Journal of Asian Earth Sciences xxx (2012) xxx–xxx

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Journal of Asian Earth Sciences

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Basaltic activity preserved in an Upper Permian radiolarian chert from thePaleo-Tethys in the Inthanon Zone, northern Thailand

Yoshihito Kamata a,⇑, Ayako Maezawa a, Hidetoshi Hara b, Katsumi Ueno c, Ken-ichiro Hisada d,Apsorn Sardsud e, Thasinee Charoentitirat f, Punya Charusiri f

a Department of Earth Sciences, Graduate School of Science and Engineering, Yamaguchi University, Yamaguchi 753-8512, Japanb Geological Survey of Japan, AIST, 1-1-1 Higashi, Tsukuba, Ibaraki 305-8567, Japanc Department of Earth System Science, Faculty of Science, Fukuoka University, Fukuoka 814-0180, Japand Graduate School of Life and Environmental Sciences, University of Tsukuba, Ibaraki 305-8572, Japane Bureau of Geological Survey, DMR, Bangkok 10400, Thailandf Department of Geology, Faculty of Science, Chulalongkorn University, Bangkok 10330, Thailand

a r t i c l e i n f o

Article history:Available online xxxx

Keywords:Basaltic activityChertGeochemistryInthanon ZoneLate PermianPaleo-TethysRadiolaria

1367-9120/$ - see front matter � 2012 Elsevier Ltd. Ahttp://dx.doi.org/10.1016/j.jseaes.2012.08.007

⇑ Corresponding author. Address: Graduate SchooSciences, University of Tsukuba, Tennodai 1-1-1, TsukTel.: +81 29 853 4302; fax: +81 29 853 7887.

E-mail address: yoshi_kamata@geol.tsukuba.ac.jp

Please cite this article in press as: Kamata, Y., etZone, northern Thailand. Journal of Asian Earth

a b s t r a c t

Basaltic sandstone composed mainly of clay- to sand-sized fragments of glass and basaltic rock has beendiscovered in a pelagic chert sequence in northern Thailand. The sandstone conformably underlies and ispartly intercalated with the Upper Permian (Wuchiapingian-early Changhsingian) radiolarian-bearingchert. Geological age dating based on radiolarians, petrographic examination of the bedded chert withthe basaltic sandstone, and geochemical studies were conducted to investigate the origin and sedimen-tary mode of the lithologic sequence. The bedded chert overlying the basaltic sandstone yielded LatePermian radiolarians and was correlatable with the Wuchiapingian Follicucullus charveti–Albaillellayamakitai assemblage zone as well as the early Changhsingian Neoalbaillella ornithoformis assemblagezone. Lithofacies and microfacies of the bedded chert indicated deposition in a pelagic realm of thePaleo-Tethys. Although the tectonic setting was difficult to estimate based on geochemical featuresbecause of element mobility and alteration, the basaltic fragments likely originated as oceanic basalt suchas oceanic island basalt. Microfacies and sedimentary structures of the chert and sandstone indicated thatthe studied sequence is composed of intermittent high sedimentation rates, mainly gravity currents ofbasaltic fragments, in a background setting of very slowly accumulating radiolarian chert. The sedimen-tary mode of the sequence, the rare terrigenous influx, and the presence of fusulinoidean or other fora-miniferal tests indicate that the basaltic rocks fragment were originally sourced from an oceanictopographic high such as a seamount or an oceanic plateau, and that the volcanic activity occurred inthe chert-accumulated oceanic basin of the Paleo-Tethys in the Wuchiapingian.

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1. Introduction The Fang chert has mainly been studied from the viewpoint of

The Paleo-Tethys existed between the Indochina and Sibumasucontinental blocks from the Middle Devonian to the Middle Triassicand was the source of various kinds of oceanic rocks such as basalt,limestone, and radiolarian chert. The Chiang Mai and Chiang Daoareas in northern Thailand have distributions of pelagic Carbonifer-ous–Permian seamount-type carbonates with a basaltic basement(the Doi Chiang Dao Limestone) and Middle Devonian–MiddleTriassic radiolarian chert (the Fang Chert) (e.g., Ueno and Charoen-titirat, 2011).

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l of Life and Environmentaluba, Ibaraki 305-8572, Japan.

(Y. Kamata).

al. Basaltic activity preserved inSciences (2012), http://dx.doi.o

radiolarian biostratigraphy and the depositional age has been esti-mated to be Middle Devonian to Middle Triassic (e.g., Caridroitet al., 1992; Sashida and Igo, 1999; Wonganan and Caridroit,2005). Recently, Hara et al. (2010) reclassified the Devonian to Car-boniferous siliceous ‘‘Fang chert’’ into an ascending sequence ofblack shale, siliceous shale, tuffaceous chert, tuff, and chert. Theyproposed that this lithological transition represented the migrationof the depositional setting from a small, closed anoxic-suboxic ba-sin at the continental margin to a broad pelagic oceanic settingthrough an area influenced by volcanic activity due to the openingof the Paleo-Tethys.

Ocean plate stratigraphy (OPS) demonstrates the history of anocean plate from creation at the mid-ocean ridge to destructionthrough subduction at an oceanic trench, with the successive for-mation of an accretionary prism by the accretion of oceanic rocks.A portion of the Paleo-Tethyan OPS has been reported (Wakita and

an Upper Permian radiolarian chert from the Paleo-Tethys in the Inthanonrg/10.1016/j.jseaes.2012.08.007

2 Y. Kamata et al. / Journal of Asian Earth Sciences xxx (2012) xxx–xxx

Metcalfe, 2005), but a more detailed description of lithologicalchanges caused by the environmental transition during migrationof the oceanic basin is required. Reconstruction of the entire Mid-dle Devonian to Middle Triassic Paleo-Tethyan OPS must be under-taken within the context of other reconstructed OPSs, especiallythose of Japanese accretionary prisms (e.g., Wakita and Metcalfe,2005). The lithological change from siliceous shale to coarse clas-tics including shale and sandstone has been interpreted to indicatethe ocean plate reaching the oceanic trench where it was suppliedwith coarse-grained siliciclastics from a terrestrial source. Innorthern Thailand, determining the age of these coarse siliciclasticsand a detailed reconstruction of the upper part of the OPS has notyet been done. The stratigraphic details of the bedded chert andbasaltic rocks that formed the oceanic basement are also unknown.Detailed reconstruction, such as age determination of lithologictransition from siliceous sediments to coarse clastics and terminalsedimentation of coarse clastics will be provide us geologic ages ofreaching to trench and subduction of the oceanic plate at thetrench in details. On the other hand, OPS represent transition ofthe sedimentary environments. For example, not only lithologicfeature of chert that consisting of microcrystalline quartz with nocoarse terrigenous grains but also long and continuous time dura-tion of chert sedimentation indicate presence the huge paleo-ocean including remote ocean basin where free from terrigenousinflux.

Recently, we discovered a conformable lithologic relationshipbetween radiolarian-bearing chert and basaltic sandstone layersfrom the Inthanon Zone in northern Thailand. Determination ofthe origin and stratigraphy of the basaltic sandstone may providevaluable information for understanding environment surroundingsof chert-accumulating basin and sedimentary environment of thebedded chert in this area. Basaltic sandstone intercalating withUpper Permian indicates that the volcanic activity at the Paleo-Thethys ocean around the late Capitanian to early Wuchiapingian.We describe the stratigraphy and lithology and preliminarily dis-cuss the origin of the basaltic sandstone layers together with thesedimentary environments of the sandstone and the overlyingradiolarian chert.

2. Geological setting

Mainland Thailand is widely considered to consist of two prin-cipal continental blocks: Sibumasu in the west and Indochina inthe east. The Sibumasu Block, one of the Cimmerian continents,had a dynamic history of rift-drift-amalgamation during the LatePaleozoic to Mesozoic (e.g., Metcalfe, 1999, 2000). The SibumasuBlock was originally located at the northern margin of Gondwana-land until the Early Permian. With rifting during the latest Paleo-zoic to the Early Mesozoic, the block drifted northward acrossthe Paleo-Tethys and ultimately collided and amalgamated withthe Indochina Block (Cathaysian continent) in the Late Triassic(Metcalfe, 1999, 2000).

Recent advances in foraminiferan and radiolarian biostratigra-phy have made it possible to establish new geotectonic subdivi-sions in northern Thailand. Ueno (1999, 2002) proposed a newgeotectonic scheme and correlated northern Thailand and the wes-tern Yunnan area of south China. According to this new scheme,northern Thailand is divided into four geotectonic units from westto east: the Sibumasu Block, the Inthanon Zone, the SukhothaiZone, and the Indochina Block (Fig. 1A).

The Sibumasu Block stratigraphy parallels that of Gondwana,including a Lower Carboniferous hiatus, Upper Carboniferous toLower Permian diamictites with Gondwana-related fauna and flora,and Middle-Upper Permian Platform carbonates (Metcalfe, 1988).

Please cite this article in press as: Kamata, Y., et al. Basaltic activity preserved inZone, northern Thailand. Journal of Asian Earth Sciences (2012), http://dx.doi.o

The Inthanon Zone in northern Thailand was originally pro-posed by Barr and Macdonald (1991) and is characterized by thedistribution of pelagic Carboniferous–Permian seamount-type car-bonates with a basaltic basement (the Doi Chiang Dao Limestone)and Middle Devonian–Middle Triassic radiolarian chert (the FangChert). This zone was redefined as the closed remnant of the mainPaleo-Tethys in northern Thailand by Ueno (1999), and thedefinition of this zone has been successively modified to includethe pre-Devonian basements such as the Cambrian sandstoneand Ordovician limestone overlain by the Paleo-Tethyan rocks(Ueno, 2002). Researchers have also reported that the Paleo-Tethysoceanic rocks in the Inthanon Zone have been displaced from theeast and emplaced on these pre-Devonian basements (i.e., amarginal part of the Sibumasu Block as tectonic nappes) (Caridroitet al., 1992; Ueno, 2002).

Ueno’s (1999, 2002) Sukhothai Zone is approximately equiva-lent to the Sukhothai Zone of Barr and Macdonald (1991) and theSukhothai Fold Belt of Bunopas (1981) and is mainly composedof deformed Paleozoic to Mesozoic sedimentary rock, volcanicrock, and Triassic granitoids of I-type affinity. The lithologies indi-cate a subduction-related tectonic setting, with the zone consid-ered to be a volcanic arc developed along the margin of theIndochina Block.

The Indochina Block is a part of the South China or IndochinaSuperterrane (Metcalfe, 2000, 2006) and has remained within thepaleo-equatorial region since its Early Devonian breakaway fromGondwana. In eastern Thailand, Upper Paleozoic shallow-marinecarbonates containing highly diversified Tethyan faunas arewidely distributed along the western margin of the IndochinaBlock.

Our study area north of Chiang Dao in uppermost northernThailand (Fig. 1B) is included in the Inthanon Zone and is charac-terized by Paleo-Tethyan seamount-type carbonates (the DoiChiang Dao Limestone) and Middle Devonian to Middle Triassicradiolarian chert (the Fang Chert).

Clastic rocks including sandstone and shale occur in associationwith the Paleo-Tethyan oceanic rocks. Sandstones are partlysheared and disrupted into lens-shaped blocks, whereas shearedshale with scaly cleavage occurs as a chaotic mélange matrix, asdescribed in detail by Hara et al. (2009), who discussed the forma-tive conditions and kinematics of this mélange related to Paleo-Tethyan subduction.

The seamount-type carbonates accumulated under pelagic con-ditions without any input of terrigenous material (Ueno and Igo,1997; Ueno, 1999; Ueno et al., 2008; Ueno et al., 2011). Fusulinoi-dean and other foraminiferal faunas are tropical Tethyan-typeranging from Carboniferous to Permian age, indicating a long dura-tion of deposition (Ueno et al., 2008; Ueno and Charoentitirat,2011). The Paleo-Tethyan carbonate in the Inthanon Zone usuallyoccurs as karst towers.

Radiolarian chert distributed in the Inthanon Zone of northernThailand is characterized by densely packed radiolarians in amicrocrystalline quartz matrix, with no terrigenous materials.The chert generally contains only siliceous fossils of radiolariansand sponge spicules, although some samples also yield conodonts(Kamata et al., 2009). The deposition of the chert occurred from theMiddle Devonian to the Middle Triassic (Caridroit et al., 1992;Sashida et al., 1993; Sashida and Igo, 1999; Wonganan andCaridroit, 2005; Feng et al., 2005; Thassasnapak et al., 2010),although Late Carboniferous to earliest Permian radiolarians arenot well documented. As mentioned above, Hara et al. (2010)described the Devonian to Carboniferous chert in particular anddiscussed the depositional setting as related to the opening ofthe Paleo-Tethys.

an Upper Permian radiolarian chert from the Paleo-Tethys in the Inthanonrg/10.1016/j.jseaes.2012.08.007

A B

Fig. 1. (A) Outline map showing the tectonic subdivisions of mainland Thailand and (B) index map of the Chiang Dao area, northern Thailand, showing the study sectionlocation.

Y. Kamata et al. / Journal of Asian Earth Sciences xxx (2012) xxx–xxx 3

3. Lithologic description of the basaltic sandstone and beddedchert

The study section is located about 40 km northwest of ChiangDao in Chiang Mai Province, northern Thailand (Fig. 1B). In thisoutcrop, chert that is about 10 m thick is exposed along a roadcut and stratigraphically overlies basaltic sandstone layers thatare about 3 m thick (Fig. 2A). Dip and strike of bedding planes ofthe both rock units are concordant and bedded chert rests con-formably on the basaltic sandstone unit (Fig. 2B).

The basaltic sandstone layers underlying the chert range from afew centimeters to 10 cm in thickness, are greenish (fresh) or lightbrownish yellow (weathered) in color, and commonly show gradedbedding (Fig. 2C and D). Microscopically, the basaltic sandstone iscomposed mainly of sand-sized fragments of glasses and basalticrocks (g and b.f. in Fig. 2E). These glasses and basaltic grains are ce-mented by a chlorite matrix (chl. in Fig. 2E). Glass grains arebrownish in color and are characterized by an irregular and cus-pate shape (Fig. 2E). Basaltic rock fragments show intersertal tex-ture, composed of thin and fine laths of plagioclase and darkopaque matrix (Fig. 2E).

The chert is gray to bluish gray in color and well bedded, rang-ing from a few centimeters to 10 cm in thickness (Fig. 2F). Chertsuccession has some minor slip surface (represented as [F] incolumnar of Fig. 5) and mesoscopic fold is presents. But radiolarianoccurrence shown in Fig. 5 indicates that there is no significantstratigraphic gap or reverse. Microscopically, the chert consists ofa microcrystalline quartz matrix with clay minerals and an abun-dance of densely packed radiolarian tests (R in Fig. 2G). Thin lam-inations representing varying densities of clay minerals are alsoobserved in the chert beds (c.l. in Fig. 2G), whereas coarse terrige-nous grains such as quartz larger than silt sized are not observed in

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the chert layers (Fig. 2G). Thin chert layers ranging in thicknessfrom a few millimeters to 1 cm are sporadically intercalated withinthe underlying basaltic sandstone layers, suggesting an originallyconformable stratigraphic relationship (Fig. 2C and D).

A polished slab surface of the lowest layer of the approximately10-cm-thick chert unit (sample No. BMH02-01 in Fig. 5) shows theintermediate lithologic characters between the basaltic sandstoneand the chert (Fig. 3). The lower part of the layer mainly consistsof a matrix of very fine fragments of basaltic glass and basalticrocks with very thin layers composed of macroscopically visiblegrains (Fig. 4A). The basaltic fragments are silt sized and showintersertal texture accompanied by bioclasts of fusulinoidean orother foraminiferal tests ranging from 1 to a few millimeters indiameter (Fig. 4A and B). Cuspate-shaped glass fragments are alsopresent in this part (c in Fig. 4B). In addition to the glasses, roundedamygdale-like grains that are filled with microcrystalline quartzare scattered within the muddy matrix (a in Fig. 4B and C). Themicrocrystalline quartz shows a zonal-like structure, and some ofthe grains contain zircon (z in Fig. 4A). A few scattered monocrys-talline silt-sized quartz grains are also present (q in Fig. 4C). In con-trast, the upper part of the layer (Fig. 3) is composed of a clay-sizedmatrix with lithologic features characteristic of siliceous shale, andradiolarian tests are very rare (Fig. 4D).

As shown in Fig. 5, the basaltic sandstone intercalated with sev-eral chert and siliceous layers. Stratigraphic younging directionindicated by the upward coarsening graded bedding of the sand-stone corresponds to younging direction documented by two radi-olarian zones in bedded chert as mentioned next chapter. Inaddition to these result, intermediate lithologic character betweenthe sandstone and chert shown in the lowest layer of the chert unit(Fig. 3) supports that the basaltic sandstone conformably underliesthe chert.

an Upper Permian radiolarian chert from the Paleo-Tethys in the Inthanonrg/10.1016/j.jseaes.2012.08.007

A

B E

C F

D G

Fig. 2. Outcrop photograph of the study section. (A) Bedded chert overlying basaltic sandstone layers, (B) radiolarian chert (upper part) conformably overlying the basalticsandstone (lower part), (C) basaltic sandstone showing graded bedding and intercalation with thin chert layers, (D) polished slab surface of the basaltic sandstone clearlyshowing graded bedding and the intercalation of thin chert layers, (E) photomicrograph of the basaltic sandstone layer (Note: the basaltic fragment showing intersertaltexture is contained within a predominantly clay- to sand-sized matrix of fragments of basaltic glass), (F) well-bedded radiolarian-bearing chert, and (G) photomicrograph ofradiolarian-bearing bedded chert showing thin laminations represented by a density difference in the clay minerals.

4 Y. Kamata et al. / Journal of Asian Earth Sciences xxx (2012) xxx–xxx

4. Radiolarian fauna and geological age

Late Permian radiolarians represented by Follicucullus scholasti-cus, F. dilatatus, F. charveti, Albaillella protolevis, A. cf. flexa, A.sp., and Neoalbaillella sp. with many types of Latentifistularia

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(Stauraxon Spumellaria) were obtained from the chert succession.These radiolarians are divided into two faunas as follows.

One of the fauna groups characterized the lower part of beddedchert unit (Figs. 5,6) and includes F. scholasticus, F. dilatatus, and F.charveti with latentifistularians such as Ishigaum sp., Nazarovella

an Upper Permian radiolarian chert from the Paleo-Tethys in the Inthanonrg/10.1016/j.jseaes.2012.08.007

Fig. 3. Polished slab surface of the lowest chert layer (sample No. BMH02-01 inFig. 5). The lower part of this layer is composed of very fine or clay-sized matrixwith layers consisting of silt-sized grains accompanied by bioclasts such asforaminiferal tests. The upper part of this layer is shale with a siliceous clay-sizedmatrix, and radiolarian tests are very rare. Letters A through D show the positions ofthe photomicrographs in Fig. 4A–D.

Y. Kamata et al. / Journal of Asian Earth Sciences xxx (2012) xxx–xxx 5

sp., and Latentifistula sp. F. scholasticus has mainly been reportedfrom the Capitanian in the USA (Noble and Jin, 2010; Nestell andNestell, 2010), Oman (De Wever et al., 1988), Italy, (Kozur, 1993),New Zealand (Takemura et al., 1999), southwest Japan (Ishigaand Imoto, 1980), and Thailand (Feng et al., 2005; Wonganan andCaridroit, 2006). F. scholasticus is a characteristic species of the F.scholasticus Assemblage Zone (Kuwahara, 1999), although co-occurrence of this species and F. charveti is restricted in the F.charveti-A. yamakitai Assemblage Zone (Kuwahara, 1999). F. charv-eti is a diagnostic species and defines the lower limit of this assem-blage zone (Kuwahara, 1999). According to Kuwahara et al. (1998),the other index species, A. yamakitai (described as Albaillella sp. Fby Kuwahara et al., 1998), occurs only in the upper part of thisassemblage zone. Considering the absence of A. yamakitai in thestudy section, the fauna obtained from the lower part of study sec-tion corresponds to the lower part of the F. charveti–A. yamakitaiAssemblage Zone (Kuwahara, 1999).

Kuwahara (1999) recognized four zones in the Upper Permianin the pelagic bedded chert sequence of the Mino Belt, southwestJapan. They assigned the F. charveti–A. yamakitai Assemblage Zoneto the early Late Permian and correlated it with other radiolarianassemblages from the Upper Permian Tatsuno Formation, south-west Japan (Caridroit and De Wever, 1986), the F. charveti Zone(Ishiga, 1991), and the F. charveti–Imotoella triangularis AssemblageZone (Kozur and Mostler; 1989). Yao et al. (2001) and Kuwahara

Please cite this article in press as: Kamata, Y., et al. Basaltic activity preserved inZone, northern Thailand. Journal of Asian Earth Sciences (2012), http://dx.doi.o

et al. (2007) assigned this zone to lower the Wuchiapingian (lowerUpper Permian) based on the co-occurrence of conodonts. Re-cently, Xia et al. (2004), Xia et al. (2005), and Sun and Xia (2006)re-examined the correlation between radiolarian and conodontbiostratigraphy for several pelagic chert sections in China andsouthwest Japan to establish these zones in the Upper Permian.Unfortunately, this series of reports contained misinterpretationsand confused the zonal correlation between both taxa, as pointedout by Nestell and Nestell (2010). Xia et al. (2004) assigned the F.charveti–A. yamakitai zone to the upper Guadalupian at the Gu-jyo-Hachian section, the same section as studied by Kuwahara(1999). Nestell and Nestell (2010) briefly described the difficultyin attempting the correlation of both taxa, and tentatively corre-lated the upper Capitanian (Guadalupian) radiolarian zones tothe F. charveti–A. yamakitai Assemblage Zone (Kuwahara, 1999).Currently, the geological age of the F. charveti–A. yamakitai Assem-blage Zone (Kuwahara, 1999) should be considered early Wuchia-pingian, but more precise age determination is required.

The second fauna group characterized the upper part of thestudy section and was predominantly composed of albaillellariansof A. protolevis, A. cf. flexa A. sp. and Neoalbaillella sp. and accompa-nied by latentifistularians (Figs. 5,6). A. protolevis and A. flexa arediagnostic species of the Neoalbaillella ornithoformis AssemblageZone (Kuwahara et al., 1998), and the former is especiallyabundant in the lower part of the zone. Radiolarian fauna obtainedfrom the study section should correlate with the N. ornithoformisAssemblage Zone (Kuwahara et al., 1998), although Neoalbaillellaoccurrence is restricted to a few poorly preserved specimens. Thiszone was correlated with the N. ornithoformis Assemblage Zone(Ishiga, 1986) and the Paleo-Tethyan N. ornithoformis AssemblageZone and N. grypa Zone by Kozur and Mostler (1989). Kuwaharaet al. (1998) assigned this zone to the early Late to late LatePermian, and Kuwahara et al. (2007) assigned this zone to the LateWuchiapingian to early Changhsingian (Upper Permian).

5. Geochemical features of the basaltic sandstone

To derive the origin of the basaltic sandstone, whole-rock geo-chemical analyses were performed. The lower coarse-grained partof a sample bed (BMH02-14) with abundant concentrated basalticfragments was selected for analysis.

The sample was crushed into powder for the geochemical anal-yses. The concentrations of 10 major elements and 13 trace ele-ments (Ba, Cr, Cu, Ga, Nb, Ni, Pb, Rb, Sr, V, Y, Z and Zr) weredetermined by X-ray fluorescence (XRF) analysis of fused glassbeads using a Rigaku RIX-3000 unit housed at the Center for Instru-mental Analysis, Yamaguchi University, Japan. Total Fe content isreported as Fe2O3. Loss on ignition (LOI) was measured by weigh-ing the sample before and after 3 h of calcination at 950 �C.Concentrations of rare earth elements (REEs) were analyzed byinductively coupled plasma mass spectrometry (ICP-MS) using aPerkin Elmer SCIEX ELAN at Activation Laboratories Ltd. (Canada).Variations in sensitivity during the analytical run were correctedusing an internal standard. Samples were prepared using a com-bined acid digestion procedure and alkali fusion.

The results of the geochemical analyses are listed in Table 1.Plots of discrimination diagrams and chondrite-normalized REEpatterns are shown in Figs. 7 and 8, respectively.

Major element chemistry of the basaltic sandstone is character-ized by Ti enrichment, whereas mobile major elements such as al-kali of Na2O and Ca show depleted values and should be removedby the alteration process. SiO2 contents of 46.43% (i.e., <52%) andthe intersertal texture observed in the fragments contained inthe sandstone indicate that these fragments originated frombasaltic rocks. Considering the high content of Ti (4.69%), these

an Upper Permian radiolarian chert from the Paleo-Tethys in the Inthanonrg/10.1016/j.jseaes.2012.08.007

A B

C D

Fig. 4. Photomicrographs of the lowest layer of the chert unit. (A) The lower part of this layer contains basaltic fragments (b.f.) showing intersertal texture and grains filledwith microcrystalline quartz that might have originated from amygdales. Note that a zircon (z) grain is contained in this layer. (B) Amygdale-like grains (a) and fusulinoideantests (F) in the lower part. (C) Monocrystalline quartz grain (q) with amygdale-like grains (a) in the lower layer. (D) The upper part of the layer is composed of a clay-sizedmatrix with few radiolarian tests.

6 Y. Kamata et al. / Journal of Asian Earth Sciences xxx (2012) xxx–xxx

fragments should be derived from alkaline basalt. Basaltic rocks arewell documented and most studies show that Ti, Al, P, Zr, and Y aregenerally immobile elements. As described previously, the ana-lyzed sample is sandstone mainly composed of clay- to sand-sizedbasaltic fragments. The geochemical data represent not only thechemical features of the basaltic rocks but also of the interstitialwater and the influence of alteration. Therefore, a discriminationdiagram using the immobile elements is required to estimate thesource of the basaltic rock fragments. The basaltic sandstone dataare plotted in the field of oceanic island tholeiite (OIT) in theTiO2/10-MnO–P2O5 diagram and in the field of mid-ocean ridge ba-salt (MORB), island-arc tholeiite, and calc-alkali basalt in the Ti/100–Zr–Y�3 diagram.

A chondrite-normalized multi-element spider diagram of thissandstone shows light rare earth element (LREE) enrichment thatis more similar to oceanic island basalt (OIB) than MORB and islandarc basalt (IAB). Therefore, the basaltic fragments most probablyoriginated in an oceanic island setting.

6. Discussion

6.1. Chert lithology, lithostratigraphy, and ocean plate stratigraphy

As previously described, the radiolarian-bearing chert is rhyth-mically well bedded, ranges from a few centimeters to 10 cm inthickness, and contains a dense abundance of radiolarian testswithin a microcrystalline quartz matrix. These lithological featurescorrespond to those of pelagic chert reported from the Paleozoicto Mesozoic accretionary complexes of the Japanese Islands.

Please cite this article in press as: Kamata, Y., et al. Basaltic activity preserved inZone, northern Thailand. Journal of Asian Earth Sciences (2012), http://dx.doi.o

Radiolarian fauna from the study section is composed predomi-nantly of albaillellarians, resembling the fauna of these accretion-ary complexes originating in the pelagic realm of Panthalassa.The study area shown in Fig. 1B is characterized by a distributionof pelagic Paleo-Tethys remnant rocks represented by MiddleDevonian to Middle Triassic chert and Carboniferous to Permianseamount-type carbonates (e.g., Sashida et al., 1993; Ueno andCharoentitirat, 2011). Lithological features and faunal contentindicate that the bedded chert in the study section originated inthe pelagic realm of the Paleo-Tethys (Kamata et al., 2009) andshould be interpreted as one part of the Inthanon Zone. Middleto Upper Permian radiolarian-bearing cherts have been reportedby Caridroit (1993), Sashida et al. (2000), and Sashida andSalyapongse (2002) in the Chiang Dao area, by Wonganan andCaridroit (2006) in the Pai area, and by Feng et al. (2005) in theMae Hong Son area.

Radiolarian faunas obtained from the study section are correlat-able with the Late Permian (Wuchiapingian to approximately earlyChanghsingian) assemblage zones. Field assessments, studies of apolished slab surface, and microscopic observation have clarifiedthat the Upper Permian chert conformably overlies the underlyingbasaltic sandstone, and the lithological change is gradual, as de-scribed previously. Considering the occurrence of the Wuchiapin-gian radiolarian fauna of the F. charveti–A. yamakitai AssemblageZone from the lower chert unit, the lithological change occurredover the late Capitanian to the early Wuchiapingian, which approx-imately corresponds to the Guadalupian–Lopingian boundaryinterval. The lower limit of the basaltic sandstone is unknown be-cause of poor exposure; however, the combined results of the chert

an Upper Permian radiolarian chert from the Paleo-Tethys in the Inthanonrg/10.1016/j.jseaes.2012.08.007

Fig. 5. Lithostratigraphic columnar section showing radiolarian occurrences and geological age of the study section based on the radiolarian data.

Y. Kamata et al. / Journal of Asian Earth Sciences xxx (2012) xxx–xxx 7

lithology, the geological age, and the occurrence of Middle toUpper Permian radiolarian-bearing chert in this area (e.g., Carid-roit, 1993; Sashida et al., 2000; Sashida and Salyapongse, 2002;Wonganan and Caridroit, 2006; Feng et al., 2005) indicate thatthe sequence of basaltic sandstone to Upper Permian bedded chertis a constituent of the ‘‘Fang chert.’’

Ocean plate stratigraphy (OPS), as first defined by Isozaki et al.(1990), is an idealized stratigraphic succession of the ocean floor,which records the geological history of the ocean floor from its cre-ation at the mid-ocean ridge to its destruction through subductionat the convergent plate margin (Matsuda and Isozaki, 1991; Isozakiet al., 1990; Wakita, 2000). In this context, reconstruction of thePaleo-Tethyan OPS is needed to understand the evolutionary his-tory and environmental transitions of the Paleo-Tethys. Wakitaand Metcalfe (2005) began reconstruction of the OPS in northernThailand, and Hara et al. (2010) have effectively documented thatthe lithology represents a small basin at the continental margintransitioning into a pelagic oceanic setting while going throughthe area influenced by volcanic activity due to the opening of thePaleo-Tethys. As a result, the sandstone that is intercalated withthe Upper Permian chert in this study area may provide cluesabout the sedimentary environment and tectonic setting of theocean basin.

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6.2. Sedimentary site of basaltic sandstone

Lithofacies, faunal content, and microfacies of chert indicatedeposition in the pelagic realm of the Paleo-Tethys as mentionedabove. In particular, the microfacies of densely packed radiolariansin a microcrystalline quartz matrix show no evidence of terrige-nous materials. A lengthy depositional time also suggests thatthe remote ocean basin was, at least during the Late Permian, freefrom terrigenous influx.

In contrast to the chert microfacies, the basaltic sandstone lay-ers consist of clay- to sand-sized basaltic glass fragments (Figs. 2and 4) and commonly show an upward fining graded structure.However, silt- and sand-sized terrigenous grains such as quartzare rare in the sandstone layers. The muddy part of the layer thatusually constitutes the upper half part of a sandstone bed consistsof clay-sized grains, but radiolarian tests are rarely present. Thesedimentary features of the sandstone beds suggest a relatively ra-pid sedimentation rate and lateral transportation due to turbidityor a gravity current, in contrast to the chert that likely accumulatedfrom suspension with a very low sedimentation rate. The studiedsequence was likely formed by intermittent sedimentation consist-ing mainly of basaltic fragment gravity currents in a backgroundsetting of very slowly accumulating radiolarian chert.

an Upper Permian radiolarian chert from the Paleo-Tethys in the Inthanonrg/10.1016/j.jseaes.2012.08.007

Fig. 6. Late Permian radiolarians from the bedded chert at the study section. (1) Albaillella cf. flexa Kuwahara, 1: BMH02-16. (2–6) Albaillella protolevis Kuwahara, 2: BMH02-16, 3: BMH02-16, 4: BMH02-16, 5: BMH-02-16, 6: BMH02-16. (7–8) Albaillella sp. 7: BMH02-16, 8: BMH02-16. (9–13) Follicucullus scholasticus Ormiston and Babcock, 9:BMH02-01, 10: BMH02-02, 11: BMH02-03, 12: BMH02-02, 13: BMH02-02. (14–17) Follicucullus charveti Caridroit and De Wever, 14: BMH02-04, 15: BMH02-04, 16: BMH02-06, 17: BMH02-06. (18–20) Follicucullus dilatatus Rudenko, 18: BMH02-03, 19: BMH02-03, 20: BMH02-06. (21–24) Follicucullus sp. A, 21; BMH02-02, 22: BMH02-02, 23:BMH02-03, 24: BMH02-03. (25–27) Follicucullus sp. C, 25: BMH02-03, 26: BMH02-06, 27: BMH02-02. (28) Neoalbaillella sp. 28: BMH-02-10. (29) Triplanospongos musashiensisSashida and Tonishi, 29: BMH02-16. (30) Latentifistula (?) sp., 30: BMH02-16. (31) Cauletella sp., 31: BMH02-16. Nazarovella sp., 32: BMH02-15, 33: BMH02-10b. (34)Pseudotormentus sp., 34: BMH02-16. (35) Entactinoshaera (?) sp., 35: BMH02-16.

8 Y. Kamata et al. / Journal of Asian Earth Sciences xxx (2012) xxx–xxx

The lateral transportation suggested by sedimentary features ofthe sandstone implies the existence of a topographic high in thechert basin. The lack of terrigenous grains in the chert and theirrarity in the sandstone indicate that the remote ocean basin wasfar from the continent. In addition, the presence of bioclasts offusulinoidean or other foraminiferal tests in the transitional portionbetween the sandstone and chert layers (Fig. 4B), combined with thetectonic setting indicated by the geochemistry of the basaltic frag-ments (Figs. 7 and 8), suggest that the topographic high was mostlikely a seamount or plateau in the ocean basin. Fusulinoidean bio-clasts found in this study section strongly suggest transportationfrom a shallow carbonate on top of the seamount to a deeper site.

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Enrichment of glasses and basaltic fragments in the sandstonelayers coupled with the conformable lithological change betweenthe dominant rock types indicates that the basaltic activity itselfwould have occurred within a chert-accumulation basin in thePaleo-Tethys during the late Capitanian to early Wuchiapingian.Paleo-Tethyan basaltic rock distributed in north Thailand has beenstudied by Barr et al. (1990), Phajuy et al. (2005), and Feng et al.(2008). Although the geological age was unclear, basaltic rocksaccompanied by limestone have been examined. Feng et al. (2008)reported that these rocks are subalkaline and potassic trachybasaltand that the geochemical characters are comparable with those ofoceanic island basalt. Phajuy et al. (2005) described the geochemical

an Upper Permian radiolarian chert from the Paleo-Tethys in the Inthanonrg/10.1016/j.jseaes.2012.08.007

Fig. 7. Discrimination diagrams for the basaltic sandstone at the study section. (a) TiO2/10-MnO–P2O5 diagram after Mullen (1983). A black solid circle indicates the studiedsample (BMH02-14). (b) Ti/100–Zr–Y�3 diagram after Pearce and Cann (1973). A black solid circle indicates the studied sample (BMH02-14). Black solid square symbols areafter Barr et al (1990), Phajuy et al (2005), and Feng et al (2008).

Table 1Results of geochemical analyses of the basaltic sandstone.

SiO2 TiO Al2O3 Fe2O3 MnO MgO CaO Na2O K2O P2O5 Total LOI

Major element (wt.%)BMH02-14 46.43 4.69 18.75 13.52 0.03 1.17 1.17 0.00 1.42 0.34 87.52 12.12

Ba Cr Cu Ga Nb Ni Pb Rb Sr V Y Zn Zr

Trace element (ppm)BMH02-14 672.30 22.20 47.60 30.72 207.90 38.49 7.93 77.40 356.40 417.50 148.10 309.70 372.40

La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu

REE (ppm)BMH02-14 957.81 491.83 529.47 428.27 232.68 157.76 148.91 109.89 77.56 58.30 50.76 40.78 33.59 31.81

Total Fe content is reported as Fe2O3.

Fig. 8. Chondrite-normalized REE patterns of the basaltic sandstone. The chondrite value and the OIB, IAB, and MORB reference patterns are after Sun and McDonough (1989)and Imai et al (1994).

Y. Kamata et al. / Journal of Asian Earth Sciences xxx (2012) xxx–xxx 9

characters of the Permian basaltic sequence in the Pang Mayao area,north of Chiang Mai, where the rock consists of tuff, basaltic flow,hyaloclastite, and pillow breccia. They concluded that these basalticrocks are alkaline and interpreted them as having formed in amature back-arc basin or a major ocean basin. These results suggestbasaltic activity in an oceanic basin, rather than in a continentalmargin setting. It is noteworthy that the calcite cement of the pillowbreccias contains fusulinid fragments of Upper Carboniferous toearly Middle Permian (Phajuy et al., 2005) age. Late Carboniferousto Middle Permian reworked fossil tests in the basaltic sequenceare concordant with the age determination of sedimentation ofthe basaltic sandstone, which should approximate the age of thebasaltic activity and formation of the sandstone in this study.

Please cite this article in press as: Kamata, Y., et al. Basaltic activity preserved inZone, northern Thailand. Journal of Asian Earth Sciences (2012), http://dx.doi.o

The Permian period is known for the occurrence of large igneousprovinces (LIPs) such as two continental flood basalt provinces ofSiberia and Emeishan. Recently, Paleozoic to Mesozoic greenstonesin Japanese accretionary complexes were interpreted as a huge ac-creted Panthalassic oceanic plateau, and it was noted that this activ-ity was contemporary with LIPs in Eurasia that may have resultedfrom superplume activity beneath Pangaea (Ichiyama et al., 2008).Reconstruction of the Paleo-Tethyan OPS, which includes not onlybedded chert but also oceanic basaltic rocks originating in a sea-mount or oceanic plateau, should be attempted to document theevolution and environmental transition of the Paleo-Tethyan ocean.

As described above, some of the layers in the basaltic sandstonecontain silt-sized monocrystalline quartz and zircon grains that are

an Upper Permian radiolarian chert from the Paleo-Tethys in the Inthanonrg/10.1016/j.jseaes.2012.08.007

10 Y. Kamata et al. / Journal of Asian Earth Sciences xxx (2012) xxx–xxx

commonly included in an amygdale-like grain consisting of micro-crystalline quartz. These grains imply terrestrial influx from a con-tinental area during the accumulation of the sandstone. However,the oceanic basin and the pelagic realm of the Paleo-Tethys shouldhave been free from terrestrial influx during the interval of chertsedimentation. During the basaltic sandstone sedimentation, how-ever, it is possible that terrestrial grains were temporarily availablein the ocean basin. More detailed study on the origin of monocrys-talline quartz and zircons grains is needed.

7. Summary

(1) Basaltic sandstone was discovered in a pelagic chertsequence. The sandstone conformably underlies and ispartly intercalated with the Upper Permian (Wuchiapin-gian-early Changhsingian) radiolarian-bearing chert andshows a gradual lithological change.

(2) The basaltic sandstone is composed mainly of fragments ofglass and basaltic rock, ranging from clay to sand sized indiameter. Some of basaltic rock fragments show an interser-tal texture that is commonly observed in basaltic rocks.

(3) Overlying bedded chert of the Late Permian represented byF. scholasticus, F. dilatatus, F. charveti, A. protolevis, A. cf. flexa,A. sp., and Neoalbaillella sp. with many types of Latentifistu-laria (Stauraxon Spumellaria) were obtained. These faunasare correlated with the Wuchiapingian F. charveti–A. yamaki-tai Assemblage Zone and the late Wuchiapingian toearly Changhsingian N. ornithoformis Assemblage Zone ofKuwahara et al. (1998).

(4) Lithofacies and microfacies of the bedded chert representingthinly and rhythmically bedded, densely packed radiolariantests and rare terrigenous grains indicate that the chert wasdeposited in the pelagic realm of the Paleo-Tethys. In thecontext of the distribution of Paleo-Tethyan rocks, the UpperPermian chert is one member of the Paleo-Tethyan remnantthat is the Inthanon Zone of northern Thailand.

(5) Although it is difficult to estimate the tectonic settingbecause of element mobility and the influence of alteration,basaltic fragments likely originated as an oceanic basalt suchas OIB.

(6) Sedimentation of the chert and sandstone estimated by themicrofacies and sedimentary structure suggests that studiedsequence was formed by intermittent high rates of sedimen-tation mainly from gravity currents of basaltic fragments, ina background setting of very slowly accumulating radiolar-ian chert.

(7) The sedimentary mode of the sequence, the rare terrigenousinflux, and the supply of fusulinoidean or other foraminiferaltests point to a likely origin in a shallow carbonate. The tran-sition from sandstone to chert indicates that the basalticrock fragments were likely derived from an oceanic topo-graphic high such as a seamount or an oceanic plateau,and that the basaltic activity occurred in the chert-accumu-lating oceanic basin of the Paleo-Tethys around the lateCapitanian to early Wuchiapingian.

Acknowledgements

The first author (Y.K.) expresses thanks to the editor Professor I.Metcalfe and two anonymous reviewers for their critical review ofthe manuscript. This work was supported in part by a Grant-in-aid(No. 15403013) from the Japanese Ministry of Education, Culture,Sports, Science and Technology. This research is part of the IGCP516 Project.

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