Lower Permian glacially influenced deposits in Phuket and adjacent islands, peninsular Thailand

Abstract

It has previously been proposed that the Sibumasu block of Southeast Asia, which contains glaciomarine deposits, became detached from the Gondwana margin during the Early Permian. A combination of facies analysis and the identification of dropstones and dump structures from a Lower Permian diamictite-bearing sequence at Phuket, Thailand, and adjacent islands suggests that the sediments originated as glaciomarine and debris-flow deposits. The Lower Permian diamictite-bearing sequence in the study area corresponds to the Ko Sire and Ko He Formations, both of which consist of three principal lithofacies: diamictite, sandstone, and fine-grained facies. The low-lying Ko Sire Formation is up to 400 m thick and is characterized by laminated mudstone; the presence of dropstones and dump structures associated with Cruziana ichnofacies indicates ice-rafted sedimentation in a glacially influenced offshore area. The Ko Sire Formation is overlain by a diamictite sequence of the Ko He Formation (up to 400 m thick). Poorly and well-stratified diamictites with tabular and lensoidal geometries, in combination with resedimentation textures, indicate that the diamictites within the Ko He Formation are debris-flow deposits. The similar lithology of clasts in the diamictites and dropstones possibly suggests that the debris-flow diamictite was presumably remobilized from pre-existing glacial deposits. The evidence of a glacially influenced offshore environment supports a previously proposed paleogeographic interpretation in which the Sibumasu block was most likely located at the Northwest Australian margin of Gondwana.

Nd isotopic composition of Late Devonian seawater in western Thailand: Geotectonic implications for the origin of the Sibumasu terrane

“…Unfortunately, for these both reconstructions the authors did not provide any clear evidence. Very recently, Ampaiwan et al (2009) studied Lower Permian glaciomarine deposits in peninsular Thailand (part of Sibumasu) and showed that they were in direct contact with the Australian basement. However, they placed Sibumasu west of New Guinea, in a distal position to Australia, whereas the Lhasa Block and West Burma were positioned to form the proximal shelf along the NW Australian margin.…”

“…The origin of this continental crustal block is well documented by Gondwanan affinity of Ordovician and Late Paleozoic biota (e.g., Burrett and Stait, 1985;Agematsu and Sashida, 2009) and the occurrence of Late Carboniferous-Early Permian glacial-marine diamictites (Stauffer and Mantajit, 1981;Stauffer and Lee, 1986;Metcalfe, 1988;Ampaiwan et al, 2009;Ridd, 2009b). Sibumasu rifted from Gondwana during Early Permian time, then dispersed, and finally collided with Indochina in the Late Triassic.…”

The Phuket Terrane: A Late Palaeozoic rift at the margin of Sibumasu

“…Recent sedimentological studies by Ampaiwan et al (2004Ampaiwan et al ( , 2009) on the Kaeng Krachan Group which crops out on the eastern shore of Phuket Island (Fig. 1) are the most detailed yet to have been carried out and provide convincing evidence that the rocks are glacio-marine as well as debris-flow deposits.…”

“…The thickest measured sections are on the eastern side of Phuket, at Laem Phap Pha (Fig. 3), and are only 400 m thick (Ampaiwan et al, 2009). And at the Kaeng Krachan Dam the four named formations of Chaodumrong et al (2007) total only 250 m thick.…”

“…measured 150 m of sandstone, siltstone and mudstone from which he obtained an Early Permian cool-water brachiopod fauna Ampaiwan et al (2009). measured nearly 300 m at Ko Phi Phi and noted that although in his view dump-structures and dropstones are absent, there are some thin intervals (<5 m) of diamictite and scattered rounded pebbles within laminated mudstone and siltstone;Ueno et al (2005) on the other hand did interpret the scattered pebbles as dropstones and furthermore identified three large-scale sedimentary cycles (cycles > 100 m) of shallow-marine sandstone passing up into thin debris-flow (diamictite) beds and then to black shale to siltstone.…”