Bulletin of the Geological Society of Malaysia, Volume 8, Dec, 1977, pp. 45 – 60
1Jabatan Geologi, Universiti Malaya, Kuala Lumpur
2Sarawak Shell Berhad, Miri
3Robertson Research Ltd., Singapore
Abstract: The Foothills Range in the Bentong-Raub area east of the Main Range in Pahang is composed of three distinct rock units: schist, chert/argillite, and redbed conglomerate/sandstone, separated by at least one and probably two major unconformities. Ultrabasic rocks, mainly serpentinite, occur in parts of the range. The chert/argillite unit contains fossil radiolarians, and shows evidence of having been deposited in a marine, reducing environment; whereas the conglomerate/sandstone unit is almost certainly continental and was probably deposited by fluviatile processes, in a piedmont environment. The structure in the Raub area is homoclinal, eastward dipping, whereas in the Bentong area, a major overturned syncline and a complementary anticline, have caused a repetition of the outcrop of the units. Hitherto these units have been regarded as facies of a single stratigraphic unit, the “Bentong Group”.
The schist, chert/argillite and conglomerate/sandstone continue along strike from Bentong southeast to the Karak and Jelebu areas, where the argillite contains Lower Devonian graptolites, and have been mapped together as facies of the “Karak Formation”. West of Bentong, in the Genting Sempah area a similar sequence of schist, chert/argillite and redbeds has been mapped as facies of the “Bentong Group”.
Evidence presented here shows that the “Bentong Group” and “Karak Formation” are not valid lithostratigraphic units, but comprise three separate formations of contrasting lithology. The suggested sequence in the Raub-Bentong area is:
(Raub Group: Early Carboniferous and Younger)
Conglomeratic redbeds: Earliest Carboniferous, or Devonian
Chert/argillite: Early Devonian
Schist: Earliest Devonian or older