Amisan Formation

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.

Amisan Formation
Stratigraphic range: Norian ~227–208.5 Ma PreꞒ Ꞓ O S D C P T J K Pg N
Type	Geological formation
Unit of	Nampo Group
Underlies	Jogyeri Formation
Overlies	Hajo Formation
Thickness	750–1,000 m (2,460–3,280 ft)
Lithology
Primary	Shale, Sandstone, Siltstone
Location
Region	South Chungcheong Province
Country	South Korea
Extent	Chungnam Basin
Type section
Named for	Amisan, Boryeong
Map and diagram of Nampo Group

Geology

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

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

Flora

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

Ferns

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

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

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

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

Conchostracans

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

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] Uncertain whether it belongs to T. dobrokhotovae.[17]
Siberioperlidae	Indeterminate				Stoneflies.[18]
Platyperla	P. sp.
Baleyopterygidae	Indeterminate
Hallakkungis	H. amisanus				A palaeontinid.[19]
Tennentsia	T. koreana				A cicadomorph.[20]
Sanmai	S?. zetavena				A tettigarctid.[21]
Magnatitan	M. jongheoni				A titanopteran.[5]
Koreaphlebia	K. iussradiae				A triadophlebiomorph odonatopteran.[6]
Koreatriassothemis	K. elongatus				A parazygopteran odonatopteran.[22]
?Isophlebioptera	Indeterminate				A possible Isophlebioptern nymph. Referred as 'Samarura-type'.[22]
Shurabia	S. taewani				A Geinitziid polyneopteran.[23]

Vertebrates

Vertebrates of the Amisan Formation
Genus	Species	Region	Member	Material	Notes	Image
Hiascoactinus	H. boryeongensis				A redfieldiiform actinopterygian.[24]
Megalomatia	M. minima				A basal actinopterygian.[25]