Abstract

Samples from the North American, Australasian, and Ivory Coast microtektite layers were examined for unmelted impact ejecta (>125 οm size). Coesite and shocked quartz, identified by X-ray diffraction, were found at all the sites where a well-defined North American microtektite layer had previously been documented. Coesite and shocked quartz were also foundin seven out of 33 cores from the Australasian strewn field; however, no coesite or shocked quartz was found associated with the Ivory Coast microtektite layer. Stishovite was also found at three of the Australasian sites. All of the Australasian cores containing coesite and shocked quartz were taken from within 2000 km of Indochina, which is believed by most to be the source area for the Australasian tektites and microtektites. Six of the seven cores have the highest concentrations of microtektites ever determined for Australasian microtektite- bearing cores. The seventh core did not contain any microtektites, which may be consistent with the hypothesis that the microtektites were deposited in a raylike pattern. The discovery of coesite and impact ejecta associated with both the North American and Australasian microtektite layers provides further support for the hypothesis of terrestrial impact origin of tektites.

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