Fluvial Architecture of Reverse Directional Channels in the Irrawaddy Sandstone, Central Myanmar
Than, Naing M.
Geosciences, Gobi Coal & Energy Pte. Ltd., Singapore, Singapore.
An outcrop of the Irrawaddy Formation (Pontian to Pliocene) in Salin Basin, Natmauk area of central Myanmar, northern tip of Bago Yoma was studied in order to provide a better understanding of the architecture associated with braided-fluvial deposits. The main section of outcrop, which is exposed over 1200 m, is interpreted to have been deposited in a proximal, sandy braided river at the eastern edge of the Salin basin.
Eleven lithofacies were identified, based on petrology and sedimentary structures. These lithofacies were grouped into five architectural elements, including channel fill, transverse bar, longitudinal bar, abandoned channel fill and overbank fines.
Different Two major current directions can be considered as a lower channel showing SSW direction and stacked by reverse directional channels from the evidence of petrology and sedimentary structures related with inversion of pull-apart central Myanmar basins.
It appears that the majority of sedimentary materials of the lowest channels were shed from the NNE site of the present area, the sediments of reverse directional, upper stacked channels were shed from SSE source.
For all provenance aspect of Irrawaddy sediments, paleocurrents, lithic grain parameters and P/F values suggest that particles comprising the Irrawaddy Formation was shed from an uplifted basement (Shan Taninthayi Block/Shan Plateau) and/or a rifted continental margin/transformed fracture zone (the western margin of Shan Taninthayi Block/Shan Plateau).
These sediments were deposited in three stages: active, abandonment, and reactivation. These reflect channel switching , waxing and waning of the fluvial system and it is further to be considered as the sediments carried by the river was less sinuous and braided in nature and shallow bathymetry.
AAPG Search and Discovery Article #90155©2012 AAPG International Conference & Exhibition, Singapore, 16-19 September 2012