A Permo-Triassic volcanic arc system, the Sukhothai Arc, is recognised between the Indochina and Sibumasu continental blocks. The Chanthaburi terrane is here interpreted as a fault-detached, highly disrupted southern segment of the Sukhothai Arc, occupying part of southeastern Thailand and extending into Cambodia. The Klaeng tectonic line is defined as the boundary between the Chanthaburi terrane and Sibumasu block. The stratigraphy of the Chanthaburi terrane is compared with that of the Sukhothai terrane in Northern Thailand. The Late Palaeozoic-Mesozoic sequences of these two volcanic arc terranes in the Sukhothai Zone share important similarities, but show marked contrasts to those of the Sibumasu and Indochina blocks, where the Late Permian-Triassic is largely absent due to the Indosinian I unconformity (western Indochina) or is dominantly carbonates with little terrigenous clastic input (Sibumasu). There is no clear evidence of pre-Carboniferous sedimentary rocks for either the Sukhothai or Chanthaburi terranes. Late Permian lyttoniid brachiopod shale near Klaeng in the Chanthaburi terrane was revisited. The brachiopod, previously reported as 'Leptodus', is re-identified to 'Oldhamina', the genus previously known, elsewhere in Southeast Asia, only in the Huai Tak Formation of the Sukhothai terrane. 'Oldhamina' in Thailand is confined to the Sukhothai Arc. The marine stratigraphy of the Sukhothai Arc is represented by a Permian-Triassic lithological succession of mixed carbonates and siliciclastics, with common volcanic material. The Late Permian and Triassic litho- and biostratigraphy of the Chanthaburi terrane are comparable with the upper Ngao and Lampang groups of the Sukhothai terrane; in particular, they share similar successions from 'Oldhamina' brachiopod bearing shale to 'Palaeofusulina-Colaniella' foraminifer bearing limestone in the latest Permian. Marine depositional conditions were terminated on the Sukhothai Arc by end-Triassic times, later than on the Indochina block (Late Permian) but earlier than on the Sibumasu block (Jurassic/Cretaceous).

The Permian-Triassic boundary (PTB) is defined in the GSSP section at Meishan, China at the base of Bed 27c and is recognised by the first appearance of the conodont 'Hindeoudus parvus'. The PTB is dated at 252.3 Ma by bracketing tuff CA-IDTIMS ages and is slightly younger than the main "end" Permian (late Changhsingian) mass extinction. Despite decades of searching, the PTB has not been located precisely to date in Malaysia and it is still unclear if a stratigraphic break occurs at the boundary. In central Peninsula Malaysia, there are three mogote hill limestone sections, Gua Panjang, Gua Bama and Gua Sei, that have yielded biostratigraphic data indicating the probably presence of the PTB. The Late Permian foraminifers 'Palaeofusulina' and 'Colaniella', which indicate a probable Changhsingian (but not latest Changhsingian) age have been reported from the lower parts of Gua Panjang and Gua Sei. Changhsingian conodonts including 'Clarkina' spp., 'Hindeodus julfensis' and 'Hindeodus typicalis', occur in the lowest part of the Gua Panjang by the presence of the Early Triassic has not yet been confirmed.

The Permian–Triassic boundary (PTB) is defined by the first appearance of the conodont species 'Hindeodus parvus' (Kozur & Pjatakova). It is now indicated to be 252.3 Ma by zircon U-Pb radio-isotopic dating (Mundil et al., 2004; Mundil et al., 2010). Despite decades of searching (e.g. Metcalfe, 1984), the PTB has not been located precisely to date in Malaysia. In Pahang, central Peninsular Malaysia, there are several limestone sections, which have yielded biostratigraphic data indicating the plausible presence of the PTB. Two of them, Gua Bama and Gua Sei, have now emerged as the most promising localities, since they both exhibit carbonate strata ranging from Upper Permian to Triassic. The Triassic nautiloid 'Sibyllonautilus bamaensis' was recently reported from the top of Gua Bama, confirming the presence of the Triassic (Sone et al., 2004). The Triassic nautiloid-bearing deposit accompanies abundant algae, which in general are extremely rare in the Early Triassic; therefore, it is interpreted that the uppermost part of the Gua Bama strata likely extends to the post-Early Triassic, most likely Middle Triassic (Sone et al., 2008). From the base of Gua Bama, Late Permian colaniellid foraminifers have been reported (Lim and Nuraiteng, 1994), and conodonts and brachiopods have recently been discovered. The conodonts include several species of 'Clarkina', 'Hindeodus julfensis' and 'Iranognathus movschovitschi', confirming a Changhsingian age. The brachiopods were found in the siliciclastic strata 2 m below the conodont beds; that is, passage strata from the underlying siliciclastic sequence to the limestones. They include the rare genus 'Dongpanoproductus', known elsewhere only from the upper Changhsingian of South China (He et al., 2005). Thus, the lowest part of Gua Bama is dated as late Changhsingian age, suggesting that the Gua Bama sequence probably includes the PTB transition.

The Permian-Triassic boundary (PTB), despite decades of searching, has not been located precisely to date in Malaysia. We are currently focusing our search for the PTB in central Peninsular Malaysia as part of our contribution to the geological heritage scheme launched by the National University of Malaysia (Universiti Kebangsaan Malaysia) and as a contribution to the new IGCP 572 Project "Restoration of marine ecosystems following the Permian-Triassic mass extinction: Lessons for the present". In central Peninsular Malaysia, there are several limestone karst hills which have yielded data indicating the possible presence of the PTB. Among them, Gua Bama has now emerged as the most prospective site, as it displays strata ranging from Upper Permian to Triassic. Its lithofacies is a thickly to massively bedded succession of limestones, with occasional tuffaceous layers.