Amisan Formation

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Amisan Formation
Stratigraphic range: Norian
~227–208.5 Ma
TypeGeological formation
Unit ofNampo Group
UnderliesJogyeri Formation
OverliesHajo Formation
Thickness750–1,000 m (2,460–3,280 ft)
Lithology
PrimaryShale, Sandstone, Siltstone
Location
RegionSouth Chungcheong Province
CountrySouth Korea
ExtentChungnam Basin
Type section
Named forAmisan, Boryeong

Map and diagram of Nampo Group

The Amisan Formation (Korean: 아미산층) is an Late Triassic geologic formation in Boryeong, South Korea. Fossil records from this formation include plants, insects, and fish remains.

Geology

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The Amisan Formation in the Chungnam Basin overlies the Hajo Formation and underlies the Jogyeri Formation. It is subdivided into five zones based on its lithology, lower sandstone, lower shale, middle sandstone, middle shale, and upper sandstone zones. Depositional environments of the lower and middle shale zones of the Amisan Formation are thought to be lacustrine settings.

The depositional age of the Nampo Group including the Amisan Formation is debated,[1][2] but plant genera Lobatannularia and Sphenophyllum from the Baegunsa Formation, which overlies the Amisan Formation and the Jogyeri Formation suggests that the Upper Triassic spans to the Baegunsa Formation.[3] Also, conchostracan fossils and some insect fossils support the Triassic origin of the Amisan Formation.[4][5][6]

Fossil content

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Most of the fossils from the Amisan Formation are from the lower shale zone and the middle shale zone.

Flora

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Flora of the Amisan Formation
Genus Species Region Member Material Notes Image
Taeniopteris[7]
  • T. eurychoron
  • T. mungyeongensis

Ferns

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Ferns of the Amisan Formation
Genus Species Region Member Material Notes Image
Neocalamites N. carrerei[8]
Cladophlebis C. nebbensis[9]
Lobatannularia L. sp.[7]
Chiropteris C. sp.[7]
Equisetites[10]
  • E. kimi
  • E. gaehwariensis
  • E. deltodon

Bennettitales

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Bennettitales of the Amisan Formation
Genus Species Region Member Material Notes Image
Anomozamites A. baegunsaensis[11]
Pterophyllum[11]
  • P. seongjuriense
  • P. daecheonense
Weltrichia W. sp.[12]

Gymnosperms

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Gymnosperms of the Amisan Formation
Genus Species Region Member Material Notes Image
Podozamites
  • P. lanceolatus
  • P. var. genuinea
  • P. schenki[7]
  • P. nampoensis[11]
Anthrophyopsis A. sp.[7]
Drepanozamites D. sp.[7]
Baiera B. cf. furcata[7][13]
Cycadocarpidium C. sp.[7]
Ctenozamites C. meogbangensis[11]
Leptostrobus L. myeongamensis[14]


Bivalves

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Bivalves of the Amisan Formation
Genus Species Region Member Material Notes Image
Margaritifera M. cf. isfarensis[15]

Conchostracans

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Conchostracans of the Amisan Formation[4]
Genus Species Region Member Material Notes Image
Euestheria
  • E. kawasakii
  • E. shimamurai
Cyclestherioides C. rampoensis
Sphaerestheria S. koreanica

Insects

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Insects of the Amisan Formation
Genus Species Region Member Material Notes Image
Turbidapsyche T. dobrokhotovae A mesopsychid scorpionfly; originally assigned to the genus Mesopsyche.[16] [17][18]
Siberioperlidae Indeterminate Stoneflies.[19]
Platyperla P. sp.
Baleyopterygidae Indeterminate
Hallakkungis H. amisanus A palaeontinid.[20]
Tennentsia T. koreana A cicadomorph.[21]
Sanmai S?. zetavena A tettigarctid.[22]
Magnatitan M. jongheoni A titanopteran.[5] File:Magnatitan jongheoni holotype.png
Koreaphlebia K. iussradiae A triadophlebiomorph odonatopteran.[6]
Koreatriassothemis K. elongatus A parazygopteran odonatopteran.[23]
?Isophlebioptera Indeterminate A possible Isophlebioptern nymph. Referred as 'Samarura-type'.[23]
Shurabia S. taewani A Geinitziid polyneopteran.[24]

Vertebrates

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Vertebrates of the Amisan Formation
Genus Species Region Member Material Notes Image
Hiascoactinus H. boryeongensis A redfieldiiform actinopterygian.[25] File:Hiascoactinus KIGAM2.jpg
Megalomatia M. minima A basal actinopterygian.[26]

References

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