Stratigraphical studies in Orville Coast and eastern Ellsworth ...
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Williams, P. L., D. L. Schmidt, C. C. Plummer, and L. E. Brown. 1972. Geology of the Lassiter Coast area, Antarctic Peninsula— Preliminary report. In: Antarctic Geology and Geophysics (R. J . Adie, ed.). Universitetsforlaget, Oslo. pp. 143-148.
Stratigraphical studies in Orville Coast and eastern Ellsworth Land M. R. A. THOMSON' British Antarctic Survey Madingley Road Cambridge CB3 OET, U K T. S. LAUDON Department of Geology University of Wisconsin-Oshkosh Oshkosh, Wisconsin 54901 J . M. BOYLES2 Department of Geological Sciences University of Texas at Austin Austin, Texas 78712
The 1977-78 geological reconnaissance of Orville Coast and eastern Ellsworth Land (Rowley, 1978) found that most of this area is underlain by sedimentary rocks of the Latady Formation. Although the Latady Formation also is widespread farther north, in the Lassiter Coast of eastern Palmer Land, the exposures there are separated by many plutonic intrusions surrounded by wide metamorphic aureoles (Rowley and Williams, in press; Vennum, 1978), and fossils become less abundant to the north. In the Orville Coast area, by contrast, exposed portions of intrusive bodies are smaller and more scattered, and fossils are locally abundant, making the Orville Coast an excellent place to study the Latady Formation. A north-south cross section of nearly 200 kilometers is exposed intermittently in mountain ranges and isolated nunataks of the Orville Coast. Depositional facies along this section range from an island arc with lagoonal or possibly lacustrine deposits in the northern Sweeney Mountains to deltaic deposits in the Hauberg and Wilkins Mountains to a more distal shelf fades at Cape Zumberge. In most places the Latady Formation consists of fine- to medium-grained sandstone and subordinate siltstone and shale. Fossils occur sporadically throughout the sequence and are locally abundant. The massive to fissile sandstones are generally arkose, but they also include subarkose and quartzite. They exhibit a wide range of weathering colors (white, gray, tan, brown, and red) and are in beds ranging in thickness from a few centimeters to more than 10 meters, with British exchange scientist, Orville Coast field party. 2Work done while employed by the U.S. Geological Survey, Denver. October 1978
the average thickness being about 1 meter. Internal lamination is absent in most places, but where present it is generally parallel and laterally persistent. Cross-bedding occurs occasionally, and there are rare examples of convolute lamination. Intraformational shale-pebble conglomerate, usually in beds a few centimeters thick, occurs frequently at the bases or tops of massively bedded sandstone units. In many places these shale-pebble conglomerates are fossiliferous and contain belemnites or buchiid bivalves. True conglomerates, apart from fine granule types, are generally absent. Carbonaceous shales and minor coals are largely restricted to the lagoonal or lacustrine facies in the northern part of the area. Despite the variation in sandstone types and bedding units, the sequence is repetitive and monotonous and contains no obvious marker beds. Thus a detailed stratigraphy is likely to be established only by a great deal of painstaking work. However, wherever possible, sections were measured to demonstrate variations in lithologic composition and bedding thicknesses from one area to another. Maximum stratigraphic thickness measured in a single section in the Orville Coast was 830 meters. The base to the Latady Formation has never been positively identified. The lower parts of the Latady Formation, exposed in the Sweeney Mountains, contain interbedded andesitic and felsic volcanic rocks, and the sedimentary rocks appear partly to overlie large masses of porphyritic rhyodacite. However, this probably represents a sedimentary sequence banked against an island arc, rather than a true basal contact. Likewise, no top to the formation was seen in the area, although apparently overlying dacitic and andesitic volcanic rocks have been reported in the Lassiter Coast (Williams et al., 1972). The marine faunas are dominantly molluscan, and large collections of ammonites, belemnites, and bivalves were made, notably in the Hauberg Mountains. Fossil floras, as well as the invertebrate faunas, also were obtained from the Behrendt Mountains and northern Sweeney Mountains. Studies of the faunas will bridge the geographical gap between those being completed by R. W. Imlay and E. G. Kauffman (unpublished data) of the U.S. Geological Survey for the Lassiter Coast area and earlier investigations in eastern Ellsworth Land (Laudon et al., 1969). Field identifications indicate that the bulk of the faunas collected this season are Late Jurassic in age, but the hitherto unique Middle Jurassic marine faunas of the southern Behrendt Mountains (Quilty, 1970) were re-collected to see if they might be recognized elsewhere in the area. These faunal collections will add significantly to our knowledge of the Mesozoic rocks in Antarctica and the distribution of fossil faunas around the world. This work was supported by National Science Foundation grant DPP 76-12557 to the U.S. Geological Survey.
References
Laudon, T. S., L. L. Lackey, P. G. Quilty, and P. M. Otway. 1969. Geology of eastern Ellsworth Land (sheet 3, eastern Ellsworth Land). In: Geologic Maps of Antarctica (Antarctic Map Folio Series, folio 12, V. C. Bushnell and C. Craddock, eds.). American Geographical Society, New York. Quilty, P. G. 1970. Jurassic ammonites from eastern Ellsworth Land, Antarctica. Journal of Paleontology, 44(1): 110-116.
Rowley, P. D. 1978. Geologic studies in Orville Coast and eastern Ellswcirtn Land. Antarctic Journat of the Us., 13(4): 7-9. Rowley, P. D., and P. L. Williams. In press. Geology of the northern Lassiter Coast and southern Black Coast, Antarctic Peninsula. In: Third Symposium on Antarctic Geology and Geophysics (C. Craddock, ed.). University of Wisconsin Press, Madison. Vennum, W.R. 1978. Igneous and metamorphic petrology of the southwestern Dana Mountains, Lassiter Coast, Antarctic Peninsula.Journal of Research of the US. Geological Survey, 6(1): 95-106. Williams, P. L., D. L. Schmidt, C. C. Plummer, and L. E. Brown. 1972. Geology of the Lassiter Coast area, Antarctic Peninsula— Preliminary report. In: Antarctic Geology and Geophysics (R. J Adie, . ed.). Universitetsforlaget, Oslo. pp. 143-148.
Scotia Arc Tectonics Project, 1977-78
Dalziel, I. W. D. In press. Pre-Jurassic history of the Scotia Arc region. In: Proceedings of the Antarctic Geology and Geophysics Symposium, August 1977. (C. Craddock, ed.). University of Wisconsin Press, Madison, Wisconsin. Dalziel, I. W. D., M. J . de Wit, and K.F. Palmer. 1974. A fossil marginal basin in the Southern Andes. Nature, 250: 291-294, Forsythe, R. 1978. Geologic reconnaissance of the Pre-Late Jurassic basement: Patagonian Andes, R/v Hero cruise 76-5. Anartic Journal of the US., 13(4): 10-12. Nelson, E., R. Forsythe, F. Herve, M. Surez, E. Valenzuela, and T. Wilson. 1977. Observaciones Estructurales en la Cordillera Darwin, Provincias Antarctica y de Tierra del Fuego: Crucero 77-4, del Riv Hero. Notas Cien4ficas, Communicaciones, 21 (Santiago, Chile). pp. 32-35.
Geologic reconnaissance of the Pre-Late Jurassic Basement: Patagonian Andes
IAN W. D. DALZIEL
Lamont -Doherty Geological Observatory 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 Geological Observatory at the South Shetland Islands, Antarctica; at Cordillera Darwin, Tierra del Fuego, Chile; in the Andean foothills, Magallanes Province, Chile; and the Patagonian coastal cordillera, Chile. The fieldwork involved the history of the Scotia Arc region from the late Paleozoic to present day. In his work in the Patagonian coastal cordillera, Randall Forsythe (1978) mapped detailed pre-Middle Jurassic basement rocks of southern South America to tie in with work in the South Orkney and South Shetland Islands (Daiziel, in press). Margaret Winslow and Terry Wilson undertook field studies of the tectonic evolution of the well-developed Andean foreland fold and thrust belt. The first detailed study of the structural geology and tectonic history of Cordillera Darwin in Tierra del Fuego, a highly deformed region on the continental side of the Early Cretaceous marginal basin in the southern Andes (Dalziel et al., 1974), was initiated by Eric Nelson (Nelson et al., 1977). Finally, Margaret Winslow undertook a detailed study of the late Mesozoic and Tertiary rocks on Byers Peninsula of Livingston Island. Laboratory work on all these individual projects, as well as my study of the basement rocks of the South Orkney and South Shetland Islands, continued at Lamont-Doherty.
References
Daiziel, I. W. D. 1975. Scotia Arc Tectonics Project, 1969-1975. Antarctic Journal of the US., 10: 70-81. 10
RANDALL D. FORSYTHE
Lamont-Doherty Geological Observatory of Columbia University Palisades, New York 10964
Over 3 months of field work have been done to define the regional geologic framework of the Pre-Late Jurassic basement exposed along the outer perimeter of southernmost Chile. This work has been carried out through the RJv Hero cruise 76-5, and more recently through the logistical support of the limestone quarry operated by the Compania de Acero del Pacifico within the region of concern. These investigations were part of the continuing study of the structural and tectonic history of the Scotia Arc supported by the National Science Foundation. (See, for example, Daiziel et al., 1975; Dalziel, 1975.) The Pre-Late Jurassic basement forms an almost continuous belt of exposure from 47° S. to 54'S. along the outer belt of islands that comprise the southern Chilean archipelago (see figure). The islands containing basement exposures that have thus far been investigated are Desolacion, Donas, Madre de Dios, and Duque de York. Desolacion Island. Over 90 percent of the basement within this region is composed of a monotonous sequence of alternating conglomerate, sandstone, and shale, all generally immature and containing many graded units of turbidite character. Tectonically emplaced into these clastic sediments are lenticular bodies of red and green rhythmically bedded chert. Structurally the flyschoid and chert units exhibit an extreme parallelism between bedding and cleavage, usually striking northwest and dipping variably to the southwest. The discontinuous nature of the chert and elastic units together with the cleavage-bedding relationships suggest massive imbrication and thrusting on a inter- and intraformational scale. Madre de Dios, Duque de York, and Donas Islands. As a result of detailed investigations carried out in this region, a geologic ANTARCTIC JOURNAL
Williams, P. L., D. L. Schmidt, C. C. Plummer, and L. E. Brown. 1972. Geology of the Lassiter Coast area, Antarctic Peninsula— Preliminary report. In: Antarctic Geology and Geophysics (R. J . Adie, ed.). Universitetsforlaget, Oslo. pp. 143-148.
Stratigraphical studies in Orville Coast and eastern Ellsworth Land M. R. A. THOMSON' British Antarctic Survey Madingley Road Cambridge CB3 OET, U K T. S. LAUDON Department of Geology University of Wisconsin-Oshkosh Oshkosh, Wisconsin 54901 J . M. BOYLES2 Department of Geological Sciences University of Texas at Austin Austin, Texas 78712
The 1977-78 geological reconnaissance of Orville Coast and eastern Ellsworth Land (Rowley, 1978) found that most of this area is underlain by sedimentary rocks of the Latady Formation. Although the Latady Formation also is widespread farther north, in the Lassiter Coast of eastern Palmer Land, the exposures there are separated by many plutonic intrusions surrounded by wide metamorphic aureoles (Rowley and Williams, in press; Vennum, 1978), and fossils become less abundant to the north. In the Orville Coast area, by contrast, exposed portions of intrusive bodies are smaller and more scattered, and fossils are locally abundant, making the Orville Coast an excellent place to study the Latady Formation. A north-south cross section of nearly 200 kilometers is exposed intermittently in mountain ranges and isolated nunataks of the Orville Coast. Depositional facies along this section range from an island arc with lagoonal or possibly lacustrine deposits in the northern Sweeney Mountains to deltaic deposits in the Hauberg and Wilkins Mountains to a more distal shelf fades at Cape Zumberge. In most places the Latady Formation consists of fine- to medium-grained sandstone and subordinate siltstone and shale. Fossils occur sporadically throughout the sequence and are locally abundant. The massive to fissile sandstones are generally arkose, but they also include subarkose and quartzite. They exhibit a wide range of weathering colors (white, gray, tan, brown, and red) and are in beds ranging in thickness from a few centimeters to more than 10 meters, with British exchange scientist, Orville Coast field party. 2Work done while employed by the U.S. Geological Survey, Denver. October 1978
the average thickness being about 1 meter. Internal lamination is absent in most places, but where present it is generally parallel and laterally persistent. Cross-bedding occurs occasionally, and there are rare examples of convolute lamination. Intraformational shale-pebble conglomerate, usually in beds a few centimeters thick, occurs frequently at the bases or tops of massively bedded sandstone units. In many places these shale-pebble conglomerates are fossiliferous and contain belemnites or buchiid bivalves. True conglomerates, apart from fine granule types, are generally absent. Carbonaceous shales and minor coals are largely restricted to the lagoonal or lacustrine facies in the northern part of the area. Despite the variation in sandstone types and bedding units, the sequence is repetitive and monotonous and contains no obvious marker beds. Thus a detailed stratigraphy is likely to be established only by a great deal of painstaking work. However, wherever possible, sections were measured to demonstrate variations in lithologic composition and bedding thicknesses from one area to another. Maximum stratigraphic thickness measured in a single section in the Orville Coast was 830 meters. The base to the Latady Formation has never been positively identified. The lower parts of the Latady Formation, exposed in the Sweeney Mountains, contain interbedded andesitic and felsic volcanic rocks, and the sedimentary rocks appear partly to overlie large masses of porphyritic rhyodacite. However, this probably represents a sedimentary sequence banked against an island arc, rather than a true basal contact. Likewise, no top to the formation was seen in the area, although apparently overlying dacitic and andesitic volcanic rocks have been reported in the Lassiter Coast (Williams et al., 1972). The marine faunas are dominantly molluscan, and large collections of ammonites, belemnites, and bivalves were made, notably in the Hauberg Mountains. Fossil floras, as well as the invertebrate faunas, also were obtained from the Behrendt Mountains and northern Sweeney Mountains. Studies of the faunas will bridge the geographical gap between those being completed by R. W. Imlay and E. G. Kauffman (unpublished data) of the U.S. Geological Survey for the Lassiter Coast area and earlier investigations in eastern Ellsworth Land (Laudon et al., 1969). Field identifications indicate that the bulk of the faunas collected this season are Late Jurassic in age, but the hitherto unique Middle Jurassic marine faunas of the southern Behrendt Mountains (Quilty, 1970) were re-collected to see if they might be recognized elsewhere in the area. These faunal collections will add significantly to our knowledge of the Mesozoic rocks in Antarctica and the distribution of fossil faunas around the world. This work was supported by National Science Foundation grant DPP 76-12557 to the U.S. Geological Survey.
References
Laudon, T. S., L. L. Lackey, P. G. Quilty, and P. M. Otway. 1969. Geology of eastern Ellsworth Land (sheet 3, eastern Ellsworth Land). In: Geologic Maps of Antarctica (Antarctic Map Folio Series, folio 12, V. C. Bushnell and C. Craddock, eds.). American Geographical Society, New York. Quilty, P. G. 1970. Jurassic ammonites from eastern Ellsworth Land, Antarctica. Journal of Paleontology, 44(1): 110-116.
Rowley, P. D. 1978. Geologic studies in Orville Coast and eastern Ellswcirtn Land. Antarctic Journat of the Us., 13(4): 7-9. Rowley, P. D., and P. L. Williams. In press. Geology of the northern Lassiter Coast and southern Black Coast, Antarctic Peninsula. In: Third Symposium on Antarctic Geology and Geophysics (C. Craddock, ed.). University of Wisconsin Press, Madison. Vennum, W.R. 1978. Igneous and metamorphic petrology of the southwestern Dana Mountains, Lassiter Coast, Antarctic Peninsula.Journal of Research of the US. Geological Survey, 6(1): 95-106. Williams, P. L., D. L. Schmidt, C. C. Plummer, and L. E. Brown. 1972. Geology of the Lassiter Coast area, Antarctic Peninsula— Preliminary report. In: Antarctic Geology and Geophysics (R. J Adie, . ed.). Universitetsforlaget, Oslo. pp. 143-148.
Scotia Arc Tectonics Project, 1977-78
Dalziel, I. W. D. In press. Pre-Jurassic history of the Scotia Arc region. In: Proceedings of the Antarctic Geology and Geophysics Symposium, August 1977. (C. Craddock, ed.). University of Wisconsin Press, Madison, Wisconsin. Dalziel, I. W. D., M. J . de Wit, and K.F. Palmer. 1974. A fossil marginal basin in the Southern Andes. Nature, 250: 291-294, Forsythe, R. 1978. Geologic reconnaissance of the Pre-Late Jurassic basement: Patagonian Andes, R/v Hero cruise 76-5. Anartic Journal of the US., 13(4): 10-12. Nelson, E., R. Forsythe, F. Herve, M. Surez, E. Valenzuela, and T. Wilson. 1977. Observaciones Estructurales en la Cordillera Darwin, Provincias Antarctica y de Tierra del Fuego: Crucero 77-4, del Riv Hero. Notas Cien4ficas, Communicaciones, 21 (Santiago, Chile). pp. 32-35.
Geologic reconnaissance of the Pre-Late Jurassic Basement: Patagonian Andes
IAN W. D. DALZIEL
Lamont -Doherty Geological Observatory 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 Geological Observatory at the South Shetland Islands, Antarctica; at Cordillera Darwin, Tierra del Fuego, Chile; in the Andean foothills, Magallanes Province, Chile; and the Patagonian coastal cordillera, Chile. The fieldwork involved the history of the Scotia Arc region from the late Paleozoic to present day. In his work in the Patagonian coastal cordillera, Randall Forsythe (1978) mapped detailed pre-Middle Jurassic basement rocks of southern South America to tie in with work in the South Orkney and South Shetland Islands (Daiziel, in press). Margaret Winslow and Terry Wilson undertook field studies of the tectonic evolution of the well-developed Andean foreland fold and thrust belt. The first detailed study of the structural geology and tectonic history of Cordillera Darwin in Tierra del Fuego, a highly deformed region on the continental side of the Early Cretaceous marginal basin in the southern Andes (Dalziel et al., 1974), was initiated by Eric Nelson (Nelson et al., 1977). Finally, Margaret Winslow undertook a detailed study of the late Mesozoic and Tertiary rocks on Byers Peninsula of Livingston Island. Laboratory work on all these individual projects, as well as my study of the basement rocks of the South Orkney and South Shetland Islands, continued at Lamont-Doherty.
References
Daiziel, I. W. D. 1975. Scotia Arc Tectonics Project, 1969-1975. Antarctic Journal of the US., 10: 70-81. 10
RANDALL D. FORSYTHE
Lamont-Doherty Geological Observatory of Columbia University Palisades, New York 10964
Over 3 months of field work have been done to define the regional geologic framework of the Pre-Late Jurassic basement exposed along the outer perimeter of southernmost Chile. This work has been carried out through the RJv Hero cruise 76-5, and more recently through the logistical support of the limestone quarry operated by the Compania de Acero del Pacifico within the region of concern. These investigations were part of the continuing study of the structural and tectonic history of the Scotia Arc supported by the National Science Foundation. (See, for example, Daiziel et al., 1975; Dalziel, 1975.) The Pre-Late Jurassic basement forms an almost continuous belt of exposure from 47° S. to 54'S. along the outer belt of islands that comprise the southern Chilean archipelago (see figure). The islands containing basement exposures that have thus far been investigated are Desolacion, Donas, Madre de Dios, and Duque de York. Desolacion Island. Over 90 percent of the basement within this region is composed of a monotonous sequence of alternating conglomerate, sandstone, and shale, all generally immature and containing many graded units of turbidite character. Tectonically emplaced into these clastic sediments are lenticular bodies of red and green rhythmically bedded chert. Structurally the flyschoid and chert units exhibit an extreme parallelism between bedding and cleavage, usually striking northwest and dipping variably to the southwest. The discontinuous nature of the chert and elastic units together with the cleavage-bedding relationships suggest massive imbrication and thrusting on a inter- and intraformational scale. Madre de Dios, Duque de York, and Donas Islands. As a result of detailed investigations carried out in this region, a geologic ANTARCTIC JOURNAL
