The Amisan Formation () is an
Late Triassic
The Late Triassic is the third and final epoch (geology), epoch of the Triassic geologic time scale, Period in the geologic time scale, spanning the time between annum, Ma and Ma (million years ago). It is preceded by the Middle Triassic Epoch a ...
geologic
formation
Formation may refer to:
Linguistics
* Back-formation, the process of creating a new lexeme by removing or affixes
* Word formation, the creation of a new word by adding affixes
Mathematics and science
* Cave formation or speleothem, a secondary ...
in
Boryeong
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Boryeong (; ), commonly known as Daecheon, is a city in South Chungcheong Province, South Korea. Boryeong is known around Korea for its beaches, particularly Daecheon Beach, and the annual Boryeong Mud Festival around July. The city's beach-m ...
,
South Korea
South Korea, officially the Republic of Korea (ROK), is a country in East Asia. It constitutes the southern half of the Korea, Korean Peninsula and borders North Korea along the Korean Demilitarized Zone, with the Yellow Sea to the west and t ...
. Fossil records from this formation include plants, insects, and fish remains.
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, but plant genera ''
Lobatannularia'' and ''
Sphenophyllum
''Sphenophyllum'' is a genus in the order Sphenophyllales. It has been placed in the family Sphenophyllaceae.
Species
Species that have been described include:
*†''Sphenophyllum angustifolium''
*†''Sphenophyllum biarmicum'' Zalessky (1937) ...
'' from the
Baegunsa Formation, which overlies the Amisan Formation and the Jogyeri Formation suggests that the Upper Triassic spans to the Baegunsa Formation.
Also, conchostracan fossils and some insect fossils support the Triassic origin of the Amisan Formation.
Fossil content
Most of the fossils from the Amisan Formation are from the lower shale zone and the middle shale zone.
Flora
Ferns
Bennettitales
Gymnosperms
Bivalves
Conchostracans
Insects
Vertebrates
References
{{Reflist
Geologic formations of South Korea
Triassic System of Asia
Mesozoic South Korea
Norian Stage
Paleontology in South Korea