The Cambrian Period is the first period of the Phanerozoic Eon of our planet Earth and witnessed the explosive appearance of the metazoans, representing the beginning of the modern earth-life system characterized by animals in contrary to the Precambrian earth-life system dominated by microbial life. However, understanding Cambrian earth-life system evolution is hampered by absence of a high-resolution timescale.
The review article by Maoyan Zhu (Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences) and his colleagues briefly summarized the historical narrative, recent advances and problems of the present international Cambrian chronostratigraphic framework and timescale. In particular, the article provide insightful discussions on the long-standing problem how to subdivision of the lower half of Cambrian Period in which the animals appeared on Earth abruptly (called the "Cambrian Explosion").
The highlight of the review is that the authors challenged the recognition of the Cambrian base through intensive analyses of the deficiency of the GSSP (Global Boundary Stratotype Section and Point) for the Cambrian base which was defined by the FAD of the ichonspecies Treptichnus pedum (Fig.1) at the Fortune Head section, Burin Peninsula, Newfoundland, Canada. Based on recent studies that (1) the Ediacaran and Cambrian skeletal faunas are transitional (Zhu et al., Geology, 2018, 45:459-462); (2) the complex trace fossils are widespread in the Ediacaran Period, including Treptichnus-type trace and bilaterian trackways (Chen et al., Sci. Adv. 2018, 4: eaao6691); and (3) new high-resolution zircon U-Pb dating, authors proposed that a prominent global carbon isotope negative excursion at the basal Cambrian (BACE excursion) should be the primary marker to define the Cambrian base with an age of 539 Ma which is 2 million years younger than that in the present International Chronstratigraphic Chart..
Meanwhile, authors revised the Cambrian chronostratigraphy of China and proposed a new Xiaotanian Stage for the Cambrian Stage 2 of China. In addition, authors further summarized the integrative stratigraphy of South China, North China and Tarim platforms respectively.
See the article:
ZHU Maoyan, YANG Aihua, YUAN Jinliang, LI Guoxiang, ZHANG Junming, ZHAO Fangchen, Soo-AHN Yeun, MIAO Lanyun. 2019. Cambrian chronostratigraphy and timescale of China. Science China Earth Sciences, 62(1): 25-60