Gondwana Research 19 (2011) 47–60 Contents lists available at ScienceDirect Gondwana Research journal homepage: www.elsevier.com/locate/gr Paleo-environments and tectonic setting of the Mesozoic Thung Yai Group in Peninsular Thailand, with a new record of Parvamussium donaiense Mansuy, 1914 Wirote Saengsrichan a,b,c,1, Thasinee Charoentitirat b,c, Assanee Meesook a, Ken-ichiro Hisada d, Punya Charusiri b,c,⁎ a Department of Mineral Resources, Rama VI Road, Bangkok 10400, Thailand b Department of Geology, Faculty of Science, Chulalongkorn University, Bangkok 10330, Thailand c Earthquake and Tectonic Geology Research Unit, Chulalongkorn University, Bangkok 10330, Thailand d Division of Earth Evolution Sciences, Graduate School of Life and Environmental Science, University of Tsukuba, Tsukuba, Ibaraki 305-8571, Japan article info abstract Article history: The Thung Yai Group extends over a large area of peninsular Thailand, along the eastern margin of the Shan Received 23 August 2009 Thai block. Bound by angular unconformities 300 m thick dominantly detritic brackish to non-marine Accepted 17 May 2010 deposits with few intercalated limestone beds between Triassic marine and Tertiary non-marine sediments, Available online 27 May 2010 represent the Thung Yai Group that comprises four formations: Khlong Min, Lam Thap, Sam Chom, and Phun Phin Formations. In the Ao Luk–Plai Phraya (ALPP) area, the Khlong Min and Lam Thap formations yield Keywords: marine, brackish-water and non-marine fossil assemblages. These include trace fossils and for the first time Jurassic–Cretaceous Paleo-environments in peninsular southern Thailand, the bivalve Parvamussium donaiense Mansuy, 1914. Based on fossil Tectonic setting determinations, the Thung Yai Group has a late Early Jurassic to Early Cretaceous age. Krabi Our new observations help unravel the tectonic history of Mesozoic Peninsular Thailand. After the complete Thung Yai Group closure of the Paleotethys in the Late Triassic, renewed inundation, from the late Early Jurassic to the early Peninsular Thailand Middle Jurassic, brought a regime of shallow to open marine and lagoon sedimentation over northwestern, Parvamussium donaiense western and southern peninsular Thailand, in the eastern part of Sundaland bordering the Mesotethys to the west. © 2010 International Association for Gondwana Research. Published by Elsevier B.V. All rights reserved. 1. Introduction Charusiri et al., 2002; Meesook et al., 2005)(Fig. 2). Our focus of interest here relates to extensive on-shore petroleum exploration. Mainland Southeast Asia comprises three major terranes: Western The present study area is part of the Ao Luk and Plai Phraya Burma, Shan–Thai and Indochina (Burrett, 1974; Stauffer, 1974; districts (ALPP) that coverapproximately400km2 within the Hutchison, 1975; Gatinsky et al., 1978; Bunopas, 1981; Burrett et al., Songkhla basin in the northern part of the Krabi Province, southern 1990; Barber and Crow, 2003; Metcalfe, 2006, 2010). Thailand peninsular Thailand (Fig. 1). Geomorphologically an intramontane consists in the west of the eastern part of the Shan–Thai terrane and sub-basin, the area of the ALPP is bound to the east by the Phanom in the east of the western part of the Indochina terrane. The Benja Range culminating at 1340 m above mean sea level (msl) and intervening tectonic units (Fig. 1) are the Lampang–Chiang Rai unit, west of it, the undulating terrains of the northwest–southeast for the eastern part of Shan–Thai, and the Nakhon Thai unit, for the trending, about 500 m high Phanom Hills extend. western part of Indochina (Charusiri et al., 2002, 2006; Hara et al., The Mesozoic sequences in Thailand comprise marine, brackish and 2009). Our study area belongs to the southern part of eastern Shan– continental facies (Meesook and Grant-Mackie, 1996). Exclusively Thai terrane, west of the Pattani suture (Charusiri et al., 2002), which marine in western Thailand, the most fully developed Jurassic sediments is considered to connect southward with the Bentong–Raub suture, in occur in the Mae Hong Son–Kanchanaburi basin of northwest and west Malaysia. The latter suture resulted from the collision of the Indochina Thailand. In peninsular Thailand, the Chumphon basin to the north and and Shan–Thai terranes (Bunopas, 1981; Hahn et al., 1986; Panjasa- the Songkhla basin, further south contain Jurassic marine sediments. watwong, 1991) mostly during Late Triassic times (Metcalfe, 1989; With exception of the continental basins in northeastern Thailand, most marine and brackish Jurassic basins are elongated north trending, normal fault or strike-slip bound (Fig. 1). In the Songkhla basin, the Ao ⁎ Corresponding author. Department of Geology, Faculty of Science, Chulalongkorn Luk–Plai Phraya (ALPP) area comprises the Thung Yai Group that University, Bangkok 10330, Thailand. Fax: +66 22185464. E-mail address: [email protected] (P. Charusiri). encompasses four formations: Khlong Min, Lam Thap, Sam Chom, and 1 Deceased. Phun Phin Formations. The Khlong Min and Lam Thap Formations yield 1342-937X/$ – see front matter © 2010 International Association for Gondwana Research. Published by Elsevier B.V. All rights reserved. doi:10.1016/j.gr.2010.05.006 48 W. Saengsrichan et al. / Gondwana Research 19 (2011) 47–60 Fig. 1. Map of Thailand showing major tectonic units, distribution of the Jurassic–Cretaceous sedimentary rocks, associated basins, and major tectonic features (modified after Polachan and Sattayarak, 1989; Charusiri et al., 2002). bivalves and some other macrofossils that provide age constraints for bivalves occur. Brackish-water heterodont bivalves among them stratigraphic correlation and the establishment of the continuity of show ecological and taxonomical diversifications (Kondo et al., lithologic units. Their relations with the better-known non-marine 2006). These play an important role in the evaluation of their paleo- Khorat Group to the east are also considered. environment and the delineation of their paleo-biogeography (Arias, Besides the first discovery of the Jurassic bivalve Parvamussium 2008). All fossils cited in the text are part of collections during donaiense Mansuy, 1914 in the Songkhla basin, other Mesozoic fieldwork by the authors, unless otherwise indicated. W. Saengsrichan et al. / Gondwana Research 19 (2011) 47–60 49 Fig. 2. Map of southern peninsular Thailand showing regional distribution of mainly clastic sedimentary rocks belonging to the Thung Yai Group (modified after Raksaskulwong, 1994; Teerarungsigul, 1999). The prime objective of this paper is to contribute a detailed Previously, Sanansiang (1977) had mapped the Mesozoic rocks lithostratigraphy and paleontology of the Mesozoic sediments in the exposed mostly in the Chumphon–Nakhon Si Thammarat and Trang Ao Luk–Plai Phraya (ALPP) basin, using simultaneously tectonic, areas as a single unit (Fig. 1). Subsequently, Asama et al. (1981) paleo-environmental, lithostratigraphic and paleontological data. described six species of fossil plants from clastic strata of the Trang area and found these to be different from those of the Khorat Group 2. General stratigraphic setting in northeastern Thailand (Kon'no and Asama, 1973) but closely similar to those of the Early Cretaceous Gagau Group in the Malayan Mesozoic rocks in southern peninsular Thailand were first peninsula (western Malaysia). reported by Kobayashi and Tokuyama (1959) with the discovery of Raksaskulwong et al. (1989) established the Mesozoic stratigraphy Triassic marine bivalve, Halobia sp. Hayami (1960) described some in the Thung Yai–Klong Thom area, recognizing five formations: Sai bivalves in argillaceous sandstone at the Hadd Sai Ri beach, Pak Nam Bon, Lam Thap, Khlong Min, Sam Chom, and Phun Phin in ascending Chumphon Bay, Chumphon Province, and proposed a probable order. Jurassic age for his Eomiodon chumphonensis Hayami, 1960. The Khlong Min Formation that yields the Jurassic fossils reported The systematic geological mapping in southern Thailand at a scale in this paper, was originally regarded as a member of the Tertiary Sin of 1:250,000 commenced as a project of the Department of Mineral Pun Formation, containing the bivalve Corbula njalindungensis (Martin Resources in 1989 with special emphasis on Mesozoic sediments. 1919), which is indicative for the Miocene (Beets, 1981). In the Bang 50 W. Saengsrichan et al. / Gondwana Research 19 (2011) 47–60 Hian area, Krabi and Surat Thani Provinces, Tantiwanit et al. (1989) sandstone. Zuoqi (1993) studied the palynology of the red-beds of subdivided the Mesozoic sequence into two formations: Sai Bon and peninsular Thailand and found a spore-pollen assemblage in sand- Lam Thap. The Sai Bon Formation consists mainly of red brown clastics stone and shale beds that consists predominantly of gymnosperm and dolomitic limestone with abundant foraminifera and bivalves, pollens, of Late Jurassic age. Further to the north, ammonite and while the Lam Thap Formation is chiefly composed of red beds, arkosic bivalve fossils indicative of the Early Bajocian (Middle Jurassic) were Fig. 3. Geologic map and cross-sections showing the distribution, ages and simple structures of major rock units in the Ao Luk–Plai Phraya area, Krabi Province. W. Saengsrichan et al. / Gondwana Research 19 (2011) 47–60 51 abundantly found in fine-grained clastic rocks of the Khao Lak overlies with an angular unconformity the marine Triassic Sai Bon Formation, in the Chumphon Province, about 80 km north (Meesook Formation that itself overlies unconformably the Paleozoic