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Nan-On Formation
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Nan-On Fm base reconstruction

Nan-On Fm

Period: 
Ordovician

Age Interval: 
Late Ordovician


Province: 
Myanmar Shan Region

Type Locality and Naming

Shan South Plateau, the type section of the Nan-On Fm (Myint Lwin Thein 1973) is located at Nan-on village 1609 m SW of Linwe village, Ye-ngan township, Shan State South. Its distribution is extensive in Shan State South in the Pindaya Range, from north to south: Kyarinn-kan, Shwepahtoe, Yechanzin (Pindaya township); Pegin, Linwe, Kyauknget, the Sinsapya areas (Ye-ngan township); in the Bawsaing Range, Khwe Aik Taung, near Heho, Taungni area, Taunggyi township; and Méné Taung, Hopong township [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

Siltstone. The Fm consists of thin- to medium-bedded yellow to buff siltstone, with minor limestone intercalations. It is 190 m thick in the type section.


Lithology Pattern: 
Siltstone


Relationships and Distribution

Lower contact

It conformably overlies the Middle Ordovician Wunbye Fm

Upper contact

It underlies the Silurian Linwe Fm or Tanshauk Mbr Fm.

Regional extent

This Fm is developed in Shan State of South. Studies suggest that Tanshauk Mbr should be considered as a part of Nan-On Fm.


GeoJSON

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Fossils

Fossils collected by Dagon University students included: brachiopods Saucrorthis irravadica, Clitambonites squamata and Rafinesquina sp.; trilobites Agnostus sp., Encrinurus sp. and Illaenus sp.; bryozoa Rhynidictya sp.; porifera Aulacopium cf. shanensis; and the crinoid Caryocrinus sp.


Age 

Late Ordovician. That faunal assemblage indicates a Darriwilian or Sandbian age.[Figure: Stratigraphical correlation of the Cambrian–Devonian rocks of Myanmar Shan region with those of northern Thailand and NW Malaysia. Asterisks indicate the levels at which fossils useful in correlation were found (after Aung&Cocks, 2017)]

Age Span: 

    Beginning stage: 
Sandbian

    Fraction up in beginning stage: 
0.0

    Beginning date (Ma): 
458.18

    Ending stage: 
Sandbian

    Fraction up in the ending stage: 
1.0

    Ending date (Ma):  
452.75

Depositional setting

As with the Kunlein Fm, the siltstone and limestone of the Nan-On Fm Fm were deposited in a warm, shallow sea with fairly high organic activity.


Depositional pattern:  


Additional Information


Compiler:  

Aye Ko Aung and L. Robin M. Cocks (Aung & Cocks, Cambrian–Devonian stratigraphy of the Shan Plateau, Myanmar (Burma), Chapter 14 in Barber, A. J., Khin Zaw & Crow, M. J. (eds) 2017. Myanmar: Geology, Resources and Tectonics. Geological Society, London, Memoirs, 48, 317-342).