Subantarctic islands in the Indian Ocean
These amphibians, which are close to but not identical with African forms, demonstrate that there are certain differences between the Lystrosaurus fauna in its type area and its expression in Antarctica. Such differences are explained by the fact that Gondwana fauna had a range covering many thousands of square kilometers. Also, these differences do not invalidate the strong resem blances between Antarctica and South Africa, as shown by specific identities of the reptiles mentioned above. Certain local variations would be expected within a fauna that was as widely distributed as the Lower Triassic tetrapod fauna of Gondwanaland. Triassic tetrapods of the Fremouw Formation thus emphasize the view that at the beginning of Mesozoic time Gondwanaland truly was a great supercontinent, within which active, landliving vertebrates could move back and forth across considerable distances. This research was supported by National Science Foundation grant GV-25431. References Colbert, Edwin H. 1973. Antarctic Lystrosaurus defined. Antarctic Journal of the U.S., VIlI(5): 273-274. Colbert, Edwin H. 1974. Lystrosaurus from Antarctica. American Museum Novitates, 2535: 1-44. Colbert, Edwin H., and John W. Cosgriff. 1974. Labyrinthodont amphibians from Antarctica. American Museum Novitates, 2552: 1-30. Colbert, Edwin H., and James W. Kitching. 1975. The Triassic reptile Procolophon in Antarctica. American Museum Novitates, 2566: 1-23.
Subantarctic islands in the Indian Ocean N. D. WATKINS Graduate School of Oceanography University of Rhode Island Kingston, Rhode Island 02881 Begun in 1967, our systematic studies of diverse geological aspects of islands in higher latitudes of the southern Indian Ocean (figure) have been com252
pleted. The following major points have emerged: Prince Edward/Marion Islands. A paleomagneti survey of Marion Island has shown that the island is confined to the Brunhes epoch (t=0.69 to 0 mi lion years), and was volcanically active during period of unusually high geomagnetic secular variation (Amerigian et at., 1975). Crozet Group. East and Possession islands are both confined to the Pleistocene and are a series of oceanites, ankaramites, olivine basalts, and feldsparphyric basalts. On East Island, these disconformably overly a basement intrusive complex (Gunn et at., 1970, 1972). The paleomagnetic data have provided results that have been used to analyze global geomagnetic field models (Watkins et at., 1972a, 1972b). Kerguelen Island. Several arguments have been presented to the effect that Kerguelen Island represents a continental fragment that existed prior to separation of Australasia and Antarctica. Watkins et at. (1974) showed that the island does not exceed Upper Oligocene to Lower Miocene in age, and that no rocks of continental affinity are present The paleomagnetic data show that the island ha migrated southward by an amount consistent with regional seafloor spreading requirements. Amsterdam and Saint Paul islands. Chemical analy4 sis of samples from Amsterdam Island show that i is intermediate in character between abyssal basal and an alkalipe volcano (Gunn et al., 1971). Paleo magnetic data from Amsterdam show that all lava are young and are of normal polarity. In addition unusual geomagnetic behavior has been recorded: here, lavas were extruded when the magnetic pole was briefly confined to tropical latitudes (Watkins and Nougier, 1973). On Saint Paul, potassiumargon and paleomagnetic results both show that the island is young (Watkins et at., 1975), and chemical analysis demonstrates that it is composed of a distinctive high-alumina plagioclase tholeiite (Gunn et at., 1975). The research was supported by National Science Foundation grant GV-32480. I acknowledge the generous help of the administrator of the Terntoire des Terres Australes et Antarctique Françaises and the Department of Public Transport, Republic of South Africa.
References Amerigian, C., N. D. Watkins, and B. B. Ellwood. 1975. Brunhes epoch geomagnetic secular variation on Marion Island: contribution to evidence for a long-term regional geomagnetic secular variation maxima. Journal of Geomagnetism and Geoelectricity, 26: 429-442. Gunn, B. M., R. Coy-Yll, N. D. Watkins, C. E. Abranson, and J . Nougier. 1970. Geochemistry of an oceanite-ankaramite-
ANTARCTIC JOURNAL
it WfI(AREUNION MA
90° 300 450 600 750
0
200V
VI J
ZI zl Ml
L
1. RIGUEZ F!
URE ZONE
Ml
>1 wI –I ml
// AMS\\TEtR.DPAMU:t3y /f
300
iS'
(\\\
/
O Z E T O +DO-KNEALRDCOGH-UEA[LREDN ETLANDWTAIRCD-I RSENDIAN
,— 300 ( jI rn / ()J
CID
,?
400
\Jt/
°°
C /1000 ( •''\ CE-__
50°
400
IS.
fl
2000
50°
Mc
Islands and island groups 600 in the southern Indian Ocean. Mercator Projection. Bathymetry in - 300 fathoms.
TO
F
450
basalt suite from East Island, Crozet Archipelago. Contributions to Mineralogy and Petrology, 28: 3 19-339. Gunn, B. M., C. E. Abranson, J . Nougier, N. 1). Watkins, and A. Hajash. 1971. Amsterdam Island: an isolated volcano in the southern Indian Ocean. Contributions to Mineralogy and Petrology. 32: 79-92. Gunn, B. M., C. E. Abranson, N. D. Watkins, and J . Nougier. 1972. Geochemistry of the Crozet Archipelago—a summary. Proceedings of the Second Conference on Antarctic Geology and Geophysics (Adie, R. J . , editor): 825-829. Gunn, B. M., N. D. Watkins, W.J. Trzcienskik, and J. Nougier. 1975. The Amsterdam—Saint Paul volcanic province and the formation of low Al tholeiitic andesites. Lithos, 8: 135-149. Watkins, N. D., C. E. Abranson, and A. Hajash. 1972. Hemispherical contrasts in support for the offset dipole hypothesis: the case on e(Iual coaxial dipole pair as the geomagnetic field source. Geophysical Journal, 28: 193-212. Watkins, N. D., A. Hajash, and C. E. Abranson. 1972. Geomagnetic secular variation during the Bruiihes epoch in the Indian and Atlantic Ocean regions. Geophysical Journal, 28: 1-25. Watkins, N. D., and j. Nougier. 1973. Excursions and secular variation of the Brunhes epoch geomagnetic field in the Indian Ocean region. Journal of Geophysical Resears-h, 78: 60606068. Watkins, N. D., B. M. Gunn, J. Nougier, and A .K. Baksi, 1974. Kerguelen continental fragment or oceanic island? Bulletin of the Geological Sociely of America, 85: 201-212.
September/October 1975
(cQ\\
60°
600 750 900 Watkins, N. D., 1. McDougall, andJ. Nougier. 1975. Paleomagnetism and potassium-argon age of St. Paul Island, southeastern Indian Ocean: contrasts in geomagnetic secular variation during the Brunhes epoch. Earth and Planetary Science Letters, 24: 377-384.
Calcium carbonate dissolution in the Weddell Sea JOHN B. ANDERSON*
Antarctic Research Facility Department of Geology The Florida State University Tallahassee, Florida 32306 Within the major ocean basins, the depth at which calcium carbonate dissolution (CCD) exceeds 253
Subantarctic islands in the Indian Ocean N. D. WATKINS Graduate School of Oceanography University of Rhode Island Kingston, Rhode Island 02881 Begun in 1967, our systematic studies of diverse geological aspects of islands in higher latitudes of the southern Indian Ocean (figure) have been com252
pleted. The following major points have emerged: Prince Edward/Marion Islands. A paleomagneti survey of Marion Island has shown that the island is confined to the Brunhes epoch (t=0.69 to 0 mi lion years), and was volcanically active during period of unusually high geomagnetic secular variation (Amerigian et at., 1975). Crozet Group. East and Possession islands are both confined to the Pleistocene and are a series of oceanites, ankaramites, olivine basalts, and feldsparphyric basalts. On East Island, these disconformably overly a basement intrusive complex (Gunn et at., 1970, 1972). The paleomagnetic data have provided results that have been used to analyze global geomagnetic field models (Watkins et at., 1972a, 1972b). Kerguelen Island. Several arguments have been presented to the effect that Kerguelen Island represents a continental fragment that existed prior to separation of Australasia and Antarctica. Watkins et at. (1974) showed that the island does not exceed Upper Oligocene to Lower Miocene in age, and that no rocks of continental affinity are present The paleomagnetic data show that the island ha migrated southward by an amount consistent with regional seafloor spreading requirements. Amsterdam and Saint Paul islands. Chemical analy4 sis of samples from Amsterdam Island show that i is intermediate in character between abyssal basal and an alkalipe volcano (Gunn et al., 1971). Paleo magnetic data from Amsterdam show that all lava are young and are of normal polarity. In addition unusual geomagnetic behavior has been recorded: here, lavas were extruded when the magnetic pole was briefly confined to tropical latitudes (Watkins and Nougier, 1973). On Saint Paul, potassiumargon and paleomagnetic results both show that the island is young (Watkins et at., 1975), and chemical analysis demonstrates that it is composed of a distinctive high-alumina plagioclase tholeiite (Gunn et at., 1975). The research was supported by National Science Foundation grant GV-32480. I acknowledge the generous help of the administrator of the Terntoire des Terres Australes et Antarctique Françaises and the Department of Public Transport, Republic of South Africa.
References Amerigian, C., N. D. Watkins, and B. B. Ellwood. 1975. Brunhes epoch geomagnetic secular variation on Marion Island: contribution to evidence for a long-term regional geomagnetic secular variation maxima. Journal of Geomagnetism and Geoelectricity, 26: 429-442. Gunn, B. M., R. Coy-Yll, N. D. Watkins, C. E. Abranson, and J . Nougier. 1970. Geochemistry of an oceanite-ankaramite-
ANTARCTIC JOURNAL
it WfI(AREUNION MA
90° 300 450 600 750
0
200V
VI J
ZI zl Ml
L
1. RIGUEZ F!
URE ZONE
Ml
>1 wI –I ml
// AMS\\TEtR.DPAMU:t3y /f
300
iS'
(\\\
/
O Z E T O +DO-KNEALRDCOGH-UEA[LREDN ETLANDWTAIRCD-I RSENDIAN
,— 300 ( jI rn / ()J
CID
,?
400
\Jt/
°°
C /1000 ( •''\ CE-__
50°
400
IS.
fl
2000
50°
Mc
Islands and island groups 600 in the southern Indian Ocean. Mercator Projection. Bathymetry in - 300 fathoms.
TO
F
450
basalt suite from East Island, Crozet Archipelago. Contributions to Mineralogy and Petrology, 28: 3 19-339. Gunn, B. M., C. E. Abranson, J . Nougier, N. 1). Watkins, and A. Hajash. 1971. Amsterdam Island: an isolated volcano in the southern Indian Ocean. Contributions to Mineralogy and Petrology. 32: 79-92. Gunn, B. M., C. E. Abranson, N. D. Watkins, and J . Nougier. 1972. Geochemistry of the Crozet Archipelago—a summary. Proceedings of the Second Conference on Antarctic Geology and Geophysics (Adie, R. J . , editor): 825-829. Gunn, B. M., N. D. Watkins, W.J. Trzcienskik, and J. Nougier. 1975. The Amsterdam—Saint Paul volcanic province and the formation of low Al tholeiitic andesites. Lithos, 8: 135-149. Watkins, N. D., C. E. Abranson, and A. Hajash. 1972. Hemispherical contrasts in support for the offset dipole hypothesis: the case on e(Iual coaxial dipole pair as the geomagnetic field source. Geophysical Journal, 28: 193-212. Watkins, N. D., A. Hajash, and C. E. Abranson. 1972. Geomagnetic secular variation during the Bruiihes epoch in the Indian and Atlantic Ocean regions. Geophysical Journal, 28: 1-25. Watkins, N. D., and j. Nougier. 1973. Excursions and secular variation of the Brunhes epoch geomagnetic field in the Indian Ocean region. Journal of Geophysical Resears-h, 78: 60606068. Watkins, N. D., B. M. Gunn, J. Nougier, and A .K. Baksi, 1974. Kerguelen continental fragment or oceanic island? Bulletin of the Geological Sociely of America, 85: 201-212.
September/October 1975
(cQ\\
60°
600 750 900 Watkins, N. D., 1. McDougall, andJ. Nougier. 1975. Paleomagnetism and potassium-argon age of St. Paul Island, southeastern Indian Ocean: contrasts in geomagnetic secular variation during the Brunhes epoch. Earth and Planetary Science Letters, 24: 377-384.
Calcium carbonate dissolution in the Weddell Sea JOHN B. ANDERSON*
Antarctic Research Facility Department of Geology The Florida State University Tallahassee, Florida 32306 Within the major ocean basins, the depth at which calcium carbonate dissolution (CCD) exceeds 253
