GFF Latest Ordovician and earliest Silurian tabulate corals of South ...

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Latest Ordovician and earliest Silurian tabulate corals of South China a

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Guangxu Wang , Renbin Zhan , Zhanqiu Deng & Changmin Yu a

State Key Laboratory of Palaeobiology and Stratigraphy, Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences (CAS), 39 East Beijing Road, Nanjing 210008, China; , , b

Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences (CAS), Nanjing 210008, China; Published online: 14 Jan 2014.

To cite this article: Guangxu Wang, Renbin Zhan, Zhanqiu Deng & Changmin Yu (2014) Latest Ordovician and earliest Silurian tabulate corals of South China, GFF, 136:1, 290-293, DOI: 10.1080/11035897.2013.866977 To link to this article: http://dx.doi.org/10.1080/11035897.2013.866977

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GFF, 2014 Vol. 136, No. 1, 290–293, http://dx.doi.org/10.1080/11035897.2013.866977

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Latest Ordovician and earliest Silurian tabulate corals of South China GUANGXU WANG1, RENBIN ZHAN1, ZHANQIU DENG1 and CHANGMIN YU2

Downloaded by [Nanjing Institute of Geology and Palaeontology] at 00:27 06 June 2014

Wang, G., Zhan, R., Deng, Z. & Yu, C, 2014: Latest Ordovician and earliest Silurian tabulate corals of South China. GFF, Vol. 136 (Pt. 1, March), pp. 290–293. q Geologiska Fo¨reningen. doi: http://dx.doi.org/10.1080/11035897.2013.866977.

Abstract: Latest Ordovician and earliest Silurian tabulate corals of the South China paleoplate are summarized at the generic level. In contrast to the abundant late Katian records, there is no record of tabulate corals in the early –middle Hirnantian rocks in South China, lithostratigraphically represented by the Kuanyinchiao Formation and its equivalents. The tabulate fauna from the late Hirnantian and the earliest Silurian rocks of South China is characterized by the occurrence of three cosmopolitan genera: Paleofavosites, Propora and Halysites. They differ morphologically from the pre-Hirnantian tabulate corals of South China. Such a long-ranging and low-diversity tabulate coral fauna also indicates a warm but somewhat unfavorable living environment during the survival interval after the second pulse of the end-Ordovician mass extinction. Keywords: tabulate corals; latest Ordovician; earliest Silurian; South China. 1

State Key Laboratory of Palaeobiology and Stratigraphy, Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences (CAS), 39 East Beijing Road, Nanjing 210008, China; [email protected], [email protected], [email protected] 2 Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences (CAS), Nanjing 210008, China, [email protected] Manuscript received 1 June 2013. Revised manuscript accepted 11 November 2013.

Introduction The latest Ordovician mass extinction is one of the Big Five extinction events of Phanerozoic (Raup & Sepkoski 1982). Most of the Ordovician – Silurian (O– S) transitional sections in South China are dominated by graptolitic shales and mudstones. In contrast, only a few localities yield calcareous mudstone and argillaceous limestone facies with diverse shelly fossils, including tabulate corals (Rong & Zhan 2004). From these sections, several major benthic invertebrate groups, including brachiopods, trilobites and rugose corals have been investigated with regard to their responses to the extinction event (e.g. Rong & Fang 2004). No similar investigations, however, have been conducted for tabulate corals, and hence their detailed macroevolution across the O –S boundary is still poorly known. The aim of this article was to summarize the available data of tabulate corals from South China during this interval under a refined stratigraphic framework, and to discuss their possible macroevolutionary implications.

Records of tabulate corals of South China The concept of tabulate corals adopted in this article follows that of Scrutton (1997). In order to get a complete picture of the faunal change across the O – S boundary interval, the tabulate corals of pre-Hirnantian and late Rhuddanian age are also included in our discussion. Tabulate corals of late Katian to late Rhuddanian age in South China occur only sporadically at a few localities in northern Guizhou (Upper Yangtze Platform), northeastern Jiangxi (Lower

Yangtze Platform) and northwestern Zhejiang (Jiangnan transitional belt) (Fig. 1A). Before the 1980s, much attention was paid to the late Katian tabulate corals from the Sanjushan Formation and its equivalents in the border region of the Zhejiang and Jiangxi provinces (e.g. Yoh 1933; Yu 1960; Lin & Zou 1977) and to the late Rhuddanian tabulate corals from the lower Xiangshuyuan Formation in Shiqian, northern Guizhou (Yang et al. 1978). In comparison, there are only a few reports of tabulates across the O–S transition (e.g. Zhang et al. 1964; Hu et al. 1983). Recently, the presence of tabulate corals was recorded in strata of late Hirnantian and middle Rhuddanian age, based on our study and additional graptolite data (Chen Xu, personal communication, 2013). These new data on tabulate corals bridge the gap, to some extent, between the late Katian and late Rhuddanian tabulate coral faunas in South China (Fig. 1B). Hirnantian tabulate corals in South China are only found in 1-m thick limestone at a few localities in Shiqian, northeastern Guizhou (Ge et al. 1979). This unit, together with its underlying rocks containing abundant shelly fossils, has been treated as the lower – middle Hirnantian Kuanyinchiao Formation (e.g. Hu et al. 1983; Li 2004; Rong & Zhan 2004; Li et al. 2005). In this study, re-examination of the O – S boundary sections at many localities on the Yangtze Platform indicates that only the lower part, where the typical early-middle Hirnantian rugose coral occur, is coeval with the Kuanyinchiao Formation. Accordingly, the limestone-yielding tabulate corals are probably of late Hirnantian age, and may be named as a new lithologic unit

GFF 136 (2014)

Wang et al.: O –S tabulate corals of South China

Henan

Jiangsu Graptolite biozones

Anhui jia n

g

Hubei

Fujian

N.extraordinarius D. micus T. typicus P. sinensis

0 250km

0

250 500km

Anji Fm.

Shiyang Fm.

Wenchang Fm.

N.persculptus

Changwu Fm.

South China Sea

A

Hirnantian

Late Ordovician

Guangxi Guangdong

Lungmachi Fm.

Wulipo Bed

unnamed limestone

Kuanyinchiao Fm.*

Kuanyinchiao Fm.*

Wufeng Fm

B

Fig. 1. Geological locations and stratigraphic distribution of the end-Ordovician and early Silurian tabulate corals in South China. A. Their geological locations. Triangle, pentagon, hexagon and circle represent the locations of late Katian, late Hirnantian, middle and late Rhuddanian tabulate coral-bearing strata, respectively. In addition, early – middle Hirnantian rocks containing rugose corals are also shown by black rhombus. B. Their stratigraphic distribution. Occurrences of tabulate corals during this interval are indicated by gray shadow. Besides, early – middle Hirnantian rocks without tabulate corals are also shown by asterisks.

Rhuddanian

Silurian

Llandovery

(unnamed in this article). Furthermore, the Akidograpneartus ascensus graptolitic biozone has recently been recognized from the lowermost Silurian beds at a nearby section (Li 2004; Li et al. 2005), which provides an additional support for our interpretation. It is worth mentioning that a middle Rhuddanian tabulate coral fauna has been discovered by us recently also from the Wulipo Bed at Gaojiang of Meitan County, northern Guizhou. Its age determination is based on several lines of evidences such as the graptolites and brachiopods from the same horizon and its underlying and overlying rocks (Rong & Zhan 2004; Rong Jiayu and Chen Xu, personal communication, 2012, 2013). All the occurrences mentioned earlier can be summarized as the most up-to-date profile of tabulate corals of the South China

paleoplate and their macroevolution across the O – S transition. Detailed data of these tabulates are reviewed as follow (Fig. 2).

Late Katian Tabulate corals of this interval are mainly from northeastern Jiangxi and northwestern Zhejiang provinces, southeast China, and most of the occurrences have been systematically described before 1980 (e.g. Yoh 1933; Yu 1960; Lin & Zou 1977). According to Lin & Webby’s (1989) revision, 24 genera are recognized for this interval: Acdalopora, Agetolitella, Agetolites, Agetolitoides, Calapoecia, Catenipora, Eofletcheria, Eofletcheriella, Fletcheriella, Heliolites, Hemiagetolitella, Kolymopora, Neosibiriolites, Neowormsi-

Fig. 2. Range chart of tabulate corals during the O– S transition in South China. Tabulate coral data from various sources (late Katian: Lin & Zou (1977) and Lin & Webby (1989); late Hirnantian: Hu et al. (1983) and middle Rhuddanian: our unpublished data).

C. vesiculosus P. acuminatus

Halysites Paleofavosites

N. extraordinarius D. micus T. typicus P. sinensis

Acdalopora Agetolitella Agetolites Agetolitoides Calapoecia Catenipora Eofletcheria Eofletcheriella Fletcheriella Heliolites Hemiagetolitina Kolymopora Neosibiriolites Neowormsipora Paragetolitella Paraheliolites Parastelliporella Plasmoporella Protoheliolites Propora Sarcinula Sibiriolites Taeniolites Wormsipora

Hirnantian Katian

N. persculptus

P. pacificus

Late

A. ascensus

Ordovician


Yunnan

Lungmachi Fm.

Wulipo, Meitan Niuchang Fm

A. ascensus

Katian

Guizhou

P. acuminatus

Sanjushan Fm.

Jiangxi

C. vesiculosus

P. pacificus

Hunan

Shiqian

Bijie

Llandovery

Meitan

Jiangshan

Rhuddanian

Changshan Yushan

Yanjiaba, Shiqian Xiangshuyuan Formation

Hongjiawu Fm.

Chongqing

Upper Yangtze Platform Parts of S Sichuan and N Guizhou

C. cyphus

Zh e

Sichuan

Border region of ZhejiangJiangxi

Xiazhen Fm.

Shanxi

291

292

Wang et al.: O – S tabulate corals of South China

pora, Paragetolitella, Paraheliolites, Parastelliporella, Plasmoporella, Protoheliolites, Propora, Sarcinula, Sibiriolites, Taeniolites and Wormsipora.

Early – middle Hirnantian Rocks of this interval are represented by the Kuanyinchiao Formation and its equivalents, which contain abundant shelly fossils, i.e. the Hirnantia fauna (Zhan & Jin 2007). Among these fossils, rugose corals are widely distributed and well studied (Fig. 1A) (He et al. 2007). No convincing tabulate corals, however, have yet been reported from this interval.


Late Hirnantian Late Hirnantian tabulate corals are only known from the unnamed limestone (formerly the upper part of the Kuanyinchiao Formation, Hu et al. 1983) at a few localities in Shiqian County, northeastern Guizhou. Ge et al. (1979) reported three tabulate genera (Paleofavosites, Halysites and Sibiriolites) from this horizon. Later, Hu et al. (1983) provided a revised tabulate list from the Yanjiaba section of the same area, including Paleofavosites, Propora and Schedohalysites. Schedohalysites is considered as a junior synonym of Halysites in this study.

Early Rhuddanian No tabulate corals are documented in South China from this time interval.

Middle Rhuddanian The only documented tabulate coral of this interval is Protoheliolites from the Wulipo Bed (middle Rhuddanian) at Wulipo of Meitan County, northern Guizhou (Zhang et al. 1964). It is problematic and needs systematic revision. New material was recently found from the Wulipo Bed at Gaojiang of Meitan, including Paleofavosites, Propora and Halysites after our provisional systematic study. These are the first reliable tabulate coral records of middle Rhuddanian age.

GFF 136 (2014) northwestern Zhejiang provinces, southeast China. They were abundant and diverse within a warm and well-oxygenated shallow water environment (Lin & Zou 1977; Rong & Chen 1987). All the members, however, abruptly disappeared from the vast area of South China paleoplate during the early-middle Hirnantian. The killing mechanism is likely seawater cooling associated with the end-Ordovician glaciation. The rocks in South China during this interval, represented by the Kuanyinchiao Formation and its equivalents, are thought to be deposited in a cool water environment (Rong & Harper 1999). The highly diverse Hirnantia fauna in these rocks was considered to be of survival-recovery affinity and adapted to cool water environments (Rong & Harper 1999). Furthermore, the associated rugose corals with dominant streptelasmatids also suggest similar paleoenvironmental conditions (He et al. 2007). Until the late Hirnantian, a low-diversity tabulate coral fauna recurred and developed at a few localities in northeast Guizhou from the unnamed limestone bed (upper Hirnantian). These tabulates include the cosmopolitan Paleofavosites, Propora and Halysites, and obviously the general composition and abundance of the fauna are substantially different from those during the pre-Hirnantian. Also, a similar tabulate coral fauna with the same generic composition was found from the younger Wulipo Bed (middle Rhuddanian) at Meitan in northern Guizhou. Interestingly, all these occurrences were paleogeographically close to the Dian-Qian-Gui Oldland, interpreted to be a warm and well-oxygenated marine environment during the survival interval after the end-Ordovician mass extinction (Rong & Zhan 2004). Such faunal change was probably associated with the deglaciation in the late Hirnantian, when the sea level rose rapidly and anoxic water became widespread in the epicontinental sea (Rong & Fang 2004). This interpretation is supported by the near-shore distribution of tabulate corals in South China during this interval. In addition, such a long duration of the low-diversity tabulate coral fauna from the late Hirnantian to middle Rhuddanian may also suggest that the survival interval began from late Hirnantian and persisted into middle Rhuddanian time.

Late Rhuddanian Tabulate corals of this interval are only known from the lower Xiangshuyuan Formation of Shiqian, northeastern Guizhou. However, only a few of these fossils have been described but without detailed stratigraphic data (Yang et al. 1978). Subsequently, Lin et al. (1988) published an incomplete list of tabulates including 23 genera from this formation (also without specific stratigraphic information), most of which are commonly seen in Silurian rocks elsewhere in the world. Due to the lack of reliable stratigraphic data and new material, the occurrences of tabulate corals of this interval are not included in this article.

Faunal change of tabulate corals across the O –S transition in South China The tabulate corals across the O –S boundary in South China provide important new data on the coral faunal changes associated with the crisis during the end-Ordovician mass extinction. From late Katian to early – middle Hirnantian, South China experienced a dramatic change in tabulate coral diversity. Late Katian tabulates are only known from northeastern Jiangxi and

Concluding remarks Based on the findings of tabulate corals across the O – S transition, some tentative conclusions can be introduced. 1. Abundant late Katian tabulate corals suddenly disappeared from the lower to middle Hirnantian rocks in the vast area of the Yangtze Platform (South China paleoplate). Such a dramatic faunal change is probably attributed to the cool water associated with the end Ordovician glaciation. 2. The tabulate coral fauna from late Hirnantian and middle Rhuddanian is characterized by the presence of cosmopolitan forms of low diversity, representing the survival interval after the second pulse of the end-Ordovician mass extinction. However, the macroevolutionary evolution of tabulate corals across the O –S boundary is far from being fully established. For example, where did those tabulate corals go during the crisis? Where did survivors in South China come from? And are there any relationships between survivors after the second pulse of

GFF 136 (2014) extinction and pre-Hirnantian tabulates? Future work is urgently needed to address these questions. Acknowledgements – Rong Jiayu, Wang Yi, Huang Bing and Wu Rongchang provided help in the field. Chen Xu and Zhou Zhiyi helped to identify the associated graptolites and trilobites, respectively. Many thanks to the two reviewers, Mari-Ann Mo¨tus and Mikael Calner, for providing constructive suggestions. Jisuo Jin from Western University (Canada) kindly helped us polishing the English of our manuscript. Financial supports for this study are from the National Natural Science Foundation of China (41221001, 41290260 and J1210006) and the State Key Laboratory of Palaeobiology and Stratigraphy. This article is a contribution to the IGCP Project 591 – The Early to Middle Paleozoic Revolution.


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