Gondwana Research 22 (2012) 238–255

Contents lists available at SciVerse ScienceDirect

Gondwana Research

j ourna l homepage: www.e lsev ie r .com/ locate /gr

Early Triassic trace fossils from Gondwana Interior Sea: Implication for ecosystemrecovery following the end-Permian mass extinction in south high-latitude region

Zhong-Qiang Chen a,⁎, Margaret L. Fraiser b, Cynthja Bolton a

a School of Earth and Environment, The University of Western Australia, 35 Stirling Highway, Crawley, Perth, Western Australia, WA 6009, Australiab Department of Geosciences, University of Wisconsin-Milwaukee, Milwaukee, WI 53211, USA

⁎ Corresponding author. Tel.: +61 864881924; fax: +E-mail address: zhong.qiang.chen@uwa.edu.au (Z.-Q

1342-937X/$ – see front matter © 2011 International Adoi:10.1016/j.gr.2011.08.015

a b s t r a c t

a r t i c l e i n f o

Article history:Received 6 February 2011Received in revised form 2 August 2011Accepted 26 August 2011Available online 23 September 2011

Handling Editor: A.S. Collins

Keywords:Early TriassicTrace fossilsRecoveryEnd-PermianMass extinctionPerth BasinGondwana

The Kockatea Shale Formation is one of few marine Early Triassic successions recorded in the Gondwana. Thisformation is exposed at the Northampton area of the northern Perth Basin, Western Australia and was depos-ited in the Gondwana interior sea during the Permian and Early Triassic. Trace fossils identified within theKockatea Shale Formation are extremely abundant and contain 16 ichnogenera (including a problematic ich-nogenus). The Gondwanan ichnoassemblage is constrained as late Smithian in age and is the most diverseamong coeval ichnofaunas around the world. Several types of grazing traces are also reported for the firsttime in the Lower Triassic. Several proxies such as bioturbation level, ichnodiversity, burrow size, trace-fossilcomplexity, and tiring level suggest that tracemakers diversified in the Gondwana interior sea during the lateSmithian. The Gondwanan ichnofauna-dominated ecosystemmay have reached the ecologic recovery stage 3of Twitchett's model in late Smithian. The rebound of ichnoassemblages in the aftermath of the end-Permianmass extinction was not controlled by particular environmental settings, all of which however were charac-terized by oxygenated substrata.

© 2011 International Association for Gondwana Research. Published by Elsevier B.V. All rights reserved.

1. Introduction

The catastrophic event occurring at the end of the Palaeozoic Eradestroyed a vast majority of animal species, both on land and in theoceans (Benton, 2003; Erwin, 2006). The causes of this decimationhave been linked to various types of environmental degradation,which may also be responsible for the delayed recovery after this di-sastrous period (Bottjer et al., 2008). However, like the enigmaticPermian–Triassic (P–Tr) mass extinction, the much delayed recoveryin the Triassic remains disputed in terms of tempo and mechanism(Erwin, 2006). Growing evidence shows that palaeoecologic ap-proaches, including the utilization of trace fossils and ichnology, arepowerful in revealing these aspects of biotic recovery (Twitchett andWignall, 1996; Twitchett, 1999; Zonneveld et al., 2002; Pruss and Bottjer,2004; Twitchett and Barras, 2004; Zonneveld et al., 2004; Beatty et al.,2005; Morrow and Hasiotis, 2007; Beatty et al., 2008; Fraiser andBottjer, 2009; Knaust, 2010; Zonneveld et al., 2010a,b; Chen et al.,2011; Hermann et al., 2011; Mata and Bottjer, 2011). Nevertheless,the previously published trace-fossil data were mainly derived fromlow-latitude regions in the northern hemisphere during the P–Tr tran-sition except for the relatively high-latitude northwestern Pangea

61 864881037.. Chen).

ssociation for Gondwana Research.

(Zonneveld et al., 2002,2004; Beatty et al., 2005,2008; Zonneveld etal., 2010a). Little has been published on the Early Triassic marine ichno-taxa frommoderate to high latitude regions in the southern hemispheresuch asGondwanaland during the P–Tr transition. It should benoted thatthe Early Triassic continental trace fossils have been reported fromGond-wana (Groenewald et al., 1998, 2001; Gastaldo and Rolerson, 2008) andAntarctica (Hasiotis, 1993; Hasiotis and Mitchell, 1993; Hasiotis et al.,1998; Miller et al., 2001; Sidor et al., 2008; Briggs et al., 2010).

Rarity of continuous P–Tr successions has hampered our understand-ing of the severity of the end-Permian crisis and the post-extinction re-covery on Gondwanaland (Dickens and Campbell, 1992). Severalrecent stratigraphic studies reveal that the possible continuous marineP–Tr boundary and Lower Triassic sequences may have accumulated insome interior seas of Gondwanaland such as the Perth Basin (Thomaset al., 2004; Metcalfe et al., 2008), which has attracted an increasingnumber of studies addressing the P–Tr mass extinction in Gondwana(Grice et al., 2005). More recently, we have detected abundant trace fos-sils from the Lower Triassic succession of the Kockatea Shale Formationexposed in the northern Perth Basin, Western Australia (Bolton et al.,2010). The Perth Basin was situated at high-latitude region of southernhemisphere during the Early Triassic (Scotese, 1994; Fig. 1). It waspart of an interior sea which faced the Palaeo-Tethys Ocean to thenortheast and extended inland into Gondwanaland to the southwest(Hocking et al., 1987; Fig. 1A). Palaeoecologic analysis of the Kocka-tea Shale trace fossils may provide a window to evaluate ecologic

Published by Elsevier B.V. All rights reserved.

Fig. 1. Location and palaeogeographical position of the Northampton areas, northern Perth Basin, Western Australia. A, Early Triassic paleogeographical map showing the position ofthe Perth Basin (base map after Scotese, 1994). B, location of the Blue Hill and Mount Minchin sections.

239Z.-Q. Chen et al. / Gondwana Research 22 (2012) 238–255

recovery of marine ecosystems following the end-Permian crisis insouth high-latitude region. Accordingly, this study aims to document,for thefirst time, awell-preserved ichnofauna from theGondwana inte-rior sea and attempts to assess the recovery of the ichnofauna after theend-Permian crisis in the southern Hemisphere.

2. Studied sections and stratigraphic setting

Lower Triassic successions deposited in the Perth Basin are referred asto the Kockatea Shale Formation (Edgell, 1964; Karajas, 1969; Skwarkoand Kummel, 1974), which lies unconformably above Silurian to lowerPermian sandstone units and is overlain by Jurassic sandstone units inthe northern Perth Basin (Karajas, 1969; Crostella and Backhouse,2000). TheKockatea Shale acts as an important oil source rock andhydro-carbon reservoir seal, and thus attracted industrial attention in the PerthBasin (Crostella and Backhouse, 2000). Lower Triassic successions areseen in many oil exploration boreholes, but are sporadically exposed in

the basin, primarily restricted to a small area nearNorthampton,WesternAustralia (Fig. 1B). In Northampton, the Kockatea Shale Formation over-lies the Silurian Tumblagooda Sandstone and truncated by the JurassicGreenough Sandstone (Karajas, 1969). The formation is generally subdi-vided into four units. Unit A comprises ferruginized massive conglomer-atic sandstone and conglomerate, 0–2 m in thickness; Unit B consists ofstromatolites, 0.2–0.5 m thick; Unit C is composed of white clay (0–6 m); Unit D is characterized by reddish, bioturbated or cross-lami-nated, ferruginized alternation of mudstone, siltstone and fine-grainedsandstone (0–2 m); Unit E is dominated by shale with minor compo-nents of siltstone and calcareous mudstone at the lower part and by silt-stone with interbeds of shale at the upper part, 10–20 m in thickness(Karajas, 1969). Of these, Units A–C arewell exposed at the Blue Hill sec-tion A (Fig. 2); and Units B–E crop out at the Blue Hill section B and theMount Minchin section (Figs. 2, 3).

At Blue Hill Section A, units A and B of the Kockatea are 20 cm and40 cm thick, respectively (Fig. 4A, C). The Lower part of Unit C, 60 cm

Fig. 2. Lower Triassic successions exposed at the Blue Hill section A and Blue Hill section B showing stratigraphic distributions of trace fossils and other biogenic structures, ammo-noid fossil horizons, sedimentary structures, ichnofabric index and bedding plane bioturbation index. Ichnofabric indices (ii) (Droser and Bottjer, 1986) are assessed as 1 to 6, in-dicating bioturbation from lowest to highest levels. Bedding plane bioturbation index (bpbi) is evaluated based on bedding plane coverage of burrows (Miller and Smail, 1997).Grain size scale: sh = shale, s = siltstone, st = sandstone, p = pebble conglomerate.

240 Z.-Q. Chen et al. / Gondwana Research 22 (2012) 238–255

in thickness, is exposed at this site and yields ammonoids (Fig. 4E)and the trace fossil Arenicolites (Fig. 2). At Blue Hill Section B, Unit Bis comparable with its counterpart at Blue Hill Section A. Unit C iscomplete and 2.4 m in thickness. Unit D is about 2 m thick and yieldabundant ammonoids and ichnotaxa (Arenicolites isp., Lockeia isp.,Palaeophycus striatus, Treptichnus bifurcus, and T. apsorum; Fig. 2). Itsbase is marked by reddish, thin-bedded siltstone with distinctive rip-ples and halite pseudomorphs. Ammonoid shell concretions (Fig. 5D)characterize the top of Unit D on which wrinkle structures are alsoconspicuous (Figs. 2, 4G). Unit E comprises a 13-m-thick succession ofalternating shale and siltstone, yielding several ichnotaxa (Arenicolitesisp. nov., Lockeia isp., Ophiomorpha nodosa, P. striatus, and Thalassinoidescallianassae; Fig. 2).

At the Mount Minchin section, Unit D (~1.2 m thick) is characterizedby the ripple-stratified siltstone at the base and alternation of mudstoneand siltstone at its middle and upper parts. Unit E (~24 m thick) isoverlain by Jurassic sandstone (Fig. 3). Wrinkle structures andtrough cross-stratifications are common in this unit. The majority ofichnotaxa described below came from the lower part of Unit E and in-clude Arenicolites isp. nov., Cochlichnus anguineus, Didymaulichnus isp.,Diplichnites isp., Diplocraterion isp., Gnathichnus isp. 1, Gnathichnus isp.

2, Laevicyclus isp., Lockeia isp., O. nodosa, P. striatus, Planolites montanus,Radulichnus isp., Taenidium serpentinum, T. callianassae, and a problematictrace.

Ammonoid fauna is also abundant and includes Arctoceras sp. indet.A, Arctoceras sp. indet. B, Prionites sp. indet., Hemiprionites sp. indet.,and Anasibirites kingianus (Waagen) (Edgell, 1964; Karajas, 1969;Skwarko andKummel, 1974). They occur in Units C–E at the studied sec-tions (Figs. 2, 3). Skwarko and Kummel (1974) assigned this ammonoidfauna to theOwenites Zone, but pointed out that theMinchin assemblagecontains elements characteristic of both the Owenites and AnasibiritesZones. These authors also considered that both the Owenites andAnasibirites faunas are mixed in most cases, although the AnasibiritesZone may overly the former zone in some places. These two ammo-noid faunas are diagnostic of the late Smithian in Guangxi and Anhui,South China (Tong et al., 2004; Brühwiler et al., 2008), southernTibet (Brühwiler et al., 2010) and India, Pakistan and Oman (Brühwileret al., 2007; Brayard et al., 2009). Both Arctoceras and Anasibirites Zonesalso characterize the late Smithian in South Primorye, Russian Far East(Shigeta et al., 2009). As such, the Kockatea Shale Formation successionexposed at the Blue Hill–Mount Minchin areas is constrained as lateSmithian in age, although the entire formation, seen in borehole of the

Fig. 3. Lower Triassic successions exposed at the Mount Minchin section showing stratigraphic distributions of trace fossils and other biogenic structures, ammonoid fossil horizons,sedimentary structures ichnofabric index (ii) and bedding plane bioturbation index (bpbi). Grain size scale is the same as those used in Fig. 2.

241Z.-Q. Chen et al. / Gondwana Research 22 (2012) 238–255

Perth Basin, may range from the Changhsingian to Smithian in age(McTavish andDickins, 1974; Thomas et al., 2004;Metcalfe et al., 2008).

3. Palaeoenvironmental analysis

3.1. Unit A

At BlueHill SectionA, Unit A has an irregular, unconformable contactwith the underlying Tumblagooda Sandstone unit in some areas, and arelatively flat contact in others. Where the contact is irregular, Unit A isdominated by conglomerates (Fig. 4A) and its thickness varies from0.2 m to 2 m. The conglomerates have a framework of angular to sub-rounded quartz grains with coarse sand matrix. Feldspar and heavyminerals are rather abundant, and boulders of the Tumblagooda

Sandstone are also occasionally present in this unit (Fig. 4F). In theplaces where the basal contact is planar, Unit A has a relatively eventhickness and is dominated by pebble conglomerates and sandstone(Fig. 4B, D). Pebbles occupy60–70%of the rock and form anopen frame-work which has been subsequently infilled by sand and silt. Pebblescomprise angular to rounded fragments of vein quartz, rounded frag-ments of sandstone, reworked quartz pebbles from the Tumblagooda,and angular to rounded feldspar grains from Precambrian rocks.

The coarse sediments, shape of the conglomerate bodies, and large-angle trough cross beddings suggest a wave-dominated littoral zone(Dafoe et al., 2010; Vakarelov et al., in press). In particular, these pebblesmay have been carried to the littoral zone by high energy streams or de-rived from the rocky coastline due to strong wave action. The pebble-dominated Unit A therefore is interpreted as lag deposits in the littoral

Fig. 4. Lithofacies from Units A–C of the Kockatea Shale at the Blue Hill sections A–B. A, Conglomeratic sandstone (Unit A) is overlain by stromatolites (Unit B), the Blue Hill section A(BH–A); B, stromatolites (Unit B) grew on pebbles of Unit A, BH–A; C, a polish slab showing the columnar stromatolites (Unit B), BH–A; D, Unit A is composed of pebbles, BH–A; theharmer is 30 cm long; E, ammonoid shell concretion on the bedding surface of siltstone at the upper part of Unit C, BH–B; F, stromatolites (Unit B) resting on coarse sandstone (UnitA), BH–A; G, wrinkle structures on the bedding surface of siltstone at the upper part of Unit D, BH–B; H, Units B–C sequence exposed at the BH–A; I, Units B–C sequence exposed atthe BH–B; the bag is 40 cm high.

242 Z.-Q. Chen et al. / Gondwana Research 22 (2012) 238–255

zone during an initial marine transgression (MacEachern et al., 1992;Arnott, 1995; MacEachern et al., 1999b; Dafoe et al., 2010). The deposi-tional environment therefore was likely supratidal to upper part of in-tertidal zones on a sandy or rocky coastline.

3.2. Unit B

This unit consists of stromatolites, which rest on pebble conglomer-ate of Unit A (Fig. 4B) or directly on fine sandstone (Fig. 4F). Its thick-ness varies from 0.2 m to 0.5 m. Stromatolites grew in a variety ofgrowth modes. Some microbialites colonized pebbles and conglomer-ates initially (Fig. 4B) and then developed into laminar columns. Othersgrew on sandstone and built thick laminae (Fig. 4F). Most stromatolitesare columnar and branching (Fig. 4C). The spaces between columns aretypically filled with well-sorted sand. Detailed morphology of thesestromatolites is the focus of a future publication.

Unit B, overall, indicates an upper intertidal to supratidal environ-ments of deposition (Karajas, 1969), equivalent to the upper foreshoreto backshore (cf. MacEachern et al., 1999a; Dafoe et al., 2010). The stro-matolites are morphologically comparable with present-day analogs atthe Shark Bay, about 80 km north of the study area, wherein stromato-lites grow in a semi-closed embaymentwith highly evaporitic conditions.

3.3. Unit C

This unit is dominated by white clay (Fig. 4H, I) and has a uniformthickness of 6 to 7 m in the study area. In the southern part of theNorth-ampton areas where the basement topography shows variation, thisunit thins and pinches out against basement highs (Karajas, 1969).The thin-bedded claystone is characterized by thin horizontal laminae(Fig. 4I) and yields ammonoid fossils (Fig. 4E), suggesting a low-energyenvironment below fair-weather wave base.

Fig. 5. Lithofacies from Units D–E of the Kockatea Shale Formation at the BH–B and Mount Minchin section (MM). A, Alternation of light gray to white mudstone and reddish silt-stone of the lower part of Unit D, BH–B; the harmer is 40 cm long; B, C, E, trough cross-beddings of siltstone (B) and fine sandstones (C, E) at the upper part of Unit E, MM; D, am-monoid shell concretions at the upper part of Unit D, BH–B; F, small-scale slump structure of siltstone at the upper part of Unit D, BH–B; G–I, Trough cross-beddings of siltstone (G)and fine sandstone (H–I) at the lower part of Unit E, MM. J, Ripples on the bedding surface of siltstone at the lower part of Unit D, BH–B; the harmer is 40 cm long.

243Z.-Q. Chen et al. / Gondwana Research 22 (2012) 238–255

3.4. Unit D

Alternation of mudstone and siltstone characterizes the lower part ofUnit D (Fig. 5A), while siltstone and fine sandstone dominate its upperpart. Siltstone in the lower part of this unit is usually thin- to medium-bedded and contains small-scale cross-stratification. Linguoid rippleson bedding surfaces are pronounced (Fig. 5J). Mudstone is composedmainly of clay. Siltstone of the upper part of Unit D is considerably biotur-bated and sandstone yields trough cross-beddings, with occasionalslump structures (Fig. 5F). Ammonoid shell concretions (Fig. 5D) andwrinkle structures (Fig. 5G) are also common on the bedding surfacesof siltstone and fine sandstone. The shell concentrations were sorted tosome extent and contain some shell fragments, indicating transportationby currents before their accumulation. Wrinkle structures are usuallyinterpreted to be formed in the upper part of subtidal to intertidal set-tings (e.g., Pruss et al., 2005), equivalent to upper shoreface to foreshore(cf. MacEachern et al., 1999a).

All lines of evidence show that the lower part of Unit D was depos-ited in the middle to lower shoreface (MacEachern et al., 1999a; Dafoeet al., 2010) where fair-weather wave action occasionally affected thestudy area. The upper part of this unit suggests depositional environ-ments varying from the middle to upper shoreface (MacEachern et al.,1999a) where the fair-weather wave action prevailed.

3.5. Unit E

This unit is dominated by gray, finely laminated shale with minorcomponents of siltstone and calcareous mudstone at the lower part,and by reddish, thin-bedded siltstone interbedded with shale at theupper part. Siltstone beds are occasionally bioturbated. Most fine-grained sandstone beds yield trough cross-bedding (Fig. 5B, C, E, G–I)and tool marks. The shale-dominated succession of the lower Unit E in-dicates a low-energy environment below fair-weather wave base occa-sionally influenced by wave action. The siltstone-dominated succession

244 Z.-Q. Chen et al. / Gondwana Research 22 (2012) 238–255

of the upper Unit E suggests deposition in a fair-weather wave actionzone, equivalent to the middle to upper shoreface (cf. MacEachern etal., 1999a; Dafoe et al., 2010). Overall, the number and thickness ofcross-stratified siltstone beds increases up the section, implying thatUnit E represents an upward-shallowing cycle at both the Blue Hill Band Mount Minchin sections.

3.6. Environmental evolution of the study area

In summary, Units A–C indicate a retrogradational sedimentary pro-cess due to a transgression in the northern Perth Basin. Unit Awas depos-ited near the shoreline during the initial transgression, while Unit C wasdeposited in a low-energy setting below fair-weather wave base duringthe maximum flooding period of the transgression. A distinct regressionis indicated by Unit D, which was deposited near fair-weather wavebase. Unit E includes several high-frequency sea-level rising–fallingcycles indicated by alternation of shale and cross-stratified siltstone,but overall points to a middle–upper shoreface setting during atransgression–regression cycle throughout the entire unit.

4. Methods

Trace fossil taxonomic identification was based on descriptions ofspecimens collected from the outcrop and field observations. Severalproxies, including burrow size, ichnodiversity, trace-fossil form andcomplexity, tiering level, and bioturbation are applied here to exam-ine ecologic recovery of trace-fossil assemblages in the aftermath ofthe P/Tr mass extinction, as analyzed elsewhere (Twitchett, 1999;Zonneveld et al., 2002; Pruss and Bottjer, 2004; Twitchett and Barras,2004; Zonneveld et al., 2004; Beatty et al., 2005,2008; Fraiser andBottjer, 2009; Zonneveld et al., 2010a; Chen et al., 2011). Measure-ments of burrow diameters were measured on bedding planes andin vertical exposures from the part of the burrow that was most rep-resentative of the average width (sensu Pruss and Bottjer, 2004).Sediment penetration depths of trace fossils were measured on ver-tical exposures, and tiering levels were assessed based on thesemeasurements (Bottjer and Ausich, 1986; Twitchett, 1999, 2006).The ichnofabric index (ii, Droser and Bottjer, 1986) and the beddingplane bioturbation index (BPBI, Miller and Smail, 1997) are powerfultools that provide a semi-quantitative way to measure the extent ofbioturbation recorded in sedimentary beds deposited after mass ex-tinctions in vertical outcrop and on bedding planes, respectively(Twitchett and Wignall, 1996; Pruss and Bottjer, 2004; Fraiser andBottjer, 2009; Chen et al., 2011; Mata and Bottjer, 2011). Ichnofabricindices (ii) are assessed as 1 to 6, with 1 representing no bioturba-tion and 6 indicating complete destruction of primary sedimentarystructures by bioturbation (Droser and Bottjer, 1986). BPBI is evalu-ated based on bedding plane coverage of burrows and has valuesthat range from 1 to 5, indicating bioturbation on the bedding sur-faces from lowest to highest levels (Miller and Smail, 1997). Both iiand bpbi values reported here were only taken from well-exposedoutcrops and bedding planes where sufficient primary biogenicand sedimentary structures were preserved for evaluation of biotur-bation levels. Where these values could not be adequately deter-mined due to lack of a bioturbate texture and primary sedimentarystructures, no data were given here (Figs. 2, 3).

5. Ichnology of the Lower Triassic trace fossils

5.1. Arenicolites Salter

Traces of Arenicolites are very common in the Lower Triassic sedi-ments and may occur in association with most of other traces describedbelow. They are usually preserved in cross section on bedding planes asa pair of holes (Figs. 6H, I, 7B, 8D–E) or prominent shafts (Figs. 6A, C,8F, 9J). The 3-dimensional outline of the U-shaped tubes is also observed

on some specimens (Fig. 6G). The U-shaped limbs are unbranched, paral-lel to one another, perpendicular to the bedding plane, and lack spreite.The basal part of the U-shaped limbs is broadly curved and thinner thanthe lateral limbs (Fig. 6E). The U-shaped tubes possess rough surfaces.Depth of penetration of burrows varies from 15mm to 30 mm. The U-shaped burrows have various limb diameters, ranging from 2mm to14 mm. The distance between the limbs ranges from 5 to 20 mm. Fillingof burrows is light-colored, coarse sediments and easily distinguishablefrom surrounding fine-grained rocks. Several characteristics, includingthe non-smooth tube surface, the relatively thinner burrow at the basalpart of U-shaped tubes, and the broadly curved base of the U-shapedtubes, distinguish the described specimens from any known ichnospeciesof Arenicolites, and thus suggest a new ichnotaxon.

This ichnogenus is believed to be the dwelling burrow of suspen-sion feeders such as polychaete worms, amphipod crustaceans, andinsects (Bromley, 1996; Rindsberg and Kopaska-Merkel, 2005).

5.2. Cochlichnus Hitchcock

Sinusoidal, unbranched, unlined burrows are preserved in positiverelief (Fig. 9F). Burrow is 2 mm in diameter and consistent in widththrough the entire length observed. Wavelength is about 10 mm, andamplitude of the wave ranges from 2 mm to 3 mm. The observed bur-row trace is identical to C. anguineusHitchcock in all aspects. This ichno-genus has been interpreted either as a grazing trace (Buatois andMangano, 1993), a locomotion trace (Metz, 1998) or a feeding structure(Eagar et al., 1985).

5.3. Didymaulichnus Lebesconte

Didymaulichnus occurs as smooth, curving bilobed trails (Fig. 7C, F).These burrows are preserved parallel to bedding planes. They are simpleand sinuous and often intersect one another. Burrow width is 3–4 mm,and length is up to 50 mm. These specimens are tentatively assigned toDidymaulichnus isp. due to incomplete preservation. Didymaulichnus isinterpreted as the trail of an arthropod, gastropod or soft-bodied organ-ism (Hakes, 1977; Trewin and McNamara, 1995; Knaust, 2004).

5.4. Diplichnites Dawson

Several straight trackways are preserved on upper surface of mud-stone beds (Fig. 8A). They commonly intersect each other. Each trackconsists of two parallel equally spaced rows of unequal fine pits, whichare the appendage impressions. The tracks on each side of the trackwaysare formed by a string of pits. Trackways are 8–9 mm wide. Small pitsvary in depth and size. The pair of pits at the start of trackways are larg-est, 2–3 mm in diameter, and deepest, 2–3 mm deep, among all pits.They become shallower in the direction the animal moved. The exactlength of trackways remains unknown because trackways disappeargradually along the axis.

Diplichnites are thought to be formed as arthropod locomotorytraces (Briggs et al., 2010).

5.5. Diplocraterion Torell

Several Diplocraterion burrows are preserved in association withArencolites burrows (Fig. 8D). They are preserved on upper beddingplanes as dumbbell-shaped structures containing two circular holesdue to removal of the fillings of the U-shaped limbs. Spreites are not vis-ible, but a prominent groove on the bedding plane indicates the presenceof spreite between the limbs (Fig. 8D). The depth of the U-shaped limbs isestimated to be up to 1 cm below the top of bedding plane. The limbs are2–4 mm in diameter and 5–7 mm apart (Fig. 10F). The poor preservationprevents precise comparison with the type ichnospecies D. parallelumTorell. Thus, the Australian traces have been assigned toDiplocraterion isp.

Fig. 6. A, Arenicolites isp. nov. (A), Lockeia isp. (L), and Palaeophycus striatus (P) on upper surface of siltstone bed, Unit E, MM. B, F, Lockeia isp. on lower surface of siltstone bed, UnitE, MM; scale bars are 10 mm and 5 mm, respectively. C, E, G, Arenicolites isp., Unit E, MM; C, broken U-shaped limbs showing no spreite between limbs; E, basal part of U-shapedlimbs on upper surface; G, complete U-shaped limbs on down surface; scale bars are 10 mm. D, J–K, Taenidium serpentinum Heer on upper surface of siltstone bed, Unit E, MM; scalebars in D, K are 5 mm; scale bar in J is 10 mm. H, T. serpentinum Heer (Ta), Arenicolites isp. nov. (A) and Thalassinoides callianassae Ehrenberg (T) on upper surface of siltstone bed, UnitE, MM; scale bar is 10 mm. I, Arenicolites isp. (A), T. serpentinum Heer (Ta), and Ophiomorpha nodosa Lundgren (O) on upper surface of siltstone bed, Unit E, MM; scale bar is 10 mm.

245Z.-Q. Chen et al. / Gondwana Research 22 (2012) 238–255

Diplocraterion is considered to be the dwelling structure of sus-pension feeding creatures (Gradzinski and Uchman, 1994). Possibletracemakers include annelids, polychaetes, crustaceans, or insect larvae(Gradzinski andUchman, 1994). It is suggested thatDiplocraterion are uti-lized by the tracemaker to siphonwater through the tube (Abbassi, 2007).

5.6. Gnathichnus Brombley

Several grazing/gnawing traces occur on the upper surface of siltstonebeds (Figs. 7D–E, I; 8G, I). Modular unit (term of Bromley, 1975) of thetrace is composed of 3–5 grooves arranged in either a regular star-shapedpattern (Figs. 7I, 8G) or branch-shaped network (Fig. 8I). These bundlesof fine grooves resemble that of Gnathichnus pentax Bromley (1975), atrace produced by the grazing activity of echinoids. These grazing tracesare collectively assignable to Gnathichnus, but represent a new ichnospe-cies. Morphologically, the grazing traces described below can be catego-rized into two groups.

The first type of grazing traces is comprised of a cross-hatched trail,sinuous to slightly meandering, and paired, intersecting, arced scratch

marks. The angle between radial scratches is varied. Each groove is curvedto slightly straight with a length between 2 and 8 mm and a width vary-ing between 200 and 400 μm and the distal end being acuminate. Thebundles of scratch marks are arranged in various ways: They may forman ovate nest-shaped trace in which paired scratch marks are straightor slightly curved, intersecting, or overlapping medially. In most cases,the tiny rasping marks are clustered whereby the paired mildly arcingor straight scratch marks meet at the midline; they can overlap eachother (Figs. 7I, 8G). The trails may be parallel to bedding planes or pene-trate into the sediment down to 8 mm. These features resembleG. pentax,but suggest more complex gnawing traces.

The second type of grazing traces is characterized by a branch-shapeddistribution of scratches (Fig. 8I). Single gnawingmarks, 1 mmwide and2–3 mm long, are usually bilobed and etched deeply into the sediment.This arrangement is different from these of typical Gnathichnus.

Observation of modern-day gnawing echinoids shows that Gnathich-nusmakers use their Aristotle lantern to feeduponepilithic and endolithicalgae and other organisms (Bromley, 1975; Försterra et al., 2005;Wisshaket al., 2005). UnlikeG. pentax that usually attaches on shells, the described

Fig. 7. A, Treptichnus bifurcus (Miller) (T) on upper surface of siltstone, Unit D, BH–B; scale bar is 10 mm. B, Treptichnus apsorum Rindsberg and Kopaska-Merkel (T) and Arenicolitesisp. nov. (A) on upper surface of siltstone, Unit D, BH–B. C, F, Didymaulichnus isp. on upper surface of siltstone bed; scale bars are 5 mm in C and 10 mm in F. D, I, Gnathichnus isp. 1on upper surface of mudstone bed; Unit E, MM; scale bars are 10 mm; E, Thalassinoides callianassae Ehrenberg (T) and Gnathichnus isp. 1 (G) on upper surface of siltstone, Unit E,MM; scale bar is 10 mm. G, a problematic trace showing paired low ridges on upper surface of siltstone bed; Unit E, MM; scale is 10 mm. H, Radulichnus isp. on supper surface ofmudstone bed; Unit E, MM; scale bar is 10 mm. J, Planolites montanus Richter on upper surface of mudstone bed; Unit E, MM; scale bar is 10 mm.

246 Z.-Q. Chen et al. / Gondwana Research 22 (2012) 238–255

traces are preserved on the mudstone or siltstone. To date, the oldestknown occurrence of Gnathichnus is confined to theMiddle–Upper Trias-sic of the Alps (Fürsich andWendt, 1977; de Gibert et al., 2007). The Aus-tralian record therefore suggests an Early Triassic occurrence ofGnathichnus and that similar trace-making behaviorwas present in the af-termath of the P–Tr crisis.

It should also be noted that the Lower Triassic scratching traces ofGnathichnus are usually large and recorded on soft substrate (mudstone)and thus are different from their Mesozoic–Cenozoic counterparts thatare very tiny and recorded on shellgrounds or hardgrounds (Bromley,1975; de Gibert et al., 2007). In contrast, they are morphologically com-parable with the Neoproterozoic–Cambrian examples of Radulichnus(see below). The latter scratches were found on the microbial mat-bound substrate and microbe-sealing was believed to be crucial for thepreservation of these unusual scratching traces (Seilacher et al. 2003,2005). Similarly, the Lower Triassic Gnathichnus is also found in associa-tion with wrinkle structures and microbial mats (Luo and Chen, submit-ted). The tracemakers therefore dwelled on soft matgrounds.

5.7. Laevicyclus Quenstedt

This vertical trace is perpendicular to bedding and preserved on theupper surface of siltstone beds. It has an anterior lined wall surroundinga central hole, which is filled with light-colored sediments and thus iseasily distinguish from the surrounding dark color rocks (Fig. 9E). Tracediameter is up to 30 mm and may penetrate about 20 mm below thetop of bedding plane. Numerous grooves, as radial imprints, radiate outfrom the central hole. Laevicyclus isp. is tentatively proposed for the illus-trated trace. Laevicyclus has been considered as the vertical dwelling bur-row of a worm, with tentacle swirl-marks around the top of the burrow(Osgood, 1970).

5.8. Lockeia James

Lockeia is preserved as both convex and concave epirelief. Specimensare almond-shaped and roughly symmetrical along the longitudinalme-dian line, 7–15 mm in length, 3–5 mm in width and 5–8 mm in height

Fig. 8. A, Diplichnites isp. on upper surface of mudstone bed, Unit E, MM; B, Ophiomorpha nodosa Lundgren on upper surface of siltstone bed, Unit E, BH–B; scale bar is 10 mm. C, O.nodosa Lundgren (O) and Lockeia isp. (L) on upper surface of siltstone bed, Unit E, MM; scale bar is 10 mm. D, Arenicolites isp. nov. (A), Diplocraterion isp. (D) and Thalassinoidescallianassae Ehrenberg (T) on supper surface of siltstone bed, Unit E, MM; scale bar is 10 mm. E, Arenicolites isp. (A) and T. callianassae Ehrenberg (T) on upper surface of siltstonebed; scale bar is 10 mm. F, Taenidium serpentinum Heer (Ta) and Arenicolites isp. (A) on upper surface of siltstone bed, Unit E, MM; coin is 10 mm in diameter. G, Gnathichnus isp. 1on upper surface of mudstone bed; Unit E, MM; scale bars are 10 mm. H, Palaeophycus striatus Hall on upper surface of siltstone bed, Unit E, MM; scale bar is 10 mm. I, Gnathichnusisp. 2 on upper surface of mudstone bed; Unit E, MM; scale bars are 10 mm.

247Z.-Q. Chen et al. / Gondwana Research 22 (2012) 238–255

(Fig. 9A–B, F). Their external surfaces are smooth and have a prominentlongitudinal crest and commissure with rounded ends. Specimens maybe perpendicular or oblique to bedding planes in various angles. Whenoblique to bedding planes in a small angle, the trace is elliptical in out-line. The Australian material resembles L. siliquaria James, the type ich-nospecies for Lockeia, in having the pronounced longitudinal crest andcommissure, but is much larger. These features also distinguish the fig-ured specimens from any known Lockeia ichnospecies and thus mayrepresent a new ichnospecies. Lockeia has been interpreted as the rest-ing trace of burrowing bivalves (Seilacher, 1953; Hakes, 1977). The dif-fering feeding habits of these shelled organisms may explain thediffering morphologies of Lockeia. Smaller specimens have been attrib-uted to ostracods or conchostracans (Buatois et al., 2000).

5.9. Ophiomorpha Lundgren

This ichnogenus is preserved as small cylindrical burrows, 3–6 mm inwidth and 10–24 mm in length with nodular external surfaces. Its tracesare very common in our collections (Figs. 6I, 8B–C; 9C, 11A–B, E–H). It

has pelletal nodules that are somewhat spherical and b1 mm in diame-ter. Burrows are usually simple, but occasionally branch with T- or Y-junctions (Fig. 11A, E). These burrows are primarily horizontal and obli-que to bedding plane with multiple vertical burrows penetratingb10 mm into the sediments. All features suggest O. nodosa Lundgren.Ophiomorpha can be gradational with Thalassinoides and Spongliomorpha(Minter et al., 2007). Frey et al. (1978) confirmed that Ophiomorpha canbe attributed to the modern day shrimp Callianassa spp. implying thatthe past Ophiomorpha may have been made by the crustaceans whichhave similar lifestyle to shrimp.

5.10. Palaeophycus Hall

Palaeophycus is represented by branched, straight to slightly curved,cylindrical burrowswith linedwalls. They are preserved as positive reliefson the upper surface of siltstone beds (Figs. 6A, 7H, 10H, 11C–D). Burrowsare smooth or striated (Fig. 7D) and can intersect and pass over one an-other. Some burrows are subparallel to the bedding plane (Figs. 6A, 8H,11C); others are oblique and even perpendicular to the bedding plane

Fig. 9. A–B, Treptichnus apsorum Rindsberg and Kopaska-Merkel on upper surface of siltstone bed, Unit E, MM. C, Ophiomorpha nodosa Lundgren on upper surface of siltstone bed,Unit E, MM. D, Planolites montanus Richter on upper surface of siltstone bed; Unit E, MM; scale bar is 10 mm. E, Arenicolites isp. nov. (A), and Laevicyclus isp. on upper surface ofsiltstone bed, Unit E, MM. F, Cochlichnus anguineus Hitchcock on upper surface of siltstone bed, Unit E, MM; scale bar is 10 mm. G, I, T. apsorum Rindsberg and Kopaska-Merkelon upper surface of siltstone bed, Unit E, MM; scale bars are 10 mm. H, Palaeophycus striatus Hall on upper surface of siltstone bed, Unit E, MM; scale bar is 10 mm. J, Arenicolitesisp. nov. (A) and P. montanus Richter (P) on upper surface of siltstone bed; Unit E, MM; scale bar is 10 mm.

248 Z.-Q. Chen et al. / Gondwana Research 22 (2012) 238–255

and penetrate into sediments up to 10 mm (Fig. 9H). These burrows are2–7 mm in diameter with length often indeterminate due to either ero-sion, disappearance into sediment, or breakage. Many, if not all, of thesespecimens may indeed be P. striatus Hall, but there are not enough diag-nostic features visible to be certain. Goldring et al. (2005) have suggestedthat P. striatus may resemble Scoyenia without the meniscate backfill.Palaeophycus is interpreted as substratal repichnia or domichnia(Häntzschel, 1975; Gouramis et al., 2003). Tracemakers could be smallpredaceous or suspension-feeding animals such as annelids, crustaceans,or other arthropods (Pemberton and Frey, 1984; Keighley and Pickerall,1997; Gouramis et al., 2003).

5.11. Planolites Nicholson

This ichnogenus includes unlined, rarely branched, straight to tortu-ous, smooth, horizontal to slightly inclined burrows, circular to ellipticalin cross-section. Burrows are usually filledwith sediment different fromthe hosting rock. Burrows are typically 2–5 mm in diameter, frequentlyintersect each other, and are densely packed (Figs. 7J, 9D, 9J, 11I).Allcharacteristics observed herein suggest P. montanus Richter.

Planolites is thought to either represent reworking of the sedimentby deposit-feeding activities of polychaetes or worm-like creatures(Crimes et al., 1977; Bromley, 1996), or feeding of mobile deposit-feeders (Pemberton and Frey, 1984) or terrestrial chironomid insectlarvae (Gradzinski and Uchman, 1994).

5.12. Radulichnus Voigt

This ichnogenus consists of very finely scratched traces restricted toclusters within a slightly meandering burrow that may penetrate about50 mm into the sediment. A modular unit (similar to the modular unitof Gnathichnus) is comprised of five radial individual scratches, 300–500 μm long that consistently repeat along the trace surface (Fig. 7H).The trackway is 40–80 mmwide and is curved tomeandering and, in ad-dition to the angle of the scratches, indicates the movement direction ofgrazers.

These traces are tentatively assigned to Radulichnus, which waserected by Voigt (1977) for tiny scratches scattered along the sedimentsurface. Radulichnus was interpreted to be produced by the radulargrazing activity of herbivorous gastropods or polyplacophorans (Voigt,

Fig. 10. Measurements of burrow diameter of Arenicolites, Didymaulichnus, Diplocraterion, Ophiomorpha, Palaeophycus, Planolites, Taenidium, Thalassinoides, and Treptichnus.

249Z.-Q. Chen et al. / Gondwana Research 22 (2012) 238–255

1977; Jüch and Boekschoten, 1980). Each radial pattern of one modularunit records a single “bite” of the tracemaker when scraping the surfacewith its radula to feed upon epilithic or shallowendolithic algae or othermicroorganisms, while individual scratches correspond to the action ofradular denticles. These actions were later confirmed by observationsand experiments with modern polyplacophoran and gastropod grazers(Thompson et al., 1997; Reyes et al., 2001).

Of special note is that the Radulichnus-like structures have alsobeen reported from the late Neoproterozoic and early Cambrian(Dornbos et al., 2004; Seilacher, 2007). They have been interpreted asthe result of primitivemolluscs grazing onmatgounds. The Lower TriassicRadulichnus-structures are similar to these Ediacaran–Cambrian formsand are much larger than the late Mesozoic forms. The tracemakers also

grazed on microbe-bound softgrounds (Seilacher et al., 2003; Dornboset al., 2004; Seilacher et al., 2005).

5.13. Taenidium Heer

Taenidium is indicated by unlined, straight or slightly curved to sin-uous burrows that contain segmented filling (Figs. 6D, H–K, 8F, 11B).Burrows also have well-spaced arcuate menisci but lack walls. The an-nular ornamentation is rather pronounced and the burrow may beslightly flanged at one end. These traces have a width of 3–4 mm andlength up to 24 mm with partitioned packeting. All features observedhere agree with the type ichnospecies T. serpentinum Heer.

Fig. 11. A, E, G, H, Ophiomorpha nodosa Lundgren on upper surface of siltstone bed, Unit E, MM; scale bars are 10 mm. B, O. nodosa Lundgren (O) and Taenidium serpentinum Heer(Ta) on upper surface of siltstone bed, Unit E, MM; scale bar is 10 mm. C–D, Palaeophycus striatus Hall on upper surface of siltstone bed, Unit E, MM; C, branching burrows; scale baris 10 mm; D, enlargement showing striatae on burrows; scale bar is 5 mm; I, Planolites montanus Richter on upper surface of siltstone bed, Unit E, MM.

250 Z.-Q. Chen et al. / Gondwana Research 22 (2012) 238–255

Keighley and Pickeril (1994) distinguished Taenidium from similartrace fossils. The lack of awall or lining differentiates Taenidium from Bea-conites, which has a distinct smooth burrow lining. Muensteria is alsomeniscate, but is clearly different from Taenidium in having distinctivewalls. Taenidium differs clearly from Anchorichnus as the latter has bothan inner meniscate fill and an outer mantle. D'Alessandro and Bromley(1987) suggested that Taenidium may be formed from animal ingestionand dispersal. Taenidiumwas also proposed to be pasichnia feeding bur-rows produced by worm-like deposit feeders (Verde et al., 2007).

5.14. Thalassinoides Ehrenberg

Thalassinoides occur as both positive and negative reliefs on uppersurfaces of siltstone beds (Figs. 6H, 7E, 8D–E). They are comprised ofbranching burrows with characteristic Y-shaped junctions. Burrowsare rounded in cross section, and have width of 15–20 mm and lengthsup to 200 mm. Burrow networks consist of predominantly horizontal tosubparallel, smooth cylindrical burrows that form incomplete intricatenetworks. These burrows are identical to T. callianassae Ehrenberg.The generation of Thalassinoides traces has been attributed to the be-havior of many organisms, including cerianthid sea anemones,

enteropneust acorn worms, fish, and decapod crustaceans (Miller etal., 2001; Ekdale and Bromley, 2003).

5.15. Treptichnus Miller

Recent taxonomic works (Maples and Archer, 1987; Buatois andMangano, 1993; Jensen, 2003; Rindsberg and Kopaska-Merkel, 2005)have greatly improved our understanding of Treptichnus. This ichno-genus is represented by T. bifurcus and T. apsorum in the Lower Triassiccollections. They are preserved as convex epirelief on the upper surfaceof siltstone beds.

T. bifurcus includes traces comprised of simple, zigzag-arranged bur-rows that join together and intersect at low angles to form projectionson both sides of a medial plane (Fig. 7A–B). The width of an individualsegment of burrow is approximately 2–3 mm. The rounded ends of pro-jections are conspicuous and situated on alternate sides of burrows.These traces demonstrate the 3-dimensional burrow system showingthe growth of T. bifurcus, as reconstructed byMaples and Archer (1987).

Treptichnus apsorum is represented by 3-dimensional burrows com-prised of uniserial segments arranged in an irregular fashion, with shal-low, broadly U-shaped segments curving upward into shafts near

251Z.-Q. Chen et al. / Gondwana Research 22 (2012) 238–255

junctions (Fig. 9A–B, G, I). Burrows, 5–8 mm in diameter, are usuallylarger than those in T. bifurcus.

Treptichnus has been attributed to either arthropods, or worm-likeorganisms, or insect larvae (Buatois et al., 1998, 2000; Knaust, 2004;Rindsberg and Kopaska-Merkel, 2005; Uchman, 2005).

5.16. Problematic trace

An unidentified convex epirelief trace is preserved on the upper sur-face of siltstone beds. It is comprised of two sets of ridges,which are dis-continuous, may be paired or unpaired, may be parallel or slightlyintersecting. A single lateral ridge originates from the midline of thetrace and tends to extend anteriorly at a small angle to the midline(Fig. 7G). These sinuous waves resemble that of Undichna, which hasbeen thought to be the swimming trails of fishes. Thus, we infer thatthis problematic trace is also a swimming trail, although the tracemakerremains unclear.

6. Ichnofabrics and trace fossils: proxies of ecologic recovery afterthe P/Tr mass extinction

6.1. Extent of bioturbation

Ichnofabric indices (ii, Droser and Bottjer, 1986) of Units B–C at allstudied sections are very low (ii 1). Unit D at the Blue Hill–B section re-cords moderate bioturbation (ii 3), but only 30% of the entire unit ex-hibits bioturbation. Ichnofabric indices increase up to ii 4 in Unit E atthe Blue Hill section B andMountMichchin section (Fig. 2). Bioturbationis exhibited in only 10% of the Unit E strata at the Blue Hill section B, andabout 40% of the entire Unit E at the Mount Minchin section (Figs. 2, 3).Bioturbation in the Kockatea Shale Formation at the studied sections var-ies from ii 1 to 4. On average, 20% of all strata exposed in the KockateaShale Formation are significantly bioturbated (ii 4).

At the Blue Hill section A, one available bedding plane was covered20% with Arenicolites, thus indicating a BPBI of 2. Other bedding planes,if available for observation, show b10% bioturbation and indicate a BPBIof 1. At the Blue Hill section B, one available bedding plane was coveredup to 40% by Arencolites, Ophiomorpha and Lockeia, indicating a BPBI of4. Two bedding planes were covered up to 30% by burrows and indicatea BPBI of 3 (Fig. 2). One ichnoassemblage includes Arenicolites, Lockeiaand Treptichnus; another comprises Paleophycus and Thalassinoides(Fig. 2). A BPBI of 4 was recorded for several bedding planes containingArenicolites, Cochlichnus, Didymaulichnus, Diplocraterion, Ophiomorpha,Palaeophycus, Planolites, Taenidium, and Thalassinoides at the MountMinchin section (Fig. 3). BPBI of 1–3 are also observed throughout theentire section at Mount Minchin (Fig. 3).

6.2. Burrow sizes of the Early Triassic ichnotaxa

The size distribution of burrow diameters of Arenicolites, Didymau-lichnus, Diplocraterion, Ophiomorpha, Palaeophycus, Planolites, Taenidium,Thalassinoides, and Treptichnus were determined from nine beddingplanes (Fig. 10). Arenicolites burrows occur in eight horizons with sizesdistributed in two groups: about 50% burrows are 2–4 mm in diameterand 35% burrows are 12–13 mm in diameter (Fig. 10A). The mean andmaximum diameters are 8.5 mm and 14 mm, respectively (n=72,Fig. 10A). Mean and maximum diameters of Palaeophycus burrows atfive horizons are 5.1 mm and 7 mm, respectively (n=62, Fig. 10G).Didymaulichnus has mean and maximum burrow diameters of 3.9 mmand 6 mm, respectively (n=31, Fig. 10F). Mean and maximum burrowdiameters of Ophiomorpha are about 10.9 mm and 13 mm, respectively(n=46, Fig. 10H). Planolites comprises 61 burrowswithmean andmax-imum diameters up to 6.7 mm and 8 mm, respectively (Fig. 10C). Taeni-dium has mean and maximum burrow diameters up to 9.4 mm and11mm, respectively (n=58, Fig. 10B). Thalassinoides includes 38 bur-rows with mean and maximum burrow diameters up to 5.3 mm and

6 mm, respectively (Fig. 10D).Mean andmaximumdiameters of Treptich-nus burrows are about 4 mm and 6mm, respectively (n=43, Fig. 10E). Ifcombining these 411 burrows of the above eight ichnogenerawith the 20burrows belonging to Diplocraterion, Cochlichnus, and Planolites, the aver-age and maximum burrow diameters of the Smithian ichnoassemblage(n=431) are approximately 7.0 mm and 14 mm, respectively.

6.3. Trace fossil forms and complexity

Awide variety of trace fossil forms occurs in the Northampton collec-tions. They include simple, horizontal burrows (Cochlichnus, Didymau-lichnus, and Planolites), horizontal nesting traces (Lockeia), walkingtrackway (Diplichnites), vertical burrows (Arenicolites,Diplocraterion, Lae-vicyclus), oblique/or horizontal, branching burrows (Ophiomorpha,Palaeophycus, Taenidium), slightly complex burrow networks (Thalassi-noides and Treptichnus), grazing traces (Gnathichnus and Radulichnus),and possible swimming traces. As a result, trace-fossil behavioral diversi-tywas considerably high. Their behavioural complexitywas also relative-ly high, reflecting at least seven types of living behavioral complexity.Among the coeval ichnocoenoses reported outside Gondwana, the lateSmithian ichnocoenoses from the Helongshan Formation of the LowerYangtze region, South China is most diverse and includes Archaeonassa,Arenicolites, Cochlichnus, Gordia, Gyrochorte, Kouphyichnium, Ophiomor-pha, Palaeophycus, Planolites, Pteridichnites, Thalassinoides, and Treptichnus(Chen et al., 2011). However, the South Chinese ichnocoenoses lack thenesting traces (Lockeia), vertical burrows (Diplocraterion), and grazingtraces (Gnathichnus and Radulichnus), and thus are less complex intrace-making behaviors than the Northampton ichnoassemblage.

In addition, the Gondwanan ichnoassemblage lacks Rhizocorallium, adistinct ichnogenus comprising complex burrow networks and often oc-curring in the recovery stage (Twitchett and Wignall, 1996; Fraiser andBottjer, 2009; Pruss and Bottjer, 2004; Chen et al., 2011; but see Zonne-veld et al., 2010a), but the relatively complicated burrow networks ofThalassinoides are very common in Northampton, indicating a highcomplexity (Twitchett and Wignall, 1996; Pruss and Bottjer, 2004).

6.4. Infaunal tiering

Infaunal tiering is indicated by depth of burrows into beds (Fig. 12).Several vertical burrows (i.e. Arenicolites, Diplocraterion and Laevicyclus),nesting trace (i.e. Lockeia), horizontal or oblique burrows (i.e. Ophiomor-pha, Palaeophycus, Planolites, and Taenidium) and slightly complex bur-row networks (Thalassinoides and Treptichnus) penetrate to a depth upto 30 mm into the sediment and their average depth of penetration is10 mm (Fig. 12), indicating the third to fourth tiering levels (3–4) if fol-lowing the tiring criteria proposed by Bottjer and Ausich (1986).

6.5. Implications for ecologic recovery from the end-Permian massextinction

6.5.1. Trace fossils from Griesbachian–Dienerian in the Perth BasinThe marine sediments of Induan age are only seen in borehole cores

in the Perth Basin. The Griesbachian–Dienerian trace fossils are veryrare except for a few small, simple, horizontal burrows of Planolites(Thomas et al., 2004). This conclusion is confirmed by our recent obser-vation of Wells Hovea–3, Per–10, and Cliff Head–3, 4, 6, about 60 kmsouth of the studied sections. The Induan trace fossils contain only Pla-nolites burrows which are 1–2 mm in diameter and parallel to the bed-ding planes with the depth of penetration less than 5 mm.

6.5.2. Smithian ichnoassemblage and ecologic recovery from the end-Permian mass extinction

As outlined above, 16 ichnospecies in 16 ichnogenera are present in a2-m-thick succession and in an about 20-m-thick succession at the BlueHill-B and Mount Minchin sections, respectively. Thus, the late Smithianichnofauna is considerably higher in diversity than the Griesbachian–

Fig. 12. Average and maximum penetration depths of 10 ichnogenera indicating tiring levels.

252 Z.-Q. Chen et al. / Gondwana Research 22 (2012) 238–255

Dienerian ichnoassemblage. Differing from the small burrows of Pla-nolites in Induan, the same ichnogenus in Smithian has the burrowsaveragely 6.4 mm in diameter. Moreover, all of the Smithian burrowshave an average burrow diameter of 7.0 mm. Unlike the Induan Plano-lites burrows having penetration depth less than 5 mm, the Smithianburrows of the same ichnogenus may penetrate up to 7 mm into sedi-ments below the bedding plane (Fig. 12). Average penetration depth ofall Smithian burrows is 10 mm and the maximum penetration depth isup to 30 mm (Fig. 12). The increasing penetration depth from Induanto Smithian indicates an increase in tiering level (Bottjer and Ausich,1986). Differing from the simple, unbranching burrows in the Induan,the Smithian ichnoassemblage has considerably high burrow complexityreflecting, at least, six types of living behavioral complexity. Accordingly,when comparing with the Griesbachian–Dienerian trace fossils from thePerth Basin, the late Smithian ichnoassemblage experienced a significantincrease in ichnodiversity, burrow size, trace-fossil complexity, tieringlevel, and bioturbation level, indicating the ecologic recovery of trace-maker communities in the Gondwana interior sea during the Smithian.

In North America, the simplified, single-species ichnoassemblage,commonly Planolites, characterizes the earliest Griesbachian, immediate-ly above the P–Tr boundary (Twitchett and Barras, 2004; Beatty et al.,2005; Pruss et al., 2005; Beatty et al., 2008; Zonneveld et al., 2010a,b).Beatty et al. (2005) also suggested that this simplification extends tothe Dienerian–Smithian (also Induan–Olenekian) boundary. Similarly,the Griesbachian trace fossils in other regions of the world are very rareand dominated by small, unbranched, horizontal burrows of Planolites(Twitchett and Wignall, 1996; Twitchett, 1999; Twitchett and Barras,2004; Chen et al., 2011) except for two exceptions from some ‘refugia’(Beatty et al., 2008; Knaust, 2010; Zonneveld et al., 2010a). In westernCanada and Spitsbergen, the Griesbachian ichnofauna is rather diverseand contains some complex forms such as Rhzicorallum (Wignall et al.,1998; Beatty et al., 2008; Zonneveld et al., 2010a). Knaust (2010) hasalso reported two ichnodiversity spikes from the Induan (early and lateInduan, respectively) from a possible low-latitude refugia in Iran. Thus,the Smithian ichnofauna from Gondwana is more diverse and haslarger burrows, higher complexity and higher tiering level than theGriesbachian–Dienerian trace fossils from most regions of the world.Despite lack of some key complex burrows such as Rhizocorallium, theGondwana ichnoassemblage shares similar diversity, complexity, bur-row size and tiering level with the Griesbachian ‘recovery’ ichnofaunasfrom northwestern Pangea (Beatty et al., 2008; Zonneveld et al., 2010a)and Iran (Knaust, 2010), respectively.

Smithian trace fossils have been reported fromwestern United States(Fraiser and Bottjer, 2009), north Italy (Twitchett and Wignall, 1996;Twitchett and Barras, 2004) and South China (Chen et al., 2011). The for-mer two ichnofaunas (8 ichnogenera in US and 6 ichnogenera in Italy)

are much less diverse than the coeval Gondwana ichnofauna. TheSmithian saw an increase in ichnodiversity in South China (Chen et al.,2011). However, the Chinese Smithian ichnofauna comprises 12 ichno-genera in the Lower Yangtze region, South China (Chen et al., 2011),and thus is slightly less diverse than the Gondwana ichnocoenose. Fur-thermore, the Chinese Smithian ichnocoenose comprises the burrowshaving average and maximum diameters of 2 mm and 4mm, and thusare smaller than the coeval burrows from Gondwana. The mean andmaximum penetration depths (8 mm and 12 mm, respectively) of theSmithian burrows from South China (Chen et al., 2011) are also smallerthan the same parameters of the coeval Gondwana burrows, indicatinga much shallower tierer.

Early Triassic ichnoassemblages reached their greatest diversity inSpathian in most regions of the world (Twitchett and Wignall, 1996;Twitchett, 1999; Pruss and Bottjer, 2004; Luo et al., 2007; Fraiser andBottjer, 2009; Chen et al., 2011; see Zonneveld et al., 2010a andKnaust, 2010 for notable exceptions). Their ichnodiversities, burrowsizes, complexities, and tiering levels increase significantly when com-pared to the Griesbachian–Smithian ichnoassemblages (Twitchett,1999; Pruss and Bottjer, 2004; Fraiser and Bottjer, 2009; Chen et al.,2011). The Gondwanan ichnocoenose is comparable with the Spathiantrace fossils in ichnodiversity, ethological behavior, burrow size andtiering level around theworld. Although the complex burrow networksof Rhizocorallium are absent in the Northampton ichnoassemblage, Tha-lassinoides is common in the Gondwana strata and it is considered to becomplex (Twitchett andWignall, 1996; Pruss and Bottjer, 2004; Fraiserand Bottjer, 2009). However, the mean and maximum depths of pene-tration (10 mm and 30 mm, respectively) of Gondwana burrows aremuch smaller than the same proxies of the Spathian ichnocoenosesfrom South China (50 mm, 70 mm; Chen et al., 2011), indicating a shal-lower tierer. Both ii and bpbi values from Northampton are 1–4, andthus are comparable with the same proxies recorded from the SpathianVirgin Limestone of western US (Pruss and Bottjer, 2004; Mata andBottjer, 2011). Nevertheless, the same proxies recorded in the Spathianstrata in north Italy and South China are usually up to 5–6 (Twitchett,1999; Twitchett and Barras, 2004; Chen et al., 2011), indicating a higherbioturbation level than that recorded in Northampton. As a result, alllines of evidence indicate that the Northampton ichnoassemblage rep-resents a pronounced rebound of ichnotaxa after the P–Tr crisis andmay have reached the recovery stage 3 of Twitchett's (2006) model.

7. Implications for environmental controls on ichnoassemblagerebounds in the aftermath of the end-Permian mass extinction

Deleterious, oxygen-deficient ocean environments are believed tohave prevailed throughout most stages of the Early Triassic in most

253Z.-Q. Chen et al. / Gondwana Research 22 (2012) 238–255

regions of the world (Hallam, 1991; Hallam andWignall, 1997; Bottjer,2004, 2005; Bottjer and Gall, 2005; Bottjer et al., 2008). Ichnofaunal re-sponses to such environmental conditions include low ichnodiversity,small-sized burrows, low penetration depths, low complexity, andlowbioturbation levels (Twitchett andWignall, 1996; Pruss and Bottjer,2004; Morrow and Hasiotis, 2007; Fraiser and Bottjer, 2009; Chen et al.,2011). The Gondwana ichnofauna has fairly high ichnodiversity andbioturbation levels and is comprised of relatively large burrows andcomplex trace systems. They therefore share many ecologic featureswith late Early Triassic and Middle Triassic ichnofaunas inhabiting nor-mal shallow marine settings (Zonneveld et al., 2001). In Northampton,most trace fossils were collected from the upper part of Unit D andthe lower part of Unit E. The former was deposited in a setting betweenfair-weather wave base to the lower part of the intertidal zone. ThelowerUnit E represents an environment above or/and near fair-weatherwave base, which was a low-energy mud flat with occasional influenceby wave action. These tracemakers therefore inhabited the environ-mental setting that had no sign of anoxic conditions, but was well-oxy-genated during the Smithian. The presence of most of the Northamptontrace fossils in shoreface settings supports the previous view that theshoreface setting provides tracemakers a possible ‘refugia’ to survive theend-Permian mass extinction (Beatty et al., 2008; Zonneveld et al.,2010a). The “habitable zone”model of Beatty et al. (2008) and Zonneveldet al. (2010a) has also been supported by the Early Triassic ichnofossilsfrom western US and South China (Chen et al., 2011; Mata and Bottjer,2011). However, the upper part of Unit E is dominated by cross-stratifiedsiltstone and fine sandstone, and thus also indicates a well-oxygenatedshoreface setting with active wave actions. The latter succession, surpris-ingly, records few trace fossils. Accordingly, ichnofaunas were notabundant and diverse in all shoreface settings in the aftermath ofthe end-Permian crisis. In addition, the ‘refugia’model for tracemakersin shoreface setting needs to be tested because no studies have beenun-dertaken to evaluate the shoreface ichnofaunal change over the end-Permian mass extinction horizon. In contrast, increase in biodiversityof the coeval benthos in late Griesbachian has been interpreted as an in-dication of fast recovery (Twitchett et al., 2004; Chen et al., 2007, 2010).

If looking at the global distributions of the Early Triassic trace fossils(Twitchett and Wignall, 1996; Twitchett, 1999; Zonneveld et al., 2002;Pruss and Bottjer, 2004; Twitchett and Barras, 2004; Zonneveld et al.,2004; Beatty et al., 2005; Morrow and Hasiotis, 2007; Beatty et al.,2008; Fraiser and Bottjer, 2009; Knaust, 2010; Zonneveld et al., 2010a,b;Chen et al., 2011;Mata and Bottjer, 2011), therewere several ichnodiver-sity spikes occurring inmiddle and late Griesbachian, late Dienerian, earlySmithian, late Smithian, respectively in various places in theworld beforetheir global proliferation in Spathian. The habitats hosting ichnodiversityspikes varied from shallow shoreface (Markhasin, 1997; Kendall, 1999;Panek, 2000; Beatty et al., 2008; Zonneveld et al., 2010a;Mata and Bottjer,2011; this study), to platform (Knaust, 2010) to highly evaporiticmargin-al sea (Chen et al., 2011), although all substrates were oxygenated.

8. Conclusions

A total of 16 ichnogenera (including a problematic ichnotaxon) isreported from the late Smithian successions in the Northampton areaof the Perth Basin, Western Australia. This ichnoassemblage is themost diverse among the coeval ichnofaunas worldwide. Several typesof grazing traces are reported for the first time in the Lower Triassic.The tracemakers likely inhabited onmicrobe-bound soft grounds. Sever-al lines of evidence, including bioturbation level, ichnodiversity, burrowsize, trace-fossil complexity, and tiering level, suggest that marine trace-makers proliferated in an oxygenated shoreface setting in theGondwanainterior sea during the late Smithian. This ichnofauna may have reachedthe ecologic recovery stage 3 of Twitchett's model. This research sug-gests that proliferation of ichnofaunas did not have any environmentalpreferences in the aftermath of the end-Permian crisis, although theirsubstrates were usually oxygenated.

Acknowledgments

We thank two anonymous reviewers for their critical comments,which have greatly improved the quality of this paper. Special thanksare also extended to A.J. Mory, D.W. Haig and J. Tong for their assistancein collecting trace fossils in the field. This study is supported by a discov-ery grant from the Australian Research Council (DP0770938 to ZQC). Itis a contribution to the IGCP 572 “Permian–Triassic ecosystems”.

References

Abbassi, N., 2007. Shallow marine trace fossils from Upper Devonian sediments of theKuh-e Zard, Zefreh Area, Central Iran. Iranian Journal of Science and Technology,Transaction A 31, 23–33.

Arnott, R.W.C., 1995. The parasequence definition—are transgressive deposits inade-quately addressed? Journal of Sedimentary Research B 65, 1–6.

Beatty, T.W., Zonneveld, J.-P., Henderson, C.M., 2005. Late Permian and Early Triassicichnofossil assemblages from the northwest margin of Pangea. Albertiana 33,19–20.

Beatty, T.W., Zonneveld, J.-P., Henderson, C.M., 2008. Anomalously diverse Early Trias-sic ichnofossil assemblages in northwest Pangea: a case for a shallow-marine hab-itable zone. Geology 36, 771–774.

Benton, M.K., 2003. When Life Nearly Died: The Greatest Mass Extinction of All Life.Thames & Hudson, London. (336 pp.).

Bolton, C., Chen, Z.Q., Fraiser, M.L., 2010. A new trace-fossil assemblage from the LowerTriassic of Western Australia. Journal of Earth Science 21, 115–117 (special issue).

Bottjer, D.J., 2004. The beginning of the Mesozoic: 70 million years of environmentalstress and extinction. In: Taylor, P.D. (Ed.), Extinctions in the History of Life. Cam-bridge University Press, pp. 202–206.

Bottjer, D.J., 2005. Bioturbation and Early Triassic environmental crises. In: Tong, J.N. (Ed.),Part 1: Program and Abstracts, International Symposium on the Triassic Chronostrati-graphy and Biotic Recovery, 23–25 May, 2005—Chaohu, China, 33. Albertiana, pp.76–79.

Bottjer, D.J., Ausich, W.I., 1986. Phanerozoic development of tiering in soft substratasuspension-feeding communities. Paleobiology 12, 400–420.

Bottjer, D.J., Gall, J.C., 2005. The Triassic recovery, the dawn of the modern biota. Comp-tes Rendus Palevol 4, 385–393.

Bottjer, D.J., Clapham, M.E., Fraiser, M.L., Powers, C.M., 2008. Understanding mecha-nisms for the end-Permian mass extinction and the protracted Early Triassic after-math and recovery. GSA Today 18, 4–10.

Brayard, A., Escarguel, G., Bucher, H., Bruhwiler, T., 2009. Smithian and Spathian (EarlyTriassic) ammonoid assemblages from terranes: paleoceanographic and paleogeo-graphic implications. Journal of Asian Earth Sciences 36, 420–433.

Briggs, D.E.G., Miller, M.F., Isbell, J.L., Sidor, C.A., 2010. Permo-Triassic arthropod tracefossils from the Beardmore Glacier area, central Transantarctic Mountains, Antarc-tica. Antarctic Science 22, 185–192.

Bromley, R.G., 1975. Comparative analysis of fossil and recent echinoid bioerosion.Palaeontology 18, 725–739.

Bromley, R.G., 1996. Trace Fossils: Biology, Taphonomy and Applications (2nd Edition).Chapman & Hall, London. (361 pp.).

Brühwiler, T., Goudemand, N., Bucher, H., Brayard, A., 2007. Smithian (Early Triassic)ammonoid successions of the Tethys: new preliminary results from Tibet, India,Pakistan and Oman. New Mexico Museum of Natural History and Science Bulletin41, 25–26.

Brühwiler, T., Brayard, A., Bucher, H., Guodun, K., 2008. Griesbachian and Dienerian(Early Triassic) ammonoid faunas from northwestern Guangxi and southern Gui-zhou (South China). Palaeontology 51, 1151–1180.

Brühwiler, T., Bucher, H., Goudemand, N., 2010. Smithian (Early Triassic) ammonoidsfrom Tulong, South Tibet. Geobios 43, 403–431.

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., Mangano, M.G., Maples, C.G., Lanier, W.P., 1998. Ichnology of an UpperCarboniferous fluvio-estuarine paleovalley: the Tonganoxie Sandstone, BuildexQuarry, eastern Kansas, USA. Journal of Paleontology 72, 152–180.

Buatois, L.A., Mangano, M.G., Fregenal-Martinez, M.A., de Gibert, J.M., 2000. Short-termcolonization trace-fossil assemblages in a carbonate lacustrine Konservat-Lager-statte (Las Hoyas Fossil Site, Lower Cretaceous, Cuenca, Central Spain). Facies 43,145–156.

Chen, Z.Q., Tong, J., Kaiho, K., Kawahata, H., 2007. Onset of biotic and environmental re-covery from the end-Permian mass extinction within 1–2 million years; a casestudy of the Lower Triassic of the Meishan Section, south China. Palaeogeography,Palaeoclimatology, Palaeoecology 252, 176–187.

Chen, Z.Q., Tong, J., Fraiser, M.J., 2011. Trace fossil evidence for restoration of marineecosystems following the end-Permian mass extinction in the Lower Yangtzeregion, South China. Palaeogeography, Palaeoclimatology, Palaeoecology 299,449–474.

Chen, Z.Q., Tong, J.N., Liao, Z.T., Chen, J., 2010. Structural changes of marine communi-ties over the Permian-Triassic transition: ecologically assessing the end-Permianmass extinction and its aftermath. Global and Planetary Changes 73, 123–140.

Crimes, T.P., Legg, I., Marcos, A., Arboleya, M., 1977. ?Late Precambrian–low LowerCambrian trace fossils from Spain. In: Crimes, T.P., Harper, J.C. (Eds.), Trace Fossils2. : Geological Journal Special Issue, 9. Seel House Press, Liverpool, U.K., pp. 91–138.

254 Z.-Q. Chen et al. / Gondwana Research 22 (2012) 238–255

Crostella, A., Backhouse, J., 2000. Geology and petroleum exploration of the central andsouthern Perth Basin, Western Australia. Geological Survey of Western AustraliaReport 57.

D'Alessandro, A., Bromley, R.G., 1987. Meniscate trace fossils and theMuensteria–Taenidiumproblem. Palaeontology 30, 743–763.

Dafoe, L.T., Gingras, M.K., Pemberton, S.G., 2010. Wave-influenced deltaic sandstonebodies and offshore deposits in the Viking Formation, Hamilton Lake area, south-central Alberta, Canada. In: Zonneveld, J.-P., Gingras, M.K., MacEachern, J.A.(Eds.), Applications of Ichnology to Petroleum Exploration: Bulletin of CanadianPetroleum Geology, 58, pp. 173–201.

de Gibert, J.M., Domenech, R., Martinell, J., 2007. Bioerosion in shell beds from the Pli-ocene Roussillon Basin, France: implications for the (macro)bioerosion ichnofaciesmodel. Acta Palaeontologica Polonica 52, 783–798.

Dickens, J.M., Campbell, H.J., 1992. Permo-Triassic boundary inAustralia andNewZealand.In: Sweet,W.C., Yang, Z., Dickins, J.M., Yin, H. (Eds.), Permo-Triassic Events in the East-ern Tethys. Cambridge University Press, Cambridge, UK, pp. 175–178.

Dornbos, S.Q., Bottjer, D.J., Chen, J.Y., 2004. Evidence for seafloor microbial mats and as-sociated metazoan lifestyles in Lower Cambrian phosphorites of Southwest China.Lethaia 37, 127–137.

Droser, M.L., Bottjer, D.J., 1986. A semiquantitative field classification of ichnofabric.Journal of Sedimentary Petrology 56, 558–559.

Eagar, R.M.C., Baines, J.G., Collinson, J.D., Hardy, P.G., Okolo, S.A., Pollard, J.E., 1985.Trace fossil assemblages and their occurrence in Silesian (mid-Carboniferous)deltaic sediments of the central Pennine Basin, England. In: Curran, H.A.(Ed.), Biogenic Structures: Their Use in Interpreting Depositional Environ-ments: Society of Economic Paleontologists and Mineralogists, Special Publica-tion, 35, pp. 99–149.

Edgell, H.S., 1964. Triassic ammonoite impressions from the type section of the Min-chin Siltstone, Perth Basin. Geological Survey of Western Australia, Annual Reportfor 1963, pp. 55–57.

Ekdale, A.A., Bromley, R.G., 2003. Paleoethologic interpretation of complex Thalassinoidesin shallow-marine limestone, Lower Ordovician, southern Sweden. Palaeogeography,Palaeoclimatology, Palaeoecology 192, 221–227.

Erwin, D.H., 2006. How Life on Earth Nearly Ended 250 Million Years Ago. PrincetonUniversity Press, Princeton. (306 pp.).

Försterra, G., Beuck, L., Häussermann, V., Freiwald, A., 2005. Shallow-water Desmophyllumdianthus (Scleractinia) from Chile: characteristics of the biocoenoses, the bioerodingcommunity, heterotrophic interactions and (paleo)-bathymetric implications. In:Freiwald, A., Roberts, J.M. (Eds.), Cold-water Corals and Ecosystems. Springer-Verlag,Berlin, pp. 937–977.

Fraiser, M.L., Bottjer, D.J., 2009. Opportunistic behavior of invertebrate marine trace-makers during the Early Triassic aftermath of the end-Permian mass extinction.Australian Journal of Earth Sciences 56, 841–857.

Frey, R.W., Howard, J.D., Pryor, W.A., 1978. Ophiomorpha—its morphologic, taxonomic,and environmental significance. Palaeogeography, Palaeoclimatology, Palaeoecol-ogy 23, 199–229.

Fürsich, F.T., Wendt, J., 1977. Biostratigraphy and palaeoecology of the Cassian Forma-tion (Triassic) of the Southern Alps. Palaeogeography, Palaeoclimatology, Palaeoe-cology 22, 257–323.

Gastaldo, R.A., Rolerson, M.W., 2008. Katbergia gen. nov., a new trace fossil from theLate Permian and Early Triassic of the Karoo Basin: implications for paleoenviron-mental conditions at the P/Tr extinction event. Palaeontology 51, 215–229.

Goldring, R., Pollard, J.E., Radley, J.D., 2005. Trace fossils and pseudofossils from theWealden Strata (non-marine Lower Cretaceous) of southern England. CretaceousResearch 16, 665–685.

Gouramis, C., Webb, J.A., Warren, A.A., 2003. Fluviodeltaic sedimentology and ichnol-ogy of part of the Silurian Grampians Group, Western Victoria. Australian Journalof Earth Sciences 50, 811–825.

Gradzinski, R., Uchman, A., 1994. Trace fossils from interdune deposits: an examplefrom the Lower Triassic Aeolian Tumlin Sandstone, Central Poland. Palaeogeogra-phy, Palaeoclimatology, Palaeoecology 108, 121–138.

Grice, K., Cao, C., Love, G.D., Bottcher, M.E., Twitchett, R., Grosjean, E., Summons, R.E.,Turgeon, S.C., Dunning, W., Jin, Y., 2005. Photic zone euxinia during the Permian–Triassic superanoxic event. Science 307, 706–709.

Groenewald, G.H., Maceachern, J.A., Evans, F.J., 1998. Ichnology of the Triassic UpperBeaufort Group (Karoo Supergroup), Venterstad area, South Africa. Journal of Afri-can Earth Sciences 27, 93–94.

Groenewald, G.H., Welman, J., MacEachern, J.A., 2001. Vertebrate burrow complexesfrom, the Early Triassic cynognathus Zone (Driekoppen Formation, BeaufortGroup) of the Karoo Basin, South Africa. Palaios 16, 148–160.

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 HousePress, Liverpool, U.K., pp. 209–226.

Hallam, A., 1991. Why was there a delayed radiation after the end-Paleozoic extinc-tions? Historical Biology 5, 257–262.

Hallam, A., Wignall, P.B., 1997. Mass Extinctions and their Aftermath. Oxford UniversityPress, New York. (319 pp.).

Häntzschel, W., 1975. Trace fossils and problematica, In: Teichert, C. (Ed.), Treatise ofInvertebrate Paleontology, (2nd Edition). Part W, Miscellanea, Supplement 1, Uni-versity of Kansas and Geological Society of America, Lawrence, Kansas. 269 pp.

Hasiotis, S.T., 1993. Ichnology of Triassic and Holocene cambarid crayfish of NorthAmerica: an overview of burrowing behavior and morphology as reflected bytheir morphologies in the geologic record. Freshwater Crayfish 9, 399–406.

Hasiotis, S.T., Mitchell, C.E., 1993. A comparison of crayfish burrow morphologies: Tri-assic and Holocene fossil, paleo- and neo-ichnological evidence, and the identifica-tion of their burrowing signatures. Ichnos 2, 291–314.

Hasiotis, S.T., Miller, M.F., Isbell, J., Babcock, L.E., Collinson, J.W., 1998. Triassic trace fos-sils from Antarctica: burrow evidence of crayfish or mammal-like reptiles? Resolv-ing crayfish from tetrapod burrows. Freshwater Crayfish 12, 71–81.

Hermann, E., Hochuli, P.A., Bucher, H., Brühwiler, T., Hautmann, M., Ware, D., Roohi, G.,2011. Terrestrial ecosystem on North Gondwana following the end-Permian massextinction. Gondwana Research 20, 630–637.

Hocking, R.M., Moors, H.T., Van de Graaff, W.J.R., 1987. Geology of the Carnarvon Basin,Western Australia. Geological Survey of Western Australia Bulletin 133, 1–307.

Jensen, S., 2003. The Proterozoic and earliest Cambrian trace fossil record, patterns,problems and perspectives. Integrative and Comparative Biology 43, 219–228.

Jüch, J.W.M., Boekschoten, G.J., 1980. Trace fossils and grazing traces produced by Lit-torina and Lepidochitona, Dutch Wadden Sea. Geologie en Mijnbouw 59, 33–42.

Karajas, J. 1969. A geological investigation of an area between Mt. Minchin and theBowes River, Northampton District, Western Australia. Unpublished Honours The-sis. University of Western Australia, Nedlands, 113 pp.

Keighley, D.G., Pickerall, R.K., 1997. Systematic ichnology of the Mabou and Cumber-land Groups (Carboniferous) of Western Cape Breton Island, Eastern Canada, 1:burrows, pits, trails and coprolites. Atlantic Geology 33, 181–215.

Keighley, D.G., Pickeril, P.K., 1994. The ichnogenus Beaconites and its distinction fromAncorichnus and Taenidium. Palaeontology 37, 305–337.

Kendall, D.R. 1999. Sedimentology and stratigraphy of the Lower Triassic Montney For-mation, Peace River Basin, subsurface of northwestern Alberta. Unpublished M.Sc.Thesis, University of Calgary, Calgary, Canada, 394 pp.

Knaust, D., 2004. Cambro-Ordovician trace fossils from the SW-Norwegian Caledo-nides. Geological Journal 39, 1–24.

Knaust, D., 2010. The end-Permian mass extinction and its aftermath on an equatorialcarbonate platform: insights from ichnology. Terra Nova 22, 195–202.

Luo, M., Shi, G., Gong, Y., 2007. Early Triassic trace fossils in Huaxi region of Guiyangand their implications for biotic recovery after the end-Permian mass extinction.Journal of Palaeogeography 9, 519–532.

MacEachern, J.A., Bechtel, D.J., Pemberton, S.G., 1992. Ichnology and sedimentology oftransgressive deposits, transgressively-related deposits and transgressive systemstracts in the Viking Formation of Alberta. In: Pemberton, S.G. (Ed.), Applications ofIchnology to Petroleum Exploration: A Core Workshop: Society of Economic Pale-ontologists and Mineralogists, Core Workshop, 17, pp. 251–290.

MacEachern, J.A., Zaitlin, B.A., Pemberton, S.G., 1999a. Coarse-grained, shore-line-attached,marginal marine parasequences of the Viking Formation, Joffre Field, Alberta, Canada.In: Bergman, K.M., Snedden, J.W. (Eds.), Isolated Shallow Marine Sand Bodies: Se-quence Stratigraphic Analysis and Sedimentologic Interpretation: SEPM Special Publi-cation, 64, pp. 273–296.

MacEachern, J.A., Zaitlin, B.A., Pemberton, S.G., 1999b. A sharp-based sandstone ofthe Viking Formation, Joffre Field, Alberta, Canada: criteria for recognition of trans-gressively incised shoreface complex. Journal of Sedimentary Research 69,876–892.

Maples, C.G., Archer, A.W., 1987. Redescription of Early Pennsylvanian trace fossil ho-lotypes from the nonmarine Hindostan Whetstone Beds of Indiana. Journal of Pale-ontology 61, 890–897.

Markhasin, B. 1997. Sedimentary and stratigraphy of the Lower Triassic Montney For-mation, subsurface of northwestern Alberta. Unpublished M.Sc. Thesis, Universityof Calgary, Calgary, Canada, 212 pp.

Mata, S.C., Bottjer, D.J., 2011. Origin of Lower Triassic microbialites in mixed carbonate–siliciclastic successions: ichnology, applied stratigraphy, and the end-Permian massextinction. Palaeogeography, Palaeoclimatology, Palaeoecology 300, 158–178.

McTavish, R.A., Dickins, J.M., 1974. The age of the Kockatea Shale (Lower Triassic), PerthBasin—a reassessment. Journal of the Geographical Society of Australia 21, 195–202.

Metcalfe, I., Nicoll, R.S., Willink, R.J., 2008. Conodonts from the Permian–Triassic tran-sition in Australia and position of the Permian–Triassic boundary. Australian Jour-nal of Earth Sciences 55, 365–377.

Metz, R., 1998. Nematode trails from the Late Triassic of Pennsylvania. Ichnos 5, 303–308.Miller, M.F., Smail, S.E., 1997. A semiquantitative method for evaluating bioturbation

on bedding planes. Palaios 12, 391–396.Miller, M.F., Hasiotis, S.T., Babcock, L.E., Isbell, J.L., Collinson, J.W., 2001. Tetrapod and

large burrows of uncertain origin in Triassic high paleolatitude floodplain deposits,Antarctica. Palaios 16, 218–232.

Minter, N.J., Braddy, S.J., Davis, R.B., 2007. Between a rock and a hard place: arthropodtrackways and ichnotaxonomy. Lethaia 40, 365–375.

Morrow, J.R., Hasiotis, S.T., 2007. Chapter 36, endobenthic response through mass extinc-tion episodes: predictive models and observed patterns. In: Miller III, W. (Ed.), TraceFossils: Concepts, Problems, Prospects. Elsevier, Amsterdam, pp. 575–598.

Osgood Jr., R.G., 1970. Trace fossils of the Cincinnati area. Paleontographic Americana 6,281–444.

Panek, R. 2000. The sedimentology and stratigraphy of the Lower Triassic Montney For-mation in the subsurface of the Peace River area, northwestern Alberta. Unpub-lished M.Sc. Thesis, University of Calgary, Calgary, Canada, 275 pp.

Pemberton, S.G., Frey, R.W., 1984. Quantitative methods in ichnology: spatial distribu-tion among populations. Lethaia 17, 33–49.

Pruss, S.B., Bottjer, D.J., 2004. Early Triassic fossils of the western United States andtheir implications for prolonged environmental stress from the end-Permianmass extinction. Palaios 19, 551–564.

Pruss, S.B., Corsetti, F.A., Bottjer, D.J., 2005. The unusual sedimentary rock record of theEarly Triassic: a case study from the southwestern United States. Palaeogeography,Palaeoclimatology, Palaeoecology 222, 33–52.

Reyes, Y., Córdova, C., Romero, L., Paredes, C., 2001. Marcas radulares producidas por gaster-ópodos pastoreadores del intermareal rocoso. Revista Peruana de Biología 8, 38–44.

Rindsberg, A.K., Kopaska-Merkel, D.C., 2005. Treptichnus and Arenicolites from theSteven C. Minkin Paleozoic footprint Site (Langsettian, Alabama, USA). In: Buta,

255Z.-Q. Chen et al. / Gondwana Research 22 (2012) 238–255

R.J., Rindsberg, A.K., Kopaska-Merkel, D.C. (Eds.), Pennsylvanian Footprints in theBlack Warrior Basin of Alabama: Monograph, 1. Alabama Paleontological Society,pp. 121–141.

Scotese, C.R., 1994. Early Triassic paleogeographic map. In: Klein, G.D. (Ed.), Pangea:Paleoclimate, Tectonics and Sedimentation during Accretion, Zenith and Breakupof a Supercontinent: Geological Soceity of America Special Paper 288, p. 7.

Seilacher, A., 1953. Studien zur Palichnologie. I. Über die Methoden der Palichnologie.Neues Jahrbuch für Geologie und Paläontologie. Abhandlungen 98, 421–452.

Seilacher, A., 2007. Trace Fossil Analysis. Springer, Berlin. (226 pp.).Seilacher, A., Grazhdankin, D., Legouta, A., 2003. Ediacaran biota: the dawn of animal

life in the shadow of giant protists. Paleontological Research 7, 43–54.Seilacher, A., Buatois, A., Mángano, M.G., 2005. Trace fossils in the Ediacaran–Cambrian

transition: behavioral diversification, ecological turnover and environmental shift.Palaeogeography, Palaeoclimatology, Palaeoecology 227, 323–356.

Shigeta, Y., Maeda, H., Zakharov, Y., 2009. Biostratigraphy: ammonoid succession. In:Shigeta, Y., Zakharov, Y., Maeda, H., Popov, A.M. (Eds.), The Lower Triassic Sys-tem in the Abrek Bay Area, South Primorye, Russia. : National Museum of Natureand Science Monographs, 38. National Museum of Nature and Science, Tokyo,pp. 24–27.

Sidor, C.A., Miller, M.F., Isbell, J.L., 2008. Tetrapod burrows from the Triassic of Antarctica.Journal of Vertebrate Paleontology 28, 277–284.

Skwarko, S.K., Kummel, B., 1974. Some marine Triassic macrofossils of Australia andPapua New Guinea. Bureau of Mineral Resources, Geology and Geophysics: Depart-ment of Minerals and Energy, Bulletin, 150, pp. 111–127.

Thomas, B.M., Willink, R.J., Grice, K., Twitchett, R.J., Purcell, R.R., Archbold, N.W.,George, A.D., Tye, S., Alexander, R., Foster, C.B., Barber, C.J., 2004. Unique marinePermian–Triassic boundary section from Western Australia. Australian Journal ofEarth Sciences 51, 423–430.

Thompson, R.C., Johnson, L.E., Hawkins, S.J., 1997. A method for spatial and temporalassessment of gastropod grazing intensity in the field: the use of radula scrapeson wax surfaces. Journal of Experimental Marine Biology and Ecology 218, 63–76.

Tong, J., Zakharov, Y.D., Wu, S.B., 2004. Early Triassic ammonoid succession in Chaohu,Anhui Province. Acta Palaeontologica Sinica 43, 192–204.

Trewin, N.H., McNamara, K.J., 1995. Arthropods invade the land: trace fossils and palaeoen-vironments of the Tumblagooda Sandstone (?Late Silurian) of Kalbarri, Western Aus-tralia. Transactions of the Royal Society of Edinburgh, Earth Sciences 85, 177–210.

Twitchett, R.J., 1999. Palaeoenvironments and faunal recovery after the end-Permianmass extinction. Palaeogeography, Palaeoclimatology, Palaeoecology 154, 27–37.

Twitchett, R.J., 2006. The palaeoclimatology, palaeoecology and palaeoenvironmentalanalysis of mass extinction events. Palaeogeography, Palaeoclimatology, Palaeoe-cology 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 Strati-graphic 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–Triassicmass extinction: evidence from Northern Italy. Palaeogeography, Palaeoclimatology,Palaeoecology 124, 137–151.

Twitchett, R.J., Krystyn, L., Baud, A., Wheeley, J.R., Richoz, S., 2004. Rapid marine recov-ery after the end-Permian mass-extinction event in the absence of marine anoxia.Geology 32, 805–808.

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.), PennsylvanianFootprints in the Black Warrior Basin of Alabama: Alabama Paleontological SocietyMonograph, 1, pp. 143–146.

Vakarelov, B.K., Ainsworth, R.B., MacEachern, J.A. Recognition of wave-dominated tide-influenced shoreline systems in the rock record: variations from a microtidal shore-line model. Sedimentary Geology (in press), doi:10.1016/j.sedgeo.2011.03.004.

Verde, M., Ubilla, M., Jimenez, J.J., Genise, J.F., 2007. A new earthworm trace fossilfrom paleosols: aestivation chambers from the Late Pleistocene Sopas Forma-tion of Uruguay. Palaeogeography, Palaeoclimatology, Palaeoecology 243,339–347.

Voigt, E., 1977. On grazing traces produced by the radula of fossil and Recent gastro-pods and chitons. In: Crimes, T.P., Harper, J.C. (Eds.), Trace Fossils 2. : GeologicalJournal Special Issues, 9. Seel House Press, Liverpool, pp. 335–346.

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. Geo-logical Magazine 135, 47–62.

Wisshak, M., Gektidis, M., Freiwald, A., Lundälv, T., 2005. Bioerosion along a bathymet-ric gradient in a cold–temperate setting (Kosterfjord, SW Sweden): an experimen-tal study. Facies 51, 93–117.

Zonneveld, J.-P., Gingras, M.K., Pemberton, S.G., 2001. Trace fossil assemblages in aMiddle Triassic mixed siliciclastic–carbonate marginal marine coastal depositionalsystem, British Columbia. Palaeogeography, Palaeoclimatology, Palaeoecology 166,249–276.

Zonneveld, J.P., MacNaughton, R., Pemberton, G., 2002. Ichnology of the Lower TriassicMontney Formation, Kahntah River and Ring Border Fields, northeastern BritishColumbia. CSPG Diamond Jubilee Convention Abstracts of Technical Talks and Post-ers, p. 342.

Zonneveld, J.-P., Henderson, C., MacNaughton, R.B., Beatty, T.W., 2004. Diverse ichnofossilassemblages from the Lower Triassic of northeastern British Columbia, Canada: evi-dence for a shallowmarine refugiumon the northwestern coast of Pangea. GeologicalSociety of America, Abstracts with Programs, 36, p. A336.

Zonneveld, J.-P., Gingras, M.K., Beatty, T.W., 2010a. Diverse ichnofossil assemblage follow-ing the P–Tmass extinction, Lower Triassic, Alberta and British Columbia, Canada: ev-idence for shallow marine refugia on the northwestern coast of Pangaea. Palaios 25,368–392.

Zonneveld, J.-P., MacNaughton, R.B., Utting, J., Beatty, T.W., Pemberton, S.C., Henderson, C.M.,2010b. Sedimentology and ichnology of the Lower TriassicMontney Formation in thePedigree-Ring/Border-Kahntah River area, northwestern Alberta and northeasternBritish Columbia. In: Zonneveld, J.-P., Gingras, M.K., MacEachern, J.A. (Eds.), Applica-tions of Ichnology to Petroleum Exploration: Bulletin of Canadian PetroleumGeology,58, pp. 1–26.