Rowley, P. D. 1978. Geologic studies in Orville Coast and eastern Dalziel, I. W. D. In press. Pre-Jurassic history Ellswcirtn Land. of the Scotia Arc Antarctic Journat of the Us., 13(4): 7-9. region. In: Proceedings of the Antarctic Geology and Geophysics Sym- Rowley, P. D., and P. L. Williams. In press. Geology of the northern posium, August 1977. (C. Craddock, ed.). University of Wisconsin Lassiter Coast and southern Black Coast, Antarctic Peninsula. In: Press, Madison, Wisconsin. Third Symposium on Antarctic Geology and Geophysics (C. Craddock, Dalziel, I. W. D., M. J. de Wit, and K.F. Palmer. 1974. ed.). University of Wisconsin Press, Madison. A fossil marginal basin in the Southern Andes. Nature, 250: 291-294, Vennum, W.R. 1978. Igneous and metamorphic petrology of the Forsythe, R. 1978. Geologic reconnaissance of the Pre-Late Jurassic southwestern Dana Mountains, Lassiter Coast, Antarctic Penin- basement: Patagonian Andes, R/v Hero cruise 76-5. Anartic Journal sula.Journal of Research of the US. Geological Survey, 6(1): 95-106. of the US., 13(4): 10-12. Williams, P. L., D. L. Schmidt, C. C. Plummer, and L. E. Brown. Nelson, E., R. Forsythe, F. Herve, M. Surez, E. Valenzuela, and T. 1972. Geology of the Lassiter Coast area, Antarctic Peninsula— Wilson. 1977. Observaciones Estructurales en la Cordillera Dar- Preliminary report. In: Antarctic Geology and Geophysics (R. J. Adie, win, Provincias Antarctica y de Tierra del Fuego: Crucero 77-4, ed.). Universitetsforlaget, Oslo. 143-148. del pp. Riv Hero. Notas Cien4ficas, Communicaciones, 21 (Santiago, Chile). pp. 32-35. Scotia Arc Tectonics Project, Geologic reconnaissance of the 1977-78 Pre-Late Jurassic Basement: Patagonian Andes IAN W. D. DALZIEL Lamont -Doherty Geological Observatory RANDALL D. FORSYTHE Columbia University Palisades, New York 10964 Lamont-Doherty Geological Observatory of Columbia University Palisades, New York 10964 During the austral winter of 1977 and the austral summer of 1977-78, Scotia Arc Tectonics Project (Dalziel, 1975) fieldwork was conducted by scientists from Lamont-Doherty Over 3 months of field work have been done to define the Geological Observatory at the South Shetland Islands, Ant- regional geologic framework of the Pre-Late Jurassic base- arctica; at Cordillera Darwin, Tierra del Fuego, Chile; in the ment exposed along the outer perimeter of southernmost Andean foothills, Magallanes Province, Chile; and the Chile. This work has been carried out through the RJv Hero Patagonian coastal cordillera, Chile. The fieldwork involved cruise 76-5, and more recently through the logistical support the history of the Scotia Arc region from the late Paleozoic to of the limestone quarry operated by the Compania de Acero present day. del Pacifico within the region of concern. These investiga- In his work in the Patagonian coastal cordillera, Randall tions were part of the continuing study of the structural and Forsythe (1978) mapped detailed pre-Middle Jurassic base- tectonic history of the Scotia Arc supported by the National ment rocks of southern South America to tie in with work in Science Foundation. (See, for example, Daiziel et al., 1975; the South Orkney and South Shetland Islands (Daiziel, in Dalziel, 1975.) press). Margaret Winslow and Terry Wilson undertook field The Pre-Late Jurassic basement forms an almost con- studies of the tectonic evolution of the well-developed Andean tinuous belt of exposure from 47° S. to 54S. along the outer foreland fold and thrust belt. The first detailed study of the belt of islands that comprise the southern Chilean structural geology and tectonic history of Cordillera Darwin archipelago (see figure). The islands containing basement ex- in Tierra del Fuego, a highly deformed region on the conti- posures that have thus far been investigated are Desolacion, nental side of the Early Cretaceous marginal basin in the Donas, Madre de Dios, and Duque de York. southern Andes (Dalziel et al., 1974), was initiated by Eric Desolacion Island. Over 90 percent of the basement within Nelson (Nelson et al., 1977). Finally, Margaret Winslow un- this region is composed of a monotonous sequence of alter- dertook a detailed study of the late Mesozoic and Tertiary nating conglomerate, sandstone, and shale, all generally im- rocks on Byers Peninsula of Livingston Island. mature and containing many graded units of turbidite Laboratory work on all these individual projects, as well as character. Tectonically emplaced into these clastic sediments my study of the basement rocks of the South Orkney and are lenticular bodies of red and green rhythmically bedded South Shetland Islands, continued at Lamont-Doherty. chert. Structurally the flyschoid and chert units exhibit an ex- treme parallelism between bedding and cleavage, usually striking northwest and dipping variably to the southwest. The References discontinuous nature of the chert and elastic units together with the cleavage-bedding relationships suggest massive im- brication and thrusting on a inter- and intraformational scale. Daiziel, I. W. D. 1975. Scotia Arc Tectonics Project, 1969-1975. Ant- Madre de Dios, Duque de York, and Donas Islands. arctic Journal of the US., 10: 70-81. As a result of detailed investigations carried out in this region, a geologic 10 ANTARCTIC JOURNAL.