The channel-fill deposits at Mount Benkert appear to represent British Antarctic Survey. 1981. British antarctic territory geologic map, Sheet fluviatile sedimentary rocks derived from hyaloclastites; the 4, Alexander Island: BAS 500G Series, 1:500,000. Cambridge: British huge channel forms that compose the main outcrop, the associ- Antarctic Survey. ated mesoscopic internal bedding forms of cut-and-fill struc- Burn, R.W., and M.R.A. Thomson. 1981. Late Cenozoic tillites associ- tures, graded bedding and crossbedding, and the association ated with interglacial volcanic rocks, Lesser Antarctica. In Ml. with nonpillowed basalt flows suggest that these rocks are of Hambrey, and W.B. Harland (Eds.), Pre-Pleistocene tillites: A record of Cambridge: Cambridge University Press. subaerial origin. The geochemically immature composition and Earths glacial history. the angularity of the grains that compose the deposit indicate a LeMasurier, W. E., and EA. Wade. 1976. Volcanic history in Marie Byrd very close source area. Vesicular basaltic dikes as much as 4 Land: Implications with regard to southern hemisphere tectonic re- meters thick are abundant in the central and eastern part of the constructions. In 0. Gonzalez-Ferran (Ed.), Andean and antarctic vol- Rome: International Association of Volcanology mountain; most are vertical and trend east to northeast. canology problems. and Chemistry of the Earths Interior. The authors thank the fellow members of the English Coast expedition, K.S. Kellogg, T.S. Laudon, D.J. Lidke, P.D. Rowley, Renner, R.G.B., B.J. Dikstra, and J.L. Martin. 1982. Aeromagnetic sur- and W.R. Vennum, for their help in collecting the field data. veys over the Antarctic Peninsula. In C. Craddock (Ed.), Antarctic This work was supported by National Science Foundation grant geosciences. Madison: University of Wisconsin Press. DPP 83-18183. Rowley, PD., K.S. Kellogg, and W.R. Vennum. 1985. Geologic studies in the English Coast, eastern Ellsworth Land, Antarctica. Antarctic Journal of the U.S., 20(5). References Vennum, W.R., and T.S. Laudon. In press. Igneous petrology of the Merrick Mountains, eastern Ellsworth Land, Antarctica. In P.D. Baker, P.E. 1976. Volcanism and plate tectonics in the Antarctic Penin- Rowley and W.R. Vennum (Eds.), Studies of the geology and mineral sula and Scotia Arc. In 0. Gonzalez-Ferran (Ed.), Andean and antarctic resources of the southern Antarctic Peninsula and eastern Ellsworth Land, volcanology problems. Rome: International Association of Volcanology Antarctica. (U.S. Geological Survey Professional Paper 1170.) Wash- and Chemistry of the Earths Interior. ington, D.C.: U.S. Government Printing Office.

basaltic volcanic and volcaniclastic rocks of probable Late Sedimentary rocks of the English Cenozoic age. The Mesozoic plutonic and volcanic rocks, and Coast, eastern Ellsworth Land, the Cenozoic volcanic rocks are described elsewhere (Rowley, Antarctica Kellogg, and Vennum, Antarctic Journal, this issue; ONeill and Thomson, Antarctic Journal, this issue). Plant fossils discussed in this report were studied and classified by Theodore Delevoryas and Carole T. Gee. T.S. LAUDON Small outcrops of sedimentary rocks occur at nine localities in the English Coast (figure 1). They make up Henkle Peak and Department of Geology two other small nunataks, unofficially called "Erehwon" and University of Wisconsin at Oshkosh "Sobaco"; they occur interbedded with volcanic rocks at Mount Oshkosh, Wisconsin 54901 Peterson, Mount Rex, Marshall Nunatak, Mount Southern, an Mount Harry; and they are intruded by plutonic rocks a D.J. LIDKE FitzGerald Bluffs. The sedimentary rocks have been struc turally deformed and most have northwesterly strikes an U.S. Geological Survey southwesterly dips. Stratigraphic correlation between outcrop Denver, Colorado 80225 is not possible on the basis of field criteria. All of the sedimentary rocks appear to have been deposited i and C.T. GEE T. DELEVORYAS terrestrial environments. At Mount Peterson, interbedded re sandstone, siltstone, and boulder conglomerate are probab Department of Botany part of an ancient alluvial fan. Deltaic or coastal swamp enviroi- University of Texas at Austin Austin, Texas 78713 ments seem to be represented by fine-grained sandstone con- taming Glossopteris leaves at "Erehwon" Nunatak, and by car- bonaceous conglomerate and sandstone, containing abundant Sixteen small nunataks or nunatak groups scattered over conifer wood, bark, and leaves, at Henkle Peak. Conspicuously more than 16,000 square kilometers of the English Coast of the crossbedded, metamorphosed quartz sandstone units at Bellingshausen Sea in eastern Ellsworth Land were examined FitzGerald Bluffs and at "Sobaco" Nunatak probably were de- for the first time during the 1984 - 1985 field season (figure 1). posited in fluvial environments. Other outcrops of sedimentary These nunataks are the westernmost exposures of the southern rocks constitute relatively minor portions of predominantly Antarctic Peninsula structural province. They are made up of volcanic sequences. sedimentary rocks of Late Paleozoic and Early Mesozoic age, The only fossils found on the English Coast are land plants. volcanic and plutonic rocks of probable Mesozoic age, and Leaves from "Erehwon" Nunatak (figure 2) belong to one or

38 ANTARCTIC JOURNAL more species of Glossopteris of Permian age (possibly extending into the Triassic). Bark, wood, and leaves from Henkle Peak include leafy twigs of Elatocladus sp. (figure 3) probably of Jurassic age.

Figure 3. Fossil plant material including leafy twig of Elatoc!adus from Henkle Peak.

Previously described Mesozoic rock units from the southern Antarctic Peninsula and Alexander Island were all formed in magmatic arc-related environments (Rowley et al. 1983). The LeMay Group on central Alexander Island contains accreted lower slope sediments and fore-arc basin deposits ranging in age at least from Triassic to Middle Cretaceous (Burn 1984). The Latady Formation of Middle and Late Jurassic age, which is the only sedimentary rock unit exposed in the Orville and Lassiter Coasts, contains predominantly marine back-arc basin deposits that intertongue with terrestrial volcanic and sedimentary rocks (not shown on figure 1) in Palmer Land, near the axis of the Figure 1. Geologic sketch map of southern Palmer Land, eastern Antarctic Peninsula (Laudon etal. 1983). The Fossil Bluff Forma- Ellsworth Land, and Alexander Island showing approximate dis- tion on eastern Alexander Island is composed of volcanogenic tribution of sedimentary rock units, and locations of nunataks men- fore-arc basin deposits of Late Jurassic and Early Cretaceous age tioned in text. ("Li.Ju. - L.K." denotes "Upper Jurassic to Lower (Thomson 1982). Cretaceous." "U. + M. Jurassic" denotes "Upper and Middle Sedimentary rocks at Henkle Peak contain Elatocladus-bear- Jurassic: "M.Cr. - Tr denotes "Middle Cretaceous to Triassic." ing strata, and they probably are lateral equivalents of terrestrial "KM" denotes "Kilometer.") facies of the Latady Formation. Sedimentary rocks exposed north and west of Henkle Peak seem to differ significantly from the Latady Formation in lithology, age, provenance, or environ- ment of deposition. Glossopteris-bearing sandstone at "Ereh- won" Nunatak is significantly older than the oldest previously dated rock from the southern Antarctic Peninsula, which is an ammonite-bearing sandstone of Middle Jurassic (Bajocian) age (Quilty 1970) from the Behrendt Mountains. Metamorphosed quartz sandstone at FitzGerald Bluffs and at "Sobaco" Nunatak appears to be of cratonic provenance, in marked contrast to the Latady Formation, the LeMay Group, and the Fossil Bluff For- mation, which are predominantly of volcanic-arc provenance. A probable alluvial fan deposit at Mount Peterson contains a variety of boulders of volcanic, plutonic, and sedimentary rocks. It is overlain by volcanic rocks and probably was deposi- ted near a fault scarp or topographic rise. At Marshall Nunatak, volcanic conglomerate contains boulders of a variety of vol- canic, plutonic, and sedimentary rocks. The presence of terrestrial sedimentary rocks, some of Late Paleozoic or Triassic age, some of apparent cratonic provenance, and some apparently deposited near fault scarps or topographic rises and volcanic centers, suggests that the English Coast may have been located on or near the Pacific Coast of southern Gondwana during, or immediately prior to, the inception of the Figure 2. Glossopteris leaf from "Erehwon" Nunatak. Gondwana breakup during the Triassic. This interpretation is

1985 REVIEW 39 consistent with a growing body of evidence supporting the Daiziel, I.W.D., and D.H. Elliott. 1982. West Antarctica: Problem child speculation that upper Paleozoic (?) to lower Mesozoic rocks of of Gondwanaland. Tectonics, 1(1), 3 - 19. the Antarctic Peninsula lithospheric plate are part of an An- Hyden, G., and P.W.G. Tanner. 1981. Late Paleozoic-early Mesozoic dean-type mountain belt that was continuous along the Pacific fore-arc basin sedimentary rocks at the Pacific margin in western margin of Gondwana from South America to New Zealand Antarctica. Geologische Rundschau, 70, 529 - 541. prior to the Gondwana breakup (e.g., Hyden and Tanner 1981; Laudon, T.S., M.R.A. Thomson, P.L. Williams, K.L. Milliken, P.D. Dalziel and Elliott 1982; Burn 1984). Rowley, and J.M. Boyles. 1983. The Jurassic Latady Formation, south- We thank the other members of the English Coast field party, ern Antarctic Peninsula. In R.L. Oliver, P.R. James, and J.B. Jago K.S. Kellogg, J.M. ONeill, P.D. Rowley, J.W. Thomson, and (Eds.), Antarctic Earth science. Canberra: Australian Academy of W.R. Vennum, for their help in many ways; and the National Science. Science Foundation Division of Polar Programs, the U.S. Navy, ONeill, J.M., and J.W. Thomson. 1985. Tertiary mafic volcanic and and ITT/Antarctic Services for essential assistance. This work volcaniclastic rocks of the English Coast, Antarctica. Antarctic Journal of the U. S., 20(5). was supported by National Science Foundation grants DPP Quilty, P.G. 1970. Jurassic ammonites from eastern Ellsworth Land, 83-18183 to the U.S. Geological Survey and DPP 83-19569 to the University of Wisconsin at Oshkosh, by a grant from the U.S. Antarctica. Journal of Paleontology, 44, 110 - 116. Geological Survey to the University of Wisconsin at Oshkosh, Rowley, PD., K.S. Kellogg, and W.R. Vennum. 1985. Geologic studies in the English Coast, eastern Ellsworth Land, Antarctica. Antarctic and by the University of Wisconsin at Oshkosh Faculty De- Journal of the U.S., 20(5). velopment Program. Rowley, PD., W.R. Vennum, K.S. Kellogg, T.S. Laudon, P.E. Carrara, J.M. Boyles, and M.R.A. Thomson. 1983. Geology and plate tectonic setting of the Orville Coast and eastern Ellsworth Land, Antarctica. References In R. L. Oliver, P.R. James, and J. B. Jago (Eds.), Antarctic Earth science. Canberra: Australian Academy of Science. Burn, R.W. 1984. The geology of the LeMay Group, Alexander Island Thomson, M.R.A. 1982. Mesozoic paleogeography of West Antarctica. British Antarctic Survey Scientific Reports (No. 109). Cambridge In C. Craddock (Ed.), Antarctic geoscience. Madison: University of Cambridge University Press. Wisconsin Press.

field area. Additional USARP fuel was made available at Mount Tectonics of West Antarctica and its Smart and Siple Station. A Twin Otter aircraft was provided by relation to East Antarctica: USARP- BAS for approximately 1 months close support of the party that BAS geology/geophysics project comprised the following scientists: from USARP, Ian W. D. Dalziel and Anne Grunow, both of Columbia University, New (1984 - 1985) York, and BS Robert J. Pankhurst and Bryan C. Storey, both of the British Antarctic Survey. The Twin Otter was piloted by BAS Chief Captain Ed Murton. I.W.D. DALZIEL The work comprised detailed field studies of the Mesozoic igneous basement and Tertiary volcanic cover rocks of the Jone Lamont-Doherty Geological Observatory Columbia University Mountains and of the igneous and metamorphic rocks o Palisades, New York 10964 Thurston Island and adjacent islands and of Lepley Nunatak Basic field observations were undertaken by the whole part

R.J. PANKHURST including detailed structural observations in the metamorphi4 rocks by Bryan Storey and Ian Dalziel. Extensive collection British Antarctic Survey were made for major and trace element geochemical analysis by Cambridge CB3 OET United Kingdom Bryan Storey and for isotope geochemical studies by Robert Pankhurst. Anne Grunow and Ian Dalziel collected 780 cores and several oriented hand specimens constituting 120 sites for The joint U.S. Antarctic Research Program-British Antarctic paleomagnetic studies. Survey (USARP-BAS) geology and geophysics project was initi- The joint USARP-BAS program will continue during the 1985 - ated in 1980 - 1981 and continued in 1983 - 1984 with the first 1986 season with airborne geophysical surveys in the area be- full seasons work in the Ellsworth Mountains/Whitmore tween Siple Station, the Ellsworth Mountains, Thurston Island, Mountains/Thiel Mountains area. Another season of geological and Byrd Station. The flight lines have been selected jointly by work was undertaken in 1984 - 1985 in the Jones Mountains! USARP and BAS scientists and will be flown by a BAS Twin Otter Thur tnn Island area. Aviation fuel was flown in by USARP to the with fuel made available by USARP at Siple and Byrd Stations. The final season of the present project is planned for 1987— 1988 in the Pensacola Mountains. It will involve detailed structural Present address: institute for Geophysics, University of Texas at Austin, geology and collecting for geochemical and paleomagnetic Austin, Texas 78751. studies.

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