand has yet to be determined. It came either is as much as 10 meters thick (unit b, figure). The lower unit from a grounded ice sheet in the Ross Sea to the east or from appears to be present in the central and southern parts of the the west at a time when a more extensive Taylor Glacier occu- valley but is thin (less than 1 meter) and is not depicted as a pied the valley. separate unit in the sections away from Commonwealth The age of the Coral Ridge sand also is not yet resolved. Stream. Except for the 2-meter-thick section of reversely polarized sand A relatively thick sand body underlies Ross Sea drift in the near the top of hole DVDP-11 (Elston and Bressler in press; floor of Taylor Valley. An incomplete section was intersected Purucker, Elston, and Bressler in press), all of the ice-cemented in core from 1.5 meters to 45 meters depth in hole ETV-2. sand (in cores of DVDP-11 and ETV-2, and in outcrops in Wales Similar, if not identical, ice-cemented sand underlies Ross Sea and Commonwealth Streams) has been found to be normally drift in exposures along the Commonwealth and Wales polarized, which suggests a Bruhnes (less than 730,000 years Streams, where incomplete sections are as great as 15 meters old) age. In light of this work and previous studies, two pos- thick. In DVDI-11, this sand was penetrated from a depth of 2 sibilities exist: (1) the sand body was deposited principally to 16 meters. The distribution indicates that the sand accu- during the Bruhnes normal polarity epoch of late Pleistocene mulated as a body across the valley, presumably as a conse- time and the reverse polarity in DVDP-11 is an anomaly, or 40 ANmRcric JOURNAL (2) the Coral Ridge sand body was deposited during a time of References normal polarity of the Gauss epoch. Additional subsurface and surface geologic and paleomagnetic study, including study of Denton, C. H., Armstrong, R. L., and Stuiver, M. 1971. The late Cen- sedimentary structures, is needed to resolve the foregoing ozoic glacial history of Antarctica. In K. K. Turekian (Ed.), The late problems that bear directly on the late Cenozoic glacial and Cenozoic glacial ages. New Haven, Conn.: Yale University Press. structural history of Taylor Valley and environs. Elston, D. P., and Bressler, S. L. In press. Magnetic stratigraphy of The Winkie drill and drill team of Garth Varcoe, James Jen- DVDP drill cores and late Cenozoic history of Taylor Valley, Transant- kins, and Roy Parish were provided by the Antarctic Division, arctic Mountains, Antarctica.