GR-01363; No of Pages 23 Gondwana Research xxx (2014) xxx–xxx Contents lists available at ScienceDirect Gondwana Research journal homepage: www.elsevier.com/locate/gr Early Cambrian palaeobiogeography of the Zhenba–Fangxian Block (South China): Independent terrane or part of the Yangtze Platform? Ben Yang a,b,⁎, Michael Steiner b,HelmutKeuppb a Institute of Geology, Chinese Academy of Geological Sciences, Baiwanzhuang Road 26, Beijing 100037, China b Department of Earth Sciences, Freie Universität Berlin, Malteserstrasse 74-100, Haus D, 12249 Berlin, Germany article info abstract Article history: Early Cambrian small skeletal fossils (SSFs) are studied and revised from the Zhenba–Fangxian Block of the tran- Received 21 June 2014 sitional zone between the Yangtze Block and the South Qinling Terrane. The study reveals a diverse fauna with 47 Received in revised form 24 September 2014 species of various biological affinities, including the new species Gapparodus gapparites sp. nov. The SSFs are Accepted 27 September 2014 assigned to the newly defined Cambroclavus fangxianensis–Rhombocorniculum cancellatum Assemblage Zone. Available online xxxx Based on the investigated SSF fauna from Zhenba County, Southeast Shaanxi of China and published data, a – Handling Editor: J.G. Meert palaeobiogeographic study is carried out for the Cambrian Stage 3 (equivalent to the Atdabanian Botoman of Si- beria). A hierarchical Pearson similarity cluster analysis of 295 species from 32 regions of the world indicates a Keywords: distinct palaeobiogeographic pattern with seven faunal provinces. The result is mostly consistent with existing Palaeobiogeography palaeogeographic reconstructions for the early Cambrian. However, it is also shown that the SSF assemblages Small shelly fossils of the Zhenba–Fangxian Block have low similarity with those of the Yangtze Block. Instead, they share high sim- Zhenba–Fangxian Block ilarity with those from Armorica, Tarim and the Karatau–Naryn terranes (South Kazakhstan/North Kyrgyzstan). Yangtze Block The Yangtze Block has a unique SSF assemblage dissimilar to most of other regions. The Terreneuvian–Cambrian Early Cambrian Stage 3 sedimentary sequence of the Zhenba–Fangxian Block is more consistent with that of the South Qinling Terrane. Besides, sedimentary Ediacaran manganese ore deposits and Cambrian barite/witherite deposits have unique distribution pattern on the Zhenba–Fangxian Block. Derived from the profound dissimilarities in faunal composition, sedimentary sequence and distribution of sedimentary ore deposits, we hypothesize that during the Neoproterozoic–Cambrian transition, the Zhenba–Fangxian Block might have been an independent terrane and more distant from the Yangtze Block. The palaeobiogeographic analysis of SSFs also indicates a closer alliance between Avalonia and Siberia. It corroborates the palaeogeographic reconstruction of North China at the margin of Gondwana, in the vicinity of Australia, Antarctica, and Armorica. © 2014 International Association for Gondwana Research. Published by Elsevier B.V. All rights reserved. 1. Introduction organisms (Ediacara-type fossils), trace fossils, mineralized small skele- tal fossils (SSFs) and diagenetically replaced soft-tissued organisms. The Cambrian bioradiation of metazoans (Cambrian “explosion”) Most distinct fossil information is derived from the skeletal fossil record represents a major biotic revolution in Earth history (Conway Morris, (Steiner et al., 2007) and soft-tissued fossil Lagerstätten (Conway 2006; Marshall, 2006). Both biotic and abiotic influences on the “Cam- Morris, 1989; Conway Morris, 1998; Shu et al., 2001; Shu et al., 2003). brian Explosion” have been discussed (Marshall, 2006). As most of the While soft-tissue preservation is exceptional and may be exclusive for clades appeared in the fossil record within a short duration (Marshall, specific organisms, bulk data for the majority of metazoans is derived 2006), necessary information on the evolution of metazoans is mostly from organic and primarily biomineralized skeletons. Small shelly fos- derived from two lines of evidence: The incomplete fossil record and sils (SSFs) represent a specific taphonomical mode in preservation typ- the biology of modern metazoans with theoretical considerations on di- ical but not exclusive for the terminal Ediacaran to Cambrian Series 2. versification of detailed bauplans (Vannier et al., 2007; Vannier et al., The common preservation as phosphatic replacement allows to extract 2010) as well as the estimates of divergences of major clades based on the microfossils in great quantities by dissolving rocks with weak acids, molecular data (Budd and Jensen, 2000; Peterson et al., 2005). Fossil in- mostly acetic and formic acid, or diluted hydrofluoric acid (Yang et al., formation on the early evolution of metazoans during the Ediacaran and 2014b) and to apply the fossils for a reconstruction of the early evolu- Terraneuvian Series is mostly derived from imprints of soft-bodied tion of metazoans, biostratigraphy and palaeobiogeography. SSFs have been widely applied as a biostratigraphic tool in the early Cambrian (Rozanov and Missarzhevsky, 1966; Qian, 1978; ⁎ Corresponding author at: Institute of Geology, Chinese Academy of Geological Sciences, Baiwanzhuang Road 26, Beijing 100037, China. Tel.: +86 10 68999697. Missarzhevsky and Mambetov, 1981; Qian, 1989; Qian and E-mail address: [email protected] (B. Yang). Bengtson, 1989; Bengtson et al., 1990; Elicki and Schneider, 1992; http://dx.doi.org/10.1016/j.gr.2014.09.020 1342-937X/© 2014 International Association for Gondwana Research. Published by Elsevier B.V. All rights reserved. Please cite this article as: Yang, B., et al., Early Cambrian palaeobiogeography of the Zhenba–Fangxian Block (South China): Independent terrane or part of the Yangtze Platfo, Gondwana Research (2014), http://dx.doi.org/10.1016/j.gr.2014.09.020 2 B. Yang et al. / Gondwana Research xxx (2014) xxx–xxx Esakova and Zhegallo, 1996; Gravestock et al., 2001; Steiner et al., Palaeobiogeographical reconstructions are rarely applied for the 2003; Steiner et al., 2004; Skovsted, 2006; Steiner et al., 2007; Cambrian and if so are mostly based on studies of trilobites (Álvaro Shabanov et al., 2008; Varlamov et al., 2008; Kouchinsky et al., et al., 2003). It would be important to further expand the knowledge 2014; Yang et al., 2014a). It has been argued that many elements of on the provincialism of Cambrian faunas. SSFs were endemic and facies-dependent (Landing, 1992; Mount The present study aims at re-studying and revising the early Cambri- and Signor, 1992; Landing et al., 2013a). However, this also allows an SSFs of the Zhenba–Fangxian Block for a detailed biostratigraphical the application of SSFs for reconstructions of the ecology and and palaeobiogeographic application. With quantitative analysis of the palaeobiogeography (Qian et al., 1999; Elicki and Pillola, 2004; SSFs, it aims to illuminate the palaeogeographic position of Yangtze Elicki, 2005; Steiner et al., 2007; Yang et al., 2014a). and Zhenba–Fangxian blocks during the early Cambrian. Palaeobiogeographical work on the critical Ediacaran to Cambrian time interval is of special significance for understanding the evolution of life and other major geological events, e.g., innovations in the atmo-, 2. Material and methods hydro- and geosphere of this time. Quantitative and semiquantitative studies of Cambrian faunas, mostly trilobites and brachiopods, have Samples were collected from the sections with a stratigraphic sam- been carried out for decades for palaeobiogeographic applications pling resolution of about two samples per one meter. Every single sam- (Pillola, 1990; Lieberman, 1997; Brock et al., 2000; Álvaro et al., ple is 1–2 kg in average except for the Dengying Formation. All samples 2003; Elicki, 2005; Williams et al., 2007; Álvaro et al., 2013). Howev- were cut with a diamond saw to obtain thin slices for sedimentological er, pre-trilobitic SSFs have only been rarely used for quantitative studies. The rest was immersed in 10% buffered acetic acid or 10% buff- palaeobiogeographic reconstructions (Steiner et al., 2007). ered formic acid (mostly for dolostone). The acids were replaced every Current palaeogeographic reconstructions for the Ediacaran to 3 days and the residue was retrieved every 1–2 weeks depending on Cambrian time remain a matter of controversy on the geometry of the the reaction speed. The residue was sieved into N2mm,N125 μm, supercontinents and the arrangement of crustal blocks. Recent N64 μm grain classes simultaneously and then dried at 60 °C in the palaeogeographic reconstructions (Li et al., 2013; Torsvik and Cocks, oven. Acid resistant residues of b 64 μm were discarded. Subsequently, 2013b) revealed that considerable uncertainties still exist on the posi- fossils were hand-picked under a binocular microscope. Selected speci- tions of several continental blocks (e.g., North China and South China) mens were glued on sample stubs by double-sided adhesive carbon or terranes (Kazakh terranes). Only larger continents, such as Baltica or tabs, coated with gold and inspected by Scanning electron microscopy Laurentia, show robust consistency in different reconstruction attempts. (SEM) at Freie Universität Berlin using a ZEISS Supra 40VP Scanning There are two major opinions considering the relative position of Yangtze electron microscope. All the figured samples are stored at the Depart- Block during the Ediacaran–Cambrian time. Some studies consider both ment