A review of evidence for a Gulf of Tonkin location  for the Australasian tektite source crater

Aubrey  Whymark

Authors

Aubrey Whymark Consultant Wellsite Geologist, Manila, Philippines

Keywords:

Australasian tektite, Gulf of Tonkin, impact crater, Pleistocene, Song Hong Basin, Yinggehai Basin

Abstract

Australasian tektites (AAT) occur across Southeast Asia, Australia, the Indian Ocean, and southwest Pacific Ocean. AAT form the youngest and most extensive major tektite strewn field. Unlike other tektite strewn fields, AAT have no known source crater. Review of the literature establishes that a single ~ 43 km post-impact diameter crater exists, possibly significantly enlarged by slumping. The
obliquity of the impact that formed the AAT would result in a crater that is less pervasive in depth but with greater downrange shock effects and melt ejection. Multiple lines of evidence, historically viewed in isolation, were examined, concatenated, contextualized, and discussed. Tektite morphology and distribution; microtektite regressions; geochemical considerations, comparisons, and iso-concentration regressions; lithological characteristics; age of source rock; and regional geological considerations are reviewed. The source material is predicted to be an abnormally thick sequence of rapidly deposited, poorly compacted, deltaic to shallow marine, shales to clay-rich siltstones of early Pleistocene to Pliocene age. The impact likely occurred in a shallow marine environment. Forty-
two maps of positive and negative parameters are presented and overlain. These indicate the AAT source crater probably lies in the central to northwestern Yinggehai - Song Hong Basin / Gulf of Tonkin. This geochemically optimal setting is characterized by exceptionally high sedimentation rates that explain the 10Be and Rb-Sr age discrepancy, the seawater signature, and apparent absence of a crater by rapid burial.

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