Bindschadler, R.A., S.N. Stephenson, D.R. MacAyeal, and S. Shabtaie. Shabtaie, S., I.M. Whillans, and C.R. Bentley. 1987 The morphology 1987 Ice dynamics at the mouth of ice stream B, Antarctica. Journal of ice streams A. B, and C, West Antarctica, and their environs. of Geophysical Research, 92(139), 8885-8894. Journal of Geophysical Research, 92(139), 8865-8883. Blankenship, D.D., R.B. Alley, and C.R. Bentley. 1989. Fabric devel- Shabtaie, S., C.R. Bentley, R.A. Bindschadler, and D.R. MacAyeal. opment in ice sheets: Seismic anisotropy. (Abstract.) EOS, 70(15), 1988. Mass-balance studies of ice streams A, B, and C, West Antarc- 462. tica, and possible surging behavior of ice stream B. Annals of Glaciol- Budd, W.F. and T.H. Jacka. 1989. A review of ice rheology for ice sheet ogy, 11, 137-149. modelling. Cold Regions Science and Technology, 16, 107-144. Whillans, I.M., J. Bolzan, and S. Shabtaie. 1987 Velocity of ice streams Engelhardt, H., N. Humphrey, B. Kamb, and M. Fahnestock. 1990. B and C, Antarctica. Journal of Geophysical Research, 92(139), 8895-8902. Physical conditions at the base of a fast moving Antarctic ice stream. Whillans, I.M., and S.J. Johnsen. 1983. Longitudinal variations in gla- Science, 248, 57-59. cial flow: Theory and test using data from the Byrd Station Strain Cow, A.J., R.B. Alley, and D. Meese. 1991. Ice-deformation processes Network, Antarctica. Journal of Glaciology, 29(101), 78-97. from mapping of c-axis fabrics. (Abstract.) EOS, 72(44), 150.

Clasts of the Swanson Formation are medium gray, slightly Glacial flow reorientation cleaved, fine-grained sandstone or argillite. These sedimentary in the southwestern rocks are thin to very-thin bedded, and the sandstones appear Fosdick Mountains, to be quartzose. The Swanson Formation crops out widely south of the Fosdick Mountains but nowhere to the north , (Wade, Cathey and Oldham 1977a, 1977b, 1977c, 1978; Wade and Couch 1982; Adams 1986; Bradshaw et al. 1983, 1991). Other locally derived clasts are present in all of these deposits. STEPHEN M. RICHARD and BRUCE P. LUYENDYK In two places along the northern side of the Fosdick Moun- tains till deposits with exotic clasts were found (figure). A cin- Institute for Crustal Studies der cone northeast of Mount Avers is mantled with colluvium University of California interpreted to include minor reworked till; this surficial deposit Santa Barbara, CA 93106-1100 consists mostly of cobbles and boulders of the underlying basalt but includes about 10 percent rounded clasts of Fosdick gneiss The orientation of glacial striations on nunataks and clast and Byrd Coast granite. In addition, the fine-grained matrix of composition in tills in the southwestern Fosdick Mountains this deposit includes 10-20 percent of feldspathic grus, similar region (76°30S 145°W) indicate that during the most recent ice to that observed on weathered surfaces of Byrd Coast granite. high-stand when these nunataks were ice covered, the princi- The talus and till deposit in the wind scoop at the north end of pal glacial flow direction was from southeast to northwest, Mount Lockhart contains boulders of basalt with acicular, nearly perpendicular to the present drainage direction inferred glomerophyric plagioclase and sparse olivene. Although this from the topography and flow features on the ice surface. The basalt resembles that found at the cinder cone northeast of Fosdick Mountains and the Phillips Mountains 15 kilometers to Mount Avers, numerous other basalt outcrops are found in the the north, trend east to west and are separated by the Balchen eastern Fosdick Mountains (Wade, Cathey, and Oldham 1977b; Glacier which now flows from east to west. The Crevasse Valley Kimbrough et al. 1990), and these boulders could have been Glacier, south of the Fosdick and Chester Mountains, now derived from up-glacier. The exotic clasts found in till deposits flows from east-northeast to west-southwest. In the course of on the north side of the Fosdick Mountains could have been studying bedrock geology in the Fosdick and Chester Moun- derived from rocks exposed along the Balchen glacier up slope tains region of Marie Byrd Land during the 1989-1990 and 1990- from their present location. 1991 austral field seasons (Kimbrough et al. 1990), we measured Colluvium consisting of weathered Byrd Coast granite that glacial striations on the relatively flat summit ridges of nuna- mantles Mount Corey contains small angular fragments of bas- taks between the Chester Mountains and Fosdick Mountains alt, uniformly distributed over the north side of the nunatak. and in the eastern Fosdick Mountains. These striae trend 115- These are interpreted as air-fall tephra derived from an erup- 1200 on the nunataks between the Chester and Fosdick Moun- tion at one of the volcanic centers in the Fosdick Mountains. tains and 150-160° on outcrops in the eastern Fosdick Moun- This interpretation requires that the most recent eruptions in tains. On the southern part of Bird Bluff, we observed roche the Fosdick Mountains post-date ice-high stands during which moutonée with long axes parallel to striae on the rock surfaces Mount Corey and nearby nunataks were ice-covered. Available and steep sides facing northwest, indicating that ice flow across potassium-argon dates from volcanic rocks in the Fosdick these outcrops was from southeast to northwest (figure). Mountains are as young as 3.4±0.3 million years at Mount Unconsolidated till and talus deposits were observed along Perkins (LeMasurier and Rex 1982), providing a minimum ex- the base of steep cliffs all along the northern side of the Fosdick posure age for Mount Corey if these are indeed the youngest Mountains. Typically these consist of cobbles to boulders of volcanic rocks. rocks found in the adjacent outcrops. Till deposits that contain Because Swanson Formation has not been observed to crop clasts not locally derived mantle parts of Neptune Nunatak, out north of the Fosdick Mountains, the simplest explanation Mount Corey, and nunataks east and southeast of Bird Bluff of these observations is that when the outcrops where the stria- (figure). All of these deposits are characterized by subrounded tions are found were most recently under the ice, glacial flow and tooled clasts of Swanson Formation and Bird Coast granite. was to the northwest and carried clasts of Byrd Coast granite

67 1991 REVIEW colluvium on cinder cone contains Bird Coast / granite and Fosdick gneiss; matrix of deposit Block Bay ) contains arkosic grit Balchen Glacier talus/moraine at N end of ridge contains / basalt blocks that resemble cinder cone / I to SIN here

Mt. Lockhart • O Mt Avers Mt. Perkins 1 Bird Bluff Li I i .. S-dicKv Mountains.rX.

H 110 Neptune N.1 km Nunataks Explanation a I till containing clasts of Bird Coast ^^- angular basaft granite and very low-grade meta- Chester Mtns. cinders present sedimentary rocks (Swanson Fm?) in colluvium glacial striations; arrow head shows transport direction indicated by roche moutonee mt. C rey 4--. \ present ice flow direction

Map showing location and orientation of glacial striations observed in the Fosdick Mounains area, and the location and nature of glacial deposits.

and Swanson Formation from regions to the south or southeast Bradshaw, J.D., PB. Andrews, and B.D. Field. 1983. Swanson Forma- where these rocks are presently abundant in outcrop. The pres- tion and related rocks of Marie Byrd Land and a comparison with ent ice surface in this area slopes to the west and west-south- the Robertson Bay Group of Northern Victoria Land. In R.L. Oliver, west, south of the Chester Mountains. Flow of the Balchen P.R. James, and J.B. Jago (Eds.), Antarctic earth science. Cambridge: Glacier north of the Fosdick Mountains and the Crevasse Valley Cambridge University Press. Glacier south of the Chester Mountains is to the west and Bradshaw, ID.!, W.D. Dalziel, V. DiVernere, S.B. Mukasa, R.B. Pank- southwest. Mountain glaciers on the south flank of the Fosdick hurst, B.C. Storey, and S.D. Weaver. 1991. The southern rim of the range now flow south to southwest and have deposited lateral Pacific: New work on the pre-Cenozoic rocks of Marie Byrd Land. In moraines at the base of the range. This change in ice-flow the proceedings from the Sixth Symposium on Antarctic Earth Sci- direction may have accompanied a decrease in ice thickness ences, Ranzan-Machi, Japan, September 1991. Kimbrough, D.L., BR Luyendyk, S.M. Richard, and C.H. Smith. 1990. which has exposed the striated nunataks. Alternatively, ice Geology of metamorphic rocks: Ford Ranges of western Marie Byrd flow direction was reoriented by uplift of the ranges above the Land. Antarctic Journal of the U.S., 25(5), 3-5. ice surface in Neogene time. LeMasurier, WE., and D.C. Rex. 1982. Volcanic record of Cenozoic This work was supported in part by National Science Foun- glacial history in Marie Byrd Land and western Ellsworth Land: Re- dation grant DPP 88-17615. Contribution of the Institute for vised chronology and evolution of tectonic factors. In C. Craddock Crustal Studies 073-02UA. (Ed.), Antarctica geoscience. Madison, Wisconsin: University of Wis- consin Press. Wade, EA., C.A. Cathey, and J.B. Oldham. 1977a. Reconnaissance geo- logic map of the Boyd Glacier quadrangle, Marie Byrd Land, Antarctica, References 1:250,000. (U.S. Antarctic Research Program Map, A-6.) Reston, Vir- ginia: U.S. Geological Survey. Adams, C.J. 1986. Geochronological studies of the Swanson Formation Wade, EA., C.A. Cathey, and J.B. Oldham. 1977b. Reconnaissance geo- of Marie Byrd Land, West Antarctica, and correlation with Northern logic map of the Guest Peninsula quadrangle, Marie Byrd Land, Antarctica, Victoria Land, East Antarctica, and South Island, New Zealand. New 1:250,000. (U.S. Antarctic Research Program Map, A-7) Reston, Vir- Zealand Journal of Geology and Geophysics, 29, 345-358. ginia: U.S. Geological Survey.

68 ANTARCTIC JOURNAL Wade, EA., C.A. Cathey, and J.B. Oldham. 1977c. Reconnaissance geo- ship with the Robertson Bay Group, northern Victoria Land. In logic map of the Alexandra Mountains quadrangle, Marie Byrd Land, Ant- C. Craddock (Ed.), Antarctic geoscience. Madison, Wisconsin: Univer- arctica, 1:250,000. (U.S. Antarctic Research Program Map, A-8.) Res- sity of Wisconsin Press. ton, Virginia: U.S. Geological Survey. Wade, EA., and T.R. Wilbanks. 1972. Geology of Marie Byrd and Ells- Wade, EA., C.A. Cathey, and J.B. Oldham. 1978. Reconnaissance geologic worth Lands. In R.J. Adie (Ed.), Antarctic geology and geophysics. Oslo: map of the Gutenko Nunataks quadrangle, Marie Byrd Land, Antarctica, Universitetsforlaget. 1:250,000. (U.S. Antarctic Research Program Map, A-li.) Reston, Weaver, S.D., J.D. Bradshaw, and C.J. Adams. 1991. Granitoids of the Virginia: U.S. Geological Survey. Ford Ranges, Marie Byrd Land, Antarctica. In M.R.A. Thomson, J.A. Wade, EA., and D.R. Couch. 1982. The Swanson Formation, Ford Crame, and J.W. Thomson (Eds.), Geological evolution of Antarctica. Ranges, Marie Byrd Land, Evidence for and against a direct relation- Cambridge, England: Cambridge University Press.

form that no years are missing in the record. Second, the "Taylor lceDome study: record must have a stratigraphy that is preserved through Reconnaissance 1990-1991 the firnification process. To determine the suitability for ice- core studies of different areas of "Taylor Dome," we dug 11 snow-pits across an 80 x 20-kilometer grid (figure 1). Ten pits to about 2 meters were sampled in detail (1-centimeter inter- P.M. GROOTES, E.J. STEIG, and C. MASSEY vals) for istopic oxygen-18. Stratigraphy, temperature as a function of depth, and hardness of the snow were recorded Quaternary Isotope Laboratory, AK-60 in each pit. Microparticle samples were taken in two of the University of Washington Seattle, Washington 98195 pits, and chemistry samples and snow density were taken in one. Detailed stratigraphy, isotope, chemistry, and micro- particle samples as well as measurements of temperature, "Taylor Dome" is a small ice dome (center above 2,450 meters density, and hardness of the snow were obtained on a 4.5- at about 77°40S 158°00E) separated from a ridge of the main meter pit near camp. Using a Polar Ice Coring Office hand- east antarctic ice sheet by a saddle at least 100 meters lower auger system, two cores were drilled to about 11 meters to (Drewry 1980). Flowline reconstruction by Drewry (1982) shows measure for microparticles and methanesulfonic acid and this dome as a local center of outflow supplying ice to the one core was drilled to about 19 meters to measure for iso- glaciers entering the McMurdo Dry Valleys of southern Victoria topes near this pit. Land from the west. Climatic changes have been recorded both Most pits show a predominantly horizontal layering with in the ice accumulating on "Taylor Dome" and in the glacial occasional hard, wind-packed layers representing buried sas- geology in the McMurdo Dry Valleys. An ice core retrieved trugi (figure 2). A pattern of multiple thin layers and crusts from "Taylor Dome" thus offers the opportunity to compare separated by thicker, more uniform snow layers probably the ice-core record of past climatic and environmental changes marks the seasonal pattern and suggests an annual accu- from an area of simple ice flow with the directly related geo- mulation of about 10-centimeter water equivalent. The area logical record of past glaciations in the adjacent McMurdo Dry to the northeast of the crest of the dome, downwind for the Valleys (e.g., Denton et al. 1989; Stuiver et al. 1981). predominant (katabatic) winds, shows more and larger sas- From 29 November 1990 to 28 January 1991, two field parties trugi at the surface and in the pit profiles. Because sastrugi of three members each (Grootes, Steig, and Massey of the Qua- deposit locally over a short period and may consist largely of ternary Isotope Laboratory and Balise, Morse, and Firestone of reworked snow, this area is less suitable for an ice-core study. the Geophysics Program of the University of Washington) car- Because our goal is to connect the "Taylor Dome" ice-core ried out a joint reconnaissance of "Taylor Dome" in preparation record to the glacial geology of the McMurdo Dry Valleys, for the selection of an ice-core drill site (see also Waddington the southwestern flank of the dome, which drains via The et al., Antarctic Journal, this issue). Portal into the , is likewise less suitable for a The goals of the Quaternary Isotope Laboratory party were deep-drill site. Near the Lashly Mountains, "Taylor Dome" to select a site (that is, to identify the area where the accumu- ends abruptly with a distinct step in ice elevation. The crest lating snow best preserves an environmental record) and to area between 20C and 30C (figure 1), away from this step determine transfer functions (that is, to determine the relation- has been chosen as the most suitable drill area. A drill site ship between the properties of the accumulating snow and will be selected during the coming year based on detailed environmental conditions). radar studies of the bedrock topography. • Site selection. Two qualities classify a preserved environmen- • Transfer functions. Pale oenvironmental studies using ice tal record in the ice as suitable for study. First, the record cores aim to reconstruct the past (local) atmospheric condi- must represent an accumulation sufficiently sizeable and uni- tions from the information contained in the ice. It is, thus, essential to make detailed weather observations (Waddington et al., Antarctic Journal, this volume) and to measure atmos- pheric water vapor, frost/rime, and falling snow to determine Taylor Ice-Dome," also referred to as "Taylor Dome," is not listed in the relationships between those conditions and deposited the Gazeteer of the Antarctic as an official name, but it is a distinct geo- snow. An array of mylar-covered boards placed in the snow, graphic feature. level with the snow surface, near bamboo poles marked with

1991 REVIEW 69