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Abstract— We have analyzed the size, shape, composition, and spatial distribution of 6 kg of layered tektite fragments excavated from a 3 m × 3 m area near the town of Ban Huai Sai in northeast Thailand. Our analysis suggests that these fragments represent a single homogeneous mass that underwent fragmentation far in the past and has undergone little disturbance since its deposition. We have also studied the stratigraphic occurrence of layered tektites exposed in situ near the town of Ban Huai Om. Tektites were found along a disconformable paleo‐erosion surface covered by recent aeolian sand, similar to other occurrences throughout Southeast Asia. This stratigraphic relationship provides little chronostratigraphic information and, thus, does not support a stratigraphic “age paradox” for the Australasian tektites. The present‐day surface density of layered tektites in this area is 2 to 20 g/m2.

We recovered Australasian tektites in place throughout a 40X130 km region in northeast Thailand extending from the Laotian border westward to a line connecting Na Pho Klang in the northeast through Det Udom to Nam Yun in the south. With two exceptions, in sites near the western edge of this region, all fragments are layered (muong-Nong-type) tektites. It appears that large layered tektites are mainly found by rice farmers in fields that were forested until the recent past. The presence of layered tektites in this 40X130 km area implies that impact melt that fell in these areas was hot enough to flow if it was deposited on a sloping surface. The absence of splashform tektites from the region indicates that the layer was still molten when masses having shapes (teardrops, dumbbells, etc.) produced by spinning reached the ground. To account for this and to allow time for the melt to flow a few tens of centimeters requires that the atmosphere remained hot (>2300 K) for a few minutes. Tektites that are in place are almost always associated with a widespread 10-cm to meter-thick layer of laterite. In two cases (one involving layered, one involving splash-form tektites), where accurate stratigraphic control demonstrated that the tektites were still in section, they were sited on top of the laterite layer just below a layer of aeolian sand. Introduction Tektites are glasses having chemical and isotopic compositions indicating that they formed by melting well-mixed continental sediments. Four fields are known; common names and approximate ages are North American, 35 Ma; Central European, 15 Ma; Ivory Coast, 1.1 Ma and Australasian, 0.77 Ma (Australasian age by lzett and Obradovich, [ 1992]; other data are from summary by Wasson and Heins, [1993]). We investigated a portion of the youngest strewn field, the Australasian. The Australasian tektites can be divided into two fundamentally different classes: (1) splash-form [more accurately, spinform] that obtained their shapes by solidifying while spinning in a low-pressure environment; and (2) layered (also called Muong-Nong-type) tektites that seem to be fragments of melt sheets, puddles or more complex flow structures that solidified on the Earth's surface [Barnes and ?itakpaivan, 1962]. The largest splash-form tektites (from the Philippines) reach 1 kg in size; the largest splash-form tektites from SE Asia have masses of ~350 g. Splash-form tektites are found on land from Guangxi, China, to Tasmania and as microtektites in sea-sediment cores from Taiwan to Madagascar [Glass, 1982]. Layered tektites have been recovered throughout a 1100-km-long band stretching from Hainan, China [Futrell and Wasson, 1993] to Cambodia [Wasson, 1991; Schnetzler, 1992]. Because those with masses >1 kg are too large Copyfight 1995 by the American Geophysical Union. Paper number 95JE01504. 0148-0227/95/95JE-01504505.00 to have undergone appreciable alluvial transport in low-gradient terrains, discovery sites are inferred to be quite close to the original formation locations. Because most Southeast...

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