Wunbye Fm
Type Locality and Naming
The Wunbye Fm was named after its type section on Wunbye Hill (1558 m), 3 km SW of Linwe village, Ye-ngan township, Shan State South (Myint Lwin Thein 1973), As well as in the type area, the Wunbye Fm is fairly widely distributed in Shan State South. It is well exposed on both eastern and western flanks of the Pindaya Range, Bawsaing Range, south of Heho, western scarp of Taunggyi Range, Montawa Cave, White Crow Lake (Kyeephyu kan), Méné Taung, Hopong township and the Phyaukseikpin area east of Kyaukse. [Original Publication: Barber, A. J., Khin Zaw & Crow, M. J. (eds) 2017. Myanmar: Geology, Resources and Tectonics. Geological Society, London, Memoirs, 48, 317-342]
Lithology and Thickness
Dolomitic limestone. The unit consists mainly of a succession of medium- to thick-bedded limestones and dolomites with minor irregular patches and lenses of yellow or dark brown siltstones. The limestone is finely crystalline, light to dark grey, locally oolitic, repeatedly interbedded with buff or yellow-coloured materials in the forms of burrows, specks, pellets or regular and irregular laminations. The burrow structure is typical of this limestone, which is commonly known as ‘the burrow limestone’ (Myint Lwin Thein 1973). It is 1633 m thick.
Relationships and Distribution
Lower contact
The unit conformably overlies the Lokepyin Fm of Early Ordovician age.
Upper contact
It underlies the Nan-On Fm of Late Ordovician age.
Regional extent
This Formation is developed in Shan South Plateau. It can be correlated with the Sitha Fm of Pyin Oo Lwin township.
GeoJSON
Fossils
Fossils from the Linwe area include: the nautiloids Actinoceras cf. moeseini, Actinoceras sp., Ormoceras cf. holmi, Intejoceras cf. angarense, Lamottoceras cf. ruedemanni; the sponge ? Paleospongia sp.; receptaculitid algae Fisherites burmensis Rietschel & Nitecki; and orthoid brachiopods. Khaing Zin Phyu (pers. comm. 2008) identified the brachiopods Paucicrura rogata, Paucicrura sp. and Trematorthis sp. Paucicrura rogata is an American late Middle Ordovician (Sandbian) species and is found in the upper part of the Wunbye Fm.
Age
Depositional setting
The sediments and sedimentary structures found commonly in the Wunbye Fm, such as cross-laminations, ripple marks, abundant pellets, intraclasts, bioclasts, horizontal burrows, high fossil diversity and high faunal content, are indicators of a subtidal environment of deposition. An extremely shallow-marine environment is suggested by the presence of the receptaculitid Isherites burmensis Rietschel & Nitecki.
Additional Information
Three major sedimentary associations of the Wunbye Fm in the Panzit area were recognized as supratidal, intertidal and subtidal (Win Naing 1991).