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In this chapter, starting with a brief review of the research history and current status in the studies of the Ordovician chronostratigraphy in China, the subdivision of the Ordovician System, definition and recognition of its series and stage boundaries, and possible stratigraphic gaps are discussed in details in order to establish a multidisciplinary stratigraphic correlation through an integrated approach including lithostratigraphy, biostratigraphy, radiometric dating, chemostratigraphy and magnetostratigraphy. Being internationally accepted, the Ordovician System is now subdivided into three series and seven stages, in ascending order, Lower (Tremadocian, Floian), Middle (Dapingian, Darriwilian) and Upper series (Sandbian, Katian, Hirnantian). Three of the seven "Golden Spikes" defining the bases of the Ordovician stages, which were established in 1997-2007, are located in China. As a regionally applied chronostratigraphy, the Ordovician System was subdivided in China into Lower (Xinchangian, Yiyangian), Middle (Dapingian, Darriwilian) and Upper series (Neichiashanian, Chientangkiangian, Hirnantian). This scheme agrees largely with the standard international classification, which can actually be directly applied to China, except for some special circumstances where the Neichiashanian and Chientangkiangian stages of the Upper Ordovician are used. Based on the new studies in recent years and distinctions and differences recognized in the development of the Ordovician System in the constituent terranes of China, a new framework for correlation among the major Chinese palaeoplates or terranes, e.g. South China, North China (including Tarim and Qaidam) and Xizang (Tibet)-western Yunnan, has been established. However, it has been recognized herein that uncertainties still remain on defining the base of the Tremadocian, Dapingian and Katian, and on the correlation between different mega-facies. More specifically, for the Tremadocian, the precise correlation of its base will depend on the better-defined conodont taxonomy, while for the Dapingian and Katian, on the correlation between different mega-facies. It is worthwhile to note that the chemostratigraphic studies of the Ordovician System in China produced the carbonate δ13C curves for the Darriwilian (Middle Ordovician) and Katian (Upper Ordovician), which show significant differences from the composite global curve. Record of the Ordovician isotopic dating is relatively rare in China, with only three reliable ages from zircons that are all from the upper Katian to Hirnantian of the Upper Ordovician. Abundant bentonite beds in the Upper Ordovician of South China will also provide unique opportunities to advance the isotopic dating and related researches. Studies on the Ordovician magnetostratigraphy need to be significantly enhanced in China, as currently all the available results are restricted to the Lower Ordovician of North China, although they can be correlated with those known from other parts of the world. The analysis of the durational unevenness of the seven stages in the Ordovician supports the possibility to further subdivide the long-durational Tremadocian, Darriwilian and Katian stages, each into two substages. [ABSTRACT FROM AUTHOR]

Silurian is a period with the shortest duration in Phanerozoic except for the Neogene and Quaternary. It represents an important and unique interval when the biotic diversity recovered quickly after the end-Ordovician mass extinction, different paleoplates or terranes conjoined, big oceans disappeared or narrowed, climate and sea level changed frequently, global biotic provincialism became weaker, some primitive plants started to occupy the land. Silurian is also the first system of which all the chronostratigraphic stratotypes (i.e. the GSSPs) including four series and seven stages were established by the International Subcommission on Silurian Stratigraphy (ISSS). Nonetheless, during the post-GSSP studies conducted by ISSS in the middle 1980s, some Silurian GSSPs were found to have some congenital defects such as no index fossils available that hinder the high resolution subdivision and correlation on a regional or global scale. In this paper, based on the latest development of Silurian study in China, the progress in biostratigraphy, chronostratigraphy, event stratigraphy (such as facies differentiation, heterochrony of black shales, marine red beds, carbonate rocks and reefs), chemostratigraphy, and tectonic stratigraphy (e.g., widespread of the late Silurian rocks in South China and its tectonic implication) are systematically summarized. Some existing problems and the areas to be focused in future work are also discussed. It is suitable for chronostratigraphic study to concentrate not only on the boundary but also doing multidisciplinary analysis on the biotic, chemical, magnetic, environmental, and chronologic aspects, in order to enhance the reliability and the potential for regional and global correlation of a certain GSSP. Some important achievements are expected in these areas in the Silurian study in China: (1) ecostratigraphy and basin analysis of the Llandovery, and the correlation of integrative stratigraphy with a high resolution; (2) establishment of the Wenlock to Pridoli chronostratigraphic framework; (3) the chemo- and magnetic stratigraphy and the age of some key intervals and horizons; (4) further investigation on paleogeography and plate tectonics; and (5) origin and early evolution of the terrestrial ecosystem. Some new breakthroughs might occur in the restudy on some of those problematic GSSPs of some particular series and stages. [ABSTRACT FROM AUTHOR]

Located northwest of the Jiangshan-Shaoxing Fault Zone, western and northwestern Zhejiang and northeastern Jiangxi provinces experienced major changes in bio- and litho-facies and paleogeography through the Ordovician-Silurian transition (late Katian, Hirnantian, and early Rhuddanian), as manifested by stratigraphic, paleontologic and synecologic records. Three geographic units under consideration are South, Central, and North areas. The western margin of the South area was occupied by the Huaiyu Mountains, whereas the other two parts were covered by the Zhe-Gan Sea during late Katian (Late Ordovician) time. In the early stage of the Changwu Formation deposition (late Katian), the sea was deepening northeastward, but with shallower conditions in the southwest and deeper conditions in the northeast. During mid to late stages of Changwu Formation deposition (latest Katian), the sea became much shallower and the sea bottom was uplifted substantially, which occurred somewhat prior to the global trend. During the Hirnantian (latest Ordovician) and early Rhuddanian (earliest Silurian), the study region became a shallow bay under expansion of the Cathaysian Oldland. There occurred a major drop of sea level and great changes in benthic biota with the occurrence of many new immigrants through the Ordovician-Silurian transition, which are closely related to a unique regional orogeny. The Yangtze and Cathaysian blocks may have amalgamated within the South China Paleoplate during this interval to cause the continuous uplifting and northwestward expansion of the Cathaysian Oldland. [ABSTRACT FROM AUTHOR]