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IU S ONES D I
IGCP Project 591 Field Workshop 2014 in conjunction with
International Subcommission on Silurian Stratigraphy (ISSS) International Subcommission on Ordovician Stratigraphy (ISOS) and International Subcommission on Cambrian Stratigraphy (ISCS)
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Nanjing University Press
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Microfossils from the Llandovery-Wenlock boundary sections m Ziyang-Langao region, southern Shaanxi, central China TANG Peng1, WANG Jian2 , WANG Chengyuan 1, UANG Yan 1 and WANG Xin 2 1
State Key Laboratory of Palaeobiology and Stratigraphy, Nanjing Institute of Geology and Palaeontology, Chinese Acadeng! of Sciences, Nanjing, 210008, China <
[email protected]> ' Xi'an Center Geological Survey, China Geological Survey, Xi'an 710054, China
In China, the Ziyang region in southern Shaanxi Province is a key region for the study of the base of the Wenlock Series (Fu et al., 2004). Several well-developed sections ranging from the upper Llandovery to lower Wenlock, contain abundant well-preserved graptolites, that have been studied for a long time (Fu, 1986; Fu and Song, 1986; ·Fu et al., 2006; Wang, 2011; Wang et al., 2013). The boundary interval in that region is in the Wuxiahe Formation that was redefined by Luo ( 1992) and Ma ( 1998). It is mainly composed of black, dark grey and light green shales, siltstones, fine sandstones and slates. Five graptolitic biozones have been recognized, including the Cyrtograptus lapworthi , the Cyrtograptus sakmaricus, the Cyrtograptus insectus, the Cyrtograptus centrifugus, and the Cyrtograptus murchisoni biozones (Fu et al. , 2006). In contrast, no microfossils including chitinozoans, conodonts, acritarchs and others have been found and documented so far from the top Llandovery to the base Wenlock in this region. The absence of microfossils is probably caused by the light metamorphism in the rocks within the South Qinling tectonic belt. Recently, 33 samples from the Langao Qiaoxi ( LQX) section and 29 from the Ziyang Bajiaokou A ( ZBA) section were processed for chitinozoans. The result is positive. Besides some poorly preserved chitinozoans, some scolecodonts, acritarchs, melanosclerites and tubular plant fragments were also obtained from the Wuxiahe Formation at ZBA section. Most importantly, 23 samples of the LQX section yield a decent amount of conodonts . No chitinozoans have been found from the LQX section, but 13 samples from the ZBA section show some traces of chitinozoans. Angochitina cf. longicollis Eisenack, which occurs throughout the Wuxiahe Formation, is the only identifiable species at this section (Fig. IA, B). Fragments of Conochitina occur occasionally. In samples QX16.3 m and QX17 . 2 m of the LQX section, aggregated graphitized acritarchs are observed belonging to Synsphaeridium (Fig. lE). From our analysis, some melanosclerites are recovered at samples PBJ19, PBJ22, PBJ26 and PBJ29 of the ZBA section, identifiable to Melanoporella clava Schallreuter, Melanoporella sp. and an indeterminate (Fig. IC, 0). All of the melanosclerites obtained are pleuriden, and no skeletons were found. Among these taxa, M. clava is the most abundant, that is also a cosmopolitan species . The present paper is the first report of melanosclerites in China. Conodonts are recovered from 23 samples in the middle Wuxiahe Formation of the LQX section
