A sedimentary profile exposed in soil quarries a few kilometers north of Noen Sa-nga district,Chaiyaphum province,NE Thailand,reveals a Quaternary geological history.The lower part of the soil profile is a gravel deposit characterized by sub-angular to well-rounded pebbles representing an abandoned river sedimentary deposit.The gravel bed in some places is coated by iron oxide as a thin layer of ferricrete at the uppermost part.The upper part of the soil profile is a bright reddish brown structureless sand deposit with fining upward sedimentary structure at the basal portion,the Yasothon soil series.A piece of tektite was discovered at the contact boundary between the two sedimentary units.It is characterized by an irregular shape with a smooth concaved surface regarding as an external mold of a piece of well-rounded pebble.This piece of tektite indicates that a solidified tektite had fallen from high sky then was remelted into a plastic form prior to reach and partly cover a piece of well-rounded pebble.These evidences suggest that there was a meteoritic or cometary impact on our earth surface somewhere in the region then catapulted numbers of melted silica ejecta with vast volume of dust into the sky.The melted silica ejecta were solidified into splash-form tektites with various shapes while they were in the high sky.After that the tektites had fallen down and remelted into a plastic form prior to reach the ground surface and then solidified as a tektite deposit followed by larger-sized sediments and angular quartz fragments forming a fining upward sedimentary structure.The finer sediments were gradually settled down forming a bright reddish brown structureless sand deposit,the Yasothon soil series.This meteoritic impact event occurred at about 0.77 Ma ago as the evidence of the previous tektite radiometric dating.
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