The Geoncheonri Formation () is an

Early Cretaceous The Early Cretaceous (geochronology, geochronological name) or the Lower Cretaceous (chronostratigraphy, chronostratigraphic name) is the earlier or lower of the two major divisions of the Cretaceous. It is usually considered to stretch from 143.1 ...

(

Aptian The Aptian is an age (geology), age in the geologic timescale or a stage (stratigraphy), stage in the stratigraphic column. It is a subdivision of the Early Cretaceous, Early or Lower Cretaceous epoch (geology), Epoch or series (stratigraphy), S ...

Albian The Albian is both an age (geology), age of the geologic timescale and a stage (stratigraphy), stage in the stratigraphic column. It is the youngest or uppermost subdivision of the Early Cretaceous, Early/Lower Cretaceous epoch (geology), Epoch/s ...

) 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 ...

of the Hayang Group in the Gyeongsang Basin of southeast

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 ...

.Geoncheonri Formation
in the

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

Fossil

ornithopod Ornithopoda () is a clade of ornithischian dinosaurs, called ornithopods (). They represent one of the most successful groups of herbivorous dinosaurs during the Cretaceous. The most primitive members of the group were bipedal and relatively sm ...

tracks, 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, officially the Kyrgyz Republic, is a landlocked country in Central Asia lying in the Tian Shan and Pamir ...

'' have been reported from the

lacustrine A lake is often a naturally occurring, relatively large and fixed body of water on or near the Earth's surface. It is localized in a basin or interconnected basins surrounded by dry land. Lakes lie completely on land and are separate from t ...

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. Although its permeabil ...

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.Blatt, H., and R.J. Tracy, 1996, ''Petrology.'' New York, New York, ...

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 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 Alluvium (, ) 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. Alluvium is also sometimes called alluvial deposit. Alluvium is ...

fluvial A river is a natural stream of fresh water that flows on land or inside caves towards another body of water at a lower elevation, such as an ocean, lake, or another river. A river may run dry before reaching the end of its course if it ru ...

and

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

Silla Silla (; Old Korean: wikt:徐羅伐#Old Korean, 徐羅伐, Yale romanization of Korean, Yale: Syerapel, Revised Romanization of Korean, RR: ''Seorabeol''; International Phonetic Alphabet, IPA: ) was a Korean kingdom that existed between ...

, Hakbong,

Haman Haman ( ; also known as Haman the Agagite) is the main antagonist in the Book of Esther, who according to the Hebrew Bible was an official in the court of the Achaemenid Empire, Persian empire under King Ahasuerus#Book of Esther, Ahasuerus, comm ...

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

Cenomanian The Cenomanian is, in the International Commission on Stratigraphy's (ICS) geological timescale, the oldest or earliest age (geology), age of the Late Cretaceous epoch (geology), Epoch or the lowest stage (stratigraphy), stage of the Upper Cretace ...

Turonian The Turonian is, in the International Commission on Stratigraphy, ICS' geologic timescale, the second age (geology), age in the Late Cretaceous epoch (geology), Epoch, or a stage (stratigraphy), stage in the Upper Cretaceous series (stratigraphy), ...

) 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 reptiles of the order (biology), order Testudines, characterized by a special turtle shell, shell developed mainly from their ribs. Modern turtles are divided into two major groups, the Pleurodira (side necked turtles) and Crypt ...

s ** ''Kirgizemys'' cf. ''exaratus'' *

Ostracod Ostracods, or ostracodes, are a Class (biology), class of the crustacean, Crustacea (class Ostracoda), sometimes known as seed shrimp. Some 33,000 species (only 13,000 of which are extant taxon, extant) have been identified,Brandão, S.N.; Antoni ...

s ** ''Cypridea'' sp. ** ''Lycopterocypris'' cf. ''profunda'' ** ''Cypria'' cf. ''elata'' *

Ichnofossil A trace fossil, also called an ichnofossil (; ), is a fossil record of biological activity by lifeforms, but not the preserved remains of the organism itself. Trace fossils contrast with body fossils, which are the fossilized remains of part ...

s ** Ornithopoda indet. ** Theropoda indet.

References

{{Reflist, 3 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