Pharaka Fm
Type Locality and Naming
Mae Sariang-Mae Sot-Umphang region. East of Mae Sot district, Tak province. Assigned to strata exposed between Km 49 and Km 62 along the Tak–Mae Sot Highway (Oeno & Charoentitirat, 2011).
Synonym: หมวดหินผาละกา ; upper Mae Yau Siltstone (Mae Yau Siltstone Fm unit 3; Buonopas, 1981 = upper part of his Doi Musur Gr). Often mapped as the Ratburi Fm (Ratburi Gr).
Lithology and Thickness
Grey shale, sandstone, carbonaceous shale and banded limestone with chert nodules. Thick – ca. 1200 m. However, from Lexicon of Stratigraphic Names of Thailand of 2013 has a different order: "Banded limestone with chert nodules; grey shale; sandstone; and carbonaceous shale". [For graphic purposes,
Relationships and Distribution
Lower contact
Unconformable. Next older regional named-unit is the Bo Phloi Fm (late Silurian) with an unnamed Mississippian-age limestone between (all contacts unformable).
Upper contact
Overlain conformably by the Doi Phawar Fm of middle Permian limestone.
Regional extent
Mae Sariang-Mae Sot-Umphang region = Western half of the Western Region of Sibumasu (south of Mae Ping Fault, north of Three Pagoda Fault).
GeoJSON
Fossils
"From a sandy limestone in the uppermost part of the formation exposed near Mae Ka Sa Falls east of Mae Ramat in western Tak Province, Ingavat & Douglass (1981) reported the fusuline Monodiexodina shiptoni. They also documented the occurrence of Monodiexodina sutchanica (later re-identified as M. shiptoni by Ueno 2006) from a sandy limestone band in quartzose sandstone at Dan Tha Ta Fang near the Thai – Myanmar border west of Mae Sariang in southern Mae Hong Son Province." (Oeno & Charoentitirat, 2011).
Age
Depositional setting
Additional Information
"Bunopas (1981) included them in the Mae Yau Siltstone (Fig. 5.15), which comprised the upper part of his Doi Musur Gr. He further divided the Mae Yau Siltstone into two parts: Unit 2 is exposed between Km 32 and Km 36 along the Tak – Mae Sot Highway (Route 105) and Unit 3 between Km 49 and Km 62. Later, Sukto et al. (1984) introduced the name Pharaka Formation for beds which Bunopas (1981) had assigned to Unit 3 of the Mae Yau Siltstone, overlain by the Middle – Late Permian Doi Phawar Formation." (Oeno & Charoentitirat, 2011).