Morphological and Chemical Properties of Microtektite Grains from Bay of Bengal (IODP Expedition 354)

This study reports the presence of Australasian microtektites in a deep-sea core (U1452) retrieved during the International Ocean Discovery Program (IODP) Expedition 354: Bengal Fan. These microtektites are found within a foraminifer-rich calcareous clay layer beneath the Matuyama-Brunhes (M–B) magnetostratigraphic boundary. The majorities are spherical and less than one millimeter in diameter. Typical splash (dumbbell, teardrop, disc etc.) and irregular-shaped forms were recovered. The most abundant microtektites are pale green in color, followed by opaque, pale brown, translucent and transparent varieties. These microtektites are characterized by various surficial attributes including pits, mounds, grooves and fractures. Geochemical analyses suggest that the major oxide compositions are very similar to Australasian tektites and microtektites reported elsewhere and also similar to the average composition of upper crustal rocks. Transparent bottle green microtektites are relatively rich in MgO and low in silica when compared to other microtektites found in U1452. Minor and trace element abundances show a wide range of distribution and individual samples show variations in their concentrations. Differences in minor and trace elements concentration are possibly due to the contamination from the impact ejecta. Other than microtektites, the presence of a possibly polymetallic exsolution structure (Widmanstatten texture), shocked minerals and unmelted and partly melted ejecta within the microtektite-bearing layer in the northern Indian Ocean provides further evidence that the Australasian microtektites might have been formed by the impact of an extraterrestrial projectile at ~0.8 Ma, somewhere in Indochina.