Where art thou “the great hiatus?” — review of Late Ordovician to Devonian fossil-bearing strata in the Korean Peninsula and its tectonostratigraphic implications

We review paleontologic evidence from the Upper Ordovician to Devonian strata in the Korean Peninsula and discuss their tectonostratigraphic origin. The Upper Ordovician–Devonian fossil-bearing strata are largely distributed in North Korea, and tectonostratigraphically in the southern margin of the Pyeongnam Basin and in the northern part of the Imjingang Belt. The fossils have been regarded as evidence that the “great hiatus” of the middle Paleozoic is not a prevalent phenomenon across the Sino-Korean Block. Examination of selected fossils with stratigraphic and paleogeographic significance reveals that the fossils from the Sangsori, Koksan and Wolyangri series and the Rimjin System are of the Late Ordovician to Devonian and display affinity to those of the coeval strata of South China. In addition, the fossils included within clasts of the Songrim Conglomerate, the basal unit of the Jurassic Taedong System, are of the Silurian to Devonian, which also display affinity to South China. The faunal and floral affinity suggests that the Upper Ordovician to Devonian strata in North Korea most likely formed in a basin(s) of or peripheral to the South China Block, which indicates that the strata are allochthonous, contrary to the traditional interpretation of their autochthonous origin by North Korean geologists. The Permo-Triassic collision between the two Chinese cratons which resulted in the amalgamation of three massifs of the Korean Peninsula is considered to be responsible for the accretion and juxtaposition of the Upper Ordovician to Devonian strata onto the Sino-Korean Block. The autochthonous origin of the strata suggests the absence of the “great hiatus” at least in North Korea, whereas the allochthonous origin its presence across the Sino-Korean Block.