"International Symposium onBIOSTRATIGRAPH)' OF MAINLAI'\ 0 SO'VTHEAST AS}..\ : FAClF..'~ & PALEONTOLOGY31 January - 5 February 1991. Oliang Mai, '111ailand

A rnixed radiolarian fauna (PermianiTriassic) from clasties of theMae Sariang area, northwestern Thailand

Martial CARIDROIT1, Dietmar BOHLKE2

, Apichart LUMJUAN3 Dietrich

HELMCKE2 and Patrick DE WEVER4

lLaboratoire de Paleolltologie, Sciences de la Terre, Universite des Sciences et Techniques de Lille,59655 Villeneuve d'Ascq, France

2/nstitute of Geology and Dynamics of the Lithosphere. University of Goettingen, Goldschmidtstr3. D-3400 GÔettingen. Germany

JGeological Survey Division, Department of Mineral Resources.Rama VI Road, Bangkok 10400, Thailand

4Departement de Geologie Sedimentaire. Universite P. et M. Curie (Paris VI), 4 Place Jussieu.75252 Paris Cedex 5. France

AB8TRACT : A clastic sequence west of Amphoe Mae Sariang was mapped in the past as of Middle

Triassic age. Recent mapping and paleontological data proved that this sequence is not of Middle Triassic

age but is younger (Late Triassic or younger). This conclusion is based on radiolarians of Middle to LatePennian age and radiolarians of Triassic age found in pebbles contained in these clastics.

The out.erops studied are located approximalely al Km 36.5 on the highway that links Mae Sariangwith Ban Mae Sam Laeb. The sequence consisls mainly of red conglomerales. sandstones, and shales and

strongly folded lowards the west; cleavage is developed in suitable rock-types. The contacts to the adjacentsequences to the east and the west are probably f3Ulls.

In a typical thin-section of the coarser varieties of these clastics, the main componenl is weIl­

rounded quartz grains derived from metamorphosed source rocks. Much less rounded and bigger pebbles of

red radiolarian chert are frequently intercalated. Since radiolarians could not be detected in the malrix of theseclastics, il is assumed that radiolarian assemblages found came from chert clasts.

INTRODUCTION

On the Chiang Mai 1:250,000 geological map sheet (Baum and others, 1981), asequence ofredconglomerates, sandstones, and shales between the valleys of the Mae NamYuam and the Salaween River is included into the Triassic. According to the cross-sectionon the map, this sequence overlaps u'ansgressively strongly deformed upper Paleozoicstrata close to the Salaween River. The pronounced angular unconfonnity shown,therefore, dates the main defonnation in this region as pre-Middle Triassic. Contrary to thissituation the red clastic sequence is mapped further to the south apparently as the basal partof a thick Triassic sequence. The strong defonnation of these Triassic strata (as indicatedin the cross-section) dates the main contractional event as Late Triassic or younger.

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Figure 1 Simplified geological map of the examÎned area (based on Baum and ailiers, 1981).

Recent field work carried out between Mae Sariang and the Salaween River andfollowed by paleontological research helped to solve this puzzling situation. It can beproved that conglomerates fonnerly included in the Triassic contain not only grains ofmetamorphic quartz but also pebbles of radiolarian cherts. These conglomerates yieldedtwo distinctly different radiolarian assemblages: one ofMiddle to Late Pennian age and oneof Triassic age.

Since the Permian and Triassic radiolarian assemblages occur in chert pebblesrather than in the matrix of the conglomerates, this suggests that the conglomerates areyounger than indicated on the published map (Baum and others, 1981).

These data are important for understanding the paleogeographie situation ofnorthwestern Thailand during Permo-Triassic times. They may help solve thepaleogeographie contradiction which exists between the Lower Pennian sequences knownfrom northern Thailand (Konishi, 1953; Baum and others, 1970), which indicate wannwater conditions, and the Lower Permian strata from western peninsular Thailand, whichare of glacial-marine origin.

AREA STUDIED

The red clastic strata occur in severallocalities between the Mae Nam Yuam valleyand the Salaween River, over a distance of approximately 75 km in a N-S direction (Baumand others, 1981). East of the Mae Nam Yuam valley no outcrops of this fonnation areknown.

The best known outcrop of the red conglomerates, red sandstones, and red shalesis located along the highway between the Thatafang police station and Ban Mae Sam Laeb(Fig. 1). The Thatafang police station is located approximately 19 km south of Amphoe MaeSariang in the Mae Nam Yuam valley and Ban Mae Sam Laeb is located on the bank of theSalaween River. These outcrops are located between km 36.0 and Km 37.5 of this highway.

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Since this highway is at present under reconstruction, the section is partly well-exposed andpartly still covered by debris. The strata are folded alld cleavage is developed in suitablerock types. The foids tend to be upnght or slightly inclined (Fig. 2). The contacts of the redclastics to the east and the west are probably faults. About 100 m to the west of Km 37, asecond section of the red clastics is exposed, probably again with faulted contacts.

The eastern parts of the main outcrop are donunated by homogeneous, fine, red(seldomyellowish) sandstoneand siltstone with intercalated shales. Coarsersandstones andfine conglomerates are only locally interbedded. To the west a more conglomeraticsequence in which thinner sandstone and siltstone layers are intercalated follows. In turn,it is followed by fine and more homogeneous soft shales, sandstones, and siltstones. Figure3 shows typical measured sections, mainly from the coarser sequences.

Due to lack of weathering and partly to poor exposure, only sedimentary SU'uctureslike wedged-out bedding, channels, and graded bedding could be observed. For the samereasons it was not possible to correlate the measured lithological columns into a morecomplete sequence. We assume that the total thickness of the sequence is at least 200-300metres.

The conglomerates have only a few different components. The main componentis angular to subangular chert clasts with an average grain size of about 1cm. The biggestpebble found is 5 cm in diameter and rounded. Different types of chen pebbles occur butit is not possible to determine whether they are Permian or Triassic pebbles. These chenpebble are :

- almost opaque, iron oxide or hematite pigmented, with partly good pr~~ervation

of radiolaria (Fig. 6),

- fine-grained, brownish, with recrystallized radiolaria and spiculitic structures,flaser structure is often developed in this variety (Fig. 7),

- coarse, brownish to colourless, without any recognizable fossils or other relictstructures.

Other components are sandstones and lithic sandstones of varying grain size androundness. Quartz-mica schists and polycrystalline quartz aggregates of metamorphicorigin are present in smaller amounts (Figs. 8, 9). Fine-grained rock fragmentsshowing preferred extinction directions could not be identified under the microscope.Probably, they are either slightly metamorphosed shales or fine-grained volcanics (Fig. 4,,5). The matrix is mainly rounded, mostly fine to medium Inonocrystalline quartz grainsand submicroscopic opaque iron oxide or clay mineraIs. The quartz grains show slightto strong undulatory extinction and defonnation lamellae as a hint of metamorphic ongin(Fig. 10). Because of deformed quartz overgrowths and concentration of defolmationlamellae near grain contacts (Fig. Il), it is assumed that not aIl quartz grains indicatea metamorphic source.

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RADtOLARIAN AGE DATING

Of the collected samples, two yielded radiolarian remains that could be dated.Being non-calcareous, each sample could be studied by a classical technique: 5 % HFetching, 50 micron sieving, and SEM observations.

Sample Th 189/91 B (approximately Km 37.4)

This sample is a conglomerate composed of a sandy matrix and clasts of variablesizes (from a sand size to several centimetres diameter). The clasts are mainly radiolaritesand sorne sandstones.

The whole sample was etched but the collected fauna came only from the clasts.As amatter of, the matrix being sandy, it seems impossible that radiolaria could be preservedin such a sediment.

From this sample al least two different assemblages, having two different ages,were determined. One is Late Permian (Guadalupian or Late Kazanian to EarlyTatarian) :

Follicucullus scholasticus Onniston and BabcockF. sp. cf. F. ventricosus Onniston and BabcockPseudoalbaillella sp.Latentifistula sp.Deflandrella sp. cf. D. manica De Weyer and CaridroitQuadricaulis sp. 1 of Caridroit (1986).

The other is Triassic (probably Anisian-Ladinian):

Triassocampe sp.Capnuchosphaera sp.numerous other CapnuchosphaeridsFragments of EptingiidaeNumerous characteristic twisted spines (Triassic)

Sample Th 04/91 He (Km 36.4-36.5)

This sample is similar to the previous one. The whole sample was etched. Like theprevious sample, at least two different assemblage were found.

The first one is Late Permian (Late Guadalupian) (rem. : radiolarianramains probably come from different elements; sorne are in siliceous material andsorne in pyrite) :

Follicucullus scholasticus Onniston and BabcockF. sp. aff F. scholasticus Onniston and BabcockAlbaillella levis Ishiga, Kito and ImotoAlbaillella excelsa Ishiga, Kito and Imoto

406

The second one is Triassic (Anisian.Ladinian) :

Triassocampe sp. cf. T. sulovensis Kozur and MostlerTriassocampe sp.Archeospongoprunum sp.Capnuchosphaera sp.Tetraedric fonn of Capnuchosphaerids? Welirel/a sp.Triassic Satumalids (with polar beam facing polar spine)Numerous characteristic twisted spines (Triassic).

For the Pennian radiolarian assemblages the Tethyan stage names 'are not used,since the correlation between radiolarian zonation and Tethyan stratigraphy is still notsufficiently established. Sorne of the radiolaria found are shown in Figure 12.

AGE OF THE CONGLOMERATRE

The age of the conglomeratic sequence must be younger than the age of theyoungest radiolarian faunas found. First the radiolarian cherts of Pennian and Triassic agehave to he brought into a position in which they can be subject of erosion. Then they haveto be eroded, transported, and newly deposited. The best way to achieve this is bycontractional defonnation orthe Permian and Triassic strata. Since a thick sequence ofMiddle Triassic syn-orogenic siliciclastics is known from the areas near Mae Sariang(Chonglakmani and others, 1991 ~ Tofke and others, 1993), we assume that this orogenicevent started during the Middle to Late Triassic. Therefore, 'the oldest age we can attributedto .these conglomerates is latest Triassic, but probably younger. During a still youngerevent, th~ red clastic sequence was finally deformed.

PALEOGEOGRAPHIe IMPLICATIONS

Mae Sariang is located in that part ofThailand which is often described as the Shan­Thai-craton. It is said that this microcontinent is underlain by high-grade metamorphic rocksof Precambrian age and many authors speculate that this craton rifted off Gondwana, driftedacross paleo-Tethys and collided finally during the Late Triassic with the Indosinia cratonalong the Nan-Uttaradit suture. The Permo-Carboniferous glacial-marine strata of thePhuket Group (peninsular Thailand) and equivalents in Burma are the best indication of theGondwana origin.

But the Lower and Middle Permian strata of northern Thailand, from Mae HongSon to the east, are long known to indicate extremely wann water conditions (Konishi,1953; Baum and others, 1970). The fusulinid faunas of this region indicate during EarlyPennian a connection with the arctic realm (Toriyama and others, 1978; Ingavat and others,1984; Toriyama, 1984). This is a strong indication'that those parts of the Shan-Thai cratonlying to the east of the line Mae Hong Son-Mae Sariang have to be regarded as positionednorth of the equator during Pennian t-imes. According to Helmcke and Kraikhong (1982),

407'

Helmcke and Lindenberg (1983), and Helmcke (1985, 1986) the Nan- Uttaradit sutureclosed during the late Middle Permian, i.e., since that time the areas of the Shan-Thai craton

.situated east of Mae Sariang-Mae Hong Son have ta be regarded as an integrated part ofpaleo-Eurasia..

The new data exclude the necessity for the Triassic basin of Mae Sariang to.have developed after a late Paleozoic orogenie event on continental crust, as discussedby Chonglakmani and others (1991), since the red conglomerates are younger than theTriassie radiolarian chens, pelagie limestones, and siliciclastics deposited by turbidityeurrents (Tofke and others, 1993). Therefore, these new data may allow the following

. iriterpretation: since pelagie sediments of Permian as weIl as Triassic age could be detectedin the vicinity ofMae Sariang, it is possible to assume that an oceanic realm persisted herefor many million years. This time interval may even be extended if the Carboniferous andPennian radiolaria described by Wu and Li CI 988) from the Changning- Menglian ophiolitebelteastofthe Baoshan Block in Yunnan (north ofMae Sariang-Mae Hong Son) come fromthe northem extension of the zone found near Mae Sariang. If pelagie sedimentationprevailed during such a long time, it is likely that the occanic realm in which theseradiolarian cherts were deposited was quite huge. Ta account for the strikingpaleoclimatologieal difference between the Lower Permian limestones of northernThailand (east ofMae Hong Son) and the glacial-marine deposits of the same age from thePhuket Group, a huge distance must be taken into consideration. Therefore, the region eastof Mae Sariang might be rightly regarded as the paleo-Eurasiatic continental margin ofpaleo-Tethys while the region west of Mae Sariang is of Gondwana origin, which, aftercrossing paleo-Tethys, stranded along this possible ten'ane boundary from Middle Triassictime onwards (Helmcke and others, in prep.).

Acknowledgements : This paper contains results of the cooperative programme betweenthe Department of Mineral Resources, Bangkok. and the Institute ofGeology and Dynamicsof the Lithosphere, Gottingen, on the geodynamic evolution of northern Thailand. We thankthe National Research Council ofThailand, Bangkok, and the German Research Foundation,Bonn-Bad Godesberg, for financial support.

REFERENCES

Baum, F., Bruan, E. von, Hess, A., Koch, K.E., Kruse, G., Quarch, H., and Siebenhuner, M.,1970, On the Geology of northem Thailand; Beih. Geoi. lb., v. 102, 23 p.,Hannover.

Baum, F., Braun, E. von, Hess, A., and Koch, K.E., 1981, Geological map of nonhemThailand 1:250,000, sheet 5 : Chiang Mai; Bundesanstalt fur Geowissenschaftenund Rohstoffe, Hannover.

Chonglakmani, C., Gabel, 1., Helmcke, D., Lumjuan, A., and Meischner, D., 1991,Geodynamic interpretation of marine Triassic basins in northem Thailand; Sev­enth regional conference on geology, mineraI and energy resources of SoutheastAsia (GEOSEA VII), Abstract, p.13, Bangkok.

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Helmcke, O., 1985, The Penno-Triassic "Paleotethys" in mainland SE Asia and adjacentparts of China; Geoi. Rdsch., v.74, p.215-228.

Helmcke, O., 1986, Die Alpiden und die Kimmeriden : Die verdoppelte Geschichte derTethys - Discussion; Geoi. Rdsch., v.75, p.495-499.

.Helmcke, O., and Kraikhong, C., 1982, On the geosynclinal and orogenie evolution ofcentral and northeastern Thailand; J. Geoi. Soc. Thailand, v.5, p.52-74.

Helmcke, D., and Lindenberg, H.G., 1983, New data on the "Indosinian" orogeny fromcentral and northeastern Thailand; Geol. Rdsch., v.72, p.317-328.

Helmcke, O., Ingavat-Helmcke, R., and Meischner, O., in prep., Spat-variszische orogeneseund terranes in SE-Asien; Gottinger Arbeiten zur Geologie u. Palaontologie.

Ingavat, R., 1984, On the correlation of the Pennian foraminiferal faunas of the western,central and eastern provinces of Thailand; Mem. Soc. Geoi. France, N.S., v.147,p.93-100.

Ingavat, R., Toriyama, R., and Pitakpaivan, K., 1980, Fusuline zonation and fuanaIcharacteristics of the Ratburi Limestone in Thailand and its equivalents inMalaysia; Geoi. Palaeont. Southeast Asia, v.21, p.43-56.

Konishi, K.,.1953, New Boultonia and other microfossils from north Thailand; Trans. Proc.. Palaeont. Soc. lapan, n.s., v.12, p.l03-110.

Tofke, T., Lumjuan, A., and Helmcke, D., 1993, Triassic syn-orogenic siliciclastics fr~m

the· area of Mae Sariang (northwestern Thailand); in T. ·Thanasuth~pitak (Ed.),Proc. BIOSEA Sym., 31 Jan. - 5 Feb. 1993, Chiang Mai, this volume.

Toriyama, R., 1984, Summary of the fusuline faunas in Thailand and Malaysia; Geoi.Palaeont. Southeast Asia, v.25, p.137-146.

Toriyama, R., Pitakpaivan, K., and Ingavat, R., 1978, The paleogeographic characteristicsoffusuline faunas of the Ratburi Group in Thailand and its equivalents in Malaysia;in P. Nutalaya (Ed.), Proc. Third Regional Conf. on Geol. and Mineral Res. ofSoutheast Asia (GEOSEA Un, p.1 07-111, Bangkok.

Wu, H., and Li, H., 1988, Carboniferous and Pennian radiolarians of western Yunnan,SW China (prelim. abstract); Geologica et Paleontologica, v.22, p.214-215.

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Figure 4 SeveraI fragments of chert in a matrlx of medium to fine-grained sandstone (quartz and ironoxide). Note the different preservation of the radiolaria. The small rock-fragment in the rightupper corner could not be detenninated (sample Th 106/91 B, km 37.2, LPL 4.5x).

Figure 5 Different fragments ofchert in a typical conglomerate. Note grain support and lower percentageof matrix in contrast to Figure 4 (sample Th 123/91 B, km 36.6, LPL 4.5x).

Figure 6 Iron oxide pigmented fragment of chert and fine sand-size quartz grains and "chertoid matrix"(sample 160f)1 B, km 36.4, LPL 15.5x).

Figure 7 Fragment of chert with flaser structure marked by dark/opaque clay mineraIs and/or iron oxide.This indicates pressure solution. Note that radiolaria are little affected by solution (sample 106/91 B, km 37.2, LPL 12.0x).

Figure 8 Fragment of metamorphic rock (quartz-mica schist) showing shistose texture caused byelongated quartz grains and separating thin mica-plates. Fragment is surrounded by differentvarieties of chert clasts and undulose quartz grains (sample 160/91 B, km 36.4, XPL 27.5x).

Figure 9 Advanced stage ofquartz overgrowth cementation. Original grain shape is marked by dust rims.Note euhedral quartz crystal growing at the bottom of the darker grain (sampie 119/91 B, km36.55, XPL 27.5x).

Figure 10 Monocrystalline quartz grains in a conglomeratic sandstone showing strong undulatoryextinction and deformation lamellae. Note slight concavo-convex grain contacts (sample Th 4b/91 He, km 36.4, XPL 55x).

Figure Il Deformation lamellae at grain contacts in single quartz crystals as a result of in situ deformation(sample Th 4b/91 He, km 36.4, XPL 55x).

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Figure 4 Several fragments of chert in a matrlx of medium to fine-grained sandstone (quartz and ironoxide). Note the different preservation of the radiolaria. The small rock-fragment in the rightupper corner could not be detenninated (sampie Th 106/91 B, km 37.2, LPL 4.5x).

Figure 5 Different fragments ofchert in a typical conglomerate. Note grain support and lower percentageof matrix in contrast to Figure 4 (sample Th 123/91 B, km 36.6, LPL 4.5x).

Figure 6 Iron oxide pigmented fragment of chert and fine sand-size quartz grains and "chertoid matrix"(sampie 160191 B, km 36.4, LPL 15.5x).

Figure 7 Fragment of chert with flaser structure marked by darle/opaque clay minerals and/or iron oxide.This indicates pressure solution. Note that radiolaria are little affected by solution (sampie 106/91 B, km 37.2, LPL 12.0x).

Figure 8 Fragment of metamorphic rock (quartz-mica schist) showing shistose texture caused byelongated quartz grains and separating thin mica-plates. Fragment is surrounded by differentvarieties of chert clasts and undulose quartz grains (sample 160/91 B, km 36.4, XPL 27.5x).

Figure 9 Advanced stage ofquartz overgrowth cementation. Original grain shape is marked by dust rims.Note euhedral quartz crystal growing atthe bottom of the darker grain (sampie 119/91 B, km36.55, XPL 27.5x).

Figure 10 Monocrystalline quartz grains in a conglomeratic sandstone showing strong undulatoryextinction and deformation lamellae. Note slight concavo-convex grain contacts (sample Th 4b/91 He, km 36.4, XPL 55x).

Figure Il Deformation lamellae at grain contacts in single quartz crystals as a result of in situ deformation(sample Th 4b/91 He, km 36.4, XPL 55x).

410

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Fig. 12·1 to 12·8: Radiolaria (rom sample Th 04/91 He

1: Follicucullus scholasticus Ormiston and Babcock (x 190)

2: ? Welirella sp. (x 170)

3: Tetraedric fonn of Capnuchosphaerid (x 345)

4: Triassocampe sp. (x 400)

5: Triassocampe sp. cf. T. sulovensis Kozur and Mostler (x 375)

6: Characteristic twisted (Triassic) spine (x 410)

7: Capnuchosphaera sp. (x 230)

8: Triassic Satumalid (polar beam is facing polar spine) (x 410)

Fig. 12·9 to 12·15: Radiolaria from sample Th 189/91 B

9: Pseudoalbaillella sp. (x265)

10: Follicucullus scholasticus Ormiston and Babcock (x165)

Il: Quadricaulis sp. 1 of Caridroit (1986) (x 165)

12: Triassocampe sp. (x360)

13: Broken Capnuchosphaerid (x265)

14: Fragment of Eptingiidae (x200)

15: Capnuchosphaera sp. (x235)

412