The Nakdong Formation (Also known as the Nagdong Formation) () is an Lower Cretaceous (Hauterivian to Aptian) geologic formation in South Korea. It has been dated from the Hauteravian to the Aptian, between 127 Ma and 118.0 ± 2.6 Ma. It is also the lowermost formation-level stratigraphic unit of the Gyeongsang Supergroup. Plant fossils from the Nakdong Formation overlap with the floral assemblage of the older Myogok Formation and show a 'mixed type' of the Tetori-Type and the Ryoseki-Type flora present in this formation. Based on bivalve fossil records, it correlates with molluscan faunas of the Japanese Kitadani Formation and Sebayashi Formation.

Geology The Nakdong Formation could be distinguished from the overlying Hasandong Formation by absence of red beds in the entire formation.

Based on facies shown in outcrops, the depositional setting of the formation has been changed from lower to upper: (A): Alluvial plain with tributaries, (B): Low sinuous channel system with bars, and (C): Sinuous channel system with splays and floodplains. The channel system of the upper Nakdong Formation is continuously extended to the Hasandong Formation.

Meanwhile, pond deposits are restricted in the formation, represented by dark gray shaly mudstone intervened between fluvial sandy deposits, showing a concave lower contact and planar upper contact, up to 2 meters thick. Ferns and bivalve fossils are occassionaly from these sediments. Based on these characteristics, pond deposits of the Nakdong Formation represent small-sized channels or small ponds deposited over the floodplains. No evaporites or stromatolites have been recorded there.

Fossil content

Molluscs Molluscs of the Nakdong Formation Genus Species Location Stratigraphic position Material Notes Images Nagdongia N. soni Also known from the Kitadani Formation and overlying Hasandong Formation Pseudohyria P. matsumotoi Also known from the Kitadani Formation and the Sengoku Formation Nippononaia N. ryosekiana Also known from the Kitadani Formation and the Sebayashi Formation Trigonioides T. bongkyuni T. wakinoensis Sphaerium S. coreanicum Viviparus V. keishoensis

Vertebrates Vertebrates of the Nakdong Formation Genus Species Location Stratigraphic position Material Notes Images Sauropoda Indeterminate Partial cervical vertebra and ribs

See also

List of dinosaur-bearing rock formations List of stratigraphic units with indeterminate dinosaur fossils

Footnotes

References Weishampel, David B.; Dodson, Peter; and Osmólska, Halszka (eds.): The Dinosauria, 2nd, Berkeley: University of California Press. 861 pp. .