No. 6] Pron. Japan Acad., 55, Ser. B (1979) 259 52. On the Geological Age of the Tanjong Malim Limestone in Peninsular Malaysia By Teiichi KOBAYASHI, M. J. A., GAN Ah Sai,' and K. N. MURTHY*) (Communicated June 12, 1979) Tanjong Malim is situated about 80 kilometres north-northwest of Kuala Lumpur. In 1978 Gan Ah Sai and K. N. Murthy discovered fossils in the metamorphosed limestone intercalated with metamor- phosed argillaceous rocks. The argillaceous rocks comprise quartz- mica schist, graphitic schist and phyllite. These rocks in the north- eastern part are thermally metamorphosed to hornfels and spotted slate by the granite. Arenaceous rocks crop out in the northwestern part of Tanj ong Malim. These rocks are mainly quartzite. The age of the argillaceous rocks are considered to be Lower Palaeozoic and the arenaceous rocks to be Upper Palaeozoic. The coarse-grained porphyritic biotite granite is Triassic. The Tanjong Malim area is presently mapped as Silurian in the Geological Survey Map of West Malaysia (Chung, 1973), but from the fossils the age is definitely older. Mr. Yin Ee Heng, chief geologist of the Geological Survey of Malaysia presented to the senior author during the Symposium of Geology and Palaeontology of Southeast Asia at Tsukuba in 1978 some fossils and photographs for identification. In 1973 a few more fossil specimens were sent to the author by Gan Ah Sai. The fossil locality is situated in a gravel pump tin mine in Tanj ong Malim. The fossils are found in metamorphosed dolomitic limestone and are not so well preserved to permit their generic deter- mination. As the result of palaeontological study the following forms are distinguishable among them. Cochlioceras ? sp. Fig. 1 (X0.45), Endoceras s. 1. sp. Fig. 2 (X0.46), Stereoplasmoceras ? sp. Fig. 3 (X0.76), Orthoceras s. 1. sp. Fig. 4 (X0.56), Ormoceras (Parormoceras ?) sp. Fig. 5 (X0.63), Ormoceroid a sp. Figs. 6a (X 0.56) and 6b (X0.83), Ormoceroid b sp. Fig. 7 ( X0.94) and Lophospira sp. Fig.8 (X0.83), beside a liospirid, other trochoid and discoidal gastropods. *' Geological Survey of Malaysia, Jalan Gurey, Kuala Lumpur 15-01, Malaysia. 260 T. KOBAYASHI, GAN A. S., and K. N. MURTHY [Vol. 55(B), Cochlioceras ? sp, is represented by a slightly expanding ortho- cone ; siphuncle submarginal, as wide as a half or one-third the conch's diameter ; septa subrectangular at neck, apparently ellipochoanoidal ; connecting ring thin and nearly straight ; septal distance fairly long; siphuncle and camerae filled with dirt. Endoceras s. 1. sp. is depressed ovate in cross section; siphuncle large, ventral and filled up with lime; endocone-structure obscure; septa separated from one another in moderate length ; no organic deposit in camerae. There are two or more kinds of orthoceroids. Stereo plasmoceras ? sp. is a gradually tapering orthocone with a narrow subcentral siphuncle, tubular but somewhat constricted at neck ; organic lining present on siphuncular wall ; organic deposit not well developed in camerae. Another orthoceroid has a narrow tubular siphuncle and short No. 6] Age of Tanj ong Malim Limestone, Malaysia 261 camerae like the preceding, but in this the siphuncle is excentric and organic deposit absent in siphuncle and camerae. It resembles also Bactroceras, but the siphuncle is not marginal. Ormoceras (Parormoceras ?) sp. is represented by a moderate sized straight conch slowly tapering; siphuncle subcentral, very nar- row, about one-tenth of conch's diameter ; septal distance fairly short; septal concavity weak ; organic deposits present on two sides of septa. The siphuncular outline is not well preserved, but the general aspect of the conch in the longitudinal section through the siphuncle resem- bles Ormoceras langkawiense and its allies, for example, Reed's Ormo- ceras sp. b from the Orthoceras bed, South Shan State, Burma. Another ormoceroid having a little broader siphuncle and crowded septa of strong concavity shows the cyrtochoanitic septal neck in longitudinal section. See a hooked neck in the right lower part of Fig. 6b. Avery small ormoceroid in Fig. 7 allied to the precedings has a very broad nummuloidal siphuncle. Thus the Ormoceratidae are represented by three distinct forms in this fauna. The family Orthoceratidae is distributed widely from Ordovician to Triassic. Less so is the family Ormoceratidae ,but its distribution is still as long as from Middle Ordovician to Lower Carboniferous. The geological range of the Endoceratidae is, on the contrary, so restricted as from late Lower Ordovician to Upper Ordovician, if the doubtful record of Cameroceras from the Middle Silurian is ignored (Teichert,1964). Cochlioceras is an Arenigian-Llanvirnian genus and Stereoplasmoceras a Middle Ordovician one, although their generic reference cannot be warranted. Although Ormoceras as a genus is long ranged, its inclusion suggests that the fauna is not older than Middle Ordovician. Therefore, judging from the cephalopods the age of the Tanjong Malim fauna is most probably Middle Ordovician. Among the gastropods the Lophospirinae is an Ordovician- Silurian subfamily. The lophospirid of Tanjong Malim resembles Middle Ordovician Lophospira a sp. from Satun, extreme south Thai- land (Kobayashi and Hamada, 1964). Maclurites is a common genus in the Ordovician faunas. The discoidal gastropod may also be a Helicotoma like H, jonesi Kobayashi, 1959 or Malayaspira like M. rugosa Kobayashi, 1958, both known from the Ordovician in the northwestern part of West Malaysia. Therefore the above age deter- mination is supported by associated gastropods. The nearest Lower Palaeozoic limestones are the Chemor lime- stone of the Kinta valley of Perak in the north and the Kuala Lumpur limestone at Setapak, Selangol in the south. While the former yields Silurian corals, the latter contains Upper Silurian corals, brachiopods, 262 T. KOBAYASHI,GAN A, S., and K. N. MURTHY [vol. 55(B), gastropods and crinoids (Jones, 1973; Hamada et al., 1975). These Silurian faunas differ from the Tanj ong Malim fauna essentially in the presence of corals and absence of cephalopods. Cephalopods are, on the contrary, often associated with gastro- pods as indicated by the gastropod limestone in the Langkawi Islands in which discoidal gastropods are common (1959) . The actinoceroid limestones are known to be wide spread from the borderland between Thailand and Malaysia (1958) to Northwest Thailand (1961) . Ormo- ceras is well represented in the Ormoceras langkawiense horizon of Pulau Tanjong Tembus Dendang. Ormoceroids occur together with Lophospira in calcareous shales at Satun at the Malaysian frontier of Thailand (Kobayashi and Hamada, 1964b) . Because Stereoplasmo- ceras, Ormoceras, Lophospira, and Maclurites are all leading members of the Machiakou-Toufangian faunas of North China and North Korea (Grabau, 1922 ; Kobayashi, 1929, 1930) , it is undeniable that the Tanjong Malim fauna is closely allied to the Toufangian fauna of Eastern Asia. This chronology and faunal affinity are in support of the fact that the fauna is quite different from the Upper Ordovician fauna of Tambak, Kedah and Telek Memplam, Pulau Langgon, Langkawi Islands (Kobayashi and Hamada, 1970, 1978), and the Silurian ones of Pulau Langgon (Kobayashi, Jones and Hamada, 1964; Kobayashi and Hamada, 1964a, 1971) in all of which trilobites are dominant. It is certainly a remarkable fact that such cephalopods and gastropods constitute the leading group of the Ordovician faunas in the Burmese Malayan geosyncline to the south from the Southern Shan State, Burma (Reed, 1936), as already pointed out (1961, 1969, 1973). Now it is ascertained that they are distributed to the south as far as the vicinity of Kuala Lumpur. Because the Tanjong Malim , fauna is Ordovician in age and most probably Middle Ordovician, the argillaceous metamorphosed rocks above and below the fossiliferous limestone are evidently younger and older respectively, although it is a question how far the age of the metamorphosed formation expands in the older Palaeozoic era. Whatever the answer may be, the senior author is of opinion that the lower Palaeozoic formation of the area and the intruding granite on the east side probably belong respectively to the less-magmatic metamorphosed outer zone and the magmatic inner zone of the axis in the Triassic folded mountains (1978). Finally the authors record their sincere thanks to Mr. Yin Ee Heng of the Geological Survey of Malaysia and Professor T. Hanai of the University of Tokyo for their assistances and kindness. No. 6] Age of Tanj ong Malim Limestone, Malaysia 263 References cited Chung, S. E. (1973) : Geological Map of West Malaysia. Scale 1:500,000. Grabau, A. W. 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