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Prelrminary Study of Middle Permian Cimmerian Foraminifers from three localities along the Western Margin of Shan-Tanintharyi Region (Sibumas of Myanmar): additional information for Middle Permian Paleogeographic Interpretation of South East Asia Region
- Permian foraminifers including fusulinids play a significant role to interpret Permian paleobiogeography of the Eastern Cimmerian continent containing Tengchong, Baoshan and Sibumasu (or Shan-Thai) blocks. Permian foraminifer from the Shan-Tanintharyi region is far less significant compare with those from western Thailand and west Yunnan. This presentation aims to sum up Permian foraminifera from three locations situated along the western margin of Shan-Tanintharyi region. Lebyin section (Thitsipin Frn.), about 150 km SSE of Mandalay that lies conformably over Carboniferous-Early Permian clastic of Lebyin Group is more than 700m thick. They contain such fusuline genera as Yangchienia, Pseudofusulina, Neoschwagerina, Sumatrina, Verbeekina, Pseudodoliolina, Afghanella, Danbarula, Orientoschwagerina'l, Nankinella and Kahlerina. Smaller foraminifers including Dagmarita, Postendothyra, Globivalvulina, Climacammina , Tetrataxis , Pachyphloia,Geinitzina, and Hemigordiopsis (or Lysites) are also abundant. Based mainly on the occurrence ofKahlerina and Sumatrina, which is somewhat similar to S. annae, this fauna is preferable to early Midian. Linwe section (Thitsipin Fm.), about 97 km SSE of Mandalay lies unconformably over peculiar phacoidal limestone of the Silurian Linwe Formation. Three fusuline assemblages can be recognized. The fusulines of the lower assemblage are Rugososchwagerina, Yangchienia, Pseudofusulina, Neofusulinella and smaller foraminifers are Langella, Eotuberitina, Climmacammina, Globivalvulina, Pachyphloia and Dagmarita representing Late Murgabian. The middle assemblage is represented by fusulinid genera of Kahlerina, Chenel/a , Dunbarula, Afghanella , Verbeekina, Pseudodoliolina, Jinzhangia, Chusenella, Staffella, Pseudofusulina, Armenina, Skinerella?, Neofusulinella and Nankinella. The third upper assemblage is essentially similar in composition to the second one, except the absence of Verbeekina and the diagnostic occurrence of an oval schwagerinid genus. Smaller forams of the second and third assemblages are Langella, Eotuberitina, Climmacammina, Globivalvulina, Pachyphloia, Dagmarita, Tetrataxis, Neodiscus, Multidiscus, Retroseptalina, Ichthyofrondina, Agathammina, Quasireich elina and Postendothyra. The second and third ones are probably assigned to the early Midian, judging from the stratigraphic position and occurrence of Kahlerina and Chenella. Zwekabin section (Moulmein Limestone), about 160 krn due E of Yangon, that lies unconformably? over Carboniferous-early Permian Taungnyo Group attains a thickness of430m. The fusuline fauna is found in two horizons of two different localities. Stratigraphically lower assemblage contains Laosella? and Yangchienia which represents middle Permian. The fauna containing gigantic Parafusulina is found in the upper part of the succession yielding two new species of Parafusulina, Minojapanella, Yangchienia, and Chenella associated with such smaller foraminifers as Abadehella, Postendothyra, Multidiscu s, Pachyphloia, Climacammina, Palaeotextularia, Ichthyofrondina, Langella, Globivalvulina, Lasiodiscus, and Eouberitina. The age is provisionally assigned as Midian judging with the occurrence of giant Parafusulina, Abadehella and Chenella. From the paleobiogeographical point of view, it is assumed that Sibumasu part of Myanmar saw ample co-eval Paleo-Tethyan foraminifers of low diversity starting from Late Murgabian while drifting from Gondwanaland to Eurasia although it seems never accommodate taxonomically higher neoschwagerinids. Another noteworthy point is that potential existence of cold water boundary current that might be flowing along the southwest coast of the Eastern Cimmerian continent, i.e., western margin of Sibumasu, at least in deeper part, could be one of the reasons that reflect the peculiar endemism of benthic foraminifers in the region (giant Shanita and Parafusulina, oval schwagerinid).
Tin Tin latt
- Conference paper
- Thirteenth Regional Congress on Geology, Mineral and Energy Resources of Southeast Asia