Quaternary Science Reviews 22 (2003) 789–807 Stratigraphy and Holocene evolution of the mud-dominated Chao Phraya delta, Thailand Susumu Tanabe a , Yoshiki Saito b, *, Yoshio Sato c , Yuichiro Suzuki d , Sin Sinsakul e , Suwat Tiyapairach e , Niran Chaimanee e a Graduate School of Science and Technology, Niigata University, Ikarashi-2 8050, Niigata 950-2181, Japan b MRE, Geological Survey of Japan, AIST. Central 7, Higashi 1-1-1, Tsukuba 305-8567, Japan c Department of Geology, Faculty of Science, Chulalongkorn University, Phya Thai Road, Bangkok, Thailand d IGRE, Geological Survey of Japan, AIST. Central 7, Higashi 1-1-1, Tsukuba 305-8567, Japan e Geological Survey Division, Department of Mineral Resources, Rama VI Road, Bangkok 10400, Thailand Received 11 January 2000; accepted 30 October 2002 Abstract The central plain of Thailand was formed over the last 8–7 kyr mainly by the deltaic processes of two major rivers, the Chao Phraya and the Mae Klong. The delta plain is the third largest delta plain in Southeast Asia after that of the Mekong and the Irrawaddy. On the basis of sedimentological and paleontological analyses of samples from three boreholes and an open-pit survey, the evolution of the delta was clarified with high-resolution 14 C dating. After the maximum transgression at between 8 and 7 cal kyr BP, the delta system migrated southward into the paleo-Gulf of Ayutthaya. A large mud shoal (the Sananivate Mud Shoal) formed near the mouth of the paleo-gulf between 7 and 3 cal kyr BP and facilitated its infilling. As a result, the delta has prograded rapidly particularly during the last 2 kyr. Deltaic sediment volume for the last 7.570.5 kyr shows that the average rate of sedimentation was 23.173.6 million t/yr, which is nearly the same as the present total sediment discharge from both rivers. The comparatively wide delta plain relative to sediment discharge resulted from the stable sea level, the shallow paleo-gulf acting as a receiving basin, and effective sediment trapping because of the mud shoal. r 2003 Elsevier Science Ltd. All rights reserved. 1. Introduction The Chao Phraya delta, located at the head of the Gulf of Thailand, has an area of 10,400 km 2 and is the third largest delta in Southeast Asia after the Mekong and Irrawaddy deltas. The Chao Phraya and the Mae Klong rivers, which are the largest rivers in terms of water and sediment discharge among those emptying into the gulf (Milliman et al., 1995), comprise the delta system. The deltaic sediments are fine grained (Cox, 1968; Moh et al., 1969; Sinsakul, 2000). Mangroves and tidal flats fringe the deltaic coast, which is classified as a microtidal low-energy coast. The Chao Phraya delta plain is wide in comparison with the sediment discharge of the delta. It is comparable in area to the Nile, Song Hong (Red River), and Mackenzie deltas (Coleman and Roberts, 1989; Orton and Reading, 1993), but the sediment discharge of the Chao Phraya River, even including the discharge of the Mae Klong River, is less than one-fifth that of these large rivers (Milliman and Meade, 1983; Milliman et al., 1995). The Late Pleistocene to Holocene marine sediments of the Chao Phraya delta are collectively known as Bangkok Clay (Cox, 1968; Moh et al., 1969; Sinsakul, 2000), and consist of the Holocene Bangkok Soft Clay unconformably overlying the Late Pleistocene Bangkok Stiff Clay (Rau and Nutalaya, 1983). The Holocene sediments are divided into lower transgressive peaty (mangrove swamp) sediments and upper regressive deltaic sediments (Somboon, 1988; Somboon and Thiramongkol, 1992; Sinsakul, 2000; Songtham et al., 2000; Woodroffe, 2000). Somboon and Thiramongkol (1992) examined the period of the mid-Holocene high- stand (MHH) and its paleogeography in detail on the *Corresponding author. Tel.: +81-298-61-3772; fax: +81-298-61- 3747. E-mail address: yoshiki.saito@aist.go.jp (Y. Saito). 0277-3791/03/$ - see front matter r 2003 Elsevier Science Ltd. All rights reserved. PII:S0277-3791(02)00242-1