Beryllium-10 in Australasian tektites: constraints on the location of the source crater

By using accelerator mass spectrometry we have measured the Be-10 concentrations of 86 Australasian tektites. Corrected to the time of tektite production similar to0.8 My ago, the Be-10 concentrations (10(6) atom/g) range from 59 for a layered tektite from Huai Sai, Thailand, to 280 for an australite from New South Wales, Australia. The average value is 143 +/- 50. When tektites are sorted by country, their average measured Be-10, concentrations increase slowly with increasing distance from Southeast Asia, the probable location of the tektite producing event, from 59 +/- 9 for 6 layered tektites from Laos to 136 +/- 20 for 20 splash-form tektites from Australia. The lowest Be-10 concentrations for tektites fall on or within a contour centered off the shore of Vietnam, south of the Gulf of Tonkin (107degreesE; 17degreesN), but also encompassing two other locations in the area of northeastern Thailand previously proposed for the site of a single tektite-producing impact. The Be-10 concentrations of layered tektites show only a weak anticorrelation (R similar to -0.3) with the numbers of relief crystalline inclusions. Loosely consolidated, fine-grained terrestrial sediments or recently consolidated sedimentary rocks are the most likely precursor materials. Dilution of sediments with other kinds of rock raises problems in mixing and is not supported by petrographic data. Sedimentary columns that have the right range of Be-10 concentrations occur off the coasts of places where sedimentation rates are high relative to those in the deep sea. A single impact into such a region, 15 to 300 m thick, could have propelled near-surface, high-Be-10 material farthest-to Australia-while keeping the deeper-lying, low-Be-10 layers closer to home. We do not rule out, however, other proposed mechanisms for tektite formation. Copyright (C) 2004 Elsevier Ltd.