The Geoncheonri Formation () is an

Early Cretaceous The Early Cretaceous ( geochronological name) or the Lower Cretaceous (chronostratigraphic name), is the earlier or lower of the two major divisions of the Cretaceous. It is usually considered to stretch from 145 Ma to 100.5 Ma. Geology Pro ...

(

Aptian The Aptian is an age in the geologic timescale or a stage in the stratigraphic column. It is a subdivision of the Early or Lower Cretaceous Epoch or Series and encompasses the time from 121.4 ± 1.0 Ma to 113.0 ± 1.0 Ma (million years ago), a ...

- Albian) 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 secondar ...

of the Hayang Group in the

Gyeongsang Basin Gyeongsang ( ko, 경상도, ''Gyeongsang-do''; ) was one of the eight provinces of Korea during the Joseon dynasty. Gyeongsang was located in the southeast of Korea. The provincial capital was Daegu. The region was the birthplace of the Kingdom ...

of southeast

South Korea South Korea, officially the Republic of Korea (ROK), is a country in East Asia, constituting the southern part of the Korea, Korean Peninsula and sharing a Korean Demilitarized Zone, land border with North Korea. Its western border is formed ...

.Geoncheonri Formation
in the

Paleobiology Database The Paleobiology Database is an online resource for information on the distribution and classification of fossil animals, plants, and microorganisms. History The Paleobiology Database (PBDB) originated in the NCEAS-funded Phanerozoic Marine Pale ...

Fossil

ornithopod Ornithopoda () is a clade of ornithischian dinosaurs, called ornithopods (), that started out as small, bipedal running grazers and grew in size and numbers until they became one of the most successful groups of herbivores in the Cretaceous world ...

tracks,Weishampel et al., 2004, pp.517-607 as well as fossils of ''

Kirgizemys ''Kirgizemys'' is an extinct genus of turtle from Early Cretaceous of China, South Korea, Mongolia, Russia and Kyrgyzstan Kyrgyzstan,, pronounced or the Kyrgyz Republic, is a landlocked country in Central Asia. Kyrgyzstan is bordered b ...

'' have been reported from the lacustrine

siltstone Siltstone, also known as aleurolite, is a clastic sedimentary rock that is composed mostly of silt. It is a form of mudrock with a low clay mineral content, which can be distinguished from shale by its lack of fissility.Blatt ''et al.'' 1980, p ...

s and

mudstone Mudstone, a type of mudrock, is a fine-grained sedimentary rock whose original constituents were clays or muds. Mudstone is distinguished from '' shale'' by its lack of fissility (parallel layering).Blatt, H., and R.J. Tracy, 1996, ''Petrology. ...

s of the formation.

Description

The Geoncheonri Formation (ca. 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

, 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 Alluvium (from Latin ''alluvius'', from ''alluere'' 'to wash against') is loose clay, silt, sand, or gravel that has been deposited by running water in a stream bed, on a floodplain, in an alluvial fan or beach, or in similar settings. Alluv ...

fluvial In geography and geology, fluvial processes are associated with rivers and streams and the deposits and landforms created by them. When the stream or rivers are associated with glaciers, ice sheets, or ice caps, the term glaciofluvial or fluviog ...

and lacustrine sediments, and the Yucheon Group, characterized by the dominance of volcanic rocks. The Hayang Group consists of Chilgok,

Silla Silla or Shilla (57 BCE – 935 CE) ( , Old Korean: Syera, Old Japanese: Siraki2) was a Korean kingdom located on the southern and central parts of the Korean Peninsula. Silla, along with Baekje and Goguryeo, formed the Three Kingdoms of K ...

, Hakbong,

Haman Haman ( ; also known as Haman the Agagite or Haman the evil) is the main antagonist in the Book of Esther, who according to the Hebrew Bible was an official in the court of the Persian empire under King Ahasuerus, commonly identified as Xerxes I ...

, 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. 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 pelecypod '' Trigonioides paucisulcatus'' in the Geonchonri Formation and in the Gyliakian Goshonoura Group (

Cenomanian The Cenomanian is, in the ICS' geological timescale, the oldest or earliest age of the Late Cretaceous Epoch or the lowest stage of the Upper Cretaceous Series. An age is a unit of geochronology; it is a unit of time; the stage is a unit in the s ...

Turonian The Turonian is, in the ICS' geologic timescale, the second age in the Late Cretaceous Epoch, or a stage in the Upper Cretaceous Series. It spans the time between 93.9 ± 0.8 Ma and 89.8 ± 1 Ma (million years ago). The Turonian is preceded by t ...

) 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.Gyeongsan City
in the

Fossil content

The following fossils were reported from the formation: *

Turtle Turtles are an order of reptiles known as Testudines, characterized by a special shell developed mainly from their ribs. Modern turtles are divided into two major groups, the Pleurodira (side necked turtles) and Cryptodira (hidden necked tu ...

s ** ''Kirgizemys'' cf. ''exaratus''Lee et al., 2009 * Ichnofossils ** Ornithopoda indet.Lee et al., 2001 ** Theropoda indet.

References

Bibliography

* * * {{citation , last1=Lee , first1=Y.-N. , first2=K.-M. , last2=Yu , first3=C. B. , last3=Wood , year=2001 , title=A review of vertebrate faunas from the Gyeongsang Supergroup (Cretaceous) in South Korea , journal= Palaeogeography, Palaeoclimatology, Palaeoecology , volume=165 , issue=3–4 , pages=357–373, doi=10.1016/S0031-0182(00)00171-1 , bibcode=2001PPP...165..357L Geologic formations of South Korea Lower Cretaceous Series of Asia Cretaceous South Korea Albian Stage Mudstone formations Siltstone formations Lacustrine deposits Ichnofossiliferous formations Paleontology in South Korea

Description

Fossil content

See also

References

Bibliography