Carbonate microfacies and depositional model of Triassic Pha Kan and Doi Long Formations, Lampang Group, Sukhothai Zone, Northern Thailand

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. These formations are mixed carbonate and siliciclastic sediments and widely exposed in the Lampang area. 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. 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. Both formations have diverse skeletal fossils, including foraminifers, sponges, calcimicrobes, calcareous algae, bivalves, echinoderm spines and fragments, ostracods, gastropods, and other fossils. Based on field observations and microfacies analysis, twelve major facies, corresponding to specific depositional environments within a carbonate setting, have been established. 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. The microfacies and sedimentological study show that this carbonate system was influenced by the nearby volcanic arc. 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.