GeoL. Soc. MaLaYJia, Bulletin 55, JuLy 1994; pp. 57-46

A stratigraphic log of Semantan Formation along part of the - Bypass,

I. METCALFE! AND K.R. CHAKRABORTY2

1 Department of Geology & Geophysics University of New England Armidale, NSW 2351, Australia 2Department of Geology University of Malaya ,

Abstract: A single 1.25 km thick sequence of the Triassic Semantan Formation has been logged along the western portion of the Mentakab-Temerloh bypass. Bivalves and ammonites indicate a Middle Triassic age. The coarse and fine tuffs and mudstones exposed in the sections represent an overall fining upwards sequence implying a possible waning of volcanic activity or shift of volcanic centres. There is no evidence of isoclinal folding or imbricate thrusts in the section which appears to form part of one limb of a large kilometer-scale broad open fold. The Semantan Formation cannot therefore form part of an accretionary prism but could form part of a forearc or intra-arc basin constructed over an accretionary wedge.

INTRODUCTION LITHOLOGY The Middle to Upper Triassic Semantan The overall sequence comprises interbedded Formation crops out in the Central Belt of coarse to fine tuffs and grey mudstones and an Peninsular Malaysia. This formation has previously overall simplified composite section and been interpreted as forming part of an accretionary representative detailed logs of exposures are given complex or a forearc sequence (Mitchell, 1977; in Figures 2-11. Mudstones are more predominant Sengor, 1986; Hutchison, 1989) in a convergent in the younger part of the sequence and coarse tuff plate margin setting. In many proposed models beds more common in the older parts of the section (Mitchell, 1977; Ridd, 1980; Sengor, 1984; thus giving a generally fining upwards sequence. Hutchison, 1989), this sequence is considered to have been involved in a later collisional deformation. SEDIMENTOLOGY This paper reports important stratigraphical and structural information from a continuous section of The coarse and fine-grained tuffs in the more than 1 km thickness which has implications sequence exhibit graded bedding most commonly of for interpreting the tectonic environment of the normal type (fining upwards) but also of inverse Semantan Formation. type (coarsening upwards). The bases of beds are In November, 1982 the authors logged exposures usually sharp but their upper boundaries are often of the Semantan Formation (Jaafar, 1976) along transitional into mudstone. Small scale cross the then under construction Mentakab-Temerloh bedding is also observed in the upper finer parts of Bypass. Rapid weathering and vegetation cover the tuff beds along with rarer ripple marks. Some has now obliterated much of the detail that was of the coarser, thicker tuff beds also contain lutite visible to the authors at that time. A single rip-up clasts. These features are well documented stratigraphic sequence of 1.25 km, with a consistent in tuff beds of the Semantan Formation elsewhere westward dip was logged between the Mentakab (Lum, 1976; Metcalfe et al., 1982) and indicate end of the Bypass and where the road crosses the deposition by turbidity currents or debris flows. railway. Nine road cutting exposures (Fig. 1) were The mudstones of the sequence are rather logged in detail. It is felt that the details of this featureless apart from some diagenetic chert and section and its implications should be made calcareous nodules. Palaeocurrent directions have available to other geologists who cannot now been determined at a few localities and both easterly unfortunately observe these due to decay of the and westerly directions are recorded, even within a exposures. single exposure. 38 I. METCALFE AND K.R. CHAKRABORTY Soft-sediment deformation is present in the specimens of Daonella have been found. This is in lower part of the sequence (sections 6-9), including contrast to other localities of the Semantan slump folds and sedimentary faults and this again Formation where Daonella occurs in abundance implies greater volcanic activity or closer proximity (Lum, 1976; Jaafar, 1976; Metcalfe et al., 1982). to volcanic centres. The reason for this may be an ecological one, with the two bivalve genera living in different PALAEONTOLOGY environments or depths of water, or it may be an effect of sedimentological sorting of bivalve shells. Pelagic bivalves and ammonites have been recorded at a number of horizons in the section STRUCTURE including the bivalve' genera Posidonia, and Daonella and the ammonite Arpadites, all The entire sequence logged exhibits a uniform suggestive of a Middle Triassic age. An interesting attitude of beds. Measured strike values range aspect of these fossil occurrences is the relative from 160°-170° and dip ranges 30°-50° westerly. abundance of Posidonia compared to Daonella. Steeper dips, of more than 60°, are occasionally Posidonia is found abundantly throughout the observed. The section described in this paper section and is extremely abundant at certain probably represents one limb of a large kilometer­ horizons whereas only one or two fragmentary scale open fold such as those previously reported

Mentakab\ 3 " I " .. ('

I / I

1 2 Km\ \ Figure 1. Map showing the locations of the nine road cut sections on the Mentakab-Temerloh Bypass. Geol. Soc. MalaY.Jia, Bulletin 35 ASTRATIGRAPHIC LOG OF SEMANTAN FORMATION ALONG PART OF THE MENTAKAB-TEMERLOH BVPASS, PAHANG 39 from the Semantan Formation (Jaafar, 1976). DISCUSSION AND IMPLICATIONS Isoclinal folding or imbricate thrusting of the sequence has been discounted since no repetition of The overall fining-upwards nature of the beds have been observed within the 1.25 km sequence indicates a waning of the supply of coarser stratigraphic section. A single axial plane cleavage volcaniclastic material to the area during the Middle is generally developed in the rocks which results in Triassic. This may be due to three possible causes, some deformation offossils present (Metcalfe et al., a deepening of the basin, waning of volcanic activity 1982). or shifting of the volcanic centres. Much more

COMPOSITE SECTION ~ SECTION NOT MEASURED. NO OUTCROP

MUDSTONE/TUFFACEOUS MUDSTONE WITH THIN TUFF LAVERS Metres COARSE GRAINED CONGLOMERATIC TUFF 1258~""""-

THICK BEDDED TUFF AND MUDSTONE (LAMINATED AND WITH THIN TUFFS)

...... •••••••• • 0 00.:,0 0 ° ~ AS ABOVE BUT WITH SLUMP AND SOFT .. :';. .•..•...•. ~ .... :: SEDIMENT DEFORMATIONAL FEATURES

['.::·.::.1 THIN INTERBEDS OF TUFF AND MUDSTONE . ... :.:.:.... TUFF BEDS 10-25 cm. THICK

~ AS ABOVE BUT WITH SLUMP AND SOFT :::....: ;:.:: SEDIMENT DEFORMATIONAL FEATURES

1:;1 CHERT LAYERS AND LENSES

I~I CALCAREOUS LENSES AND NODULES

o SMALL SCALE CROSS BEDDING

~ GRADED BEDDING, FINING UP'WARDS

~ GRADED BEDDING, COARSENING UPWARDS

1 vvv 1 RIPPLES

1_ 1 LUTITE CLASTS WITH APPARENT MAXIMUM 10 DIAMETER IN cm. 100m I~I BIVALVES f 50 o [IJ AMMONITE

IY FAULT

Figure 2. Composite section exposed in the Bypass compiled from road cuts 1-9. July 1994 40 I. METCALFE AND K.R. CHAKRABORTY

Metres 36 72 108 144

F 70 ..rl:-:-:="""'" F

F

CH' j:..:..:..:~'-'l1l155

......

~:... ::.:.::. ;: :::::u:: ...... ::::::::::

::.:-:.:':: ::: 158 TOP· ::.:.:.: .....:: CH' 11280

...... ::::.:: :0',:

......

Base 0 36 72 108 144 CH 10920

Figure 3. Detailed stratigraphic section recorded at road cut no. 9. For legend see Figure 2.

Geot. Soc. MataYJia, Bulletin 55 ASTRATIGRAPHIC LOG OF SEMANTAN FORMATION ALONG PART OF THE MENTAKAB-TEMERLOH BYPASS, PAHANG 41

Metres CH 12255 " ..... 621

,',' ..... : .. : Metres 478 IOf' eH 118,)~

:::::::;:~. :....-:::..-::...-...... --- ...... -- :.:.:.:~:.:.:.•. :.:-: ------';..:':..,:'..:." ~

---:,:,:,:,,~,: :':,,:: 565 601 0.0 .. G o ~o.o JjlJ Westerly transport ~~oo~-.! 599'65 [7 ...... ,':: JP Easterly transport

597 oo~~~~ -10 596·5 F F ~ ..... 595 'o' ..... '. :. ~ b- b-

-',.,' ;:',',.: ~ 593 b-

...... 591 ~~.o~o.. '! 590 .'!,:,.C! .~.9', -:- ····it:.:.··· South Eosterly transport ...... YJ7 :,',: .: .. : .... :. 587-4 _1 -1 :.:.:~.. :-:.... :.',.: 586-2 -1 CH 11775 443 549 ......

Figure 4. Detailed stratigraphic section Figure 5. Detailed stratigraphic section recorded at road cut no. 7. recorded at road cut no. 8. For legend see For legend see Figure 2. Figure 2.

JuLy 1994 42 I. METCALFE AND K.R. CHAKRABORTY

Metres ....------­ ":.':: :', ','::: ::: ::: CH ·12757 ...... 764 ...... " '" ......

'::.: :', •... : ',';. !...... ~ (: ). ~:/(::: .. : ...... : ...... :...::

~=.::.::C .:: : ':. ','.' ~', " ~:: : ::.~ ~ ;:.:. :.: ...... " ::.::::::'-ff. ','::,'::::.~-- II DISTURBED .­ ..... :: .... ,. .. " ZONE" F /" ...... '" ./ F ...... ~ ......

t::...... -=

689 749

685·5 Chevron folds. 2 m amp

683 ------:----=-.- Wih/(:}

--- ~~-:. \C;.nri·j : •...... " ~ " : " .

673 CH 12525

Figure 6. Detailed stratigraphic section recorded at road cut no. 6. For legend see Figure 2.

GeoL. Soc. MalaYJia, Bulletin 35 A STRATIGRAPHIC LOG OF SEMANTAN FORMATION ALONG PART OF THE MENTAKAB-TEMERLOH BYPASS, PAHANG 43

Metres

//// //// ,/ /,// ,,////' ,///// 850 ...... =- - -= ...... WESTWARD -----...... TRANSPORT ----- JP' :: ..... ::.' .. " 877 ~---- ~-- r-...... __ _ ® Posidonio ...... ~ Rich zone ~ ...... 874 -- .. '" ....

:.' ,',',',', : :: 1-__ :..,.- ././ /',/,,- ...... //// }I!J 871 //// CH 13245 //// 901 //// - --- //// //// WESTWARD //// //// ...... //// //// - -:.: TRANSPORT //// / /// //// ...... ," //// ,~~~ //// ./ /// ---- //// //// :.: :' : :.:.:.: ~: //// //// //// //// -- --- //// //// ...... //// //// //// // // ---_. //// ////'" /////.' .... , ., .. //// --,-- //// // /// //// //// ''//// //// - //// ///// //59// ...... //// //// //// //// -----...... //// //// //// //// //// //// -=- --- //// 862 /=/ /// // //// //// ...... //// ----- ////, ...... 860 ."././,/ /' --- - '.~: //// ...... ",/ /,// . --:--- . ,'/'/ /,'" ._- ','///' . . . . . " . .. . //// ,/ ///. /// ;' ,/ ././,/ ----- '// // 'c;?/,// / 4Z!r> / ///.' CH 13805 ...... //// "',/ /, ..., /' --- -- " //,'/ '/ ///. 826 --- - //,' ,/ '." /,'.'" '"

Figure 7. Detailed stratigraphic section recorded at road cut no. 5. For legend see Figure 2.

JuLy 1994 44 I. METCALFE AND K.R. CHAKRABORTY

Metres 1078·6

Conglomerate in basal port 1046 clasts ~ 5 em .:"':::::: W·:\~.;;:;\) b. 1044.2 ':::"::.:,:':';:: b. :&d'd'd~''': Metres 1041·7 00 ()o /,//,/ //// ...... : .... :::::::: CH 13605 //// 989 ...... //// //// I-::.... __ _ //// //// ...... //// ;::::::: ::.: /./// //// 1---­ //// - --- //// ...... //// 0 ...... //// ...... //// I-::..-_-_-__=_ //// //// ...... //// • 0 ...... " 1096 r: e •••••••••• //// / / / / //// //// .0...... //// ...... //// //// //// .' .... //// .... ::: ...... //// ...... //// //// :::::.:::: ..:: 1---- //// //// •: ...... :: : "0": //// ~.;\;;:::)/:} b...... e." .... //// //// //// [\(/X;; ~ //// ...... - //// ...... //// //// 1------//// //// ...... -.. //// ...... //// //// ...... , r::.... __- //// //// ...... -. //// ...... //// //// 1056 1086·2 //// ...... //// ...... //// ...... ///// //// //// //// 978 ///// '/ /// //// //// //// 977 ///// // / / ...... //// //// ...... /// // :::... ::::..... // // 1080 -- --= CH 1312~ 1019

••• •• ••• 0 •• 974 0···· ...... ·.0 .•.. _. CH 13545

Figure 8. Detailed stratigraphic section recorded Figure 9. Detailed stratigraphic section recorded at road cut no. 3. For legend at road cut no. 4. For legend see Figure 2. see Figure 2.

Geol. Soc. Malay"ia, Bulletin .J5 ASTRATIGRAPHIC LOG OF SEMANTAN FORMATION ALONG PART OF THE MENTAKAB-TEMERLOH BYPASS, PAHANG 45

Metres //// //// Metres //// // // // // //// / /,/ /' //,//' //// //// '// // ,;,. //,/ //// //// "/,/,/ /' //// /// / //// //// //// /// ,/ //// // // //// //// //// //// //// '//// //// //// //// //// /// / //// //// //// 1182 //// //// //// //// '//// //// //// //// //// //// //// //// // // //// //// //// //// ~ ~ //// //// //// //// //// //// //// //// /,>/ //// //// /// / //// //// //// //// //// //// //// //// //// //// //// //// //// //// //// //// //// //// //// //// '/// / //// //// '//// //// ///// ////. //// /////. //// //// //// //// 1258 ,./-,//~ ... TOP OF BY-PASS //// //// //// //// //// //// //// ///// //// //// //// SECTION //// //// //// //// //// ///// //// //// ( 114 Km from junction of //// "//// //// //// //// //// ///// ,/,/ /// BY - PASS and K.L //// '// // '///// //// //// //// ///// //// Mentakab Road) //// //// //// //// //// ///// .. ///,/ //// //// ,//// //// //// //// //// //// //// //// //// //// //// ,///// //// /// / //// //// //// //// //// // // ///// //// //// /// / / /// //// ///// '/// / //// //// ///// //// //// //// ///// //// //// //// 1169 //// //// //// ;.}: ~:; li 'i :~~:~; ~:: //,/ / //// //// //// //// //// 1168·2 ///// //// //// //// ///// ~ //// //// //// (§) //// //// ///// //// //// ...... , ..... - ~ //// //// ~ 1167 //// //// //// //// //// //// ...... //// //// //// //// 1166 ///// ~ //// //// //// //// ///// //// //// ///// /// / //// //// //// ///// //// //// ///// / /// //// //// //// ///// //// ~ //// ///// //// /// / //// //// ///// ///// //// /////. //// //// /// / //// ///// //// //// ///// //// //// //// /,,/,,: ./ ///// //// //// ///// //// /// / //// //// ///// //// //// ////. //// //// //// //// ///// //// //// ///// ///// //// //// //// ///// //// //// //// ///// //// //// //// ///// //// //// ~ //// ///// / / / /,' ///.', ///// ///// //,.',,/~ //," ./ //// ///// ',',,' /' ,". .. -./' ,/" //// ///// "/ /.- ,'. ,/ " /." 1128 //// /////. 1210 /' ,,"'/,/ /',",.' /'. .. /.,' /;,'.

Figure 10. Detailed stratigraphic section recorded at Figure 11. Detailed stratigraphic section recorded at road cut no. 1. For road cut no. 2. For legend see Figure 2. legend see Figure 2.

July 1994 46 I. METCALFE AND K.R. CHAKRABORTY detailed sedimentological work is required to resolve Malaya Research Grant No. F28/78. Thanks are these possibilities. due to Mr. S. Srinivas for drafting works. The presence of an undisturbed 1.25 km thick section which forms part of the Middle to Upper REFERENCES Triassic Semantan Formation and which is considered to be probably entirely of Middle Triassic CHAKRABORTY, K.R., 1987. Tectonomagmatic evolution of age has implications for total thickness estimations Peninsular Malaysia: some observations and comments. of the Semantan Formation. The measured Warta Geologi 13, 61 (Abstract). thickness, together with other isolated sections of CHAKRABORTY, K.R., 1988. Subduction-collision models for the Malay Peninsula: An appraisal. Warta Geologi 14, Middle and Upper Triassic Semantan suggest a 266 (Abstract). minimum thickness of 2 km for the formation. This HUTCHISON, CS., 1989. Geological Evolution of . is in accord with the thickness of around 2 km Clarendon Press, Oxford, 355p. suggested by Khoo (1983). JAAFAR BIN AHMAD, 1976. The geology and mineral resources The strike and dip are essentially constant of the Karak and Temerloh areas, Pahang. District throughout the measured section and no repetition Memoir Geol. Surv. Malaysia, IS, 138p. of beds was detected. There is therefore no evidence KHoo, H.P., 1983. Mesozoic stratigraphy in Peninsula Malaysia. In: Proceedings of the workshop on stratigraphic of isoclinal folding, or imbricate thrusts which would correlation of Thailand and Malaysia, Volume I, Technical result in repetition of beds. This data should be Papers,370-383. Geol. Soc. Thailand/Geol. Soc. Malaysia. taken into account for tectonic models of the region. LUM KOKE CHEONG, 1976. Geology and petrology of the Since there is no evidence of imbricate thrusting, area, Pahang, Malaysia. Unpublished B.Sc. the Semantan Formation cannot be an accretionary (Hons.) Thesis, University of Malaya. prism as has been suggested by some workers. It METCALFE, I., SIVAM, S.P., AND STAUFFER, P.H., 1982. also appears that the Semantan Formation has not Stratigraphy and sedimentology of Middle Triassic rocks been subjected to strong compressional orogenic exposed near Lanchang, Pahang, Peninsular Malaysia. deformation. This appears to lend support to the Geol. Soc. Malaysia Bull., IS, 19-30. MITCHELL, A.H.G., 1977. Tectonic settings for explacement of views expressed by Chakraborty (1987, 1988) who Southeast Asia tin granites. Geol. Soc. Malaysia Bull., 9, argued against Late Triassic collision in the Malay 123-140. Peninsula. The data presented here however does RInD, M.F., 1980. Possible Palaeozoic drift of S.E. Asia and not preclude the Semantan having formed in a Triassic collision with China. J. Geol. Soc. London, 137, fore-arc or intra-arc basin developed over an 635-640. accretionary wedge. SENGOR,A.M.C, 1984. TheCimmerideorogenic system and the tectonics of Eurasia. Geol. Soc. Am. Spec. Pap., 195, 82 p. ACKNOWLEDGEMENT SENGOR, A.M.C, 1986. Die Alpiden und die Kimmeriden: die verdoppelte Geschichte der Tethys: Reply. KRC gratefully acknowledges the University of Geologische Rundschau 75, 501-510.

------.~.~~-...------Manuscript received 13 February 1993

GeoL. Soc. MaLaYJia, BuLLetin 55