Chao Phraya Gr

Chao Phraya River of the Upper Central Plain, which flows through Bangkok and empties into the Gulf of Thailand. The earlier large river system (or systems), generally referred to as the paleo-Chao Phraya River, supplied large quantities of sediment to the Pattani and North Malay basins of the eastern Gulf and into other basins in the western and central Gulf. Therefore, the upper basin units (usually late Miocene to Recent) that is deposited as deltaic and transgressive-regressive Quaternary cycles onto the different rift basins are given a generalized name of the Chao Phraya Gr (e.g., Fig. 10.16 in Morley and Racey, 2011).

Synonym: Chumphon Basin Unit III, Pattani Basin Univ V, North Malaya Basin Formation 3, etc.

Interbedded sandstones and brown clays with minor coal horizons that were deposited predominantly in a fluviatile flood plain environment, occasionally with some marine influence. In Chumphon Basin, this "Unit III" is ca. 500 m that is composed predominantly of alluvial plain and transgressive marine clays and shales with interbedded medium- to coarse- grained fluviatile sands. In the Kra and western basins, it is approximately 1500 m. (Morley and Racey, 2011)

Marine and palynology

The Chao Phraya Group shows an influence of fluvial, deltaic and marine conditions and ranges between estuarine, intertidal and shallow-marine facies.