Late Viséan to Early Serpukhovian Rugose Corals from the Yashui Section, Guizhou, South China Wei LIN1, Xiangdong WANG1, Edouard POTY2 & Markus ARETZ3
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GEOLOGICA BELGICA (2012) 15/4: 329-339 Late Viséan to Early Serpukhovian Rugose Corals from the Yashui Section, Guizhou, South China Wei LIN1, Xiangdong WANG1, Edouard POTY2 & Markus ARETZ3 1LPS, Nanjing Institute of Geology and Palaeontology, China Academy of Science, No. 39 East Beijing Road, Nanjing, P. R. China; [email protected]; [email protected] 2Service de Paléontologie animale, Université de Liège, Bâtiment B18, Allée du 6 Août, Sart Tilman, B-4000 Liège, Belgium; e.poty@ ulg.ac.be 3Université de Toulouse, UPS (OMP), GET, 14 Avenue Edouard Belin, F-31400 Toulouse, France; [email protected] ABSTRACT. Abundant rugose corals are recorded in the Yashui Section in Huishui County of Central Guizhou, South China. The section is mainly composed of light-coloured bioclastic limestone with intercalations of some beds of dolomitized limestone and punctuated by a certain number of unconformities. Totally 20 species belonging to 13 genera are recognized. The composition of the fauna shows resemblance to the Western European faunas of latest Viséan to early Serpukhovian age. Many well-known European taxa such as Dibunophyllum bipartitum, Palaeosmilia murchisoni, Lithostrotion decipiens, Siphonodendron pauciradiale and Aulina rotiformis appear in Yashui, but with different stratigraphic ranges. There are also some endemic taxa such as Arachnolasma sinense, Yuanophyllum kansuense, Kueichouphyllum sinense and Stylostrotion petalaxoidae which can be used for correlations throughout South China. The coral diversity of the Yashui section shows: (1) a diversity decrease in the uppermost part of the Viséan, and (2) a poorly renewed fauna in the Serpukhovian, which is the similar pattern recorded in Palaeotethys. Therefore, a coral based biostratigraphic succession to separate the early Serpukhovian from latest Viséan is difficult to establish. Among the 20 species, 18 are described and illustrated, including 2 in open nomenclature. Two species are omitted from the description due to their bad preservation. KEY WORDS: Rugose corals, Biostratigraphy, Mississippian, Viséan-Serpukhovian boundary. 1. Introduction near the Viséan/Serpukhovian boundary (Poty et al., 2006) or/ and frequent appearances of subaerial exposure surfaces in Mississippian rugose corals are relatively diversified and shallowing-upwards cycles (Smith & Read, 2000; Al-Tawil et al., have received much attention in the past decades. Generalized 2003). These lithofacies changes are probably linked to global distributional patterns and biostratigraphic successions of the scale glacial and tectonic events. As a result, the rugose corals are Mississippian rugose corals have been developed and summarized often rare in Serpukhovian strata, and furthermore, it is relatively (e.g. Sando, 1990; Sando & Bamber, 1985; Fedorowski, 1981; difficult to recognize the Viséan/Serpukhovian boundary by Mitchell, 1989; Poty et al., 2006; Somerville, 2008). In general, rugose corals. limited information on the temporal and spatial distribution of rugose corals is available for the Serpukhovian. This is probably During the Mississippian, South China had a tropical due to the decrease in coral occurrences caused by sudden archipelago layout (Scotese et al., 1979; Scotese & McKerrow, change of sedimentary facies from carbonate to siliciclastic 1990; Torsvik & Van der Voo, 2002). The Mississippian in Table 1. Mississipian coral zonations in China. C.: Cystophrentis; P.: Pseudouralinia; T.: Thysanophyllum; Y.:Yuan- ophyllum; U.: Uralinia; Nam.: Namurian; Serp.: Serpukhovian. 330 W. LIN, X. WANG, E. POTY & M. ARETZ most parts of South China consists of shallow-water carbonates Land to the northwest and the Cathaysia Old Land to the east, intercalated with some terrigenous clastics. Abundant rugose together with numerous small intra-continental basins in the corals occur in the Mississippian, especially in Tournaisian and western part. The northern part of the Guizhou province belongs Viséan strata, which have been intensively studied, starting with to the southern Upper Yangtze Old Land. The Carboniferous the early taxonomic work of Yabe & Hayasaka (1915, 1920) sediments in central and southern Guizhou can be subdivided into and Grabau (1922, 1928). Yu (1931, 1933, 1937) proposed three distinctive lithostratigraphic regions representing carbonate the first biostratigraphic zonation of rugose corals of the platform to slope-basin: the Dushan-Weining region, the Puan- Fengningian System (= Lower Carboniferous) on the basis of Mawei region, and the Langdai-Luodian region. collections from southern Guizhou, central Hunan and western The Yashui section is located in the south-eastern part of Gansu (with additional data by Chi, 1931, 1935). Within the the Huishui County, about 90 km south of the city of Guiyang (Fig. Fengningian System, he established four rugose coral zones in 1). It is mainly composed of light-coloured bioclastic limestone ascending order which are Cystophrentis zone, Pseudouralinia with intercalations of some beds of dolomitized limestone, which zone, Thysanophyllum zone and Yuanophyllum zone. This is typical for the Dushan-Weining lithostratigraphic region. A biostratigraphic zonation has been applied in other parts of certain number of unconformities associated with palaeokarst South China (Wu, 1964; Luo, 1984; Xu & Poty, 1997; Poty et features and terrigeneous clastic deposits that should be considered al., 2006) with some modifications (Table 1). However, despite as palaeosol punctuate the section. Most of the limestone beds the relative frequent occurrences of rugose corals during the of the section are rich in fossils such as corals, brachiopods, Mississippian, the resolution of the zonation is still rather low, chaetetid sponges, foraminifers and calcareous algae. e.g. the Yuanophyllum zone covers a very long range from the The Yashui section was first presented during the 11th middle Viséan to the Serpukhovian. International Congress on the Carboniferous stratigraphy and The main aim of this paper is to describe and illustrate geology in 1987. It was selected as the stratotype of the local the coral fauna from the Yashui Section in Huishui County of Chinese stage Dewuan (Wu, 2003). Although the section is a Central Guizhou, which displays a continuous succession from typical representative of the shallow water carbonate facies, it the Upper Viséan through the entire Serpukhovian in shallow has not been studied in detail in terms of sedimentological and water facies. paleontological aspects. Wu (2003) and Wu et al. (2009) published some data of foraminifers from Viséan/Serpukhovian boundary 2. Geological setting and materials interval, but only few specimens were illustrated. A more recent study on foraminifers in the Yashui section by Groves et al. (in In the Carboniferous, a large carbonate platform developed on press) uses the first appearance datum (FAD) of Janischewskina the Yangtze Block (South China), with the Upper Yangtze Old delicata to suggest a provisional Viséan/Serpukhovian boundary at 41.6m from the base of the section. Other fossil groups have not been studied yet from the section. The Yashui section was measured in 2008 and permanent markers (metal pins) have been installed throughout the whole section meter by meter. Rugose corals were sampled for the first time in 2008 and were additionally sampled in 2010 and 2011. All specimens were numbered by the true thickness from the base of the section. The material presented in this study is from the collections of the first sampling, which includes nearly 300 thin sections made from 68 specimens. 3. Composition of rugose coral fauna and discussion 20 rugose species belonging to 13 genera of the families Aulophyllidae, Lithostrotionidae, Palaeosmilidae and Axophyllidae were identified. Seven genera are solitary and six are colonial. In the latter group, three genera are massive and three are fasciculate. The rugose coral association is composed of several endemic taxa and more abundant taxa known in the Palaeotethys. The common abrasion of the dissepimentarium of solitary corals and the fragmentation of the compound corals indicates a shallow water environment with relatively high energy. Most of the rugose samples were collected from the lower part of the Yashui section (0-25 m). Locally, corals are concentrated at the bottom or top of limestone beds. The rugose coral association in the lower part of the section is dominated by large dissepimented solitary corals such as Palaeosmilia murchisoni, Kueichouphyllum sinense, Axophyllum cf. lonsdaleiforme, Arachnolasma sinense, Dibunophyllum bipartitum and “Dibunophyllum” tingi, accompanied by some colony fragments of Siphonodendron pauciradiale, Diphyphyllum fasciculatum and Palastraea sp. (Fig. 2). Aulina rotiformis is not present in the first sampling from the lower part, but it was found 6 m below the base of the measured section based on the preliminary observation of the later samplings. The occurrence of Palastraea, Dibunophyllum bipartitum, Siphonodendron pauciradiale and Aulina rotiformis indicate a late Viséan and early Serpukhovian age. Similar association can be found in zone RC8 (Belgium, France) and RC9 (South France, Poty et. al., 2006), faunal divisions H-K in Britain (Mitchell, 1989) and the Figure 1. Location and geological map of the Yashui section. Legend: upper Viséan in North Africa (Aretz, 2010, 2011). 1. Devonian; 2. Carboniferous; 3. Permian; 4. Triassic; 5. Cretaceous; 6. Quaternary; 7. Dip fault; 8. Strike slip fault; 9.