Chao Nen Quartzite Fm

Tha Chao Nen Quartzite Formation correlates to Units A and B of Hagen and Kemper (1976); therefore an upward succession of:

A (lower unit) Quartzite: brown-grey, grey and dirty white, well-bedded with beds from 10 cm to 1.0 m; dispersed pyritohedra up to 3 mm; common laminae of quartz mosaic with varying amounts of biotite and muscovite.

B (upper unit) Phyllite and calcareous phyllite: 200 – 500 m thick; increasingly calcareous upwards; quartzite intercalations; wavy bedding and locally sharp chevron folding. Upper portion is dominated by carbonate.

"Bunopas (1981) describes two fossil collections he made from the type locality of the Chao Nen Quartzite where he estimates its total thickness at 600m. From fine-grained sandstone 100–200 m above the base of his section (it is not clear whether this correlates to Unit A or Unit B) he describes Opisthoparian trilobites of Late Cambrian age. In graded sandstones in the upper 250 m of the formation (probably correlating to Unit B), he found a 70 m interval with incomplete cephalopods indicating a possible Llandeilo (Mid-Ordovician) age as well as the brachiopod Strophomena sp. and the gastropod Palaeomphalus cf. giganteus also indicating a probable Mid-Ordovician age. From what prob- ably correlates to Unit B, Wolfart (2001) describes an assemblage of small trilobites from 200–300 m of reddish brown sandstone on the left bank of the Kwae Noi River, north of Kanchanaburi city, and considered it to be of Arenig age. On the basis of these faunas, the Cambrian–Ordovician boundary would be in the Chao Nen Quartzite, that is, probably within unit B." (Kidd, 2011)