Exploring the aftermath of the Cambrian explosion: The evolutionary significance of marginal- to...

Palaeogeography, Palaeoclimatology, Palaeoecology 374 (2013) 1–15

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Palaeogeography, Palaeoclimatology, Palaeoecology

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Exploring the aftermath of the Cambrian explosion: The evolutionary significance ofmarginal- to shallow-marine ichnofaunas of Jordan

M. Gabriela Mángano a,⁎, Luis A. Buatois a, Richard Hofmann b, Olaf Elicki c, Rafie Shinaq d

a Department of Geological Sciences, University of Saskatchewan, Saskatoon, Saskatchewan Canada S7N 5E2b Palaeontological Institute and Museum, Zurich University, Karl-Schmid Strasse 4, CH-8006, Zürich, Switzerlandc Freiberg University, Geological Institute, Department of Palaeontology, Bernhard-von-Cotta-street 2, Freiberg, D-09599, Germanyd Al Al-Bayt University, Institute of Earth and Environmental Sciences, Mafraq, Jordan

⁎ Corresponding author.E-mail addresses: [email protected] (M.G.

[email protected] (L.A. Buatois), richard.hofmann@[email protected] (O. Elicki), Shinaqrafie@yahoo

0031-0182/$ – see front matter © 2012 Elsevier B.V. Alldoi:10.1016/j.palaeo.2012.05.029

a b s t r a c t
a r t i c l e i n f o
Article history:Received 29 December 2011Received in revised form 23 May 2012Accepted 24 May 2012Available online 11 July 2012

Keywords:Trace fossilsMacroevolutionCambrian explosionTide-dominated marineDeltasJordan

Themiddle Cambrian HannehMember of the Burj Formation and themiddle to upper Cambrian Umm Ishrin For-mation of the Dead Sea area, Jordan, contain well-preserved and abundant ichnofaunas. Trace fossils are presentin a wide variety of depositional environments, from tide-dominated shelf to prodelta, delta front andinterdistributary-bay tidal flats. Twelve trace fossil assemblages have been identified within a number ofsequence-stratigraphic settings, namely early transgressive subtidal dune and bar complex, late transgressive iso-lated dune patches and dune-field abandonment, highstand deltaic progradation, and forced-regressive deltaicprogradation. These ichnofaunas provide information that helps us to understand the nature of Cambrian ecosys-tems in the aftermath of the Cambrian radiation. The Jordan ichnofaunas display evidence of firm groundconditions at or near the sea bottom. These include (1) well-preserved scratch marks in most Cruziana andRusophycus ichnospecies, (2) adhering Gyrolithes polonicus burrows, and (3) unlined passively filledDiplocraterionisp. penetrating into underlyingmudstone.Whereas theDiplocraterion isp. occurrences are a classic example of theGlossifungites ichnofacies linked to erosional exhumation, the firmground G. polonicus is associated to a maximumflooding surface with no erosion involved. The trace fossil suites dominated by trilobite structures are firmgroundexamples of the Cruziana ichnofacies, raising issueswith respect to the substrate affinities of this ichnofacies,whichis typically considered indicative of softgrounds. Our study underscores evolutionary controls on this ichnofacies,suggesting that lower Paleozoic occurrences, which are dominated by trilobite trails and trackways, reflect firmsubstrates and younger ones represent the typical softground examples. The occurrence of abundant bilobatetrace fossils, scratch marks and trackways in interdistributary-bay tidal flats within a braidplain delta complexin the Umm Ishrin Formation provides evidence that arthropods were able to foray into marginal-marinebrackish-water settings during the Cambrian. Analysis of the tiering structure indicates relatively simple commu-nities and limited use of the infaunal ecospace. Low-energy fully marine and marginal-marine ichnofabrics aredominated by shallow-tier deposit- and detritus-feeding trace fossils. Deep-tier structures of detritus feeders arepresent in ichnofabrics from fullymarine low-energy settings,whereas deep-tier trace fossils of suspension feedersare dominant in high-energy subtidal zones.

© 2012 Elsevier B.V. All rights reserved.

1. Introduction

By the end of the early Cambrian, the Cambrian explosionwas essen-tially over, and the body-fossil record shows no further increases in di-versity and disparity during the rest of the period (Marshall, 2006).The ichnology of the Ediacaran–Cambrian transition has been exploredin a number of papers (e.g. Crimes, 1992, 1994; Jensen, 2003; Seilacheret al., 2005; Jensen et al., 2006). However, the aftermath of the explosionhas received considerably less attention because few ichnologic studies

Mángano),im.uzh.ch (R. Hofmann),.com (R. Shinaq).

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focus on the middle Cambrian. Superbly exposed outcrops of marginal-to shallow-marine rocks are present in the southern Dead Sea area ofJordan (Fig. 1). In particular, the middle Cambrian Hanneh Member ofthe Burj Formation displays a complex facies mosaic, including tide-dominated shelf and deltaic deposits (Amireh et al., 1994; Hofmann etal., 2012). The overlyingmiddle to upper Cambrian Umm Ishrin Forma-tion also locally contains trace fossils preserved in marginal-marine de-posits. Trace fossils are abundant in these units, providing an excellentopportunity to document the ichnology of Cambrian marginal- toshallow-marine ecosystems right after the most dramatic evolutionaryradiation in the history of life. The aim of this paper is to discuss howichnologic information can illuminate our understanding of shallow-marine to coastal ecosystems in the aftermath of the Cambrianradiation. Some of the relevant evolutionary aspects involve landward

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Fig. 1. Map of Jordan and the Southern Dead Sea Area showing the positions of the studied localities. a, Wadi Issal (31°11′21.1″N, 35°33′16.2″E); b, Wadi Uhaymir (31°9′7.0″N,35°33′45.5″E); c, Wadi Qunai (31°5′48.8″N, 35°33′27.1″E); d, Wadi Al Hisa (31°0′50.2″N, 35°32′20.6″E); e, Wadi Umm Jafna (30°56′39.40″N, 35°29′58.30″E); f, Wadi Fifa(30°55′54.00″N, 35°28′42.00″E); and g, Zerqa Ma'in (31°37′52.1″N, 35°34′27.9″E).

2 M.G. Mángano et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 374 (2013) 1–15

expansion of benthic faunas and colonization of marginal-marine set-tings. Accordingly, placing these ichnofaunas within a paleoenviron-mental and sequence-stratigraphic framework is a pre-requisite for asound evaluation of the evolutionary implications.

2. Stratigraphy, depositional setting and age

The Burj and Umm Ishrin formations are exposed near the southernportion of the Dead Sea, Jordan (Figs. 1, 2). The Burj Formation occursabove themostly continental lower Cambrian Salib Formation, and con-sists of three members, Tayan, Numayri and Hanneh (Bender, 1974;Powell, 1989; Amireh et al., 1994; Rushton and Powell, 1998;Schneider et al., 2007; Shinaq and Elicki, 2007). The lower Cambrian–middle Cambrian transition is placed close to the base of the Numayrimember, based on trilobites and various microfauna (Rushton and

Numayri Mb.

Hanneh Mb.

Fig. 2. General view of the stud

Powell, 1998; Geyer and Langing, 2004; Shinaq and Elicki, 2007;Elicki, 2011; Elicki and Geyer, in press).

The lower two members and the lower interval of the HannehMember represent a transgressive succession, recording the transitionfrom shallow-intertidal to supratidal siliciclastics (Tayan Member) tomarginal- and open-marine carbonates (Numayri Member) and tide-dominated shallow-marine siliciclastics (Hanneh Member) (Amireh etal., 1994; Elicki, 2007; Shinaq and Elicki, 2007). Within the HannehMember, a maximum flooding surface separates subtidal deposits ofthe lower part of the member from prodelta to delta-front depositsrecorded in the upper part (Hofmann et al., 2012).

The Burj Formation is sharply overlain by the Umm Ishrin Forma-tion, which records an abrupt basinward facies migration as a result ofa forced regression. The base of this formation is, therefore, consideredas a regressive surface of marine erosion. The Umm Ishrin Formation

Umm Ishrin Fm.

ied units in Wadi Uhaymir.

image of Fig.�2

Table 1Summary of trace-fossil assemblage composition and distribution.

Trace fossilassemblage

Ichnotaxonomic composition Associated lithology and sedimentarystructures

Depositionalenvironment

Stratigraphic distribution and geographiclocation

Diplocraterionisp.

Diplocraterion isp. Planar and trough cross-bedded, andcurrent ripple-laminated fine- tomedium-grained sandstone

Small compound dunes Lower interval of the Hanneh Membernear Wadi Uhaymir and near the contactbetween the Tayan and Numayrimembers in Wadi Umm Jafna

Arenicolitesisp.,

Arenicolites isp., Palaeophycus tubularis,and Skolithos linearis

Trough cross-bedded and tabularcross-bedded fine- to medium-grainedsandstone

Tidal bars, compounddunes and simple dunes

Lower interval of the Hanneh Member inWadi Issal and Wadi Uhaymir

Cruzianasalomonis

Cruziana salomonis, Rusophycus burjensis,Dimorphichnus cf. D. obliquus andMonomorphichnus isp. A. Planolitesbeverleyensis, Planolites montanus,Palaeophycus tubularis, Phycodes isp.,Heminthoidichnites tenuis, Bergaueriasucta, and Gordia marina locally present

Thinly bedded current-ripplecross-laminated very fine- to fine-grainedsandstone and thicker-bedded troughcross-stratified fine-grained sandstone

Channelized areaswithin the tidal-sandbarcomplex, bottomsets oftidal dunes and areasbetween dunes

Lower interval of the Zerqa Ma'in section(Numayri Mbr), the middle interval of theWadi Qunai section and the upper intervalof the Wadi Uhaymir section within theHanneh Member

Rosselia isp. Rosselia isp., Asterosoma isp., Planolitesmontanus, and Palaeophycus tubularis

Current-ripple cross-laminated very fine-to fine-grained sandstone intercalatedwithin heterolithic intervals with flaser-,wavy-, and lenticular-bedded fine- andvery fine-grained sandstone and siltstone

Areas between tidaldunes

Near the top of the lower interval of theHanneh Member in Wadi Uhaymir, WadiIssal and Wadi Qunai

Gordia marina Gordia marina, Helminthoidichnites tenuis,and Diplichnites isp.

Thinly bedded very fine- to fine-grainedsandstone, with current ripples, flaserbedding and mudstone drapes,interbedded with mudstone

Areas between dunepatches

Near the base of the middle interval of theHanneh Member in Wadi Uhaymir, WadiUmm Jafna, and Wadi Issal

Gyrolithespolonicus

Gyrolithes polonicus Base of a massive fine-grained sandstonebed, penetrating into the underlyingmudstone

Abandonment of thetidal-dune field

Upper part of the middle interval of theHanneh Member in Wadi Uhaymir (belowthe maximum flooding surface)

Archaeonassafossulata

Archaeonassa fossulata Current- and wave-ripple cross-laminatedvery fine- to fine-grained sandstone

Prodelta Upper interval of the Hanneh Member inWadi Qunai

Bergaueriasucta

Bergaueria sucta, Palaeophycus tubularis,Planolites montanus, Rusophycus burjensis,and arthropod scratch marks

Current-ripple cross-laminated veryfine-grained sandstone

Prodelta to distal deltafront

Upper interval of the Hanneh Member inWadi Uhaymir

Rusophycusaegypticus

Rusophycus aegypticus, Cruziana jordanica,and Skolithos linearis

Wave-ripple cross-laminated very fine-to fine-grained sandstone, locally withmudstone drapes, interbedded withsiltstone

Distal delta front Upper interval of the Hanneh Member inWadi Umm Jafna

Fugichnia Escape trace fossils Parallel-laminated fine- tomedium-grained sandstone

Proximal delta front Uppermost interval of the HannehMember in Wadi Uhaymir

Cruzianaproblematica

Cruziana problematica, Rusophycuscarbonarius and Rusophycus isp.

Current- and wave-ripple cross-laminatedand also in parallel-laminated very fine-to fine-grained sandstone

Proximal delta front andtidal flats within abraidplain delta

Near the contact between the HannehMember and the Umm Ishrin Formation,and within the latter unit in Wadi Al Hisaand Wadi Ram

Diplichnitesisp.

Diplichnites isp. and Dimorphichnus cf.D. obliquus

Current- and wave-ripple cross-laminatedand also in parallel-laminated very fine-to fine-grained sandstone; wrinkle markslocally

Proximal delta front andtidal flats within abraidplain delta

Near the contact between the HannehMember and the Umm Ishrin Formation,and within the latter unit in Wadi Issal,Wadi Uhaymir, Wadi Qunai, Wadi UmmJafna, and Wadi Ram

3M.G. Mángano et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 374 (2013) 1–15

records deposition in a braided delta complex, and is regarded as latemiddle to late Cambrian (Furongian) in age, based on stratigraphic rela-tions (Makhlouf and Abed, 1991).

3. Ichnofaunal composition

Nineteen ichnogenera and twenty-eight ichnospecies have beenidentified. Detailed descriptions are provided in Hofmann et al. (2012),and therefore there is no need of repetition here. Collected specimensare housed at the Geological Institute of Freiberg University(Germany) under collection numbers FG 603. The ichnofauna comprisesa wide variety of architectural patterns, including vertical burrows(Arenicolites isp., Diplocraterion isp., Gyrolithes polonicus, Rosselia isp.,Skolithos linearis, escape trace fossils), horizontal simple burrows andtrails (Archaeonassa fossulata, Gordia marina, Helminthoidichnites tenuis,Palaeophycus tubularis, Planolites beverleyensis, Planolites montanus),plug-shaped burrows (Bergaueria sucta), horizontal branched burrows(Asterosoma isp., Phycodes isp., Treptichnus cf. T. pedum), bilobate struc-tures (Cruziana jordanica, Cruziana problematica, Cruziana salomonis,Rusophycus aegypticus, Rusophycus carbonarius, Rusophycus burjensis,Rusophycus cf. leifeirikssoni and Rusophycus isp.), and trackways

and scratch marks (Diplichnites isp., Dimorphichnus cf. D. obliquus,Monomorphichnus isp.).

4. Sequence-stratigraphic and paleoenvironmental distribution oftrace fossil assemblages

Twelve trace fossil assemblages have been identified: Diplocraterionisp., Arenicolites isp., C. salomonis, fugichnia, Rosselia isp., G. polonicus,G. marina, B. sucta, R. aegypticus, C. problematica, and A. fossulata assem-blages (Hofmann et al., 2012) (Table 1). Distribution of these trace fossilassemblages is closely linked to the sedimentary facies, revealing an in-timate relationship between benthic faunas and the prevailingenvironmental conditions during the transgressive–regressive cycle(Fig. 3; Table 1). Detailed descriptions of each of these trace fossil as-semblages and their associated deposits have been presented else-where (Hofmann et al., 2012).

4.1. Early transgressive subtidal dune and bar complex

The transition between the Tayan and Numayri members is charac-terized by several greenish gray coarse-grained sandstone layers(Fig. 4A), which are interpreted as transgressive lags, recording the initial

4m

vfsc vc bm pc cf g

NumayriMember

ArenicolitesAssemblage

Fugichnia Assemblage

Gyrolithes Assemblage

Transgressivesubtidal

sand dunesand bars

and bottomsetsheterolithics

Dune field abandonment(Transgressive maximum)

Prodelta

Delta front

Forced regressiveDelta front

Umm IshrinFormation

Dune patches andheterolithic mantlings

LEGEND

Sandstone

Mudstone

Limestone

LITHOLOGY

Trough-cross bedding

Planar cross bedding

Convolute bedding

Parallel lamination

Hummocky-cross stratification

Mud drapes

Current ripples

Wave ripples

Balls and pillow

SEDIMENTARY STRUCTURES

DiplocraterionAssemblage

DiplocraterionAssemblage

Rosselia Assemblage

Gordia marina Assemblage

Bergaueria suctaAssemblage

CruzianasalomonisAssemblage

RusophycusaegypticusAssemblage

CruzianaproblematicaDiplichnites

&isp.

Assemblages

ArchaeonassafossulataAssemblage

Forced-RegressiveDeltaic Progradation

HighstandDeltaic Progradation

Late TransgressiveIsolated Dune Patches andDune-Field Abandonment

Early TransgressiveSubtidal-Dune andBar Complex

Fig. 3. Composite section of the Hanneh Member showing the distribution of sedimentary facies and trace fossil assemblages within a sequence-stratigraphic framework.


flooding of shallow-intertidal to supratidal deposits (Elicki, 2007).The lower interval of the Hanneh Member consists of trough cross-bedded and tabular cross-bedded fine- to medium-grained sandstone(Figs. 5A–B, 6A–B) forming moderate-size tidal bars, compound dunesand simple dunes, locally dissected by channels, revealing an ongoingtransgression. These thick-bedded sandstone units are intercalated

A

Fig. 4. Diplocraterion isp. assemblage and associated facies in Wadi Umm Jafna. A. Coarse-grainterval. Scale bar is 10 cm long. B. Sandstone base showing high density of Diplocraterion

with heterolithic intervals consisting of thinly bedded current-ripplecross-laminated very fine- to fine-grained sandstone and mudstone,displaying flaser-, wavy-, and lenticular-bedding, and recording deposi-tion in the bottomsets of tidal dunes and in the low-energy areas be-tween the dunes. The whole lower interval displays a clear fining- andthinning-upward trend.

B

ined sandstone beds representing transgressive lags passing upwards into a heterolithicisp. Scale bar is 5 cm long.

A B

C D

Fig. 5. Arenicolites isp. assemblage and associated facies in Wadi Issal. A. Tabular cross-bedded fine- tomedium-grained sandstone. Scale bar is 1 m long. B. General view of a sandstonelayer with high density of Arenicolites isp. Scale bar is 10 cm long. C. Close-up of an Arenicolites isp. specimen showing well-defined U-shape. Scale bar is 1 cm long. D. Skolithos linearis.Scale bar is 2 cm long.


Three trace fossils assemblages characterize these deposits:Diplocraterion isp., Arenicolites isp., and C. salomonis assemblages(Table 1). TheDiplocraterion isp. assemblage occurs in twodifferent set-tings: one related with the transgressive erosional surfaces and theother recording colonization of small compound dunes (Fig. 4B). TheArenicolites isp. assemblage reflects colonization of tidal bars, com-pound dunes and simple dunes (Fig. 5B–D). The C. salomonis assem-blage characterizes the bottomsets of tidal dunes and the low-energyareas between the dunes (Fig. 6C–D). In addition, it may be present atthe base of channelized trough cross-bedded sandstone units, albeitwith very low ichnodiversity.

B

C

A

D

Fig. 6. Cruziana salomonis assemblage and associated facies. A. Close-up of tabular cross-bedping direction of foresets. Zerqa Ma'in. Scale bar is 30 cm long. B. General view of tabular c33 cm. C. Base of sandstone showing Rusophycus burjensis. Zerqa Ma'in. Scale bar is 3 cmMa'in. Scale bar is 1 cm long.

4.2. Late transgressive isolated dune patches and dune-fieldabandonment

The middle interval of the HannehMember consists of a fining- andthinning-upward package made of greenish gray planar cross-beddedand current-ripple cross-laminated very fine- to fine-grained sandstoneintercalated with flaser-, wavy-, and lenticular-bedded fine- and veryfine-grained sandstone and siltstone (Figs. 7A, 8A–B, 9A). This intervalrecords the gradual mantling of the early transgressive tidal-dune andbar complex preserved in the lower interval, its replacement bysand-starved dune patches, and its final abandonment recording by

ded fine- to medium-grained sandstone with thin mudstone drapes. Note opposite dip-ross-bedded fine- to medium-grained sandstone. Wadi Uhaymir. Length of hammer islong. D. Sandstone base containing superimposed specimens of C. salomonis. Zerqa

C D

A B

Fig. 7. Rosselia isp. assemblage and associated facies in Wadi Uhaymir. A. General view of intensely bioturbated very fine- to fine-grained sandstone and siltstone. Scale bar is 10 cmlong. B. Bedding-plane view showing high density of burrows. Scale bar is 10 cm long. C. Close-up of specimen displaying typical concentric infill in bedding-plane view. Scale bar is1 cm long. D. Close-up of specimen showing typical funnel-shaped morphology in cross section. Scale bar is 2 cm long.


mudstone blanketing. The top of the middle interval is delineated by amaximum flooding surface.

Three trace fossil assemblages characterize this late transgressive sce-nario: Rosselia isp., G. marina, and G. polonicus assemblages (Table 1). The

A

C D

Fig. 8. Gordia marina assemblage and associated facies. A. General view of planar cross-beddwith siltstone. Wadi Uhaymir. Length of hammer is 33 cm. B. Close-up showing planar cross-Wadi Issal. Scale bar is 1 cm long. D. Diplichnites isp. Wadi Uhaymir. Scale bar is 3 cm long.

Rosselia isp. assemblage is present in areas located between the tidaldunes (Fig. 7B–D), whereas the G. marina assemblage records coloniza-tion of dune-patch deposits, particularly in the low-energy zones of thesystem (Fig. 8C–D). The G. polonicus assemblage records the final

B

ed and current-ripple cross-laminated very fine- to fine-grained sandstone intercalatedbedding and mudstone drapes. Wadi Uhaymir. Length of hammer is 33 cm. C. G. marina.

B

C

A

Fig. 9. Gyrolithes polonicus assemblage and associated facies in Wadi Uhaymir. A. General view of interbedded very fine- to fine-grained sandstone and siltstone, displaying a thinning-and fining-upward trend. Scale bar is 5 m long. B and C. Close-up views of G. polonicus. Scale bars are 2 cm long.


abandonment of the tidal-dunefield, penetrating from the base of a sand-stone layer into the underlying mudstone, below the maximum floodingsurface (Fig. 9B–C).

4.3. Highstand deltaic progradation

The upper interval of the Hanneh Member is represented by acoarsening- and thickening-upward succession comprising interbeddedgreenish gray mudstone and current- and wave-ripple cross-laminatedvery fine-grained sandstone, locally with mudstone drapes (Fig. 10A).This interval represents the progradation of a mixed deltaic system, af-fected by waves and fluvial discharge with subordinate tidal action,encompassing deposition in prodelta to delta-front environments.

The highstand-delta interval is characterized by three trace fossil as-semblages: A. fossulata, B. sucta, and R. aegypticus assemblages (Table 1).The A. fossulata assemblage reflects colonization windows betweensedimentation events, essentially recording pauses in sedimentation.Burrowing took place under low-energy conditions in a stressedprodeltaic environment affected by substantial freshwater discharge(Fig. 11A–B). The B. sucta assemblage occurred in an environmentwith fluctuating energy levels, most likely ranging from the prodeltato the distal delta front (Fig. 12A–B). The R. aegypticus assemblage ispresent in distal delta-front deposits characterized by important fresh-water input and fluctuating energy conditions (Fig. 10B–C).

4.4. Forced-regressive deltaic progradation

The base of the uppermost interval of theHannehMember is strong-ly erosive and sharp, and consists of light gray parallel-laminated andcurrent andwave ripple-cross laminatedfine- tomedium-grained sand-stone (Figs. 13A–B, 14A–B, 15A). The overlying Umm Ishrin Formationcomprises light gray thick-bedded trough and planar cross-beddedcoarse- to medium-grained sandstone (Fig. 15B) that alternates withthin heterolithic packages of light gray fine- to very fine-grained sand-stone and redishmudstone, commonly showing flaser, wavy and lentic-ular bedding and locallywithwrinklemarks. Soft-sediment deformationstructures of various scales are pervasive, including pseudonodules(Fig. 15C), balls and pillows (Fig. 15D), convolute lamination andslumps. This interval records the abrupt basinwardmigration of the del-taic system as a response to a relative fall in sea level. The deposits stud-ied represent accumulation in proximal delta-front and delta-plain

settings. The forced-regressive delta displays a strong dominance ofriver processeswith a development of a prograding braidplain, althoughtidal-flat environments were locally present in interdistributary-bayareas.

Three trace fossil assemblages are present in these deposits: thefugichnia, C. problematica, and Diplichnites isp. assemblages (Table 1).The former has only been observed in the Uhaymir section in proximaldelta-front sheet-flood deposits (Fig. 13C), whereas the C. problematica(Fig. 14C–D) and Diplichnites isp. assemblages (Fig. 15E–F), both domi-nated by arthropod trackways, tend to occur in proximal delta-frontand tidal-flat deposits interbedded with channelized units of theUmm Ishrin Formation.

5. Evolutionary significance

TheHannehMember andUmm Ishrin Formation ichnofaunas reflectresponses of the benthic faunas to environmental parameters in a widevariety of depositional settings during a transgressive–regressive cycle(Fig. 16A–D), providing information that helps us to understand the na-ture of Cambrian ecosystems in the aftermath of the Cambrian radia-tion. The evaluation of these ichnofaunas provides insights into criticalissues to understand the impact of the Cambrian explosion in majorbreakthroughs in evolutionary paleoecology outlining feedbackmecha-nisms between the biota and their physical environment. In particular,we will address (i) the nature of marine substrates, (ii) the expansionof benthic animals inmarginal-marine environments, and (iii) the com-plexity of tiering structure in shallow-marine benthic ecosystems.

5.1. Early Paleozoic substrates and the nature of the Cruziana ichnofacies

The unusual presence of trails and burrows ornamented withbioglyphs, open furrows, and floating and adhering burrows inCambrian–Ordovician shallow-marine deposits has been regardedas evidence of widespread firm bottom substrates (Droser et al.,2002, 2004; Dornbos et al., 2004, 2005; Jensen et al., 2005).Firmground conditions may have resulted from limited extent anddepth of bioturbation in the virtual absence of a mixed layer. Thefact that these styles of preservation persisted well into the Silurianindicates that the formation of the mixed layer was a protracted pro-cess (Tarhan et al., 2012), and may not have been achieved in all en-vironments at the same time.

A

B

C

Fig. 10. Rusophycus aegypticus assemblage and associated facies in Wadi Umm Jafna.A. Interbedded mudstone and current- and wave-ripple cross-laminated very fine-grained sandstone. Note local presence ofmudstone drapes. Scale bar is 2 cm long. B. Gen-eral view of a sandstone base containing high density of R. aegypticus and Cruziana jordanica.Scale bar is 30 cm long. C. Close-up of various specimens of R. aegypticus and C. jordanica.Scale bar is 2 cm long.


The Jordan ichnofaunas display evidence of firmground conditions ator near the sea bottom in various depositional environments, from fullytomarginal-marine settings. Evidence include (1)well-preserved scratchmarks in most Cruziana and Rusophycus ichnospecies, (2) adheringG. polonicus burrows, and (3) unlined passively filled Diplocraterionisp. penetrating into underlying mudstone. Well-preserved scratch

A

Fig. 11. Archaeonassa fossulata assemblage. A. General view of specimens inWadi Umm Jafna.

marks characterize R. burjensis and C. salomonis and, to a lesser extent,R. aegypticus and Cruziana aegyptica. Although these trailswere emplacedbelow the sediment surface along a sandstone–mudstone interface,they were mostly formed at relatively shallow depth, not far from thesediment–water interface, therefore suggesting firm sea-bottom sub-strates. Classic firmground ichnofaunas are dominated by dwellingstructures of suspension feeders and passive predators, and com-pacted substrates are regarded as lacking utilizable organic matter(MacEachern et al., 1992, 2007). However, this is not the case withlower Paleozoic marine firmgrounds which display an abundance oftrace fossils produced by deposit feeders, such as trilobites and other ar-thropods (Seilacher, 1985).

G. polonicus occurs forming amonospecific suite at the base of a sand-stone layer andpenetrating into the underlyingmudstone. Specimens areunlined, subcircular in cross-section, and passively filled with sedimentcoming from the overlying sandstone. The spiral structures are not verypenetrative into the mudstone (i.e. less than two whorls). Gyrolithes hasbeen documented in cohesive substrates elsewhere (Netto et al., 2007;Wetzel et al., 2010). In contrast to younger firmgrounds in siliciclasticsediments, there is no evidence in favor of erosional exhumation in theJordan example (cf. MacEachern et al., 1992, 2007). TheGyrolithes assem-blage occurs in the maximum flooding surface within the HannehMem-ber. Interestingly, firmground (and hardground) suites associated withmaximum flooding surfaces typically occur in carbonates, but not insiliciclastics elsewhere (Buatois and Mángano, 2011a). In this context,the firmground nature of the substrate may have resulted from verylow sedimentation rates in the absence of a well-developed mixedlayer. This is a cautionary note to the extrapolation to the early Paleozoicof current applications of substrate-controlled ichnofacies, which arebased on younger examples characterized by a well-established mixedlayer.

Moderate-density suites of Diplocraterion isp. are present near thecontact between the Tayan and Numayri members in the Wadi UmmJafna section. Specimens are unlined and filled with coarse-grainedsand from the overlying layers. These trace fossil suites are associatedwith transgressive lags, and may record erosional exhumation duringravinement rather than stiff substrates at the sea bottom (seeMacEachern et al., 1992, 2007).

The Diplocraterion isp. occurrences may be regarded as a classicexample of the Glossifungites ichnofacies. It is likely that the firmgroundG. polonicus assemblage may also illustrate the Glossifungites ichnofa-cies, albeit without erosional exhumation. However, the trace fossilsuites dominated by trilobite structures are typical examples of theCruziana ichnofacies. This raises certain issues with respect to the sub-strate affinities of the Cruziana ichnofacies, which is one of the classicrepresentatives of the so-called “Softground Marine Ichnofacies”.Ichnofacies models of marine deposits are based on a cyclic notion ofgeologic time, and currently do not takemacroevolutionary innovationsinto account (see Buatois and Mángano, 2011b, and Mángano andBuatois, in press). However, the Cruziana ichnofacies clearly reflectsan evolutionary control, involving compositional turnovers and the

B

Scale bar is 4 cm long. B. Close-up viewof specimens inWadi Qunai. Scale bar is 2 cm long.

A B

Fig. 12. Bergaueria sucta assemblage. A. General view of specimens in Wadi Umm Jafna. Scale bar is 10 cm long. B. Close-up of specimens in Wadi Uhaymir. Scale bar is 4 cm long.


changing nature of marine substrates, with classic lower Paleozoic oc-currences dominated by trilobite trails and trackways produced onfirm substrates and younger ones representing the typical softgroundexamples.

A

C

B

Fig. 13. Fugichnia assemblage and associated facies in Wadi Uhaymir. A. General viewof parallel-laminated and ripple-cross laminated fine- to medium-grained sandstone.Length of hammer is 33 cm. B. Close-up of parallel-laminated and wave ripple-crosslaminated fine-grained sandstone. Scale bar is 4 cm long. C. Close-up of escape tracefossil. Scale bar is 2 cm long.

Interestingly, it has been recently noted that Lower Triassic shallow-marine ichnofaunas tend to be dominated by shallow-tier burrows, com-monly having sharp walls and preserving well-defined ornamentation(e.g. Spongeliomorpha), trails with scratch marks (e.g. Cruziana),and arthropod trackways with well-preserved appendage imprints(e.g. Diplichnites) (Buatois and Mángano, 2011b). These ichnofaunasindicate that the sediment was firm enough to allow preservation ofdelicate morphologic features, suggesting that the end-Permianmass extinction may have had a detrimental impact on the mixedlayer in marine environments (see also Hofmann et al., 2011). Thishypothesis is further supported by the widespread presence of wrin-kle marks and other MISS (microbially induced sedimentary struc-tures) in Lower Triassic marine deposits (Pruss et al., 2004).

5.2. The landward expansion of the Cambrian explosion

The invasion of marginal-marine and continental environments hasreceived significant attention in recent years (e.g. Davies and Gibling,2009; Davies et al., 2010, 2011; Kennedy and Droser, 2011; Retallack,2011; McIlroy, 2012; Davies and Gibling, 2012; Kennedy and Droser,2012). The earliest widely accepted ichnologic evidence of terrestrialfaunas is represented by arthropod trackways from Upper Ordovicianpond deposits (Johnson et al., 1994; see discussion by Davies et al.,2011). Periodic incursions into the land by amphibious arthropods sig-nificantly predate the appearance of truly terrestrial faunas, as indicatedby trackways and bilobate trace fossil preserved in upper Cambrian toLower Ordovician supratidal or backshore deposits (MacNaughton etal., 2002; Collette et al., 2010; Hagadorn et al., 2011). Tidal flats havebeen colonized even earlier, with ichnofaunas present in intertidal de-posits since the early Cambrian (see review in Buatois and Mángano,2011a). Understanding of colonization trends should clearly differenti-ate between brackish-water ichnofaunas, ichnologic evidence of peri-odic excursions of amphibious organisms into the land, and trueterrestrial ichnofaunas (Buatois et al., 1998, 2005; Davies et al., 2011).It has long been noted that arthropods have the ability to periodicallymigrate inland due to amphidromy or via salt-water wedges (Maplesand Archer, 1989; Buatois et al., 2005). Marine influence is common indelta-plain deposits. In some cases, brackish-water conditions andtidal influence have been detected up to 65 km inland (Shanley et al.,1992).

Most of the trace fossils recorded in the studied deposits occur in fullymarine conditions or in the distal portions of a prograding delta system(where times of freshwater discharge alternated with periods ofnormal-marine salinity), but bilobate structures (C. problematica,R. carbonarius and Rusophycus isp.), trackways (Diplichnites isp.), andscratch marks (Dimorphichnus cf. D. obliquus) occur in more proximalsettings near the top of the Hanneh Member and in the overlyingUmm Ishrin Formation. Although it may be tempting to interpret someof the Umm Ishrin trace fossils as the evidence of an invasion of terrestri-al settings during the Cambrian, extreme care should be made in inte-grating ichnologic and sedimentologic datasets within a sequence-stratigraphic framework. In particular, detailed understanding of thearchitecture of interfingering fluvio-deltaic and tidal-flat deposits is

C D

A B

Fig. 14. Cruziana problematica assemblage and associated facies. A. General view of a thickening- and coarsening-upward interval dominated by parallel-laminated and waveripple-cross laminated fine-grained sandstone. Wadi Qunai. Scale bar is 20 cm long. B. Close-up showing wave ripples on top and abundant mudstone intraclasts. Wadi Qunai.Scale bar is 5 cm long. C. General view of sandstone base with high density of C. problematica and Rusophycus carbonarius. Wadi Al Hisa. Scale bar is 1 cm long. D. Close-up ofC. problematica and R. carbonarius. Wadi Qunai. Scale bar is 1 cm long.


a key to demonstrate the ecologic affinities of the Umm Ishrintracemakers. Makhlouf and Abed (1991) noted the intercalation ofbraided-channel deposits and finer-grained tidally influenced facies intheUmm Ishrin Formation. Evidence ofmarine influence and tidal actionis recorded by the presence of linguliformean brachiopods and abundantmudstone drapes. The local presence ofwrinklemarks suggests stabiliza-tion by microbial mats. Makhlouf and Abed (1991) indicated that tidalflats developed in response to periodic shifting of the active braidedchannels.

The occurrence of the C. problematica and Diplichnites isp. assem-blages in the Umm Ishrin Formation provides further evidence of theinterfingering of tidal flats within the braidplain delta, and is consistentwith available models on the colonization of brackish-water settingsthrough the Phanerozoic (Buatois et al., 2005). These authors noted thatthe Cambrian–Ordovician represented a prelude to the major invasionthat occurred during the remaining of the Paleozoic. During the early Pa-leozoic, arthropods were able to foray into brackish-water environments(Selley, 1970; Martin, 1993; Mikuláš, 1995; Braddy and Almond, 1999;Mángano and Buatois, 2003; Baldwin et al., 2004; Weber and Braddy,2004). The Umm Ishrin Formation indicates that relatively large arthro-pods were able to foray into stressed, marginal-marine environmentsearly in the Phanerozoic. In any case, intensity of bioturbation andichnodiversity levels remained relatively low during the early Paleozoic(Buatois et al., 2005).

5.3. The evolving complexity of infaunal tiering structure

Evaluation of the tiering structure of infaunal communities is essen-tial to refine our understanding of evolutionary changes in the aftermathof the Cambrian explosion. Complexity of the tiering structure provides aproxy to evaluate organic delivery to the substrate, and ultimately the

coupling of the plankton and the benthos in marine Cambrian ecosys-tems. Based on the analysis of body fossils, it has been suggested thatthe ecologic structure of Cambrian communities was relatively simple.Lower to middle Cambrian faunas include thirty modes of life, thereforerepresenting roughly only one third of the modes of life used by recentfaunas (Bambach et al., 2007). Overall, the Cambrian evolutionary faunarepresents the occupation of eleven megaguilds (sensu Bambach,1983).

Study of selected ichnofabrics from the HannehMember provides in-formation to understand tiering structure in middle Cambrian shallow-to marginal-marine communities (Fig. 17A–I). In particular, ichnofabricsfrom three main depositional settings have been considered: (1) high-energy fully marine, (2) low-energy fully marine, and (3) marginal-marine deltaic. Ichnofaunas from more proximal settings (i.e. tidal flatswithin the braidplain delta) consist of superficial to very shallow struc-tures in the absence of infaunal tiering.

High-energy fully marine ichnofabrics are represented by occur-rences of the Arenicolites isp. and Diplocraterion isp. assemblages(Fig. 17A–B) in trough and planar cross-bedded sandstone of the trans-gressive tidal-bar and dune complex (Hofmann et al., 2012). Depositsare typically sparsely bioturbated (bioturbation index or BI of Taylorand Goldring (1993), is 1). Both assemblages are dominated bydomichnia, and probably equilibrichnia, of suspension feeders. Most oc-currences are characterized bymonospecific suites; only in a few cases,S. linearis and P. tubularis are added in one of the preservational variantsof the Arenicolites assemblage. This increase in ichnodiversity is accom-panied by a significant increase in the degree of bioturbation (BI 4–5).The tiering structure is simple, consisting of shallow-tier P. tubularisand deep-tier (up to 10 cm) Arenicolites isp. and S. linearis. BecauseDiplocraterion isp. is preserved at the base of sandstone beds, the actualbioturbation depth is not possible to evaluate, although a similar tier

Fig. 15. Diplichnites isp. assemblage and associated facies. A. General view of coarsening- and thickening-upward sandstone-dominated interval. Wadi Issal. B. General view of athick-bedded trough and planar cross-bedded coarse- to medium-grained sandstone succession. Wadi Issal. C. Pseudonodule. Wadi Uhaymir. Length of hammer is 33 cm. D. Balls andpillows. Wadi Uhaymir. Length of hammer is 33 cm. E. Diplichnites isp. Wadi Issal. Scale bar is 1 cm long. F. Dimorphichnus cf. D. obliquus. Wadi Uhaymir. Scale bar is 2 cm long.


position to Arenicolites isp. is envisaged. Invariably, structures penetrateinto the substrate from a colonization surface at the top of the sand-stone body.

The style of bioturbation suggests opportunistic colonization duringperiods of comparative quiescence (short-term colonization windows).The slight increase in ichnodiversity and the remarkable increase in de-gree of bioturbation in some sandstone units may reflect more continu-ous colonization windows under slightly lower energy conditions. Thistype of ichnofabrics dominated by deep-tier suspension-feeder struc-tures is typical of post-agronomic revolution high- to moderate-energyCambrian marine settings (see Seilacher, 1999). Before the appearanceof deep-tier suspension-feeder burrowers, these nearshore sandy sub-strates remained uncolonized (Buatois and Mángano, 2004). Deepburrowing undoubtedly increased the oxygen concentration in the sed-iment and was conducive to significant changes in the geochemicalcycle. Bioturbation was therefore responsible for an average deepeningof the redox discontinuity surface, the expansion of aerobic bacteria,an increased rate of organicmatter decomposition, and the regenerationof nutrients, which resulted in complex ecologic feedbacks (Mánganoand Buatois, 2004a).

With a few exceptions (e.g. Droser et al., 1994), high-energy sandysubstrates, both in the upper shoreface of wave-dominated shorelinesand the subtidal region of tide-dominated environments, were charac-terized by simple tiering structures (e.g. Mángano and Buatois, 2004a;Davies et al., 2009; Desjardins et al., 2010). Colonization of deep tiersis clearly an adaptation to strong erosion and high hydrodynamic ener-gy at the sediment–water interface. Although the Jordan ichnofabricsonly rarely display high indexes of bioturbation, Skolithos pipe rocksare a typical example of these nearshore ichnofabrics. As noted byDroser (1991), there is a remarkable decrease in pipe-rock occurrencesafter the Ordovician. The reasons of such a decrease are still unclear, butincreased predators pressuremay have contributed to a decline in largesessile suspension-feeders (McIlroy and Garton, 2004). Also, Desjardinset al. (2010) proposed that the Ordovician diversification event mayhave lead to greater spatial competition, negatively affecting theSkolithos tracemakers. Although nearshore high-energy settings arestressful environments characterized by relatively low ichnodiversitieseven in post-Paleozoic deposits, the Mesozoic radiation of crustaceandecapodswas responsible for the appearance ofmore complex patternsof infaunal tiering (Carmona et al., 2004).

A

C D

Early transgressive subtidal duneand bar complex

Highstand deltaic progradation Forced-regressive deltaic progradation

Late transgressive dune patchesand dune-field abandonmentB

Diplocraterion isp.assemblage

Arenicolites isp.assemblage

Cruziana salomonisassemblage

Rosselia isp.assemblage

Gordia marinaassemblageGyrolithes polonicus

assemblage

Archaeonassa fossulataassemblage

Bergaueria suctaassemblage

Rusophycus aegypticusassemblage

Fugichniaassemblage

Cruziana problematicaassemblage

Diplichnites isp.assemblage

S/SW

S/SWS/SW

S/SW

N/NEN/NE

N/NEN/NE

Fig. 16. Depositional evolution and paleoenvironmental distribution of trace fossil assemblages. A. Early transgressive subtidal dune and bar complex. B. Late transgressive isolateddune patches and dune-field abandonment. C. Highstand deltaic progradation. D. Forced-regressive deltaic progradation.


Low-energy marine ichnofabrics are represented by the C. salomonis,Rosselia isp., G. marina, and G. polonicus assemblages (Fig. 17C–F).Whereas the former is present in the bottomsets of tidal dunes and thelow-energy areas between the dunes of the early transgressive complex,the other three are linked to the establishment of the late transgressiveisolated dune patches and the subsequent abandonment of the dunefield. Low-energy fully marine environments represent stable settings,which are ideal for the establishment of complex animal–substrate inter-actions (Buatois and Mángano, 2011a). However, the pattern emergingfrom the study of the middle Cambrian ichnofabrics from Jordan isquite different. The four ichnofabrics are characterized by simple tieringstructures and amarked dominance of shallow- to, more rarely, mid-tierstructures of deposit and detritus feeders. The only deep-tier structure isRosselia isp., which penetrates up to 27 cm into the sandy substrate. If alllow-energy marine trace fossil assemblages are considered as a whole,15 ichnotaxa are present. However, alpha ichnodiversity (sensu Buatoisand Mángano, 2011a) is quite low, typically ranging from 1 to 4, withonly the C. salomonis assemblage reaching 11 ichnotaxa. In fact, onlyfour ichnospecies occur in more than one of these assemblages, andthese shared forms are represented by the facies-crossing ichnogeneraPlanolites, Palaeophycus, Helminthoidichnites and Gordia. This pattern in-dicates a high beta ichnodiversity (sensu Buatois and Mángano,2011a), reflecting low species differentiation within a niche, but highspecies differentiation between habitats. Degree of bioturbation is lowto moderate (BI 1–4). Overall, the emerging picture is one of poorlyspecialized communities showing limited colonization of the infaunalecospace. The paucity of deep deposit-feeding burrowers in earlyPhanerozoic marine communities may indicate limited amounts offood buried in the sediment (Bambach, 1993).

Marginal-marine settings affected by frequent changes in salinityconditions are not conducive to the establishment of complex animal–substrate interactions (MacEachern and Pemberton, 1994; Mánganoand Buatois, 2004b). Highstand deltaic deposits of the Hanneh Member,including prodelta and delta-front heterolithic facies, show variable pro-portions of sandstone and mudstone and host the A. fossulata, B. sucta,and R. aegypticus assemblages (Fig. 17G–I). As in the case of theirlow-energy fully marine counterparts, most ichnofabrics in these de-posits are characterized by simple tiering structures and a dominance

of shallow-tier feeding and grazing traces of deposit and detritus feeders.Ichnodiversity is typically low, and degree of bioturbation is almost neg-ligible (BI 0–1) because almost all trace fossils are emplaced along sand-stone–mudstone interfaces, causing no disturbance of the primary fabric.The R. aegypticus assemblage is dominated by shallow-tier trilobite tracefossils, and the deep-tier S. linearis most likely represents a subsequentcolonization event. Interestingly, a slightly more complex tiering struc-ture is detected in connectionwith the B. sucta assemblage, which occursin prodelta to distal delta-front deposits. Tiering structure consists of ashallow tier with B. sucta, P. tubularis and P. montanus, and a slightlydeeper-tier R. burjensis. This more complex tiering structure may havebeen developed during times of relative stability between depositionalevents.

In short, tiering analysis in the Hanneh Member indicates relativelysimple community structures and limited use of the infaunal ecospace.Shallow-tier deposit- and detritus-feeding trace fossils are dominant inlow-energy fully marine andmarginal-marine environments. Deep-tierstructures of detritus feeders may occur in fully marine low-energy set-tings, whereas deep-tier trace fossils of suspension feeders are domi-nant in high-energy subtidal zones.

6. Conclusions

(1) The studied ichnofaunas from the Cambrian of Jordan occur infour different sequence-stratigraphic contexts: early transgres-sive subtidal dune and bar complex, late transgressive isolateddune patches and dune-field abandonment, highstand deltaicprogradation, and forced-regressive deltaic progradation.Where-as the former three are represented by the middle CambrianHanneh Member, the latter is for the most part illustrated by thelate middle to upper Cambrian Umm Ishrin Formation. Theseichnofaunas yield insights into the nature of Cambrian ecosys-tems in the aftermath of the Cambrian radiation.

(2) TheHannehMember ichnofaunas display evidence of firmgroundconditions at or near the sea bottom, including well-preservedscratch marks in most Cruziana and Rusophycus ichnospecies,adhering G. polonicus burrows, and unlined passively filledDiplocraterion isp. penetrating into underlying mudstone. The

image of Fig.�16

Pa

Sk

Ar

Arenicolites isp.Assemblage

A

Dp

Diplocraterion isp.Assemblage

B

Ro As

Pa Pl

Rosselia isp.Assemblage

D

Gy

Gyrolithes polonicusAssemblage

F

Pa PlBe Ru

Bergaueria suctaAssemblage

H

Cr

MoRu

Dm

Cruziana salomonisAssemblage

C

G

Archaeonassa fossulataAssemblage

An

I

Rusophycus aegypticusAssemblage

Sk

RuCr

Gordia marinaAssemblage

EGo DiHe

High-energy fully marine Low-energy fully marine Marginal-marine

Fig. 17. Tiering structure of the Hanneh Member ichnofaunas in high-energy fully marine, low-energy fully marine and marginal-marine deltaic settings. A. Arenicolites isp. assemblage.The tiering structure consists of very shallow-tier Palaeophycus tubularis (Pa), and deep-tier Arenicolites isp. (Ar) and Skolithos linearis (Sk). B. Diplocraterion isp. (Dp) assemblage.C. Cruziana salomonis assemblage. The tiering structure consists of very shallow-tier Dimorphichnus cf. obliquus (Dm) and Monomorphichnus isp. (Mo), and shallow-tier C. salomonis(Cr) and Rusophycus burjensis (Ru). Other ichnotaxa may be present, but are not abundant enough to be included in the tiering diagram. D. Rosselia isp. assemblage. The tiering structureconsists of shallow-tier Planolites montanus (Pl), Asterosoma isp. (As) and P. tubularis (Pa), and a deep-tier Rosselia isp. (Ro). E. Gordia marina assemblage. The tiering structure consists ofvery shallow-tier Diplichnites isp. (Di), and a slightly less shallow tier comprising G. marina (Go) and Helminthoidichnites tenuis (He). F. Gyrolithes polonicus (Gy) assemblage.G. Archaeonassa fossulata (An) assemblage. H. Bergaueria sucta assemblage. The tiering structure consists of shallow-tier B. sucta (Be), P. tubularis (Pa), P. montanus (Pl), and a mid-tierR. burjensis (Ru). I. Rusophycus aegypticus assemblage. The tiering structure consists of shallow-tier R. aegypticus (Ru) and Cruziana jordanica (Cr), and a deep-tier S. linearis (Sk). The lattermay represents a subsequent colonization event.


Diplocraterion isp. occurrences represent classic examples of theGlossifungites ichnofacies due to erosional exhumation of the sub-strate. In contrast, the firmground G. polonicus is associated toa non-erosive maximum flooding surface and the trilobite-dominated trace fossil suites illustrate firmground examples ofthe Cruziana ichnofacies in the absence of erosional exhumation.Our study suggests that lower Paleozoic occurrences of theCruziana ichnofacies dominated by trilobite-produced trace fos-sils reflect firm substrates, rather than the softground conditionsthat characterize younger occurrences of this ichnofacies.

(3) The occurrrence of arthropod trace fossils in interdistributary-baytidal flats within a braidplain delta complex in the Umm IshrinFormation suggests that arthropods were able to colonizemarginal-marine settings during the Cambrian, providing furthersupport to models addressing colonization of brackish-water en-vironments through geologic time.

(4) The tiering structure of the middle Cambrian ichnofaunas is rel-atively simple. The dominance of shallow-tier structures, partic-ularly in low-energy settings, suggests limited use of the infaunalecospace. Deep-tier trace fossils of suspension feeders are domi-nant in high-energy subtidal zones.

Acknowledgments

Financial support for this study was provided by the Natural Sci-ences and Engineering Research Council (NSERC) Discovery Grants311727-05/08 and 311726-05/08 awarded to Mángano and Buatois,

respectively, the German Research Foundation (DFG) research projectsELICKI 144/14 and ELICKI 144/17, the Jordan Higher Council for Scienceand Technology (HCST), and the Natural Resources Authority of Jordan(NRA) to Elicki and Shinaq. We thank the two anonymous Palaeo-3 re-viewers for their valuable comments. Replicas from latex casts of largetrace fossil surfaces were produced by H. Luginsland (Tübingen Univer-sity) and H. Rathaj (Chemnitz Museum of Natural History). Luis Quirozis thanked for his work on the illustrations.

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