Geoncheonri Formation

The Geoncheonri Formation (Korean: 건천리층; Hanja: 乾川里層; RR: Geoncheolli-cheung) is an Early Cretaceous (Aptian-Albian) geologic formation of the Hayang Group in the Gyeongsang Basin of southeast South Korea.^[1] Fossil ornithopod tracks,^[2] as well as fossils of Kirgizemys have been reported from the lacustrine siltstones and mudstones of the formation.^[3]

Geoncheonri Formation
Stratigraphic range: Albian ~112–100 Ma PreꞒ Ꞓ O S D C P T J K Pg N
Type	Geological formation
Unit of	Hayang Group
Underlies	Yucheon Group  Jusasan Formation (volcanics)
Overlies	Chaeyaksan Formation (volcanics)
Thickness	Up to 800 m (2,600 ft)
Lithology
Primary	Mudstone
Other	Siltstone
Location
Coordinates	35.9°N 128.6°E / 35.9; 128.6
Approximate paleocoordinates	45.2°N 122.7°E / 45.2; 122.7
Region	Daegu, Gyeongsangbuk-do, Gyeongsangnam-do
Country	South Korea
Extent	Gyeongsang Basin
Geoncheonri Formation (South Korea)

Description

The Geoncheonri Formation (ca. 800 metres (2,600 ft) thick) is the uppermost formation of the Hayang Group, belonging to the Gyeongsang Supergroup. The Gyeongsang Supergroup is widely distributed in the southeastern part of the Korean Peninsula, mainly within the Gyeongsang Basin, which is the largest sedimentary basin of South Korea. It is divided into the Shindong and Hayang Groups, consisting mainly of thick siliciclastic sequences of alluvial, fluvial and lacustrine sediments, and the Yucheon Group, characterized by the dominance of volcanic rocks.^[4]

The Hayang Group consists of Chilgok, Silla, Hakbong, Haman, Banyawol, Songnaedong, Chaeyaksan and Geoncheonri Formations in ascending order. The Geoncheonri Formation is conformably underlain by the Chaeyaksan Formation and overlain by the Jusasan Formation, the lowermost of the Yucheon Group.^[4]

Since plant fossils were first reported in the Geoncheonri Formation in 1925, a series of paleontological studies has been made with molluscs, spores and pollen, charophytes, and dinosaur footprints. Plant fossils from the Geoncheonri Formation were correlated with the Monobegawa Group and the Gyliak Series (Lower to "Middle" Cretaceous) in Japan. Yang (1978) noted that the co-occurrence of a bivalve Trigonioides paucisulcatus in the Geonchonri Formation and in the Gyliakian Goshonoura Group (Cenomanian to Turonian) of Japan. However, primitive angiosperm pollen (Retimonocolpites peroreticulatus and Tricolpites sp.) and other palynological features suggest that the age of the Geoncheonri Formation is Aptian to Albian. The charophytes from the Geoncheonri Formation also indicate an Aptian to Albian age.^[4]

Fossil content

The following fossils were reported from the formation:^[1]

• Turtles
  • Kirgizemys cf. exaratus^[3]
• Ostracods^[5]
  • Cypridea sp.
  • Lycopterocypris cf. profunda
  • Cypria cf. elata
• Ichnofossils
  • Ornithopoda indet.^[6]
  • Theropoda indet.^[6]

See also

• List of dinosaur-bearing rock formations
  • List of stratigraphic units with ornithischian tracks
    • Ornithopod tracks
• Gugyedong Formation
• Haman Formation
• Hasandong Formation
• Jinju Formation
• Sagog Formation