Tada et al. Progress in Earth and Planetary Science
https://doi.org/10.1186/s40645-020-00378-4(2020) 7:66

Progress in Earth andPlanetary Science

RESEARCH ARTICLE

Open AccessIn situ occurrence of Muong Nong-type
Australasian tektite fragments from the
Quaternary deposits near Huai Om,
northeastern Thailand
Toshihiro Tada1* , Ryuji Tada1,2,3, Praphas Chansom4, Wickanet Songtham4, Paul A. Carling5 and Eiichi Tajika1

Abstract
There are several reports of Australasian tektites found within a stratum called “laterite” layer widely distributed in
Indochina. However, it has been debated whether these tektites are in situ or reworked. This uncertainty is because
a detailed description of their field occurrence is lacking. Here, we describe the detailed occurrence of a cluster oftektite fragments recovered from the “laterite” layer near Huai Om, northeastern Thailand, and demonstrate theevidence of in situ occurrence of the tektites. At least 331 tektite fragments with a total weight of 713 g were foundfrom a 40 × 30 cm area with 10 cm thickness in the uppermost part of the “laterite” layer. The very angular shapes
and very poorly sorted nature of the fragments, restoration of larger tektite fragments into one ellipsoidal Muong
Nong-type (MN) tektite mass, and the similar chemical composition of the fragments suggest that these MN tektite
fragments represent a tektite mass that fragmented in situ. The fact that the fragments were found within the“laterite” layer is inconsistent with a previous interpretation that the upper surface of the “laterite” layer is a paleoerosional surface, on which the tektites are reworked. The size distribution of the fragments is bi-fractal following
two power laws in the range from 10 to 26 mm and from 26 to 37 mm, respectively, with fractal dimensions (Ds) of
2.2 and 7.5. The Ds for the coarse fraction of the tektite fragments is larger than the Ds for rock fragments
generated by rockfalls and rock avalanches and similar to the Ds for the coarser fraction fragments generated byhigh-speed impact experiments, suggesting that the tektite fragments were formed through intense fragmentation
by a relatively high energetic process. The occurrence of the fragments forming a cluster indicates that the
fragments were not moved apart significantly after fragmentation and burial. Based on these results, we concluded
that the mass of a tektite was fragmented at the time of the landing on the ground after traveling a ballistic
trajectory and has not been disturbed further.
Keywords: Australasian tektite, Impact ejecta, Southeast Asia

1 Introduction
Tektites are objects composed entirely of glass formedby meteorite impacts (Koeberl 1994). Tektites are foundfrom at least four broad areas of the Earth’s surface,called strewn fields (e.g., Koeberl 1994; Glass and* Correspondence: ttada@eps.s.u-tokyo.ac.jp
1
Department of Earth and Planetary Science, The University of Tokyo, 7-3-1
Hongo, Bunkyo-Ku, Tokyo 113-0033, Japan
Full list of author information is available at the end of the article

Simonson 2012). The Australasian tektites were formed
ca. 0.8 Ma and occur as the largest and youngest strewn
field extending from southwestern China, through Indochina, Australia to Antarctica (Folco et al. 2016). Despite
the largest size and youngest age of the strewn field, thesource crater has never been identified. Nevertheless, it
is expected that the record of the impact and consequentenvironmental perturbations are well preserved because
the impact event which made Australasian tektites (here© The Author(s). 2020 Open Access This article is licensed under a Creative Commons Attribution 4.0 International License,
which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give
appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate ifchanges were made. The images or other third party material in this article are included in the article's Creative Commonslicence, unless indicated otherwise in a credit line to the material. If material is not included in the article's Creative Commonslicence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain
permission directly from the copyright holder. To view a copy of this licence, visit http://creativecommons.org/licenses/by/4.0/.

Tada et al. Progress in Earth and Planetary Science(2020) 7:66

we term the Australasian Tektite Event; AATE) is the
youngest among the large impact events on the Earth.
Thus, the AATE has broader significance to the study ofthe meteorite impact phenomena on Earth.
Based on their morphology, Australasian tektites havebeen classified into three groups (e.g., Koeberl 1994): (1)splash-form tektites, (2) ablated form tektites, and (3)Muong Nong-type (MN) tektites (also called layered tektites). Among these, MN tektites have blocky shapes andinternal layered texture. Their sizes are typically > 10

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cm, and the largest MN tektite so far recovered weighs
24.1 kg (Koeberl 1992). MN tektites primarily are distributed across southern Laos, northeastern Thailand,
Vietnam, Cambodia, and Hainan island in China (Fig. 1)(Schnetzler 1992; Wasson et al. 1995; Schnetzler and
McHone 1996; Fiske et al. 1999).
Although there are a large number of studies on thegeochemistry and microstructure of Australasian tektites, many of them were conducted on samples of unknown or uncertain provenance (e.g., Fudali et al. 1987;

Fig 1 Map of Indochina showing sites where Australasian tektites have been found. Sites where the tektites were found from strata are also
shown (after Schnetzler 1992 and references listed in Table 1). The names of locations mentioned in the text are also shownTada et al. Progress in Earth and Planetary Science(2020) 7:66

Wasson 1991; Schnetzler and McHone 1996; Herzog
et al. 2008). There are several reports of tektites foundin the Quaternary deposits of Indochina (Fig. 1), of
which some occurrences are listed in Table 1 (Barnes
and Pitakpaivan 1962; Tamura 1992; Wasson et al. 1995;
Fiske et al. 1996, 1999; Schnetzler and McHone 1996;
Songtham et al. 2011, 2012). In these studies, tektites
were found in a loose gravel (granule to pebble-bearingsand) layer with abundant reddish-black spherical- toirregular-shaped ferruginous nodules, called a “laterite”
layer, but the details of the occurrence of the tektites
were not described.
Several authors have considered that the tektites recovered from the “laterite” layer were directly depositedin the strata from which they were recovered and hence
were found in situ (Wongsomsak 1986; Tamura 1992;
Songtham et al. 2011, 2012; Nuchanong et al. 2014).
However, the possibility that the tektites have beenreworked has been claimed based on reasoning advanced
below (Fiske et al. 1996; Koeberl and Glass 2000; Keates
2000; Langbroek 2015).
Fiske et al. (1996) conducted field surveys at two sites:
Huai Sai and Huai Om in northeastern Thailand. At
Huai Om, they found two MN tektite fragments fromthe top of the “laterite” layer exposed along a dam spillway. At Huai Sai, they excavated a 2 × 3 m area andfound 1139 fragments of a MN tektite forming a cluster
at the top boundary of the “laterite” layer. Based on thesize distribution of the tektite fragments that follows apower law, similar chemical composition of each fragment, and the fact that many fragments form a cluster,Fiske et al. (1996) concluded that the tektite fragments
originated from one large tektite mass that underwent
fragmentation.
Fiske et al. (1996) interpreted the top of the “laterite”
layer as a paleo-erosional surface based on the hardcemented appearance (of the upper surface of the “laterite” layer) that looks like an erosional pavement andinterpreted the MN tektite fragments found at the upperboundary of the “laterite” layer to have been reworkedon the paleo-erosional surface. However, the interpretation that the upper boundary of the “laterite” layer represents a paleo-erosional surface is based only on theirvisual observation of the upper surface of the “laterite”
layer in the field. Despite concluding that the tektites are
reworked, Fiske et al. (1996) noted that there was little
evidence that the tektite fragments have undergone significant lateral transport and remained clustered. Thus,
the interpretation of Fiske et al. (1996) that tektites
found at the top of the “laterite” layer are of reworked
origin does not seem to be well supported by their own
observations. Nonetheless, this point has long been overlooked and their conclusion that most tektites have beenreworked has been widely accepted. Australasian tektites

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in Australia generally are found in deposits that havebeen dated as younger in age than the impact event, andthus, these tektites are considered to be reworked (e.g.,
Fudali 1993). By analogy with the observation inAustralia, Koeberl and Glass (2000) and Keates (2000)
argued that tektites found in Indochina might also havebeen reworked, although no field evidence from SE Asia
was advanced.
In this study, we report a detailed occurrence of tektite
fragments found within the “laterite” layer at a section
designated HO06 located about 15 km southwest of Huai
Om in northeastern Thailand in order to test whether the
MN tektite fragments of similar occurrence are of primarydepositional origin or reworked. We conducted a fieldsurvey at the HO06 section and made a detailed description of the field occurrence of the MN tektite fragments.
We also measured the major element compositions ofnine MN tektite fragments by electron probe microanalysis (EPMA) to confirm that these glass fragments are Australasian MN tektites and to demonstrate that thesefragments have chemical composition similar to eachother. We restored a part of an original tektite mass usinglarge tektite fragments recovered from a block sample todemonstrate that tektite fragments forming a cluster originally formed a large MN tektite mass.

2 Study site and lithostratigraphy
The HO06 section (14° 34′ 45.2″ N 105° 16′ 30.0″ E) islocated about 15 km southwest of Huai Om, Ubon
Ratchatani Province, northeastern Thailand (Fig. 1). As
noted above, Fiske et al. (1996) reported MN tektites
from the top of the “laterite” layer at Huai Om. The
HO06 section is exposed along the spillway of reservoirs
named Huai Phueng and Phlan Suea Ton Lang (Fig. 2).
The weathered Cretaceous sedimentary basement andoverlying Quaternary deposits are exposed continuously
laterally for at least 200 m along both sides of the spillway. A cluster of Australasian MN tektite fragments wasfound in the section at the north bank. We did not findany evidence of tectonic disturbance of the basement
and the overlying Quaternary deposits.
The basement rock at the HO06 section is whitish
gray (weathered) to purplish-gray (less weathered) veryfine quartzo-feldspathic sandstone of the Cretaceous
Khok Kruat Formation, the uppermost part of the
Khorat Group (Nuchanong et al. 2014). The exposed
thickness of the basement sandstone is approximately 2
m. The basement sandstone dips approximately 10° to
the west and is exposed continuously along the spillway(Fig. 3a, b).
The Quaternary deposits overlie the Cretaceous basement unconformably and can be divided into threelithostratigraphic units (Units 1 to 3 in ascending order;
Fig. 3) that are similar to those reported at Huai Om

Tada et al. Progress in Earth and Planetary Science(2020) 7:66

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Table 1 Sites in Indochina where Australasian tektites were reported in strata
LocalityCountry Latitude

Longitude

Tektitetype

Occurrence

Reference

Phang Daenga

Thailand N 16° 48′

E 104° 24′

MN

At least 10 kg of MN tektite fragments were
found in the “laterite” layer, ~ 0.3 m below
the ground surface. Tektite fragments wereconcentrated in a small area

Barnes andPitakpaivan 1962

Nong Saponga

Thailand N 17° 12′

E 104° 42′

MN

MN tektite fragments were found in the“laterite” layer, ~ 0.7 m below the groundsurface. Tektite fragments were concentrated
in a small area

Barnes andPitakpaivan 1962

81 km west of Nakhon
SakhonaThailand N 17° 30′

E 103° 30′

MN

MN tektite fragments were found in the“laterite” layer, ~ 0.7 m below the groundsurface

Barnes andPitakpaivan 1962

Huai Sai

Thailand N 14° 53′

E 105° 25′

MN

A cluster of 1139 MN tektite fragments witha total mass of 6 kg was partly exposed at
the surface. The largest piece weighed 701.7 g.
The fragments were concentrated in 2 × 3 m
area and 30 cm in depth. These fragments werein the uppermost light gray sandy soil layer andin the upper 10 cm of the quartz pebble-bearing“laterite” layer. Most of the fragments were
found at the boundary of these two layers

Fiske et al. 1996

Huai Om

Thailand N 14° 35′

E 105° 17′

MN

Two MN tektite fragments with a total weightof 2 g were found from the top of the “laterite”
layer. 14 MN tektite fragments with a total weightof 43.5 g were in float but clearly derived fromthe immediate strata above

Fiske et al. 1996

1 km WNW of Ban E Sae

Thailand N 15° 07.0′

E 104° 07.0′

Sp

Two splash-form tektites were from the very topof the “laterite” layer

Wasson et al.
1995

400 m NNW of Ban Ta Ko

Laos

N 16° 22.336′ E106°27.595′ MN

MN tektite fragments were found in the upper
20 cm of the pebbly “laterite” layer, ~ 1 m below
the surface. 450 g of tektite fragments was foundin total from a 12 m2 area

Fiske et al. 1999

500 m N of the entranceof Muong Nong

Laos

N 16° 22.800′ E 106° 30.00′ MN

Two small MN tektite fragments were found at
the top of the pebbly “laterite” layer. Ten fragmentsof MN tektite with a total mass of 250 g were foundon the surface of a quarry

Fiske et al. 1999

7 km N of Khe Sahn

Vietnam

N 16° 40.71′

E 106° 42.33′ MN

86 MN tektite fragments with a total mass of 500 g
were concentrated in the upper 10 cm of the pebbly
quartzite clast layer

Fiske et al. 1999

~ 1 km S of Xeno

Laos

N 16° 39.6′

E 105° 00.5′

MN

Two MN tektite fragments with a total weight of 3.9 g
were found from a reddish “laterite” layer containing
scattered quartz pebbles

Schnetzler and
McHone 1996

~ 9 km S of Xeno

Laos

N 16° 35.2′

E 105° 02.3′

MN

Four MN tektite fragments with a total weight of 4.8 g
were found from a reddish “laterite” layer containing
scattered quartz pebbles

Schnetzler and
McHone 1996

~ 11 km of Xeno

Laos

N 16° 34.2′

E 105° 01.9′

MN

A MN tektite fragment with weight of 3.0 g was foundfrom a reddish “laterite” layer containing scattered quartz
pebbles

Schnetzler and
McHone 1996

Ban FangThailand N 16° 27.83′

E 102° 37.83′ Not described

One tektite is from the upper part of the “laterite” layer, ~1.2 m below the ground surface

Tamura 1992

Khon Kaen University

Thailand N 16° 28.83′

E 102° 49.91′ Not described

One tektite is from the upper part of the “laterite” layer, ~1.2 m below the ground surface

Tamura 1992

Ban Non Chai

Thailand N 16° 22.83′

E 102° 51.45′ Not described

One tektite is from the “laterite” layer, partly exposed in the Tamura 1992
ground surface

Ban SamranThailand N 16° 32.73′

E 102° 49.85′ Not described

One tektite is from the “laterite” layer, partly exposed in the Tamura 1992
ground surface

Ban Khan Kaem Khun

Thailand N 16° 40.50′

E 102° 48.33′ Not described

One tektite is from the “laterite” layer, partly exposed in the Tamura 1992
ground surface

Noen Sa-nga

Thailand N 15° 36.50′

E 101° 58.00′ Irregular shape A small piece of an irregular-shaped tektite with a weightof 8.75 g is found at the top of the “laterite” layeraApproximate site location from sketch map and name assigned from a nearby village (after Schnetzler 1992)
MN Muong Nong-type, Sp splash form

Songtham et al.
2011, 2012

Tada et al. Progress in Earth and Planetary Science(2020) 7:66

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Fig. 2 Locality map of the HO06 section. The location where we found the cluster of the MN tektite fragments is also shownsection where lithological description was reported(Tada et al. 2019). Unit 1 is a whitish-gray silty very finesand layer. The thickness of this unit is 70 cm. The basal
contact is sharp, largely horizontal, slightly undulating,and forms an angular unconformity (Fig. 3). Unit 2 is areddish-brown, poorly sorted, granule- to pebble-bearing
medium to coarse sand layer. The thickness of this unit
is 55 cm. The basal contact is sharp and generally planar.
The gravel clasts are 0.2–3 cm in diameter and are composed mainly of white quartzite pebbles and their fragments (Fig. 3e). This unit is partly cemented by reddishbrown iron oxides to form reddish black pebble size
spherical- to irregular-shaped nodules, which are coalescent to each other in some cases (Fig. S1). This observation is consistent with the descriptions of the “laterite”
layer (e.g., Songtham et al. 2011, 2012). Unit 3 is composed of whitish- to brownish-gray massive fine sand of
2 m thickness (Fig. 3d). It overlies Unit 2 with a sharp,
planar conformable contact with no evidence of erosion.
This unit is capped by ca. 20 cm thick modern soil witha gradational contact.
The MN tektite fragment cluster was found in theupper part of Unit 2 (ca. 10 cm below the upper unit
boundary) (Fig. 2, 4). The detailed occurrence of the
MN tektite fragments is described in the “Results anddiscussion” section.

3 Methods
A block sample of 25 × 15 cm area with 10 cm thickness
was taken for three-dimensional (3D) computed

tomography (CT) scanning from the area where the MN
tektite fragment cluster was found, using a handheld
electric cutter. The block sample was dismantled in thelaboratory after the CT scanning, and MN tektite fragments larger than 5 mm diameter were recovered. Aftertaking the block sample, we further recovered MN tektite fragments by gradually expanding the excavated area
until no large (> 1 cm diameter) tektite fragments were
found. In total, a ca. 40 × 30 cm area was excavated.
There is a possibility that we overlooked small (< 1 cm
diameter) tektite fragments spread further away.
The major element compositions of nine selected tektite fragments were determined by EPMA on thin sections. EPMA was conducted using a JEOL JXA-8900 L
electron probe microanalyzer at the Department of Earthand Planetary Science, the University of Tokyo. The analysis was performed using 15-kV accelerating voltage
and 7.5-nA beam current, with a defocused electron
beam of 5 μm. Counting times were 10 s on peak and 5 son the background. Analyzed elements were Si, Al, Fe,K, Mg, Ca, Na, Ti, and Mn. Sodium and potassium wereanalyzed before other elements to reduce possible
volatilization effects followed by the method of Glasset al. (2020). The precision of the EPMA was evaluatedby the analysis of the composition-known magnetite.
Based on the analysis of the magnetite that was repeated
ten times, the analytical precision was better than 0.5%
in concentration for all the elements.
Ten to twenty points were measured on each thin section. Because the total percentage of measured elements

Tada et al. Progress in Earth and Planetary Science(2020) 7:66

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Fig. 3 Field photographs and columnar section of the HO06 section. a field photograph of the section on the southern side of the spillway; bcartoon of the stratigraphy shown in a. The legend b is the same as that for c. c Columnar representation of the stratigraphy section made on
the southern side where a good exposure was observed. Note the stratigraphic position of the MN tektite fragment cluster which was found in
the upper part of Unit 2 on the northern side of the spillway. d Close photograph of Unit 3. e Close photograph of Unit 1 and Unit 2

Tada et al. Progress in Earth and Planetary Science(2020) 7:66

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Fig. 4 Field photograph of the cluster of tektite fragments within the upper part of Unit 2. a The white allows point to each fragment partly
exposed on the outcrop surface; b a wider photograph showing that the cluster of tektite fragments are ca. 10 cm below the upper
unit boundary

varies between 96 and 100 wt. %, we used data, the total
percentage of which is larger than 98%, for calculating
an average and standard deviation of major oxide composition for each thin section. After the data screening,each thin section still has ten to fifteen measured points.
The standard deviation of major oxide compositions,which is 1.3% as a maximum (Table 2), includes variation due to heterogeneity of sample and uncertainty ofmeasurement.
Consideration of the distribution of fragments sizes isoften used to infer fragmentation processes (e.g., Farrisand Paterson 2007; Bjørk et al. 2009; Roy et al. 2012).
Fragmentation due to crushing or fracturing rock or
glass leads to mass distributions that can be describedby power law functions in which fragment frequency increases with a decrease in fragment size, due to scale invariance of the fragmentation process (e.g., Turcotte1986). The relationship between fragment size and cumulative frequency can be represented by the power law
equationN ð ≥ rÞ ¼ kr − Dsð1Þ

where r is a radius of a fragment, N (≥ r) is the numberof fragments with a radius greater than r, and k is a fitting parameter. Ds is the fractal dimension for fragment
size distribution.
The size and weight of each fragment was recorded in
the laboratory. We measured the long, intermediate, andshort axes (a, b, and c axes) defined as the dimensions ofa fragment in three mutually orthogonal planes (a > b >c). The dimensions were measured using a caliper withan accuracy of 0.05 mm.

The block sample was subjected to X-ray CT imaging
using micro-CT scanner TESCO TXS320-ACTIS at the
National Museum of Nature and Science, Tokyo. Each
MN tektite fragment was separated using the segmentation editor in Amira 5.4.3 software based on the contrastof X-ray transmittance between tektite fragments andsurrounding matrix. Because smaller tektite fragments
are more difficult to recognize on CT images, we identified tektite fragments larger than 1 cm. The identification of the tektite fragments in the CT images was
confirmed by comparing each fragment to the tektite
fragments collected from the dismantled block sample.
In this study, only the preliminary result of observationof CT images is presented.

4 Results and discussion
4.1 Description of the MN tektite fragments

The MN tektite fragments found at the HO06 section
are black in color, vesicular, and show submillimeterscale layering (Fig. 5). Under an optical microscope, thinsections of the fragments show layering composed of thedark-brownish–colored and light greenish-colored glass
stripes, which are parallel to each other. Each stripe has
10-μm scale subparallel lamination characterized by alternation of dark-brownish and pale greenish lenses.
Elongated vesicles of submillimeter size, the long axes ofwhich are roughly parallel to the layering, are occasionally observed (Fig. 6). Mineral inclusions which are several micrometers in diameter are sparsely contained, butthey are too small to identify mineral species under an
optical microscope. These characteristics are typical for
MN Australasian tektites found in Indochina (e.g., Wasson 1991; Glass et al. 2020).

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Table 2 Major element compositions of the MN tektite fragments from the HO06 section
SampleSiO2 (1σ)

Al2O3
(1σ)

MgO
(1σ)

FeO (1σ) CaO (1σ) Na2O
(1σ)

HO06MN16

79.29(1.30)

9.64 (0.62)

1.25(0.14)

3.63(0.29)

1.10(0.15)

1.01 (0.07) 2.27
(0.10)

0.09(0.06)

0.56(0.08)

98.84 (0.53)

HO06MN7978.52(2.90)

10.29(1.76)

1.46(0.31)

3.70(0.58)

1.00(0.19)

1.03 (0.14) 2.27
(0.09)

0.08(0.05)

0.62(0.08)

98.97 (0.62)

HO06MN105

79.56(1.25)

9.72 (0.85)

1.37(0.18)

3.61(0.32)

0.89(0.14)

0.96 (0.12) 2.30
(0.13)

0.07(0.05)

0.61(0.06)

99.11 (0.45)

HO06MN119

80.18(1.27)

9.19 (0.93)

1.20(0.13)

3.45(0.40)

1.21(0.08)

0.97 (0.08) 2.13
(0.14)

0.09(0.06)

0.58(0.05)

99.01 (0.59)

HO06MN121

79.46(1.02)

9.86 (0.74)

1.37(0.10)

3.58(0.20)

1.14(0.07)

0.92 (0.06) 2.34
(0.08)

0.11(0.07)

0.58(0.04)

99.36 (0.53)

HO06MN122

79.6 (1.07)

9.46 (0.64)

1.33(0.09)

3.44(0.32)

1.17(0.13)

0.98 (0.06) 2.17
(0.19)

0.10(0.07)

0.55(0.07)

98.85 (0.51)

HO06MN12479.54(0.80)

9.59 (0.60)

1.14(0.09)

3.48(0.29)

0.80(0.04)

1.03 (0.05) 2.27
(0.11)

0.10(0.06)

0.56(0.08)

98.51 (0.43)

HO06MN129

79.36(1.13)

9.61 (0.56)

1.22(0.19)

3.50(0.38)

1.19(0.09)

1.00 (0.05) 2.31
(0.10)

0.11(0.07)

0.57(0.06)

98.86 (0.57)

HO06MN141

79.17(1.33)

9.87 (0.90)

1.22(0.16)

3.52(0.28)

0.86(0.10)

0.98 (0.07) 2.32
(0.05)

0.10(0.04)

0.63(0.07)

98.69 (0.25)

Average

79.41(0.42)

9.69 (0.29)

1.29(0.10)

3.55(0.09)

1.04(0.15)

0.99 (0.03) 2.27
(0.07)

0.10(0.01)

0.58(0.03)

98.91 (0.23)

Koeberl 1992 (n = 19)

78.95(1.52)

10.19(0.98)

1.43(0.13)

3.75(0.35)

1.21(0.15)

0.92 (0.09) 2.42
(0.10)

0.08(0.01)

0.63(0.05)

99.59 (0.25)

Fiske et al. 1996 (n = 3)79.83
(0.15)

9.11 (0.15)

1.51(0.03)

3.39(0.04)

1.46(0.03)

1.52 (0.04) 2.27
(0.02)

0.09(0.00)

0.61(0.01)

99.78 (0.24)

Herzog et al. 2008 (n = 2)78.56
(0.35)

11.02(0.19)

1.71(0.01)

4.10(0.06)

1.65(0.01)

0.80 (0.03) 2.45
(0.01)

0.07(0.03)

0.70(0.01)

101.05(0.06)

Glass and Koeberl 1989 (n =
1)

79.2

10.3

1.41

3.76

1.09

0.87

0.09

0.62

99.78

Three-hundred and thirty-one MN tektite fragments
were found in the small (~ 40 cm × 30 cm) area with 10
cm in thickness in the upper part of Unit 2 (Fig. 4)(One-hundred and seventy-seven fragments were recovered in the field after taking the block sample, and 154
fragments were recovered in the laboratory from the dismantled block sample.) The total weight of the 331 fragments is 713 g.
The length of a, b, and c axes of the fragments ranges
from 2.00 to 52.80 mm, 1.95 to 40.00 mm, and 0.70 to
30.80 mm, respectively. The average length and standard
deviation (in parenthesis) are 16.3 (8.7), 11.3 (7.1), and7.2 (5.5) mm, respectively. These large standard deviations of the size of the tektite fragments correspond to“very poor sorting” in the scale of sorting for sediments(Folk and Ward 1957). The fragments are very angular,
and fragile edges are well preserved, as shown in Fig. 5.
Forty-six large fragments recovered from inside theblock sample and seven large fragments recovered in thefield after taking the block sample (53 tektite fragments
in total) are fitted together to form a large MN tektite
mass of ~ 370 g that shows an ellipsoidal shape (Fig. 7a).
The rest of the fragments are too small and so many that

K2O (1σ) MnO
(1σ)

2.44

TiO2 (1σ) Total (1σ)

it is difficult to find their positions to conduct restoration of the original tektite mass. However, the preliminary restoration result strongly suggests that tektite
fragments forming the cluster composed one large tektite mass of > 713 g weight before the landing. The majority of the outermost part of the restored tektite mass
was peeled off showing the section of the internal layered structure (Fig. 7b), while a typical pitted andgrooved surface similar to that in splash-form tektites
was preserved in some part (Fig. 7c) suggesting the original surface of the tektite mass was preserved. The fracture surfaces of the MN tektite fragments from HO06
are matt compared to a fresh fracture surface due to thepresence of small pits, as shown in Fig. 7d. These mattsurfaces of the tektites were formed by soil etching after
their burial (Rost 1969; La Marche et al. 1984), suggesting that fracturing occurred in the geological past.
Nearly all fragments have iron-oxide cement and calcite
cement in some cases adhering to some of the fragment
surfaces, and some vesicles open to the surface are filledwith the iron-oxide and calcite cement materials indicating that the laterization of Unit 2 occurred after theirfragmentation.

Tada et al. Progress in Earth and Planetary Science(2020) 7:66

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Fig. 5 Photographs taken of differing orientations of examples of the tektite fragments recovered from HO06 section. a Sample HO06MN34. b
Sample HO06MN79. c Sample HO06MN32_a and 32_b. The MN tektite fragments are black vesicular glass showing layering structure and haveangular shapes with fragile edges

Fig. 6 Thin section photographs of sample HO06MN12 (the contrast of the photographs is enhanced). The layering texture is composed of thedark- and light-colored glass lenses, and the elongated vesicles are shown. a Lower magnification view showing submillimeter-scale alteration ofdark and light stripes. b Higher magnification view of the same section in a

Tada et al. Progress in Earth and Planetary Science(2020) 7:66

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Fig. 7 The photographs taken of differing orientations of the restored tektite mass. b Photograph of a part of the surface which was peeled off
showing the section of the internal layered structure cut by low angle. c Photograph of a part of the surface which is considered as thepreserved original surface of the tektite mass showing a typical pitted and grooved surface. d Photograph of the fracture surface of the MN
tektite fragment, which is matt due to the presence of small pits

The fact that most of large tektite fragments recoveredfrom the block sample fitted together to form a large ellipsoidal tektite mass with the original surface partly preserved indicates the tektite fragments were formed as aresult of the fragmentation of one large tektite mass.
The very poorly sorted nature of the MN tektite fragments, the very angular shapes with well-preserved fragile edges, and the occurrence of tektite fragments
forming a cluster suggest that these MN tektite fragments were not transported a long distance but rather
fragmented in situ.
4.2 Major element composition

The major element compositions of all nine MN tektite
fragments from the HO06 section, together with their average compositions and standard deviations, are given in
Table 2. The major element compositions of these samples

fall within the range of compositions of previous analysesof MN tektites from Ubon Ratchathani province within 1σ,
for most elements (Glass and Koeberl 1989; Koeberl 1992;
Fiske et al. 1996; Herzog et al. 2008) (Fig. 8a), indicatingthat they are not distinguishable chemically from previously
reported Australasian MN tektites from Ubon Ratchathani
province.
Figure 8b shows SiO2 vs Al2O3, FeO, K2O, and MgOvalues for the nine MN tektite fragments from theHO06 section plotted with values reported for other
Australasian MN tektites from Ubon Ratchatani province ( Glass and Koeberl 1989; Koeberl 1992; Fiske et al.
1996; Herzog et al. 2008). The major element composition of the nine fragments is closely plotted in a narrow
area and indistinguishable from each other within 1σ.
This narrow range of the major element composition of
the nine fragments is consistent with the idea that theTada et al. Progress in Earth and Planetary ScienceFig. 8 (See legend on next page.)(2020) 7:66

Page 11 of 15

Tada et al. Progress in Earth and Planetary Science(2020) 7:66

Page 12 of 15(See figure on previous page.)
Fig. 8 Major element compositions of the MN tektite fragments from the HO06 section. a Comparison of the major element compositions of the
MN tektite fragments from the HO06 section and the average of other MN tektites from the same region, Ubon Ratchathani province, previously
reported. b X–Y plots of the concentrations of SiO2 versus Al2O3, FeO, K2O, and MgO of the MN tektite fragments from the HO06 section
compared with other MN tektites from the same region, Ubon Ratchathani province, previously reported by Koeberl (1992), Fiske et al. (1996),
Herzog et al. (2008), and Glass and Koeberl (1989). The error bars represent 1σ of ten to fifteen measurements of each section

MN tektite fragments collected at HO06 section originally formed one large MN tektite mass.

4.3 Size distribution of the MN tektite fragments

Ds for the fragments generated by fragmentation ofrocks or glass is proportional to the intensity of fracturing in which fragments generated by higher magnitude
and rate of stress loading tend to have higher value ofDs, although Ds is affected also by the inherent strength
properties of the rock or glass (e.g., Takagi et al. 1984;
Jébrak 1997; Roy et al. 2012; Xu 2018). For instance, Ds
for rock fragments generated by weathering of andesite
in the field and hammering of a limestone cube by handis 2.5–2.7 (calculated from the data of Domokos et al.
2015), and that for rock fragments generated by rockfalls
and rock avalanches with various lithology ranges from
1.6 to 4.7 (Crosta et al. 2007; Ruiz-Carulla and Corominas, 2020). Rock fragments generated by complete fragmentation of target rocks in hypervelocity impact
experiments show bi- or tri-fractal distributions in which
Ds for the finer fraction is 1.7 to 4.3 and Ds for thecoarser fraction is 4.8 to 11.9 (calculated from the dataof Takagi et al. 1984; Michikami et al. 2016). The Ds forfragments of a block on the Moon fragmented by a small
meteorite impact is around or higher than 4 (Ruesch
et al. 2020).
Figure 9 shows the cumulative size distribution of the
MN tektite fragments at HO06 section. The size of thefragment is represented by the length of its equivalentpﬃﬃﬃﬃﬃﬃﬃ
spherical diameter (r = 3 abc ). The cumulative size dis-tribution increases rapidly from 37 to 26 mm and thenincreases slowly in a range smaller than 26 mm. It showsa bi-fractal distribution described by two power laws in
the range from 10 to 26 mm and from 26 to 37 mm,with Ds of 2.2 and 7.5, respectively. The position of thepoint dividing the two power laws is calculated byadjusting the dividing point every 0.5 cm to maximize
the average of the R2 values. The bi-fractal distributionof fragment size implies that the size distribution of thefragments was affected by two different fragmentation
mechanisms (e.g., Schultz and Gault 1990). Although theeffect of the difference of physical properties between
the tektite glass and rocks need to be considered, thehigh Ds value (7.5) for the coarse fraction of the tektite
fragments is larger than the range of Ds previously reported for rock fragments generated by rockfalls androck avalanches (1.6–4.7; Crosta et al. 2007; RuizCarulla and Corominas 2020) and similar to the Ds forthe coarser fraction fragments generated by hyperspeed
impact experiments (4.8–11.9; calculated from the dataof Takagi et al. 1984; Michikami et al. 2016) and impact
fragmentation on the Moon (3.3–6; Ruesch et al. 2020),
suggesting that the tektite fragments were formed
through intense fragmentation by a relatively high energetic process.
Based on the close spatial association of the MN tektite fragments at Huai Sai, Fiske et al. (1996) proposedthat the fragmentation of an original MN tektite mass
was a low-energy process such as weather or climaterelated temperature-induced fracturing after the deposition of the MN tektite mass. However, as is mentioned

Fig. 9 Cumulative size distribution of the MN tektite fragments from the HO06 section for size range of r > 10 mm

Tada et al. Progress in Earth and Planetary Science(2020) 7:66

above, the size distribution of the coarse fraction of the
MN tektite fragments from HO06 section measured inthis study suggests a relatively high-energy process rather than a low-energy process such as weather or
climate-related temperature-induced fracturing. The
possibility that the MN tektite mass was broken by tectonic movement after deposition is also unlikely because
we did not see any evidence of tectonic deformation at
the outcrop. The other possibility is that the fragmentation occurred during the flight by high-speed collision ofejecta materials before the deposition. However, thispossibility is also unlikely because if the fragmentation
occurred during the flight, the fragments would haveseparated before they landed on the ground and would
not have formed a cluster. Consequently, the timing of
the fragmentation of the MN tektite mass is constrained
to the time of the landing on the ground. We proposethat an original tektite mass was fragmented by collisionof the MN tektite mass with the ground. Either the MN
tektite fragments were considered to have been codeposited with other ejecta materials immediately after(or almost the same time) the fragmentation or the MN
tektite mass was fragmented during penetration into theunconsolidated ejecta of Unit 2 so that the fragments
remained as a cluster.
As for the fragmentation mechanism for the finer fraction of the MN tektite fragments, one possibility is thatsome of the tektite fragments were further fractured byweather or climate-related thermal fracturing after thedeposition. Another possibility is that some of the tektite
fragments generated by the collision of the original tektite mass with the ground surface were secondarily fractured by collision with the surrounding other ejecta
materials immediately after the first fragmentation,
resulting in the bi-fractal size distribution of the tektite
fragments. In any case, the whole size distribution of thetektite fragments, especially the high Ds value for thecoarse fraction, is different from the size distributions ofrock fragments generated by low-energy processes.
4.4 Preliminary observation of CT scan 3D image of theblock sample

In CT cross-section images, tektite fragments appear as
angular-shaped areas with moderate X-ray transmittance, exhibiting elongated vesicles. The preliminary CT
scan 3D image observation of the block sample revealed
that the MN tektite fragments are distributed in 20 × 10
× 10 cm space as if they were expanded from the originaltektite mass by fragmentation. This distribution of thetektite fragments suggests either that the tektite fragments were buried immediately after fragmentation on
landing by co-deposited other ejecta materials of Unit 2or that fragmentation occurred during the tektite mass
penetrated into the ground cover of unconsolidated

Page 13 of 15

ejecta (granule to pebble-bearing sand) of Unit 2 so thattektite fragments have not been spread significantly. This
distribution of the tektite fragments is inconsistent withthe previous interpretation in which these tektites wereconsidered to have been reworked on the paleo surface
because if reworked on the paleo surface, the fragments
would be distributed on a plane.
4.5 Stratigraphic position of MN Australasian tektite inIndochina

As is proposed in the previous sections, the fragmentation of the MN tektite mass occurred at the time of thelanding on the ground, and either the fragments wereburied immediately with other ejecta materials or thetektite mass penetrated into the ground covered by unconsolidated ejecta deposit and fragmented within theejecta. In either case, the fragments were preserved as acluster. Thus, the MN tektite fragments in the upper
part of Unit 2 (“laterite” layer) at the HO06 section are
considered as in primary position.
Fiske et al. (1996) considered that layered tektites foundat the top of Unit 2 at the Huai Om and Huai Sai sections
to be reworked because, in their opinion, the top of Unit 2
represents a paleo-erosional surface. However, the factthat MN tektite fragments are found not at the top of the“laterite” layer but within the “laterite” layer at the HO06
section does not support this interpretation. Also, there
was no evidence of erosion at the top of Unit 2 at the
nearby Huai Om section (Tada et al. 2019) as well as several other sections in the region. Furthermore, our fieldobservation of the “laterite” layer in other localities (for example, an active sand pit at Noen Sa-nga in Chaiyaphum
province) suggests that laterization (precipitation of ironhydroxides) of this layer can occur within a few years afterroad cuts and pit walls were formed, indicating that thehard-cemented appearance of the “laterite” layer was notformed as an erosional pavement before the impact, butformed on the outcrop surface by recent ferricretization(Fig. S2). Koeberl and Glass (2000) and Keates (2000)
pointed out that the Australasian tektites in Australia generally are found in deposits younger than the age of the
impact, and interpreted by analogy that the tektites in
Indochina may be of similar reworked origin. However,this analogy is not based on observational evidence. It
should also be considered that dating of Quaternary sediments in Indochina is replete with methodological difficulties that may result in young ages being reported forstrata that are considerably older (Carling et al. 2020).
The in situ occurrence of the MN tektite fragments in
Unit 2 at the HO06 section supports the idea that the
Quaternary depositional sequence of Units 1–3 in thisregion is an ejecta deposit of the Australasian tektite
event based on the finding of shocked quartz from Units
1–3 at Huai Om section (Tada et al. 2019). The fact that

Tada et al. Progress in Earth and Planetary Science(2020) 7:66

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both the MN and splash-form tektites generally were
found in the upper part of or at the top of the “laterite”
layer at sites in the wide area of eastern Indochina(Table 1, Fig. 1) further supports the idea that theAustralasian tektites found from the “laterite” layer were
deposited in situ as an ejecta.

Authors’ contributions
PAC, RT, and TT designed the study and planned the field survey. TT, RT,
PAC, WS, and PC conducted the field survey. PC found the cluster of thetektite fragments in the field. TT, PC, and RT took the samples, and TT
conducted all the measurements. ET helped in interpreting the data andrevising the manuscript. TT drew the figures and tables and wrote a draft ofthe manuscript. RT, ET, and PAC supervised TT. The authors read andapproved the final manuscript.

5 Conclusions
We described in detail the occurrence of a cluster of MN
tektite fragments found at the HO06 section, Ubon Ratchathani province, northeastern Thailand. At least 331 fragments of MN tektite with a total weight of 713 g wereconcentrated in a small (40 × 30 cm) area within the upper
part of a sandy gravel layer corresponding to the “laterite”
layer. The occurrence as a cluster, the very angular shapes
and the very poorly sorted nature of the fragments, the restoration of larger tektite fragments into one ellipsoidal MN
tektite mass, and the similar chemical composition of thefragments suggest that these MN tektite fragments were
not transported in long distances but rather fragmented insitu at the landing from a ballistic trajectory. This conclusion is contrary to the previous interpretation that similar
tektite fragments were reworked on the upper surface of
the “laterite” layer which was interpreted as the paleoerosional surface (Fiske et al. 1996).
The size distribution of the MN tektite fragments is bifractal following two power laws in the range from 10 to
26 mm and from 26 to 37 mm in r, respectively, with Dsof 2.2 and 7.5. The high Ds value for the coarse fraction of
the tektite fragments is larger than the range of Ds previously reported for rock fragments generated by rockfalls
and rock avalanches and similar to Ds for the coarser fraction fragments generated by hyperspeed impact experiments, suggesting that the tektite fragments were formed
through intense fragmentation by a relatively high energetic process at the landing on the ground.

Funding
This study was supported by the Japan Society for the Promotion of Science(JSPS) KAKENHI Fostering Joint International Research (B) 18KK0092 (20182021) to R. Tada, and the Fujiwara Natural History Foundation Grant in 2016
and Grant-in-aid for JSPS Research Fellow Number 19 J13252 awarded to T.
Tada. P. A. Carling held a Leverhulme Emeritus Fellowship (2016–2018) which
directly supported the project.

6 Supplementary information
Supplementary information accompanies this paper at https://doi.org/10.
1186/s40645-020-00378-4.
Additional file 1:. Supplementary Information.

Abbreviations
AATE: Australasian Tektite Event; 3D: Three dimensions; CT: Computed
tomography; MN: Muong Nong-type; EPMA: Electron probe microanalysis;
Ds: Fractal dimension; r: equivalent spherical diameter
Acknowledgments
We sincerely thank Pratueng Jintasakul, the director of Khorat Fossil Museum,and Pakkaporn Singhwachiraworakul for their hospitality during the fieldsurvey. We would also like to thank Hideto Yoshida for his help in theelectron microprobe analyses. We are much obliged to Chisako Sakata andManabe Makoto for conducting the CT scanning of the block sample. We
are grateful to Takanobu Tsuihiji, Seisiro Tada, Ayano Mizukami, Noriyuki
Wakimizu, Kazuko Yoshizawa, and Hirochika Ueda for their kind help on theanalysis of the CT scan images.

Availability of data and materials
The datasets used and/or analyzed during the current study are available
from the corresponding author on request.
Competing interests
The authors declare that they have no competing interests.
Author details
Department of Earth and Planetary Science, The University of Tokyo, 7-3-1
Hongo, Bunkyo-Ku, Tokyo 113-0033, Japan. 2Institute for Geo-Cosmology,
Chiba Institute of Technology, 2-17-1 Tsudanuma, Narashino, Chiba 275-0016,
Japan. 3Research Center for Earth System Science, Yunnan University,
Chenggong District, Kunming 650500, PR China. 4Northeastern ResearchInstitute of Petrified Wood & Mineral Resources, Nakhon Ratchasima Rajabhat
University, Baan Kroke Duen Ha, Suranaree Sub-district, Muang Nakhon
Ratchasima District, Nakhon Ratchasima 30000, Thailand. 5School of
Geography and Environmental Science, University of Southampton,
University Road, Southampton SO17 1BJ, UK.
1

Received: 6 July 2020 Accepted: 29 September 2020

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