Bulletin of the Geological Society of Malaysia, Volume 20, August 1986, pp. 311 – 361
BP, Tanglin P.O. Box 288, Singapore 9124
Abstract: A dominantly clastic succession separates the Ordovician-Silurian/Devonian Thung Song Limestone from the Permian Rat Buri limestone in peninsular and western Thailand. The stratigraphic organization, nomenclature, correlation and palaeogeography of these mid-Palaeozoic strata have been the subject of considerable misunderstanding and dispute.
Confusion began with the misconception (Brown et al., 1951) that part of this sequence (the “Phuket series”) was of Cambrian age and therefore distinct from strata shown to be Silurian to Carboniferous (the “Kanchanaburi series”). Although this error was clarified by subsequent fossil discoveries (Baum and Koch, 1968; Young and Jantaranipa, 1970), attempts to order the stratigraphy from limited areas and failure to realise that the top of the sequence is diachronous have resulted in various overlapping,·irreconcilable and internally inconsistent interpretations.
An attempt is made here to resolve the stratigraphic organization of these rocks in terms of the American Code of Stratigraphic Nomenclature, although it is not yet possible to formalize all the rock units involved.
The precedence accorded by Baum and Koch (1968) to the name Kanchanaburi is followed here as is the assignment of group status to the Phuket by Mitchell et al. (1970). The tentaculite-bearing shales of the original “Kanchanaburi series” are placed in the new Bannang Sata Group and the Kanchanaburi therefore assumes supergroup rank to embrace these two rock units. Whilst further work needs to be done to establish the component formations of the (Silurian-Middle Devonian) Bannang Sata, the Phuket Group is here subdivided into the Khlong Kaphon formation (Middle Devonian – Lower Carboniferous) below and the Pathiu formation (Lower Carboniferous to Lower Permian) above.
The Kanchanaburi supergroup is thought to constitute a continental margin sequence, probably generated on the flanks of Gondwanaland and behind a volcanic arc. In part the Bannang Sata group is of restricted basin (euxinic) facies. The Khlong Kaphon formation is largely comprised of a distinctive, and much-discussed, pebbly mudstone, diamictite or tilloid plus greywacke. Whilst also including mudstone and greywacke, more mature arenite is the dominant component of the Pathiu formation, possibly indicative of another source area and certainly pointing to shallowing of the basin of deposition. The Pathiu may, however, be absent, in part or in entirety due either to non-deposition and/or erosion prior to the major Permian transgression.
The origin of the Phuket group is deliberated upon and, following the hypotheses of Ridd (1971a) and Asnachinda (1978), it is thought that the bulk of this rock unit was deposited in a graben formed as a continental fragment (“Shan-Thai”) rifted away from Gondwanaland. Despite increasing suggestions that the Phuket is glaciogenic, in part or in whole, no unequivocal contribution from glacial sources is evident.