On the contrary, the younger Pha Daeng, Kang Pla, and Wang Chin Formations deposited in the Phrae Sub-basin are confined to the Upper Triassic ( Chaodumrong, 1992 Chonglakmani, 2011). The Lampang Sub-basin comprises five formations of Lower to Upper Triassic, namely Phra That, Pha Kan, Hong Hoi, Doi Long, and Pha Daeng Formations ( Bunopas, 1994 Chonglakmani, 2011). The Lampang Group was interpreted to be deposited in two sub-basins, Lampang Sub-basin and Phrae Sub-basin. There is no report or publication about the microfacies in the two formations located in the northeastern Mae Moh, southwestern Chae Hom, and Ngao areas. (2018) are overlapping and only distributed in certain areas. Paleontological studies have provided some evidence of the depositional age and environment, but the sample areas in Chaodumrong and Rao (1992), Kobayashi et al. In the Pha Kan and Doi Long Formations, sedimentology and microfacies from the carbonate rocks have only been done in the central and northern Lampang areas (e.g., Chaodumrong, 1992 Chaodumrong and Rao, 1992 Miyahigashi et al., 2012). However, the depositional model and the volcanic influence have not been clarified or reported in this area. Reconstruction of carbonate depositional environment associated with arc development is important for understanding the paleoenvironment and volcanic arc activity that occurred in the Sukhothai Zone. The Triassic carbonate successions, including Pha Kan and Doi Long Formations, of the Lampang Group developed in response to volcanic arc activity of the Sukhothai Zone ( Sone and Metcalfe, 2008 Hara et al., 2017). The depositional age of the Lampang Group was assigned to Early to Late Triassic (Olenekian to Carnian age) based on ammonoids, bivalves, and foraminifers ( Chonglakmani and Grant-Mackie, 1993 Carey et al., 1995 Kobayashi et al., 2006 Chonglakmani, 2011). They are mainly sandstone, mudstone, and limestone, known as the Triassic Lampang Group (e.g., Charoenprawat et al., 1994 Chaodumrong and Burrett, 1997 Kobayashi et al., 2006 Chonglakmani, 2011 Ueno and Charoentitirat, 2011). Triassic sedimentary successions, which formed as intra-arc facies of the Sukhothai Zone, are widely distributed in northern Thailand. Consequently, our study shows that the Lampang Group in northern Thailand can be correlated with the Lincang Massif of the western Yunnan Province, PRC and the northwestern Lao PDR. The microfacies and sedimentological study show that this carbonate system was influenced by the nearby volcanic arc. The inferred depositional environment is a carbonate platform with a well-developed lagoon, small-scale reefs, and bioclastic and oolitic shoals, as parts of a carbonate ramp. Based on field observations and microfacies analysis, twelve major facies, corresponding to specific depositional environments within a carbonate setting, have been established. Both formations have diverse skeletal fossils, including foraminifers, sponges, calcimicrobes, calcareous algae, bivalves, echinoderm spines and fragments, ostracods, gastropods, and other fossils. The goal of this study is to analyze the lithology and microfacies of the carbonate rocks of the Pha Kan and Doi Long Formations and reevaluate the existing depositional models and carbonate settings. These deposits are important for the reconstruction of depositional environments and regional correlations of the Triassic carbonate rocks with respect to the volcanic arc of the Sukhothai Zone during the Triassic. These formations are mixed carbonate and siliciclastic sediments and widely exposed in the Lampang area. Triassic carbonate rocks of Pha Kan and Doi Long Formations of Lampang Group consist mostly of carbonate successions deposited in the Sukhothai Zone, northern Thailand.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |