Carboniferous-Permian sequences of the western margin of Sibumasu Block: Implications for new lithostratigraphic correlation in the eastern Highlands of Myanmar

Abstract

The Eastern Highlands of Myanmar are characterized by Precambrian to Mesozoic rock formations, with Carboniferous-Permian sequences prominently present in the Shan Scarp and Shan Plateau zones. These sequences are particularly concentrated in the western margin of the Sibumasu Block. Although Permian sequences are abundant in this region, they are complicated by geological faults. Consequently, a lithostratigraphic study was conducted to establish correlations across an extensive area spanning 1200 km from Mandalay City in the north to Kawthaung City in the south and 250 km wide, bordered by the Sagaing Fault to the west and Inle Lake to the east. The Permian sequences can be categorized into lower siliciclastic units and upper carbonate units. These siliciclastic units encompass the Mergui Group, locally referred to as the Lebyin Group, Mawchi Series, Taungnyo Group, and Mergui Group, as well as the Yinyaw Formation. Additionally, there is a carbonate unit known as the Moulmein Formation in the Thaton, Hpa-an, and Mawlamyine areas, and the Tenasserim Formation in the Myeik and Bokepyin areas within the Shan Scarp zone. In the late Lower Permian sequences, the Mwedaw Beds are exclusively found in the Linwe area. However, the Thitsipin Formation, which is an equivalent of the Moulmein Formation, and the Nwabangyi Formation are also exposed in the Shan Plateau zone. Lower Carboniferous sequences, such as the Loikaw Beds, are sporadically visible in the Loikaw area but are overlain by the Thitsipin Formation. This study elucidates the presence of a diamictite unit (Mergui Group) and its associated units (Yinyaw and Thitsipin/Moulmein Formations) in the geo-structurally complex zones of the Shan Plateau and Shan Scarp through lateral lithostratigraphic correlation, shedding light on the Carboniferous-Permian period at the western margin of the Sibumasu Block.