Tektites

Tektites are typically rounded black silicate glass objects, and range from less than a millimeter wide to chunks weighing several pounds.  The parent material is sedimentary rock from the Earth's surface.  They formed under conditions of high pressure and sudden intense heating, most likely from meteorite impacts.  Areas where tektites of similar composition are found are called strewn fields.  Each strewn field is thought to have been formed by a single event.

The Australasian tektite strewn field is the largest in the world, covering 1/10th of the surface of the Earth.  Yet no source crater has ever been found, though many have searched for it in Indochina.

But this area is just where one would expect to find debris from a giant impact north of Madagascar and heading west to east.

Map from Giuli, Gabriele, Maria Rita Cicconi, Sigrid Griet Eeckhout, Giovannie Pratesi, Eleonora Paris, Luigi Folco. 2014. Australasian microtektites from Antarctica: XAS determination of the Fe oxidation state. Meteoritics & Planetary Science, Vol. 49, No. 4, pp. 696-705 doi: 10.1111/maps.12283

On the above map of the Australasian strewn field, the dashed line is the tentative boundary.  Dark black asterisks are tektites on land, as are the shaded spots in Antarctica; open circles are microtektites on the ocean floor; small "x"s are core samples where no tektites were found.

Microtektites that appear to be part of the Australasian strewn field have been found about 3000 km south of eastern Australia, in the Victoria Land Transantarctic Mountains of Antarctica.
Folco, L., P. Rochette, N. Perchiazzi, M. D'Orazio, M.A. Laurenzi, M. Tiepolo. April 2008. Microtektites from Victoria Land Transantarctic Mountains. Geology, Vol. 36, No. 4, pp. 291-294.

Large tektites from forward jetting would fall to Earth faster than microtektites.  In the Australasian strewn field, large tektites are found on land that was down range of the impact in the original protocontinent.

  

                     

(Muong Nong tektites from Indochina; scale in centimeters)

 "The largest strewn fields originate from an approximately 30 degree impact (more oblique impacts eject a lot of high velocity melt, but it moves through the low, dense atmosphere, while less oblique impacts eject melt into steep trajectories)."  "Ejecta with the highest velocity (and hence - the most distal [farthest]) originate from a very thin surface layer."  If the meteorite is small, "all ejected material is quickly decelerated by the atmosphere; molten droplets cool quickly, and descend at the distances of a few crater radii."
Artemieva, N. March 2008. Tektites: model versus reality. 39th Lunar and Planetary Science Conference, LPI Contribution No. 1391, p. 1651.

 

Above is a map of an ash layer overlapping or just above the microtektite layer.1  The black dots are ocean floor drilling sites where this combination has been found.  The shaded area is the presumed area covered by the ash, estimated to be 3.7 x 107 km2.  The "X" at Toba is a volcanic caldera proposed as an ash source by some, though it is doubtful that an ash cloud would spread both east and west.  However, it does fit well with an impact in the West Somali Basin, which would loft volcanic ash and tektites downwind together.

Glass produced in atomic bomb tests shares most of the characteristics of tektites, including shape, color, transparency, inclusions of quartz and other minerals, iron ratios, and very low water content.  Even the percentages of types of shapes are similar.2

1.  Glass, Billy P., Christian Koeberl. 2006. Australasian microtektites and associated impact ejecta in the South China Sea and the Middle Pleistocene supereruption of Toba. Meteoritics and Planetary Science, Vol. 41, No. 2, pp. 305-326.

2.  Rocca, M.C.L. 2005. Australasian tektites and atomic bomb glass: close similarity in their shape percentages. Meteoritics & Planetary Science, Vol. 40, Supplement, Proceedings of the 68th Annual Meeting of the Meteoritical Society, September 12-16, 2005, Gatlinburg, Tennessee. Abstract, p. 5001.