Trace fossil evidence for restoration of marine ecosystems following the end-Permian mass extinction in the Lower Yangtze region, South China

Palaeogeography, Palaeoclimatology, Palaeoecology 299 (2011) 449–474

Contents lists available at ScienceDirect

Palaeogeography, Palaeoclimatology, Palaeoecology j o u r n a l h o m e p a g e : w w w. e l s ev i e r. c o m / l o c a t e / p a l a e o

Trace fossil evidence for restoration of marine ecosystems following the end-Permian mass extinction in the Lower Yangtze region, South China Zhong-Qiang Chen a,b,⁎, Jinnan Tong a, Margaret L. Fraiser c a b c

Key Laboratory of Biogeology and Environmental Geology of Ministry of Education, China University of Geosciences, Wuhan 430074, China School of Earth and Environment, The University of Western Australia, 35 Stirling Highway, Crawley, WA 6009, Australia Department of Geosciences, University of Wisconsin-Milwaukee, Milwaukee, WI 53211, USA

a r t i c l e

i n f o

Article history: Received 13 May 2010 Received in revised form 25 October 2010 Accepted 25 November 2010 Available online 30 November 2010 Keywords: Trace fossils Early Triassic Ecosystem recovery Ichnofabric index Lower Yangtze region South China

a b s t r a c t Unlike the high-abundance, low-diversity macrofaunas that characterize many Early Triassic benthic palaeocommunities, ichnofossils were relatively common in the aftermath of the end-Permian mass extinction worldwide. Ichnofossils therefore are a good proxy for ecosystem recovery after the end-Permian biotic crisis. This paper documents 14 ichnogenera and one problematic form from Lower Triassic successions exposed in the Lower Yangtze region, South China. Post-extinction ichnodiversity remained rather low throughout the Griesbachian–early Smithian period and abruptly increased in the late Smithian. However, several lines of evidence, including extent of bioturbation, burrow size, trace-fossil complexity, and tiering levels, indicate that diversification of ichnotaxa in the late Smithian did not signal full marine ecosystem recovery from the Permian/Triassic (P/Tr) mass extinction. Marine ichnocoenoses did not recover until the late Spathian in South China. The marginal sea provided hospitable habitats for tracemakers to proliferate in the aftermath of the end-Permian mass extinction. © 2010 Elsevier B.V. All rights reserved.

1. Introduction As the largest Phanerozoic extinction event, the Permian/Triassic (P/Tr) mass extinction not only severely impacted biodiversity (Bambach et al., 2004), but also profoundly degraded marine ecosystems to ones characterized by high-abundance, low-diversity skeletonised metazoan communities (Bottjer et al., 2008). There is some evidence that global marine biodiversity did not recover until the early Middle Triassic (Erwin and Pan, 1996), perhaps 5 million years after the mass extinction (Lehrmann et al., 2006). Biotic recovery after the P/Tr crisis is believed to be much delayed due to devastating environmental conditions prevailing in the Early Triassic oceans (see references in Bottjer et al., 2008). Accordingly, the recovery of the devastated ecosystems has attracted an increasing number of multidisciplinary studies to reveal the tempo and mechanisms of recovery after the P/Tr crisis (e.g., Payne et al., 2004; Twitchett, 1999, 2006; Tong et al., 2007). Palaeoecologic methods are powerful tools to study biotic crises and their subsequent recovery (Twitchett, 2006 and references therein). In particular, trace-fossil assemblages can be crucial to revealing the timing and pattern of ecologic recovery following mass extinctions because post-extinction ⁎ Corresponding author. School of Earth and Environment, The University of Western Australia, 35 Stirling Highway, Crawley, WA 6009, Australia. Tel.: +61 864881924; fax: +61 864881037. E-mail address: [email protected] (Z.-Q. Chen). 0031-0182/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.palaeo.2010.11.023

macrofaunas can be unevenly distributed and poorly preserved (Fraiser and Bottjer, 2005; Fraiser et al., 2010). Several recent ichnological studies have greatly enhanced our understanding of ecologic recovery following the P/Tr mass extinction (Beatty et al., 2005, 2008; Fraiser and Bottjer, 2009; Pruss and Bottjer, 2004; Twitchett, 1999; Twitchett and Barras, 2004; Twitchett and Wignall, 1996; Zonneveld et al., 2002, 2004, 2010). However, most of the trace fossil-based studies concerning the Early Triassic ecologic recovery are based on data derived from North America (Fraiser and Bottjer, 2009; Pruss and Bottjer, 2004; Twitchett and Barras, 2004), western Tethys (Twitchett, 1999; Twitchett and Wignall, 1996), or northern high-latitude regions (Beatty et al., 2005, 2008; Wignall et al., 1998; Zonneveld and Beatty, 2007; Zonneveld et al., 2002, 2004, 2010). Very little has been published on the trace fossils from South China as proxies of ecosystem recovery following the P/Tr crisis, although a few localized Early Triassic ichnoassemblages have been described (Bi et al., 1995, 1996; Liu and Wang, 1990; Luo et al., 2007; Yang, 1988; Wang, 1987; 1997). This paper aims to document Early Triassic ichnotaxa in the Chaohu and neighbouring Yashan areas, and to evaluate marine ecosystem recovery following the P/Tr crisis using trace fossil assemblages as proxies. Abundant new trace fossils from the Lower Triassic successions in the Chaohu and neighbouring Yashan areas (Fig. 1A) are described herein, and the previously published data of the Lower Triassic trace fossils from the Lower Yangtze region (Bi et al., 1995, 1996; Liu and Wang, 1990) are also critically reviewed and revised (Table 1).

450

Z.-Q. Chen et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 299 (2011) 449–474

Fig. 1. Location of the West Pingdingshan–Majiashan section, Chaohu and the Yashan section, Nanling, Anhui Province, South China.

2. Geological setting, studied sections, and stratigraphical distributions of ichnotaxa 2.1. Geological and stratigraphical settings Lower Triassic rocks are widely distributed cross the entire South China block (Tong and Yin, 2002). The P/Tr boundary beds and Lower Triassic successions are particularly complete in the Lower Yangtze region including southern Anhui, southern Jiangsu, northern Jiangxi and western Zhejiang Provinces (Fig. 1). Sound biostratigraphy in combination with high-resolution isotopic geochemistry and abundant skeletonised fossils enabled us to analyze the recovery of marine ecosystems following the P/Tr mass extinction in the Chaohu area (Chen et al., 2010; Tong et al., 2007). During the P/Tr transition, the South China block was located near the tropical zone at the eastern part of the Tethys Ocean (Ziegler et al., 1998). The uppermost Permian to Lower Triassic marine successions are well-exposed in the Lower Yangtze region. Here, the Lower Triassic successions are comprised of the Yinkeng, Helongshan and Nanlinghu Formations in ascending order, which correlate well with one another from place to place in this region. The Yingkeng Formation is Griesbachian to early Smithian in age, while the Helongshan and Nanlinghu Formations are late Smithian and Spathian in age, respectively (Figs. 2 and 3). The uppermost Permian sediments were accumulated primarily in shelf settings and are represented by the Talung Formation, except for several localities (i.e., Huangzhishan section) that record a platform succession at the end of the Permian (Chen et al., 2009, 2010). Overall, the Lower Triassic succession is dominated by siliciclastics at its lower part and carbonates at its upper part. Complete conodont, ammonoid and bivalve zones have been established throughout the entire Lower

Triassic successions in most localities (Chen et al., 2002, 2010; Tong and Yin, 2002). In particular, high-resolution biostratigraphy has been undertaken for the Triassic in the Chaohu areas, Anhui Province, South China (Fig. 1A) since the 1990s (Tong et al., 2003, 2004, 2005; Zhao et al., 2007; L. Zhao et al., 2008; Fig. 2). Thus, the Lower Triassic succession of Chaohu was referred to as the standard succession for Lower Triassic correlations within South China (Tong et al., 2003). 2.2. West Pingdingshan and southern Majiashan sections The West Pingdingshan (WP) and Majiashan (MJS) sections are situated in a southeastern suburb of the city Chaohu, Anhui Province, South China (Figs. 1 and 4A). Here the Upper Permian to Lower Triassic succession is comprised of marine sediments and underlies Middle Triassic evaporitic dolomites (Tong et al., 2003, 2005; Fig. 2). The P/Tr boundary beds and the lower part of the Lower Triassic succession are well exposed at the western slope of Pingdingshan Hill (Fig. 4B and C). The upper Lower Triassic succession is better exposed at the southern slope of the Majiashan Hill, about 2 km away from Pingdingshan Hill (Tong et al., 2003, 2005, 2007; Zhao et al., 2007; L. Zhao et al., 2008). The West Pingdingshan section records the complete P–Tr and Induan–Olenekian boundary successions and yields abundant conodont, ammonoid, bivalve, and brachiopod faunas, and thus was nominated as a candidate of the Global Stratotype Section and Point (GSSP) for the Induan–Olenekian boundary (Tong et al., 2003). The Permian Talung Formation is 4–5 m thick and consists of black mudstone and cherty shale yielding deep-water facies conodonts, radiolarians, ammonoids, bivalves, and brachiopods of Changhsingian age (Peng et al., 2001; Yin et al., 1995; Zhang et al., 1992). The P/Tr boundary beds at West Pingdingshan are comprised of a white claystone layer (Bed 3), a black shale bed (Bed 4), a yellow, medium-

Z.-Q. Chen et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 299 (2011) 449–474

451

Table 1 Lower Triassic ichnotaxa from the studied sections and other areas of the Lower Yangtze region with their revisions. Ichnotaxa

References

Formation and age

Locality

Revision

Agrichnium fimbriatus Pfeiffer Arenicolites sp. Arenicolites isp.

Bi et al. (1996, p. 719, pl. 2, fig. 5) Bi et al. (1996, p. 719, pl. 2, fig. 9) This study

HLS, late Smithian NLH, Spathian HLS, late Smithian

Microbial mat Arenicolites isp.

Arenicolites isp.

This study

NLH, Spathian

Asterichnus chaohuensis Bi et al. Beaconites isp.

Bi et al. (1996, p. 719, pl. 1, fig. 4) This study

NLH, Spathian NLH, Spathian

Chondrites sp. Chondrites sp. Chondrites isp. Cochlichnus anguineus Histchcock

Bi et al. (1996, p. 719, pl. 4, fig. 5) Liu and Wang (1990, pl. 1, fig. 6) This study Bi et al. (1996, p. 720, pl. 1, fig. 5); This study Bi et al. (1996, p. 720, pl. 3, fig. 2)

HLS, late Smithian HLS, late Smithian NLH, Spathian HLS, late Smithian

Dalishan, Zhengjiang Dalishan, Zhengjiang WP, Chaohu; YS, Nanling WP, Chaohu; YS, Nanling Majiashan, Chaohu WP, Chaohu; YS, Nanling Dalishan, Zhengjiang Zhuoshan, Shusong WP, Chaohu YS, Nanling

YK, early Smithian

Didymaulichnus sp. Diplocraterion parallelum Richter Diplocraterion isp. Florichnus curtipetatus Bi et al. Furculosus carpathicus Roniewicz and Pienkowski Gordia sp. Gordia isp. Gyrochorte isp. Gyrochorte isp. Gyrolithes sp. Keckia cf. annulata Glocker

Bi et al. (1996, p. 720, pl. 1, fig. 7) Bi et al. (1996, p. 720, pl. 3, fig. 1) This study Bi et al. (1996, p. 721, pl. 4, fig. 3) This study

HLS, late Smithian NLH, Spathian NLH, Spathian YK, early Smithian NLH, Spathian

Bi et al. (1996, p. 721, pl. 4, fig. 2) This study This study This study Bi et al. (1996, p. 721, pl. 3, fig. 3) Bi et al. (1996, p. 721, pl. 2, fig. 3)

NLH, Spathian HLS, late Smithian HLS, late Smithian NLH, Spathian HLS, late Smithian NLH, Spathian

Kouphichnium sp.

Bi et al. (1995, pls. 1–3; 1996, p. 722, pl. 4, fig. 7) Bi et al. (1996, p. 722, pl. 1, fig. 2) Bi et al. (1996, p. 722, pl. 2, fig. 4) Bi et al. (1996, p. 722, pl. 3, fig. 5) Bi et al. (1996, p. 722, pl. 3, fig. 4) Bi et al. (1996, p. 723, pl. 1, fig. 3) This study Bi et al. (1996, p. 723, pl. 1, fig. 1) Bi et al. (1996, p. 723, pl. 3, fig. 7) Bi et al. (1996, p. 724, pl. 4, fig. 9) Bi et al. (1996, p. 724, pl. 4, fig. 1) This study This study Bi et al. (1996, p. 724, pl. 4, fig. 8) Bi et al. (1996, p. 724, pl. 1, fig. 9)

HLS, late Smithian

Dendrotichnium llarenai Farres

Laevicyclus sp. Lockeia sp. Megagrapton sp. ?Micatuba sp. Monocraterion sp. Monocraterion tentacultum Torell. Monomorphichnus lineatus Crimes Nodituba obtusangula Bi et al. Ophiomorpha nodosa Lundgren Palaeophycus tubularis Hall Palaeophycus isp. Palaeophycus isp. Pelecypodichnus sp. Phycodes coronatum Crimes and Anderson Treptichnus spsorum Rindsberg and Kopaska-Merkel

Guimenguan, Chaohu Yashan, Nanling Zhangzhu, Yixing WP, Chaohu Yueshan, Anqing WP, Chaohu Shanghuang, Liyang YS, Nanling YS, Nanling WP, Chaohu Dalishan, Zhengjiang Xiaozhishan, Fengchong Yashan, Nanling Dalishan, Zhengjiang Dalishan, Zhengjiang Zhangzhu, Yixing Dalishan, Zhengjiang Zhangzhu, Yixing WP, Chaohu Majiashan, Chaohu Yaotouling, Jixian Yueshan, Anqing Yashan, Nanling WP, Chaohu WP, Chaohu Yueshan, Anqing YS, Nanling

This study

HLS, late Smithian HLS, late Smithian NLH, Spathian HLS, late Smithian HLS, late Smithian NLH, Spathian HLS, late Smithian HLS, late Smithian HLS, late Smithian HLS, late Smithian HLS, late Smithian NLH, Spathian YK, early Smithian YK, early Smithian; HLS, late Smithian HLS, late Smithian

Bi et al. (1996, p. 724, pl. 2, fig. 6)

NLH, Spathian

Shatian, Huangshi

Planolites sp.

Liu and Wang (1990, pl. 1, fig. 2–3)

HLS, late Smithian

Zhuoshan, Shusong

Planolites montanus Richte Planolites montanus Richte Planolites beverleyensis (Billing)

This study This study This study

HLS, late Smithian NLH, Spathian NLH, Spathian

Planolites isp.

This study

Planolites isp. Phycus sp. Pteridichnites sp. Rhizocorallium isp. Rugicirichnus amorphus Bi et al.

This study Liu and Wang (1990, pl. 1, fig. 1, 5; pl. 2, fig. 1–3) Bi et al. (1996, p. 725, pl. 2, fig. 2) This study Bi et al. (1996, p. 725, pl. 2, fig. 8)

YK, Giresbachian–early Smithian HLS, late Smithian HLS, late Smithian

WP, Chaohu WP, Chaohu WP, Chao; YS, Nanling WP, Chao; YS, Nanling YS, Nanling Zhuoshan, Shusong

HLS, late Smithian NLH, Spathian NLH, Spathian

Salebrichnus amblyodontus Bi et al. ?Scalarituba sp.

Bi et al. (1996, p. 725, pl. 2, fig. 7) Bi et al. (1996, p. 726, pl. 4, fig. 6)

HLS, late Smithian YK, Griesbachian

Taphrhelminthopsis podhalensis Roniewicz and Pienkowski Teichichnus sp. Thalassinoides sp. Thalassinoides isp. Thalassinoides saxonicus (Geinitz)

This study Bi et al. (1996, pl. 3, fig. 6) Bi et al. (1996, p. 726, pl. 4, fig. 4) This study This study

Wrinkle structures

Planolites montanus Richter P. montanus Richter Cochlichnus anguineus Histchcock Thalassinoides isp. Gordia isp. Arenicolites isp. Microbial mat

Gordia isp.

Coprolites Beauconites isp. Kouphichnium isp. Unidentiable Sedimentary structure Gordia isp. Gordia isp. Arenicolites isp. Microbial mat Treptichnus bifurcus Miller Ophiomorpha isp. Treptichnus bifurcus Miller

Lockeia isp. Treptichnus coronatum (Crimes and Anderson)

YS, Nanling Planolites cf. montanus Richter Planolites beverleyensis (Billing)

Planolites isp. Palaeophycus isp. Pteridichnites isp.

NLH, Spathian

Dalishan, Zhengjiang YS, Nanling Yangongtong, Jingxian Dalishan, Zhengjiang Yangjiashan, Tongling YS, Nanling

HLS, late Smithian HLS, late Smithian NLH, Spathian NLH, Spathian

Dalishan, Zhengjiang Zhangzhu, Yixing YS, Nanling Majiashan, Chaohu

Treptichnus bifurcus Miller Thalassinoides isp.

Rugicirichnus amorphus Bi et al. Archaeonassa isp. Beauconites isp.

(continued on next page)

452

Z.-Q. Chen et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 299 (2011) 449–474

Table 1 (continued) Ichnotaxa

References

Formation and age

Locality

Revision

Treptichnus sp. Treptichnus bifurcus Miller Undichna-like trace Zoophycus sp. coprolites

Bi et al. (1996, p. 726, pl. 2, fig. 1) This study This study Bi et al. (1996, p. 726, pl. 1, fig. 6) Bi et al. (1996, p. 727, pl. 1, fig. 8)

HLS, late Smithian HLS, late Smithian NLH, Spathian HLS, late Smithian HLS, late Smithian

Yashan, Nanling YS, Nanling Majiashan, Chaohu Zhangzhu, Yixing Dalishan

Treptichnus bifurcus Miller

Microbial mat Coprolites

YK = Yinkeng Formation; HLS = Helongshan Formation; NLH = Nanlinghu Formation; WP = West Pingdingshan; YS = Yashan.

bedded marlstone (Bed 5), and another white claystone (Bed 6) in ascending order (Figs. 2 and 4C). These four beds correlate well with their counterparts at the Meishan section (Yin et al., 1995; Peng et al., 2001; Fig. 1B), the GSSP for the P/Tr boundary (Yin et al., 2001). The Yinkeng Formation comprises greenish/black shale interbedded with marlstone (Beds 3–37). The Helongshan Formation is characterized by thin-bedded dolomitic limestone interbedded with calcareous mudstone (Beds 38–53). The upper part of the section consists of mediumbedded limestone interbedded with mudstone (Beds 54–58) belonging to the lower Nanlinghu Formation (Fig. 2). The Griesbachian succession is defined by the Hindeodus typicalis and Neogondolella krystyni conodont Zones, ammonoid Ophiceras–Lytophicears Zone, and bivalve Claraia stachei–C. aurita Assemblage (Tong et al., 2003, 2004; L. Zhao et al., 2008; Zhao et al., 2007). The Dienerian is characterized by the Neospathodus kummeli and Ns. dieneri conodont Zones, ammonoids Prionolobus–Gyronites Zone, and the lower part of the bivalve Eumorphotis inaequicostata–E. huancangensis Assemblage (Tong et al., 2004; L. Zhao et al., 2008; Zhao et al., 2007). The Smithian includes the Ns. waageni ecowaageni and Ns. waageni waageni conodont Zones and the ammonoid Flemingites–Euflemingites and Anasibirites Zones. The lower Spathian succession contains Ns. pingdingshanensis and Ns. homeri conodont Zones and the ammonoid Columbites–Tirolites Zone (Tong et al., 2003, 2004; L. Zhao et al., 2008; Zhao et al., 2007). Ichnotaxic diversity is moderate to high, using after Beatty et al.'s (2008) ichnodiversity criteria. Arenicolites isp., Beaconites isp., Chondrites isp., Diplocraterion isp., Furculosus carpathicus, Monocraterion tentacultum, Palaeophycus isp., Planolites isp., Planolites montanus, P. beverleyensis, and Thalassinoides isp. are found at the Pingdingshan section. Most ichnotaxa occur in the upper Helongshan and lower Nanlinghu Formations (Fig. 2). The complete Spathian succession is exposed at the southern Majiashan section where the Helongshan and lower Nanlinghu Formations correlate well with their counterparts at the West Pingdingshan section. Apart from the Ns. pingdingshanensis and Ns. homeri conodont Zones, the Ns. anhuiensis Zone was also established for the Nanlinghu Formation (Zhao et al., 2007). Ammonoids Columbites– Tirolites and Subcolumbites Zones are also present in Majiashan (Tong et al., 2004; Zhao et al., 2007). These biozones constrained the Nanlinghu Formation as Spathian in age (Tong et al., 2003, 2004). Trace fossils are relatively rare at Majiashan and include Gyrochorte isp., Thalassinoides saxonicus, and large problematic traces (Fig. 2).

2.3. Yashan section The Yashan section is located at the town Yashan of Nanling County, Anhui Province, South China (Fig. 1A). Here, the P/Tr boundary beds (Fig. 5A) and Lower Triassic successions correlate well with their counterparts at the West Pingdingshan and southern Majiashan

sections (Fig. 3). Like those exposed at Chaohu, the Lower Triassic sediments were deposited in a shelf setting, and the Changhsingian Talung Formation is represented by black cherty mudstone. Xu and Xing (1992) have studied the lithostratigraphy and biostratigraphy of this section. Most of the conodonts, ammonoids and bivalves reported from Yashan are comparable with those found in the Chaohu area (Fig. 3). It is noteworthy that both the Yinkeng and Helongshan Formations, 140 m and 297 m thick, respectively, are much thicker than the units exposed at the West Pingdingshan section. Alternation of dolomitic limestone and greenish shale characterizes the upper Yinkeng Formation here. Thin-bedded dolomitic limestone and distinct halite pseudomorphs typify the Helongshan Formation (Fig. 3). Massive vermicular limestone dominated by densely arranged burrow-like structures (X.M. Zhao et al., 2008; Fig. 7D) marks the lower Nanlinghu Formation and is pronounced throughout the entire formation (Fig. 3). Limestone of the Nanlinghu Formation is usually highly bioturbated with inchnofabric index of 5 (Figs. 5H and 7B–C). Both conodont and ammonoid biostratigraphy suggests that the Yinkeng Formation is Griesbachian to early Smithian in age and the Helongshan Formation is early Smithian to earliest Spathian in age. The Nanlinghu Formation at Yashan is of early-late Spathian age (Fig. 3). The number of ichnotaxa is moderate to high at this locality, including Arenicolites isp., Beaconites isp., Gordia isp., Gyrochorte isp., Planolites beverleyensis, P. montanus, Rhizocorallium isp., Taphrhelminthopsis cf. podhalensis, Thalassinoides isp., Treptichus apsorum, and Treptichus bifurcus. Most traces occur in the upper Helongshan and Nanlinghu Formations. Bi et al. (1996) also reported Treptichus coronatum from the upper Yinkeng Formation of early Smithian age from this site. Bi et al. (1995, 1996) described Cochlichnus anguineus, Gordia isp., Kouphyichnium isp., T. coronatum, and T. bifurcus from the upper Helongshan Formation at the same section (Table 1). 3. Palaeoenvironmental analysis 3.1. Yinkeng Formation The Yinkeng Formation was deposited during the Griesbachian to early Smithian at Chaohu and was accumulated during the Griesbachian to earliest Smithian at Yashan. However, it is approximately 75 m thick in Chaohu, and 140 m thick in Yashan. 3.1.1. Chaohu In Chaohu, the lower part of the Yinkeng Formation (Beds 2−21; Fig. 2) is composed of alternating shale and marlstone/or limestone (Fig. 4B). Small-scale cycles are recognized throughout the lower Yinkeng Formation. Generally, black shale or greenish mudstone characterizes the lower parts of cycles whereas grey marlstone or muddy limestone for the upper parts. All cycles are characterized by relatively deeper water facies overlain by shallower facies. The lower

Fig. 2. P/Tr boundary beds and Lower Triassic succession exposed at the West Pingdingshan–Majiashan sections showing stratigraphical distributions of trace fossils. Ichnofabric indices (ii) (Droser and Bottjer, 1986) are assessed as 1 to 5, indicating bioturbation from lowest to highest levels. Bedding plane bioturbation indices (BPBI) are also evaluated based on bedding plane coverage of burrows (Miller and Smail, 1997). Bed numbers and biozones follow Tong et al. (2003, 2004) and Zhao et al. (2007). St. = stage, SS = sedimentary structures, En. = environment; environmental settings including distal offshore ramp (dor), proximal ramp near storm wave base (prswb), proximal ramp between storm and fairweather wave bases (prsfwwb), lower shoreface, and marginal sea.

Z.-Q. Chen et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 299 (2011) 449–474

453

454

Z.-Q. Chen et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 299 (2011) 449–474

Z.-Q. Chen et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 299 (2011) 449–474

455

Fig. 4. Griesbachian−Smithian (Lower Triassic) successions from the West Pingdingshan (WP) section. A, road cutting showing the Lower Triassic succession at the western slope of the Pingdingshan Hill; the power pole is 10 m high. B, mudstone-dominated Yinkeng Formation with muddy limestone interbeds and the Induan/Olenekian (I/O) boundary at its upper part. C, Permian−Triassic boundary (PTB) beds exposed at southern slope of the Pingdingshan Hill; siliceous mudstone of the Talung Formation (at lower left corner) is exposed below the PTB bed; PTB bed and above strata belong to the Yinkeng Formation. D, hummocky-like cross beddings on limestone bed just below the I/O boundary at the Yinkeng Formation. E, alternation of thin-bedded mudstone and muddy limestone at the upper Yinkeng Formation. F−G, thin-bedded mudstones interbedded with calcareous mudstone and muddy limestone layers at the lower Helongshan Formation. H−I, thin- to medium-bedded muddy limestones interbedded with mudstone layers at the upper Helongshan Formation.

units of the small-scale cycles dominated by black shale become thicker and thicker up section, while the upper units thin up-section. As a result, the entire cycle is dominated by finely laminated black shale, indicating that the depositional environment deepens upwards.

The lower Yinkeng Formation also yields small, thin-shelled fossils such as bivalves Claraia spp. and ammonoids Ophicears spp., which form a high-abundance, low-diversity community (Chen et al., 2010). Trace fossils are very rare. When present, they are typically small,

Fig. 3. Lower Triassic succession exposed at the Yashan section showing trace-fossil stratigraphical distributions. Ichnofabric indices (ii) (Droser and Bottjer, 1986) are assessed as 1 to 5, indicating bioturbation from lowest to highest levels. Bedding plane bioturbation indices (BPBI) are also evaluated based on bedding plane coverage of burrows (Miller and Smail, 1997). Bed numbers and biozones follow Xu and Xing (1992). St. = stage, SS = sedimentary structures, En. = environment; environmental settings including distal offshore ramp (dor), proximal ramp near storm wave base (prswb), proximal ramp between storm and fair-weather wave bases (prsfwwb), lower shoreface, highly evaporitic marginal sea, and marginal sea.

456

Z.-Q. Chen et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 299 (2011) 449–474

Fig. 5. Lower Triassic successions from the Yashan section. A, PTB beds at Yashan; hammer is 10 cm long. B, alternation of medium-bedded limestone and mudstone at the upper Yinkeng Formation. C, alternating grey mudstone and thin-bedded calcareous mudstone/or muddy limestone at the middle Helongshan Formation. D, top surface of mudstone bed yielding abundant trace fossils. E, alternation of mudstone and limestone at the lower Nanlinghu Formation. F, calcareous mudstone and thin-bedded limestone of the lower Nanlinghu Formation. G, cave-collapsing breecia of the uppermost Nanlinghu Formation; hammer is 10 cm long. H, bioturbated limestone of the upper Nanlinghu Formation.

simple, horizontal burrows of Planolites isp., which are typical of dysoxic deposition (Bottjer and Droser, 1994; Martin, 2004). This is similar to other ichnofossil assemblages that occur in the immediate aftermath of the end-Permian mass extinction elsewhere in the Palaeo–Tethys and Panthalassa Oceans (Twitchett and Barras, 2004; Twitchett and Wignall, 1996). As a result, the black shale-dominated succession, combined with the epifaunal Claraia–Ophiceras Assem-

blage (Chen et al., 2010) and lack of any cross bedding sedimentary structures, suggests a relatively deep distal offshore ramp setting (below storm wave base) with anoxic conditions for the lower Yinkeng Formation (Chen et al., 2010; Tong et al., 2003). This is the same depositional environment interpreted for the same formation of the Meishan section, South China (Chen et al., 2002, 2007; Wignall and Hallam, 1993).

Z.-Q. Chen et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 299 (2011) 449–474

The alternation of greenish mudstone and marlstone to limestone also characterizes the middle part of the Yinkeng Formation on (Beds 22−29; Fig. 2), which, however, is characterized by increasing thickness of the upper unit of limestone/or marlstone and decreasing thickness of the lower unit (Fig. 4E), suggesting a progradationally depositional pattern. Hummocky-like cross stratifications are also occasionally present in limestone beds (Fig. 4D), pointing to the storm wave action zone, like the similar sedimentary structures of the same formation interpreted at the Meishan section, South China (Chen et al., 2007). Epifaunal assemblage and ichnoassemblage are similar to these occurring in the lower Yinkeng Formation. Consequently, the depositional environment of the middle Yinkeng Formation is interpreted as the storm wavebase action zone at a proximal ramp setting. At the upper part of the Yinkeng Formation (Beds 30−37; Fig. 2), the lower units of the small-scale cycles dominated by black shale thicken up section, while the upper units become thinner and thinner up section. As a result, the entire cycle is dominated by finely laminated black shale, indicating that the depositional environment deepens upwards. Faunal assemblage and ichnoassemblage are similar to these preserved in the lower Yinkeng Formation. Accordingly, like its lower part, the upper part of the Yinkeng Formation also represents a relatively deep distal offshore ramp setting. 3.1.2. Yashan At Yashan, the lower part of the Yinkeng Formation at Yashan (Beds 1–11; Fig. 3) is composed of the same lithologic packages, fossil assemblages and ichnoassemblage as its counterparts at Chaohu, and thus indicates a relatively deep distal offshore ramp setting. The middle and upper parts of the Yinkeng Formation (Beds 12–17; Fig. 3) are characterized by medium-bedded limestone and dolomitic limestone interbedded with black shale of Dienerian–early Smithian age (Fig. 5B). Small-scale cross beddings are present in limestone beds, while ammonoid Flemingites fauna are preserved in mudstone beds. Ichnoassemblage comprises Planolites isp. and Treptichnus coronatum (Bi et al., 1996). These burrows however cannot indicate the precise depositional environment due to their broad bathymetric ranges from deep sea to nearshore settings. Thus, both lithologic features and faunal assemblages of the middle-upper Yinkeng Formation point to a proximal ramp near storm wave action zone. 3.1.3. Palaeoenvironmental changes during the Griesbachian to early Smithian At Chaohu, an important feature of the lower-middle Yinkeng Formation is that the light grey marlstone and muddy limestone increase and thicken up-section, whereas the black shale and greenish mudstone thin (Fig. 2). Bed thickness of the marlstone, muddy limestone and limestone changes from typically ∼ 1 cm thick (Beds 1– 22 at Chaohu) to 1–5 cm thick (Beds 23–29 at Chaohu). Above this level of the number of limestone beds significantly decreases and beds thicken down to 1–2 cm (Beds 23–37 at Chaohu). The lithologic switch from the shale/mudstone dominated sedimentary packages at the lower part of the Yinkeng Formation to the carbonate dominated successions, coupled with hummocky-like stratified beddings, at its middle part reflects a broad shallowing-upward trend from a deep distal offshore ramp setting in the Griesbachian and Dienerian to a relatively shallow proximal ramp (near storm wave base) in the earliest Smithian. Re-appearance of the mudstone-dominated sedimentary packages at the upper Yinkeng Formation indicates that the habitat deepened to a distal offshore ramp setting again. At Yashan, a broad shallowing-upward trend from a deep distal offshore ramp setting (below storm wave base) in the Griesbachian to a relatively shallow proximal ramp during the Dienerian to early Smithian is also reflected by the lithologic switch from the black shale-dominated sedimentary packages at the lower part of the Yinkeng Formation to the carbonate-dominated successions at its

457

middle and upper parts (Fig. 3). The deepening cycle throughout the early Smithian is not indicated by the sediments of the upper Yinkeng Formation, which, however, indicate a relatively shallow proximal ramp setting near storm wave base (Fig. 3). The entire early Smithian sea level changes appeared a shallowing cycle because the lower Helongshan Formation of early Smithian age indicates a relatively shallow primal ramp habitat above storm wave base (see below). Overall, the Dienerian-early Smithian depositional environment was shallower in Yashan than in Chaohu. 3.2. Helongshan Formation The Helongshan Formation is very different in thickness, lithologies and ichnoassemblages at both the Chaohu and Yashan areas. At Chaohu, this formation is 20 m thick and is comprised of the alternation of thin-bedded dolomitic limestone and calcareous mudstone. It is late Smithian in age (Fig. 2). At the Yashan locality, the Helongshan Formation is very thick and characterized by alternation of dolomitic limestone and calcareous mudstone yielding halite pseudomorphs. Its lower part is early Smithian in age, while its middle and upper parts are late Smithian in age (Xu and Xing, 1992; Fig. 3). 3.2.1. Chaohu The lower part of the Helongshan Formation (Beds 38−45; Fig. 2) is dominated by medium-bedded muddy limestone with interbeds of calcareous mudstone (Fig. 4H−I). The carbonate-dominated sedimentary packages are overall comparable with that of the middle Yinkeng Formation. However, muddy limestone layers, ~5–12 cm thick, are much thicker than their counterparts at the Yinkeng Formation. Moreover, calcareous mudstone, instead of black shale, characterizes the Helongshan Formation, indicating a relatively shallower habitat than that the middle Yinkeng Formation represents. The facts that horizontally laminated stratifications are common and cross stratification is absent throughout the lower Helongshan Formation suggests a low-energy, proximal ramp environment between fair-weather and storm wave bases. The upper Helongshan Formation (Beds 46–53; Fig. 2) is characterized by an increasing number and thickness of calcareous mudstone beds (Fig. 4F–G). Muddy limestone units thin up section. Carbonate units are usually finely laminated and lack any cross beddings. When compared with the lower Helongshan Formation, a decrease in thickness of limestone units and an increase in thickness of mudstone units suggest that the depositional environments may have deepened throughout the Helongshan Formation. In addition, the upper Helongshan Formation at the Pingdingshan Hill yields microbialites, microbial mats and ostrocod shell concretions (Jia et al., 2010), which usually suggest a marine habitat near storm action zone. A diverse marine fish assemblage has also been reported from the mudstone-dominated units of the upper Helongshan Formation at Pingdingshan (Tong et al., 2004). Accordingly, all lines of evidence indicate that the upper Helongshan Formation represents a proximal ramp near storm wave base. 3.2.2. Yashan The lower part of the Helongshan Formation (Beds 19–21; Fig. 3) is characterized by alternation of thin-bedded micritic limestone, dolomitic limestone and calcareous mudstone yielding abundant conodonts and ammonoids (Xu and Xing, 1992). When compared with the proximal ramp facies of the upper Yinkeng Formation, the lower Helongshan Formation at Yashan is characterized by dolomitic limestone and calcareous mudstone, suggesting a shallower habitat than that indicated by the Yinkeng Formation. Moreover, no any cross beddings and relatively abundant animal fossils are present in the lower Helongshan at Yashan. The fact that finely laminated stratification is common and cross stratification is absent suggests a

458

Z.-Q. Chen et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 299 (2011) 449–474

Fig. 6. Spathian (Lower Triassic) successions from the West Pingdingshan (WP) and Majiashan (MJS) sections. A, the contact between the Helongshan and Nanlinghu Formations at WP; thin- to medium-bedded muddy limestone and calcareous mudstone (Bed 54) belong to the Helongshan Formation, while thick-bedded limestone (Bed 54) to the Nanlinghu Formation. B−C, massive limestones (Beds 54−56) of the lower Nanlinghu Formation at WP. D, large ripples on bedding surface of Bed 57 at WP. E, ripples and burrows on the top surface of Bed 58 at WP. F, medium- to thick-bedded limestone of the upper Nanlinghu Formation at MJS. G, water-escaping structures on the bedding surface (Bed 87) at MJS. H, thin- to medium-bedded limestone at the upper Nanlinghu Formation at MJS. I, medium-bedded limestones interbedded with volcanic layer from the topmost Nanlinghu Formation at MJS.

relatively shallow proximal ramp habitat between storm wave and fair-weather wave action zones. The middle Helongshan Formation (Beds 22–27; Fig. 3) comprises the alternating dolomitic limestone and calcareous mudstone (Fig. 5C) and yields the pronounced halite pseudomorphs, suggesting

a marginal marine environment within highly evaporitic conditions. This environmental interpretation is also supported by the unique ichnoassemblage, which is characterized by abundant Treptichnus bifurcus (Fig. 5D) and Kouphyichnium isp. The former ichnospecies was originally described by Miller (1889) from Lower Pennsylvanian

Z.-Q. Chen et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 299 (2011) 449–474

459

Fig. 7. Ichnofabric indices. A, sediments of the Yinkeng Formation at the Majiashan section, Chaohu with no bioturbation recorded (ii1); the hammer as scale. B–C, the highly bioturbated limestone at the Nanlinghu Formation at Yashan (ii5). D, vermicular limestone of the lower Nanlinghu Formation at Yashan showing the coverage of bioturbation up to 80% (BPBI 5).

freshwater tidal flat deposits in Indiana, USA. The typical Treptichnus has been reported only from freshwater or marginal marine settings (Rindsberg and Kopaska-Merkel, 2005). Kouphichnium traces represent trackways of limulids, which usually inhabit shallow marine to marginal marine environments (Bi et al., 1996). The upper part of the Helongshan Formation (Bed 28; Fig. 3) is characterized by alternation of dolomitic/or muddy limestone and mudstone (Fig. 5E). Muddy limestone is usually finely laminated. No cross stratifications are observed throughout this unit. These lithologic features suggest a proximal ramp habitat between storm wave and fair-weather wave action zones. 3.2.3. Palaeoenvironmental changes during the late Smithian In Chaohu, lithologic switch from limestone-dominated succession at the lower Helongshan Formation to mudstone-dominated packages, coupled with the presence of ostracod shell concretions, at the upper part of the formation, clearly indicates a sea-level rise during the late Smithian. In Yashan, the lower part of the Helongshan Formation belongs to the lower Smithian (Xu and Xing, 1992) and represents a proximal ramp setting during that time. In contrast, a sedimentary facies change from a closed, highly evaporitic marginal sea to proximal ramp habitat below fair-weather storm wave base is recorded throughout the middle-upper Helongshan Formation, indicating a sea-level rise during the late Smithian. As a result, the late Smithian sea level changes in both Chaohu and Yashan was consistent one another. Moreover, this formation overall represents a much shallower depositional environment in Yashan than in Chaohu during the late Smithian. 3.3. Nanlinghu Formation (Spathian) The Nanlinghu Formation is very thick in both Chaohu and Yashan areas, but lithology is slightly different one another (Figs. 2 and 3). 3.3.1. Chaohu The lower part of the Nanlinghu Formation (Beds 54–58; Fig. 2) is composed of medium- to thick-bedded limestone (Fig. 6A–C), yielding large ripples (Fig. 6D) and wavy cross-beddings. The massive limestone bed is usually highly bioturbated (Fig. 6E). These lithologic features and sedimentary structures suggest a lower shoreface environment near fair-weather wave base. As stated above, the upper Helongshan Formation was likely deposited in a proximal ramp

near storm wave base. Thus, it can be interpreted that sea-level fell across the boundary between the Helongshan and Nanlinghu Formations (also the Smithian–Spathian boundary) (Fig. 2). The middle part of the Nanlinghu Formation exposed at the southern Majiashan section is characterized by thin- to mediumbedded limestone, trace fossils Gyrochorte and Thalassinoides, ammonoid Columbites–Tirolites Assemblage, and marine reptile and fish assemblages. In particular, abundant large marine fishes and reptile and lack of any cross beddings suggest a proximal ramp habitat between fair-weather and storm wave bases. The upper part of the Nanlinghu Formation comprises medium- to thick-bedded muddy limestone and dolomites (Fig. 6F and H–I), which are overlain by terrestrial sediments of Middle Triassic age. Muddy limestone yields water-escaping structures (Fig. 6G) and large problematic traces similar to the fish swimming trail Undichna (see below). All lines of the evidence show that the upper Nanlinghu Formation may represent a marginal sea setting. 3.3.2. Yashan The lower Nanlinghu Formation (Beds 29–33; Fig. 3) is dominated by muddy limestone (Fig. 5F) and marked by the presence of vermicular limestone. Large vertical burrows of Arenicolites and large ripples are common on the surface of limestone beds. Thus, the lower part of the Nanlinghu Formation may represent a rather shallow, lower shoreface environment. Clearly, a sea-level fall across the Helongshan–Nanlinghu Formation boundary is evident in Yashan. The middle part of the Nanlinghu Formation (Beds 34–37; Fig. 3) is dominated by massive, highly bioturbated vermicular limestone (Figs. 5H and 7B–D), indicating a significant increase in bioturbation intensities when compared with the lower Nanlinghu Formation. Ammnoids and conodonts are also abundant in this part of the formation (Xu and Xing, 1992). Lithologic and faunal evidences point to a shallow, proximal ramp between storm and fair-weather wave bases. The upper Nanlinghu Formation (Bed 38; Fig. 3) is characterized by massive limestone bearing cave solution breccias (Fig. 5G), which indicate palaeokarst sedimentation induced by exposure of carbonate platform. 3.3.3. Palaeoenvironmental changes during the Spathian The Nanlinghu Formation successions at both Chaohu and Yashan represent environmental changes from lower shoreface to proximal

460

Z.-Q. Chen et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 299 (2011) 449–474

Fig. 8. A and C, Diplocraterion isp. on the upper bedding plane of the Nanlinghu (NLH) Formation (Bed 58), West Pingdingshan (WP) section; C, close-up of Diplocraterion burrows showing dumbbell-shaped structure. B, Thalassinoides isp. from the upper NLH Formation (Bed 35), Yashan section, upper surface. D, Palaeophycus isp. from Bed 57, NLH Formation, WP section, upper surface. E, Arenicolites isp. (arrow indicated) from the upper bedding plane of Bed 58, NLH Formation, WP section. F, Arenicolites isp. (arrow indicated) from the upper bedding plane of Bed 27, the Helongshan (HLS) Formation, Yashan section. G, Furculosus carpathicus from Bed 57, NLH Formation, WP section. H, Arenicolites isp. (black arrows indicated) and Planolites isp. (white arrow indicated) on the upper bedding plane of Bed 46, HLS Formation, WP section. I, Gordia isp. and Planolites isp. from Bed 27, HLS Formation, Yashan section. J, highly bioturbated limestone showing Arenicolites isp. and other burrows from upper NLH Formation (Bed 36), Yashan section.

ramp between fair-weather and storm wave bases, and then to marginal sea, indicating that sea-level fell, then rose and fell again through the Spathian time. After the end of the Spathian, the Lower Yangtze region including the Chaohu–Yashan areas uplifted and became terrestrial settings due to the consolidation between the South China and North China blocks (Tong and Yin, 2002).

4. Methodology Trace fossil taxonomic identification was based on field observations and descriptions of specimens collected from the outcrops. Several proxies were analyzed to examine ecologic recovery in the aftermath of the P/Tr mass extinction as indicated

Z.-Q. Chen et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 299 (2011) 449–474

461

Fig. 9. A, Arenicolites isp. from Bed 31, NLH Formation, Yashan section, upper surface. B–D, Arenicolites isp. (black arrows indicated) and Beaconites isp. (white arrow indicated) from Bed 35, NLH Formation, Yashan section, upper surface. E–F, Arenicolites isp. on the upper bedding surface of Bed 34, NLH Formation, Yashan section. G, Rhizocorallium isp. (arrows indicated) on the supper surface of Bed 34 (fresh surface), NLH Formation, Yashan section; black line indicates section of burrow that was measured. H–J, Rhizocorallium isp. on upper surface of Bed 34 (weathered surface), NLH Formation, Yashan section; white lines indicates sections of burrow that were measured. K, Planolites beverleyensis (Billings) on Bed 35, NLH Formation, Yashan section, upper surface. L, Taphrhelminthopsis cf. podhalensis from Bed 31, NLH Formation, Yashan section; upper surface. M, P. beverleyensis (Billings) on Bed 31, NLH Formation, Yashan section, upper surface.

by trace fossils, including burrow size variation, ichnodiversity, forms and complexity, and tiering, as these characteristics have been analyzed elsewhere (Beatty et al., 2005, 2008; Fraiser and

Bottjer, 2009; Pruss and Bottjer, 2004; Twitchett, 1999; Twitchett and Barras, 2004; Zonneveld et al., 2002, 2004, 2010). Taxonomic revision of the Lower Triassic trace fossils previously described

462

Z.-Q. Chen et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 299 (2011) 449–474

from the Lower Yangtze region (Bi et al., 1995, 1996; Liu and Wang, 1990) was undertaken based on the original fossil descriptions and illustrations (Table 1). Measurements of burrow diameters were measured on bedding planes and in vertical exposures following the methods by Pruss and Bottjer (2004). Most burrow diameters were measured at the part of the burrow that was most representative of the average width. Rhizocorallium burrow diameters were measured at the outer edges of the U-shaped burrow at its widest part. Sediment penetration depths of trace fossils were also measured on vertical exposures, and tiering levels were assessed based on these measurements (Bottjer and Ausich, 1986; Twitchett, 1999, 2006). The ichnofabric index (Droser and Bottjer, 1986) and the bedding plane bioturbation index (Miller and Smail, 1997) are powerful tools that provide a semi-quantitative way to measure the extent of bioturbation recorded in sedimentary beds deposited after mass extinctions (Fraiser and Bottjer, 2009; Pruss and Bottjer, 2004; Twitchett and Wignall, 1996). The methods of measuring ichnofabric indices in vertical outcrop (Droser and Bottjer, 1986; Fig. 7A–B) and on bedding planes (Miller and Smail, 1997; Fig. 7C–D) were applied here to examine bioturbation throughout the Early Triassic epoch. Ichnofabric indices (ii1–5) indicate bioturbation varying from lowest to highest levels. The bedding plane bioturbation index (BPBI) was employed to determine the approximate percentage of bedding planes covered by burrows (Miller and Smail, 1997).

the outcrop is 20 cm. The lining is 0.5–1 mm thick, and meniscate packets are 4–6 mm wide, equal to or slightly thinner than overall burrow width (Fig. 11J). Walls of burrows are usually obscure or absent. When the walls have been preserved, they are very thin, and inconsistent throughout the trace fossil. The identity of the organisms for the construction of Beaconites also remains controversial. The trace fossil has been attributed to polychaete worms, limbless vertebrates, limbed reptiles, ostracoderms, lungfish, arthropods, and arthropleurids (see Gordon, 1988 for a review).

5.3. Chondrites von Sternberg

5. Ichnotaxonomic characterization of Early Triassic trace fossils

Chondrites burrows are preserved in convex epirelief on the upper surface of a muddy limestone at the basal Nanlinhu Formation at Pingdingshan (Fig. 2). Fine, branching burrows form plantlike dendritic patterns of small cylindrical ramifying burrow systems. Individual burrows are neither crossing each other nor interpenetrating. Most of them are exposed parallel to the bedding plane in compact groups (Fig. 11K). Burrows are typically filled with yellowcoloured, relatively coarsely grained sediments, and thus are distinct from the surrounding sediments that are light-grey and fine-grained. Burrows do not have walls, and surfaces are rough. Although ethological interpretation for this ichnogenus is still in dispute, Chondrites has been widely accepted as fodinichnia and is to be regarded as feeding structures of sediment-eating animals (i.e., Bromley and Ekdale, 1984; Löwemark et al., 2004).

Fifteen ichnogenera (including one undetermined ichnogenus) are described and illustrated herein.

5.4. Diplocraterion Torell

5.1. Arenicolites Salter Traces of Arenicolites are seen in cross section on bedding planes in most specimens examined. They are preserved in calcareous mudstone and muddy limestone at both the Pingdingshan and Yashan localities. Broken hand samples show parts of the limbs, which are unbranched, parallel to one another, perpendicular to the bedding plane, and lack spreite. On bedding planes, burrows occur as either pairs of holes (Fig. 8E–F, H, and J) or paired shafts (Fig. 9A–F). Depth of penetration of burrows is difficult to measure, but some broken specimens show that the depth of U-shaped tubes varies from 5 mm to 70 mm. The U-shaped burrows can be semiquantitatively categorized into three groups based on limb diameters and burrow depth. The first group has small limbs, 0.5 to 3.0 mm in diameter with burrow depth b10 mm (Figs. 8E–F, and H, and 10A–B); the second group has limbs 3–8 mm in diameter with burrow depth 10–25 mm (Figs. 9A and 10C); and the limbs of the third group are relatively large, 7–12 mm in diameter, penetrating down to 20–70 mm (Figs. 8J, 9B–F, and 10D). The distance between the limbs ranges from 2 to 6 mm within all three groupings. Filling of most burrows consists of relatively coarse sediments that are easily distinguishable from surrounding fine-grained sediments. These burrows are assigned to an uncertain ichnospecies of Arenicolites due to poor preservation. This ichnogenus has been interpreted as a dwelling trace (domichnia), which could be produced by various kinds of organisms such as polychaete worms, amphipod crustaceans, and insects (Bromley, 1996; Knaust, 2004; Rindsberg and Kopaska-Merkel, 2005). 5.2. Beaconites Vialov Several horizontal burrows, preserved as convex epireliefs, are straight to curved, unbranched, lined, and meniscate (Figs. 9C–D and 11J). They are identified here as Beaconites Vialov. Burrow diameter ranges from 5 to 8 mm (Fig. 12G), and maximum length observed on

Diplocraterion from the Pingdingshan section is preserved in a muddy limestone of the lower Nanlinghu Formation (Fig. 2), and is typically seen in two dimensions on upper bedding plane surfaces as dumbbell-shaped structures containing two circular holes due to removal of the fillings of the U-shaped limbs. Spreite are not visible, but common prominent grooves on the bedding planes indicate the top of spreite laminae that connect both limbs (Fig. 8A and C). The basal part of the U-shaped limbs is not visible in the examined material, but the depth of the U-shaped limbs is estimated to be up to 1 cm below the top of bedding plane. The burrow diameters are 2– 6 mm in diameter (Fig. 12F) and the limbs are 5–10 mm apart. The poor preservation prevents precise comparison with Diplocraterion parallelum Torell. Thus, the Chaohu traces are assigned to Diplocraterion isp. Taxonomy of Diplocraterion has been systematically revised by Fürsich (1974) and Fillion and Pickerill (1990). This ichnogenus is usually classified as a domichnial permanent dwelling structure (Bromley, 1996) produced by suspension feeders or benthic predators (Fürsich, 1975). It is also known as an “equilibrium structure” responding to sedimentation and erosion (Bromley, 1996).

5.5. Furculosus Roniewicz and Pienkowski Several negative reliefs of cylindrical burrows occur on limestone bedding planes of the lower Nanlinghu Formation (Fig. 2). They form tight, fork-like loops with endings parallel to each other (Fig. 8G). The burrows are 4–9 mm in diameter, smooth or sometimes ornamented with fine longitudinal furrows. The widths of the entire trace fossil (including both branches of the loops) range from 16 to 32 mm wide. Overall, these traces are identical to Furculosus carpathicus Roniewicz and Pienkowski, 1977 described from the Eocene flysch succession in the Podhale Basin, Polond, although only negative relief is preserved. The tracemaker likely fed along the water-sediment boundary (paschichnia) (Roniewicz and Pienkowski, 1977).

Z.-Q. Chen et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 299 (2011) 449–474

463

Fig. 10. Size measurements of Arenicolites burrows throughout the Lower Triassic succession at both Chaohu and Yashan areas. A–D, Burrow diameter frequency distributions; N = number of burrows. E, burrow size variations throughout the late Smithian to late Spathian. Note the line with small circles showing the variations of the maximum diameter values and the line with dots showing the variations of the average diameter values.

5.6. Gordia Emmons

5.8. Monocraterion Torell

Several long, slender, smooth, worm-like trails occur as both positive and negative reliefs in muddy limestone of the Helongshan Formation at Yashan (Fig. 3). They are curved to straight and cross one another. Burrows, 1–2 mm wide, are uniform in thickness throughout the entire trace. Burrows display a rounded base in cross section, and some of the specimens show more tendency to meandering (Fig. 13F and K). These burrows fit the definition of Gordia, but they do not fit the definition of any known species within the ichnogenus. The insufficient amount of material prevents justifying the proposal of a new ichnospecies. The tracemakers could have been worms as burrows overall resemble the hair-worm Gordius (Häntzschel, 1975). Some burrows cross one another at the same horizon indicating that the tracemakers were epifaunal animals.

Funnel-shaped structures with an indented knob on the floor of the funnel are preserved as positive epireliefs on limestone bedding planes of the lower Nanlinghu Formation (Bed 58) at Pingdingshan (Fig. 11A–E). The funnels are 1–4 cm in diameter with the greatest depth up to 2 cm. The basal knob is pronounced, but the short, vertical tubular structures that are seen on type specimens as a continuation of the funnel (Schlirf and Uchman, 2005) are broken in most of specimens examined here. The centrally located, tube-like process is prominent at the floor of the funnel and appears as a small concentric circle in plain view (Fig. 11D). Numerous small burrows, 4–5 mm in diameter, extend from the central knob and were likely the “tentacle” structures described in this trace elsewhere. These “tentacles” are slightly curving, oblique to the bedding plane, rarely branching, occasionally lined, and tubular with smooth outer surfaces. Monocraterion has long been misunderstood because the type ichnospecies was poorly defined without illustrations (Westergärd, 1931), and the figured specimens by Häntzschel (1975) are not type material. Schlirf and Uchman (2005) re-studied the type material including the lectotype selected by Jensen (1997) for M. tentaculatum, the type ichnospecies of the ichnogenus, and have re-diagnosed Monocraterion and diagrammed the lectotype (Schlirf and Uchman, 2005, Figs. 11–12). At Pingdingshan the funnel-shaped structures are densely arranged on the bedding plane. All features observed here justify the assignment of the Lower Triassic materials to M. tentaculatum Torell, although most parts of the extended tubular structures are absent. According to Schlirf and Uchman (2005), the undoubted M. tentaculatum has been found only in the Lower

5.7. Gyrochorte Heer This horizontal trace is distributed on bedding planes of calcareous mudstone. It is up to 5 mm wide and preserved as plaited ridges with biserially arranged, obliquely aligned pads of sediment. The bifurcated trail is separated into two parallel tubes by a median groove, up to 1 cm in width, in convex relief (Figs. 11I and 13H–I). The trace fossil can strongly wind and sharply change direction, and its length varies greatly over exposures. This trace may cut across itself and other traces on bedding planes. These traces are assignable to Gyrochorte isp. This trace may have been produced by either a gastropod or a polychaete-like worm (Gibert and Ekdale, 1999; Heinberg, 1973).

464

Z.-Q. Chen et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 299 (2011) 449–474

Fig. 11. A–E, Monocraterion tentacultum Torell from Bed 58, NLH Formation, WP section; upper surface; A, C–E, plane view; B, lateral view. F, Thalassinoides saxonicus (Geinitz) from lower NLH Formation at Majiashan, upper surface. G, Planolites beverleyensis (Billings) from Bed 58, NLH Formation, WP section; upper surface. H, Planolites montanus Richter from Bed 57, NLH Formation, upper surface. I, Gyrochorte isp. from the lower NLH Formation, MJS section; upper surface. J, Beaconites isp. from Bed 78, NLH Formation, WP section, upper surface. K, Chondrites isp. from Bed 57, NLH Formation, WP section; upper surface. L–M, problematic traces from the upper NLH Formation, MJS section; upper surface.

Cambrian Mickwitzia sandstone, Sweden (Jensen, 1997). The Chaohu material therefore could represent the first record of M. tentaculatum outside Sweden and younger than the Cambrian. Although Laevicyclus includes vertical traces perpendicular to bedding plane and comprises concentric circles on bedding planes and thus is comparable with

Monocraterion, it lacks the “tentacle” structures. Jensen (1997) interpreted the funnel structure as an originally open burrow and the small horizontal tubular structures as permanent structures, possibly used for excursions by the tracemaker. However, the relationship between funnel and tentacle structures remains poorly

Z.-Q. Chen et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 299 (2011) 449–474

465

Fig. 12. Burrow size measurements of Palaeophycus, Thalassinoides, Treptichnus, Rhizocorallium, Beaconites, and Diplocraterion from the Lower Triassic succession at both Chaohu and Yashan areas.

understood and M. tentaculatum is likely a composite trace fossil (Schlirf and Uchman, 2005).

ichnospecies. These burrows therefore are assigned to Palaeophycus isp.

5.9. Palaeophycus Hall 5.10. Planolites Nicholson Palaeophycus is represented by branched, curved, cylindrical burrows preserved as negative or positive reliefs on upper surfaces of limestone and calcareous mudstone of the lower Nanlinghu Formation at Pingdingshan (Figs. 8D, 13L, and 14E–F and L–N). Burrows are 0.5–5 mm in width (Fig. 12A–B) and commonly intersect and pass over one another. They are subparallel to bedding planes (Figs. 8D, 13L, and 14E and N). It should also be noted that some burrows have been weathered out so that the burrows seem to be oblique to bedding plane (Fig. 14F). Burrows are mostly smooth. Of the known Palaeophycus ichnospecies, the studied material is most allied to P. tubularis, which, however, includes burrows that are much larger than the Lower Triassic traces. The poor preservation state of the studied burrows prevents a precise comparison with the known

This ichnogenus includes various-sized vermiform burrows occurring at 11 horizons throughout the Changhsingian to the Spathian at the studied sections (Figs. 2–3, and 15). They are typically unlined, rarely branched, straight to sinuous, smooth to irregularly walled or ornamented, horizontal to slightly inclined burrows that are circular to elliptical in cross-section. Burrows are usually filled with different sediments from the host rocks. Intraspecific variations of these burrows are evident. Smooth burrows are assigned to both Planolites montanus and Planolites beverleyensis, while three other ichnospecies, Planolites annularus, Planolites terraenovae and Planolites constriannulatus, usually possess ornamented burrows (Stanley and Pickerill, 1994).

466

Z.-Q. Chen et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 299 (2011) 449–474

Fig. 13. A–E and J, Treptichnus bifurcus (Miller); A, upper surface showing densely arranged burrows; B, E, close-up of T. bifurcus burrow, upper surfaces; C, close-up of T. bifurcus (coarse burrow), incorporating with fine burrow of Gordia isp; upper surface; D, close-up of T. bifurcus burrow, lower surface. F and K, Gordia isp. on upper surface; F, Gordia isp. associated with T. bifurcus; K, burrows of Gordia isp.. G and M, Treptichnus apsorum Rindsberg and Kopaska–Merkel. H–I, Gyrochorte isp.; upper surface. L, Palaeophycus ichnosp.; upper surface. All specimens were collected from Bed 27, HLS Formation, Yashan section.

In the studied sections, Planolites beverleyensis (Billings) includes the burrows that are relatively large, smooth, straight to gently curved, and unlined or rarely lined (Figs. 9K, M, and 11G). Burrows are subparallel to bedding planes and commonly intersect and/or pass over one another. The filling is coarser than the host rock. The relatively small, unlined, curved to contorted, smooth, cylindrical burrows are assigned to Planolites montanus Richter (Figs. 11H; 14C–D, G–I, and K). They are normally preserved as convex hyporelief. Burrows are short, parallel to subparallel to bedding planes, and densely packed. They also frequently intersect each other (Fig. 14C–D).

Several burrows are rather small, 0.5–5 mm in diameter (Fig. 12A– B), elliptical to circular in cross section, gently curved, strictly parallel to bedding planes, and do not intersect one another (Figs. 8H–I and 14A–B). They cannot be assigned to P. everleyensis because of their extremely small diameter, or to Planolites montanus due to their less curved burrows. These horizontal burrows therefore are assigned to Planolites isp. The simple form of this ichnogenus means that many different animals may produce these burrows, which often are ascribed to a worm or worm-like animal, but many phyla may be responsible (Bromley, 1996). This inference of varied tracemakers is also

Z.-Q. Chen et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 299 (2011) 449–474

467

Fig. 14. A, Planolites isp. from the topmost Talung Formation; upper surface. B, Planolites isp. from Bed 17, Yinkeng Formation; upper surface. C–D, Planolites montanus Richter from Bed 58, NLH Formation, upper surface; C, a slab showing densely arranged burrows; D, close-up of the Planolites burrows. E, Palaeophycus isp. from Bed 55, NLH Formation, upper surface. F, Palaeophycus isp. from Bed 56, NLH Formation, upper surface. G–I, K, Planolites beverleyensis (Billings) from the NLH Formation, upper surfaces; G, from Bed 58; H–I, K, from Bed 57. J, Thalassinoides saxonicus (Geinitz) from Bed 55, NLH Formation, upper surface. L–N, Thalassinoides saxonicus (Geinitz) from Bed 58, NLH Formation, upper surfaces. All burrows are preserved at the WP section.

reinforced by the highly varied burrow sizes of Planolites through the Early Triassic (Fig. 15). However, Planolites is a feeding trace (e.g., Bromley, 1996), and deposit-feeding worms or infaunal holothuroids have been proposed as tracemakers.

5.11. Rhizocorallium Zenker Traces of Rhizocorallium are preserved as both positive and negative reliefs on upper surfaces of limestone beds in the upper Nanlinghu

468

Z.-Q. Chen et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 299 (2011) 449–474

Fig. 15. Burrow size measurements of Planolites throughout the Lower Triassic succession at the studied section. A–G, burrow size frequency distributions in various horizons. H, burrow size variations through the Early Triassic epoch. Note the line with small circles showing the variations of the maximum diameter values and the line with dots showing the variations of mean diameter values.

Formation (Beds 34–36) at Yashan (Fig. 3). Most traces are subparallel or oblique to bedding planes and consist of irregular, narrow, flattened, U-shaped burrows with poorly preserved spreiten (Fig. 9G–J). Trace widths, measured from the outside edges of the U-shaped structure Fig. 9J), are 9–14 mm (Fig. 12F). Distances between the tubes are 3–10 mm, and the tube diameters are 10–18 mm. The Ushaped tubes are elliptical in cross section, have inconsistent widths, and possess rough surfaces. The burrow may extend as deep as 10 mm into the sediment. The U-shaped tubes are filled with yellow clastic sediments distinguished from the surrounding dark limestone. The morphology of this ichnogenus has been recently described (Fürsich, 1998; Knaust, 2007; Rodriguez-Tovar and Perez-Valera, 2008; Worsley and Mørk, 2001; Zonneveld et al., 2001). The Yashan material does not belong to any known ichnospecies, and is thus assigned to Rhizocorallium isp. due to poor preservation. The formation of Rhizocorallium is attributed to dwelling and feeding behaviours of deposit-feeding crustaceans (Häntzschel, 1975; Rodriguez-Tovar and Perez-Valera, 2008; Seilacher, 1967; Vossler and Pemberton, 1989), annelids (Pemberton, 1992), or insects (Knaust, 2007). 5.12. Taphrhelminthopsis Sacco Taphrhelminthopsis is characterized by a freely winding and meandering burrow course. The trace is bilobate and preserved as

positive epirelief on upper bed surfaces. It is represented by two parallel meandering ridges separated by a distinct, rather large median furrow; the median groove ranges from 3 to 8 mm wide with a gently flat floor where some sediments have collected and formed discontinuous low ridges. Lateral ridges are 3–5 mm in cross section, and they commonly cross and overlap (Fig. 9L). These features agree well with T. podhalensis Roniewicz and Pienkowski (1977, p. 278, pl. 4, figs. a–c) except for some discontinuous, incipient median ridges in the median groove. The tracemaker could have been a large soft-bodied echinozoan or mollusc-grade animal that actively grazed or ingested sediment at the sediment–water interface (Hagadorn et al., 2000). 5.13. Thalassinoides Ehrenberg Thalassinoides is preserved in mudstone and muddy limestone of the Nanlinghu Formation (Figs. 2–3). It occurs as branching burrows that form networks with characteristic Y-shaped junctions. Variations suggest two ichnospecies for these burrows. One group of burrow networks is represented by a set of mediumsized, smooth, rounded burrows, which may penetrate to a depth of 10 mm. Most preserved burrows are 2–3 mm in diameter (Fig. 12D) and bifurcate to form incomplete intricate networks (Fig. 11F and 14J). These traces are filled with dark greenish, fine organic

Z.-Q. Chen et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 299 (2011) 449–474

sediments, and are distinguished from the surrounding light grey mudstone. These features agree well with Thalassinoides saxonicus (Geinitz) illustrated by Häntzschel (1975, fig. 70.2b). Several burrows that frequently intersect and pass over one another and are subparallel or oblique to bedding planes (Fig. 14L–M) are also tentatively assigned to T. saxonicus due to their Y-shaped branching. Another burrow type is comprised of rounded burrows which commonly broaden at the Y-shaped junctions and thin distally. Burrows bifurcate to form intricate networks in plane view (Fig. 8B). Burrow diameter varies from 2 mm to 5 mm, but most burrows are 3– 4 mm in diameter (Fig. 12C). These burrows are filled with coarsely grained, light coloured sediments and are thus distinguished from surrounding dark organic limestone. Burrows may penetrate to a depth b2 cm. The expanded junctions distinguish the Nanlinghu traces from any known ichnospecies. They therefore are assigned to Thalassinoides isp. The formation of Thalassinoides traces has been attributed to the behaviour of many organisms, including cerianthid sea anemones, enteropneust acron worms, fish, and decapod crustaceans (Carvalho et al., 2007; Ekdale and Bromley, 2003; Hakes, 1977; Myrow, 1995; Rodriguez-Tovar and Uchman, 2006). 5.14. Treptichnus Miller Treptichnus is preserved as convex hyporelief or concave epirelief on the upper surface of muddy limestone of the Helongshan Formation at Yashan (Fig. 3). Traces are comprised of simple, zigzag-arranged burrows intersecting each other at low angles (Fig. 13A–E, J). The width of an individual segment is approximately 2–3 mm. Short projections extend from the points of juncture between elongated segments. Projections are situated on alternate sides of the burrow. Individual segment lengths range from 2.0 to 8.4 mm; projection lengths range from 1.2 to 2.7 mm; and angle of segment intersection ranges from 126 to 168°. These traces agree well with the type materials of Treptichnus bifurcus refigured by Maples and Archer (1987). Treptichnus apsorum is represented by subhorizontal burrows comprised of segments arranged in a zigzag fashion with shallow, broadly V-shaped segments that curve upward into shafts near junctions (Fig. 13G and M). Burrows, 3–5 mm in diameter, are usually larger than those in Treptichnus bifurcus. However, longitudinal striae cannot be seen due to the poor preservation. Previously, the definition of Treptichnus has been broadened and includes morphologically varied forms. This ichnogenus is also confused with several allies such as Plangtichnus Miller and Belorhaphe Fuchs. Maples and Archer (1987) showed that Plangtichnus is a preservational aspect of Treptichnus. The former therefore has been treated as a synonym of Treptichnus (Buatois and Mangano, 1993; Jensen, 1997). Both Belorhaphe and Treptichnus are independent of one another, but some ichnospecies previously ascribed to Treptichnus should be re-assigned to Belorhaphe (Rindsberg and Kopaska-Merkel, 2005). Rindsberg and Kopaska-Merkel (2005) categorized Treptichnus ichnospecies into three groups: 1) Treptichnus pedum and similar forms including Treptichnus coronatum, Treptichnus lublinensis, Treptichnus rectangularis, and Treptichnus triplex; 2) Belorhaphe-like “feather-stitch” burrows including Treptichnus aequalternus, Treptichnus meandrinus, and Treptichnus protopalaeodictyum; and 3) Treptichnus bifurcus and similar forms including Treptichnus pollardi and Treptichnus apsorum. Dzik (2005) established Manykodes to accommodate Treptichnus rectangularis and Treptichnus pedum and Podolodes to include T. triplex. Rindsberg and Kopaska-Merkel (2005) suggested that the “featherstitch” burrows are better assigned to Belorhaphe than Treptichnus. Thus, groups 1 and 2 can be re-assigned to Manykodes/Podolodes and “Belorhaphe”, respectively, while Treptichnus is retained to T. bifurcus and its allies. Both T. bifurcus and T. apsorum are recognizable in the Lower Triassic collections. The typical Treptichnus was interpreted as

469

representing deposit-feeding in a zigzag or other segmented, serial pattern with older segments abandoned after use (Rindsberg and Kopaska-Merkel, 2005). The zigzag configuration supports either a deposit-feeding or a farming and trapping life strategy. The tracemaker could have been insect larvae (Rindsberg and Kopaska-Merkel, 2005; Uchman, 2005) or a worm-like organism (Seilacher, 2007). 5.15. Problematic traces A pair of subparallel grooves meander freely on upper surfaces of limestone of the upper Nanlinghu Formation at Majiashan (Figs. 2 and 11L–M). One groove is consistently narrow and deep throughout the entire trail. The other groove is broad and shallow with a poorly defined floor, and is separated from surrounding host rock by a narrow, distinct ridge. A broad, gently elevated but poorly defined median fold with rough surfaces occurs between the grooves throughout this trail. Some trails are arranged as sinusoidal waves. These bilobate putative traces possess certain elements akin to Undichna trails, but most trails meander along the bedding plane and the distance between the grooves varies throughout the trail. Thus, the biogenicity and taxonomy of these structures remain problematic. 6. Trace fossil assemblages as proxies of rebuilding marine ecosystems after the P/Tr mass extinction in South China 6.1. Extent of bioturbation Ichnofabric indices (ii) were assessed throughout the Lower Triassic successions at the studied localities (Figs. 2 and 3). At the Chaohu area, ichnofabric indices throughout the entire Yingkeng Formation are low (ii1). In the Helongshan Formation, 95% of strata have the lowest ichnofabric index (ii1), while only 5% (Bed 46) of strata are characterized as ii2 (Fig. 2). In the Nanlinghu Formation, about 30% strata are considerably more bioturbated (ii1, 4, 5). In particular, the lower Nanlinghu Formation at the Pingdingshan section contains beds of ii5 (Fig. 2). At the Yashan section, the Yinkeng Formation and lower Helongshan Formation contain very few bioturbated beds and the dominant bioturbation level is ii1. Bioturbation levels increase drastically from ii1 to ii5 in the upper Helongshan Formation, coinciding with the presence of the ammonoid Anasibirites Zone. Sixty percent of the Nanlinghu Formation is highly bioturbated (ii5) (Fig. 3). At the Pingdingshan section, for the three bedding planes containing Planolites in the Yinkeng Formation, the coverage was b10% and thus indicates a BPBI of 1. In the Helongshan Formation several bedding planes containing Arenicolites, Palaeophycus and Planolites exhibit coverage up to 10%, indicating a BPBI of 2. The same coverage, up to 10%, is also found on several bedding planes containing Arenicolites, Chondrites, Palaeophycus, Planolites, and Thalassinoides in the lower Nanlinghu Formation (Fig. 2). Several bedding planes containing Planolites (Figs. 11G and 14C–D) have coverage up to 80%, suggesting a BPBI of 5 for these beds (Fig. 2). Coverage up to 60% is found on the bedding planes containing Diplocraterion (Fig. 8A–C), Thalassinoides and problematic swimming traces in the Nanlinghu Formation. Thus, a BPBI of 4 is suggested for these horizons (Fig. 2). At Yashan, the bedding planes in the Yinkeng Formation containing Planolites have the coverage b10% (BPBI 1). In contrast, several bedding planes in the Helongshan Formation containing Treptichnus and its associated forms have the coverage up to 60%, suggesting BPBI 4. In the Nanlinghu Formation the bedding planes yielding Arenicolites, Planolites, Rhizocorallium, Taphrelminthopsis, and Thalassinoides have coverage up to 80%, and thus suggest a BPBI of 5. In addition, vermicular limestone (Fig. 7D) is conspicuous at the Nanlinghu Formations in Yashan. Burrowing and other organism activities are hypothesized to have played important roles in the formation of

470

Z.-Q. Chen et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 299 (2011) 449–474

Fig. 16. A, number of ichnogenera in the Griesbachian–early Smithian, late Smithian and Spathian intervals. Blocks with oblique strips show ichnogeneric richness from the studied sections, while the dot blocks show ichnogeneric richness from the entire Lower Yangtze region collected from the literature. B, burrow size variations in the Griesbachian–early Smithian, late Smithian, early Spathian, and late Spathian intervals. Note the line with small circles showing the variations of the maximum diameter values and the line with dots showing the variations of mean diameter values. C, tiering levels indicated by the mean and maximum penetration depths increase significantly in late Smithian.

vermicular limestone (X.M. Zhao et al., 2008). If so, the coverage of bioturbation can be up to 80% (BPBI 5) (Fig. 3). The limestone of the upper Nanlinghu Formation is also highly bioturbated with coverage N80% (Fig. 7B–C). It should be noted that bioturbation increases up the section regardless of environmental changes from nearshore–lower shoreface to proximal ramp to marginal sea through the entire Nanlinghu Formation (Fig. 3), as analyzed above.

6.2. Trace fossil diversity The Griesbachian–early Smithian trace fossils include only Treptichnus coronatum and Planolites isp. at the studied sections. Elsewhere in the Lower Yangtze region, Beaconites isp. was also found in the lower Yinkeng Formation (Griesbachian), and both Lockeia isp. and Thalassinoides isp. were reported from the upper Yinkeng Formation (early Smithian) (Bi et al., 1996; Table 1). The late Smithian (Helongshan Formation) recorded an increase in trace-fossil diversity in both studied areas and the entire Lower Yangtze region. Ten ichnospecies in eight ichnogenera, including Arenicolites isp., Cochlichnus anguineus, Gordia isp., Gyrochorte isp., Kouphyichnium isp., Palaeophycus isp., Planolites montanus, P. isp., Treptichnus bifurcus, and Treptichnus apsorum, have been recognized from both the Chaohu and Yashan areas. In addition, Archaeonassa isp., Arenicolites isp., Gordia isp., Ophiomorpha isp., Palaeophycus isp., Planolites montanus, Pteridichnites isp., and Thalassinoides isp. have been reported from the Helongshan

Formation elsewhere in the Lower Yangtze region (Bi et al., 1995, 1996; Liu and Wang, 1990; Table 1). The Spathian (Nanlinghu Formation) ichnoassemblage includes 15 ichnospecies in 12 ichnogenera at the studied sections: Arenicolites isp., Beaconites isp., Chondrites isp., Diplocraterion isp., Furculosus carpathicus, Gyrochorte isp., Monocraterion tentacultum, Palaeophycus isp., Planolites montanus, Planolites beverleyensis, Rhizocorallium isp., Taphrhelminthopsis cf. podhalensis. Thalassinoides isp., Thalassinoides saxonicus, and problematica. Moreover, Arenicolites isp., Beaconites isp., Gordia isp., Rugicirichnus amorphous, and Planolites montanus have been reported from the Nanlinghu Formation elsewhere in the Lower Yangtze region (Bi et al., 1996; Table 1). Post-extinction ichnodiversity was rather low (1–2 ichnogenera) throughout the Griesbachian–early Smithian interval and abruptly increased in late Smithian. Ichnodiversity underwent a step-wise increase from the Griesbachian–early Smithian to the late Smithian to the Spathian. The regional trace-fossil data from the literature also exhibit the same ichnodiversity pattern throughout the Griesbachian to Spathian (Fig. 16A). It should be noted that palaeo-oceanic environmental amelioration may result in an increase in biodiversity (Chen et al., 2007) and ichnodiversity (Beatty et al., 2008; Zonneveld et al., 2010) in the aftermath of the end-Permian crisis. In the studied areas, ichnodiversity increased significantly in the latest Smithian at Chaohu (Fig. 2) and in the early phase of the late Smithian at Yashan (Fig. 3). The former diversification happened in a proximal ramp setting near storm wave base. The same environmental setting occurred in Dienerian in Chaohu and in Dienerian–earliest Smithian in Yashan. However, no significant increase in ichnodiversity occurred in that time. The latter ichnoassemblage diversification took place at a highly evaporitic marginal sea setting, which is much more deleterious than the proximal ramp habitat of early Smithian age in the same area. Consequently, post-extinction diversification of ichnoassemblages in the studied areas was not due to habitat amelioration in the aftermath of the end-Permian crisis. 6.3. Size variations among ichnotaxa Trace fossils on more than 10 bedding planes were measured to determine the size distribution of the burrow diameters of Arenicolites, Beaconites, Chondrites, Diplocraterion, Gordia, Furculosus, Gyrochorte, Rhizocorallium, Palaeophycus, Planolites, Thalassinoides, and Treptichnus throughout the Early Triassic epoch. In particular, both Arenicolites and Planolites occur in numerous horizons throughout the Lower Triassic succession. The broad stratigraphical distributions of these two ichnogenera allowed comparisons of burrow size of the same ichnogenus throughout the Early Triassic. The smallest Planolites burrows occurred in the Griesbachian to early Smithian interval; the mean burrow diameter for four horizons at the Yinkeng Formation was 1.1 mm (n = 37) and the greatest burrow diameter is 2.5 mm (Fig. 15B). Burrow sizes of the late Smithian Planolites still remained rather small, with mean and maximum burrow diameters reaching 1.5 mm and 3.0 mm, respectively (Fig. 15C). The earliest Spathian exhibits a significant increase in size for Planolites burrows, and burrow sizes increased rapidly during the Spathian, as indicated by mean and maximum burrow diameter values (Fig. 15H). The Changhsingian Planolites burrows are larger than the Griesbachian–Smithian burrows (Fig. 15H), suggesting an impact of the P/Tr crisis on the tracemakers. The Smithian–Spathian also marked burrow size changes of Arenicolites (Fig. 10E). Although there is no record of Arenicolites in the Griesbachian–early Smithian strata, this ichnogenus has the same burrow size variation pattern as Planolites in the Smithian–Spathian interval, showing both mean and maximum burrow diameters increased rapidly within the early Spathian (Fig. 10E). Furthermore, Palaeophycus had much larger burrows in the early Spathian (Fig. 12A) than in the late Smithian (Fig. 12B). The mean and

Z.-Q. Chen et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 299 (2011) 449–474

maximum burrow diameters of Thalassinoides in the late Spathian are slightly greater than those in the early Spathian (Fig. 12C–D). Thus, these ichnogenera demonstrate an increase in their burrow sizes during the Spathian. Trace-fossil size has been a proxy for palaeoenvironmental conditions (Pruss and Bottjer, 2004; Savrda and Bottjer, 1987; Twitchett, 1999). In general, small-sized traces are usually found in poorly oxygenated sediments (Savrda and Bottjer, 1987), brackish environments (Buatois et al., 2005; Pemberton and Wightman, 1992; Pemberton et al., 1982), or habitats with low nutrient supply (Jumars and Wheatcroft, 1989). Thus, small traces can be characteristic of stressed environments (Marenco and Bottjer, 2008; Pruss and Bottjer, 2004; Twitchett, 1999; Zonneveld et al., 2010). The extremely small sizes of the Griesbachian–early Smithian traces suggest prolonged environmental stress following the P/Tr crisis (Pruss and Bottjer, 2004; Zonneveld et al., 2010). If all burrow sizes for all ichnogenera from the Griesbachian–early Smithian, late Smithian, early Spathian, and late Spathian substages are combined, significant increases in both the mean and maximum burrow diameters from the late Smithian to early Spathian are demonstrated (Fig. 16B). Palaeoenvironmental analysis reveals that the early Spathian habitats were the lower shoreface settings in both Chaohu and Yashan, while the late Smithian habitats were the proximal ramp near storm wave base in Chaohu but the proximal ramp between storm and fair-weather wave bases in Yashan. Of these, the proximal ramp setting between storm and fair-weather wave bases re-occurred in middle Spathian when a rather diverse ichnoassemblage containing some large and complex burrows in the same section. This means that the proximal ramp settings were also favourable for tracemakers to produce large and complex burrows. Consequently, significant increase in burrow sizes was not affected by the environmental setting that tracemakers inhabited. In addition, after analyzing the Griesbachian trace fossils preserved in various facies settings from western Canada, Beatty et al. (2008) and Zonneveld et al. (2010) found that the lower shoreface ichnoassemblages were extraordinarily abundant and diverse and also contain large, complex burrows. Similarly, significant increase in burrow sizes occurs in the lower shoreface ichnoassemblage of early Sapthian age at the studied sections. Has the lower shorefacies setting controlled the diversification of ichnoassemblages in the aftermath of the end-Permian crisis? It is true that the lower shoreface ichnoassemblage possessed the greatest ichnodiversity through the entire Early Triassic in Chaohu. However, the most diverse and abundant ichnoassemblage through the Early Triassic occurred in the highly evaporitic marginal sea setting in Yashan, where the more complex traces occurred in the proximal ramp habitat of middle Spathian age. As a result, significant increases in postextinction ichnodiversity, burrow sizes and complexity have not been affected by environmental changes. In contrast, the small post-extinction burrow sizes exemplify the Lilliput effect among trace-making organisms (Twitchett, 2006). Trace fossils from Lower Triassic strata in other parts of the world typically are larger during the final stage of the biotic recovery (Twitchett, 2006). Thus, the increased burrow sizes across the Smithian–Spathian boundary in South China may indicate some aspects of marine ecosystem recovery after the P/Tr crisis. 6.4. Trace fossil forms and complexity Other authors report that Griesbachian and Dienerian trace fossils from other Lower Triassic strata are dominated by small, simple, horizontal burrows of Planolites (Pruss and Bottjer, 2004; Twitchett and Barras, 2004). In South China, although trace fossils became more complex due to the presence of the slightly complex burrow system Treptichnus, a significant increase in trace fossil complexity occurred in late Smithian when the vertical burrows of Arenicolites, traces of Kouphichnium, and complex burrow networks of Treptichnus characterized the ichnoassemblage at the studied sections. In the Spathian,

471

even greater morphological diversification and complexity of trace fossils was marked by the addition of vertical and complex burrow networks such as Beaconites, Chondrites, Diplocraterion, Gyrochorte, Rhizocorallium, and Thalassinoides. Trace-fossil complexity, and thus behavioural complexity of tracemakers, was rather low during the Griesbachian–early Smithian because traces were simple, horizontal burrows (i.e. Planolites). Then, ichnoassemblages show an increase in complexity, varying from the late Smithian less complex burrow networks (i.e. Treptichnus) to more complicated burrow systems such as Rhizocorallium and Thalassinoides in the Spathian. Vertical burrows changed from the late Smithian relatively simple, small and shallow traces of Arenicolites, to the large, deep and backfilled traces such as Diplocraterion recorded in the Spathian. In particular, Rhizocorallium and Thalassinoides are complex burrow networks that have been interpreted by most authors as an indication of recovery of tracefossil assemblages after major biotic mass extinction (Morrow and Hasiotis, 2007; Pruss et al., 2005; Twitchett, 1999, 2006), although these traces also occasionally occur in the Griesbachian succession (Zonneveld et al., 2010). As state above, palaeo-oceanic environmental conditions were not the primary factors controlling the in crease in burrow complexity in the aftermath of the end-Permian mass extinction. 6.5. Infaunal tiering The tiering changes throughout the Early Triassic are indicated by depth of burrows into beds (Fig. 16C). The Griesbachian–early Smithian Planolites usually has small, horizontal burrows extending a mean depth of only 3 mm into the sediment indicating the lowest tiering level (sensu Droser and Bottjer, 1986). Some late Smithian vertical burrows (Arenicolites) and slightly complex burrow networks (Treptichnus) penetrated the sediment down to a mean depth of 8 mm and thus occupied the second tiering level. The Spathian vertical burrows (i.e., Arenicolites and Diplocraterion) and complex burrow networks (i.e., Chondrites, Gyrochorte, Rhizocorallium, and Thalassinoides) extended to a mean depth of 50 mm into the sediment, indicating a rather deep tiering level. Thus, tiering and the maximum depth of burrowing increased dramatically in the Smithian and Spathian and particularly across the Smithian–Spathian boundary (Fig. 16C). 6.6. Ecosystem restoration after the P/Tr mass extinction: a trace fossil proxy The post-extinction ichnoassemblage exhibited diversification first in the late Smithian when the number of ichnogenera increased from 2 to 8, up 300%, and from 5 to 12, up 140% in the studied areas and over the entire Lower Yangtze region, respectively. Ichnodiversity underwent a minor increase across the Smithian–Spathian boundary of only 50% and 16.7% in the studied areas and entire Lower Yangtze region, respectively. As such, the early–late Smithian boundary marks a pronounced change, at least in ichnodiversity, in the post-extinction ichnotaxa. Ichnodiversity increase also coincides with the appearance of vertical burrows, slightly complex burrow networks, and trackways. Vermicular limestone with an ii5 also occurs in the late Smithian. These features of trace fossil assemblages may indicate some rebound among tracemakers after the P/Tr crisis, but they do not reflect the final recovery of the ichnocoenoses because two other important proxies, burrow size and tiering level, still remained at considerably low levels in the late Smithian (Fig. 16C). Both the mean and maximum burrow diameters in the late Smithian are similar to those in earlier substages. Following Twitchett's (2006) model, the late Smithian trace fossil ecosystem may have reached recovery stages 2–3 because the ichnoassemblage still lacked large vertical burrows and really complex burrow networks. In contrast, a pronounced increase in both burrow size and tiering level across the Smithian–Spathian boundary (Fig. 16C), combined

472

Z.-Q. Chen et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 299 (2011) 449–474

with considerably higher ichnodiversity, trace-fossil complexity, and bioturbation, suggests even greater recovery of ichnocoenoses in the Spathian, and in the middle Spathian in particular. However, the Spathian ichnofauna is relatively less diverse than the Middle Triassic Muschelkalk ichnofauna from Germany which contains 41 ichnospecies in 28 ichnogenera (Knaust, 2007) and the Ladinian ichnofossil assemblage at Williston Lake, British Columbia, Canada which includes more than 45 ichnogenera (Zonneveld et al., 2001). Some burrows (i.e., Planolites and Arenicolites, Figs. 10 and 12) remained small at the beginning of the Spathian, and some large vertical burrows and complex burrow networks such as Rhizocorallium did not occur until late Spathian. Several lines of evidence suggest that late Smithian and late Spathian marine ichnocoenoses may be categorized as recovery stages 2 and 5, respectively (sensu Twitchett, 2006). This is in agreement with the recovery timing previously revealed from both northern Italy (Twitchett, 1999) and the western US (Fraiser and Bottjer, 2009; Pruss and Bottjer, 2004). In addition, Beatty et al. (2008) interpreted the occurrence of the anomalously diverse Griesbachian ichnofossil assemblages in northwest Pangea as the environmental control rather than the earlier suggestion of latitude control (Wignall et al., 1998). After undertaking further analysis of northwest Pangean ichnofossil assemblages, Zonneveld et al. (2010) concluded that the tracemakers can survive the P–Tr mass extinction and proliferated during the Early Triassic in the habitatble zone between the lower shoreface and the upper part of offshore, which also corresponds to the zone between fair-weather wave base and storm wave base. Ichnofossils from the studied sections in the Lower Yangtze region partly support the environmental control model (Beatty et al., 2008; Zonneveld et al., 2010) because an increase in ichnodiversity and bioturbation intensity occurred together in a shallow setting above storm wave base. In particular, ichnofossils tended to diversify in late Smithian at both Chaohu and Yashan. However, the marginal sea facies ichoassemblage at Yashan is much more diverse than the proximal ramp facies ichnofossil assemblage at Chaohu. Diverse ichnoassemblages and high bioturbation intensity are recorded in the lower and middle Nanlinghu Formation, which indicates proximal ramp and shallower environments. In addition to Beatty et al.'s (2008) habitable zone model, we propose herein that the marginal sea is also a favourable habitat for tracemakers to proliferate in the aftermath of the P–Tr mass extinction. Like the marginal sea to brackish facies ichnoassemblages in other geological periods (Buatois et al., 2005), the marginal sea facies ichnofossil assemblage was also rather diverse in the aftermath of the end-Permian mass extinction. 7. Conclusions A total of 15 ichnogenera (including a problematic ichnotaxon) and their palaeoecologic characteristics are reported from the Lower Triassic successions in the Lower Yangtze region, South China. The late Smithian exhibited an abrupt increase in ichnodiversity after the P/Tr crisis in the Lower Yangtze region. However, several lines of evidence, including extent of bioturbation, ichnodiversity, burrow size, tracefossil complexity, and tiering levels, suggest that marine ichnocoenoses only initially rebounded in the late Smithian, and the ecosystem did not recover until the late Spathian, which is in agreement with the previous studies elsewhere in the world. Like the traces recorded in lower shoreface setting in Griesbachian, ichnoassemblage may also diversify in marginal sea environment in the aftermath of the endPermian mass extinction. Acknowledgements We are grateful to John-Paul Zonneveld, an anonymous reviewer and journal editor Prof. Finn Surlyk for their comments and constructive suggestions, which have improved the quality of the paper. This study was supported by a discovery grant from the

Australian Research Council (DP0770938 to ZQC), and three research grants from the National Natural Science Foundation of China (No. 40830212 to JNT; No. 40872003 and 40972003 to LS Zhao). It is a contribution to the IGCP 572 “Permian–Triassic ecosystems”. References Bambach, R.K., Knoll, A.H., Wang, S.C., 2004. Origination, extinction, and mass depletions of marine diversity. Paleobiology 30, 522–542. Beatty, T.W., Zonneveld, J.P., Henderson, C.M., 2005. Late Permian and Early Triassic ichnofossil assemblages from the northwest margin of Pangea. Albertiana 33, 19–20. Beatty, T.W., Zonneveld, J.-P., Henderson, C.M., 2008. Anomalously diverse Early Triassic ichnofossil assemblages in northwest Pangea: a case for a shallow-marine habitable zone. Geology 36, 771–774. Bi, D.C., Guo, P.X., Qian, M.P., 1995. Discovery of limulid tracks from Qinglong Formation (Lower Triassic) in Nanling, Anhui. Acta Palaeontologica Sinica 34, 714–721. Bi, D.C., Guo, P.X., Qian, M.P., 1996. Trace fossils from Triassic Qinglong Formation of Lower Yangtze Valley. Acta Palaeontologica Sinica 34, 714–729. Bottjer, D.J., Ausich, W.I., 1986. Phanerozoic development of tiering in soft substrata suspension-feeding communities. Paleobiology 12, 400–420. Bottjer, D.J., Droser, M.L., 1994. The history of Phanerozoic bioturbation. In: Donovan, S.K. (Ed.), The Palaeobiology of Trace Fossils. John Wiley and Sons, West Sussex, pp. 155–176. Bottjer, D.J., Clapham, M.E., Fraiser, M.L., Powers, C.M., 2008. Understanding mechanisms for the end-Permian mass extinction and the protracted Early Triassic aftermath and recovery. GSA Today 18, 4–10. Bromley, R.G., 1996. Trace Fossils: Biology, Taphonomy and Applications, 2nd edition. Chapman & Hall, London. 361 pp. Bromley, R.G., Ekdale, A.A., 1984. Chondrites: a trace fossil indicator of anoxia in sediments. Science 224, 872–874. Buatois, L.A., Mangano, M.G., 1993. Ecospace utilization, paleoenvironmental trends, and the evolution of early nonmarine biotas. Geology 21, 595–598. Buatois, L.A., Gingras, M.K., MacEachern, J., Mangano, M.G., Zonneveld, J.-P., Pemberton, S.G., Netto, R.G., Martin, A., 2005. Colonization of brackish-water systems through time: evidence from the trace-fossil record. Palaios 20, 321–347. Carvalho, C.N.de, Viegas, P.A., Cachao, M., 2007. Thalassinoides and its producer: populations of Mecochirus buried within their burrow systems, Boca do Chapim Formation (Lower Cretaceous), Portugal. Palaios 22, 104–109. Chen, Z.Q., Shi, G.R., Kaiho, K., 2002. A new genus of rhynchonellid brachiopod from the Lower Triassic of South China and implications for timing the recovery of Brachiopoda after the end-Permian mass extinction. Palaeontology 45, 149–164. Chen, Z.Q., Tong, J., Kaiho, K., Kawahata, H., 2007. Onset of biotic and environmental recovery from the end-Permian mass extinction within 1–2 million years: a case study of the Lower Triassic of the Meishan section, South China. Palaeogeography, Palaeoclimatology, Palaeoecology 252, 176–187. Chen, Z.Q., Tong, J.N., Zhang, K.X., Yang, H., Liao, Z.T., Song, H.J., Chen, J., 2009. Environmental and biotic turnover across the Permian–Triassic boundary from shallow carbonate platform in western Zhejiang, South China. Australian Journal of Earth Sciences 56, 775–797. Chen, Z.Q., Tong, J., Liao, Z., Chen, J., 2010. Structural changes of marine communities over the Permian–Triassic transition: ecologically assessing the end-Permian mass extinction and its aftermath. Global and Planetary Change 73, 123–140. Droser, M.L., Bottjer, D.J., 1986. A semiquantitative field classification of ichnofabric. Journal of Sedimentary Petrology 56, 558–559. Dzik, J., 2005. Behavioral and anatomical unity of the earliest burrowing animals and the cause of the “Cambrian explosion”. Paleobiology 31, 503–521. Ekdale, A.A., Bromley, R.G., 2003. Paleoethologic interpretation of complex Thalassinoides in shallow-marine limestone, Lower Ordovician, southern Sweden. Palaeogeography, Palaeoclimatology, Palaeoecology 192, 221–227. Erwin, D.H., Pan, H.Z., 1996. Recoveries and radiations: gastropods after the Permo– Triassic mass extinction. In: Hart, M.B. (Ed.), Biotic Recovery from Mass Extinction Events: Geological Society Special Publication, 12, pp. 223–229. Fillion, D., Pickerill, R.K., 1990. Ichnology of the Upper Cambrian? to Lower Ordovician Bell Island and Waban Groups of eastern Newfoundland, Canada. Palaeontolographica Canadiana 7, 1–119. Fraiser, M.L., Bottjer, D.J., 2005. Fossil preservation during the aftermath of the endPermian mass extinction: taphonomic processes and paleoecological signals. In: Over, D.J., Morrow, J.R., Wignall, P.B. (Eds.), Understanding Late Devonian and Permian–Triassic Biotic and Climatic Events: Towards and Integrated Approach. Elsevier B.V., pp. 229–311. Fraiser, M.L., Bottjer, D.J., 2009. Opportunistic behavior of invertebrate marine tracemakers during the Early Triassic aftermath of the end-Permian mass extinction. Australian Journal of Earth Sciences 56, 841–857. Fraiser, M.L., Clapham, M.E., Bottjer, D.J., 2010. Mass extinctions and changing taphonomic processes. In: Allison, P.A., Bottjer, D.J. (Eds.), Taphonomy: Process and Bias Through Time, Second Edition. Springer–Verlag, Berlin, pp. 569–590. Fürsich, F.T., 1974. On Diplocraterion Torell, 1870 and the significance of morphological features in vertical, spreiten-bearing, U-shaped trace fossils. Journal of Paleontology 48, 952–962. Fürsich, F.T., 1975. Trace fossils as environmental indicators in the Corallian of England and Normandy. Lethaia 8, 151–172. Fürsich, F.T., 1998. Environmental distribution of trace fossils in the Jurassic of Kachchh (Western India). Facies 39, 243–272.

Z.-Q. Chen et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 299 (2011) 449–474 Gibert, J.M.De., Ekdale, A.A., 1999. Trace fossil assemblages reflecting stressed environments in the Middle Jurassic Carmel Seaway of central Utah. Journal of Paleontology 73, 711–720. Gordon, E.A., 1988. Body and trace fossils from the Middle–Upper Devonian Catskill magnafacies, southeastern New York, U.S.A. In: McMillan, N.J., Embry, A.F., Glass, D.J. (Eds.), The Devonian of the World: Canadian Society of Petroleum Geologists Memoir, 14, pp. 139–156. Hagadorn, J.W., Schellenberg, S.A., Bottjer, D.J., 2000. Paleoecology of a large Early Cambrian bioturbator. Lethaia 33, 142–156. Hakes, W.G., 1977. Trace fossils in Late Pennsylvanian cyclothems, Kansas. In: Crimes, T.P., Harper, J.C. (Eds.), Trace Fossils 2: Geological Journal Special Issue, 9. Seel House Press, Liverpool, U.K., pp. 209–226. Häntzschel, W., 1975. Trace fossils and problematica. In: Teichert, C. (Ed.), Treatise of Invertebrate Paleontology (2nd Edition), part W, Miscellanea, Supp 1. University of Kansas and Geological Society of America, Lawrence, Kansas. 269 pp. Heinberg, C., 1973. The internal structure of the trace fossils Gyrochorte and Curvolithus. Lethaia 6, 227–238. Jensen, S., 1997. Trace fossils from the Lower Cambrian Mickwitzia Sandstone, south– central Sweden. Fossil and Strata 42, 1–110. Jia, Z.H., Yang, F.M., Hong, T.Q., Zhang, L.W., 2010. The Smithian microstromatolites in Triassic in Chaohu, East China. Journal of Earth Sciences 21, 137–140 (Special issue). Jumars, P.A., Wheatcroft, R.A., 1989. Responses of benthos to changing food quality and quantity with a focus of deposit feeding and bioturbation. In: Berger, W.H., Smetacek, V.S., Wefer, G. (Eds.), Productivity in the Ocean: Past and Present. Wiley, Chichester, pp. 235–253. Knaust, D., 2004. Cambro–Ordovician trace fossils from the SW Norwegian Caledonides. Geological Journal 39, 1–24. Knaust, D., 2007. Invertebrate trace fossils and ichnodiversity in shallow-marine carbonates of the German Middle Triassic (Muschelkalk). In: Bromley, R., Buatois, L.A., Mángano, M.G., Genise, J., Melchor, R. (Eds.), EDS Sediment-Organism Interactions: A multifaceted ichnology: SEPM Special Publication, 88, pp. 223–240. Lehrmann, D.J., Ramezani, J., Bowring, S.A., Martin, M.W., Montgomery, P., Enos, P., Payne, J.L., Orchard, M.J., Hongmei, W., Jiayong, W., 2006. Timing of recovery from the end-Permian mass extinction: geochronologic and biostratigraphic constraints from south China. Geology 34, 1053–1956. Liu, Z.J., Wang, W.B., 1990. Lower Triassic trace fossils from the Lower Yangtze region and their environmental significance. Journal of Stratigraphy 14, 203–208. Löwemark, L., Schönfeld, J., Werner, F., Schöfer, P., 2004. Trace fossils as a paleoceanographic tool: evidence from Late Quaternary sediments of the southwestern Iberian margin. Marine Geology 204, 27–41. Luo, M., Shi, G., Gong, Y., 2007. Early Triassic trace fossils in Huaxi region of Guiyang and their implications for biotic recovery after the end-Permian mass extinction. Journal of Palaeogeography 9, 519–532. Maples, C.G., Archer, A.W., 1987. Redescription of Early Pennsylvanian trace fossil holotypes from the nonmarine Hindostan Whetstone Beds of Indiana. Journal of Paleontology 61, 890–897. Marenco, K.N., Bottjer, D.J., 2008. The importance of Planolites in the Cambrian substrate revolution. Palaeogeography, Palaeoclimatology, Palaeoecology 258, 189–199. Martin, K.D., 2004. A re-evaluation of the relationship between trace fossils and dysoxia. In: McIlroy, D. (Ed.), Application of Ichnology to Palaeoenvironmental and Stratigraphic Analysis: Geological Society of London, Special Publication, 228, pp. 141–156. Miller, S.A., 1889. North American Geology and Paleontology for the Use of Amateurs, Students and Scientists: Cincinnati. Western Methodist Book Concern, Ohio. 664 pp. Miller, M.F., Smail, S.E., 1997. A semiquantitative method for evaluating bioturbation on bedding planes. Palaios 12, 391–396. Morrow, J.R., Hasiotis, S.T., 2007. Chapter 36, Endobenthic response through mass extinction episodes: predictive models and observed patterns. In: Miller III, W. (Ed.), Trace Fossils: Concepts, Problems, Prospects. Elsevier, Amsterdam, pp. 575–598. Myrow, P.M., 1995. Thalassinoides and the enigma of Early Paleozoic open-framework burrow systems. Palaios 10, 58–74. Payne, J.L., Lehrmann, D.J., Wei, J.Y., Orchard, M.J., Schrag, D.P., Knoll, A.H., 2004. Large perturbations of the carbon cycle during recovery from the end-Permian extinction. Science 205, 505–509. Pemberton, S.G., 1992. Applications of Ichnology to Petroleum Exploration: A Core Workshop: Core Workshop, 17. Society for Sedimentary Geology, Tulsa, Oklahoma, pp. 1–429. Pemberton, S.G., Wightman, D.M., 1992. Ichnological characteristics of brackish water deposits. In: Pemberton, S.G. (Ed.), Application of Ichnology to Petroleum Exploration: Core Workshop, 17. Society of Economic Paleontologists and Mineralogists, pp. 141–167. Pemberton, S.G., Flach, P.D., Mossop, G.D., 1982. Trace fossils from the Athabasca Oil Sands, Alberta, Canada. Science 217, 825–827. Peng, Y., Tong, J., Shi, G.R., Hansen, H.J., 2001. The Permian–Triassic boundary stratigraphic set: characteristics and correlation. Newsletters on Stratigraphy 39, 55–71. Pruss, S.B., Bottjer, D.J., 2004. Early Triassic fossils of the western United States and their implications for prolonged environmental stress from the end-Permian mass extinction. Palaios 19, 551–564. Pruss, S.B., Corsetti, F.A., Bottjer, D.J., 2005. The unusual sedimentary rock record of the Early Triassic: a case study from the southwestern United States. Palaeogeography, Palaeoclimatology, Palaeoecology 222, 33–52. Rindsberg, A.K., Kopaska-Merkel, D.C., 2005. Treptichnus and Arenicolites from the Steven C. Minkin Paleozoic footprint Site (Langsettian, Alabama, USA). In: Buta, R.J., Rindsberg,

473

A.K., Kopaska-Merkel, D.C. (Eds.), Pennsylvanian Footprints in the Black Warrior Basin of Alabama: Monograph, 1. Alabama Paleontological Society, pp. 121–141. Rodriguez-Tovar, F.J., Perez-Valera, F., 2008. Trace fossil Rhizocorallium from the Middle Triassic of the Betic Cordillera, southern Spain: Characterization and environmental implications. Palaios 23, 78–86. Rodriguez-Tovar, F.J., Uchman, A., 2006. Ichnological analysis of the Cretaceous– Palaeogene boundary interval at the Caravaca section, SE Spain. Palaeogeography, Palaeoclimatology, Palaeoecology 242, 313–325. Roniewicz, P., Pienkowski, G., 1977. Trace fossils of the Podhale flysch Basin. In: Crimes, T.P., Harper, J.C. (Eds.), Trace Fossils 2. Seel House Press, Liverpool, pp. 273–288. Savrda, C.E., Bottjer, D.J., 1987. The exaerobic zone, a new oxygen-deficient marine biofacies. Nature 327, 54–56. Schlirf, M., Uchman, A., 2005. Revision of the ichnogenus Sabellarifex Richter, 1921 and its relationship to Skolithos Haldeman, 1840 and Polykladichnus Fürsich, 1981. Journal of Systematic Palaeontology 3, 115–131. Seilacher, A., 1967. Bathymetry of trace fossils. Marine Geology 5, 413–428. Seilacher, A., 2007. Trace Fossil Analysis. Springer, Berlin. 226 pp. Stanley, D.C.A., Pickerill, R.K., 1994. Planolites costriannulatus isp. nov. from the late Ordovician Georgian Bay Formation of southern Ontario, eastern Canada. Ichnos 3, 119–123. Tong, J.N., Yin, H.F., 2002. The Lower Triassic of South China. Journal of Asian Earth Sciences 20, 803–815. Tong, J., Zakharov, Y.D., Orchard, M.J., Yin, H., Hansen, H.J., 2003. A candidate of the Induan–Olenekian boundary stratotype in the Tethyan region. Science in China, Series D 46, 1182–1200. Tong, J., Zakharov, Y.D., Wu, S.B., 2004. Early Triassic ammonoid succession in Chaohu, Anhui Province. Acta Palaeontologica Sinica 43, 192–204. Tong, J., Zhao, L., Zuo, J., 2005. Yinkengian and Chaohuan of Lower Triassic and their boundary. Journal of Stratigraphy 29, 548–564. Tong, J., Zuo, J., Chen, Z.Q., 2007. Early Triassic carbon isotope excursions from South China: Proxies for devastation and restoration of marine ecosystems following the end-Permian mass extinction. Geological Journal 42, 371–389. Twitchett, R.J., 1999. Palaeoenvironments and faunal recovery after the endPermian mass extinction. Palaeogeography, Palaeoclimatology, Palaeoecology 154, 27–37. Twitchett, R.J., 2006. The palaeoclimatology, palaeoecology and palaeoenvironmental analysis of mass extinction events. Palaeogeography, Palaeoclimatology, Palaeoecology 232, 190–213. Twitchett, R.J., Barras, C.G., 2004. Trace fossils in the aftermath of mass extinction events. In: McIlroy, D. (Ed.), Application of Ichnology to Palaeoenvironmental and Stratigraphic Analysis: Geological Society of London, Special Publication, 228, pp. 395–415. Twitchett, R.J., Wignall, P.B., 1996. Trace fossils and the aftermath of the Permo–Triassic mass extinction: evidence from Northern Italy. Palaeogeography, Palaeoclimatology, Palaeoecology 124, 137–151. Uchman, A., 2005. Treptichnus-like traces made by inset larvae (Diptera: Chironomidae, Tipulidae). In: Buta, R.J., Rindsberg, A.K., Kopaska-Merkel, D.C. (Eds.), Pennsylvanian footprints in the Black Warrior Basin of Alabama. : Monograph, 1. Alabama Paleontological Society, pp. 143–146. Vossler, S.M., Pemberton, S.G., 1989. Ichnology and paleoecology of offshore siliciclastic deposits in the Cardium Formation (Turonian, Alberta, Canada). Palaeogeography, Palaeoclimatology, Palaeoecology 74, 217–239. Wang, S., 1987. Trace fossils and their sedimentary environments in the Lower Triassic Daye Formation of Huaxi area, Guiyang. Guizhou Geology 4, 454–460. Wang, S., 1997. Trace fossils from the Lower Triassic condensed sections in the Guiyang region, Guizhou. Sedimentary Facies and Palaeogeography 17, 58–62. Westergärd, A.H., 1931. Diplocraterion, Monocraterion and Scolithus from the Lower Cambrian of Sweden. Sveriges Geologiska Undersökning, Serie C 372, 1–25. Wignall, P.B., Hallam, A., 1993. Griesbachian (earliest Triassic) palaeoenvironmental changes in the Salt Range, Pakistan and southeast China and their bearing on the Permo–Triassic mass extinction. Palaeogeography, Palaeoclimatology, Palaeoecology 102, 215–237. Wignall, P.B., Morante, R., Newton, R., 1998. The Permo–Triassic transition in Spitsbergen; ∂δ13Corg chemostratigraphy, Fe and S geochemistry, facies, fauna and trace fossils. Geological Magazine 135, 47–62. Worsley, D., Mørk, A., 2001. The environmental significance of the trace fossil Rhizocorallium jenense in the Lower Triassic of western Spitsbergen. Polar Research 20, 37–48. Xu, D., Xing, Y., 1992. The Early Triassic conodont fauna in the Yashan area, Nanling County, Anhui Province. Regional Geology of China 1992 (4), 335–344. Yang, S.-P., 1988. Permian-Triassic flysch trace fossils from the Guoluo and Yushu regions, Qinghai. Acta Sedimentologica Sinica 6, 1–11. Yin, H., Ding, M., Zhang, K., Tong, J., Yang, F., Lai, X., 1995. Dongwuan–Indosinian (Late Permian–Middle Triassic) Ecostratigraphy of the Yangtze Region and its Margins. Science Press, Beijing. 338 pp. Yin, H., Zhang, K., Tong, J., Yang, Z., Wu, S., 2001. The Global Stratotype Section and Point (GSSP) of the Permian–Triassic Boundary. Episodes 24, 102–114. Zhang, K.X., Wu, S.B., Liu, Y.Q., 1992. Radiolarians and conodonts from the Dalong Formation at Hushan of Nanjing and their biofacies significance. Earth Science– Journal of China University of Geosciences 1992 (3), 19–25. Zhao, L., Orchard, M.J., Tong, J., Sun, Z., Zuo, J., Zhang, S., Yun, A., 2007. Lower Triassic conodont sequence in Chaohu, Anhui Province, China and its global correlation. Palaeogeography, Palaeoclimatology, Palaeoecology 252, 24–38. Zhao, L., Tong, J., Zhang, S., Sun, Z., 2008a. An update of conodonts in the Induan– Olenekian boundary strata at West Pingdingshan section, Chaohu, Anhui Province. Journal of the China University of Geosciences 19, 207–216.

474

Z.-Q. Chen et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 299 (2011) 449–474

Zhao, X.M., Tong, J.N., Yao, H.Z., Zhang, K.X., Chen, Z.Q., 2008b. Anachronistic facies in the Lower Triassic of South China and their implications to the ecosystems during the recovery time. Science in China, Series D–Earth Sciences 51, 1646–1657. Ziegler, A.M., Gibbs, M.T., Hulver, M.L., 1998. A mini-atlas of oceanic water masses in the Permian Period. Proceedings. Royal Society of Victoria 110, 323–344. Zonneveld, J.-P., Beatty, T.W., 2007. Ichnology of the Lower Triassic Blind Fiord and Bjorne Formations, Sverdrup Basin, Arctic Canada. Geological Society of America Abstracts with Programs 39, 206. Zonneveld, J.-P., Gingras, M.K., Pemberton, S.G., 2001. Trace fossil assemblages in a Middle Triassic mixed siliciclastic-carbonate marginal marine coastal depositional system, British Columbia. Palaeogeography, Palaeoclimatology, Palaeoecology 166, 249–276.

Zonneveld, J.-P., MacNaughton, R., Pemberton, G., 2002. Ichnology of the Lower Triassic Montney Formation, Kahntah River and Ring Border Fields, northeastern British Columbia. CSPG Diamond Jubilee Convention Abstracts of Technical Talks and Posters, p. 342. Zonneveld, J.-P., Henderson, C., MacNaughton, R.B., Beatty, T.W., 2004. Diverse ichnofossil assemblages from the Lower Triassic of northeastern British Columbia, Canada: evidence for a shallow marine refugium on the northwestern coast of Pangea. Geological Society of America, Abstracts with Programs 36, A336. Zonneveld, J.-P., Gingras, M.K., Beatty, T.W., 2010. Diverse ichnofossil assemblage following the P–T mass extinction, Lower Triassic, Alberta and British Columbia, Canada: evidence for shallow marine refugia on the northwestern coast of Pangaea. Palaios 25, 368–392.