Morphological and chemical properties of Microtektite grains from Bay of
Bengal (IODP Expedition: 354)
Abstract
This study reports the presence of Australasian microtektites in a
deep-sea core (U1452) retrieved during International Ocean Discovery
Program (IODP) Expedition 354: Bengal Fan. These microtektites are found
within a foraminifera-rich calcareous clay layer beneath the
Brunhes–Matuyama (B–M) magnetostratigraphic boundary. Most of them are
spherical and are less than one millimeter in diameter. Typical splash
(dumbbell, teardrop, button 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.
They 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 microtektites,
Australasites reported elsewhere and also to the average composition of
upper crustal rocks. Transparent bottle green microtektites are
relatively richer in MgO content and lower in silica to other
microtektites found in U1452. Minor and trace elements show a wide range
of distribution and individual samples show variation. Differences in
minor and trace elements concentration are possibly due to the
contamination from the impact ejecta. Other than microtektites, presence
of possibly polymetallic exsolution texture, shocked minerals and
unmelted and partly melted ejecta within the microtektite-bearing layer
in the northern Indian Ocean provides further evidence that the
Australasites and Australasian microtektites might have been formed by
the impact of an extraterrestrial projectile at ~0.8 Ma,
somewhere in Indochina.