Depositional history, tectonics, and provenance of the Cambrian-Ordovician boundary interval in the western margin of the North China block: COMMENT

Myrow et al. (2015) detailed the sedimentology, biostratigraphy, and chemostratigraphy of the Cambrian-Ordovician succession in the western North China block (or Sino-Korean block) at Wuhai, Inner Mongolia, China, and recorded an ∼30 m.y. unconformity that formed during the upper Cambrian Series 3−upper Middle Ordovician. They provided a valuable description of the succession accompanied by excellent illustrations of sedimentary facies as well as detailed data on chemostratigraphy, thus providing an important basis for further geologic studies in the region. In addition, they presented a discussion on the origin of the ∼30 m.y. unconformity and suggested that the western Sino-Korean block would have been placed near the western Himalaya during the early Paleozoic, where a hiatus of similar magnitude has been reported (Myrow et al., 2006, 2016). This result seems to support the theory of McKenzie et al. (2011), who first suggested a close paleogeographic affinity between the Sino-Korean block and Himalaya based on detrital zircons and trilobites. However, the paleogeographic interpretation of Myrow et al. (2015) requires further discussion because of the following reasons: (1) incorrect description of the “unconformities” in other localities of the Sino-Korean block, and (2) presence of other potential options on the formative mechanism of this unconformity, including tectonic tilting and eustatic sea-level change. In the following section, we describe each topic in detail and discuss the nature and implication of this unconformity.