Occurrence, Distribution, and Age of Australian Tektites

Abstract

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 australites 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 essentially 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 australites 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 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.