Available online at www.sciencedirect.com ScienceDirect Palaeoworld 29 (2020) 552–567 Early Permian radiolarians from Southern Thailand, the deglaciation of Gondwana and the age of the basal Ratburi Group Hathaithip Thassanapak a , Mongkol Udchachon a,c,* , Jirasak Chareonmit b , Clive Burrett c a Applied Palaeontology and Biostratigraphy Research Unit, Department of Biology, Faculty of Science, Mahasarakham University, Mahasarakham 44150, Thailand b Geological Survey Division, Department of Mineral Resources, Rama VI Road, Ratchathewi, Bangkok 10400, Thailand c Palaeontological Research and Education Centre, Mahasarakham University, Maha Sarakham 44150, Thailand Received 2 November 2018; received in revised form 29 May 2019; accepted 21 June 2019 Available online 2 July 2019 Abstract The first radiolarian fauna obtained from Permian carbonates in Thailand is of late Kungurian age and is present in the basal beds of the carbonate–mudstone–chert Phap Pha Formation, Ratburi Group. This succession contains several species of the radiolarian Pseudoalbaillella, and some sponge spicules. The radiolarian fauna consists of abundant Pseudoalbaillella aidensis and P. elegans together with P. fusiformis, P. longtanensis, P. m. rhombothoracata and P. sp. A. Other species include P. cf. aidensis, P. cf. elongata, P. cf. fusiformis, P. cf. ishigai, P. cf. lomentaria, P. cf. longicornis, P. cf. longtanensis, P. cf. ornata, P. cf. simplex, P. cf. m. scalprata, P. cf. m. postscalprata, P. cf. u–forma m. I, P. cf. u–forma m. II, and P. spp. The radiolarian assemblage suggests its correlation to the P. longtanensis Zone which, in turn, is correlated to the P. ishigai Zone of late Kungurian age. The occurrence of an abundant but generically low–diversity radiolarian fauna suggests restricted physical conditions and, with other evidence, suggests deposition along a cool deglaciating or deglaciated continental margin with an abundance of silica possibly provided by glacial meltwaters. The abundant chert in the Phap Pha Formation is part of the widespread Permian Chert Event. © 2019 Elsevier Ireland Ltd Elsevier B.V. and Nanjing Institute of Geology and Palaeontology, CAS. Published by Elsevier B.V. All rights reserved. Keywords: Radiolarian; Limestone; Gondwana; Deglaciation; Peninsular Thailand; Permian Chert Event 1. Introduction The stratigraphic succession and global correlation of Per- mian radiolarian zones are well established (Aitchison et al., 2017; Zhang et al., 2018; Shen et al., 2019). Here we describe the first radiolarian occurence from the Permian carbonate formations of Thailand and assess its stratigraphic and palaeoen- vironmental significance. The Permian of Thailand is well known for its abundant marine faunas and evidence for Early Permian terrane rifting and Gondwana glaciation (Ridd, 2007, 2009a, 2009b, 2016; Ueno and Charoentitirat, 2011; Burrett et al., 2014). Widespread, tower-karsted Permian limestones are a major scenic attraction in Thailand and are placed in the Ratburi * Corresponding author at: Palaeontological Research and Education Centre, Mahasarakham University, Maha Sarakham 44150, Thailand. E-mail address: Mongkol.c@msu.ac.th (M. Udchachon). Group in the Sibumasu Terrane (or Shan–Thai Terrane, in part) of western Thailand, in the Saraburi Group in the Indochina Ter- rane of eastern Thailand, and in the Doi Chiang Dao Formation in the Inthanon Terrane of northern Thailand (Figs. 1–3). The Ratburi Group limestones of the Sibumasu Terrane con- formably overlie glacially influenced Lower Permian Kaeng Krachan Group siliciclastics (Figs. 4, 5) (Tantiwanit et al., 1983; Ueno et al., 2005; Chaodumrong et al., 2007; Ampaiwan et al., 2009; Chaodumrong, 2010). Faunas of the Upper Carboniferous–Permian of the Inthanon and Indochina terranes are exclusively thermophilic and ‘Cathaysian’ (or ‘Tethyan’) and contain abundant fusulinids, hermatypic corals and conodonts; whereas Lower Permian (Cisuralian) faunas from the Sibumasu Terrane have mainly cold-cool water Gondwana affinities and then generally become more thermophilic through the Permian (Fontaine et al., 1994; Shi and Archbold, 1995; Wang et al., 2013). However, the age of the transition from the siliciclas- tic Kaeng Krachan Group to the carbonate Ratburi Group is https://doi.org/10.1016/j.palwor.2019.06.003 1871-174X/© 2019 Elsevier Ireland Ltd Elsevier B.V. and Nanjing Institute of Geology and Palaeontology, CAS. Published by Elsevier B.V. All rights reserved.