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Middle Permian Cimmerian Foraminifers from the Linwe Area, Myanmar and its Paleobiogeographic Significance
- In terms of geotectonic subdivision, the eastern part of Myanmar which is a part of the Sibumasu Block constitutes the eastern part of Gondwana-derived Cimmerian continent. The Permian foraminiferal assemblage of the Eastern Cimmerian Continent is well-known to be peculiar with its low taxonomic diversity compared with that of coeval Paleo-equatorial Tethyan domains such as Indochina and South China. Permian carbonates of Myanmar (Moulmein Limestone and Plateau Limestone) show two different successions. One represents unconformable deposition over clastic sediments of probable Late Carboniferous Early Permian age, and the other shows comfortable unconformable relationship with older Paleozoic sediments. The studied section is located in Ywa-ngan (Ye-ngan) township in Southern Shan State of Eastern Myanmar where the Plateau Limestone lies uncomfortably upon peculiar phacoidallimestone of the Linwe Formation of Silurian age. We recognized four foraminiferal assemblages in the section. The lower-most assemblage contains Rugososchwagerina, Pseudofusulinasp. A, Yangchienia, Neofusulinella, Eotuberitina, Langella, Climacammina, Globivalvulina, Pachyphloia and Dagmarita (Late Murgabian). In the second assemblage, Rugososchwagerina is substituted by verbeekinids and sumatrinids. It include Afghanella, Pseudodoliolina, Armenina, Verbeekina, Kahlerina, Pseudofusulina sp. B, Chusenella sp. A, Nankinella sp. A, Staffe lla, Jinzhangia, Neofusulinella, Dunbarula, Chenella, and Postendothya. Important newly appeared smaller foraminifers are Retroseptellina, Midiella and Geinitzina (Early Midian) . The third assemblage is characterized by the replacement of verbeekinids with inflated or oval schwagerinids. Important ones are Pseudofusulina furoni, P. spp., Chusenella spp., Sumatrina, Nankinella spp., Midiella, Retroseptellina, Ichthyofrondina, Hoyenella?, Neodiscus, Multidiscus, Hemigordius and Cribrogenerina (Midian). The fourth assemblage is remarked by the occurrence of Parafusulina. In the section, Late Murgabian foraminiferal assembl age with Cimmerian-type genus Rugososchwagerina was replaced by the Midian asseemblages yielding more Tethys-type genera such as Afghanella, Verbeekina and Pseudodoliolina. Somewhat similar Midian fusuline assemblage containing Tethys-type neoschwagerinids and verbeekinids had been reported from the Perm ian Plateau Limestone exposed in the Lebyin area, about 50 km south of the Linwe area. After judging with its Middle Permian foraminiferal assemblages, we concluded that those parts of eastern Cimmerian areas had paleobiogeographic influences from the paleo-equatorial Tethys region starting from Midian time.
Tin Tin Latt
- Conference paper
- The 7th AUN/SEED-Net Geological Engineering Conference (AGEC) & The 2nd AUN/SEED-Net Natural Disaster Conference (ANDC