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Lassiter Coast copper deposit (Farrar et al. in press; age re- Laudon, T. S. 1972 Stratigraphy of eastern Ellsworth Land. In R. J. calculated for the new decay constants of Dalrymple 1979). Adie (Ed.), Antarctic geology and geophysics. Oslo, Norway: Uni- The west Behrendt batholith, occurring in scattered un- versitetsforlaget. named nunataks west of the Behrendt Mountains, has an Laudon, T. S., Lackey, L. L., Quilty, P. C., and Otway, P. M. 1969. exposed diameter of about 12 kilometers. The rock is a Geology of eastern Ellsworth Land (Sheet 3, eastern Ellsworth uniform medium- to coarse-grained high-quartz grano- Land). In V. C. Bushnell and C. Craddock (Eds.), Geologic maps of diorite. The K-Ar age is 104.5 million years (biotite) to 108.9 Antarctica (Antarctic map folio series, Folio 12, Plate 3). New York: American Geographical Society. million years (hornblende). The ages reported here are similar to those reported for Mehnert, H. H., Rowley, P. D., and Schmidt, D. L. 1975. K-Ar ages plutons from the Lassiter and Black Coasts (Farrar et al. in of plutonic rocks in the Lassiter Coast area, Antarctica. U.S. Geo- logical Survey Journal of Research, 3(2), 233-236. press; Mehnert, Rowley, and Schmidt 1975) and eastern Ellsworth Land (Halpern 1967). Clearly the plutons in the Rowley, P. D. 1978. Geologic studies in Orville Coast and eastern southern Antarctic Peninsula belong to a single restricted Ellsworth Land, Antarctic Peninsula. Antarctic Journal of the U.S., 13(4),7-9. Late Cretaceous magmatic event, in contrast to other plu- tons in the northern Antarctic Peninsula, which range in Rowley, P. D. 1979. Orville Coast-eastern Ellsworth Land project, age from Jurassic to Tertiary. 1978-1979. Antarctic Journal of the U.S., 14(5), 21-22. This work was supported by grants from the National Rowley, P. D., and Williams, P. L. In press. Geology of the northern Science Foundation (DPP 78-24214) and the National Sci- Lassiter Coast and southern Black Coast, Antarctic Peninsula. In ence and Engineering Research Council of Canada. We C. Craddock (Ed.), Third Symposium on Antarctic Geology and Geophysics, August 1977. Madison: University of Wisconsin thank C. J. Adams and J. E. Gabites, Institute of Nuclear Press. Science, Department of Scientific and Industrial Research, Lower Hutt, New Zealand, in whose laboratory the K-Ar Rowley, P. D., Williams, P. L., and Schmidt, D. L. 1977. Geology of an Upper Cretaceous copper deposit in the Andean province, analyses were performed, for their kind assistance. Lassiter Coast, Antarctic Peninsula. U.S. Geological Survey Profes- References sional Paper 984. Rowley, P. D., Williams, P. L., and Schmidt, D. L., Reynolds, R. L., Dalrymple, G. B. 1979. Critical tables for conversion of K-Ar ages Ford, A. B., Clark, A. H., Farrar, E., and McBride, S. L. 1975. from old to new constants. Geology, 7(11), 558-560. Copper mineralization along the Lassiter Coast of the Antarctic Farrar, E., McBride, S. L., and Rowley, P. D. In press. Ages and Peninsula. Economic Geology, 70(5), 982-992. tectonic implications of Andean plutonism in the southern Ant- arctic Peninsula. In C. Craddock (Ed.), Third Symposium on Ant- Thomson, M. R. A., Laudon, T. S., and Boyles, J . M. 1978. Strati- arctic Geology and Geophysics, August 1977. Madison: University graphical studies in Orville Coast and eastern Ellsworth Land. of Wisconsin Press. Antarctic Journal of the U.S., 13(4), 9-10. Halpern, M. 1967. Rubidium-strontium age measurements of plu- Williams, P. L., Schmidt, D. L., Plummer, C. C., and Brown, tonic igneous rocks in eastern Ellsworth Land and northern L. E. 1972. Geology of the Lassiter Coast area, Antarctic Antarctic Peninsula, Antarctica. Journal of Geophysical Research, Peninsula—Preliminary report. In R. J. Adie (Ed.), Antarctic Geol- 72(20), 5133-5142. ogy and Geophysics. Oslo, Norway: Universitetsforlaget. Late Jurassic ammonite faunas can be traced southward into the Orville Coast area and the Behrendt Mountains (Rowley 1978; Thomson, Laudon, and from the Latady Formation, Boyles 1978). Thus this formation occurs over approximately Orville Coast 40,000 square kilometers (figure) and perhaps considerably more if some areas of metasedimentary rocks in north- eastern Palmer Land are proven eventually to be part of the same sequence (cf. Taylor, Thomson, and Willey 1979). Be- M. R. A. THOMSON cause the Latady Formation is strongly folded, is exposed in isolated nunataks and mountains, and fossils are rare or British Antarctic Survey Natural Environment Research Council absent over substantial thicknesses of it, a clear strati- Madingley Road graphic picture may not emerge for a long time. However, Cambridge CB3 OET, United Kingdom ammonite faunas previously reported from the Latady For- mation range from Middle to Late Jurassic in age (Quilty 1970; Rowley and Williams in press). Reconnaissance geologic mapping by a U.S. Geological In the Orville Coast area (figure), exposures in the Latady Survey field party from 3 November 1977 to 2 February Formation demonstrate a north-to-south facies change from 1978 showed that the Jurassic Latady Formation of the Las- (1) lacustrine or lagoonal along the "southern" margin of siter Coast (Williams, Schmidt, Plummer, and Brown 1972) a Mesozoic magmatic arc through (2) a high-energy and southern Black Coast (Rowley and Williams in press) nearshore or shallow-shelf environment with abundant 28 ANTARCTIC JOURNAL Sketch map of the Orville Coast region showing the principal mountains and nunataks mapped. shale-pebble conglomerates to (3) open marine. Thus am- toides Spath, the Orville Coast faunas seem largely to pre- monites are found at only one place in the Sweeney Moun- date those of eastern Alexander Island (Thomson 1979), and tains, are uncommon through the Hauberg and Wilkins there is little in common between the ammonite faunas of mountains, but are relatively abundant at Cape Zumberge. the two areas. Kossmatia Uhlig, also known from western Rarely do more than one or two ammonite species occur at Palmer Land (Thomson 1975), occurs commonly at one lo- a single outcrop so that there are few assemblage faunas. cation in the Wilkins Mountains and rare single specimens This makes it difficult to judge the stratigraphic age re- were collected at nearby outcrops. However, they seem to lationships between the species present in the area. be closer to Himalayan and Indonesian species than their With the exception of a single fragment of an oppeliid antarctic relatives. from southern Wilkins Mountains and a new genus of One fauna, from Cape Zumberge, stands out as distinct uncertain affinities from northern Wilkins Mountains, all from the rest. Characterized by the genera Blanfordiceras the ammonites obtained are perisphinctids. The most com - Cossmann and Berriasella Uhlig, it is probably Late Tith- mon are multispiral forms with bifurcate ribbing and de- onian in age and is comparable to a similar fauna from the pressed whorl cross sections, reminiscent of such genera as Ablation Valley (70°49S 68°25W) area of Alexander Island Subdichotomoceras Spath, Torquatisphinctes Spath, and possi- (Thomson 1979). This is the youngest fauna reported so far bly Pachysphinctes Dietrich. Precise identification of these from the Latady Formation. genera is proving extremely difficult because of their frag- An interesting feature of these faunas is the complete mentary preservation and distortion of many specimens. lack of phylloceratids and lytoceratids, generally regarded Nevertheless, such forms suggest that much of the se- as offshore or open-ocean types. This contrasts strongly quence may be Kimmeridgian or perhaps Early Tithonian with the Late Jurassic marine faunas in the Fossil Bluff in age. Local occurrences of Katroliceras Spath (?),Subplanites Formation of Alexander Island (Thomson 1979) where such Spath (?) and Aspidoceras Zittel are also consistent with this forms are common. The more sheltered paleogeographical broad age estimate. position of the Latady Formation sea in a rear-arc position, Although there are a few fragments that may refer to the as opposed to the fore-arc location of the Fossil Bluff For- Tithonian genera Virgatosphinctes Uhlig and Aulacosphinc- mation sea, may account for these differences. 1980 REVIEW 29 The field work for this project was funded by National Taylor, B. J., Thomson, M. R. A., and Willey, L. E. 1979. The Science Foundation grant DPP 76-12557 to the U.S. Geolog- geology of the Ablation Point-Keystone Cliffs area, Alexander ical Survey. I am indebted to my colleagues P. D. Rowley, Island. British Antarctic Survey Scientific Reports, 82, 37 pp. J. M. Boyles, P. Carrara, K. S. Kellogg, T. S. Laudon, and W. R. Thomson, M. R. A., 1975. Upper Jurassic Mollusca from Carse Vennum for collecting many of the specimens mentioned. Point, Palmer Land. British Antarctic Survey Bulletin, 41 and 42, 31-42. References Thomson, M. R. A. 1979. Upper Jurassic and Lower Cretaceous ammonite faunas from the Ablation Point area, Alexander Is- Quilty, P. G. 1970. Jurassic ammonites from eastern Ellsworth land. British Antarctic Survey Scientific Reports, 97, 65 PP. Land, Antarctica. Journal of Paleontology, 44(1), 110- 116. Rowley, P. D. 1978. Geologic studies in Orville Coast and eastern Thomson, M. R. A., Laudon, T. S., and Boyles, J . M. 1978. Strati- Ellsworth Land, Antarctic Peninsula. Antarctic Journal of the U.S., graphical studies in Orville Coast and eastern Ellsworth Land. 13(4),7-9. Antarctic Journal of the U.S., 13(4), 9- 10. Rowley, P. D., and Williams, P. L. In press. Geology of the northern Williams, P. L., Schmidt, D. L., Plummer, C. C., and Brown, L. E. Lassiter Coast and southern Black Coast, Antarctic Peninsula. In 1972. Geology of the Lassiter Coast area, Antarctic Peninsula— C. Craddock (Ed.), Antarctic Geoscience. Madison: University of Preliminary report. In R. J . Adie, (Ed.), Antarctic Geology and Wisconsin Press. Geophysics.

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