Marine Geophysical Observations
of rock types from regional patterns is more likely to reflect the occurrence of in-situ than of ice-rafted materials, which are most unlikely to be selectively associated with physiographic features. Preliminary results suggest that the materials dredged from the Macquarie Arc contain much in situ material. These materials are being subjected to examinations of magnetic and opaque mineralogical properties (Watkins and Haggerty, 1967, 1968) and are being integrated into continuing comparisons of cooling histories and chemical and magnetic properties (Watkins et al., 1967; Gunn and Watkins, 1968). The same samples are also being examined in order to determine their suitability for potassium-argon isotope dating, the results of which are highly relevant to the crustalspreading hypothesis, as shown by Dymond et al. (1968). An incidental result of the above examination of the Eltanin dredged materials is shown in Fig. 3. For reasons which are not at present clearly understood, the recovered manganese nodules are systematically restricted to those hauls from water depths greater than 1,500 fathoms, although slight manganese staining occurs at all depths. This observation is being analyzed in terms of other, possibly related, variables, such as the dependence of oxygen solubility on pressure. References Abdel-Monem, A., N. D. Watkins, and P. W. Gast. 1967. Volcanic history of the Canary Islands. American Geophysical Union. Transactions, 48(1): 226. Abstract. Dymond, J . , N. D. Watkins, and Y. R. Nayudu. 1968. The age of the Cobb Seamount. Journal of Geophysical Research, 73(12): 3977. Geitzenauer, K. R., S. V. Margolis, and D. S. Edwards. 1968. Evidence consistent with Eocene glaciation in a South Pacific deep sea sedimentary core. Earth and Planetary Science Letters, 4(2) : 173-177. Goodell, H. G. and N. D. Watkins. 1968. Paleomagnetic stratigraphy of the Southern Ocean, 200 W. to 160 0 E. Deep-Sea Research, 15: 89. Goodell, H. G., N. D. Watkins, T. Mather, and S. Koster. 1968. Antarctic glaciation as recorded in deep sea sediments of the Southern Ocean. Paleogeography, Paleoclimatology, and Paleoecology. In press. Gunn, B. M. and N. D. Watkins. 1968. The petrological effect of the simultaneous cooling of adjacent rhyolitic and basaltic magmas. Geochimica et Cosmochimica Acta. In press. Watkins, N. D. 1968a. Short geomagnetic polarity events in deep-sea sedimentary cores. Earth and Planetary Science Letters. In press. Watkins, N. D. 1968b. Comments on the interpretation of linear magnetic anomalies. Pure and Applied Geophysics.
In press. Watkins, N. D. 1968c. Comments on the relationship between magnetic anomalies, crustal spreading, and continental drift. Earth and Planetary Science Letters, 4:
257. Watkins, N. D. and S. E. Haggerty. 1967. Primary oxidation variation and petrogenesis in a single lava. Contributions in Mineral Petrology, 15: 251.
September-October 1968
Watkins, N. D. and S. E. Haggerty. 1968. Oxidation and polarity variation in Icelandic lavas and dikes. Geophysical Journal of the Royal Astronomical Society, 15: 305. Watkins, N. D., C. W. Holmes, and S. E. Haggerty. 1967. Variation of the Th : U ratio in a single lava. Science, 155: 579. Watkins, N. D., R. Self, N. Mark, and H. G. Goodell. 1968. A description of the Eltanin dredged submarine rocks from the South Pacific and Scotia Seas. American Geophysical Union. Transactions, 49(1): 214. Abstract.
Marine Geophysical Observations Aboard Elf anin, 1967-1968 DENNIS E. HAYES Lamont Geological Observatory Columbia University In the early part of 1967, a Graf sea-gravimeter and an Anschutz gyrotable were installed on Eltanin for operation beginning with Cruise 28. With this addition, the geophysical equipment enabled continuous and simultaneous acquisition of gravity, magnetic, and seismic-profiler data. Nearly continuous data have been collected along approximately 50,000 track miles during Eltanin Cruises 28-33. With the aid of analog error correction devices and the Navy satellite navigation system, the gravity measurements made on these cruises are believed to be among the most accurate ever obtained in remote, deep-water areas; a grid survey made in the Tasman Sea indicates that the measurements were accurate to about 3 mgal in moderate to rough seas. Measurements made on Eltanin now provide a major portion of our knowledge of surface gravity in the oceans south of 40° S. The magnetic data taken on Eltanin continue to be vital in evaluating the patterns of global tectonics and sea-floor spreading. In addition, they are most important in the regional analysis of the Earth's main field and its secular variations. A report on sediment distribution and an accompanying isopach map of sediment thickness for the South Pacific based largely on Eltanin seismic-profile data south of 40° S. are in the final stages of preparation. On Cruise 32, Eltanin made her first crossing of the western continental margin of Antarctica and the adjacent Pacific-Antarctic Ridge, along which gravity, magnetic, and seismic information was simultaneously recorded. Bathymetric, gravimetric, and magnetic data obtained on these cruises are being systematically reduced and analyzed according to a standard format by using digital computers and x-y plotters. These parameters are plotted as profiles (e.g., depth vs. track distance), and pertinent navigational and time information is annotated on the plots. In the figure, an example is given of such a plot for the first part of Eltanin Cruise 29. The ship's three crossings of the Peru-Chile trench are clearly shown in the depth pro171
M G
-29 -74 -75 -76
tL L!O ----H-*:
N S
20
S (0
1flP12Th M
AN W M -
S w 01
i l
U) mI9oxnSo .q K oo o
e'' ';
01 .n 0 tp(UcDm .l 01 0 0 0 I .
Plot of depth (D), free-air gravity anomaly (G), and total intensity magnetic anomaly (M) versus distance in nautical miles along a portion of Eltanin's Cruise 29. Scales are shown on the left: depth (D) in fathoms, gravity anomaly (G) in milligals, and magnetic anomaly (M) in gammas. Navigational information (coordinates at times of course or speed changes) are annotated near the bottom. Ship time is annotated near the top.
Our tentative conclusion is that both fractions yield file (D), as well as in the large negative free-air gravity anomalies (G). These plots, accompanied by chartlets and a short scientific description of the cruises, will eventually be distributed as Eltanin geophysical-data reports.
Geochronological Studies of Antarctic Deep-Sea Cores J. K. OSMOND and H. G. GOODELL Department of Geology Florida State University The geochronological study of deep-sea cores (NSF grant GA-602) obtained on Eltanin cruises has been 172
concerned with the determination of sedimentation rates by means of ionium (Th-230) /uranium disequilibrium dating. We have shown that (1) foraminiferal and other biologic oozes are more reliable indices for ionium dating than expected; (2) sedimentation rates in the southern oceans have varied in the last 300,000 years (there is some evidence that sedimentation rates have actually decreased over this period); and (3) the basic immobility assumptions for thorium and uranium are valid for many types of sediments, although the diffusion of radium may be more pronounced in southernocean sediments than elsewhere. In analyzing these questions, we have taken some relatively new approaches to ionium dating. First, we have found it necessary to separate, by physical processes, the clay and the organic fractions of several cores and to analyze each by alpha isotopic methods. ANTARCTIC JOURNAL
In press. Watkins, N. D. 1968c. Comments on the relationship between magnetic anomalies, crustal spreading, and continental drift. Earth and Planetary Science Letters, 4:
257. Watkins, N. D. and S. E. Haggerty. 1967. Primary oxidation variation and petrogenesis in a single lava. Contributions in Mineral Petrology, 15: 251.
September-October 1968
Watkins, N. D. and S. E. Haggerty. 1968. Oxidation and polarity variation in Icelandic lavas and dikes. Geophysical Journal of the Royal Astronomical Society, 15: 305. Watkins, N. D., C. W. Holmes, and S. E. Haggerty. 1967. Variation of the Th : U ratio in a single lava. Science, 155: 579. Watkins, N. D., R. Self, N. Mark, and H. G. Goodell. 1968. A description of the Eltanin dredged submarine rocks from the South Pacific and Scotia Seas. American Geophysical Union. Transactions, 49(1): 214. Abstract.
Marine Geophysical Observations Aboard Elf anin, 1967-1968 DENNIS E. HAYES Lamont Geological Observatory Columbia University In the early part of 1967, a Graf sea-gravimeter and an Anschutz gyrotable were installed on Eltanin for operation beginning with Cruise 28. With this addition, the geophysical equipment enabled continuous and simultaneous acquisition of gravity, magnetic, and seismic-profiler data. Nearly continuous data have been collected along approximately 50,000 track miles during Eltanin Cruises 28-33. With the aid of analog error correction devices and the Navy satellite navigation system, the gravity measurements made on these cruises are believed to be among the most accurate ever obtained in remote, deep-water areas; a grid survey made in the Tasman Sea indicates that the measurements were accurate to about 3 mgal in moderate to rough seas. Measurements made on Eltanin now provide a major portion of our knowledge of surface gravity in the oceans south of 40° S. The magnetic data taken on Eltanin continue to be vital in evaluating the patterns of global tectonics and sea-floor spreading. In addition, they are most important in the regional analysis of the Earth's main field and its secular variations. A report on sediment distribution and an accompanying isopach map of sediment thickness for the South Pacific based largely on Eltanin seismic-profile data south of 40° S. are in the final stages of preparation. On Cruise 32, Eltanin made her first crossing of the western continental margin of Antarctica and the adjacent Pacific-Antarctic Ridge, along which gravity, magnetic, and seismic information was simultaneously recorded. Bathymetric, gravimetric, and magnetic data obtained on these cruises are being systematically reduced and analyzed according to a standard format by using digital computers and x-y plotters. These parameters are plotted as profiles (e.g., depth vs. track distance), and pertinent navigational and time information is annotated on the plots. In the figure, an example is given of such a plot for the first part of Eltanin Cruise 29. The ship's three crossings of the Peru-Chile trench are clearly shown in the depth pro171
M G
-29 -74 -75 -76
tL L!O ----H-*:
N S
20
S (0
1flP12Th M
AN W M -
S w 01
i l
U) mI9oxnSo .q K oo o
e'' ';
01 .n 0 tp(UcDm .l 01 0 0 0 I .
Plot of depth (D), free-air gravity anomaly (G), and total intensity magnetic anomaly (M) versus distance in nautical miles along a portion of Eltanin's Cruise 29. Scales are shown on the left: depth (D) in fathoms, gravity anomaly (G) in milligals, and magnetic anomaly (M) in gammas. Navigational information (coordinates at times of course or speed changes) are annotated near the bottom. Ship time is annotated near the top.
Our tentative conclusion is that both fractions yield file (D), as well as in the large negative free-air gravity anomalies (G). These plots, accompanied by chartlets and a short scientific description of the cruises, will eventually be distributed as Eltanin geophysical-data reports.
Geochronological Studies of Antarctic Deep-Sea Cores J. K. OSMOND and H. G. GOODELL Department of Geology Florida State University The geochronological study of deep-sea cores (NSF grant GA-602) obtained on Eltanin cruises has been 172
concerned with the determination of sedimentation rates by means of ionium (Th-230) /uranium disequilibrium dating. We have shown that (1) foraminiferal and other biologic oozes are more reliable indices for ionium dating than expected; (2) sedimentation rates in the southern oceans have varied in the last 300,000 years (there is some evidence that sedimentation rates have actually decreased over this period); and (3) the basic immobility assumptions for thorium and uranium are valid for many types of sediments, although the diffusion of radium may be more pronounced in southernocean sediments than elsewhere. In analyzing these questions, we have taken some relatively new approaches to ionium dating. First, we have found it necessary to separate, by physical processes, the clay and the organic fractions of several cores and to analyze each by alpha isotopic methods. ANTARCTIC JOURNAL
