Stratigraphy and paleoenvironment of Mae Tha Formation, Eastern Chiang Mai Basin

Abstract

The tectonic setting of the provenance and the paleoenvironment of deposition of the Mae Tha Formation were reconstructed based on the study of stratigraphy, petrography, and geochemistry of the clastic rocks. The ratio of quartz extinction variety suggests the source rock composition of the Mae Tha Formation is granite. The results of the Q-F-L ternary plot indicate that the tectonic setting of the provenance of the Mae Tha Formation was craton interior continental block and recycled orogen. Geochemical analysis indicates that the mud particle was derived from the continental block due to the presence of kaolinite. These results are used to infer the deposition process and paleoenvironment of the Mae Tha Formation. The Mae Tha Formation is classified into two facies base on the sedimentary texture and sand-to-shale ratio. C1 facies is medium- to coarse-grained sandstone interbedded with shale. Sand-to-shale ratio of facies C1 is 92.08:7.92. C2 facies is fine- to medium-grained sandstone interbedded with shale. The average sand-to-shale ratio of this facies is 63.06:36.94. Small scale cross-bedding and plane-bedding are found at some area. The relationship of the sedimentation period of the two facies and the stratigraphic relationship between the two facie could not be determined because both facies are cut by numerous faults. However, both facies have the same minerals composition, provenance, and similar sedimentary texture. These findings suggest that the sandstones are from the same formation but deposited in different conditions. Minerals-maturity, textural-maturity, and remaining sedimentary structure suggest that the sediment were deposited shallow-marine environment.