The Devonian Period

The Late Devonian Frasnian–Famennian Event in South China — Patterns and causes of extinctions, sea level changes, and isotope variations

The Global Boundary Stratotype Sections and Points (GSSPs) for the bases of all seven international Devonian stages have been formally defined and ratified by IUGS till 1996, and nowadays, the main tasks for Devonian stratigraphers include further subdivision of these standard stages, strictly constrained absolute ages for the boundaries, and precise neritic-pelagic and marine-terrestrial correlations using multidisciplinary stratigraphy methods. Establishment of high-resolution Devonian integrative stratigraphy framework and timescale of China would play an important role in improving regional and international correlation, facilitating the recognition of important stratigraphic levels in different paleogeographic settings, and understanding the evolution pattern of biota, paleoclimate and paleoenvironment during this critical interval. Based on well-studied bio- and chronostratigraphy of Devonian in South China and adjacent areas, in combination with recent achievements in carbon isotope stratigraphy, event stratigraphy and radioactive isotope ages, this paper briefly summarize the research history and current status of Devonian chronostratigraphy of China, and for the first time introduce Devonian integrative stratigraphy framework of China. Up to date, few studies have been conducted on the astronomical cyclostratigraphy and high-resolution radioactive isotope dating in Devonian of China, which should be our main focuses in the near future.

Devonian integrative stratigraphy and timescale of China

Devonian FlorasDevonian Floras, a Study of the Origin of Cormophyta.E. A. Newell Arber

A series of major geological and biological events which altered the evolutionary processes of whole biosphere occurred during the earth history. Establishing a high-resolution stratigraphic framework and timescale is essential to understand their tempo and causes. High-resolution biostratigraphy remains the most useful approach and forms the basis of dividing the chronostratigraphic system and making the inter-continental and regional correlation. China possesses nearly complete strata from Ediacaran to Quaternary covering wide palaeogeographic regions and containing abundant well-preserved fossils. Traditional biostratigraphy based on sytematic palaeontology of various fossil groups have played an important role in establishing the GSSPs and improving the International and Chinese Stratigraphic Charts. 11 out of 72 establised GSSPs are located in China. Recently, more high-precision geochronology, chemostratigraphy, cyclostrtatigraphy have been applied for stratigraphy and correlation and important advances have been made in some periods. This volume invited Chinese palaeontologists and stratigraphers to summarize the progresses of stratigraphy and timescale from Ediacaran to Quaternary and intercontinental and regional correlation during the last two decades.

Preface: New advances in the integrative stratigraphy and timescale of China

Givetian through middle Famennian brachiopods of Hunan are used to define five biozones, comprising, in ascending order, the Stringocephalus Abundance Zone, the Ambocoeliid-Leiorhynchid Assemblage Zone, the Cyrtospiriferid Assemblage Zone, the Yunnanellina-Sinospirifer Assemblage Zone, and the Yunnanella-Hunanospirifer Assemblage Zone. They correspond approximately to the Po. hemiansatus Zone to Po. varcus Zone, S. hermanni Zone to Pa. punctata Zone, Pa. hassi Zone to Pa. linguiformis Zone, Pa. triangularis Zone to Upper Pa. crepida Zone, and Uppermost Pa. crepida Zone to Pa. marginifera Zone, respectively. Intensified rifting activity in South China during the Devonian began in the middle of the Lower Po. varcus Zone (a level marked by the first appearance of Po. rhenanus), which is consistent with the Lower-Middle Givetian substage boundary suggested by the International Subcommission on Devonian Stratigraphy (SDS). This assumed that rifting activity in the Lower Po. varcus Zone was signified by the deposition of the Baqi Formation in Guangxi and was marked largely by the extensive deposition of the Qiziqiao Formation in central Hunan, which probably led to an opposite pattern of relative sea level change-rising in deeper water trough areas and lowering in carbonate platform areas. The previously recognized S. hermanni Zone sea level rise in platform margin areas of Guangxi can be identified not only in the trough areas but also in platform areas, which probably indicates an overall marine transgression at this time, rather than tectonically induced sea level change. Similarly, this level coincides with the Middle-Upper Givetian substage boundary suggested by the SDS. Although the sea level rise may have occurred in the deeper water trough areas of South China towards the end of the Givetian, platformal areas experienced uplifting at various degrees, especially in the central and northern regions of Hunan where Early Frasnian deposits were apparently absent in many places. Similarly, the end-Frasnian regression led to exposure of many places and absence of early Famennian deposits, which probably accounts for the restricted distribution of the Yunnanellina brachiopod fauna.

Xueping Ma

Papers

Devonian integrative stratigraphy and timescale of China

Middle and Late Devonian brachiopod assemblages, sea level change and paleogeography of Hunan, China

Devonian paleoclimate and its drivers: A reassessment based on a new conodont δ18O record from South China