oa Shallowing-Upward Sequence in a Late Middle-Permian (Midian) Alatoconchid-Bearing Strata, Khao Khwang Carbonate Platform, Central Thailand

Extensive field work to establish the occurrence and distribution of Permian alatoconchid-bearing strata in Thailand has been carried out in recent years. Alatoconchid faunas occur in limestone sequences within both the Indochina and Sibumasu (Shan-Thai) Terranes. In the Indochina Terrane, they were found in Khao Khwang and Pha Nok Khao platforms of the Saraburi Group. In the Sibumasu Terrane they were observed in carbonate platform sequences in the Ngao, Ratburi and Chantaburi Groups in northern, western and eastern Thailand, respectively. The current research has been carried out in the Saraburi Group. The key localities include Khao Somphot, Pak Chong and Tha Sa-ad sections in Lopburi, Nakhon Ratchasima and Loei areas, respectively. Microfacies study and palaeontological data indicate that shallow marine environments of deposition prevailed at all of these localities during Middle Permian time. In addition, evidence of occasional storm events and subaerial exposure were observed within shallowing-upward sequences at Khao Somphot.