Zebingyi Fm

Shan North Plateau, Zebingyi area, Anisakan–Phaungdaw area, Pyin Oo Lwin

township. Shan mid-Plateau (Pyin Oo Lwin), Shan South Plateau. This was named the Zebingyi Stage by La Touche (1913) and Krishnan & Jacob (1955); the Zebingyi Beds by Pascoe (1959), Amos (1975) and Mitchell et al. (1977); and the Zebingyi Fm by IGCP (1980), Brinckmann in Bender (1983) and Wolfart et al. (1984). It was redefined by Aye Ko Aung (2008, 2012), and is named after Zebingyi village, Pyin Oo Lwin 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]

Limestone. The Zebingyi Fm consists of a sequence of fossiliferous carbonate, arenaceous and argillaceous rocks. Its lower Khinzo Chaung Limestone Mbr, 65 m thick, consists of dense black, earthy limestone separated by layers of light-coloured, purple, black shale and buff-coloured siltstone. The Khinzo Chaung Limestone Mbr is overlain by the In-ni Chaung Limestone Mbr, 35 m thick, of whitish to light grey, flaggy, thin bedded, partially dolomitized micrite, which is succeeded in turn by the Doganaing Chaung Orthoquartzite Mbr, about 12 m thick, consisting of thin-bedded, reddish-brown orthoquartzite. The upper part of the latter is characterized by clast-supported conglomerates in association with grey lime-mudstone and pinkish-brown siltstone.

[Figure: Stratigraphical log of the type section of the Zebingyi Formation. Doganaing chaung, approximately 2.5 km south of Zebingyi village, Pyin Oo Lwin township, Mandalay Division (after Aung&Cocks, 2017)]

[Figure: Outcrops of the Lower Devonian Zebingyi Formation: (a, b) Emsian limestone pebble conglomerate, Taungchun hill, Paungdaw–Anisakan, Pyin Oo Lwin township; (c, d) Doganaing Chaung Orthoquartzite Member, Doganaing Chaung; (e, f) In-ni Chaung Limestone Member: (e) Myinthe Chaung; and (f) Thandaung, Khinzo Chaung Limestone Member; (g) Pebin Chaung; and (h) Khinzo Chaung (after Aung&Cocks, 2017)]

Contains corals and conodonts, including the rugose coral Dohmophyllum graveyardense Yu & Jell, which is common in the late Emsian Db1 Mbr of the Burges Fm in Broken River Province, north Queensland (Aye Ko Aung 1991). Species of the genera Tryplasma, Lythophyllum and Breviphrentis are closely comparable to those from the Lower Devonian (Emsian) Rugosa of the Izarne Fm, Montagne Noire, France (Pedder & Feist 1998). That faunal assemblage is not found in the rest of the Zebingyi Fm, and its age is identified by the presence of the conodont Ozarkodina prolata Mawson which is not known earlier than the Emsian. The lower part contains the zonal conodont Eognathodus sulcatus Philip, indicating the sulcatus Zone of Pragian age.

[Figure: Lower Devonian macrofossils of the Zebingyi Formation. (a) Nowakia acuaria (Richter); (b, c) Monograptus atopus Bou˘cek; (d, e) odontopleurid trilobite gen. et sp. indet.; (f) Phacops taungtalonensis Tint & Wai; (g) Plectodonta forteyi Boucot & Cocks; (h) Calymene sp.; (i) Clorinda sp. cf. wongwanichi; (j) Michelinoceras sp. (after Aung&Cocks, 2017)]

[Figure: Macro and microfossils of the Emsian limestone pebble conglomerate of the Zebingyi Formation, 5 km NE of Phaungdaw village, Anisakan, Pyin Oo Lwin township. (a, b) Dohmophyllum graveyardense Yu & Jell, transverse sections; (c, d) Tryplasma sp.: (c) transverse section; and (d) longitudinal section; (e, f) Breviphrentis sp., transverse sections; (g, h) Lithophyllum sp.: (g) transverse section; and (h) longitudinal section; (i, j) Ozarkodina prolata Mawson: (i) oral view; and (j) aboral view; and (k) Ozarkodina sp. lateral view (after Aung&Cocks, 2017)]

The Zebingyi Fm as a whole is interpreted as a pelagic–shallowing-upwards sequence, locally with an intertidal channel environment. (Aye Ko Aung & Kyaw Min 2011). In the Zebingyi area, westernmost part of the Pyin Oo Lwin township, the lower part of the Zebingyi Fm (Khinzo Chaung Limestone Mbr) is characterized by the tentaculitid biomicrite–wackestone/packstone macrofacies, contains significant amounts of allochems, mud-supported to grainsupported, and large tentaculitids, brachiopods and ostracods, suggesting a stable, relatively deeper-water environment (Heckel 1972). The scarcity of laminae and the presence of broken fossil fragments could be attributable to bioturbation, indicating oxygenating bottom conditions and slow deposition. The occurrence of a few intraclasts suggests that the bottom sediments were affected by intermittent storms. Those rocks are followed by a shallowing-upwards sequence, the In-ni Chaung Limestone Mbr, and red soil on the top of that unit indicates probable subaerial exposure to an oxidizing environment. The In-ni Chaung Limestone Mbr is chiefly dolomitized lime mudstone (dolomitized micrite), and is believed to have formed in a supratidal environment (Reeckmann & Friedmann 1981). The overlying Doganaing Chaung Orthoquartzite Mbr in the upper part is typical of a shallow-marine environment. In the Anisakan–Phaungdaw area, the depositional environment of the Zebingyi Fm is rather different from that of the Zebingyi area described above. In the Khinzo Chaung Limestone Mbr, the presence of burrow structures and mottled structures (bioturbation) in siltstone and wackestone, respectively, suggests deposition in a shallow-marine intertidal– subtidal environment. This is supported by the presence of low-angle cross-bedding and an abundant shallow-marine benthic fauna of brachiopods, bivalves, trilobites and bryozoans in the wackestone.