Upper Ordovician and Silurian deposits in the Pyeongnam Basin: Sangsori and Koksan series

In the early 1970s, Silurian corals were found from the upper part of the Mandal Series in the Suan-Koksan-Singye areas, Hwanghaebuk-do, which has previously been considered as the Middle Ordovician in age. The discovery led to the designation of the Koksan Series, and the subsequent finding of Agetolites from the base of the Koksan Series in 1975 paved way for the recognition of the Sangsori Series. Corals of the Sangsori Series show the remarkable resemblance to those in the border area between the Jiangxi and Zhejiang provinces of southeastern China. This similarity strongly suggests intimate paleobiogeographic relationship between the two areas. The corals of the Koksan Series mainly consists of tabulates and are compositionally similar to those of the Silurian corals in the clasts of Early Jurassic (?) Songrim Conglomerate. These corals of the Sangsori and Koksan series are not previously known from the Sino-Korean Platform and are instead comparable to those of the South China fauna known for its endemic characteristics. The normal marine carbonate deposits of the Sangsori and Koksan series contrast the origin of the Songrim Conglomerate which resulted from erosion and deposition of Silurian to Devonian (?) strata during the Early Jurassic. North Korean geologists postulated the existence of a narrow seaway of the "Mira" and "Koksan-Songrim" seas extending from the South China to Pyongnam Basin as the main depocenter of the Sangsori and Koksan series. On the other hand, South Korean geologists do not rule out the possibility that these are the remnant of the Late Permian to Trassic collision between the Sino-Korean and South China blocks. It warrants a detailed regional stratigraphic correlation between the two Koreas in order to fully comprehend the Phanerozoic crustal evolution and accretional processes of the east Asian continent.