Suan Mark Limestone Fm

The type section is Khlong Suan Mark, 4 km west of Pong Nam Ron village, about 70 km west of Kamphaeng Phet province. Named by Bunopas (1976, 1981). Upper unit in the Khlong Wang Chao Gr. [had been previously mapped as part of the Thung Song Gr by Bunopas (1976)]

Synonym: หมวดหินปนู สวนหมาก

Clayey limestone, well banded with alternating horizons of grey slate and quartzite. Over 827 m thick.

Seems correlative with limestone-dominated units S and T of Baum et al. (1970) – description is from Ridd (2011):

T (lower unit) = Dark, locally arenaceous and locally fossiliferous shale with a Middle to Upper Ordovician fauna: ?Metriophyllidae or Streptelasmatinae gen. indet., Clionychia cf. crispa,

S (upper unit) = Limestone: 80 – 100 m thick (but ca. 800 measured by Bunopas in same region); thin-bedded and nodular in lower part, becoming massive and light-to medium-grained upwards. Local algal reefs near Mae Sariang. Conodont faunas indicate ages of Lower, Middle and Upper Ordovician. Locally (e.g. north of Mae Sariang) the limestone passes laterally into unit T.