DISCOVERY OF CARBONATES OF EDIACARAN TO EARLY CAMBRIAN POTENTIAL BETWEEN THE OKCHEON METAMORPHIC BELT AND THE EARLY PALEOZOIC TAEBAEKSAN BASIN IN SOUTH KOREA AND THEIR GEOLOGICAL AND TECTONIC SIGNIFICANCE

There has been considerable controversy as to whether the entire Korean peninsula has evolved since the Neoarchean as part of the Sino-Korean Craton, or whether it is the result of the assembly of several continental fragments in the early Mesozoic Era. The relationship between the Neoproterozoic Okcheon Metamorphic Belt (OMB) and the Early Paleozoic Tabaeksan Basin (TB) in the central region of the Korean Peninsula has the potential to provide an answer to this question. Between the Cryogenican Seochangni Formation of OMB and the Cambrian Jangsan Formation of TB, there are carbonate rocks that have not been studied much because fossils are not preserved. As widely distributed in TB, they have previously been considered Ordovician carbonates, but the carbon and oxygen isotope values analyzed in this study require different interpretations. There are regions with δ¹³C values ranging from -3.3 to +1.14 ‰, which agrees with Ordovician seawater values, such as carbonate rocks distributed in TB. However, over a much larger area, δ¹³C values show mostly positive values from +3.9 to +7.6 ‰. In addition, significant negative excursion of δ¹³C values down to -6.9 ‰ occurs near where the highest values were measured. These high positive values and distinct negative excursion are differ from Ordovician seawater, but are present in Ediacaran or Early Cambrian carbonates. These values are distinct from Ordovician seawater and are thought to be correlated with Ediacaran or Early Cambrian carbonates. The section showing significant δ¹³C negative anomaly may correspond to Wonoka-Shuram excursion in Ediacaran or BACE excursion in Early Cambrian. The discovery of carbonate rocks possibly of Ediacaran or Early Cambrian is the first in South Korea. This supports that the Neoproterozoic OMB and Early Paleozoic TB have a tectonic evolutionary history of continuous deposition rather than an assembly of different continental fragments. This relationship is also correlated with the relationship between the Neoproterozoic Sangwon Supergroup and the Paleozoic Pyongnam Basin of North Korea. These findings support that the southern and northern parts of the Korean peninsula and North China have evolved from at least the Neoproterozoic as one linked Sino-Korean Craton.