Radiolarian Kalimnasphaera from the Cambrian Shuijingtuo Formation in South China

Marine Micropaleontology xxx (2013) xxx–xxx

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Marine Micropaleontology

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Research paper

Radiolarian Kalimnasphaera from the Cambrian Shuijingtuo Formation inSouth China

Wenchao Cao, Qinglai Feng ⁎, Fanbin Feng, Wenli LingState Key Laboratory of Geological Processes and Mineral Resources, China University of Geosciences, Wuhan, Hubei, 430074, P.R. China

⁎ Corresponding author at: Room 202, State Key LaboraMineral Resources, China University of Geosciences, No.3P.R. China. Tel.: +86 18971193331; fax: +86 276788300

E-mail address: [email protected] (Q. Feng).

0377-8398/$ – see front matter © 2013 Elsevier B.V. All rihttp://dx.doi.org/10.1016/j.marmicro.2013.06.005

Please cite this article as: Cao, W., et al.,Micropaleontol. (2013), http://dx.doi.org/1

a b s t r a c t
a r t i c l e i n f o
Article history:Received 2 November 2012Received in revised form 30 May 2013Accepted 4 June 2013Available online xxxx

Keywords:Early CambrianRadiolarianKalimnasphaeraEvolutionSouth China

The origin of radiolarians and their early evolution are of great interest for paleontologists and biologists. Theneedle-like or spicular construction of radiolarians represented by Order Archaeospicularia has been consideredas an ancestor of radiolarians until Braun et al. (2007) discovered some radiolarians with latticed shells from theEarly Cambrian in South China. The two radiolarian tests reported here were collected from the ShuijingtuoFormation corresponding to the basal part of Cambrian Series II, in South China. One of them is spherical, latticed,and similar to the radiolarians described by Braun et al. (2007). The other is grouped within the genusKalimnasphaera formerly reported only from the Ordovician. The result indicates that the oldest known radiolar-ian fauna does not belong toOrder Archaeospicularia. The hypothesis that Archaeospicularia is the representativeof the oldest radiolarian group needs to be reexamined. Further investigation of early forms of radiolarians in theEarly Cambrian or older strata is warranted.

© 2013 Elsevier B.V. All rights reserved.

1. Introduction

The origin and early evolution of radiolarians are exceedingly inter-esting problems for discussion. Although there are many reports aboutPrecambrian radiolarians, they are generally disregarded (De Weveret al., 2001). Won and Below (1999) reported well-preserved, diverseMiddle Cambrian radiolarians from Australia, which are character-ized by one or more point-centered spicule(s). The fauna combinedwith Late Cambrian and Ordovician radiolarian faunas with similarstructure was assigned to a new radiolarian order: Archaeospicularia(Dumitrica et al., 2000). The order is supposed to be the representa-tive of the oldest radiolarian group and to have given rise to the or-ders Entactinaria, Albaillellaria, and probably Spumellaria by thereduction of the number of initial spicules in the Early Paleozoic(Dumitrica et al., 2000).

However, Braun et al. (2007) discovered that radiolarians from theEarly Cambrian of China have latticed shells, and are not composed ofspicules, which does not support the hypothesis. Last year, we foundtwo radiolarian tests from the Early Cambrian Shuijingtuo Formation:one with a latticed shell is similar to the radiolarians described byBraun et al. (2007), the other can be compared with KalimnasphaeraWebby and Blom formerly recorded only from theOrdovician. Althoughthere are only two tests discovered in this study, they are rare preciousmaterials for discussing the early evolution of radiolarians.

tory of Geological Processes and88 Lumo Road, Wuhan, Hubei,2.

ghts reserved.

Radiolarian Kalimnasphaera0.1016/j.marmicro.2013.06

2. Geological setting and stratigraphy

During the Cambrian, the Yangtze Plate was located in a low latitudearea and was composed of a shallow platform and a southeastern slopebasin (Fig. 1, Feng et al., 2004). Technically the study area is in thenorthern part of the Yangtze Plate and is located in Zigui, Yichang,Hubei Province. The study section (30°53′8.40″N, 110°52′0.12″E) isclose to a small village, Jiuqunao, on the bank of the Yangtze River(Figs. 1 and 2).

In study area, Cryogenian, Ediacaran, and Cambrian strata crop outextensively (Fig. 2). The Cambrian includes the Yanjiahe, Shuijingtuo,and Shipai formations in ascending order. The Yanjiahe Formation iscorrelated to Terreneuvian and the Shuijingtuo and Shipai formations,to Lower Cambrian Series II (Fig. 3, Zhu, 2010).

The Shuijingtuo Formation is subdivided into three parts: the lowerpart consists of carbonaceous shale with lenticular limestone, themiddlepart is composed of carbonaceous shale with thin-bedded limestone in-terbeds and contains trilobites: Sinodiscus, Tsunyidiscus, and Hupeidiscus(Wang et al., 1987; Dai and Zhang, 2011), and the upper part is char-acterized by oomicrite (Fig. 3). According to the trilobite fauna, theShuijingtuo Formation is correlated to the Qiongzhusian Stage, corre-sponding to the base of Cambrian Series II (Wang et al., 2002; Peng,2009; Zhu, 2010).

3. Materials and methods

The sample studied here was an approximately 5 kg limestonenodule collected from the basal part of the Shuijingtuo Formation.The nodule was enveloped by carbonaceous shale in the outcrop

from the Cambrian Shuijingtuo Formation in South China, Mar..005

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Fig. 1.Map showing the tectonic setting of the studied area (grey part is the SE slope basin of the Yangtze Plate).

2 W. Cao et al. / Marine Micropaleontology xxx (2013) xxx–xxx

and consists of dark grey micrite. The sample was crushed into smallpieces of about 1 cm3. The fragments of the sample were etched in5–8% glacial acetic acid solution for two weeks at room temperature.The acid residues were subsequently removed into other containersfilled with water until neutral. The container holding the sample wasrefilled with new glacial acetic acid solution. After repeating thewhole process for two months, the residues were sieved through asieve with a mesh diameter of 0.054 mm and dried for examinationunder a binocular microscope.

We looked for radiolarian tests by a binocular microscope for sixmonths and obtained two radiolarian tests. One of them is identifiedas Kalimnasphaera sp. and the other can not be assigned because it ispoorly preserved (Fig. 4).

Fig. 2. Geological map of Zigui, Yichang, South China.

Please cite this article as: Cao, W., et al., Radiolarian KalimnasphaeraMicropaleontol. (2013), http://dx.doi.org/10.1016/j.marmicro.2013.06

4. Taxonomy

The two radiolarian tests studied in this paper are deposited in theGeological Museum of China University of Geosciences, Wuhan, thePeople's Republic of China.

Subclass RADIOLARIA Muller, 1858Order POLYCYSTIDA Ehrenberg, 1838, emend. Riedel, 1967Suborder SPUMELLARINA Ehrenberg, 1875Family INANIGUTTIDAE Nazarov and Ormiston, 1984Genus KalimnasphaeraWebby and Blom, 1986Kalimnasphaera sp.Fig. 4A–KDescription: The specimen is composed of three shells (Fig. 4D, E).

The outer shell which is very poorly preserved is a reticulate, looseand fenestrate shell. It consists of thin bars, its pores are round orsubround, and the diameter of the outer shell is approximately 135 μm.The outer and cortical shells are linked by numerous by-spines and afew primary spines. The cortical shell which consists of cylindrical porebars is robust and spherical and its diameter is about 100 μm. Thepores vary in size and shape, their diameters range from 2 μm to15 μm in size, and their shapes are round, nearly round, or irregular.Most of the medullary shell has been dissolved and only some partsare still preserved (Fig. 4D, E). Seven primary spines can be seen andthey arise from the surface of the pore bars. The length of the primaryspines is more than 70 μm where they are well preserved. The spinesare with irregular arrangement and round or nearly round in axial sec-tion. Numerous, short and slender by-spines radiate extending outward,with varying length from 5 μm to 20 μm.

Remarks: According to the characters of the three shells, the speci-men can be grouped within Kalimnasphaera Webby and Blom. Thegenus was formerly reported only from the Ordovician (Webby andBlom, 1986; Renz, 1990; Goto et al., 1992; Umeda et al., 1992; Nobleand Webby, 2009). In comparison with the Ordovician materialsassigned to this genus, the shell described here is smaller and its prima-ry spines are shorter and more in number. However, we leave the newspecimen an open nomenclature because only one specimen was dis-covered in this study.



Fig. 3.Columnar section and radiolarian occurrence in the Jiuqunao section, Zigui, Yichang,South China.

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In outline, the specimen is similar to some species of CambrianSpongomassa, such as S. nannosphaerea (Won and Below, 1999),and some species of Ordovician Parentactinia, such as P. nevadensis(Kozur et al., 1996), but their inner structures are very different tothe specimen studied.

Suborder, family, genus indeterminateSpherical radiolarianFig. 4L–N


Description: The specimen is a stout, spherical, latticed shell. Its di-ameter is approximately 240 μm. The pores are circular and their diam-eters are about 15 μm. The pore frames are pentagonal or hexagonal. Itsinner structure is unclear because of strong recrystallization.

Remarks: The specimen is similar to the Lower Cambrian sphericalradiolarians from the Kuanchuanpu Formation in Ningqiang, southernShanxi, China in outline and pore characters (Braun et al., 2007), butthe latter is smaller and with short spines.

5. Discussion

The genus Kalimnasphaerawas first found from Late Ordovician cal-careous concretions in southern Eureka County, Nevada byDunhamandMurphy (1976), although they did not assign it a formal name. Webbyand Blom (1986) reported a well-preserved Late Ordovician radiolari-an fauna, including the genus, from the graptolitic Malongulli Forma-tion of central New South Wales, Australia and proposed a new genus,Kalimnasphaera. They thought the genus had four shells: outer shell,cortical shell, and twomedullary shells. Renz (1990) reworked the radi-olarians from calcareous concretions collected by Dunham andMurphy(1976), but did not observe the twomedullary shells in the genus. Gotoet al. (1992) discovered the genus in a radiolarian fauna from the LateOrdovicianMalongulli Formation of the Lachlan Fold Belt, southeasternAustralia. Umeda et al. (1992) found some radiolarians that possiblybelonged to the genus from Middle Ordovician bedded chert in theStawell Terrane of the Lachlan Fold Belt, western Victoria. Recently,Noble and Webby (2009) investigated the radiolarian fauna againin the localities reported by Webby and Blom (1986). They de-scribed the genus Kalimnasphaera as having a double walled latticedmedullary shell, rather than twomedullary shells. To sumup, all reportsabout Kalimnasphaera are from the Middle and Upper Ordovician inAustralia and U.S.A. The genus is described from the Early Cambrianfor the first time in this paper.

The test has a strong cortical shell, a loose outer shell, and an in-complete medullary shell. Therefore, it should be assigned to thegenus Kalimnasphaera. It has some characteristics that are differentfrom known species of Kalimnasphaera. Its shell is smaller, its prima-ry spines are finer and shorter, and its cortical shell is intensive andwith smaller pores. These characters indicate that it is possibly anearlier species.

The two specimens are much older than the known species of OrderArchaeospicularia. In structure, they are strongly different to the knownCambrian and Ordovician species of Order Archaeospicularia, but aremore similar to other younger Palaeozoic radiolarians. This observationsupports the result of Braun et al. (2007). The hypothesis that OrderArchaeospicularia is the representative of the oldest radiolarian groupneeds to be tested by examining older materials than those reportedherein. In addition, our materials combined with data described byBraun et al. (2007) show that the known Early Cambrian radiolarianfauna was complex in structure and diverse in morphological expres-sion. It is necessary to investigate simpler, original radiolarian faunasin older strata.

Acknowledgments

This work was supported by NSFC (40839903 and 40921062) andthe 973 program (2011CB808800). We express our sincere thanks toDr. Ren Limin for help in the fieldwork and to Prof. Zhang Suxin forprocessing the scanning electron micrographs. Special thanks are dueto Prof. Jonathan C. Aitchison and Dr. Richard W. Jordan for reviewingthe manuscript.

Appendix A. Supplementary data

Supplementary data associated with this article can be found inthe online version, at http://dx.doi.org/10.1016/j.marmicro.2013.06.005.




Fig. 4. Radiolarian fossils from the Jiuqunao section, Zigui, Yichang, South China. D and E are Micro-CT photos, others are SEM photos. A–K: Kalimnasphaera sp.; L–N: spherical radiolarian.Os: outer shell; Cs: cortical shell; Ms: medullary shell.

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These data include Googlemaps of themost important areas described inthis article.

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Radiolarian Kalimnasphaera from the Cambrian Shuijingtuo Formation in South China