A Smithian (Early Triassic) ichnoassemblage from Lichuan, Hubei Province, South China: Implications for biotic recovery after the latest Permian mass extinction

Accepted Manuscript A Smithian (Early Triassic) ichnoassemblage from Lichuan, Hubei Province, South China: Implications for biotic recovery after the latest Permian mass extinction

Xueqian Feng, Zhong-Qiang Chen, Adam Woods, Yuheng Fang PII: DOI: Reference:

S0031-0182(17)30242-0 doi: 10.1016/j.palaeo.2017.03.003 PALAEO 8226

To appear in:

Palaeogeography, Palaeoclimatology, Palaeoecology

Received date: Revised date: Accepted date:

29 October 2016 23 February 2017 3 March 2017

Please cite this article as: Xueqian Feng, Zhong-Qiang Chen, Adam Woods, Yuheng Fang , A Smithian (Early Triassic) ichnoassemblage from Lichuan, Hubei Province, South China: Implications for biotic recovery after the latest Permian mass extinction. The address for the corresponding author was captured as affiliation for all authors. Please check if appropriate. Palaeo(2017), doi: 10.1016/j.palaeo.2017.03.003

This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

ACCEPTED MANUSCRIPT A Smithian (Early Triassic) ichnoassemblage from Lichuan, Hubei Province, South China: implications for biotic recovery after the latest Permian mass extinction

SC

RI

PT

Xueqian Fenga, Zhong-Qiang Chena, *, Adam Woodsb, Yuheng Fanga a State Key laboratory of Biogeology and Environmental Geology, School of Earth Science, China University of Geosciences (Wuhan), Wuhan 430074, China b Department of Geological Sciences, California State University Fullerton, Fullerton, CA 92834, USA *Corresponding author (ZQC): e-mail: [email protected] Abstract

AC

CE

PT E

D

MA

NU

A late Smithian ichnoassemblage is reported from the Lower Triassic succession from the Lichuan section, western Hubei Province, South China. This ichnoassemblage comprises 13 ichnogenera, which include simple, horizontal traces (Cochlichnus, Cosmorhaphe, Didymaulichnus, Gordia, Circulichnis, and Planolites), vertical traces (Arenicolites, Laevicyclus), oblique- or horizontal branching traces (Palaeophycus), slightly complex burrow networks (Thalassinoides, and Treptichnus), and grazing traces (Cosmorhaphe and Gyrochorte). These traces are also categorized into fodinichnia, domichnia, pascichnia, and repichnia ethologic types, suggesting a fairly high degree of behavioral complexity. Of these, the fodinichnia traces are most abundant. The ichnoassemblage horizons usually have rather high ichnofabric indices (ii), reaching ii 4–5. Bedding plane coverage is up to 70–90%, resulting in high bedding plane bioturbation index as well (BPBI 4–5). The Lichuan ichnoassemblage traces have mean and maximum diameters of 4.8 mm and 9 mm, respectively (n = 342). The traces penetrate to a depth of up to 30 mm into the sediment, with an average depth of penetration of 15 mm, indicating third to fourth tiering levels (3–4). Overall, the Lichuan ichnofauna shows an abrupt increase in ichnodiversity, burrow width, behavioral complexity, and ecologic tiering level, which are indicative of recovery stages of 2–3 in the late Smithian. When compared to five coeval ichnoassemblages from other sections in South China (Yashan, Susong, Daxiakou, Gaimao, and Tianshengqiao) and coeval ichnoassemblages from elsewhere (northern Italy, Western Australia, western US), the Lichuan trace-fossil assemblage reaches similar level of diversity during this time interval. Paleoenvironmental analysis indicates that the late Smithian recovery pulse is typically confined to the offshore transition setting, whereas more distal zones record much lower levels of recovery. Therefore, time and environmental conditions were the two crucial factors controlling the rate and degree of recovery of trace-making organisms in the aftermath of the latest Permian mass extinction.

ACCEPTED MANUSCRIPT Keywords: ichnofauna; ecologic tiering; bioturbation; recovery rate; ichnodiversity; Lower Triassic 1. Introduction

AC

CE

PT E

D

MA

NU

SC

RI

PT

The latest Permian mass extinction severely devastated the diversity of marine organisms; the functional diversity of ecosystems was mostly unaffected at the global scale, but was affected regionally and within certain habitats (Twitchett and Wignall, 1996; Twitchett, 1999, 2006; Twitchett and Barras, 2004; Pruss and Bottjer, 2004; Beatty et al., 2008; Fraiser and Bottjer, 2009; Zonneveld et al., 2010; Knaust, 2010; Chen et al., 2011, 2012, 2015; Luo and Chen, 2014; Zhao et al., 2015; Shi et al., 2015; Foster and Twitchett, 2014; Scheyer et al., 2014; Foster et al., 2015; Luo et al., 2016). There is strong evidence to suggest that trace-makers may have rebounded earlier than many metazoan clades, with the return of full ecosystems occurring in the early Middle Triassic (Chen and Benton, 2012). Ichnoassemblages occur occasionally (Wignall et al., 1998; Beatty et al., 2008; Zonneveld et al., 2010; Hofmann et al., 2011, 2015; Shi et al., 2015), but, overall ichnofossils are rare in pre-Spathian strata in many regions, and did not re-diversify until the Spathian when trace-makers recovered worldwide (Twitchett, 1999; Pruss and Bottjer, 2004; Fraiser and Bottjer, 2009; Chen et al., 2011; Zhao et al., 2015; Luo et al., 2016). The stratigraphic distribution of Lower Triassic trace fossils is very uneven, particularly in South China. In general, most Lower Triassic strata are barren of trace fossils or yield only a few traces. However, in many cases, trace fossils are densely packed into thin stratal intervals (less than several meters in thickness), and contain extraordinarily abundant and diverse ichnotaxa (Chen et al., 2011; Shi et al., 2015; Zhao et al., 2015; Luo et al., 2016). These Early Triassic trace fossils provide detailed ichno-ecologic characteristics that allow the assessment of biotic recovery processes after the latest Permian mass extinction. Here, we report on one such ichnoassemblage from the Smithian upper Daye Formation from the Lichuan area, western Hubei Province, South China (Fig. 1). The newly found ichnoassemblage is exposed at a quarry near the city of Lichuan and contains multiple ichnotaxa. Ichno-ecologic analysis of this assemblage reveals a high recovery stage of trace-making organisms; therefore, this paper aims to document all ichnotaxa within the ichnofossil assemblage. In order to evaluate the recovery processes acting within marine ecosystems following the latest Permian crisis, results from this study are compared to five other coeval ichnoassemblages from elsewhere in South China (Chen et al., 2011; Zhao et al., 2015; Shi et al., 2015; Luo et al., 2016), as well as coeval ichnoassemblages from around the world (northern Italy, northern Hungary, Western Australia, western US and Slovakia) (Twitchett and Wignall, 1996; Twitchett, 1999; Simo and Olsavsky, 2007; Mata and Woods, 2008; Fraiser and Bottjer, 2009; Hofmann et al., 2011, 2015; Chen et al., 2012; Foster et al., 2015). 2. Geologic background

ACCEPTED MANUSCRIPT 2.1. Geologic setting

MA

NU

SC

RI

PT

Lower Triassic successions are well developed across the entire South China block (Benton et al., 2013). The P–Tr boundary beds and Lower Triassic successions are fairly complete in the Middle and Upper Yangtze regions, including areas within Hubei, northwest Hunan, Guizhou, Chongqing, eastern Yunnan, and Sichuan (Fig. 1). During the P–Tr transition, the South China block was located near the tropical zone within the eastern part of the Paleotethys Ocean (Ziegler et al., 1998). The Lichuan area was situated in an offshore to shelf basin setting on the northern margin of the Middle Yangtze Platform during this time (Ziegler et al., 1998; Zhao et al., 2013), and directly faced the eastern Paleotethys Ocean (Feng et al., 1997). Uppermost Permian strata are comprised of the Changxing or Dalong Formations, while the Lower Triassic consists of the Griesbachian–Smithian Daye Formation and the Spathian Jialingjiang Formation. Conodont, ammonoid, and bivalve biozones have been determined across Lower Triassic successions from most localities in South China. In particular, Triassic conodont biostratigraphy has been determined for the western Hubei and southern Guizhou regions (Zhao et al., 2005, 2013; Ji et al., 2011; Yang et al., 2012; Yan et al., 2013, 2014), and provides a high-resolution biochronostratigraphic framework for paleoecologic studies of ecosystem recovery following the latest Permian mass extinction. 2.2. Lichuan section biostratigraphy

AC

CE

PT E

D

The Lichuan ichnoassemblage (GPS: N30º30.014´, E108º48.209´) is located 22 km north of Lichuan City, western Hubei Province, South China (Fig. 1). Uppermost Permian to Lower Triassic successions are continuously exposed along roadcuts from Lichuan City to the top of Qiyueshan Mountain. The uppermost Permian Changxing Formation is dominated by bioclastic limestone and yields abundant conodonts assignable to the Clarkina yini Zone, which is indicative of the latest Changhsingian in South China (Zhao et al., 2013; Chen et al., 2015). The Lower Triassic Daye Formation is characterized by a microbialite at its base, which uncomformably overlies bioclastic limestone of the uppermost Permian Changxing Formation, alternating layers of thin-bedded muddy limestone and medium-bedded grainstone to packstone in the middle part of the unit, and alternations of muddy limestone, bioclastic limestone and oolite in the upper part of the formation. The Jialingjiang Formation is dominated by thin-bedded, laminated muddy limestone, massive limestone and dolomitic limestone. The P–Tr boundary is placed within the lower part of the microbialite due to the first occurrence of the conodont Hindeodus parvus (Wang and Cao, 1981; Wang and Xia, 2004; Zhao et al., 2013; Fig. 2). The lower Daye Formation yields abundant conodonts assignable to the Hindeodus parvus and Isarcicella isarcica Zones and bivalves of the Claraia stachei-C. aurita Assemblage (Wang and Cao, 1981; Zhao et al., 2013). The middle part of the Daye Formation yields conodonts from the Dienerian Ns. dieneri Zone. The upper Daye Formation is constrained by conodonts of the Novispathodus

ACCEPTED MANUSCRIPT waageni Zone and ammonoids of the Flemingites-Euflemingites and Anasibirites Zones (Wang and Cao, 1981; Zhao et al., 2013). 2.3 Depositonal setting

AC

CE

PT E

D

MA

NU

SC

RI

PT

The lower Daye Formation (Beds 4–14; Fig. 2) is dominated by alternating mudstone and thin-bedded limestone, and also yields abundant thin-shelled fossils including bivalves (Claraia spp.) and ammonoids (Ophiceras spp.) Trace fossils are rarely present, but when they do occur, they are typically small, simple, horizontal Planolites-type burrows, which are typical of deposition under dysoxic conditions (Bottjer and Droser, 1994; Martin, 2004). This is similar to other ichnofossil assemblages that occur in the immediate aftermath of the latest Permian mass extinction elsewhere in the Paleotethys and Panthalassic Oceans (Twitchett and Wignall, 1996; Twitchett and Barras, 2004; Chen et al., 2011, 2015). As a result, the black mudstone-dominated succession, combined with the Claraia-Ophiceras assemblage (Chen et al., 2010), and a lack of any cross stratification, suggest a relatively deep offshore to distal ramp setting (below storm wave base) for the lower Daye Formation, similar to the lower Yinkeng Formation of the Lower Yangtze region (Chen et al., 2011). Alternations of muddy limestone, oolitic limestone, and bioclastic limestone (grainstone to packstone) or bioclastic limestone characterizes the middle to upper part of the Daye Formation at Lichuan (Beds 15–37; Figs. 2, 3). The bioclastic or oolitic limestone units thicken higher in the section, while muddy limestone units become thinner (Fig. 3), suggesting a shallowing-upward depositional pattern. In particular, the oolitic units increase in thickness up-section. Giant ooid banks, with ooid diameters larger than 2 mm (Mei, 2008) occur in the uppermost Daye Formation (Bed 36; Fig. 2).The giant ooids point to a high-energy zone above fair-weather wave base (Mei, 2008). Epifaunal assemblages and ichnoassemblages also show evidence of diversification in the middle-upper Daye Formation; in particular, both body and trace fossils are relatively abundant in these mud-rich beds, which are interpreted to indicate a relatively low energy setting (Fig. 2). To sum up, both oolitic and bioclastic limestones of the middle-upper Daye Formation represent deposition within the reach of fair-weather waves in a proximal ramp setting. The calcareous mudstone-dominated horizons are likely the result of mud settling following storms, and were likely deposited in the storm sheet zone below fair-weather wave base (Fig. 2). The middle-upper Daye Formation, overall, represents deposition within an offshore to offshore transition setting. 3. Methodology Trace fossil taxonomic identification is based on field observations and descriptions of specimens collected from outcrop. Several proxies were analyzed to assess ecologic recovery in the aftermath of the latest Permian mass extinction as indicated by the trace fossils, including variation in burrow size, ichnodiversity,

ACCEPTED MANUSCRIPT

SC

RI

PT

behavioral complexity, and tiering. Measurements of burrow diameters were undertaken on bedding planes and in vertical exposures following Pruss and Bottjer (2004). Burrow diameters were measured at the part that was most representative of the average width. Sediment penetration depths of trace fossils were also measured on vertical exposures, and tiering levels were assessed based on these measurements (Bottjer and Ausich, 1986). The ichnofabric index (ii, Droser and Bottjer, 1986) in vertical outcrop and the bedding plane bioturbation index (BPBI, Miller and Smail, 1997) were applied in order to examine changes in the degree of bioturbation across the Lower Triassic succession. Ichnofabric indices are used to indicate bioturbation intensity from lowest (ii = 1) to highest (ii = 5) levels. The BPBI was employed to determine the approximate percentage of bedding planes covered by burrows (Miller and Smail, 1997). 4. Characteristics of the Lichuan trace-fossil assemblage

NU

4.1. Paleoecology and taphonomy

AC

CE

PT E

D

MA

The Lichuan ichnoassemblage is found within thin-bedded, muddy limestones at a quarry near Lichuan City, where the ichnofossil-rich thin slabs are mined for construction and pavement materials. The late Smithian ichnoassemblage includes 13 ichnogenera (Figs. 5–10): Arenicolites, Circulichnis, Cochlichnus, Cosmorhaphe, Didymaulichnus, Glockerichnus, Gordia, Gyrochorte, Laevicyclus, Palaeophycus, Planolites, Thalassinoides, and Treptichnus. Ethologically, the Lichuan ichnotaxa are categorized into four ethologic types: domichnia (Arenicolites, Thalassinoides, Laevicyclus, Palaeophycus, and Circulichnis), repichnia (Didymaulichnus), fodinichnia (Glockerichnus, Planolites, Gordia, Treptichnus, and Gyrochorte), and pascichnia (Cosmorhaphe, Cochlichnus). The Lichuan ichnoassemblage is dominated by fodinichnia if the burrow abundance of each ichnotaxon is taken into account. Fodinichina occupy 60% of the ichnotaxa of the Lichuan ichnoassemblage, followed by domichnia, which include nearly 25% of all traces of the Lichuan ichnoassemblage (Fig. 4A). Interestingly, if the number of ichnotaxa is taken into account, the Lichuan ichnoassemblage is dominated by both fodinichnia and domichnia, each of which occupies 38.5% of the ichnotaxa (Fig. 4B). The burrows are extremely abundant and densely packed on slabs (Fig. 5A−D). Traces are usually preserved in convex epirelief, and exhibit an extremely high level of bioturbation on bedding planes, with coverage of up to 70−90% (Fig. 5C−D). Gyrochorte, Planolites, Palaeophycus, and Cosmorhaphe burrows are very common on the upper surfaces of slabs. In vertical profile, Arenicolites, Laevicyclus, Thalassinoides, and Treptichnus burrows are commonly present, resulting in an ii of 5 (Fig. 5D). In most cases, burrow infills are easily distinguished from the host rocks (Figs 6H, 7G–H and 10E, G, I), with a relatively darker color and finer grain size.

ACCEPTED MANUSCRIPT 4.2. Ichnologic notes

SC

RI

PT

4.2.1. Arenicolites Salter, 1857 Arenicolites isp. Most traces of Arenicolites are preserved in thin-bedded muddy limestone at the Lichuan locality and occur on bedding planes. Burrows appear as paired shafts (Fig. 6A). Most burrows have diameters of 4−5 mm; the distance between limbs ranges from 5 to 20 mm. Fillings of most burrows consist of relatively coarse sediments that are easily distinguishable from surrounding fine-grained sediments. These burrows are assigned to an uncertain ichnospecies of Arenicolites due to poor preservation. This ichnogenus has been interpreted as a dwelling trace (domichnia), which may have been produced by various kinds of organisms, including polychaete worms, amphipod crustaceans, and insects (Bromley, 1996; Knaust, 2004; Rindsberg and Kopaska-Merkel, 2005).

PT E

D

MA

NU

4.2.2. Circulichnus Keighley and Pickerill, 1997 Circulichnus isp. Circulichnus is a ring-shaped trace, almost circular in shape, and is preserved in the muddy limestone beds at Lichuan. These traces are parallel to the bedding plane and always preserved in convex epirelief (Fig. 6C–D). The diameter of the circular shape ranges from 20–30 mm; burrow size ranges from 2–8 mm in diameter. This ichnogenus of circular to ovate traces first noted from the Triassic of Russia was originally termed Circulichnis by Vyalov (1971), but the correct orthography is actually Circulichnus, as discussed by Keighley and Pickerill (1997). Circulichnus is widely distributed in various types of marine sedimentary rocks and is a monospecific facies-crossing ichnotaxon that has been recorded not only in marine deposits but also in non-marine facies (Fillion and Pickerill, 1984; Keighley and Pickerill, 1997). The origin of Circulichnus remains enigmatic.

AC

CE

4.2.3. Cochlichnus anguineus Hitchcock, 1858 Sinusoidal, unbranched, unlined burrows are preserved in positive relief (Fig. 6G). Burrows are 4–5 mm in diameter and consistent in width throughout the entire observed length. Wave length is ~15 mm, and wave amplitude ranges from 2 mm to 3 mm. The burrows observed are identical to C. anguineus Hitchcock in all aspects. The smaller burrow size, sinusoidal curve, and consequent burrow distinguish it from other ichnospecies.This ichnogenus has been interpreted as either a grazing trace (Buatois and Mangano, 1993), a locomotion trace (Metz, 1998) or a feeding structure (Eagar et al., 1985). 4.2.4. Cosmorhaphe sinuosa Azpeitia Moros, 1933 Simple, smooth, unbranched burrows with free meanders, preserved in positive relief; the meanders not physically close to each other, but are always parallel to bedding planes (Figs. 6H, 7A). Burrow size is 3–10 mm in diameter and consistent in width. Sediments filling the burrows are usually darker in color, and are thus easily

ACCEPTED MANUSCRIPT distinguished from the relatively lighter-colored host rocks. Observed burrows are identical to C. sinuosa which is characterized by the low amplitude of the secondary undulations and a relatively small burrow diameter. Cosmorhaphe is a typical grazing trail (Häntzschel, 1975; Seilacher, 1977; Azpeitia Moros, 1933).

SC

RI

PT

4.2.5. Didymaulichnus lyelli Young, 1972 Didymaulichnus traces were originally described as Fraena lyelli by Rouault (1850), but later referred to as D. lyelli by Young (1972). They are characterized by smooth, simple, and sinuous curving bilobed trails. D. lyelli is a common ichnotaxon occurring in the Lower Triassic of the Yangtze region (Chen et al., 2011). In Lichuan, Didymaulichnus occurs as smooth, curving bilobed trails (Fig. 7B–C) that are preserved parallel to bedding planes. They are simple and sinuous, and often intersect one another, with burrow widths of 3–4 mm and burrow lengths up to 50 mm. Didymaulichnus is usually interpreted as the trail of an arthropod, gastropod or soft-bodied organism (Hakes, 1977; Trewin and McNamara, 1995; Knaust, 2004).

PT E

D

MA

NU

4.2.6. Glockerichnus Pickerill, 1982 Glockerichnus isp. This ichnogenus is represented by radial or starlike traces with several long rays that are straight, commonly dichotomous, and radiate from a central point, there are several small rays between the main ribs. The main ribs are usually 5–15 mm long, and the small rays often range from 2 to 8 mm in length (Fig. 6E). The burrow is 3–5 mm in diameter and consistent in width through the entire burrow. These burrows are preserved parallel to bedding planes. The trace is a feeding structure that is produced by various kinds of organisms (e.g., polychaete worms; Pickerill et al., 1987).

AC

CE

4.2.7. Gordia marina Emmons, 1844 Several long, slender, smooth, worm-like trails occur in both positive and negative relief in the thin-bedded, muddy limestone of the Daye Formation at the Lichuan locality (Figs.6F, 7E, 9F). The traces are curved to straight and cross one another. The 2–6 mm wide burrows are uniform in thickness throughout the entire trace. The burrows display a rounded base in cross section, and some specimens show a tendency to meander. These characteristics fit well with the definition of the ichnospecies Gordia marina. The trace-maker could be a worm, as the burrows overall resemble the hair-worm Gordius (Häntzschel, 1975). Some burrows cross one another at the same horizon, indicating that the trace-makers were likely epifaunal. 4.2.8. Gyrochorte comosa Heer, 1865 This horizontal trace is distributed on bedding planes of the thin-bedded muddy limestone. It is preserved as plaited ridges with biserially arranged, obliquely aligned pads of sediment. The bifurcated trail is separated into two parallel tubes by a median groove, up to 8 mm in width, in convex relief (Fig. 8A, C–E) or negative relief (Fig. 8B, G). The trace fossil can strongly wind and sharply change direction, and its length varies greatly over exposures. This trace may cut across itself and other traces on

ACCEPTED MANUSCRIPT bedding planes. These traces are assignable to Gyrochorte comosa based on the biserially arranged plaited ridges with obliquely aligned pads of sediment. This trace may have been produced by either a gastropod or a polychaete-like worm (Gibert and Ekdale, 1999; Heinberg, 1973).

MA

NU

SC

RI

PT

4.2.9. Laevicyclus mongraensis Verma, 1970 This ichnotaxon is commonly present in the Lichuan collection and is preserved as regular concentric circles with a central canal in plane view (Figs. 9A–B, H, 10A). This vertical trace is perpendicular to the bedding plane with a circular outline on the upper surface of muddy limestone beds. The Lichuan traces resemble Laevicyclus mongraensis in size and morphology, as reported from the Silurian Melbourne Formation in southeastern Australia (Shi et al., 2009). The same ichnogenus has also been reported from the Spathian Virgin Limestone Member of western United States (Pruss and Bottjer, 2004), and the Smithian Kockatea Shale Formation of the Perth Basin, Western Australia (Chen et al., 2012). The string diameter is up to 7 mm, and the ring diameter is up to 47 mm (Fig. 11E–F). This trace may penetrate up to~30 mm below the top of the bed. Numerous grooves, as radial imprints, radiate out from the central hole. Laevicyclus is considered to be the vertical dwelling burrow of a worm, with tentacle swirl-marks around the top of the burrow (Osgood, 1970; Chen et al., 2012).

AC

CE

PT E

D

4.2.10. Palaeophycus Hall, 1847 Palaeophycus tubularis Hall, 1847 Palaeophycus tubularis is represented by unbranching, curved, and cylindrical burrows preserved in negative or positive relief on the upper surfaces of the thin-bedded muddy limestone and calcareous mudstone of the Daye Formation (Figs. 7D, 9C, 10C). Burrows are 2–7 mm wide (Fig. 11H). Of the known Palaeophycus ichnospecies, the studied material is most allied to P. tubularis (Pemberton and Frey, 1984; Keighley and Pickerall, 1997; Gouramis et al., 2003). Palaeophycus isp. Palaeophycus isp. commonly intersect and pass over one another, they are subparallel to the bedding plane. Some burrows, however, have been strongly weathered so that they appear to be oblique to bedding planes. Burrows are mostly smooth (Figs. 7F, 9G, 10B). 4.2.11. Planolites Nicholson, 1873 Planolites montanus Richter, 1937 This ichnospecies is preserved in convex hyporelief on muddy limestone. The cylindrical, straight to gently curved burrows rarely branch, and are up to 15 cm long and 1.5–3 mm in diameter. Burrows are usually filled with sediment distinguishable from the host rock (Figs. 8H, 9E). Planolites beverleyensis Billing, 1862 They are typically 2–4 mm in diameter (Figs. 5C−D, 6B, 10D−E, 11A), frequently intersect each other, and are densely packed. The burrows are smooth,

ACCEPTED MANUSCRIPT straight to tortuous, horizontal to slightly inclined, and are circular to elliptical in cross-section. Planolites is thought to either represent reworking of sediment by the deposit-feeding activities of polychaetes or worm-like creatures (Crimes et al., 1977; Bromley, 1996; Chen et al., 2011), or is the result of feeding of mobile deposit feeders (Pemberton and Frey, 1984).

MA

NU

SC

RI

PT

4.2.12. Thalassinoides Ehrenberg, 1944 Thalassinoides isp. This trace fossil occurs as branching burrows that form networks with characteristic Y-shaped junctions. Burrow networks are represented by a set of medium-sized, smooth, rounded burrows, which may penetrate to a depth of 10 mm into the sediment. Most preserved burrows are 3–4 mm in diameter (Fig. 11C), and bifurcate to form incomplete intricate networks (Figs. 9D, I, 10E, G–I). These traces are filled with dark greenish, fine, organic-rich sediments, and stand out from the surrounding light grey mudstone. The formation of Thalassinoides traces has been attributed to the behavior of many organisms, including cerianthid sea anemones, enteropneustacron worms, fish, and decapod crustaceans (Carvalhoet al., 2007; Ekdale and Bromley, 2003; Hakes, 1977; Myrow, 1995; Rodriguez-Tovar and Uchman, 2006).

AC

CE

PT E

D

4.2.13. Treptichnus Miller, 1889 This ichnogenus is represented by T. bifurcus and T. pollardi in the Lichuan collections. They are preserved as convex epireliefs on the upper surface of muddy limestone beds. Treptichnus bifurcus Miller, 1889 Treptichnus bifurcus includes traces comprised of simple, zigzag-arranged burrows that join together and intersect at low angles to form projections on both sides of a medial plane (Figs. 7G–H, 10F). The width of an individual segment of burrow is approximately 5–8 mm (Fig. 11B). The rounded ends of projections are conspicuous and situated on alternate sides of burrows. These traces demonstrate a 3-dimensional burrow system that shows the growth pattern of T. bifurcus (see also Maples and Archer, 1987). Treptichnus pollardi Buatois and Mangano, 1993 Treptichnus pollardi is represented by simple, curved burrows with small subcircular to circular pits at the angle of juncture. Pits are considered outlets of vertical shafts. The burrow system pattern is irregular (Fig. 8F); the burrows, 1–3 mm in diameter, are usually smaller than those of T. bifurcus. Treptichnus has been attributed to either arthropods or worm-like organisms, or insect larvae (Buatois et al., 1998, 2000; Knaust, 2004; Rindsberg and Kopaska-Merkel, 2005; Uchman, 2005). 5. Ichnofabrics and other ichno-ecologic proxies following the latest Permian mass extinction

ACCEPTED MANUSCRIPT

5.1. Extent of bioturbation

RI

PT

Ichnofabric indices (ii) were assessed across the Griesbachian to Smithian succession at the study locality (Fig. 2). Ichnofabric indices from the Griesbachian to middle Smithian are rather low (ii 1–2), while ichnofabrics are usually ii 4 and reach ii 5 in several beds from the late Smithian strata (Figs. 2, 12C). The bedding planes from the Griesbachian to middle Smithian successions contain Planolites with coverage < 10% (BPBI 1). In contrast, most bedding planes in the late Smithian successions contain Gyrochorte, Laevicyclus, Palaeophycus, Treptichnus, and other associated forms, and have coverage of up to 70%, with the ichnoassemblage horizons reaching 90–100% coverage, with an overall BPBI of 4–5 (Fig. 12C).

SC

5.2. Burrow sizes, trace-fossil forms and complexity, and infaunal tiering

AC

CE

PT E

D

MA

NU

Burrow sizes of Arenicolites, Palaeophycus, Planolites, Thalassinoides, Laevicyclus, Gyrochorte, and Treptichnus were determined from five bedding planes from the Lichuan section (Fig. 11; Table 1). A total of 342 burrows from the Lichuan ichnoassemblage were measured, and their maximum and mean diameters are 4.8 mm and 9 mm, respectively (Fig. 13C). The 13 ichnogenera from the Lichuan ichnoassemblage (Fig. 13A) represent a wide variety of morphologic forms. They include simple, horizontal burrows (Cochlichnus, Cosmorhaphe, Didymaulichnus, Gordia, Circulichnis, and Planolites), vertical burrows (Arenicolites, Laevicyclus), oblique- or horizontal branching burrows (Palaeophycus), slightly complex burrow networks (Thalassinoides, and Treptichnus), and grazing traces (Cosmorhaphe, Gyrochorte) (Fig. 12C). These traces are also categorized into fodinichnia, domichnia, pascichnia, and repichnia ethologic types (Fig. 4A−B). As a result, trace-fossil behavioral diversity is considerably high. Infaunal tiering is indicated by the depths of burrows into beds (Fig. 13B). Several vertical burrows (i.e. Arenicolites and Laevicyclus), horizontal or oblique burrows (i.e. Palaeophycus, Planolites, and Gyrochorte), and slightly complex burrow networks (Thalassinoides and Treptichnus) penetrate to a depth of up to 30 mm into the sediment, and their average depth of penetration is 15 mm (Fig. 13B), indicating the third to fourth tiering levels (3–4) if the tiering criteria proposed by Bottjer and Ausich (1986) are followed. 6. Comparisons with coeval ichnoassemblages elsewhere in the world and implications for biotic recovery 6.1. Coeval ichnoassemblages reported elsewhere in the world Although Lower Triassic successions are well-exposed in South China (Benton et al., 2013), ichnofossil-rich Smithian-aged successions are only exposed in the following five localities: the Yashan (Chen et al., 2011) and Susong (Luo et al., 2016)

ACCEPTED MANUSCRIPT

AC

CE

PT E

D

MA

NU

SC

RI

PT

sections of the Lower Yangtze region, the Daxiakou section (Zhao et al., 2015) of the Middle Yangtze region, and the Gaimao (Shi et al., 2015) and Tianshengqiao (Luo et al., 2016) sections of the Upper Yangtze region. The ichnofabrics and several ichno-ecologic proxies from the Lichuan ichnoassemblage are compared with those of the coeval ichnoassemblages reported elsewhere in South China (see below; Fig. 12). The Yashan section is located in the town Yashan of Nanling County, Anhui Province, South China. Both conodont and ammonoid biostratigraphy suggest that the Helongshan Formation is early Smithian to earliest Spathian in age. The lithologic features and absence of cross stratification suggest deposition in shoreface and offshore transition settings (Chen et al., 2011). The Susong section is located within the Susong County, Anhui Province, ~200 km from the Yashan section, however, the Lower Triassic succession is almost same as that of Yashan (Luo et al., 2016). The Daxiakou section is located 6 km east of the town of Xiakou, Xingshan County, western Hubei Province, South China. The Smithian-aged ichnofossils are found in the Daye Formation. Sedimentary facies and paleoecologic analyses indicate that the Daye Formation in this locality represents sedimentation in an offshore setting (Zhao et al., 2015). The Gaimao section is located 100 m east of the village of Gaimao, of Guiyang City, Guizhou Province, southwestern China. The upper part of the Daye Formation is Smithian in age, and represents deposition in shoreface to offshore transition settings (Shi et al., 2015). The Tianshengqiao section is situated near Tianshengqiao village, ~20 km west of the Shizong County, eastern Yunnan Province. The Smithian-aged ichnofossils occur in the lower Jialingjiang Formation which is interpreted as the result of sedimentation in an offshore transition setting (Luo et al., 2016). Outside South China, the Smithian ichnoassemblages have also been reported from the Campil Member of the Werfen Formation, Dolomites region, northern Italy (Twitchett and Wignall, 1996; Twitchett 1999; Hofmann et al., 2011, 2015), the upper part of the Bódvaszilas Sandstone Formation, Aggtelek Karstis, northern Hungary (Foster et al., 2015), the upper part of the Bodvaszilas Formation and the lower part of the Szin Formation, Western Carpathians, Slovakia (Simo and Olsavsky, 2007), the Kockatea Shale Formation, northern Perth Basin, Western Australia (Chen et al., 2012; Luo and Chen, 2014), and the Sinbad Limestone Member of the Moenkopi Formation and the Lower Member of the Union Wash Formation, western US (Mata and Woods, 2008; Fraiser and Bottjer, 2009; Hofmann et al., 2014). 6.2. Extent of bioturbation During the early-middle Smithian, five of six sections (Yashan, Susong, Lichuan, Daxiakou, and Gaimao) record rather low ichnofabric indices (ii 1–2). In contrast, about 50% of strata examined from Tianshengqiao display rather high ichnofabric indices (ii 3–4). The upper Smithian strata have a high ichnofabric index (ii 4; several beds reach ii 5) in five of the six sections examined in South China, with the exception of the Daxiakou section, which still exhibits low ichnofabric indices (ii 1–2) during this time (Fig. 12).

ACCEPTED MANUSCRIPT

AC

CE

PT E

D

MA

NU

SC

RI

PT

In Yashan and Susong, lower-middle Smithian bedding planes contain Planolites, and have < 10% coverage, indicating a BPBI of 1. Six ichnogenera, Arenicolites, Gordia, Gyrochorte, Palaeophycus, Planolites, and Treptichnus, are commonly present on upper Smithian bedding planes, which exhibit coverage of up to 80%, corresponding to a BPBI of 4–5. The lower-middle Smithian bedding planes at Daxiakou yield Planolites and Didymaulichnus, and have <30% coverage, resulting in a BPBI of 1–2. In contrast, most of the upper Smithian bedding planes from Lichuan contain Gyrochorte, Palaeophycus, Treptichnus, Laevicyclus, and other associated forms, with coverage up to 70–90%, indicating a BPBI 4–5. Although only Planolites occurs in the lower-middle Smithian strata in Tianshengqiao, these bedding planes have >40% coverage, indicating a BPBI of 3. Its counterpart in Gaimao has < 20% coverage (BPBI 1). The upper Smithian bedding planes yield Planolites, Palaeophycus, Treptichnus, Rhizocorallium, Phycodes, and other associated forms at Gaimao, and they have up to 70% coverage, resulting in a BPBI of 4 (Fig. 12). There are very few trace fossils resulting in rather low ichnofabric indices (ii 1–2) for the Campil Member of the Werfen Formation, northern Italy (Twitchett and Wignall, 1996; Twitchett 1999; Hofmann et al., 2011, 2015). The upper part of the Bódvaszilas Sandstone Formation, Aggtelek Karstis, northern Hungary, yields only Arenicolites, and has a BPBI of 2–3 and ii 1–2 (Foster et al., 2015). The bioturbation index (BI, Taylor and Goldring, 1993) of the Smithian-aged successions in the Western Carpathians, Slovakia is BI 1–3 (Simo and Olsavsky, 2007). In the northern Perth Basin, Western Australia, up to 40% of a few bedding planes are covered by Arencolites, Ophiomorpha, and Lockeia, indicating a BPBI of 3–4 and ii 4 (Chen et al., 2012). The Sinbad Limestone Member exhibits primarily low to moderate vertical bioturbation, athough ichnofabric indices ranging 1 to 5 are recorded. Horizontal bioturbation is moderate to extensive, and a few bedding planes are between 60–100% disrupted (BPBI 5) (Fraiser and Bottjer, 2009). To sum up, the Lichuan section records relatively highly bioturbated upper Smithian strata and possesses similar ii and BPBI values to those determined from the Yashan, Susong, Gaimao, and Tianshengqiao sections, all of which record much higher bioturbation indices than the Daxiakou section (ii 1 and BPBI 1–2) during late Smithian time. When compared with trace fossil records from elsewhere in the world, the bioturbation indices of Western Australia and the western US can reach the same level as those noted at Lichuan, while other localities have lower bioturbation indices. 6.3. Ichnodiversity, burrow sizes, trace-fossil forms and complexity, and infaunal tiering 6.3.1. Ichnodiversity Lower–middle Smithian trace fossils are very rare, and only Palaeophycus, Planolites, and Treptichnus occur in the entire Yangtze region. However, ichnotaxa clearly diversified in most areas of South China during the late Smithian, except for Daxiakou, where only Planolites and Didymaulichnus are present (Fig. 12). Eight

ACCEPTED MANUSCRIPT

CE

PT E

D

MA

NU

SC

RI

PT

ichnogenera: Arenicolites, Gordia, Cochlichnus, Gyrochorte, Palaeophycus, Planolites, Treptichnus, and Kouphichnium occur at Yashan, and 11 ichnogenera: Arenicolites, Archaeonassa, Chondrites, Laevicyclus, Monocraterion, Palaeophycus, Planolites, Phycodes, Thalassinoides, Treptichnus, and Trichichnus are found at Susong (Fig. 12). The coeval ichnoassemblage in Gaimao consists of nine ichnogenera: Arenicolites, Beaconichnus, Chondrites, Palaeophycus, Planolites, Phycosiphon, Phycodes, Rhizocorallium, and Thalassinoides. Seven ichnogenera appear in the upper Smithian strata at Tianshengqiao: Arenicolites, Chondrites, Planolites, Psammichnites, Skolithos, Taenidium, and Trichichnus (Fig. 12). There are few trace fossils in the Dolomites region, northern Italy (Planolites, Palaeophycus, Diplocraterion, Cochlichnus, and Asteriacites), and these are generally confined to a few bedding planes (Twitchett and Wignall, 1996; Twitchett, 1999). Smithian strata yield only Arenicolites in northern Hungary (Foster et al., 2015). Diplocraterion, Skolithos and Arenicolites are reported from Lower Triassic successions from the Western Carpathians, Slovakia (Simo and Olsavsky, 2007). Trace fossils identified within the Kockatea Shale Formation of the Perth Basin, Western Australia are extremely abundant and contain 16 ichnogenera: Arenicolites, Cochlichnus, Didymaulichnus, Diplocraterion, Diplichnites, Scalpoichnus, Laevicyclus, Lockeia, Ophiomorpha, Radulichnus, Palaeophycus, Planolites, Taenidium, Thalassinoides, Treptichnus and a problematic trace (Chen et al., 2012; Luo and Chen, 2014). Eight ichnogenera are present in 41 beds in the Sinbad Limestone Member of the Moenkopi Formation: Arenicolites, Diplichnites, Gyrochorte, Palaeophycus, Planolites, Rhizocorallium, Skolithos, Thalassinoides and only Planolites in the Union Wash Formation, western US (Fraiser and Bottjer, 2009; Mata and Woods, 2008). Thus, the Lichuan ichnoassemblage is more diverse than any of the late Smithian ichnoassemblages from South China and most places documented elsewhere in the world, but less diverse than Western Australian ichnoassemblage, which contains 16 ichnogenera.

AC

6.3.2. Burrow sizes The Griesbachian–early Smithian burrows of Yashan (Chen et al., 2011) and Gaimao (Shi et al., 2015) are very small in size across the entire interval, suggesting prolonged environmental stress following the latest Permian crisis (Pruss and Bottjer, 2004; Zonneveld et al., 2010; Chen et al., 2011). Burrow diameters increase dramatically in the upper Smithian strata of five of the six sections examined in South China (Yashan, Susong, Lichuan, Gaimao, and Tianshengqiao), but none of the burrows exceed 20 mm in diameter. In contrast, late Smithian burrows (mainly Planolites) in Daxiakou are <2 mm in diameter (Zhao et al., 2015) and have a similar size range to burrows from Griesbachian–early Smithian strata (Fig. 13C). When compared with burrows from the other five sections, the Lichuan burrows possess mean and maximum diameters of 4.8 mm and 9 mm, respectively, and thus are much larger than coeval burrows from Yashan, which have mean and maximum

ACCEPTED MANUSCRIPT

NU

SC

RI

PT

diameters of 2.3 mm and 5 mm (n = 189 burrows), respectively. The coeval ichnotaxa from the other four localities in South China do not have detailed statistics of burrow sizes, and thus prevent further comparisons to the Lichuan ichnotaxa. Outside South China, the Lichuan burrows are much smaller than coeval burrows reported from the Kockatea Shale Formation of the Perth Basin, Western Australia (Chen et al., 2012). The latter are preserved in a well-oxygenated habitat and have mean and maximum burrow diameters of 7 mm and 14 mm (n = 431 burrows), respectively (Chen et al., 2012). The trace fossils of the Sinbad Limestone Member of the Moenkopi Formation have a mean burrow diameter of 5 mm (n = 456 burrows) which is almost the same size as the Lichuan burrows (Fraiser and Bottjer, 2009). In addition, Planolites is the most common ichnogenus that occurs in upper Smithian collections from the sections examined here, except for the Tianshengqiao locality. The Lichuan Planolites burrows are significantly smaller than those from Gaimao in both mean and maximum diameter, but slightly larger than those preserved in the Yashan and Susong sections and much larger than those from Daxiakou (Fig. 13C).

AC

CE

PT E

D

MA

6.3.3. Trace-fossil forms and complexity A wide variety of trace fossils occur in upper Smithian rocks from South China, including simple, horizontal burrows (Archaeonassa, Cochlichnus, Cosmorhaphe, Didymaulichnus, Gordia, Circulichnis, and Planolites), resting traces (Lockeia), vertical burrows (Arenicolites, Laevicyclus, Phycodes, and Skolithos), oblique- or horizontal, branching burrows (Palaeophycus, Psammichnites, and Taenidium), slightly complex burrow networks (Thalassinoides, and Treptichnus), and grazing traces (Gyrochorte, Cosmorhaphe and Chondrites) (Fig. 12). As a result, trace-fossil behavioral diversity and complexity are very high, with at least six types of behavioral complexity. Of these, five types of lifestyle occur at Lichuan. The complexity of the Lichuan ichnotaxa therefore is rather high. Moreover, the Western Australian traces include simple, horizontal burrows, horizontal resting traces, walking trackways, vertical burrows, oblique/or horizontal, branching burrows, slightly complex burrow networks, grazing traces, and possible swimming traces. As a result, trace-fossil behavioral diversity is considerably high. Behavioral complexity was also relatively high, reflecting at least seven types of living behavioral complexity, although some complex burrow network ichnotaxa (i.e., Rhizocorallium) did not occur (Chen et al., 2012). In addition, the upper Smithian strata in Gaimao and the Sinbad Limestone Member of the Moenkopi Formation yield Rhizocorallium, a distinct ichnogenus that comprises complex burrow forms and often occurs during the recovery stage 3 (Twitchett et al., 2004; Twitchett, 2006; Fraiser and Bottjer, 2009; Pruss and Bottjer, 2004; Chen et al., 2011; but see Zonneveld et al., 2010). However, Rhizocorallium of Gaimao and the western US possesses are considerably smaller size and shallower penetration level in comparison with the same ichnogenus from Spathian and younger strata (Zonneveld et al., 2001; Knaust, 2013; Luo et al., 2016). The Smithian Rhizocorallium has limited environmental and geographic distributions (Fig. 12). Its

ACCEPTED MANUSCRIPT occurrence in Smithian strata, therefore, cannot be used to indicate the later stages of ecologic recovery. Instead, the Smithian Rhizocorallium is perhaps a good marker for an anomalous recovery, when most of the other biota still suffered post-extinction biotic depletion and environmental stress.

D

MA

NU

SC

RI

PT

6.3.4. Infaunal tiering The average and maximum penetration depths of the Lichuan burrows, 15 mm and 30 mm, respectively, are greater than those determined from any of the other sections examined here (Fig. 13B), indicating the third to fourth (3–4) tiering levels. The Susong ichnotaxa demonstrate the second deepest tiering (12 mm, 25 mm) and also reach the third to fourth (3–4) tiering levels, followed by both the Gaimao (12 mm, 20 mm) and Tianshengqiao (8 mm, 18 mm) ichnoassemblages (Fig. 13B). The latter two are indicative of the 2nd to 3rd tiering levels (2–3). The Daxiakou ichnotaxa possess the shallowest penetration depths (2 mm, 4 mm) (Fig. 13B), pointing to the lowest tiering level (1). Outside South China, the Lichuan burrows have similar penetration depths to those preserved in the Kockatea Shale Formation of the Perth Basin, Western Australia (10 mm, 30 mm) (Chen et al., 2012), and thus share a similar tiering level. The average penetration depth of the burrows in northern Italy is almost 10 mm (Twithcett, 1999). The penetration depths of infauna in the Sinbad Limestone Member of the Moenkopi Formation of the western US and the Diplocraterion-dominated beds in Slovakia can reach 6–12 cm, which is much deeper than most areas from elsewhere world at the time (Simo and Olsavsky, 2007; Fraiser and Bottjer, 2009).

PT E

6.4. Implications for biotic recovery following the latest Permian mass extinction

AC

CE

Griesbachian–Dienerian trace fossils are very rare in South China, except for a few small, simple, horizontal Planolites burrows (Chen et al., 2011; Zhao et al., 2015; Luo et al., 2016). The Lichuan traces strengthen this observation. In Lichuan, the Griesbachian–Dienerian ichnoassemblage contains only Planolites, which is 1–2 mm in diameter and parallel to the bedding plane, with depth of penetration of <3 mm. The late Smithian ichnoassemblage (13 ichnogenera) from Lichuan is the most diverse among all coeval ichnotaxa from South China (Fig. 13A), representing re-diversification of ichnotaxa during this time. Moreover, when compared with Griesbachian–middle Smithian traces, the late Smithian ichnofossils are much larger burrows, with greater average and maximum penetration depths (15 mm and 30 mm, respectively) (Fig. 13B). Behavioral complexity (up to five types) is much higher in comparison with the simple, unbranched burrows of the Griesbachian–Dienerian ichnotaxa. Clearly, the late Smithian ichnoassemblage is indicative of a significant increase in ichnodiversity, burrow size, trace-fossil complexity, tiering level, and bioturbation intensity. All lines of evidence indicate, therefore, that trace-making organisms rebound during the late Smithian in Lichuan, and, perhaps, reached recovery stages 2–3, if following the criteria for biotic recovery (Twitchett, 2006) that was revised by Pietsch and Bottjer

ACCEPTED MANUSCRIPT

AC

CE

PT E

D

MA

NU

SC

RI

PT

(2014). Moreover, the Gaimao ichnoassemblage may have reached recovery stage 3 (Fig. 12C), while the Daxiakou ichnotaxa still remain at the lowest recovery level (stage 1) during this time (Fig. 12D). Other coeval ichnoassemblages also reach similar or slightly lower recovery levels to the Lichuan ichnoassemblage. If taking environmental setting into account, it is clear that ichnofossils primarily re-diversified near the offshore transition (i.e., Yashan, Susong, Lichuan, Gaimao, Tianshengqiao, Western Australia, and western US) and partially re-diversified in shoreface settings (i.e., Yashan) during the late Smithian (Fig. 12A–C, E–F). Ichnofossils did not diversify during the late Smithian if trace-makers inhabited offshore setting (i.e., Daxiakou; Fig. 12D). During the early-middle Smithian, ichnotaxa remain at a rather low ichnodiversity in offshore habitats (Fig. 12A–D). They may have slightly higher ichnodiversity or bioturbation levels in shoreface to offshore transition settings (Fig. 12A, C, E–F) when compared to offshore environments, even if ichnotaxa do not rebound significantly during that time. Clearly, ichnotaxa re-diversification was favored during the late Smithian in the offshore transition (or, to a lesser extent, shoreface) setting. Integrating all ichnofauna-environmental data collected from the Lower Triassic sections examined here, we find that (1) ichnotaxa did not re-diversify until late Smithian even if favorable offshore transition habitats occurred in the early–middle Smithian (i.e., Yashan, Lichuan, Gaimao, Tianshengqiao, and Western Australia; Fig. 12A, E–F), and that (2) ichnofauna still did not re-diversify during the late Smithian if in offshore habitats (i.e., Daxiakou; northern Hungary, and the Union Wash Formation, western US, Fig. 12D). Thus, timing and environment are two crucial factors controlling the recovery of trace-making organisms in the aftermath of the latest Permian mass extinction in South China. Ichnotaxa did not re-diversify prior to late Smithian (Chen et al., 2011; Shi et al., 2015; Zhao et al., 2015; Luo et al., 2016; this study), and ichnodiversity rebounds only in the habitable zone (lower shoreface to offshore transition settings sensu Beatty et al., 2008) after the middle Smithian. Previously, Wignall et al. (1998) suggested that ichnofaunas may have recovered earlier in higher latitude regions. Beatty et al. (2008) and Zonneveld et al. (2010) proposed that the habitable zone is crucial for the rapid rebound of ichnodiversity following the latest Permian crisis. When compared with those relatively higher latitude ichnoassemblages (Wignall et al., 1998; Beatty et al., 2008; Zonneveld et al., 2010), the South Chinese ichnoassemblages reveal a much lower recovery level during the same Early Triassic timespans. However, these ichnoassemblages from the South Chinese sections indicate that the habitable zone did not guarantee recovery of trace-making organisms. Similarly, late Smithian ichnoassemblages from the ‘habitable zone’ of the Gondwana interior sea only indicate a low recovery stage (e.g. Chen et al., 2012). Therefore, the latitude, perhaps through variations in seawater temperature, may have been an important factor in the recovery rate of ichnofaunas during the Early Triassic. 7. Conclusions

ACCEPTED MANUSCRIPT

D

MA

NU

SC

RI

PT

An exceptionally well-preserved trace-fossil assemblage is documented from the late Smithian succession of the Lichuan area, western Hubei Province, South China. This ichnoassemblage contains 13 ichnogenera, and they comprise simple, horizontal burrows, vertical burrows, oblique- or horizontal branching burrows, slightly complex burrow networks, and grazing traces. These traces are also categorized into fodinichnia, domichnia, pascichnia, and repichnia ethologic types, suggesting a high degree of behavioral complexity. The ichnoassemblage horizons are usually highly bioturbated, with ichnofabric indices (ii) reaching ii 4–5 along with a rather high bedding plane bioturbation index (BPBI 4–5). The Lichuan burrows have mean and maximum diameters of 4.8 mm and 9 mm, respectively (n = 342), and average and maximum penetration depths of 15 mm and 30 mm, respectively, indicating the third to fourth tiering levels (3–4). The Lichuan ichnoassemblage shows an abrupt increase in ichnodiversity, burrow size, behavioral complexity, and tiering level during the late Smithian, suggesting recovery stages 2–3 after the latest Permian crisis. Comparisons with five coeval ichnoassemblages from South China (Yashan, Susong, Daxiakou, Gaimao, and Tianshengqiao sections), and coeval ichnoassemblages (northern Italy, Western Australia, and western US) reveals that most ichnofaunas reached similar recovery levels to the Lichuan ichnoassemblage, except for the Daxiakou ichnotaxa that reached recovery stage 1, during the late Smithian. Furthermore, trace-making organisms re-diversified mostly in the offshore transition and partially in shoreface habitats, but did not rebound in offshore settings (i.e., Daxiakou) during the late Smithian. Thus, time and depositional setting are two crucial factors influencing the recovery of trace-making organisms during the Early Triassic.

PT E

Acknowledgements

AC

CE

We thank reviewers Richard Hofmann and William Foster, editor Isabel Patricia Montanez and guest editor Shane Schoepfer for their critical comments and constructive suggestions, which have improved the quality of the paper. This study was supported by the 111 Program of China, Ministry of Education of China (B08030), two NSFC research grants (41272023, 41572091), two research grants from the State Key Laboratory of Biogeology and Environmental Geology (GBL11206) and the State Key Laboratory of Geological Processes and Mineral Resources (GPMR201302), China University of Geosciences, and a scholarship from China University of Geosciences (Wuhan) sponsored the first author to visit California State University Fullerton. References Azpeitia Moros, F., 1933. Datos para el estudio paleontologico del Flysch de la Costa Cantabrica y de algunos otras puntos de Espafia. Instituto Geologico y Minero de Espaiia Boletin, 53, 1–65. Beatty, T.W., Zonneveld, J.-P., Henderson, C.M., 2008. Anomalously diverse Early Triassic ichnofossil assemblages in northwest Pangea: a case for a shallow-marine

ACCEPTED MANUSCRIPT

AC

CE

PT E

D

MA

NU

SC

RI

PT

habitable zone. Geology 36, 771–774. Benton, M. J., Zhang, Q.Y., Hu, S.X., Chen, Z.Q., Wen, W., Liu, J., Huang, J.Y., Zhou, C.Y., Xie, T., Tong, J.N., Choo, B., 2013. Exceptional vertebrate biotas from the Triassic of China, and the expansion of marine ecosystems after the Permo–Triassic mass extinction. Earth-Sci. Rev. 123, 199–243. Bottjer, D.J., Ausich, W.I., 1986. Phanerozoic development of tiering in soft substrata suspension-feeding communities. Paleobiology 12, 400–420. Bottjer, D.J., Droser, M.L., 1994. The history of Phanerozoic bioturbation. In: Donovan, S.K. (Ed.), The Palaeobiology of Trace Fossils. John Wiley and Sons, West Sussex, pp. 155–176. Bromley, R.G., 1996. Trace Fossils: Biology, Taphonomy and Applications (2nd edition). Chapman & Hall, London, 361 pp. Buatois, L.A., Mángano, M.G., 1993. The ichnotaxonomic status of Plangtichnus and Treptichnus, Ichnos 2, 217–224. Buatois, L.A., Mangano, M.G., Maples, C.G., Lanier, W.P., 1998. Ichnology of an Upper Carboniferous fluvio-estuarine paleovalley: the Tonganoxie Sandstone, Buildex Quarry, eastern Kansas, USA. J. Paleontol. 72, 152–180. Buatois, L.A., Mangano, M.G., Fregenal-Martinez, M.A., de Gibert, J.M., 2000. Short-term colonization trace-fossil assemblages in a carbonate lacustrine Konservat-Lagerstätte (Las Hoyas Fossil Site, Lower Cretaceous, Cuenca, Central Spain). Facies 43,145–156. Buatois, L.A., Gingras, M.K., Maceachern, J., Mangano, M.G., Zonneveld, J-P., Pemberton, S.G., Netto, R.G., Martin, A., 2005. Colonization of brackish-water systems through time: Evidence from the trace-fossil. PALAIOS 20, 321–347. Carvalho, C.N.de, Viegas, P.A., Cachao, M., 2007. Thalassinoides and its producer: populations of Mecochirus buried within their burrow systems, Boca do Chapim Formation (Lower Cretaceous), Portugal. PALAIOS 22, 104–109. Chen, Z.Q., Benton, M.J., 2012. The timing and pattern of biotic recovery following the end-Permian mass extinction. Nat. Geosci. 5, 375–383. Chen, Z.Q., Tong, J.N., Liao, Z.T., Chen, J., 2010. Structural changes of marine communities over the Permian–Triassic transition: ecologically assessing the end-Permian mass extinction and its aftermath. Global Planet. Chang. 73, 123–140. Chen, Z.Q., Tong, J.N., Fraiser, M.L., 2011. Trace fossil evidence for restoration of marine ecosystems following the end-Permian mass extinction in the Lower Yangtze region, South China. Palaeogeogr. Palaeoclimatol. Palaeoecol. 299, 449–474. Chen, Z.Q., Fraiser, M.L., Bolton, C., 2012. Early Triassic trace fossils from Gondwana interior sea: Implication for ecosystem recovery following the end-Permian mass extinction in south high-latitude region. Gondwana Res. 22, 238–255. Chen, Z.Q., Yang, H., Luo, M., Benton, M.J., Kaiho, K., Zhao, L.S., Huang, Y.G., Zhang, K.X., Fang, Y.H., Jiang, H.S., Qiu, H., Li, Y., Tu, C.Y., Shi, L., Zhang, L., Feng, X.Q., Chen, L.,2015. Complete biotic and sedimentary records of the

ACCEPTED MANUSCRIPT

AC

CE

PT E

D

MA

NU

SC

RI

PT

Permian–Triassic transition from Meishan section, South China: Ecologically assessing mass extinction and its aftermath. Earth-Sci. Rev. 149, 67‒107. Crimes, T.P., Legg, I., Marcos, A., Arboleya, M., 1977. ?Late Precambrian–low Lower Cambrian trace fossils from Spain. In: Crimes, T.P., Harper, J.C. (Eds.), Trace Fossils 2. Geological Journal Special Issue, 9. Seel House Press, Liverpool, U.K., pp. 91–138. Droser, M.L., Bottjer, D.J., 1986. A semiquantitative field classification of ichnofabric. J. Sediment. Petrol. 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 Environments. SEPM, Spec. Publ. 35, 99–149. Ehrenberg, K., 1944. Ergänzende Bemerkungen zu den seinerzeit aus dem Miozän von Burgschleinitz beschriebenen Gangkernen und Bauten dekapoder Krebse. Paläontol. Z. 23, 345–359. Ekdale, A.A., Bromley, R.G., 2003. Paleoethologic interpretation of complex Thalassinoides in shallow-marine limestone, Lower Ordovician, southern Sweden. Palaeogeogr. Palaeoclimatol. Palaeoecol. 192, 221–227. Emmons, E., 1844. The Taconic System: Based on Observations in New York, Massachusetts. Maine. Vermont and Rhode Island. Carol1 and Cook (Albany). 68 pp. Feng, Z., Bao, Z., Liu, S., 1997. Lithofacies Palaeogeography of Early and Middle Triassic of South China. Petroleum Industry Press, Beijing, 311 pp (in Chinese). Fillion, D., Pickerill, R., 1984. Systematic ichnology of the Middle Ordovician Trenton Group, St Lawrence Lowland, eastern Canada. Atl. Geol. 20, 1–41. Foster, W.J., Twitchett, R.J., 2014. Functional diversity of marine ecosystems following the late Permian mass extinction event. Nat. Geosci. 8, 233–238. Foster, W.J., Danise, S., Sedlacek, A., Price, G.D., Hips, K., Twitchett, R.J., 2015. Environmental controls on the post-Permian recovery of benthic, tropical marine ecosystems in western Palaeotethys (Aggtelek Karst, Hungary). Palaeogeogr. Palaeoclimatol. Palaeoecol. 192, 374–394. Fraiser, M.L., Bottjer, D.J., 2009. Opportunistic behavior of invertebrate marine tracemakers during the Early Triassic aftermath of the end-Permian mass extinction. Aust. J. Earth Sci. 56, 841–857. Gibert, J.M.De., Ekdale, A.A., 1999. Trace fossil assemblages reflecting stressed environments in the Middle Jurassic Carmel Seaway of central Utah. J. Paleontol. 73, 711–720. Gouramis, C., Webb, J.A., Warren, A.A., 2003. Fluviodeltaic sedimentology and ichnology of part of the Silurian Grampians Group, Western Victoria. Aust. J. Earth Sci. 50, 811–825. Hakes, W.G., 1977. Trace fossils in Late Pennsylvanian cyclothems, Kansas. In: Crimes, T.P., Harper, J.C. (Eds.), Trace Fossils 2. Geological Journal SpecialIssue, 9. Seel HousePress, Liverpool, U.K., pp. 209–226.

ACCEPTED MANUSCRIPT

AC

CE

PT E

D

MA

NU

SC

RI

PT

Hall, J., 1847. Palaeontology of New York, Volume 1. State of New York (Albany, New York). 338 pp. Häntzschel, W., 1975. Trace fossils and problematica. In: Teichert, C. (Ed.), Treatise of Invertebrate Paleontology (2nd Edition), Part W, Miscellanea, Supp 1. University of Kansas and Geological Society of America, Lawrence, Kansas, 269 pp. Heer, O., 1865. Die Urwelt der Schweitz. F. Schulthess, Zurich. 622 pp. Heinberg, C., 1973. The internal structure of the trace fossils Gyrochorte and Curvolithus. Lethaia 6, 227–238. Hitchcock, E., 1858. Ichnology of New England. A report on the Sandstone of the Connecticut Valley. Especially its Footprints. W. White, Boston. 220 pp. Hofmann, R., Goudemand, N., Wasmer, M., Bucher, H., Hautmann, M., 2011. New trace fossil evidence for an early recovery signal in the aftermath of the end-Permian mass extinction. Palaeogeogr. Palaeoclimatol. Palaeoecol. 310, 216–226. Hofmann, R., Buatois, L.A., MacNaughton, R.B., Mangano, M.G., 2015. Loss of the sedimentary mixed layer as a result of the end-Permian extinction. Palaeogeogr. Palaeoclimatol. Palaeoecol. 428, 1‒11. Ji, W.T., Tong, J.N., Zhao, L.S., Zhou, S.Q., Chen, J., 2011. Lower–Middle Triassic conodont biostratigraphy of the Qingyan section, Guizhou Province, Southwest China. Palaeogeogr. Palaeoclimatol. Palaeoecol. 308, 213–223. Jumars, P.A., Wheatcroft, R.A., 1989. Responses of benthos to changing food quality andquantity with a focus of deposit feeding and bioturbation. In: Berger, W.H., Smetacek, V.S., Wefer, G. (Eds.), Productivity in the Ocean: Past and Present. Wiley, Chichester, pp. 235–253. Keighley, D.G., Pickerill, R.K., 1997. Systematic ichnology of the Mabou and Cumberland Groups (Carboniferous) of Western Cape Breton Island, eastern Canada1: burrows, pits, trails, and coprolites. Atl. Geol. 33, 181–215. Knaust, D., 2004. Cambro–Ordovician trace fossils from the SW Norwegian Caledonides. Geol. J. 39, 1–24. Knaust, D., 2010. The end-Permian mass extinction and its aftermath on an equatorial carbonate platform: insights from ichnology. Terra Nova 22, 195–202. Knaust, D., 2013. The ichnogenus Rhizocorallium: classification, trace makers, palaeoenvironments and evolution. Earth-Sci. Rev. 126, 1–47. Luo, M., Chen, Z.Q., 2014. New arthropod traces from the Lower Triassic Kockatea Shale Formation, northern Perth Basin, Western Australia: ichnology, taphonomy and palaeoecology. Geol. J. 49, 163–176. Luo, M., George, A.D., Chen, Z.Q., 2016. Sedimentology and ichnology of two Lower Triassic sections in South China: Implications for the biotic recovery following the end-Permian mass extinction. Glob. Planet. Chang. 144, 198–212. Maples, C.G., Archer, A.W., 1987. Redescription of Early Pennsylvanian trace fossil holotypes from the nonmarine Hindostan Whetstone Beds of Indiana. J. Paleontol. 61, 890–897. Marenco, K.N., Bottjer, D.J., 2008. The importance of Planolites in the Cambrian

ACCEPTED MANUSCRIPT

AC

CE

PT E

D

MA

NU

SC

RI

PT

substrate revolution. Palaeogeogr. Palaeoclimatol. Palaeoecol. 258, 189–199. Martin, K.D., 2004. A re-evaluation of the relationship between trace fossils and dysoxia. In: McIlroy, D. (Ed.), Application of Ichnology to Palaeoenvironmental and Stratigraphic Analysis. Geol. Soc. London, Spec. Publ. 228, pp. 141–156. Mata, S.A., Woods, A.D., 2008. Sedimentology and paleoecology of the Lower Member of the Lower Triassic (Smithian-Spathian) Union Wash Formation, east-central California. PALAIOS 23, 514–524. Mei, X.M., 2008. Significance of the unusual giant oolite and its morphologic diversity in Phanerozoic, a case of the Daye Formation of the Lower Triassic, Lichuan, Hubei Province. Mod. Geosci. 22, 683–698. Metz, R., 1998. Nematode trails from the Late Triassic of Pennsylvania. Ichnos 5, 303–308. Miller, S.A., 1889. North American Geology and Paleontology for the Use of Amateurs, Students and Scientists: Cincinnati. Western Methodist Book Concern, Ohio, 664 pp. Miller, M.F., Smail, S.E., 1997. A semiquantitative method for evaluating bioturbation on bedding planes. PALAIOS 12, 391–396. Myrow, P.M., 1995. Thalassinoides and the enigma of Early Paleozoic open-framework burrow systems. PALAIOS 10, 58–74. Nicholson, H.A., 1873. Contributions to the study of the errant annelids of the older Paleozoic rocks. Proc. Roy. Soc. London 21 pp. 288–290. Osgood, R. G. 1970. Trace fossils of the Cincinnati area. Palaeontogra. Am. 6, 281–444. Pemberton, S.G., Frey, R.W., 1984. Quantitative methods in ichnology: spatial distribution among populations. Lethaia 17, 33–49. Pemberton, S.G., Flach, P.D., Mossop, G.D., 1982. Trace fossils from the Athabasca OilSands, Alberta, Canada. Science 217, 825–827. Pemberton, S.G., Wightman, D.M., 1992. Ichnological characteristics of brackish water deposits. In: Pemberton, S.G. (Ed.), Application of Ichnology to Petroleum Exploration: Core Workshop 17. Society of Economic Paleontologist and Mineralogist, pp. 141–167. Pickerill, R. K., 1982. Glockerichnus, a new name for the trace fossil ichnogenus Glockeria Ksiaikiewicz, 1968. J. Paleontol. 56, 816. Pickerill, R.K., Fyffe, L.R., Forbes, W.H., 1987. Late Ordovician-Early Silurian trace fossils from the Metapedia Group, Tobique River, Western New Brunswick, Canada. Maritime Sediments and Atlantic Geology 23, 77–88. Pietsch, C., Bottjer, D.J. 2014. The importance of oxygen for the disparate recovery patterns of the benthic macrofauna in the Early Triassic. Earth-Sci. Rev. 137, 65–84. Pruss, S.B., Bottjer, D.J., 2004. Early Triassic fossils of the western United States and their implications for prolonged environmental stress from the end-Permian mass extinction. PALAIOS 19, 551–564. Richter, R., 1937. Marken und Spuren aus allen Zeiten. I–II. Senckenbergiana 19, 150–169.

ACCEPTED MANUSCRIPT

AC

CE

PT E

D

MA

NU

SC

RI

PT

Rindsberg, A.K., Kopaska-Merkel, D.C., 2005. Treptichnus and Arenicolites from the Steven C. Minkin Paleozoic footprint Site (Langsettian, Alabama, USA). In: Buta, R.J., Rindsberg, A.K., Kopaska-Merkel, D.C. (Eds.), Pennsylvanian Footprints in the Black Warrior Basin of Alabama, Monograph 1. Alabama Paleontological Society, pp. 121–141. Richter, R., 1937. Marken und Spuren aus allen Zeiten. I–II. Senckenbergiana 19, 150–169. Rodriguez-Tovar, F.J., Uchman, A., 2006. Ichnological analysis of the Cretaceous–Palaeogene boundary interval at the Caravaca section, SE Spain. Palaeogeogr. Palaeoclimatol. Palaeoecol. 242, 313–325. Rouault, M., 1850. Note preliminaire sur une nuvelle formation de couvert dans le terrainsilurien inferieur de la Bretagne. Bull. Soc. Geol. Fr. 7, 724–744. Salter, J.W., 1857. On annelide-burrows and surface making from the Cambrian rocks of the Longmynd. Geol Soc London Quart Jour, 13, 199–206. Savrda, C.E., Bottjer, D.J., 1987. The exaerobic zone, a new oxygen-deficient marine biofacies. Nature 327, 54–56. Scheyer, T.M., Romano, C., Jenks, G., Bucher, H., 2014. Early Triassic marine biotic recovery: the predators’ perspective. PLoS ONE 9, e88987. Seilacher, A., 1977. Pattern analysis of Paleodictyon and related trace fossils. In: Crimes, T.P., Harper, J.C. (Eds), Trace Fossils.Geol. J. Spec. Iss. 9, 289–334. Shi, G., Woods, A.D., Yu, M.Y., Wei, H.Y., 2015. Two episodes of evolution of trace fossils during the Early Triassic in the Guiyang area, Guizhou Province, South China. Palaeogeogr. Palaeoclimatol. Palaeoecol. 426, 275–284. Shi, G.R., Gong, Y.M., Potter, A., 2009. Late Silurian trace fossils from the Melbourne Formation, Studley Park, Victoria, southeastern Australia. Alcheringa 33, 185– 209. Šimo, Olšavskỳ, V., 2007. Diplocraterion parallelum Torell, 1870, and other trace fossils from the Lower Triassic succession of the Drienok Nappe in the Western Carpathians, Slovakia. Bull. Geosci. 82, 163–173. Taylor, A.M., Goldring, R., 1993. Description and analysis of bioturbation and ichnofabric. Geol. Soc. London. 150, 141–148. Trewin, N.H., McNamara, K.J., 1995. Arthropods invade the land: trace fossils and palaeoenvironments of the Tumblagooda Sandstone (?Late Silurian) of Kalbarri, Western Australia. Trans. Roy. Soc. Edinburgh, Earth Sci. 85, 177–210. Twitchett, R.J., 1999. Palaeoenvironments and faunal recovery after the end-Permian mass extinction. Palaeogeogr. Palaeoclimatol. Palaeoecol. 154, 27–37. Twitchett, R.J., 2006. The palaeoclimatology, palaeoecology and palaeoenvironmental analysis of mass extinction events. Palaeogeogr. Palaeoclimatol. Palaeoecol. 232, 190–213. Twitchett, R.J., Barras, C.G., 2004. Trace fossils in the aftermath of mass extinction events. In: McIlroy, D. (Ed.), Application of Ichnology to Palaeoenvironmental and Stratigraphic Analysis. Geol. Soc. London Spec. Publ. 228, 395–415. Twitchett, R.J., Wignall, P.B., 1996. Trace fossils and the aftermath of the Permo–Triassic mass extinction: evidence from Northern Italy. Palaeogeogr.

ACCEPTED MANUSCRIPT

AC

CE

PT E

D

MA

NU

SC

RI

PT

Palaeoclimatol. Palaeoecol. 124, 137–151. Uchman, A., 2005. Treptichnus-like traces made by insect larvae (Diptera: Chironomidae, Tipulidae). In: Buta, R.J., Rindsberg, A.K., Kopaska-Merkel, D.C. (Eds.), Pennsylvanian footprints in the Black Warrior Basin of Alabama Monograph 1. Alabama Paleontological Society, pp. 143–146. Verma, K.K., 1970. Occurrence of trace fossils in the Bagh Beds of Amba Dongar area, Gujarat State. J. Indian Geosci. Assoc. 12, 37–40. Vyalov, O., 1971. Rare Mesozoic problematica from the Pamir and Caucasus. Paleontologicheskiy Sbornik 7, 85–93. Wang, G.Q., Xia, W.C., 2004. Conodont zonation across the Permian–Triassic boundary at the Xiakou section, Yichang city, Hubei Province and its correlation with the Global Stratotype Section and Point of the PTB. Canad. J. Earth Sci. 41, 323–330. Wang, Z.H., Cao, Y.Y., 1981. Conodonts of the Early Triassic from the Lichuan area, Hubei Province. Acta Palaeontol. Sin. 20, 363–378. 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. Geol. Mag. 135, 47–62. Yan, C.B., 2013. Conodont Biostratigraphy of the Nanpanjiang Basin during the Early and Middle Triassic. Doctoral dissertation of China University of Geosciences. China University of Geosciences Press, Wuhan (in Chinese). Yang, B., Lai, X.L., Wignall, P.B., Jiang, H.S., Yan, C.B., Sun, Y.D., 2012. A newly discovered earliest Triassic chert at Gaimao section, Guizhou, southwestern China. Palaeogeogr. Palaeoclimatol. Palaeoecol. 344–345, 69–77. Young, F.G., 1972. Early Cambrian and older trace fossils from the southern Cordillera of Canada. Can. J. Earth Sci. 9, 1–17. Zhao, L., Chen,Y., Chen, Z.Q., Cao,L., 2013.Uppermost Permian to Lower Triassic conodont zonation from Three Gorges area, South China. PALAIOS 28, 523–540. Zhao, X., Tong, J., Yao, H., Niu, Z., Luo, M., Huang, Y., Song, H., 2015. Early Triassic trace fossils from the Three Gorges area of South China: Implications for the recovery of benthic ecosystems following the Permian–Triassic extinction. Palaeogeogr. Palaeoclimatol. Palaeoecol. 429, 100–116. Ziegler, A.M., Gibbs, M.T., Hulver, M.L., 1998. A mini-atlas of oceanic water masses in the Permian Period. Proc. Roy. Soc. Victoria 110, 323–344. Zonneveld, J.-P., Gingras, M.K., Pemberton, S.G., 2001. Trace fossil assemblages in a Middle Triassic mixed siliciclastic-carbonate marginal marine depositional system, British Columbia. Palaeogeogr. Palaeoclimatol. Palaeoecol. 166, 249–276. Zonneveld, J.-P., Gingras, M.K., Beatty, T.W., 2010. Diverse ichnofossil assemblages following the P–T mass extinction, Lower Triassic, Alberta and British Columbia, Canada: evidence for shallow marine refugia on the northwestern coast of Pangaea. PALAIOS 25, 368–392.

Figure captions

ACCEPTED MANUSCRIPT

Fig. 1. A, Location of the Lichuan ichnoassemblage in the Qiyueshan area, 22 km northwest of Lichuan city, western Hubei Province, South China. B, Early Triassic paleogeography of the South China block (base map follows Feng et al., 1997), showing the position of the Lichuan section. Section abbreviations: 1-Yashan (YS) section, 2-Susong (SS) section, 3-Daxiakou (DXK) section, 4-Gaimao (GM) section, 5-Tianshengqiao (TSQ) section.

NU

SC

RI

PT

Fig. 2. Stratigraphic section of the Lower Triassic succession exposed at Lichuan, and the stratigraphic distributions of trace fossils. Ichnofabric indices (ii) (Droser and Bottjer, 1986) are assessed as ii 1 to 5, indicating bioturbation from lowest to highest intensities, respectively. Bedding plane bioturbation indices (BPBI) are evaluated based on the degree of bedding plane coverage by burrows (Miller and Smail, 1997), which range from 1 to 5, indicating coverage from least to most, respectively. Conodont zones updated by Zhao et al. (2013), based on the original zonation established by Wang and Cao (1981).

D

MA

Fig. 3. A, Thin-bedded muddy limestone slabs from a quarry within the Lichuan section contain abundant ichnofossils. B, Field photo showing thin-bedded, laminated muddy limestone. C, Field photo showing slabs containing abundant trace fossils at Lichuan quarry. D, Ichnofabric viewed in vertical profile. E, Thin-bedded, laminated muddy limestone in the upper part of the Daye Formation. F, Thin-bedded muddy limestone without bioturbation in the lower part of the Daye Formation.

PT E

Fig. 4. A, Pie diagram of the upper Daye Formation trace-fossil assemblage from the Lichuan section showing the percentage of ethologic types based on burrow abundance. B, Pie diagram showing the ichnofaunal percentage of each ethologic type based on the number of ichnotaxa.

AC

CE

Fig. 5. Bioturbation on bedding planes of slabs from the Lichuan ichnoassemblage (upper Daye Formation). A–B, Abundant Gyrochorte comosa on the upper surface of the beds, showing a rather high bioturbation index (BPBI 3–4). C–D, Abundant Planolites beverleyensis on the upper surface of the beds, also showing a high degree of bioturbation (BPBI 4–5). Fig. 6. A, Arenicolites isp. (Ar) on the upper surface of Bed 35. B, Planolites beverleyensis on the upper surface of Bed 32. C–D, Circulichnus isp. on the upper surface of Bed 32. E, Glockerichnus isp. on the upper surface of Bed 34. F, Gordia marina on the upper surface of Bed 35. G, Cochlichnus anguineus on the upper surface of Bed 34. H, Cosmorhaphe sinuosa on the upper surface of Bed 33. All trace fossils are from the upper Daye Formation, Lichuan section. Fig. 7. A, Cosmorhaphe sinuosa (Cos, white arrows) on the upper surface of Bed 33. B–C, Didymaulichnus lyelli on the upper surface of Bed 35. D, Palaeophycus

ACCEPTED MANUSCRIPT tubularis on the upper surface of Bed 28. E, Gordia marina on the upper surface of Bed 35. Note that one burrow is preserved as positive relief, and another as negative relief. F, Palaeophycus isp. on the upper surface of Bed 35. G, Treptichnus bifurcus on the upper surface of Bed 34. H, Close-up of boxed area in G showing alternatively branching burrows. All trace fossils are from the upper Daye Formation, Lichuan section.

RI

PT

Fig. 8. A–E, G, Gyrochorte comosa on the upper surfaces of Beds33–34. Note that A and C–E are preserved as convex reliefs, while B and G are concave reliefs. B shows biserially arranged plaited ridges (white lines). F, Treptichnus pollardi on the upper surface of Bed 30. H, Planolites montanus on the upper surface of Bed 32. All traces are from the upper Daye Formation, Lichuan section.

MA

NU

SC

Fig. 9. A–B, H, Laevicyclus mongraensis on upper the surfaces of Beds 33–34. C, Palaeophycus tubularis on the upper surface of Bed 28. D, Thalassinoides isp. on the upper surface of Bed 34. Note that the branch penetrates into the bedding plane (white arrow). E, Planolites montanus on the upper surface of Bed 35. F, Gordia marina on the upper surface of Bed 34. G, Palaeophycus isp. on the upper surface of Bed 35. I, Gordia marina (Gor) and Thalassinoides isp. (Th) on the upper surface of Bed 34. All traces are from the upper Daye Formation, Lichuan section.

PT E

D

Fig. 10. A, Laevicyclus mongraensis on the upper surfaces of Beds 33–34. B, Palaeophycus isp. from Bed 32. C, Palaeophycus tubularis on the upper surface of Bed 34. D, Planolites beverleyensis on the upper surface of Bed 30. E, Planolites beverleyensis (Pl) and Thalassinoides isp. (Th) on upper surface of Bed 34. F, Treptichnus bifurcus on upper surface of Bed 37. G–H, Thalassinoides isp. on the upper surface of Bed 35. I, Thalassinoides isp. on the upper surface of Bed 33. All traces are from the upper Daye Formation, Lichuan section.

AC

CE

Fig. 11. Measurements of burrow diameters of Planolites, Treptichnus, Thalassinoides, Gyrochorte, Laevicyclus, Arenicolites, and Palaeophycus from the Lichuan ichnoassemblage. N = number of burrows; MD = mean diameter. Fig. 12. Distribution of ichnotaxa, ichnofabric indices (ii) and bedding plane bioturbation indices (BPBI) from the Smithian successions of the Yashan (YS), Susong (SS), Lichuan (LC), Daxiakou (DXK), Gaimao (GM), and Tianshengqiao (TS) sections, South China. Facies associations (FA) and depositional environment (DE) interpretations of YS, SS, DXK, GM, and TS follow Chen et al. (2011), Zhao et al. (2015), Shi et al. (2015), and Luo et al. (2016). Fig. 13. A, Ichnodiversity as indicated by the number of ichnogenera from late Smithian ichnoassemblages from six sections from South China (Yashan, Susong, Lichuan, Daxiakou, Gaimao and Tianshengqiao) and five localities from elsewhere: northern Italy (NI), Western Australia (WA), western US (WU), northern Hungary

ACCEPTED MANUSCRIPT

AC

CE

PT E

D

MA

NU

SC

RI

PT

(NH) and Slovakia (SL). B, Tiering levels indicated by mean and maximum penetration depths from these 11 sections documented in Fig 13A. C, Mean and maximum diameters of late Smithian Planolites burrows from South China (except for the Tianshengqiao section), western US (WU) and Western Australia (WA), and mean and maximum diameters of all the burrows from the Lichuan and Yashan sections of South China, and Western Australia (WA).

AC

CE

PT E

D

MA

NU

SC

RI

PT

ACCEPTED MANUSCRIPT

Figure 1

Figure 2

AC

CE

PT E

D

MA

NU

SC

RI

PT

ACCEPTED MANUSCRIPT

Figure 3

AC

CE

PT E

D

MA

NU

SC

RI

PT

ACCEPTED MANUSCRIPT

SC

RI

PT

ACCEPTED MANUSCRIPT

AC

CE

PT E

D

MA

NU

Figure 4

MA

NU

SC

RI

PT

ACCEPTED MANUSCRIPT

AC

CE

PT E

D

Figure 5

AC

CE

PT E

D

MA

NU

SC

RI

PT

ACCEPTED MANUSCRIPT

Figure 6

AC

CE

PT E

D

MA

NU

SC

RI

PT

ACCEPTED MANUSCRIPT

Figure 7

AC

CE

PT E

D

MA

NU

SC

RI

PT

ACCEPTED MANUSCRIPT

Figure 8

AC

CE

PT E

D

MA

NU

SC

RI

PT

ACCEPTED MANUSCRIPT

Figure 9

AC

CE

PT E

D

MA

NU

SC

RI

PT

ACCEPTED MANUSCRIPT

Figure 10

AC

CE

PT E

D

MA

NU

SC

RI

PT

ACCEPTED MANUSCRIPT

Figure 11

AC

CE

PT E

D

MA

NU

SC

RI

PT

ACCEPTED MANUSCRIPT

Figure 12

AC

CE

PT E

D

MA

NU

SC

RI

PT

ACCEPTED MANUSCRIPT

Figure 13

ACCEPTED MANUSCRIPT Table 1. Measurements of mean and maximum burrow diameters of selected ichnotaxa Mean diameter (mm)

Maximum diameter (mm)

Arenicolites

4.6 5.2 6.3 3.3 3.6 5.3 3.9 44.5

6 7 9 6 6 8 7 47

Gyrochorte Treptichnus Planolites Thalassinoides Laevicyclus

SC

Ring diameters of

AC

CE

PT E

D

MA

NU

Laevicyclus

23 34 108 26 43 32 31 31

RI

Palaeophycus

Individual numbers

PT

Ichnotaxa

AC

CE

PT E

D

MA

NU

SC

RI

PT

ACCEPTED MANUSCRIPT

Graphical abstract

ACCEPTED MANUSCRIPT Highlights 

A late Smithian ichnoassemblage is reported from the Lichuan section, South

China; 

Fodinichnia traces are most abundant;



The ichnofauna horizons usually have rather high ichnofabric indices (ii),

PT

reaching ii 4–5; Suggest recovery stages of 2–3 following the latest Permian mass extinction;



The trace-making organisms re-diversified mostly in offshore transition habitats

RI



AC

CE

PT E

D

MA

NU

SC

during the late Smithian.