H-32--- basalt from pillow in basal part of a palagonitizedbasalt breccia, northern exposure at Carapace Nuna-tak. Collected by H. W. Borns and B. A. Hall.

References

Compston, W., I. McDougall, and K. S. Heier. 1968. Geochem-ical comparison of the Mesozoic basaltic rocks of Antarctica,South Africa, South America and Tasmania. Geochimica etCo.rmochimica Acta, 32: 129-149.

Faure, G., and D. H. Elliot. 1971. Isotope composition ofstrontium in Mesozoic basalt and dolerite from DronningMaud Land. British Antarctic Survey Bulletin, 25: 23-27.

Faure, G., R. L. Hill, L. M. Jones, and D. H. Elliot. 1972. Iso-tope composition of strontium and silica content of Mesozoicbasalt and dolerite from Antarctica. In: Antarctic Geologyand Geophysics (R. J . Adie, ed.). Oslo, Uniz'ersitetsforlagei.617-624.

Hill, R. L. 1969. Strontium isotope composition of basaltic rocksof the Transantarctic Mountains, Antarctica. M.Sc. thesis,The Ohio State University. 87 p.

Jukes, L. M. 1969. Trace-element values for dolerites fromwestern Queen Maud Land. British Antarctic Survey. Bulle-tin, 22: 95-96.

McDougall, I. 1962. Differentiation of the Tasmanian dolerites.Red Hill dolerite-granophyre association. Geological Societyof America. Bulletin, 73: 279-315.

A volcanic ash deposit, Wright Valley

Lois M. JONES, JAMES A. WHITNEY, andJOHN C. STORMER, JR.

Department of GeologyUniversity of Georgia

We are reporting evidence for a possible ash fall thatmay have extended throughout Wright Valley. Uponexamination of water-deposited sediment, samples fromtwo localities contained material with a density appre-ciably less than that of quartz. These localities are shownin fig. 1. Site A is located approximately 2.5 kilometerssoutheast of the easternmost edge of Lake Vanda, andsite B is a deposit underlying an alluvial fan on thelake's north shore.

This low-density material was separated from a seriesof samples collected from site A. The higher-densitymaterial mainly consists of grains of quartz, feldspar,biotite, hornblende, and lithic fragments that probablywere derived from the local bedrock. The amount oflow-density material from a depth profile is given intable 1. The actual percentage of this material may beconsiderably higher, but it was advantageous to removethe -250 mesh fraction prior to the density separations.No ash is found in the shallower samples, but its amountincreases with depth through the profile that extendedto 85 centimeters.

The ash dominantly is composed of an amorphous,friable, light-gray material (fig. 2, A and B). This ma-terial is very similar in appearance to water-laid volcanicash from the Mojave Desert, California (G. 0. Allard,personal communication) and to other volcanic ash de-

Table 1. Percent ash (d < 2.6 of the +250 mesh fraction forsamples from a depth profile at site A, southeast of Lake Vanda.

+250 mesh

d>2.6 d<2.6

(heavy) (light)

(percent) (percent)

100.0 0.0

100.0 0.0

78.3

22.7

61.7

38.3

54.2

45.8

59.0

41.0

31.3

68.7

47.4

52.6

+250Laboratory Depth mesh

number (centimeters)

(percent)

492

0-3

84.4

496

3-8 56.2

495 8-18

29.6

491 18-28

51.7

494

28-40 57.7

493

40-55 55.7

589

55-70

45.3

590

70-85 52.3

* R. E. Behling's sample locality WVB-58.

270 ANTARCTIC JOURNAL

Figure 2. Scanning electronmicrographs of volcanic ma-terial from site A (40 to 55centimeters in depth). (A)Typical grain of the amor-phous, light-gray ash. Mostof the volcanic material con-sists of this kind of ash. (B)Close-up view of the particleshown in (A). (C) Grain ofchlorophaeite. (D) Close-upview of the grain shown in(C). (E) and (F) Typical as-pects of the vesicular par-

ticles.

scribed by Heiken (1972). This light-gray ash showsall gradation into a khaki-colored, massive substanceexhibiting conchoidal fracture (fig. 2, C and D). Thismaterial is found at maximum concentration 2 per-cent) at depths of Z10 to 55 centimeters. Its refractiveindex is variable from 1.554 to 1.560 and it often showsweak birefringence. Powder x-ray diffraction analysisindicates no pronounced crystalline nature. A few diffusemaxima are present in the pattern, however, and thesepeaks correspond to those reported by Stokes (I 97 1)for the mineraloid chlorophaeite.

Grains of the khaki-colored substance (chiorophacite?)were analyzed chemically with an electron microprobe.Twenty spot analyses were made on a total of six grains.The material was altered by the beam, possibly indicativeof a high water content. The chlorophacite is suite vari-able in composition (table 2) . This analysis is similar

\

B'•

'7

4 1

N cA

0 2 k

Figure 1. Location of sediments in Wright Valley (sites A and B)that contain volcanic ash.

to those reported for chlorophaeite by Stokes (1971),with the exception that the A 1 ° and FeO contents arelower for the Wright Valley material.

September-October 1973 271

Vesiculated volcanic fragments (fig. 2, E and F) com-prise a fraction of 1 percent of the ash. These fragmentsunquestionably are of volcanic origin and lend credenceto a volcanic source for the light ash and chlorophaeite.The sediment apparently has been water-deposited (R. E.Behling, personal communication). The presence of anaqueous environment would promote the alteration ofthe ash to material such as chlorophaeite.

A sample from site B consists dominantly of light-grayash. A few grains of khaki-colored substance were pres-ent. The similarity of this sediment to that of site Ais striking, and strongly suggests a relationship betweenthe material of these two localities. It is quite possiblethe two were deposited contemporaneously.

Holdsworth (1969) reported the presence of wind-blown vesicular basaltic particles in the eastern morainesof the Meserve Glacier, located in the eastern part ofWright Valley. Small cinder cones of McMurdo basaltare located in the accumulation basin of this glacier.These and other local, glacially overridden (?) coneswere the source of the basalt incorporated within themoraines and probably of the wind-blown particles aswell.

The most likely sources for volcanic material are (1)small basaltic cinder cones located in the vicinity of theMeserve and Bartley Glaciers and on the south wall ofthe valley above the Loop Moraine, and (2) Ross Island.The variable chemical composition and the possible oc-currence of aqueous alteration make it difficult to assign aspecific source for this material. The material's value isgreatest, however, in establishing a time horizon withinthe sediments of Wright Valley, and possibly elsewherein southern Victoria Land.

We are indebted to Robert E. Behling, West VirginiaUniversity, for the excellent series of samples from siteA. Maurice and Eileen McSaveney, Institute of PolarStudies, Ohio State University, provided the sample fromsite B. David Baskin assisted with the microprobe anal-yses and Janet Johnson gave valuable assistance duringthe operation of the scanning electron microscope.

Table 2. Electron microprobe analysis of chioro-phaeite (?), Wright Valley. The range in per-cent is given for 20 spot analyses of six grains

of the material.

Oxide Range (percent)

Si0255-35

Al 2031.0-0.5

FeO* 2-9.5

MgO 2-8.0

CaO 0-20

Na20 0-0.2

* Total Fe reported as FeO.

References

Heiken, G. 1972. Morphology and petrography of volcanicashes. Geological Society of America. Bulletin, 83(7): 1961-1988.

Holdsworth, G. 1969. Mode of flow of Meserve Glacier, WrightValley, Antarctica. Ph.D. Dissertation, The Ohio State Uni-versity. 342 p.

Stokes, K. R. 1971. Further investigations into the nature of thematerials chlorophaeite and pal agonite. Mineralogical Maga-zine, 38: 205-214.

Antarctic and other Gondwananonmarine deposits

PAul. TASCH

Department of GeologyWichita State University

Completely or incompletely carbonized conchostracanvalves (Mesozoic interbeds of dolerite flows, Transant-arctic Mountains) may serve as geothermometers. Tem-perature-related experiments on modern conchostracanvalves led to compilation of a char scale. Further re-finements and analyses are under way (Tasch, in prepara-tion).

The duration of a nonmarine interbed at BlizzardHeights is determined to be 306 ± 26 years, based onsuccessive, seasonal conchostracan generations. It is thefirst indication of the time between successive doleriteflows represented by such interbeds. A time-related eval-uation of electron microprobe data for two successiveflows becomes feasible with this framework, assumingthat the nonmarine deposits would have continued ifany considerable time lapse intervened before the upperflow eliminated the basin (Tasch and Gafford, in prep-aration, a).

Geochemical data which permit paleosalinity deter-mination have been developed for antarctic Mesozoicconchostracan interbeds (Tasch and Gafford, in prepara-tion, b). There are indications, for example, that at StormPeak the upper interbed has a salinity of 31 parts perthousand and that it becomes more brackish only duringthe time represented by the uppermost portion (21 partsper thousand).

Field study, in collaboration with the Indian Geologi-cal Survey, covered the Triassic (Panchet Formation,Raniganj Basin), and the Jurassic (Kota Formation,Pranhita-Godovarj Basin). Conchostracan faunas extendthrough some 519 meters of the Panchet Formation.Clarification of the conchostracan biostratigraphy willallow useful comparisons with the Triassic of westernAustralia, in particular (Tasch et al., 1973). The con-chostracan faunas of the western Australian basins havebeen studied in collaboration with colleagues of theBureau of Mineral Resources, Geology and Geophysics.

272 ANTARCTIC JOURNAL