Volcanic rocks of the Early Cambrian Taylor formation ...
other time of normal polarity in the recent past. There is no evidence, however, either geological or from radiometric age data, to suggest post emplacement remagnetization. As suggested by Kellogg and Reynolds (1974) for the northern Lassiter Coast intrusives, plutonism and dike emplacement in the central Lassiter Coast may have occurred largely during middle to late Cretaceous time when Earth's field predominantly was of normal polarity (1-leisley and Steiner, 1969). The paleomagnetic pole (the mean of the virtual geomagnetic poles, VGP5, of the eight acceptable units) is 87°S. 54°W. The paleomagnetic pole of Cretaceous igneous rocks of the central Lassiter Coast is very close to other paleomagnetic poles and VGPS determined for rocks of similar age from the Antarctic Peninsula tectonic province (Blundell, 1962; Dalziel et al., 1973; Kellogg and Reynolds, 1974; and Scharnberger, 1974). Only the Stonington Island VGP of Scharnberger (51°S. 26°E.) does not lie near the other paleomagnetic poles and VGPS calculated from rocks within this region. Other than the Stonington Island VGP, these paleomagnetic poles and VGP5 are near the present geographic South Pole. Apparently little latitudinal movement of this province has occurred since middle Cretaceous time. In addition, as mentioned by Kellogg and Reynolds (1974), the steep inclination of the paleomagnetic vector at this high latitude makes an analysis of tectonic rotation very imprecise; no such rotation could be discerned from the results of this investigation. Work continues on the rock magnetic properties of samples collected for paleomagnetic analysis. This study was supported by National Science Foundation grant AG-187.
Rowley, P. D. 1973. Geologic observations on the no them Lassiter Coast and southern Black Coast. Antarctic Journal of the U.S., VII(4): 154-155. Scharnberger, C. K. 1974. Paleomagnetism of rocks from Graham Land, Antarctica. American Geophysical nion. Transactions, 55(4): 225. Williams, P. L., and P. D. Rowley. 1971. Geologic studies of the Lassiter Coast. Antarctic Journal of the U.S., VI(4): 120. Williams, P. L., D. L. Schmidt, C. C. Plummer, and . E. Brown. 1972. Geology of the Lassiter Coast area, Antarctic Peninsula; a preliminary report. In: Anta rctic Geology and Geophysics (Adie, R. 3 . , editor).International Union of Geological Sciences. Oslo, Univer itetsforlaget, Series B(l): 143-148.
Volcanic rocks of the Early Cambrian Taylor formation, central Transantarctic Mountains EDMUND STUMP Institute of Polar Studies The Ohio State University Columbus, Ohio 43210 Field and petrographic investigations of rocks of the Taylor formation have shown that it is compsed in large part of volcanic material. The Taylor foimation was named by Wade et al. (1965) for a seqwnce of "quartzites, conglomerates, calcareous quart:ites, and marbles" that crops out adjacent to Shackbton Glacier. It represents the pre-Devonian baseraent rocks, excluding the granite suite, in this vicinity. My field work during the 1970-1971 summei, as a member of The Ohio State University part y in the central Transantarctic Mountains, revealed the
References Blundell, D. J . 1962. Paleomagnetic investigations in the Falkland Islands Dependencies. British Antarctic Survey. Scientific Report, 39. 24p. Daiziel, I. W. D., W. Lowrie, R. Kligfield, and N. P. Opdyke. 1973. Paleomagnetic data from the southernmost Andes and Antarctandes. In: Implications of Continental Drift to the Earth Sciences (Tarling, D. H., and S. K. Runcorn, editors). New York, Academic Press. I: 87-101. Fisher, R. A. 1953. Dispersion on a sphere. London, Royal Society. Proceedings, (A) 217: 295-305. Heisley, C. E., and M. B. Steiner. 1969. Evidence for long intervals of normal polarity during the Cretaceous Period. Earth and Planetary Science Letters, 5(5): 325-332. Kellogg, K. S., and R. L. Reynolds. 1974. Paleomagnetic study of igneous rocks of the northern Lassiter Coast, Antarctic Peninsula. Antarctic Journal of the U.S., IX (2): 38-40. Mehnert, H. H., P. D. Rowley, and D. L. Schmidt. In press. K-Ar ages of plutonic rocks in the Lassiter Coast area, Antarctica. USGS Journal of Research.
228
Figure 1. Silicic volcanic rock (sample E5-53) from north of Mount Kenny, with enibayed quartz, flow banding or welded shard structure, and spherulites. Plane light. (Bar scale, 0.5 milliriet.rs.)
ANTARCTIC JOURNAL
presence of the massive bodies of silicic, porphyritic volcanic rocks, together with similarly composed units interbedded with clastic strata and carbonates. Much of the material consists of quartz, potassium-feldspar and plagioclase phenocrysts set in a microcrystal line grourdmass. Embayed quartz is ubiquitous in rocks on the east side of Shackleton Glacier. The Taylor formation has been correlated with fossiliferous Cambrian units in other areas of the Transantarctic Mountains (La Prade, 1969; McGregor and Wade, 1969; Minshew, 1967). Fossils found at the Taylor Nunatak section in 1970-1971 have been identified as Early Cambrian Cloudina(?) (Yochelson and Stump, in press), thus providing a paleontological basis for the suggested correlations.
References La Prade, K. E. 1969. Geology of Shackleton Glacier area Queen Maud Range, Transantarctic Mountains, Antarctica. Ph.D. dissertation (unpublished), Texas Technological College. Lubbock, Texas. 394p. McGregor, V. R., and F. A. Wade. 1969. Geology of the western Queen Maud Mountains. Antarctic Map Folio Series, 12: plate XV. Minshew, V. H. 1967. Geology of the Scott Glacier and Wisconsin Range areas, central Transantarctic Mountains, Antarctica. Ph.D. dissertation (unpublished), The Ohio State University. Columbus, Ohio. 268p. Wade, F. A., V. C. Yeats, J . R. Everett, D. W. Greenlee, K. E. La Prade, and J . C. Shenk. 1965. Geology of the central portion of the Queen Maud Range, Transan tare tic Mountains. Science, 150: 1808-1809. Yochlson, E. L., and Edmund Stump. In press. Fossil evide uce of Early Cambrian at Taylor Nunatak, Antarctica. Antarctic Research Series.
Figure 2. Silicic volcanic rock (sample ES-13) from Lobbock Ridge, with a large pumice fragment and scattered glass shards. The dark color is due to staining. Plane light. (Bar scale, 0.5 millimeters.)
September-October 1974
Paleomagnetic data from unit 13, DVDP hole 2, Ross Island B. E. MCMAHON Institute of Polar Studies The Ohio State University Columbus, Ohio 43210 HENRY SPALL
Geological Society of America Boulder, Colorado 80302 Dry Valley Drilling Project (DvDP) hole 2 (77.85 0 S. 166.67°E.) on Ross Island encountered 161.66 meters of flows and pyroclastic units above the Hut Point pyroclastic sequence (Treves and Kyle, 1973). All 15 units overlying the Hut Point pyroclastic sequence are reversely magnetized. On the basis of revised correlations the units are considered to belong to the Observation Hill and older sequences (Treves and Kyle, personal communication, 1974). Cox (1966) reported reversed polarity for a surface collection made of the Observation Hill sequence. On the basis of available radiometric dates (Forbes et al., 1974) the units encountered in hole 2 are considered to be older than one million years. Consequently it appears that all of the units encountered in hole 2 predate the Jaramillo polarity event (0.89 to 0.95 million years) of the Matuyama reversed epoch. Directional stability and magnetic field configuration. Only unit 13, hole 2, has been examined in detail. From this unit, a lava flow 43.77 meters thick (101.35 to 145.12 meters deep), 22 samples (divided into 43 specimens) have been extracted. Experimentation and measurements indicate that the unit possesses a very stable directional magnetization. Experimentation has included alternating field (AF) demagnetization, thermal demagnetization, susceptibility measurements, and calculation of the Koernigsberger ratio. During both AF and thermal demagnetization the major magnetic component continued to be vertical and very little migration of the magnetic vector was noted. The Koenigsberger ratio, based on natural remanent magnetization (NRM) data (Q - J / xH, where H is taken as 1 oe), yields values for Q. larger than 0.5 (fig. 2). A Q,, value larger than 0.5 indicates magnetic stability and suggests that grains of single domain and pseudo single domain size (d 20) make a significant contribution to the magnetic moment (Stacey, 1967; Stacey and Banerjee, 1974). Examination of polished sections under reflected light indicates that the degree of oxidation of the magnetic minerals places a significant proportion of them into classes IV and V (Wilson and Watkins, 229
Rowley, P. D. 1973. Geologic observations on the no them Lassiter Coast and southern Black Coast. Antarctic Journal of the U.S., VII(4): 154-155. Scharnberger, C. K. 1974. Paleomagnetism of rocks from Graham Land, Antarctica. American Geophysical nion. Transactions, 55(4): 225. Williams, P. L., and P. D. Rowley. 1971. Geologic studies of the Lassiter Coast. Antarctic Journal of the U.S., VI(4): 120. Williams, P. L., D. L. Schmidt, C. C. Plummer, and . E. Brown. 1972. Geology of the Lassiter Coast area, Antarctic Peninsula; a preliminary report. In: Anta rctic Geology and Geophysics (Adie, R. 3 . , editor).International Union of Geological Sciences. Oslo, Univer itetsforlaget, Series B(l): 143-148.
Volcanic rocks of the Early Cambrian Taylor formation, central Transantarctic Mountains EDMUND STUMP Institute of Polar Studies The Ohio State University Columbus, Ohio 43210 Field and petrographic investigations of rocks of the Taylor formation have shown that it is compsed in large part of volcanic material. The Taylor foimation was named by Wade et al. (1965) for a seqwnce of "quartzites, conglomerates, calcareous quart:ites, and marbles" that crops out adjacent to Shackbton Glacier. It represents the pre-Devonian baseraent rocks, excluding the granite suite, in this vicinity. My field work during the 1970-1971 summei, as a member of The Ohio State University part y in the central Transantarctic Mountains, revealed the
References Blundell, D. J . 1962. Paleomagnetic investigations in the Falkland Islands Dependencies. British Antarctic Survey. Scientific Report, 39. 24p. Daiziel, I. W. D., W. Lowrie, R. Kligfield, and N. P. Opdyke. 1973. Paleomagnetic data from the southernmost Andes and Antarctandes. In: Implications of Continental Drift to the Earth Sciences (Tarling, D. H., and S. K. Runcorn, editors). New York, Academic Press. I: 87-101. Fisher, R. A. 1953. Dispersion on a sphere. London, Royal Society. Proceedings, (A) 217: 295-305. Heisley, C. E., and M. B. Steiner. 1969. Evidence for long intervals of normal polarity during the Cretaceous Period. Earth and Planetary Science Letters, 5(5): 325-332. Kellogg, K. S., and R. L. Reynolds. 1974. Paleomagnetic study of igneous rocks of the northern Lassiter Coast, Antarctic Peninsula. Antarctic Journal of the U.S., IX (2): 38-40. Mehnert, H. H., P. D. Rowley, and D. L. Schmidt. In press. K-Ar ages of plutonic rocks in the Lassiter Coast area, Antarctica. USGS Journal of Research.
228
Figure 1. Silicic volcanic rock (sample E5-53) from north of Mount Kenny, with enibayed quartz, flow banding or welded shard structure, and spherulites. Plane light. (Bar scale, 0.5 milliriet.rs.)
ANTARCTIC JOURNAL
presence of the massive bodies of silicic, porphyritic volcanic rocks, together with similarly composed units interbedded with clastic strata and carbonates. Much of the material consists of quartz, potassium-feldspar and plagioclase phenocrysts set in a microcrystal line grourdmass. Embayed quartz is ubiquitous in rocks on the east side of Shackleton Glacier. The Taylor formation has been correlated with fossiliferous Cambrian units in other areas of the Transantarctic Mountains (La Prade, 1969; McGregor and Wade, 1969; Minshew, 1967). Fossils found at the Taylor Nunatak section in 1970-1971 have been identified as Early Cambrian Cloudina(?) (Yochelson and Stump, in press), thus providing a paleontological basis for the suggested correlations.
References La Prade, K. E. 1969. Geology of Shackleton Glacier area Queen Maud Range, Transantarctic Mountains, Antarctica. Ph.D. dissertation (unpublished), Texas Technological College. Lubbock, Texas. 394p. McGregor, V. R., and F. A. Wade. 1969. Geology of the western Queen Maud Mountains. Antarctic Map Folio Series, 12: plate XV. Minshew, V. H. 1967. Geology of the Scott Glacier and Wisconsin Range areas, central Transantarctic Mountains, Antarctica. Ph.D. dissertation (unpublished), The Ohio State University. Columbus, Ohio. 268p. Wade, F. A., V. C. Yeats, J . R. Everett, D. W. Greenlee, K. E. La Prade, and J . C. Shenk. 1965. Geology of the central portion of the Queen Maud Range, Transan tare tic Mountains. Science, 150: 1808-1809. Yochlson, E. L., and Edmund Stump. In press. Fossil evide uce of Early Cambrian at Taylor Nunatak, Antarctica. Antarctic Research Series.
Figure 2. Silicic volcanic rock (sample ES-13) from Lobbock Ridge, with a large pumice fragment and scattered glass shards. The dark color is due to staining. Plane light. (Bar scale, 0.5 millimeters.)
September-October 1974
Paleomagnetic data from unit 13, DVDP hole 2, Ross Island B. E. MCMAHON Institute of Polar Studies The Ohio State University Columbus, Ohio 43210 HENRY SPALL
Geological Society of America Boulder, Colorado 80302 Dry Valley Drilling Project (DvDP) hole 2 (77.85 0 S. 166.67°E.) on Ross Island encountered 161.66 meters of flows and pyroclastic units above the Hut Point pyroclastic sequence (Treves and Kyle, 1973). All 15 units overlying the Hut Point pyroclastic sequence are reversely magnetized. On the basis of revised correlations the units are considered to belong to the Observation Hill and older sequences (Treves and Kyle, personal communication, 1974). Cox (1966) reported reversed polarity for a surface collection made of the Observation Hill sequence. On the basis of available radiometric dates (Forbes et al., 1974) the units encountered in hole 2 are considered to be older than one million years. Consequently it appears that all of the units encountered in hole 2 predate the Jaramillo polarity event (0.89 to 0.95 million years) of the Matuyama reversed epoch. Directional stability and magnetic field configuration. Only unit 13, hole 2, has been examined in detail. From this unit, a lava flow 43.77 meters thick (101.35 to 145.12 meters deep), 22 samples (divided into 43 specimens) have been extracted. Experimentation and measurements indicate that the unit possesses a very stable directional magnetization. Experimentation has included alternating field (AF) demagnetization, thermal demagnetization, susceptibility measurements, and calculation of the Koernigsberger ratio. During both AF and thermal demagnetization the major magnetic component continued to be vertical and very little migration of the magnetic vector was noted. The Koenigsberger ratio, based on natural remanent magnetization (NRM) data (Q - J / xH, where H is taken as 1 oe), yields values for Q. larger than 0.5 (fig. 2). A Q,, value larger than 0.5 indicates magnetic stability and suggests that grains of single domain and pseudo single domain size (d 20) make a significant contribution to the magnetic moment (Stacey, 1967; Stacey and Banerjee, 1974). Examination of polished sections under reflected light indicates that the degree of oxidation of the magnetic minerals places a significant proportion of them into classes IV and V (Wilson and Watkins, 229
