Diplocraterion Parallelum from North China: Ethologic Significance and Facies Controls

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A Bollettino della Società Paleontologica Italiana, 56 (2), 2017, 117-125. Modena

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Middle Cambrian Diplocraterion parallelum from North China: Ethologic significance and facies controls

Li-Jun Zhang, Luis A. Buatois, M. Gabriela Mángano, Yong-An Qi & Chao Tai

L.-J. Zhang, Institute of Resources and Environment, Key Laboratory of Biogenic Traces & Sedimentary Minerals of Henan Province, Collaborative Innovation Center of Coalbed Methane and Shale Gas for Central Plains Economic Region, Henan Polytechnic University, 2001 Century Avenue, 454003 Jiaozuo, P.R. China; [email protected] L.A. Buatois, Department of Geological Sciences, University of Saskatchewan, 114 Science Place, CDN-S7N 5E2 Saskatoon, Saskatchewan, Canada; [email protected] M.G. Mángano, Department of Geological Sciences, University of Saskatchewan, 114 Science Place, CDN-S7N 5E2 Saskatoon, Saskatchewan, Canada; [email protected] Y.-A. Qi, Institute of Resources and Environment, Key Laboratory of Biogenic Traces & Sedimentary Minerals of Henan Province, Collaborative Innovation Center of Coalbed Methane and Shale Gas for Central Plains Economic Region, Henan Polytechnic University, 2001 Century Avenue, 454003 Jiaozuo, P.R. China; [email protected] C. Tai, Institute of Resources and Environment, Key Laboratory of Biogenic Traces & Sedimentary Minerals of Henan Province, Collaborative Innovation Center of Coalbed Methane and Shale Gas for Central Plains Economic Region, Henan Polytechnic University, 2001 Century Avenue, 454003 Jiaozuo, P.R. China; [email protected]

KEY WORDS - Diplocraterion, Cambrian, Standardized, North China, Mianchi.

ABSTRACT - The middle Cambrian Mantou Formation of the Mianchi section of western Henan Province, North China provides an opportunity to address infaunal colonization during the aftermath of the Cambrian explosion. The trace fossil Diplocraterion is common within intertidal very fine-grained sandstone of the Member II of the Mantou Formation (Stage 5).Diplocraterion consists of perpendicular to bedding plane, lined U-shaped burrows with well-developed marginal tubes, having distinctive, dark and light colored, laminae forming retrusive and protrusive spreiten reflecting the activity of a suspension feeder. No scratches are observed on the wall of the marginal tubes. SEM-EDS mapping detection shows that the dark laminae are dominated by Si, Al and Fe, whereas the light laminae are dominated by Ca and Si. Based on ichnological, stratigraphical and SEM-EDS features, it is suggested that the specimens of Diplocraterion studied here results from the equilibrium behavior and that the delayed appearance of this ichnotaxon in North China is due to lack of appropriate siliciclastic facies.

RIASSUNTO - [Diplocraterion parallelum dal Cambriano medio della Cina Settentrionale: significato etologico e controllo di facies] - La Formazione di Mantou (Cambriano), affiorante nella sezione di Mianchi (Provincia occidentale di Henan, Cina Settentrionale), permette di discutere la colonizzazione infaunale durante l’esplosione del Cambriano. La traccia fossile Diplocraterion è comune nelle arenarie fini del Membro II della Formazione di Mantou (Stage 5). Diplocraterion consiste di tane ad U perpendicolari alla stratificazione; gli esemplari sono caratterizzati da rivestimento ed esibiscono tubi marginali ben sviluppati. Sono presenti lamine scure e chiare che formano spreiten retrusivi e protrusivi, riflettenti l’attività di un organismo sospensivoro. Non si osservano bioglifi sulle pareti dei tubi marginali. La mappatura SEM-EDS rivela che le lamine scure sono dominate da Si, Al e Fe, mentre le lamine chiare sono contraddistinte da Ca e Si. Sulla base delle caratteristiche icnologiche, stratigrafiche e dell’analisi SEM-EDS, si suggerisce che gli esemplari di Diplocraterion qui studiati riflettano un comportamento di equilibrio. La mancanza di appropriate facies siliciclastiche spiega la comparsa ritardata di questo icnotaxon nella Cina Settentrionale.

INTRODUCTION 1986; Olóriz & Rodríguez-Tovar, 2000; Šimo & Olšavský, 2007; Rodríguez-Tovar & Pérez-Valera, 2013; Martin et An abrupt increase in the degree and depth of al., 2016). This distinctive trace fossil ranges from early bioturbation occurred during the early Cambrian, Cambrian to Holocene in age. It occurs in a wide variety of corresponding to the rapid radiation of metazoans, depositional settings, involving carbonate and siliciclastic which led to the first mixground ecosystems in an event rocks. This ichnotaxon is often used for environmental referred to as the “Agronomic Revolution” (Seilacher & characterization of shallow-marine depositional systems Pflüger, 1994; Seilacher, 1999). Major components of (Cornish, 1986; Šimo & Olšavský, 2007; Mángano this ecological revolution include the first appearance et al., 2013; Rodríguez-Tovar & Pérez-Valera, 2013). of vertical burrows and the development of tiered Diplocraterion typically provides valuable information infaunal communities (Seilacher & Pflüger, 1994; on environmental factors, such as hydrodynamic energy Mángano & Buatois, 2014, 2016, in press). In addition, level, substrate consistency, rates of sedimentation and the early Cambrian reveals several profound biotic and erosion, and distribution of organic matter (Goldring, environmental events that progressively influenced 1964; Cornish, 1986; Olóriz & Rodríguez-Tovar, microbialites, such as local occurrence of stromatolites 2000; Rodríguez-Tovar & Pérez-Valera, 2013) and it is and thrombolites (Dornbos et al., 2005; Riding, 2011). regarded as a key ichnotaxon (as are Rhizocorallium and The well-known ichnogenus Diplocraterion is one of Thalassinoides) to reflect the level of benthic ecosystem the common trace fossils globally (Fürsich, 1974; Cornish, complexity and recovery during evolutionary events,

ISSN 0375-7633 doi:10.4435/BSPI.2017.14 118 Bollettino della Società Paleontologica Italiana, 56 (2), 2017 such as the Cambrian explosion and the end-Permian collected from the Cambrian Series 3 Member II of the mass extinction (Twitchett & Barras, 2004; Mángano & Mantou Formation (M2) of the Mianchi section exposed Buatois, 2014). at 34°49ʹ13ʺ N, 111°53ʹ15ʺ E, which mainly consists of The middle Cambrian Mantou Formation (Stage muddy siltstone and very fine-grained sandstone and thin- 5) in the Mianchi section (western Henan Province, bedded limestone (Fig. 1). North China) contains well-preserved Diplocraterion The Mantou Formation is subdivided into three parallelum Torell, 1870. Here we report several macro- members. Member I (M1) mainly comprises grey- and micro-features of Diplocraterion, providing new yellow thin-bedded shale and siltstone interbedded evidence pertaining to the behavior of the Diplocraterion with limestone, argillaceous limestone and laminar tracemaker, its ecological significance, and the relationship algal limestone. Member II (M2) consists of grey thick- between tracemaker and substrate in the aftermath of the bedded oolitic limestone and argillaceous limestone Cambrian explosion. intercalating with grey-brown thin-bedded shale and sandstone. Member III (M3) is mainly composed of thin- and medium-bedded oolitic limestone, nodular GEOLOGICAL SETTING limestone and thrombolites intercalating with grey-green thin-bedded shale and siltstone. Body fossils are common Excellent lower Paleozoic outcrops, particularly of in the Mantou Formation, especially abundant trilobites, Cambrian strata, occur in the area of Mianchi in Henan and small shelly fauna in the shale and limestone (Pei, Province, North China (Fig. 1). The studied section is 2000). The trilobite fauna indicates a Series 2 age for M1 located in the northwest part of Henan Province and and a Series 3 age for M2 and M3 (Fig. 1c; Pei, 2000; belongs to the Cambrian western Henan subarea (Pei, Peng, 2009). 2000). Cambrian strata are exposed along the Rencun The Mantou Formation conformably overlies the Mountain ridge on a ca. 5 km long section. Cambrian lower Cambrian Zhushadong Formation and underlies the strata in this area were deposited along a continental middle Cambrian Zhangxia Formation. The Zhushadong margin, forming laterally extensive tidal flats during times Formation consists of pebble conglomerate, silty of tectonic quiescence. In the Mianchi section, Cambrian mudstone and dolomitic limestone with scarce fossils, strata are up to 800 m thick and range from Series 2 to most likely deposited in a restricted shallow-marine Furongian. The trace fossils described in this paper were environment periodically exposed subaerially in a

Fig. 1 - a-b) Maps showing the Cambrian subarea in Henan and the study section location in North China. NCB = North China Block, SCB = South China Block, TB = Tarim Block, I1, I2 and I3 represent the stratigraphic subarea of Cambrian in Henan. I1 = Taihan Mountain, I2 = western Henan, I3 = eastern Henan. c) Generalized stratigraphic column of the Cambrian strata in the Mianchi section, North China. Star shows the occurrence of Diplocraterion ( = Dip). L.-J. Zhang et alii - Middle Cambrian Diplocraterion parallelum from North China 119

in Jiaozuo, China. The scanning electron microscope provides element and micro-scale morphological features of Diplocraterion which allows a more detailed discussion of its morphology and ethology.

RESULTS

Diplocraterion parallelum The investigated Diplocraterion parallelum specimens occur on the bedding plane of silty very fine-grained sandstone with carbonate cement. They consist of perpendicular to bedding, U-shaped, spreiten-bearing burrows with well-developed marginal tube (Fig. 3). On the bedding surface, the spreite consists of alternating dark and light laminae (Fig. 3b). The overall shape of the marginal tube in planar view is semi-circular (Fig. 3c). Examination of the spreite in thin section shows that the lining is argillaceous, and microscope analysis indicates the presence of illite. Nearly all individuals are truncated upward by erosion surfaces. Specimens are Fig. 2 - Detailed section of the trace fossil-bearing interval (c.a. 1 very shallow, penetrating down and up to the top of the m thick) in the basal part of the Mantou Formation (Member II, overlying muddy layer (Fig. 2). No scratch marks are M2). S = Sandstone sheet, BI = strong bioturbation bed, B = muddy preserved on the marginal tube. Burrow width is 8-23 breccia bed, MS = muddy siltstone sheet, es = erosion surface, cs mm and burrow depth is 2-4 mm. The diameter of the = cross lamination, pl = parallel lamination, Dip = Diplocraterion. marginal tube (or limbs) is constant in each specimen (3-5 mm). The maximum depth of Diplocraterion parallelum is difficult to estimate because they were truncated during seasonally dry, probably subarid, climate. The Zhangxia numerous episodes of erosion. No other trace fossils were Formation mainly consists of grey thick bedded oolitic found in this layer. limestone intercalating with thin-bedded oolitic limestone in the lower part and grey-yellow thin-bedded dolostone SEM-EDS features in the upper part. This unit was formed in an open tidal- SEM-EDS analysis indicates that light laminae influenced carbonate platform. in Diplocraterion parallelum spreite are commonly The trace fossils described in this paper occur in the relatively thin (750 μm) and consist of calcareous siltstone lower part of M2 (Fig. 1), which records a transition with high percentage of calcium (Fig. 4d). Dark laminae from restricted platform (the Zhushadong Formation and are commonly thick (1 mm) and contain more muddy, M1) to a storm-affected tidal flat environment (M2 and clay minerals around siliceous spheres, displaying mostly M3). The ichnofossil-bearing interval (Fig. 2) starts with coarse and many empty pores (Fig. 4a) in the surface of cross-bedded, very fine-grained sandstone, overlain by dark laminae under the SEM. Through the SEM mapping, a 10 cm-thick siltstone unit with moderate bioturbation dark laminae were dominated by Si, Al and Fe, whereas (Bioturbation index [BI] = 4), which, in turn, is overlain light laminae were dominated by Ca and Si (Fig. 4c-e). by a 8 cm-thick, parallel-laminated, muddy siltstone. The siliceous spheres were only found within the dark Above this, thinner bedded siltstone is intercalated with laminae of Diplocraterion (Fig. 4b). abundant mudstone breccia, which, in turn, is overlain by a 4 cm-thick siltstone and a 5 cm-thick, erosively based, wave-ripple cross-laminated and parallel-laminated, DISCUSSION silty sandstone, which is interpreted as storm deposits (tempestites). Diplocraterion occurs at the top of this Diplocraterion ethology and tracemakers layer. Diplocraterion typically occurs in Phanerozoic strata formed in the high-energy intertidal and uppermost subtidal zone of tide-dominated shorelines (e.g., Fürsich, METHODS 1974, 1975; Cornish, 1986; Mángano & Buatois, 2004a) or in nearshore areas (shoreface sandstones to Diplocraterion and the host strata were sampled, offshore tempestites) of wave-dominated shorelines cleaned and coated with carbon and gold, respectively. (e.g., Stanistreet, 1989; Gaillard & Racheboeuf, 2006). Samples were analyzed both petrographically and Occurrences in other depositional settings, such as deltaic chemically in a Quanta 250 field emission gun scanning (e.g., Mason & Christie, 1986), estuarine (e.g., Gingras et electron microscope (FEI Quanta 250 FEG-SEM) al., 1999), deep-marine (e.g., Buatois & López-Angriman, equipped with a Bruker Nano with X-Max 30 mm2 detector 1992) and even continental (e.g., Kim & Paik, 1997), have energy dispersive X-ray spectrometer (Bruker Quantax been documented as well. Diplocraterion was shown to 200 XFlash 6|30 EDS) at the Key Laboratory of Biogenic be common in Phanerozoic examples of the Skolithos and Traces & Sedimentary Minerals of Henan Province Glossifungites Ichnofacies (Buatois & Mángano, 2011). It 120 Bollettino della Società Paleontologica Italiana, 56 (2), 2017

Fig. 3 - Morphology of Diplocraterion in planar view. a) Dense Diplocraterion on the bedding surface. b) The opposite concave laminae in a spreite as indicated by white arrow. D1 and D2 represent early and late suites of Diplocraterion, respectively. c) Marginal tube in planar view. Yellow arrow shows the lining of Diplocraterion. d) Early suite of Diplocraterion (D1) crosscut by a late suite (D2). e) The oblique view of the collected specimen showing the marginal tube (MT) on the bedding surface (BS) and the spreite in cross section (CS). f) Close-up of view of the spreite in the cross section. has been extremely useful as an aid to the interpretation different morphologies of Diplocraterion in cross section of sequence-stratigraphic surfaces, stratal patterns, and and planar view (i.e., the opposite concave laminae in depositional environments (Olóriz & Rodríguez-Tovar, the planar view, which represented the retrusive spreite 2000; Šimo & Olšavský, 2007; Mángano et al., 2013; created by the tracemaker) (Fig. 5). Bromley & Hanken Rodríguez-Tovar & Pérez-Valera, 2013; Singh et al., (1991) suggested that downward adjustment would 2014). Diplocraterion probably represents the activity represent a minimal modification of the Diplocraterion of infaunal, suspension feeding invertebrates (Fürsich, tracemaker, whereas upward adjustment behavior 1974; Häntzschel, 1975; Ekdale & Lewis, 1991; Seilacher, might have taken a longer time to become incorporated 2007). into the repertoire of the burrower. The occurrence of Changes in dimensions of the spreite are interpreted Diplocraterion parallelum in middle Cambrian strata of as being a consequence of the growth of the tracemaker North China demonstrates that downward and upward (Bromley & Hanken, 1991). Variations in dimensions burrow adjustments were attained early in the evolutionary of the trace fossil reflect the interplays between growth history of this ichnotaxon. of the animal and variation in rate of deposition and The Diplocraterion studied here are the oldest erosion. Goldring (1964) demonstrated the response of spreite trace fossils recorded in the Cambrian of North the D. parallelum producer to the interplay of erosion China. Diplocraterion most likely reflects colonization and deposition, resulting in yoyo-like combinations of immediately after deposition from a storm event. The protrusive and retrusive elements of spreite construction. absence of the funnel indicates subsequent erosion. Two Chakraborty & Bhattacharya (2013) documented the possible suites of Diplocraterion (D1-D2) have been L.-J. Zhang et alii - Middle Cambrian Diplocraterion parallelum from North China 121

Fig. 4 - Scanning electron microscope (SEM) images of the dark and light laminae within the Diplocraterion spreite. a) Boundary of dark and light laminae. The white dotted line box is the mapping scan area. b) Siliceous spheres in the dark laminae. The white cross bar represents the detected point of X-ray. c-e) Elemental maps showing the component differences in dark and light laminae. DL = dark laminae, LL = light laminae. distinguished on the basis of crosscutting relationships Body fossils (e.g., trilobites) are present in the lower part (Fig. 3b-d). D1 is locally deformed and is cross-cut by D2. of the Mantou Formation. Well-preserved Thalassinoides The Diplocraterion tracemaker burrowed in several stages. occurs in the Stage 2 Zhushadong Formation (Zhang et First, the tracemaker burrowed downwards and cached al., 2017). Body fossils in the Member II of the Mantou food obtained from the surface within freshly-exposed Formation comprise mainly trilobites (e.g, Redlichia soft sediment. Subsequently, the burrower constructed chinensis Walcott, 1905, Yaojiayuella granosa Walcott, the retrusive spreiten during normal equilibrium behavior. 1905, Hsuchuangia triangularis Zhang et Wang, 1985). All of these features support the interpretation of The presence of Diplocraterion suggests that other types Diplocraterion parallelum as recording the equilibrium of invertebrates, most-likely soft-bodied, were part of the behavior of the tracemaker, which adjusted the position ecosystem. Candidates proposed as possible tracemakers of the burrow in response to aggradation and erosion. include polychaetes (Schäfter, 1972), echiurids (Schäfter, 1972) and amphipods (Seilacher, 2007). However, U-shaped burrows with spreite have also been attributed to the activities of crustaceans in Triassic and Cretaceous rocks (Olóriz & Rodríguez-Tovar, 2000; Rodríguez-Tovar & Perez-Valera, 2013). The U-shaped morphology of the Cambrian specimens may have represented a behavioral function similar to modern examples, therefore recording equilibrium traces. The primary ecologic function of U-shaped burrow is most likely for protection in a turbulent environment. Vertical burrowing provides the organism protection from fluctuations in temperature, salinity, and desiccation. Fig. 5 - Sketch map showing the morphology of Diplocraterion These environmental stress factors possibly affected (modified from Šimo & Olšavský, 2007 and Chakraborty & the behaviors of the invertebrate fauna of the Mantou Bhattacharya, 2013). a) 3D morphology of Diplocraterion including Formation tidal flat. marginal tube (MT) and spreiten (SP). b) Horizontal view of the protrusive spreiten. Marginal tube appears as an ellipse at both ends Environmental conditions and colonization trends and the backfill structure is represented by opposite convexities showing alternation of dark and light laminae. c) Horizontal view The use of trace fossils as a tool to interpret sediment of the retrusive sprieten. The laminated structure is represented by reworking, sedimentation rate, current intensity, and opposite concavities showing alternation of dark and light laminae. substrate stability and coherence has been known for 122 Bollettino della Società Paleontologica Italiana, 56 (2), 2017

Ichnospecies Stratigraphical unit and location Age Host rock Depositional environment References

Donkey Creek beds, Mt Baldwin Diplocraterion isp. early Cambrian Sandstone Tidal flat Walter et al., 1989 Fm. (Australia) Diplocraterion isp. Ocieseki Sandstone Fm. (Poland) early Cambrian Sandstone Shallow marine Orlowski, 1989 Diplocraterion Parachilna Fm. (Australia) early Cambrian Sandstone Lowe intertidal Mount, 1989 parallelum Diplocraterion isp. Badaowan Mb. (China) early Cambrian Siltstone Subtidal Crimes & Jiang, 1986

Diplocraterion isp. Lake Louis Fm. (Canada) early Cambrian Sandstone Inner shelf Desjardins et al., 2010

Diplocraterion isp. Lake O’Hara Mb. (Canada) early Cambrian Sandstone Subtidal to inner shelf Desjardins et al., 2010

Diplocraterion isp. Menin-1 bore hole (Czech Republic) early Cambrian Siltstone-sandstone Shallow marine Vavrdova et al., 2003 Diplocraterion Bromley & Hanken, Dividalen Group (Norway) early Cambrian Sandstone Shallow marine parallelum 1991 Diplocraterion Clausen & Balka Sandstone (Denmark) early Cambrian Sandstone Offshore parallelum Vilhjálmsson, 1986 early-middle Diplocraterion isp. Parahio Fm. (India) Siltstone-sandstone Subtidal flat Singh, 2009 Cambrian Diplocraterion early-middle Shallow subtidal and Mángano & Buatois, Campanario Fm. (Argentina) Sandstone parallelum Cambrian intertidal 2004a Hofmann et al., 2012; Diplocraterion isp. Hanneh Member (Jordan) middle Cambrian Sandstone Small compound dunes Mángano et al., 2013 Diplocraterion isp. Ladoga Fm. (Russia) middle Cambrian Sandstone Shallow marine Natalin et al., 2010

Diplocraterion isp. Mb. B, Dhaulagiri Fm. (India) middle Cambrian Siltstone Shallow marine Singh et al., 2014 Kowalewski & Demko, Diplocraterion isp. Bolsa Quarizite (USA) middle Cambrian Sandstone Shallow marine 1996 Hickory Sandstone Mb., Tidal-channel, Diplocraterion isp. late Cambrian Sandstone Cornish, 1986 Riley Fm. (USA) tidal-sand-bar, tidal flat Diplocraterion isp. Gushan Fm. (China) late Cambrian Limestone Carbonate platform Zhou et al., 2011 Diplocraterion Bjerstent & Erickson, Postdam sandstone (USA) late Cambrian Sandstone Tidal flat parallelum 1989 Tilcara Mb., Santa Rosita Fm. Mángano & Buatois, Diplocraterion isp. late Cambrian Sandstone Tidal-dominated estuarine (Argentina) 2003 Upper offshore to offshore Mángano & Buatois, Diplocraterion isp. San Bernardo Fm. (Argentina) Early Ordovician Sandstone transition 2003 Diplocraterion Calcareous Bjerstent & Erickson, Theresa Fm. (USA) Early Ordovician Subtidal and pertidal parallelum sandstone 1989 Diplocraterion isp. Isthmus Bay Fm. (Canada) Early Ordovician Limestone Tidal flat Pratt & James, 1986

Diplocraterion isp. Badger Flat Fm. (USA) Middle Ordovician Limestone Peritidal Ross et al., 1989

?Diplocraterion isp. Dobrotivá Fm. (Czech Republic) Middle Ordovician Sandstone Tidal flat Mikuláš,1993

Diplocraterion isp. Stairway Sandstone (Australia) Middle Ordovician Sandstone Nearshore Davies et al., 2011 Diplocraterion Calcareous Stanley & Pickerill, Georgian Bay Fm. (Canada) Late Ordovician Subtidal parallelum sandstone 1993 Lower Cwm Rhiwarth siltstone Diplocraterion isp. Late Ordovician Siltstone Shallow marine Pickerill, 1977 (Wales) Diplocraterion isp. Queenston Fm. (Canada) Late Ordovician Limestone Tidal flat Brogly et al., 1998

Tab. 1 - Selected Cambrian-Ordovician Diplocraterion occurrences. many years (Pemberton & Frey, 1984; Pervesler & is consistent with the energy gradient along a tidal flat Uchman, 2004; Zonneveld et al., 2012; Pandey et al., depositional profile, suggesting shoreline progradation 2014; Zhang, 2014). Sedimentation rate, hydrodynamic (Mángano & Buatois, 2004a, b). Food particles were kept energy level and substrate consistency are considered in suspension by uni-directional currents and oscillatory key environmental factors controlling in the development flow, favoring suspension-feeding strategies. However, and characteristics of Diplocraterion (Fürsich, 1975; during times of continuous bedform migration, organisms Pemberton & Frey, 1984; Cornish, 1986; Gingras et al., were not able to colonize the shifting substrate (Desjardins 1999; Olóriz & Rodríguez-Tovar, 2000; Šimo & Olšavský, et al., 2012). 2007; Loughlin & Hillier, 2010). The dark laminae consist of Al and Si, whereas the An overall upward decrease in hydraulic energy and light laminae are composed of Ca and Si. Significant sedimentation rate is inferred in the studied interval, which numbers of siliceous spheres are present in the dark L.-J. Zhang et alii - Middle Cambrian Diplocraterion parallelum from North China 123 laminae. The components of the light laminae are similar consistency of the sea floor may have favored burrowing to the surrounding rock. Composition of the spreite by providing a more cohesive sediment, therefore suggests that the tracemaker has responded to the interplay promoting burrow stability. of erosion and deposition. The tracemaker penetrated into the sediment during the initial waning phase of the storm, and the spreite was subsequently formed in response to CONCLUSIONS substrate aggradation following the storm event. The delayed appearance of Diplocraterion, an The trace fossil Diplocraterion parallelum is ichnotaxon present since Cambrian Age 2 elsewhere described from shallow-marine deposits of the middle (Mángano & Buatois, 2014), in the Mantou Formation Cambrian Stage 5 Mantou Formation in North China. This (Age 5) may have resulted from facies constrains (Tab. 1). ichnotaxon comprises shallow, perpendicular to bedding The presence of U-shaped vertical burrows underscores plane, U-shaped spreite burrows enclosed by a marginal the ability of infaunal organisms to colonize sandy tube, with dark and light laminae in planar view. SEM- shorelines. In contrast, shallow carbonate substrates were EDS analysis indicates that the dark laminae of the spreite apparently not suitable for infaunal colonization by the consist of Al, Si and many silicon spheres, whereas the Diplocraterion producers. Due to long time denudation, light laminae and surrounding rocks consist of Ca and deposition in the Mianchi area started during Cambrian Si. The delayed appearance of Diplocraterion in North Age 3 (Peng, 2009). Following an overall transgression, China was controlled by facies constrains, reflecting the a carbonate platform (Zhushadong Formation) was dominance of carbonate deposition in the study area. first established, then tidal flat were formed (Mantou Formation), and finally deposition took place in a carbonate platform (Zhangxia Formation). Accordingly, ACKNOWLEDGEMENTS carbonate substrates might be suitable for survival of microbial-dominated ecosystems, as indicated by the This work is a contribution to the call for papers arising from the Fourth International Congress on Ichnology “Ichnia 2016 - widespread occurrence of stromatolites and thrombolites Ichnology for the 21st century: (palaeo)biological traces towards in early transgressive carbonate platforms from the sustainable development”, held in Idanha-a-Nova (Portugal), 6-9 Zhushadong Formation and Member I of the Mantou May 2016. Formation (M1). Financial support for this study was provided by the Diplocraterion appeared slightly later than Arenicolites Natural Science Foundation of China (41602112, 41472083, in the early Cambrian (e.g., Bromley & Hanken, 1991), 41290260), China Postdoctoral Science Foundation Funded Project with the spreite representing an innovation not present in (2016M592288), the Key Scientific Research Fund of University the latter. Diplocraterion is also as a key ichnogenus to of Henan Province (17A17001), the Specialized Research Fund show the dramatic increase in depth of bioturbation in the for the Doctoral Program of Higher Education (20134116120002), the Key Scientific Research Fund of University of Henan Province early Cambrian. The appearance of deep-tier suspension (17A170001) and Program for Innovative Research Team (in Science feeders (e.g., the tracemakers of Skolithos, Diplocraterion, and Technology) in University of Henan Province (16IRTSTHN014) and Arenicolites) in Cambrian Age 2 had a major impact to Zhang and Qi, and by the Natural Sciences and Engineering in marine ecosystems, coupling the plankton productivity Research Council of Canada (NSERC) Discovery Grants 311727-15 and the benthos, playing a role in the turnover from and 311726-13 awarded to Mángano and Buatois, respectively. We matgrounds to mixgrounds (Signor & Vermeij, 1994; also gratefully thank Patricio Desjardins, Katherine N. Marenco and Butterfield, 2004; áM ngano & Buatois, 2014, 2016, in guest editors Andrea Baucon and Carlos Neto de Carvalho for their press). Diplocraterion mainly occurs in shallow marine insightful reviews and comments on the manuscript. siliclastics during the early-middle Cambrian (Tab. 1). The oldest Diplocraterion occurrence in carbonate was REFERENCES reported from the late Cambrian Gushan Formation (Furongian) of North China (Zhou et al., 2011). Since Bjerstedt T.W. & Erickson J.M. (1989). Trace fossils and the Early Ordovician, Diplocraterion normally occurs in bioturbation in peritidal facies of the Potsdam-Theresa both shallow-marine siliciclastics and carbonates (Pratt Formations (Cambrian-Ordovician), Northwest Adirondacks. & James, 1986). Therefore, the delayed appearance of Palaios, 4: 203-224. Diplocraterion in M2 may be due to the lack of suitable Brogly P.J., Martini I.P. & Middleton G.V. (1998). The Queenston siliclastic facies in the lower Cambrian of North China. 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