«To cite this version: Aihua Yuan. Latest Permian Deep-Water Ostracod (Crustacea) Fauna from South China. Pa- leontology. Universit´ Pierre et Marie ...»
Becker & Wang, 1992; Hao, 1992a, 1993, 1994, 1996; Yi, 1992, 1993, 2004). These studies have greatly increased our knowledge on Late Permian shallow water ostracods of South China. Ostracoda are very sensitive to their habitats and greatly vary in different environments. For drawing a general conclusion, the thorough investigations in deep water ostracod faunas are indispensable.
The other problem, which restricts our comprehensive understanding on Late Permian ostracods, is the very poor knowledge on ostracods during the Permian-Triassic events in South China. This problem obviously emerges when we discuss the ostracod extinction. For example, Jin et al. (2000) proposed the “sudden extinction” in ostracod fauna of the Meishan Section (GSSP) during the Permian-Triassic events.
Note that the Changhsingian ostracods in the Meishan Section were systematically studied even though the revision is necessary (Shi & Chen, 1987). In contrast, ostracods from the Permian-Triassic boundary and Lower Triassic were poorly investigated. Thus the results were probably influenced by the low research extent on ostracods from the Permian-Triassic boundary interval and did not mean real extinction at all. At present, in South China, the available data are focused on either the Late Permian (e.g.
Shi & Chen, 1987, 2002) or the Early-Middle Triassic (e.g. Zheng, 1976, 1988) ostracods. In the few reported ostracod faunas spaning the Permian-Triassic boundary (Wang, 1978; Yi, 1992, 2004; Hao, 2 Yuan Aihua: Latest Permian Deep-Water Ostracod (Crustacea) Fauna from South China 2008/5 1994, 1996; Wang & Wang, 1997), only the lowermost Triassic was involved. Thus it is difficult to trace the ostracod evolution during the Permian-Triassic events.
In a word, the expansion in two aspects is important for Late Permain ostracod study in South China.
The first is to expand studies on faunas from different paleoenvironments. The other expansion is to choose the ostracod faunas completely spaning the Permian-Triassic events as the study objective. This thesis will focus on latest Permian deep water ostracod faunas in South China. The second expansion has been evolved in the author’s new project and will be carried out in the future work.
This dissertation: significance, study area, method and acquired results
With a view to the first expansion, this dissertation will focus on the latest Permian deep water ostracod faunas in South China for the first time and aims to enrich our understanding on Late Permian ostracods. In addition, it should be noticeable that the only world-wide data available on Permian deep-water ostracods were from the Early Permian of Timor, Indonesia (Gründel & Kozur, 1975; Bless,
1987) and Middle Permian-Wuchiapingian of Sicily, Italy (Kozur, 1991a, b; Crasquin-Soleau et al., 2008). Thus this study will also fill the gap on the latest Permian deep water ostracod faunas worldwide.
In this dissertation, four sections from the deep water strata in South China are studied in detail for latest Permian deep water ostracods, i.e. the Dongpan Section and the Liuqiao Section from Guangxi, the Shaiwa Section from Guizhou and the Chaohu Section of Anhui deposited in the lower Yangtze basin. The following table shows the preparative work in the earlier stage of this dissertation.
In method, this dissertation is characterized by the combination of ostracod study and integrated analyses. For ostracod study, the systematic taxonomy is carried out as the preliminary work and then the paleoenvironments (paleobathymetry and oxygen-level) are reconstructed based on the ostracod taxa and assemblages. The paleoenvironmetal results are then compared and integrated with different data (other fossils, sedimentology, mineralogy, geochemistry) of intra-section. Afterwards, the comparison is evolved between studied faunas. At last, the similarity and difference are discussed to the 3 2008/5 PhD dissertation of University of Pierre Marie Curie & China University of Geosciences (Wuhan) contemporary shallow water ostracod faunas and the deep water ostracod faunas in other geological time.
Through the above mentioned studies, four main achievements are obtained in this dissertation.
(1) Systematic taxonomy is carried out for the four studied ostracod faunas. The diverse fauna (43 genera, 128 species) greatly substantiates our understanding on the latest Permian deep water ostracods for the first time.
(2) Ostracods are successfully applied in the paleobathymetric and oxygen-level reconstruction in the latest Permian deep water strata. The paleobathymetric results are accordant to those from radiolarians, sedimentology and mineralogy. The oxygen-level reconstruction, based on the FF% model (see §4.3), is firstly applied in the deep water ostracod fauna. Although its usability needs further validation, the corresponding with foraminifer and trace element analyses still aroses our confidence to this model.
(3) The ostracod “extinction” in the deep water faunas is discussed herein. Two apparent extinction horizons are proposed for the Dongpan fauna. The First (major) apparent extinction was accordant to the regression event, strong volcanic activities and possible anoxia/dysoxia in the Dongpan Section. This proposition steps the primary foot on understanding the deep water extinction in the Permian-Triassic boundary interval.
(4) The studied deep water ostracod faunas are compared to the contemporary shallow water ostracod faunas in composition, paleoecological assemblage, diversity, abundance and “extinction” process.
Both the similarities and differences, revealed through the comparison, demonstrate the necessity of deep water ostracod research for comprehensive understanding the ostracod faunas.
4 Yuan Aihua: Latest Permian Deep-Water Ostracod (Crustacea) Fauna from South China 2008/5 5 2008/5 PhD dissertation of University of Pierre Marie Curie & China University of Geosciences (Wuhan)
Chapter 1 Regional Geology and Stratigraphic Correlation
The geographical domain of South China spans over Guangdong, Guangxi, Guizhou, Sichuan, Hunan, Hubei, Jiangxi, Zhejiang, Fujian and some parts of Yunnan, Anhui and Jiangsu (Fig.1-A).
Geologically, the South China Block, is bordered to the North China Block by the Qinling-Dabie orogenic belt on the north, bounded by the Songpan-Ganzi orogenic belt on the northwest, bordered to the Siamo Block by the Ailaoshan suture zone on the southwest and the Indochina Block by the Songma suture zone on the south (Ren, 1980; Metcalfe, 1996, 2002; Yin et al., 1999；Ingersoll et al., 2002; Wang, 2004; Lehrmann et al., 2005).
Fig. 1-A Geographical and geological sketch map of South China (after Wang, 2004, Fig. 1.1; Lehrmann et al., 2005, Fig.1) The continuous Changhsingian strata are well and widely developed in South China. A variety of facies have been recognized, including the terrestrial, the littoral, the carbonate platform, the slope and the basin (trough) facies. The basin facies were distributed mainly in three basins, southern Qinling 6 Yuan Aihua: Latest Permian Deep-Water Ostracod (Crustacea) Fauna from South China 2008/5 basin, lower Yangtze basin and the Hunan-Guizhou-Guangxi basin (Feng et al., 1994; Feng & Gu, 2002; Wang, 2004; Wang & Cao, 2004). Deep water sediments∗ are well exposed in these regions especially in Guizhou and Guangxi. In this work, four sections in two of these basins were chosen for latest Permian deep water ostracod study, i.e. the Dongpan Section and the Liuqiao Section from Guangxi, the Shaiwa Section from Guizhou and the Chaohu Section of Anhui deposited in the lower Yangtze basin (Fig.1-B).
1.1.1 Dongpan Section (DP) & Liuqiao Section (LQ) During the Late Paleozoic, western Guangxi was in the open marine to pelagic environment. The present shallow-water platforms were islands interspersed among the open marine (Kuang & Wu, 2002).
Wu et al. (1994) and Wu (1999) interpreted the western Guangxi as archipelago through the studies on sedimentary rocks and volcanics. In addition, regional geological survey investigated that the patch reef on the margin of the platform was surrounded by the deep-water siliceous rocks and calcareous
turbidites. In Bunong, 20 km west away from the studied area, the basalt with thickness of 100m was recognized. The presence of Palaeofusulina sp. yielded in the limestone interlayered with the basalt, suggests the rift tectonic background during the Changhsingian. Eastwardly, the basalt becomes thinner and turned to be tuff in the studied area. Then, in the studied area, the archipelagic palaeogeography constituted of deep-water basin and shallow platform is widely confirmed and adopted.
In southwestern Guangxi, the Late Palaeozoic strata are well exposed. The lowermost strata are the open carbonate platform sediments deposited in the Carboniferous to the Middle Permian. The Dongwu Tectonic Movement gave rise to multi-facies sedimentary. The reef facies in some areas lasted until latest Permian. During the Late Permian, the carbonate platform was broken and dropped. Along with the areal tectonic uplift, the reef on the margin of the platform not submerged was interspersed in the deep water basin. In Dongluo, north to the studied sections, coal-bearing nearshore to marsh sediments retained all the time. Most strata of the studied sections were dominated by siliceous organic limestones in the confined platform facies during the Wuchiapingian and deep water siliceous rocks, siliceous mudstone and organic limestone in the Changhsingian. The Early Triassic sediments consist of mudstones, muddy limestones and nodule limestones and graduate to brecciated limestones. The Middle Triassic is mainly composed of terrigenous clastic turbidites (Kuang & Wu, 2002).
The Dongpan Section (22°16.196′ N, 107°41.505′ E) is located approximately 5km southwest of Dongpan Village, Liuqiao Town, Fusui County, southwestern Guangxi (Fig. 1-1-A (a)). It is adjacent to the milepost of 884.5km on the 322 national highway between Hengyang, Hunan and Youyiguan, Guangxi. The Liuqiao Section is situated along the highway in Liuqiao Town and near the Dongpan Section (Fig. 1-1-A (a)). It is very convenient for working in the two sections.
Dongpan Section displays a continuous uppermost Permian (upper Dalong Formation) to lowermost Triassic (Luolou Formation) sedimentary sequence (Fig. 1-2) (BGMRGZAR, 2001). The Dalong Formation, as exposed, is 11.2m thick and divided into 12 beds. The Dalong Formation is mainly composed of thin-bedded siliceous rocks, muddy siliceous rocks and siliceous mudstones with claystones interlayered. The age of the Dalong Formation, determined by the associated radiolarians (Neoalbaillella optima zone in the beds from 03DP2 to 03DP6 (Yao et al. 2001)) and ammonoids (Huananoceras cf. perornatum Chao and Liang, Laibinoceras cf. compressum Yang (Yang et al., 1987), Qianjiangoceras sp. at the top of the bed 03DP12), is Late Changhsingian (Feng et al., 2004, 2006, 2007a; He et al., 2005; Meng, 2005; Jin et al., 2007; Zhang et al., 2007a, 2007b). The Triassic Luolou Formation overlies the Dalong Formation in conformity. The lithology of the Luolou Formation is represented by interbedded yellow mudstones, grey claystones, grey thin-bedded calcareous mudstones and muddy limestones. The Early Triassic age was proved by the Triassic ammonoids Ophiceras sp., Ophiceras tingi Tien and the bivalve Claraia dieneri Nakazawa yielded from the base of the bed 03DP13 (He et al., 2005).
In Liuqiao Section, only uppermost Permian (upper Dalong Formation) is exposed (Fig. 1-2). The upper Dalong Formation is mainly composed of muddy siliceous rocks and siliceous mudstones interlayered with mudstones in the upper part and intercalated by claystones in the lower part. The 8 Yuan Aihua: Latest Permian Deep-Water Ostracod (Crustacea) Fauna from South China 2008/5 Changhsingian age of the Dalong Formation in Liuqiao Section is also determined by the radiolarian Neoalbaillella optima zone.
The detailed stratigraphic descriptions for each bed of the Dongpan Section and Liuqiao Section are displayed as follows (Fig. 1-1-A (b), Fig. 1-2) (further information about the lithology for each sub-bed see Meng et al., 2005a). In each section, the descriptions are from top to bottom.
———————— Base unknown ———————— 1.1.2 Shaiwa Section (SW) The Shaiwa Section is located in Shaiwa Village, 15km northwestern of Houchang Town, Ziyun County, southwestern Guizhou (Fig.1-1-B) (i.e. the Sidazhai Section in Gao et al. (1999), Yang et al.
(2000) and Gu et al. (2002), due to its locality, the designation of Shaiwa Section is adopted here following Feng & Gu, 2002; Gao et al., 2005; Chen et al., 2006).
Fig.1-1-B: Location of the Shaiwa Section (modified after Gao et al., 2005 and Chen et al., 2006) During the Late Permian, southwestern Guizhou was situated at the NW-trending Shuicheng-Ziyun aulacogen in the Nanpanjiang basin on the southern margin of the Yangtze platform (Fig.1-B). This aulacogen became a deep water trough during the Changhsingian.
Changhsingian deep water sediments are well exposed in Shaiwa Section along a road with a huge thickness of 762m (Yin et al., 1999; Gao et al., 2001; Wang et al., 2006). Most of the Changhsingian deep water strata, composed of siliceous rocks and siliceous mustones, are named as Dalong Formation in South China (detailed discussion about the sedimentary facies of the Dalong Formation see Yin et al., 1995, p.62-68). However, in southern Guizhou, the strata are recognized as Shaiwa Group (BGMRGP, 1987; Jin et al., 2000; Feng & Gu, 2002) which is turbidity current deposit mainly consisting of siliciclastic and carbonate clastic sediments. The Shaiwa Group is divided into 95 beds belonging to 13 2008/5 PhD dissertation of University of Pierre Marie Curie & China University of Geosciences (Wuhan) four members as follows (Gao et al., 2005; Chen et al., 2006). The descriptions for the section below are from top to bottom.