Geologic studies of the Black Coast, Antarctic Peninsula
Terrestrial geology and geophysics Geologic studies of the Black Coast, Antarctic Peninsula P.D. ROWLEY
hurst 1980; British Antarctic Survey 1982) and to the south are named the Lassiter Coast Intrusive Suite of mostly Early Cretaceous age (Vennum and Rowley 1986). The volcanic rocks of the Antarctic Peninsula Volcanic Group represent the Jurassic part of the magmatic arc, which generally underlies the axis of the Antarctic Peninsula. The Latady Formation intertongues with the Antarctic Peninsula Volcanic Group and lies to the east
U.S. Geological Survey Denver, Colorado 80225
A PACIFIC OCEAN
B.C. STOREY
WEDDELL SEA
"ZC'Jrr British Antarctic Survey Cambridge CB3 OET, England
A. B. FORD ENGLISH COAST
U.S. Geological Survey Menlo Park, California 94025
In 1986-1987, a joint British Antarctic Survey (BA5)/U.S. Geological Survey (usGs) field party (Storey led and Rowley, Ford, and Wever participated) mapped the geology of 12,000 square kilometers of the previously unvisited central Black Coast, eastern Palmer Land (figure). Earlier mapping by BAS to the north and by USGS to the south (British Antarctic Survey 1982) showed that this part of the Antarctic Peninsula represents a Jurassic (or older) to Cretaceous magmatic arc and related sedimentary basins. The purpose of the joint project was to study the rocks in the central Black Coast and to compare them with those of adjoining areas. Three principal rock units have been recognized north and south of the central Black Coast: (1) silicic to intermediate, calcalkalic volcanic rocks of the Antarctic Peninsula Volcanic Group (Thomson 1982), which to the south includes the Mount Poster Formation of Middle and Late Jurassic age (Rowley, Schmidt, and Williams 1982); (2) mostly black, fine-grained clastic sedi mentary and metasedimentary rocks, which to the north are named the Mount Hill Formation (Singleton 1980) (of undocumented age) and to the south are named the Latady Formation (Williams et al. 1972) (of Middle and Late Jurassic age); and (3) plutons of greatly varied size and of mostly silicic composition which to the north yield Early Cretaceous isotopic ages (Pank1987 REVIEW
FU BLACK COAST LASSITER COAST
ELLSWORTH LAND
H.E. WEVER British Antarctic Survey Cambridge CB3 QET, England
71° 30'
—ORVILLE COAST
0
Mt. Jackson.(.;::(. Rowley1 • Massif Schirmacher Massif Musson Nunatak—O
Kamenev Nunatak- .:••• Mt. Whiting CO°'
Cape Knowles
72° Blanchard Nunataks 00'
Dietz Bluff
o . ( ..:.
o
- UIldd!'.S
•WJlSOfl':
Mt Hlort Massif
Bergen Nunataks 0(j 30
Sverdrup Nunataks 65°W 0
61°W 40
80 KILOMETERS
A. Map showing location of Black Coast, Antarctica (B, cross-hatched). The hachured lines mark edges of ice shelves. B. Map of major topographic features in the Black Coast. The stippled pattern marks major rock exposures, which are surrounded by snow and ice. i
of this unit. The Latady Formation was derived from the volcanic arc by erosion (Williams et al. 1972; Rowley and Williams 1982; Laudon et al. 1983; Rowley et al. 1983; Rowley, Kellogg, and Vennum 1985; Storey and Garrett 1985), and it was interpreted to be deposited in a back-arc basin (Suárez 1976). The Mount Hill Formation is probably correlative with the Latady Formation (Singleton 1980). The Jurassic volcanic and sedimentary rocks were folded parallel to the trend of the Antarctic Peninsula and locally thrust eastward (Kellogg 1979, 1980; Rowley et al. 1983), after which they were intruded by arcrelated Cretaceous plutons. The central Black Coast also consists in large part of the same three rock units. Volcanic and metavolcanic rocks of silicic to intermediate composition, mostly ash-flow tuff and volcanic mudflow breccia, occur along the crest of the Antarctic Peninsula and are assigned to the Antarctic Peninsula Volcanic Group. A folded and cleaved, dark sequence of argillite, siltstone, shale, and minor sandstone east of the volcanic rocks is tentatively correlated with the Mount Hill Formation. The sedimentary rocks and some, if not all, of the volcanic rocks in the central Black Coast were then folded and in turn intruded by large, mostly silicic, granitoid stocks and batholiths. In addition to the three major rock units, a series of distinctive, highly deformed zones are exposed in the central Black Coast. The deformed rocks include foliated mafic plutonic rocks, homogeneous to layered quartzofeldspathic gneiss and interlayered schist, mylonite, pseudotachylite, and fault breccia. The deformed rocks are similar to a metamorphic complex described by Singleton (1980) in the northern Black Coast. Although Singleton suggested that the metamorphic complex may be Paleozoic and correlative with the "basement complex" of Adie (1954), more recent work by Meneilly (1983) and Meneilly et al. (1987) demonstrated that much of the complex formed by intense shearing of Lower Jurassic early arc rocks and perhaps younger arc rocks. Comparable rocks have not been reported from south of our field area. Preliminary analysis of structural data from the deformed rocks indicates that they represent fault zones showing normal, reverse, and strike-slip movement, similar to those described by Meneilly (1983) and Meneilly et al. (1987). The deformed zones can be traced laterally into two relatively unsheared protoliths. The first is a sequence of black to dark-gray, massive, amygdaloidal basaltic rocks exposed in the eastern and central parts of the field area. The unit is interbedded with thin- to medium-bedded, light-gray, fine- to medium-grained quartzite, and it locally intertongues westward with gray, porphyritic to massive, silicic volcanic rocks. Singleton (1980) included similar basalts within the Mount Hill Formation to the north and Rowley et al. (1987) mapped them also in the Sverdrup Nunataks to the south. This unit is informally named the amygdaloidal basalt of Kamenev Nunatak; it may be part of the Antarctic Peninsula Volcanic Group. The second protolith consists of intermediate to mafic plutons, notably gabbro, which locally contain cumulus textures and associated pyroxenitic ultramafic material. Sheared plutonic rock at Musson Nunatak, Mount Whiting, Schirmacher Massif, eastern Blanchard Nunataks, Dietz Bluff, and Bergen Nunataks may be of Early Jurassic age, like that identified by Meneilly (1983) and Meneilly et al. (1987), but such an age assignment will have to await isotopic dating. Some similar plutons are unsheared, as at Rowley Massif, Cape Knowles, and nunataks east of Hjort Massif, and these rocks probably are the same age as the sheared plutons. The amygdaloidal basalt of
Kamenev Nunatak may have been extrusive products of the mafic plutons. A single occurrence of deformed metasedimentary rocks different from the Latady and Mount Hill Formations is exposed on the eastern scarp of Hjort Massif. It consists of quartzite, shale, and siltstone informally named the metasedimentary rocks of Hjort Massif. The stratigraphic position of the unit is uncertain; although these rocks are overlain by about 100 meters of amygdaloidal basalt of Kamenev Nunatak, a slight discordance in attitude between these two units when viewed from a distance suggests that the volcanic rocks have been structurally emplaced. The central Black Coast contains geologic elements found to the north and south. Future studies will concentrate on deformed and undeformed volcanic and plutonic suites and their relation to the development of the back-arc basin, which may have had an early extensional phase of basaltic volcanism (Meneilly 1983; Meneilly et al. 1098). The deformed volcanic and plutonic rocks may represent large shear zones formed during closure of the basin and the consequent folding of the sedimentary fill. The field party was placed in the central Black Coast by BAS Twin Otter on 9 December 1986, and evacuated on 17 February 1987. BAS ships carried the field party from Port Stanley, Falkland Islands, to Antarctica, and return; we thank E.M.S. Phelps and his crew of the R.R.S. John Biscoe and M.J. Cole and his crew of the R.R.S. BransfIeld for their efforts. We are grateful to Charles Swithinbank and M.R.A. Thomson for arranging this cooperative project; to General Assistants A.R. Simpson and P.T. Marquis, also members of the field party, for numerous forms of assistance; to John Hall and many others at Rothera base, Adelaide Island, for considerable logistic support; to pilots Richard Hasler and M.R. Bailey for air support; and to K.S. Kellogg and J.M. O'Neill for technical review of the manuscript. For the USGS geologists, transportation and expenses from the United Kingdom to Antarctica and return were paid by BAS, salary was paid by USGS, and some travel and miscellaneous expenses were paid by National Science Foundation grant DPP 85-17151. References Adie, R.J. 1954. The petrology of Graham Land: I. The basement complex; Early Palaeozoic plutonic and volcanic rocks. Falkland Islands Dependencies Survey Scientific Reports, (No. 11). Cambridge: British Antarctic Survey. British Antarctic Survey. 1982. British Antarctic Territory geologic map, Sheet 5, northern Palmer Land; BAS 500G Series, 1:500,000. Cambridge: British Antarctic Survey. Kellogg, K.S. 1979. Structural geology of Orville Coast and eastern Ellsworth Land. Antarctic Journal of the U.S. 14(5), 19-21. Kellogg, K.S. 1980. Paleomagnetic evidence for oroclinal bending of the southern Antarctic Peninsula. Geological Society of America Bulletin I,
91, 414-420. Laudon, T.S., M.R.A. Thomson, P.L. Williams, K.L. Milliken, P.D. Rowley, and J.M. Boyles. 1983. The Jurassic Latady Formation, southern Antarctic Peninsula. In R.L. Oliver, P.R. James, and J.B. Jago (Eds.), Antarctic earth science. Canberra: Australian Academy of Science. Meneilly, A.W. 1983. Deformation of granitic plutons in eastern Palmer Land. British Antarctic Survey Bulletin, 61, 75-79. Meneilly, A.W., S.M. Harrison, B.A. Piercy, and B.C. Storey. 1987. Structural evolution of the magmatic arc in northern Palmer Land, Antarctic Peninsula. In G.D. McKenzie (Ed.), Gondwana Six: Structure, tectonics, and geophysics. (Geophysical Monograph 40.) Washington, D.C.: American Geophysical Union. ANTARCTIC JOURNAL
Pankhurst, R.J. 1980. Radiometric dating (appendix). In D.C. Singleton (Ed.), The geology of the central Black Coast, Palmer Land. (British Antarctic Survey Science Reports, No. 102.) Cambridge: British Antarctic Survey. 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., 19(5), 34-36.
Rowley, PD., K.S. Kellogg, W.R. Vennum, R.B. Waitt, and S.J. Boyer. 1987. Geology of the southern Black Coast, Antarctic Peninsula. In P.D. Rowley and W.R. Vennum (Eds.), Studies of the geology and mineral resources of the southern Antarctic Peninsula and eastern Ellsworth Land, Antarctica. (U.S. Geological Survey Professional Paper 1351.) Wash-
ington: U.S. Government Printing Office. Rowley, RD., D.L. Schmidt, and P.L. Williams. 1982. Mount Poster Formation, southern Antarctic Peninsula and eastern Ellsworth Land. Antarctic Journal of the U.S., 17(5), 38-39.
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. In R.L. Oliver, P.R. James, and J.B. Jago (Eds.), Antarctic cart/i science. Canberra: Australian Academy of Science.
Seymour Island expedition, 1986-1987 WILLIAM
J. ZINSMEISTER
Department of Earth and Atmospheric Sciences Purdue University West Lafayette, Indiana 47907
The expedition to Seymour Island on the northeast tip of the Antarctic Peninsula during December and January of the 1986-1987 austral summer marks the fourth major field effort to Seymour Island sponsored by the National Science Foundation's Division of Polar Programs (Zinsmeister 1982, 1985). As with the previous three expeditions (1981, 1984, and 1985), this year's expedition resulted in a number of major paleontologic and geologic discoveries which are providing new insight, not only into the geologic history of the Antarctic Peninsula but also to our understanding of the climatic and biogeographic history of the Southern Hemisphere. Because of past discoveries, a large party (12 scientists and a camp manager) was sent to Seymour Island. The party consisted of William J. Zinsmeister, Chief Scientist, Purdue University; Rodney M. Feldmann, Kent State University; David H. Elliot, Ohio State University; and M.O. Woodburne, M.A. Kooser, and Judd Case, University of California, Riverside. In addition to the senior personnel, Jeff Stilwell, Dan Chaney, Fred Barbis, and Tim Kelley served as field assistants to the science programs. Rob Robbins, Antarctic Services, acted as camp manager during the season. In contrast to the 1985 season which was conducted from the K/v Polar Duke without helicopter support, this season was supported by the Coast Guard icebreaker USCGC Glacier. Support by the USCGC Glacier allowed for the extensive use of the Coast Guard helicopters which enabled members of the field party to conduct field work on James Ross, Vega, and Cockburn islands. 1987
REVIEW
Rowley, RD., and P.L. Williams. 1982. Geology of the northern Lassiter Coast and southern Black Coast, Antarctic Peninsula. In C. Craddock (Ed.), Antarctic geoscience. Madison: University of Wisconsin Press. Singleton, D.C. 1980. The geology of the central Black Coast, Palmer Land. (British Antarctic Survey Scientific Reports, No. 102.) Cambridge: British
Antarctic Survey. Storey, B.C., and S.W. Garrett. 1985. Crustal growth of the Antarctic Peninsula by accretion, magmatism and extension. Geology Magazine, 122(1), 5-14.
Suárez, M. 1976. Plate-tectonic model for southern Antarctic Peninsula and its relation to southern Andes. Geology, 4, 211-214. Thomson, M.R.A. 1982. Mesozoic paleogeography of West Antarctica. In C. Craddock (Ed.), Antarctic geoscience. Madison: University of Wisconsin Press. Vennum, W.R., and P.D. Rowley. 1986. Reconnaissance geochemistry of the Lassiter Coast Intrusive Suite, southern Antarctic Peninsula. Geological Society of America Bulletin, 97, 1521-1533.
Williams, RL., D.L. Schmidt, C.C. Plummer, and L.E. Brown. 1972. Geology of the Lassiter Coast area, Antarctic Peninsula: Preliminary report. In R.J. Adie (Ed.), Antarctic geology and geophysics. Oslo:
Universitetsforlaget.
The primary objectives of field party were to make a detailed survey of the faunal changes across the Cretaceous/Tertiary (K/T) boundary and to search for additional vertebrate fossils in the Late Eocene part of the sequence at the north end of the island. As a consequence, two camps were established: a primary camp at the south end of the island to study the KIT part of the sequence and a northern camp for vertebrate fossil program. The use of the four-wheel, all-terrain vehicle allowed for travel and movement of supplies and personnel between the two camps. In contrast to the 1985 season, weather conditions were ideal and only a total of I day was lost to poor weather. As a consequence to the excellent weather conditions that prevailed, a number of important scientific discoveries was made during the season. The highlights of the field season are summarized here. • A nearly complete basiliosaurine whale skeleton in the Upper Eocene La Meseta Formation was discovered. This specimen represents the oldest occurrence and most complete specimen of a Late Eocene whale discovered in the Southern Hemisphere. • Partial jaw fragment of a large crocodile from the La Meseta Formation. • Skeletal elements of large phororhacoid (large land bird), which attained a height of approximately 2 meters, were found. The occurrence of this land bird, together with the crocodile remains, provides additional evidence of a continuous land connection between southern South America during the early Tertiary. • Stratigraphic study of the KIT shallow-water sequence on Seymour Island is unique, because deposition across the sequence was continuous, whereas other shallow-water K/T sections are characterized either by a hiatus or a condensed section. • Preliminary analysis of the macrofossil fauna across the K/T boundary indicates that in contrast to other K/T boundary sections, there is no abrupt change in the marine benthic fauna but rather a gradual transition over approximately 40 meters of section which includes the boundary.
hurst 1980; British Antarctic Survey 1982) and to the south are named the Lassiter Coast Intrusive Suite of mostly Early Cretaceous age (Vennum and Rowley 1986). The volcanic rocks of the Antarctic Peninsula Volcanic Group represent the Jurassic part of the magmatic arc, which generally underlies the axis of the Antarctic Peninsula. The Latady Formation intertongues with the Antarctic Peninsula Volcanic Group and lies to the east
U.S. Geological Survey Denver, Colorado 80225
A PACIFIC OCEAN
B.C. STOREY
WEDDELL SEA
"ZC'Jrr British Antarctic Survey Cambridge CB3 OET, England
A. B. FORD ENGLISH COAST
U.S. Geological Survey Menlo Park, California 94025
In 1986-1987, a joint British Antarctic Survey (BA5)/U.S. Geological Survey (usGs) field party (Storey led and Rowley, Ford, and Wever participated) mapped the geology of 12,000 square kilometers of the previously unvisited central Black Coast, eastern Palmer Land (figure). Earlier mapping by BAS to the north and by USGS to the south (British Antarctic Survey 1982) showed that this part of the Antarctic Peninsula represents a Jurassic (or older) to Cretaceous magmatic arc and related sedimentary basins. The purpose of the joint project was to study the rocks in the central Black Coast and to compare them with those of adjoining areas. Three principal rock units have been recognized north and south of the central Black Coast: (1) silicic to intermediate, calcalkalic volcanic rocks of the Antarctic Peninsula Volcanic Group (Thomson 1982), which to the south includes the Mount Poster Formation of Middle and Late Jurassic age (Rowley, Schmidt, and Williams 1982); (2) mostly black, fine-grained clastic sedi mentary and metasedimentary rocks, which to the north are named the Mount Hill Formation (Singleton 1980) (of undocumented age) and to the south are named the Latady Formation (Williams et al. 1972) (of Middle and Late Jurassic age); and (3) plutons of greatly varied size and of mostly silicic composition which to the north yield Early Cretaceous isotopic ages (Pank1987 REVIEW
FU BLACK COAST LASSITER COAST
ELLSWORTH LAND
H.E. WEVER British Antarctic Survey Cambridge CB3 QET, England
71° 30'
—ORVILLE COAST
0
Mt. Jackson.(.;::(. Rowley1 • Massif Schirmacher Massif Musson Nunatak—O
Kamenev Nunatak- .:••• Mt. Whiting CO°'
Cape Knowles
72° Blanchard Nunataks 00'
Dietz Bluff
o . ( ..:.
o
- UIldd!'.S
•WJlSOfl':
Mt Hlort Massif
Bergen Nunataks 0(j 30
Sverdrup Nunataks 65°W 0
61°W 40
80 KILOMETERS
A. Map showing location of Black Coast, Antarctica (B, cross-hatched). The hachured lines mark edges of ice shelves. B. Map of major topographic features in the Black Coast. The stippled pattern marks major rock exposures, which are surrounded by snow and ice. i
of this unit. The Latady Formation was derived from the volcanic arc by erosion (Williams et al. 1972; Rowley and Williams 1982; Laudon et al. 1983; Rowley et al. 1983; Rowley, Kellogg, and Vennum 1985; Storey and Garrett 1985), and it was interpreted to be deposited in a back-arc basin (Suárez 1976). The Mount Hill Formation is probably correlative with the Latady Formation (Singleton 1980). The Jurassic volcanic and sedimentary rocks were folded parallel to the trend of the Antarctic Peninsula and locally thrust eastward (Kellogg 1979, 1980; Rowley et al. 1983), after which they were intruded by arcrelated Cretaceous plutons. The central Black Coast also consists in large part of the same three rock units. Volcanic and metavolcanic rocks of silicic to intermediate composition, mostly ash-flow tuff and volcanic mudflow breccia, occur along the crest of the Antarctic Peninsula and are assigned to the Antarctic Peninsula Volcanic Group. A folded and cleaved, dark sequence of argillite, siltstone, shale, and minor sandstone east of the volcanic rocks is tentatively correlated with the Mount Hill Formation. The sedimentary rocks and some, if not all, of the volcanic rocks in the central Black Coast were then folded and in turn intruded by large, mostly silicic, granitoid stocks and batholiths. In addition to the three major rock units, a series of distinctive, highly deformed zones are exposed in the central Black Coast. The deformed rocks include foliated mafic plutonic rocks, homogeneous to layered quartzofeldspathic gneiss and interlayered schist, mylonite, pseudotachylite, and fault breccia. The deformed rocks are similar to a metamorphic complex described by Singleton (1980) in the northern Black Coast. Although Singleton suggested that the metamorphic complex may be Paleozoic and correlative with the "basement complex" of Adie (1954), more recent work by Meneilly (1983) and Meneilly et al. (1987) demonstrated that much of the complex formed by intense shearing of Lower Jurassic early arc rocks and perhaps younger arc rocks. Comparable rocks have not been reported from south of our field area. Preliminary analysis of structural data from the deformed rocks indicates that they represent fault zones showing normal, reverse, and strike-slip movement, similar to those described by Meneilly (1983) and Meneilly et al. (1987). The deformed zones can be traced laterally into two relatively unsheared protoliths. The first is a sequence of black to dark-gray, massive, amygdaloidal basaltic rocks exposed in the eastern and central parts of the field area. The unit is interbedded with thin- to medium-bedded, light-gray, fine- to medium-grained quartzite, and it locally intertongues westward with gray, porphyritic to massive, silicic volcanic rocks. Singleton (1980) included similar basalts within the Mount Hill Formation to the north and Rowley et al. (1987) mapped them also in the Sverdrup Nunataks to the south. This unit is informally named the amygdaloidal basalt of Kamenev Nunatak; it may be part of the Antarctic Peninsula Volcanic Group. The second protolith consists of intermediate to mafic plutons, notably gabbro, which locally contain cumulus textures and associated pyroxenitic ultramafic material. Sheared plutonic rock at Musson Nunatak, Mount Whiting, Schirmacher Massif, eastern Blanchard Nunataks, Dietz Bluff, and Bergen Nunataks may be of Early Jurassic age, like that identified by Meneilly (1983) and Meneilly et al. (1987), but such an age assignment will have to await isotopic dating. Some similar plutons are unsheared, as at Rowley Massif, Cape Knowles, and nunataks east of Hjort Massif, and these rocks probably are the same age as the sheared plutons. The amygdaloidal basalt of
Kamenev Nunatak may have been extrusive products of the mafic plutons. A single occurrence of deformed metasedimentary rocks different from the Latady and Mount Hill Formations is exposed on the eastern scarp of Hjort Massif. It consists of quartzite, shale, and siltstone informally named the metasedimentary rocks of Hjort Massif. The stratigraphic position of the unit is uncertain; although these rocks are overlain by about 100 meters of amygdaloidal basalt of Kamenev Nunatak, a slight discordance in attitude between these two units when viewed from a distance suggests that the volcanic rocks have been structurally emplaced. The central Black Coast contains geologic elements found to the north and south. Future studies will concentrate on deformed and undeformed volcanic and plutonic suites and their relation to the development of the back-arc basin, which may have had an early extensional phase of basaltic volcanism (Meneilly 1983; Meneilly et al. 1098). The deformed volcanic and plutonic rocks may represent large shear zones formed during closure of the basin and the consequent folding of the sedimentary fill. The field party was placed in the central Black Coast by BAS Twin Otter on 9 December 1986, and evacuated on 17 February 1987. BAS ships carried the field party from Port Stanley, Falkland Islands, to Antarctica, and return; we thank E.M.S. Phelps and his crew of the R.R.S. John Biscoe and M.J. Cole and his crew of the R.R.S. BransfIeld for their efforts. We are grateful to Charles Swithinbank and M.R.A. Thomson for arranging this cooperative project; to General Assistants A.R. Simpson and P.T. Marquis, also members of the field party, for numerous forms of assistance; to John Hall and many others at Rothera base, Adelaide Island, for considerable logistic support; to pilots Richard Hasler and M.R. Bailey for air support; and to K.S. Kellogg and J.M. O'Neill for technical review of the manuscript. For the USGS geologists, transportation and expenses from the United Kingdom to Antarctica and return were paid by BAS, salary was paid by USGS, and some travel and miscellaneous expenses were paid by National Science Foundation grant DPP 85-17151. References Adie, R.J. 1954. The petrology of Graham Land: I. The basement complex; Early Palaeozoic plutonic and volcanic rocks. Falkland Islands Dependencies Survey Scientific Reports, (No. 11). Cambridge: British Antarctic Survey. British Antarctic Survey. 1982. British Antarctic Territory geologic map, Sheet 5, northern Palmer Land; BAS 500G Series, 1:500,000. Cambridge: British Antarctic Survey. Kellogg, K.S. 1979. Structural geology of Orville Coast and eastern Ellsworth Land. Antarctic Journal of the U.S. 14(5), 19-21. Kellogg, K.S. 1980. Paleomagnetic evidence for oroclinal bending of the southern Antarctic Peninsula. Geological Society of America Bulletin I,
91, 414-420. Laudon, T.S., M.R.A. Thomson, P.L. Williams, K.L. Milliken, P.D. Rowley, and J.M. Boyles. 1983. The Jurassic Latady Formation, southern Antarctic Peninsula. In R.L. Oliver, P.R. James, and J.B. Jago (Eds.), Antarctic earth science. Canberra: Australian Academy of Science. Meneilly, A.W. 1983. Deformation of granitic plutons in eastern Palmer Land. British Antarctic Survey Bulletin, 61, 75-79. Meneilly, A.W., S.M. Harrison, B.A. Piercy, and B.C. Storey. 1987. Structural evolution of the magmatic arc in northern Palmer Land, Antarctic Peninsula. In G.D. McKenzie (Ed.), Gondwana Six: Structure, tectonics, and geophysics. (Geophysical Monograph 40.) Washington, D.C.: American Geophysical Union. ANTARCTIC JOURNAL
Pankhurst, R.J. 1980. Radiometric dating (appendix). In D.C. Singleton (Ed.), The geology of the central Black Coast, Palmer Land. (British Antarctic Survey Science Reports, No. 102.) Cambridge: British Antarctic Survey. 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., 19(5), 34-36.
Rowley, PD., K.S. Kellogg, W.R. Vennum, R.B. Waitt, and S.J. Boyer. 1987. Geology of the southern Black Coast, Antarctic Peninsula. In P.D. Rowley and W.R. Vennum (Eds.), Studies of the geology and mineral resources of the southern Antarctic Peninsula and eastern Ellsworth Land, Antarctica. (U.S. Geological Survey Professional Paper 1351.) Wash-
ington: U.S. Government Printing Office. Rowley, RD., D.L. Schmidt, and P.L. Williams. 1982. Mount Poster Formation, southern Antarctic Peninsula and eastern Ellsworth Land. Antarctic Journal of the U.S., 17(5), 38-39.
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. In R.L. Oliver, P.R. James, and J.B. Jago (Eds.), Antarctic cart/i science. Canberra: Australian Academy of Science.
Seymour Island expedition, 1986-1987 WILLIAM
J. ZINSMEISTER
Department of Earth and Atmospheric Sciences Purdue University West Lafayette, Indiana 47907
The expedition to Seymour Island on the northeast tip of the Antarctic Peninsula during December and January of the 1986-1987 austral summer marks the fourth major field effort to Seymour Island sponsored by the National Science Foundation's Division of Polar Programs (Zinsmeister 1982, 1985). As with the previous three expeditions (1981, 1984, and 1985), this year's expedition resulted in a number of major paleontologic and geologic discoveries which are providing new insight, not only into the geologic history of the Antarctic Peninsula but also to our understanding of the climatic and biogeographic history of the Southern Hemisphere. Because of past discoveries, a large party (12 scientists and a camp manager) was sent to Seymour Island. The party consisted of William J. Zinsmeister, Chief Scientist, Purdue University; Rodney M. Feldmann, Kent State University; David H. Elliot, Ohio State University; and M.O. Woodburne, M.A. Kooser, and Judd Case, University of California, Riverside. In addition to the senior personnel, Jeff Stilwell, Dan Chaney, Fred Barbis, and Tim Kelley served as field assistants to the science programs. Rob Robbins, Antarctic Services, acted as camp manager during the season. In contrast to the 1985 season which was conducted from the K/v Polar Duke without helicopter support, this season was supported by the Coast Guard icebreaker USCGC Glacier. Support by the USCGC Glacier allowed for the extensive use of the Coast Guard helicopters which enabled members of the field party to conduct field work on James Ross, Vega, and Cockburn islands. 1987
REVIEW
Rowley, RD., and P.L. Williams. 1982. Geology of the northern Lassiter Coast and southern Black Coast, Antarctic Peninsula. In C. Craddock (Ed.), Antarctic geoscience. Madison: University of Wisconsin Press. Singleton, D.C. 1980. The geology of the central Black Coast, Palmer Land. (British Antarctic Survey Scientific Reports, No. 102.) Cambridge: British
Antarctic Survey. Storey, B.C., and S.W. Garrett. 1985. Crustal growth of the Antarctic Peninsula by accretion, magmatism and extension. Geology Magazine, 122(1), 5-14.
Suárez, M. 1976. Plate-tectonic model for southern Antarctic Peninsula and its relation to southern Andes. Geology, 4, 211-214. Thomson, M.R.A. 1982. Mesozoic paleogeography of West Antarctica. In C. Craddock (Ed.), Antarctic geoscience. Madison: University of Wisconsin Press. Vennum, W.R., and P.D. Rowley. 1986. Reconnaissance geochemistry of the Lassiter Coast Intrusive Suite, southern Antarctic Peninsula. Geological Society of America Bulletin, 97, 1521-1533.
Williams, RL., D.L. Schmidt, C.C. Plummer, and L.E. Brown. 1972. Geology of the Lassiter Coast area, Antarctic Peninsula: Preliminary report. In R.J. Adie (Ed.), Antarctic geology and geophysics. Oslo:
Universitetsforlaget.
The primary objectives of field party were to make a detailed survey of the faunal changes across the Cretaceous/Tertiary (K/T) boundary and to search for additional vertebrate fossils in the Late Eocene part of the sequence at the north end of the island. As a consequence, two camps were established: a primary camp at the south end of the island to study the KIT part of the sequence and a northern camp for vertebrate fossil program. The use of the four-wheel, all-terrain vehicle allowed for travel and movement of supplies and personnel between the two camps. In contrast to the 1985 season, weather conditions were ideal and only a total of I day was lost to poor weather. As a consequence to the excellent weather conditions that prevailed, a number of important scientific discoveries was made during the season. The highlights of the field season are summarized here. • A nearly complete basiliosaurine whale skeleton in the Upper Eocene La Meseta Formation was discovered. This specimen represents the oldest occurrence and most complete specimen of a Late Eocene whale discovered in the Southern Hemisphere. • Partial jaw fragment of a large crocodile from the La Meseta Formation. • Skeletal elements of large phororhacoid (large land bird), which attained a height of approximately 2 meters, were found. The occurrence of this land bird, together with the crocodile remains, provides additional evidence of a continuous land connection between southern South America during the early Tertiary. • Stratigraphic study of the KIT shallow-water sequence on Seymour Island is unique, because deposition across the sequence was continuous, whereas other shallow-water K/T sections are characterized either by a hiatus or a condensed section. • Preliminary analysis of the macrofossil fauna across the K/T boundary indicates that in contrast to other K/T boundary sections, there is no abrupt change in the marine benthic fauna but rather a gradual transition over approximately 40 meters of section which includes the boundary.
