SMITHSONIAN CONTRIBUTIONS TO THE EARTH SCIENCES • NUMBER 17 Occurrence, Distribution, and Age of Australian Tektites R. 0. Chalmers, E. P. Henderson, and Brian Mason 1376 SMITHSONIAN INSTITUTION PRESS City of Washington 1976 ABSTRACT Chalmers, R. O., E. P. Henderson, and Brian Mason. Occurrence, Distribution, and Age of Australian Tektites. Smithsonian Contributions to the Earth Sciences, number 17, 46 pages, 17 figures, 10 tables, 1976.—Extensive field work has shown that the Australian strewnfield is less extensive than previously thought, being essentially restricted to the region south of latitudes 24° to 25°S. The few aus- tralites found north of this region probably represent specimens transported by man. Throughout much of the desert interior australites are weathering out of a late Pleistocene or early Recent horizon in a well-consolidated calcareous red sandy aeolianite; field evidence indicates that in most places they are found es- sentially where they fell, or stream erosion and sheet wash has transported them short distances and concentrated them in claypans and playas. Distribution within the strewnfield is irregular and can be ascribed to: (1) original nonuniform fall; (2) burial by recent deposition; (3) removal by erosion. Australites (excluding the doubtful HNa/K type) show a continuous range of composition from 80% to 66% SiO2 with related variations in other major constituents, which is reflected in the range of specific gravities (2.36-2.52) and refractive indices (1.493-1.529). The composition range is not uniform over the strewnfield, the high-silica aus- tralites being concentrated along a northwest trending band extending from western Victoria to the Lake Eyre region. Other noteworthy features are: (1) a variation in the average size of australites from place to place, those on the Nullarbor Plain being notably smaller (average <1 gram) than those of other regions (average 3-5 grams); (2) the occurrence of many large australites (>100 grams) in the southwestern part of Western Australia. Unsolved problems include: (1) the inconsistency between geological age (7000- 20,000 years BP) and K-Ar and fission track ages (700,000-860,000 years); (2) the relationship, if any, between australites and the "microtektites" in Indian Ocean sediments; and (3) the source region of the australite material. OFFICIAL PUBLICATION DATE is handstamped in a limited number of initial copies and is recorded in the Institution's annual report, Smithsonian Year. SERIES COVER DESIGN: Aerial view of Ulawun Volcano, New Britain. Library of Congress Cataloging in Publication Data Chalmers, Robert Oliver Occurrence, distribution, and age of Australian tektites. (Smithsonian contributions to the earth sciences ; No. 17) Supt. of Docs, no.: SI 1.26:17 Bibliography: p. 1. Tektite—Australia. I. Henderson, Edward P., joint author. II. Mason, Brian Harold, 1917— joint author. III. Title. IV. Series: Smithsonian Institution. Smithsonian contributions to the earth sciences ; no. 17. no. \1 [QE399] 550'.8s [523.5'1] 75-619432 Contents Page Introduction 1 Geographical Distribution and Relative Abundance 4 Mode of Occurrence 9 The Extent of the Australite Strewnfield 11 Australites in Relation to the Indoaustralian Strewnfield 15 Physical Properties and Chemical Composition 16 Form 16 Form Analysis 25 Weight 25 Specific Gravity 31 Refractive Index 32 Chemical Composition 36 Chemical Composition and the Origin of Tektites 38 Age and Stratigraphical Relationships 39 Literature Cited 44 ui Occurrence, Distribution, and Age of Australian Tektites R. 0. Chalmers, E. P. Henderson, and Brian Mason Introduction Australian tektites were first made known to sci- ence by Charles Darwin. In 1844, in his book Geological Observations on the Volcanic Islands Visited during the Voyage of H.M.S. Beagle, he de- scribed and illustrated a specimen (Figure 1) he received from Sir Thomas Mitchell in Sydney in January 1836. Mitchell had collected it "on a great sandy plain between the rivers Darling and Mur- ray," presumably during his exploration of the Darling River valley in 1835. (The location as- cribed to this australite by Baker (1973)—approxi- mately 34°20'S, 143°10'E—appears to be erroneous, since Mitchell did not travel south of 32°30'S, near the present site of Menindee, on his 1835 journey.) Darwin compared this australite to obsidian, but noted that it was found "several hundred miles FIGURE 1.—Front, back, and side view of the australite given from any volcanic region," suggesting that it might to Charles Darwin by Sir Thomas Mitchell in 1836; specimen have been transported either by aborigines or by is 26 X 22 X 7 mm (Institute of Geological Sciences, London). natural means. The suggestion that it might have been a transported specimen was a prescient one; very few australites have been found along the Dar- ling, and the exceptional quality of Darwin's speci- them essentially as glassy meteorites, and "austra- men would attract an aboriginal. Additional lites" as those tektites found in Australia. Tektites records of the occurrence of tektites in Australia occur in four general regions of the world. The are scattered through nineteenth- and twentieth- first and largest is the Indoaustralian region (Von century literature from 1855 to the present. This Koenigswald, 1960), encompassing, besides Austra- information is summarized in the classic mono- lia, Hainan Island and the adjacent mainland of graphs of Suess (1900) and Baker (1959a). China in the extreme southern section of Kwang- tung Province, Vietnam, Cambodia, Laos, and Suess introduced the terms "tektites," denning Thailand (indochinites), the Philippines (philippi- R. O. Chalmers, Australian Museum, Sydney, Australia. E. P. nites), Malaysia (malaysianites), and Indonesia. Henderson and Brian Mason, Smithsonian Institution, Wash- Barnes (1963) introduced the term "indomalaysian- ington, D.C. 20560. ites" to refer to tektites from Malaya, Java, Borneo, SMITHSONIAN CONTRIBUTIONS TO THE EARTH SCIENCES and the adjacent small islands of Billiton and thus supported the suggestion by Nininger (1943) Bunguran, and those few other Indonesian islands that a meteorite impact on the moon was the on which an occasional specimen is found. Outside mechanism that sent tektites to Earth. When plans the Indoaustralian region two more geographically were being made for manned moon landings, sci- defined groups are moldavites (vltavines) from the entists at the National Aeronautics and Space Ad- Moldau (Vltava) River valley and areas further to ministration began an intensive study of all things the east in Czechoslovakia, and bediasites from connected with the moon, including tektites. Chap- Texas. Finally, tektites are found on the Ivory man and Larson (1963) further adduced a great Coast, West Africa. Materials sometimes classed as deal of aerodynamic evidence to substantiate the tektites, but distinct from them in appearance and theory of lunar origin. On the other hand, the work composition, are silica glass from the Libyan Desert of Taylor (1962, 1966) and Taylor and Kaye (1969) and Darwin Glass from Mt. Darwin in Tasmania. showed that the composition of tektites was com- The australites occupy a unique position among parable to that of sedimentary rocks of the sub- the tektites. Their strewnfield is by far the most greywacke type. Bouska (1968) considered that all extensive of any of the above-named groups. They tektites from the entire Indoaustralian region show a wider range of composition (e.g., 66%-80% might have been derived from impact on igneous SiO2) than most tektite groups. Whereas practically rocks, but that tektites from other regions were all other tektites have been found in alluvial de- derived from sedimentary rocks. These findings posits and have lost their original surface by abra- suggested a possible origin by meteoritic impact on sion or solution, many australites have been Earth and not on the moon. This possibility was recovered with their original surface well preserved, strengthened by the discovery that moldavites had showing delicate markings produced by aerody- the same K-Ar age as the Ries crater in southern namic ablation. This enables significant deductions Germany and that the Ivory Coast tektites were the to be made regarding their original form and its same age as the glass in the Bosumtwi crater in modification during passage through the Earth's Ghana (Cohen, 1963, Gentner et al., 1963, Faul, atmosphere. 1966). As a result, the extraterrestrial origin once Interest in tektites as a group, and australites in widely accepted was seriously challenged, and an particular, has waxed and waned from time to time. origin due to large-scale impact on Earth gained Comparatively little research on australites was favor. reported in the first thirty years of this century. Because of this increased interest, the demand for Then Dr. Charles Fenner, in a series of papers pub- research material has steadily expanded, and the re- lished between 1933 and 1955, provided a large quirements therefor have become more rigorous, amount of new information on numbers, forms, in terms of exact locality, mode of occurrence, and and distribution. Commencing in 1937, Dr. George quality of preservation. On this account, we or- Baker wrote a large number of papers on austra- ganized in 1963 an expedition designed to provide lites, especially those from localities in Victoria more and better documented material for our re- and South Australia. In 1959 his comprehensive spective institutions: the Australian