Cambrian Ichnofossils from Northeastern Egypt

N. Jb. Geol. Paläont. Abh. 270/2 (2013), 129–149 Article Stuttgart, November 2013

Cambrian ichnofossils from northeastern Egypt

Olaf Elicki, Mohamed Abdel Ghany Khalifa, and Sherif Mohamed Farouk With 5 figures and 1 table

Abstract: New finds of ichnofossils from the Cambrian Araba Formation are described from the Eastern Desert and Sinai Peninsula (northeastern Egypt), and recent knowledge on Cambrian ichnofossils from these regions is summarized. Five ichno-assemblages from Sinai Peninsula and two from the Eastern Desert represent ichnocoenoses of low diversity, dominated by arthropod and vermiform traces. The assemblages are attributed to the Cruziana and Skolithos ichnofacies realms of a tidally influenced, marginal marine to probably freshwater affected depositional area. Based on the occurrence of Cruziana salomonis (Seilacher, 1990) and Rusophycus burjensis Hofmann, Mángano, Elicki & Shinaq, 2012, an early Middle Cambrian age (basal stage 5 of series 3) can be deduced. The Cambrian ichnofauna of northeastern Egypt points to close palaeogeographic affinity with the Jordan Rift Valley (southern Dead Sea and northern Wadi Araba). In contrast to this latter area, the sedimentological character of the northeastern Egyptian Cambrian succession indicates a somewhat more proximal position on the northern Gondwana shelf relative to that interpreted from depositional conditions documented for the Jordanian Cambrian in the central to southern Wadi Araba.

Key words: Cambrian, Palaeozoic, Araba Formation, ichnofossils, Egypt, Eastern Desert, Sinai Pe- ninsula.

1. Introduction 2011, and below). The Cambrian sediments of Egypt are represented exclusively by siliciclastic rocks, so the Egypt represents an area that is not only important impetus of investigations was not only on their strati- due to its renowned cultural history and iconic land- graphic context, but also on characterisation of the marks, but also for its geological endowment. Mineral depositional facies for which the included ichnofossils and hydrocarbon resources, as well as water manage- have a particular potential. ment play a crucial role in the region (Said 1990). Ichnological data – and palaeontological infor- Knowledge of the geology of Egypt – and also of its mation in general – are rather rare for the Cambrian Cambrian succession which is of particular interest succession of Egypt (Klitzsch 1990a). Seilacher here – mainly results from extensive geological map- (1990) reported some ichnofossils from the Eastern ping activities and hydrogeological and hydrocarbon Desert about 30 km south of the fossiliferous localities exploration during the last few decades (Klitzsch et documented herein, and some further material from al. 1984; Klitzsch1986; Said 1990; Tawadros 2001, the Umm Bogma area of southwestern Sinai Penin- 2012). Regarding the earliest Palaeozoic rocks it was sula (Tab. 1, Fig. 1). Further palaeontological infor- not until the 1980s that a Cambrian age was confirmed mation was provided by Andrawis et al. (1983) and in specific cases by palaeontological data (see Wanas El Dakkak (1988), who mentioned the occurrence of

eschweizerbart_xxx 130 O. Elicki et al.

Fig. 1. Regional geographic map (1a) and scheme of location of sections (1b, indicated in 1a by black rectangle) investigated in this study. For coordinates of ichnofossil sites see text. Modified from Mountain High Maps 2.1 (Digital Wisdom, 1996).

eschweizerbart_xxx Cambrian ichnofossils from northeastern Egypt 131

Table 1. Ichnofossils reported from Cambrian successions of Egypt.

Klitzsch (1990a) and Present study Seilacher (1990) Eastern Sinai Eastern Sinai Desert Peninsula Desert Peninsula Rusphycus aegypticus (Seilacher, 1990) ••• Rusophycus burjensis Hofmann, Mángano, Elicki & Shinaq, 2012 • • Cruziana salomonis (Seilacher, 1990) •• • Cruziana isp. • Diplichnites isp. • Dimorphichnus quadrifidus Seilacher, 1990 • Dimorphichnus cf. quadrifidusS eilacher, 1990 • Dimorphichnus cf. obliquus Seilacher, 1955 • Bergaueria sucta Seilacher, 1990 • ?Bergaueria isp. • Diplocraterion isp. • Arenicolites isp. • Teichichnus rectus Seilacher, 1955 • Skolithos isp. •• Palaeophycus tubularis Hall, 1847 •• Planolites montanus Richter, 1937 • Fucusopsis isp. • Helminthopsis tenuis Książkiewicz, 1968 • isp. indet. (?Dydimaulichnus, ?Archaeonassa) • biomat structures •

brachiopods and single trilobites from two cored drill- This record must be considered dubious because nei- holes in the Western Desert that indicate a Cambrian ther Klitzsch (1990a) nor two of the present authors age (possibly Middle Cambrian, G. Geyer, Würzburg, (O.E and S.M.F. in 2010) were able to relocate either personal communication 2013). The same age is in- the type locality or any related lithofacies in the field, dicated by palynomorphs reported from the northern even though Omara (1972) described both in detail. area of the Western Desert (Gueinn & Rasul 1986, Additionally, P.L. Brenckle (in Keeley 1994) stated Keeley 1989). According to Klitzsch (1990a), a few that the ostensible archaeocyathan material of Omara additional wells from northwestern Egypt have also (1972) probably represents Cretaceous/Palaeogene red intersected Cambrian sedimentary rocks, whereas ear- algae, and that Carboniferous strata lie directly on lier reports on the probable occurrence of Cambrian top of Proterozoic basement in the area considered by strata in southwestern Egypt were discounted by that Omara (1972). Finally, F. Debrenne (personal commu- author. A report of archaeocyathans (a sponge group nication, 2013), one of the leading specialists on ar- almost exclusively restricted to the Early Cambrian) chaeocyaths, has clearly rejected the affiliation of the together with stromatolites from the Abu Durba area remains published by Omara to the Archaeocyatha). in southwestern Sinai was published by Omara (1972). Summing up all these critical remarks by various au- If correct, this report would be surprising because ar- thors, the data and stratigraphic conclusions published chaeocyathans or favourable facies are not otherwise by Omara (1972) must be dismissed. known from anywhere in the broader palaeogeograph- The objects of the present paper are to report new ic region (northeastern Africa, Middle East, Arabia). information on Cambrian ichnofossils from the East-

eschweizerbart_xxx 132 O. Elicki et al. ern Desert and Sinai Peninsula of Egypt, to evaluate unconformable on basement, succeeded by the Araba their stratigraphic significance, and to extent know- Formation after a further unconformity (El-Araby & ledge of their palaeoecological and palaeogeographic Abdel-Motelib 1999). In western Sinai Peninsula and distribution. Field data were collected during two field in the Eastern Desert, the Taba Formation is missing trips (2009 and 2010) by the authors. The working area and the upper part of the Araba Formation rests direct- is located in the Eastern Desert (Wadi Mor, Somr el ly on basement rocks (Fig. 2A-B). The Araba Forma- Qaa, Jebel el Zeit) and on Sinai Peninsula (Wadi Sara- tion generally consists of fluviatile to shallow marine, bit el Khadem) (Fig. 1). cross-bedded sandstone, and minor conglomerates Illustrated specimens are housed in the collection of the (and a palaeosol) at its base and can be subdivided into Geological Institute of Freiberg University (archive number three major units: the lower unit consists of basal con- FG 630). glomerate and fluviatile, cross-bedded sandstone. The 2. Geological background middle unit is represented by shallow marine, dark red silt and fine sandstone (ichnofossil bearing unit, In Egypt, Proterozoic basement is mainly exposed in Fig. 2C-D). The upper unit is predominated by trough eastern Egypt as the Arabian-Nubian Shield and as cross-bedded sandstone. Altogether, the formation has small extensions of the older East Sahara Craton in the a thickness of up to 190 m. Detailed sedimentological southwest (Klitzsch 1986; Schandelmeier et al. 1987; investigations of the Araba Formation in northeastern Said 1990). The region was mainly affected by the Egypt have been published by Abdel-Wahab et al. Pan-African Orogeny during formation of the Neopro- (1992) and Khalifa et al. (2006). In the Eastern Des- terozoic Gondwana supercontinent, and by subsequent ert (Somr el Qaa), also fine-grained siliciclastic rocks extensional tectonics (Schandelmeier et al. 1987; Pet- (siltstone and shale) also occur (for details see Tawad- ters 1991; Stern 1994; Boger & Miller 2004; sum- ros 2012). mary in Khalifa et al. 2006). Following amalgamation In contrast to the Cambrian, Egypt was a topo- of the Arabian-Nubian Shield and succeeding tecton- graphically positive area with no deposition during ics, several basins originated and subsequently filled nearly the whole of the Ordovician (Klitzsch 1990a). during the Phanerozoic (e.g., Klitzsch 1990b; Keeley Sandstones were deposited only locally, in the very 1994; Hawat 1997; Guiraud 1999). southwest (Jebel Uweinat, Klitzsch 1990a). Strati- Palaeozoic deposition commenced on the igne- graphic reports from petroleum companies and some ous and metamorphic basement, producing a distinct other reports on the occurrence of Ordovician strata erosional unconformity (Fig. 2A-B). Cambrian to Car- have been rejected by Klitzsch (1990a) as represent- boniferous rocks are known from Sinai Peninsula, the ing rocks of either Cambrian or post-Ordovician age. Jebel Uweinat area in the southwest as well as from Nevertheless, an Ordovician age is accepted by various southern Egypt, the Eastern Desert, and subsurface authors (e.g., Issawi & Jux 1982; Khalifa et al. 1996; in northern Egypt (Klitzsch 1990a, b; Giraud 1999; Alsharhan & Salah 1997) for a non-fossiliferous, flu- Tawadros 2001, 2012; Garfunkel 2002; Wanas 2011). viatile sandstone succession (Naqus Formation, up to Whereas Silurian (sandstone and shale), Devonian 200 m thick) overlying the Araba Formation (Wanas (sandstone, conglomerate, carbonate) and Carbonifer- 2011). ous sedimentary rocks (sandstone, shale, carbonate, Weissbrod (1969) has confused the stratigraphic coal) have been securely dated by their fossil content, framework by proposing a lithostratigraphic scheme biostratigraphic data from Cambro-Ordovician rocks based on a succession in northeastern Sinai (outside are limited (summary by Tawadros 2012). Egypt) and the southern Jordan Rift Valley. He recog- Cambrian sedimentary rocks are exposed in lim- nised five formations (Palaeozoic Nubian Sandstone ited areas on Sinai Peninsula, the western coast of the and Hakhlil, Nimra, Mikhrot and Shehoret forma- Gulf of Suez (Jebel el Zeit) and in the Eastern Desert tions) united within the Yam Suf Group, to the lower (northern Wadi Qena; Fig. 1), and are represented by part of which he attributed a Cambrian age. Tawadros the Araba Formation and the underlying, geographi- (2012) considered all these formations as members of cally limited Taba Formation (Hassan 1967; Said the Araba Formation and stated that only equivalents 1990; Khalifa et al. 2006; Wanas 2011). Towards of the oldest (Palaeozoic Nubian Sandstone Forma- eastern Sinai Peninsula, the Palaeozoic succession tion) and the youngest (Shehoret Formation, also ex- begins with siliciclastic rocks of the Taba Formation clusively of sandstone) of Weissbrod’s units can be (“Infra-Cambrian” fluviatil sandstone and paIaeosol), recognized in southwestern Sinai. These units are

eschweizerbart_xxx Cambrian ichnofossils from northeastern Egypt 133 unconformably overlain by sandstone of the Netafim Arenicolites isp. Group (interpreted as Ordovician by Weissbrod 1969), Fig. 2F-G overlain in turn (again, unconformable) by Carbonifer- ous rocks (Abu Durba Formation). Material: About 15 specimens; Wadi Mor section (Eastern Desert: 28°29’32.20”N, 32°27’49.00”E; Fig. 1), middle Araba Formation, a short distance above erosional contact 3. Ichnofossil palaeontology with granitic basement. Remark: If not indicated differently, assignment of type Description: Small U-tubes preserved in convex (positive) ichnospecies below is by original designation. hyporelief. No spreiten observed. Walls smooth. Width of burrow tunnels commonly 3 mm (ranges from 2.5-3.5 mm); A) Vertical burrows diameter generally around 10 mm (range 9-11 mm). Burrow depth not recognisable. Rarely, circular openings are visible where specimens are eroded. Orientation perpendicular to bedding plane. Diplocraterion Torell, 1870 Remarks: Arenicolites isp. occurs in pale to light red, Type ichnospecies: Diplocraterion parallelum Torell, micaceous, fine-grained, somewhat heterolithic, small 1870; Lower Cambrian of Sweden. sandstone bars intercalated by portions of very micaceous and so somewhat darker siltstone laminations. The lateral distribution of the specimens is not consistent and is rather Diplocraterion isp. random. Co-occurring ichnofossils exclusively consist of Rusophycus aegypticus (Seilacher, 1990) and rare Fig. 2E Skolithos (see below). Some of the Rusophycus resting traces have been subsequently penetrated by Arenicolites. Material: About 50 specimens; Wadi Mor section (Eastern More detailed determination is not possible because of Desert: 28°29’32.20”N, 32°27’49.00”E; Fig. 1), middle inadequate preservation, but also due to the needed but Araba Formation, a short distance above erosional contact still unavailable taxonomic revision of this ichnogenus with granitic basement. (Mángano et al. 2002). Arenicolites is commonly regarded as the domichnion Description: Specimens preserved as dumb-bell shaped, structure of a suspension-feeding worm (Fürsich 1974) or of concave (negative) epirelief structures of typical U-tubes a deposit feeder (Bromley 1999) of shallow marine higher- of this ichnogenus. In some cases spreiten are recognisable. energy environments (Gérard & Bromley 2008). However, The smooth-walled burrows have a width commonly of 4-5 the taxon has also been reported from deep and marginal mm (range 4-8 mm); diameter generally around 25 mm marine and lacustrine settings (Bromley & Asgaard 1979; (range 20-30 mm). Orientation perpendicular to bedding Buatois & Mángano 1992; Gillette et al. 2003; Hofmann plane. 2008). Arenicolites is stratigraphically widely distributed through the entire Phanerozoic. Remarks: Diplocraterion isp. has been observed in fine- to medium-grained sandstone with fine, dark grey siltstone interlayers. The lateral distribution of the ichnofossils is Skolithos Haldemann, 1840 relatively consistent. Size and general shape of the specimens are quite uniform. Because of the rather poor preservation, Type ichnospecies: Fucoides? linearis Haldeman, 1840; determination to ichnospecies-level is not possible. No other Lower Cambrian of Pennsylvania. ichnofossils occur together with Diplocraterion isp. Diplocraterion is commonly regarded as a burrow of the shallow marine suspension feeder characteristic of Skolithos isp. higher energy conditions (Seilacher 1967). However, the Figs. 2H, 3A ichnofossil is also known from other environments (e.g. tidal flats, deep marine, non-marine) and various stratigraphic Material: Numerous specimens are documented in situ in the levels (entire Phanerozoic) (e.g., Crimes 1977; Fillion & field; Jebel el Zeit section (Eastern Desert: 27°59’39.70”N, Pickerill 1990; Kim et al. 2005; Hofmann 2008; Hofmann 33°27’18.00”E; Fig. 1); middle Araba Formation, various et al. 2012). horizons from about 12 m to about 31 m above erosional contact with granitic basement; Wadi Mor section (Eastern Desert: 28°29’32.20”N, 32°27’49.00”E), middle Araba Formation, a short distance above the erosional contact with Arenicolites Salter, 1857 granitic basement.

Type ichnospecies: Arenicola carbonaria inney B , 1852, by Description: Vertical, straight, cylindrical, unbranched subsequent designation of Richter (1924); Carboniferous of burrows. Tube diameter 2-4.5 mm, maximum tube depth UK. 70-80 mm.

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Fig. 2.

eschweizerbart_xxx Cambrian ichnofossils from northeastern Egypt 135

Remarks: In Jebel el Zeit section Skolithos isp. has been Material: Several tens of specimens; Jebel el Zeit section observed in medium- to coarse-grained (locally conglomer- (Eastern Desert: 27°59’39.70”N, 33°27’18.00”E; Fig. atic) sandstone, stratified by grainsize alternations in trough 1), middle Araba Formation, about 22 m above erosional cross-bedded units and subaqueous (three-dimensional) contact with the granitic basement. dunes; subhorizontally bedded, heterolithic, finer-grained alternations are intercalated (Fig. 2C-D). The ichnofossil is Description: Small, and vertically or subvertically stacked, common on top of sandstone beds. Here, Skolithos is quite backfilled tunnels, resulting in a subvertical wall of frequent within the uppermost few centimetres of the sand- gutter-shaped structures representing retrusive remains of stone beds forming distinct horizons. Stratigraphically, the vertically shifted horizontal tunnels. Typical spreiten are ichnofossil occurs at various distinct levels, in which it can developed as a result of this retrusive displacement. Width be found in high density. No other ichnofossils have been of tunnels comparably small, most commonly 5-6 mm observed associated with this ichnogenus. In the Wadi Mor (generally 3-9 mm). The wall-like succession of spreiten section, this ichnofossil occurs in rippled heterolithic rocks is mostly, but not strictly, perpendicular to bedding planes, comprising fine-grained sandstone and fine micaceous silt- but sometimes also slightly tilted up to 30° and attaining stone. Here, Skolithos is associated with Rusophycus aegyp- 15 mm depth. Visible length of tunnels commonly about ticus (Seilacher, 1990) and rarely with Arenicolites. 15-20 mm (generally 10-30 mm). Laterally, they are nearly Skolithos is mostly known from sandy settings and is straight and only in a few cases, slightly curved. Vertical indicative of shallow-water conditions (Alpert 1974). An bending of tunnels is very slight. No branching has been extensive taxonomic splitting of this ichnotaxon has been observed; in the few ambiguous cases such tunnels seem criticized by the same author because of the generally very to rather represent intersection of two discrete specimens simple morphology of Skolithos. The ichnofossil is mainly originating at different times – an interpretation which is reported from high-energy, shallow marine environments, also supported by the differing tunnel diameters of the but non-marine examples are also known (Bromley & intersecting specimens. Asgaard 1979). Suspension-feeding producers of the domichnion Skolithos may have been annelids or phoronids Remarks: The specimens occur in fine-grained red (Alpert 1974; Schlirf & Uchman 2005). In the present siltstone. The features described above are typical for the case, more precise taxonomic determination is not possible ichnospecies; the only peculiarity consists in the relatively because of poor preservation. Skolithos occurs through the small size of the structures. Even though still within the size entire Phanerozoic. range of the ichnotaxon, size and specimen numbers may point to an assemblage of juveniles or of specimens with size limitation, perhaps due to ecological reasons. The red Teichichnus Seilacher, 1955 colouration of the host rock is interpreted here as a secondary effect of alteration. The original colour of the siltstone Type ichnospecies: Teichichnus rectus Seilacher, 1955; might have been grey due to a high organic content within Lower Cambrian of Salt Range, Pakistan. a probably dysaerobic sediment. The light yellow to whitish colour of the somewhat coarser tunnel fillings, produced by a worm-like animal may support such an interpretation: Teichichnus rectus Seilacher, 1955 according to Seilacher (1955), Bromley (1999), Mørk & Fig. 3B-D Bromley (2008), Buatois & Mángano (2011), and Knaust &

Fig. 2. A – Sandstone of Araba Formation unconformably overlies Proterozoic basement with distinct erosional contact (white arrows). Wadi Sarabit el Khadem section, central western Sinai Peninsula. B – Detail of unconformity between Prot- erozoic granitic basement and cross-bedded coarse siliciclastic rocks of Araba Formation (white arrows). Wadi Mor section, Eastern Desert. Width of field about 7 m. C – Heterolithic sandstone-siltstone succession of Araba Formation at Jebel el Zeit section, Eastern Desert. Note recurring subaqueous three-dimensional dunes (white arrows) with typical flat base and wavy top, separated by fine-grained sandstone to siltstone. Maximum height of large dune in centre about 1 m.D – Detail of Araba Formation at Jebel el Zeit section, Eastern Desert. Note fine-grained sandstone-siltstone layers intercalated between sandstone bodies figured in Fig. 2C. One of the authors (M.K.) for scale. E – Numerous specimens of Diplocraterion isp. preserved as typical U-tube structures in negative epirelief. Middle Araba Formation, Wadi Mor section, Eastern Desert. Diameter of lenscap 6.5 cm. F – Positive hyporelief structures of Arenicolites isp. and Rusophycus aegypticus (Seilacher, 1990). Typical U-tube turns of some Arenicolites isp. specimens indicated by solid white arrows. Note one Rusophycus resting trace penetrated by Arenicolites isp. (hollow white arrow). Rusophycus aegypticus (Seilacher, 1990) specimens show same orientation at right angle to ripple troughs. Middle Araba Formation, Wadi Mor section, Eastern Desert. Diameter of lenscap 4 cm. G – Details of Fig. 2E showing U-tube turn of large Arenicolites isp. specimen indicated in Fig. 2E by left solid white arrow. (1) oblique view; (2) enlarged slightly oblique view. Scale bars = 0.5 cm. H – Monospecific mass occurrence of Skolithos isp. in distinct uppermost few centimetres of sandstone bodies. Middle Araba Formation, Jebel el Zeit section, Eastern Desert. Hammer for scale is 33 cm long.

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Fig. 3.

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Bromley (2012) Teichichnus represents a sediment-feeding Peninsula: 29° 01’11.90”N, 33°24’56.40”E; Fig. 1), middle burrow (fodinichnion), but an additional protective function Araba Formation, about 27–35 m above erosional contact is also possible. In the present case, the strongly reduced with the granitic basement. amount of organic matter within the burrow fillings may have resulted from subsequent consumption of the organic Description: Cylindrical burrows preserved as convex matter along the tunnel and from the import of biologically (positive) hyporelief with variable diameter, in most cases more depleted sediment from above. very slightly curved. Outer surface smooth, without orna- Teichichnus is a common representative of various mentation other than local faint lines. Burrows horizontal ecological zones, from tropical to glacial, and from shallow with very limited vertical fluctuation, diameter 4-8.5 mm, to deep (Knaust & Bromley 2012). Hence, it is common in length much greater than 70 mm but cannot be estimated the Cruziana ichnofacies, in the lower shoreface to offshore due to broken nature of slabs. Locally, specimens intersect transition, but also occurs in deltas, lagoons and estuaries, each other; branching does not occur. Burrow fill identical as well as in deeper marine locales (Bromley 1999; Gérard to enclosing host rock. & Bromley 2008; Buatois & Mángano 2011). Teichichnus is quite common in Cambrian environments, especially in Remarks: Palaeophycus tubularis Hall, 1847, has been heterolithic sediments of shallow marine siliciclastic systems, observed in fine-grained, somewhat stratified sandstone. but there is no stratigraphic value related to this ichnofossil. The ichnofossil is seemingly common in distinct horizons of the Wadi Mor section (Eastern Desert), in which few other, very indistinct simple traces are rarely associated B) Horizontal simple burrows with the assemblage. In the Sarabit el Khadem section (Sinai Peninsula), specimens have been observed in association with an arthropod resting trace (Rusophycus burjensis Palaeophycus Hall, 1847 Hofmann, Mángano, Elicki & Shinaq, 2012, see below) and to arthropod crawling trace Cruziana salomonis (Seilacher, Type ichnospecies: Palaeophycus tubularis Hall, 1847, 1990), (see below). In these cases the determination is a by subsequent designation of Miller (1889); Cambrian of little problematic due to poor preservation. Interestingly, USA. where associated with Rusophycus the ichnofossil oriented parallel to the axis of this bilobate arthropod structure; a similar phenomenon has been observed elsewhere (Brandt Palaeophycus tubularis Hall, 1847 2008; Hofmann 2008: pl. II-23B; Hofmann et al. 2012: fig. Fig. 3E-F 12-1). According to Pemberton & Frey (1982), Fillion & Material: About 15 specimens; Wadi Mor section (Eastern Pickerill (1984) and Bromley (1999) Palaeophycus Desert: 28°29’32.2”N, 32°27’49.0”E; Fig. 1), middle Araba represents a eurybathic domichnion of a predaceous, Formation, a short distance above erosional contact with the deposit-feeding or suspension-feeding organism (probably granitic basement; Wadi Sarabit el Khadem section (Sinai polychaete annelids). The ichnotaxon is quite common

Fig. 3. A – Slab with Skolithos isp., poorly preserved Rusophycus aegypticus (Seilacher, 1990) and some simple vermiform traces. Middle Araba Formation, Wadi Mor section, Eastern Desert. Scale bar = 2 cm. B – Teichichnus rectus Seilacher, 1955, in fine red siltstone. Note lack of any preferred orientation of burrows. View perpendicular to bedding plane. Mid- dle Araba Formation, Jebel el Zeit section, Eastern Desert. Scale bar = 1 cm. C – Teichichnus rectus Seilacher, 1955. No branching, but rarely, crossing of specimens is visible. View perpendicular to bedding plane. Middle Araba Formation, Jebel el Zeit section, Eastern Desert. Scale bar = 1 cm. D – Teichichnus rectus Seilacher, 1955; (1-3): various specimens in vertical section. Note distinct retrusive character of these vertically shifted horizontal tunnels, producing typical spreiten structures. Scale bars = 0.5 cm. E – Palaeophycus tubularis Hall, 1847. Note that some specimens cross each other, but branching does not occur, and that burrow fill is identical to host sediment. Middle Araba Formation, Wadi Mor section, Eastern Desert. Scale bar = 1 cm. F – Several specimens of Palaeophycus tubularis Hall, 1847, together with poorly preserved specimen of arthropod crawling trace Cruziana salomonis (Seilacher, 1990) at bottom right (above lensecap). Middle Araba Formation, Wadi Sarabit el Khadem section, Sinai Peninsula. Diameter of lenscap 6.5 cm. G – Planolites montanus Richter, 1937. Strongly bioturbated layer with monospecific ichnofossil content. Middle Araba Formation, Wadi Mor section, Eastern Desert. Scale bar = 2 cm. H – Planolites montanus Richter, 1937, Middle Araba Formation, Somr el Qaa section, Eastern Desert. Scale bar = 3 cm.

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Fig. 4.

eschweizerbart_xxx Cambrian ichnofossils from northeastern Egypt 139 in, but not restricted to, shallow marine sand-dominated As for Palaeophycus, Planolites is also commonly environments and stratigraphically known from Ediacaran interpreted as a eurybathic form actively produced by to Recent (Häntzschel 1975; Gérard & Bromley 2008). deposit-feeding organisms. Whereas most authors suggest vagile infaunal producer of vermiform affinity, in fact there are several phyla which could be responsible for such Planolites Nicholson, 1873 traces (Alpert 1975; Pemberton & Frey 1982; Fillion & Pickerill 1984). Planolites is stratigraphically known from Type ichnospecies: Planolites vulgaris Nicholson & the Ediacaran to Recent (Häntzschel 1975). Hinde, 1875, by subsequent designation of Miller (1989); Cambrian of USA. C) Horizontal simple trails

Planolites montanus Richter, 1937 Helminthopsis Heer, 1877 Figs. 3G-H, 4A Type ichnospecies: Helminthopsis hieroglyphica Wetzel Material: Many specimens in mass occurrences; Wadi & Bromley, 1996 (by subsequent designation); Palaeogene Mor section (Eastern Desert: 28°29’32.2”N, 32°27’49.0”E; of Switzerland. Fig. 1), middle Araba Formation, a short distance above erosional contact with granitic basement; Somr el Qaa section (Eastern Desert: 28°11’32.8”N, 32°29’12.6”E; Fig. 1), middle Araba Formation, a short distance above Helminthopsis tenuis Książkiewicz, 1968 erosional contact with the granitic basement. Fig. 4B

Description: Tunnel-shaped burrows with round (rarely el- Material: One specimen; Wadi Mor section (Eastern liptical) cross-section in convex and concave hyporelief and Desert: 28°29’32.2”N, 32°27’49.0”E; Fig. 1), middle Araba in full relief preservation. Tubes unlined, horizontal, straight Formation, several meters above erosional contact with to slightly sinuous, and vertically contorted. Branching oc- granitic basement. curs very rarely; crossovers common. No ornamentation observable. Infillings structureless and somewhat finer- Description: Simple, elongate, cylindrical tube without grained than host sediment. Burrow diameter less than 5 branching. Trail follows bedding plane horizontally and mm (generally 1-5 mm). Length difficult to estimate due to shows low- to moderate-amplitude irregular turns; no dis- tortuousity of burrows (observed as up to 50 mm). tinct kinks have been observed. Looping, distinct meandering, overlap or self-crossing does not occur. Outer surface Remarks: Planolites montanus Richter, 1937, has been smooth, cross-section round. Burrow diameter constant at found in alternations of mostly fine-grained, rippled about 3 mm, observable length greater than 500 mm (lim- sandstone and siltstone. The present specimens represent ited by size of slab). The specimen preserved in convex the near-monospecific ichnofossil content (one additional epirelief. trace of Diplichnites occurs, see below and Fig. 4A) of moderately to intensely bioturbated layers (Fig. 3G-H) very Remarks: With Helminthopsis hieroglyphica Wetzel & similar to many reports by former authors (e.g., Pemberton Bromley, 1996, the described ichnotaxon shares an ab- & Frey 1982; Fillion & Pickerill 1984; Mángano et al. sence of high-amplitude horseshoe-like turns. Within the 1996; Hofmann et al. 2012; Stachacz 2012). former, however, turns are “composed of low-angle kinks

Fig. 4. A – Planolites montanus Richter, 1937, in wave rippled sandstone. (2) detail of area indicated by white rectangle in (1) showing specimen of co-occurring Diplichnites isp. Middle Araba Formation, Wadi Mor section, Eastern Desert. Scale: (1) diameter of lenscap 6.5 cm, (2) scale bar = 2 cm. B – Helminthopsis tenuis Książkiewicz, 1968 preserved as convex epirelief on medium-grained sandstone bed of a heterolithic succession. Middle Araba Formation, Wadi Mor section, Eastern Desert. Diameter of lensecap 6.5 cm. C – Unassigned trace fossil igen. et isp. indet. Remains could represent a Didymaulichnus- or an Archaeonassa-like ichnofossil (for discussion see text). Middle Araba Formation, Jebel el Zeit section, Eastern Desert. Scale bar = 1 cm. D-E – Various specimens of Cruziana salomonis (Seilacher, 1990). Middle Araba Formation, Wadi Sarabit el Khadem section, Sinai Peninsula. Scale bar = 2 cm. See Fig. 3E for additional specimen. F-G – Two specimens of Rusophycus burjensis Hofmann, Mángano, Elicki & Shinaq, 2012. Note probable Palaeophycus tubularis Hall, 1847 parallel to axis of specimen pictured in Fig. 4G (for discussion see text). Middle Araba Formation, Wadi Sarabit el Khadem section, Sinai Peninsula. Scale bar = 2 cm.

eschweizerbart_xxx 140 O. Elicki et al. and straight sections giving the trace a box-shaped fold siltstone (weathered hillside talus). So it cannot be deter- appearance”, which is a very important diagnostic feature mined whether the raised trail margins represent epirelief of that species (Fillion & Pickerill 1984). In H. tenuis or hyporelief structures. According to an inspection of field Książkiewicz, 1968, such turns are clearly not present. The photographs by G. Mángano (University of Saskatchewan, same authors point out that “somewhat similar forms occur Canada), Scolicia de Quatrefages, 1849, can be ruled out in Helminthopsis tenuis Książkiewicz, 1968, but the strings because of the absence of characteristic features such as are much thinner and the box-like arrangement is not so meniscate backfill and parallel faecal strings. The almond- well developed”. Some similarity of Helminthopsis in gen- shaped structure at the end of one of the trails (Fig. 4C) eral may also exist to Helmintoidichnites Fitch, 1850, but could resemble Lockeia James, 1879, but this ichnotaxon is the trace described here does not show meandering (Hof- typically associated with the chevronate trail Protovirgu- mann & Patel 1989; Lerner et al. 2007). Certain general laria M’Coy, 1850 (Mángano et al. 1998) or with a series similarities can also be seen with Gordia Emmons, 1844, but of elongate mounds, referred to as Ptychoplasma Fenton & the studied specimen never shows self-crossing or circular Fenton, 1937a. None of these identifications are viable for patterns. Nevertheless, Han & Pickerill (1995) and Wet- the present material. Considering the abovementioned un- zel & Bromley (1996) have revised the ichnogenus Hel- certainty regarding the orientation of the slab, it can only be minthopsis and discussed these points. They dramatically stated that the structure resembles Archaeonassa Fenton & reduced the number of ichnospecies within Helminthopsis. Fenton, 1937b (if the traces are preserved on the top), or if The latter authors reinvestigated the type material, coming they are on the base, they represent Didymaulichnus Young, to the result that most of the established ichnospecies of this 1972. In both cases the producer(s) of these facies-crossing, taxon up to that date are not valid. Further, they as well as long-lived ichnogenera have been related to Mollusca (al- other authors such as Fillion & Pickerill (1984), Han & though Didymaulichnus Young, 1972 can also intergrade Pickerill (1995) and Lerner et al. (2007) pointed out that into Diplichnites Dawson, 1873) (G. Mángano, personal there are common intergradations between the abovemen- communication 2013). tioned ichnogenera and ichnospecies. The trace described here occurs on a slab of fine- to medium-grained sandstone of a heterolithic succession. D) Bilobate burrows No other traces are present. Over some distance the burrow is weathered which is why the tube appears as “pseu- do-“concave hyporelief. The preservation is similar to that Cruziana d’Orbigny, 1842 described by Fillion & Pickerill (1984) for Helminthopsis isp. from the Ordovician of eastern Canada, where a narrow Type ichnospecies: Cruziana rugosa d’Orbigny, 1842, by longitudinal furrow (sometimes visible in the middle of the subsequent designation of Miller (1889). tube) is interpreted as due to partial collapse of the burrow. Helminthopsis occurs from the Ediacaran to the Recent and is regarded as a grazing trace produced by a worm- Cruziana salomonis (Seilacher, 1990) like organism. However, other trace-makers as insects or Fig. 4D-F bivalves have been invoked for younger examples (Lerner et al. 2007). The trace is facies-crossing and has been ob- Material: Five specimens; Wadi Sarabit el Khadem sec- served in marine environments, but is also known from la- tion (Sinai Peninsula: 29° 1’11.90”N, 33°24’56.40”E; Fig. custrine and fluviatil settings. 1), middle Araba Formation, about 35 m above erosional contact with granitic basement.

igen. et isp. indet. Description: Typical bilobate Cruziana trace preserved by Fig. 4C endopodal scratch marks in relatively shallow convex hyporelief. Width of furrows 30-50 mm, depth up to about 5 Material: Three specimens; Jebel el Zeit section (East- mm. Endopodal scatch marks bundled, somewhat arcuate ern Desert: 27°59’39.70”N, 33°27’18.00”E; Fig. 1), middle and commonly preserved in groups of three parallel ridges Araba Formation, about 34 m above erosional contact with slightly inclined (nearly perpendicular) to trace axis. Exo- granitic basement. podal scratch marks are absent.

Description: Horizontal bilobate trails oriented parallel to Remarks: Whereas Seilacher (1990) in his original de- bedding plane. Trails slightly and irregularly curved and scription included both cruzianiform and rusophyciform ex- medially grooved, with raised longitudinal ridgelike mar- pressions within this ichnospecies, here we follow Hofmann gins. No ornamentation or segmentation visible. The two et al. (2012) in systematically separating these two forms as preserved specimens show a superposition. In one specimen C. salomonis (Seilacher, 1990) and Rusophycus burjensis an almond-shaped structure (2.5 x 4 mm) is visible at one Hofmann, Mángano, Elicki & Shinaq, 2012. end. Width of trails is 6 mm for the one, and 4 mm for the Cruziana salomonis (Seilacher, 1990) has been ob- other. served at the somewhat weathered lower surface of thick, fine-grained, rippled sandstone beds which alternate with Remarks: It is not clear whether the traces are situated fine-grained siltstone layers. Occasionally, the ichnotaxon on the top or on the base of the thin slab of non-stratified is accompanied by the resting trace of the same producer

eschweizerbart_xxx Cambrian ichnofossils from northeastern Egypt 141

(Rusophycus burjensis Hofmann, Mángano, Elicki & Shi- a probable Bergaueria isp. is associated (see below). naq, 2012, see below). Rarely, Palaeophycus also occurs to- Clearly, the specimens from Sinai Peninsula are gen- gether with this trace. Due to comprehensive palaeontologi- erally smaller than those from the Dead Sea (compare cal investigation, as well as revision of older and extensive Seilacher 1990; Shinaq & Elicki 2007; Hofmann et al. new trilobite material from the Cambrian of the Dead Sea 2012). Stratigraphic and facies relations of the ichnospe- (Shinaq & Elicki 2007; Elicki 2011; Hofmann et al. 2012; cies are identical to those stated above for C. salomonis Elicki & Geyer 2013), the latter authors concluded that the (Seilacher, 1990). bathynotid trilobite Myopsolenites Öpik, 1975, is the producer of C. salomonis (Seilacher, 1990). For C. salomonis (Seilacher, 1990) a sand digging be- Rusophycus aegypticus (Seilacher, 1990) haviour is suggested (Seilacher 1990). The trace is exclusively known from fully marine, heterolithic tidal sand-bar Fig. 5C-F complexes, tidal dunes and interdune areas of the late “Ear- ly” to early “Middle” Cambrian of the Middle East, Sinai Material: About 25 specimens; Wadi Mor section (Eastern Peninsula and ?Near East (Mángano et al. 2013). Desert: 28°29’32.20”N, 32°27’49.00”E; Fig. 1), middle Araba Formation, a short distance above erosional contact with granitic basement. Rusophycus Hall, 1852 Description: Nearly cardioform, elongate Rusophycus trace preserved in convex hyporelief. Although generally Type ichnospecies: Rusophycus clavatus Hall, 1852, by poorly preserved due to weathering, some specimens show subsequent designation of Miller (1889). an internal lobe tapering posteriorly and an external lobe mostly parallel to this. Lobes slightly diverge anteriorly. In- ternal and external lobes separated by a ridge. Rusophycus burjensis Hofmann, Mángano, Elicki & Traces relatively small with length about 20 mm (only a Shinaq, 2012 few smaller specimens occur) and width about 15 mm (gen- Figs. 4G-H, 5A-B erally 13-18 mm). Depth of the rather shallow burrows 5-8 mm. Material: About fifteen specimens; Wadi Sarabit el Khadem section (Sinai Peninsula: 29° 1’11.90”N, 33°24’56.40”E; Remarks: As already explained by Hofmann et al. (2012), Fig. 1), middle Araba Formation, about 35 m above erosion- the original diagnosis of Cruziana aegyptica (Seilacher, al contact with granitic basement. 1990) was based on rusophyciform type material. Here we follow Hofmann et al. (2012) and understand Rusophycus Description: Typical bilobate elongate Rusophycus trace as a separate ichnotaxon. Consequently, the “rusophyciform preserved as distinct, somewhat arcuate endopodal scratch Cruziana aegyptica” of Seilacher (1990) was transferred marks in convex hyporelief. Traces medium-sized with to Rusophycus aegypticus (Seilacher, 1990) by Hofman et length in range 45-70 mm; width more pronounced ante- al. (2012). Accordingly, Seilacher’s “cruzianiform Cruz- riorly and commonly about 45 mm (generally 35-55 mm). iana aegyptica” has been redefined as Cruziana jordanica Lobes typically diverge anteriorly, so that this part of trace Hofmann, Mángano, Elicki & Shinaq, 2012 by the same is wider. In two cases a differentiation of scratch marks authors. into proverse scratches (anteriorly) and transverse scratches Rusophycus aegypticus (Seilacher, 1990) occurs at the (posteriorly) has been observed. Depth of burrows 10-20 lower surface of thin, fine-grained sandstone layers within mm. sandstone-siltstone heterolithic couplets. The fine siltstone has a high mica content and is represented by successions of Remarks: As already expressed above, here we follow Hof- submillimetre-thick laminations. The very distinct ripple- mann et al. (2012; see that publication for further references) cross lamination is noteworthy. and do not include cruzianiform and rusophyciform expres- Commonly, Egyptian specimens of Rusophycus aegyp- sions together within a single ichnospecies, as suggested by ticus (Seilacher, 1990) are clearly oriented more or less at Seilacher (1990). Rusophycus burjensis Hofmann, Mán- right angles to the current (according to the orientation of gano, Elicki & Shinaq, 2012, corresponds to the rusophy- ripples) and are excavated within the ripple troughs. Sev- ciform expression of Cruziana salomonis in the sense of eral specimens are partially imbricated (short rows of mul- Seilacher (1990). tiple traces), but they do not form the long, continuous rows As with C. salomonis (Seilacher, 1990) described typical of specimens of the Cambrian of the Dead Sea area above, Rusophycus burjensis Hofmann, Mángano, Elicki (Hofmann et al. 2012). & Shinaq, 2012 also occurs on the lower surface of thick, The assemblage of the Wadi Mor section also yields fine-grained, rippled sandstone beds. The preservation var- some Skolithos and rare Arenicolites together with Ruso- ies, but is generally rather poor due to weathering. In rare phycus aegypticus (Seilacher, 1990). On one slab a very cases, several specimens overlap each other. Rarely, on a poorly preserved Diplichnites and a probable Cruziana few slabs, they are associated with Cruziana salomonis trace have been observed. (Seilacher, 1990) or with simple string-like traces which Rusophycus aegypticus (Seilacher, 1990) is hitherto are very poorly preserved and undeterminable. In one case, known from late “Early” to early “Middle” Cambrian of

eschweizerbart_xxx 142 O. Elicki et al.

Fig. 5.

eschweizerbart_xxx Cambrian ichnofossils from northeastern Egypt 143

Egypt (Eastern Desert and Sinai Peninsula) and the Jordan ?Bergaueria isp. Rift Valley. Host deposits of the Dead Sea area are inter- Fig. 5G preted as delta-front sediments affected by waves and fluvial discharge, with fluctuating energy conditions and sub- Material: One specimen; Wadi Sarabit el Khadem section ordinate tidal action (Hofmann 2008; Mángano et al. 2013). (Sinai Peninsula: 29° 1’11.90”N, 33°24’56.40”E; Fig. 1), middle Araba Formation, about 35 m above erosional contact with granitic basement. Diplichnites Dawson, 1873 Description: Discoidal cylindrical burrow with circular Type ichnospecies: Diplichnites aenigma Dawson, 1873; cross-section, concentric ridges and shallow central depres- Carboniferous of Nova Scotia, Canada. sion; diameter 18 mm. No displacement pattern observable.

Remarks: The only available specimen is very poorly Diplichnites isp. preserved in fine-grained sandstone in convex hyporelief. Fig. 4A Associated with the trace fossil in question is Rusophycus burjensis Hofmann, Mángano, Elicki & Shinaq, 2012. It Material: Four poorly preserved specimens; Wadi Mor cannot be definitely determined whether if the lack of addi- section (Eastern Desert: 28°29’32.20”N, 32°27’49.00”E; tional ornamentation, as described for various ichnospecies, Fig. 1), middle Araba Formation, a short distance above and of displacement structures (typical of B. sucta Seilach- erosional contact with granitic basement. er, 1990), represents a primary feature or is simply due to the strongly weathered character of the slab. The size and Description: Best preserved specimen shows a short and the discoidal rather than plug-shaped habit, together with rather simple trackway consisting of two parallel rows of reports of Bergaueria sucta ichnofossils from the nearby distinct elongate imprints (Fig. 4A). These are regularly Umm Bogma area (Seilacher 1990) suggest an affinity with spaced (2 mm) and nearly oblique (slightly inclined) to main that species for the described specimen. axis of trace. Width of trace about 20 mm; maximum pre- Bergaueria is commonly interpreted as cubichnion or served length 20 mm. domichnion of actinian or ceriantharian coelenterates. The ichnogenus is typically shallow marine and is described Remarks: Diplichnites isp. occurs very rarely in the stud- from shallow subtidal to intertidal and lagoonal settings; it ied sections. The trace is always very poorly preserved in is known from the Late Ediacaran to the Recent (Alpert convex hyporelief. It has been found in alternations of fine- 1973; Pemberton et al. 1988; Seilacher 1990; Gérard & grained, rippled sandstone and siltstone. In one case, the Bromley 2008; Hofmann et al. 2012). host rock is intensively bioturbated by Planolites montanus Richter, 1937 (see above); in another case, Rusphycus ae- F) Biosedimentary structures gypticus (Seilacher, 1990) is an associated ichnofossil (for details see above). Few other remains seem to belong to this ichnotaxon, but the very poor preservation does not permit Biomat structures a reliable determination. Fig. 5H Diplichnites is accepted as an arthropod locomotion trace occurring in shallow and deep marine environments, Material: A few slabs; Wadi Mor section (Eastern Desert: as well as freshwater and terrestrial settings, from the Cam- 28°29’32.20”N, 32°27’49.00”E; Fig. 1), middle Araba For- brian to the Cretaceous (Fillion & Pickerill 1990; Hof- mation, a short distance above erosional contact with gra- mann 2008). nitic basement.

E) Plug-shaped burrows Description: Typically corrugated wrinkle structures showing various patterns of puckering and plication on one slab of about 30 x 60 cm size. Bergaueria Prantl, 1946 Remarks: Biomat structures were observed relatively rare- Type ichnospecies: Bergaueria perata Prantl, 1946; Or- ly in the working area. They occur in heterolithic facies. dovician of Bohemia, Czech Republic. No associated ichnofossils have been observed. Regardless

Fig. 5. A-B – Rusophycus burjensis Hofmann, Mángano, Elicki & Shinaq, 2012. Scale bar = 2 cm. C-F – Rusophycus aegypticus (Seilacher, 1990). Specimens pictured in Fig. 5C and 5D are from same slab. White rectangle in Fig. 5E outlines detail in 5F (slab broken during transport and subsequently glued). Scale bars = 1 cm. G – ?Bergaueria isp. (1) and (2) represent same specimen photographed at different angles. Scale bar = 1 cm. H – Biomat structure. Diameter of lenscap 6.5 cm

eschweizerbart_xxx 144 O. Elicki et al. of the scarcity of finds of distinct mat structures, the pres- characterized by either this prominent cubichniid ervation of the ichnofossils described above may generally ichnofossil and/or its repichniid equivalent, Cruziana point to their original existence, because a minimum sedi- salomonis (both produced by a myopsolenid trilobite, ment consistency is needed for ichnofossils to be preserved. The positive role of microbes and biomats in this respect is see above). Rarely, Palaeophycus, ?Bergaueria or in- widely accepted. determinable simple worm traces co-occur. This sub- assemblage also includes both deposit and suspension 4. Palaeoecological conclusions feeders. The host sediment is also rippled and heterolithic. However, in contrast to the Rusophycus ae- The Cambrian ichnofossils of the Eastern Desert gypticus sub-assemblage, the present sub-assemblage and Sinai Peninsula generally occur in distinct, is hosted by alternating sediments that are generally relatively thin horizons within successions of mainly coarser-grained; the proportion of finer-grained sedi- trough cross-bedded and minor tabular cross-bedded, ment is less and the thickness of the coarser-grained medium- to fine-grained sandstone with occasional sandstone beds is larger (decimetre scale). Due to the intercalated siltstone (sporadic heterogeneous limited size of available slabs and hand specimens, it distribution sensu Gingras et al. 2011). The ichnofossils cannot be stated with certainty if there is an orienta- can be grouped into seven assemblages belonging tion of traces also in this sub-assemblage. Due to the to the Cruziana and Skolithos ichnofacies sensu aforementioned sedimentological differences and the Seilacher (1967), according to their occurrence and limited occurrence of suspension feeders, somewhat related depositional characteristics. Assemblages (1) to higher-energy conditions are deduced for this envi- (5) have been observed in sections of Sinai Peninsula ronment. Sedimentological and ichnological data (see and the Eastern Desert, whereas assemblages (6) to (7) above) point to a tidal bar/sand dune complex as the occur exclusively in the Jebel el Zeit section (Eastern depositional regime. The less pronounced orientation Desert). of the Rusophycus ichnofossils as in the other sub-assemblage may also be explained by biological differ- 1) Cruziana assemblage ences (e.g. by their distinctly larger size). The trilobite resting trace Rusophycus is the promi- Generally, the Cruziana assemblage occurs with- nent trace fossil of this assemblage. However, there are in a shallow marine, high-energy, tidally influenced two characteristic sub-assemblages: setting, in which the Rusophycus burjensis sub-as- The Rusophycus aegypticus sub-assemblage is char- semblage indicates a more agitated (more proximal) acterized by this prominent cubichniid trace fossil locale than that of the Rusophycus aegypticus sub- and the co-occurrence of Skolithos and indetermina- assemblage. This ecological difference, rather than ble simple worm traces, as well as by the occasional stratigraphic separation, can explain why R. burjensis occurrence of Arenicolites and very rare Diplichnites. and C. salomonis have never been observed together Thus, deposit feeders (most probably trilobite arthro- with R. aegypticus in the same assemblage (Seilacher pods) are associated with vermiform suspension feed- 1990; Shinaq & Elicki 2007; Hofmann et al. 2012). ers. The host sediments are heterolithic, consisting of Based on trilobites and their related traces in the Cam- rippled, fine-grained sandstone and siltstone deposited brian succession of the Death Sea (Elicki & Geyer in a delta-front setting (see above). The proportion 2013), these sub-assemblages represent more or less of finer-grained sediments is relatively large and the the same stratigraphic level. sandstone beds have only limited, centimetre-scale thickness. The remarkable orientation of all R. aegyp- 2) Diplocraterion assemblage ticus traces at right-angles to ripple troughs, as well as This ichnofossil assemblage made by suspension feed- the occasional occurrence of short rows of multiple (2- ers is monospecific. It occurs in decimetre-thick sand- 3) traces, may be the expression of a specific behaviour stones within rippled sandstone-siltstone alternations of the producer adapted to better dietary use available characterized by tabular cross-bedding and some me- suspended matter, within a relatively high-energy, dium-scale trough cross-bedding. The rare occurrence resource-poor environment (Brandt 2008). Addition- of this monospecific assemblage may point to a rather ally, orientation facing the current head-on could have unstable environment with moderate sediment sup- simply provided more stability than facing it sideways ply under shallow marine, higher-energy conditions (P. Kruse, personal communication 2013). (Seilacher 1967). A similar occurrence recently de- The Rusophycus burjensis sub-assemblage is scribed from time-equivalent strata of Jordan probably

eschweizerbart_xxx Cambrian ichnofossils from northeastern Egypt 145 indicates deposition within a transgressive regime in very regular, small-scale, bimodal grainsize alterna- a tidal-dune complex, on tidal flats or representing an tions of medium/coarse sand or of coarse sand/fine erosional surface of initial transgression (Hofmann et conglomerate. In times of non-migration of these sedi- al. 2012). Due to the aforementioned sedimentological ment bodies, Skolithos-producing animals colonized characteristics, a shallow marine, tidally influenced the substrate rather rapidly, constructing their dwelling (tidal flat to subtidal) setting with small migrating tubes. Sediment input and movement was seemingly dunes seems to be the most reasonable environmen- distinctly greater than in settings characterising other tal interpretation for the ichnofossil assemblage of the ichno-assemblages. Due to the abovementioned sedi- Eastern Desert. mentological data and ichnofacies characteristics, a fresh water (fluvial) influence and high sediment input 3) Planolites assemblage and movement rate within a marginal marine locale This assemblage occurs in strongly bioturbated, is the most reasonable interpretation for the evidently definite sandstone beds within rippled fine-grained strongly constrained ecological conditions. sandstone-siltstone couplets. Although the ichnotaxon itself is facies-crossing, its monospecific occurrence 6) Teichichnus and 7) ?Didymaulichnus/?Archae- is remarkable and may point to an unstable ecologi- onassa assemblages cal environment with alternating energy conditions. These two ichno-assemblages occur in non-stratified Massive colonisation and by deposit feeders has taken red siltstone layers of millimetre-scale thickness in place during phases of reduced sediment input in a horizontally layered fining-upward cycles. Both as- probable tidal flat environment. semblages are monospecific, but they occur in the same lithofacies and specific depositional unit. This 4) Helminthopsis assemblage distinctive unit is only 3.5 m thick, intercalated within Only a single occurrence of Helmithopsis has been the general succession of coarse-grained sand bodies observed. No other ichnofossils are associated. Nev- described in (6). Whereas (7) is facies-crossing and ertheless, in the same locality and in the same hetero- without value for defining the ecological conditions, lithic lithofacies, slabs with distinct biomat structures Teichichnus represents a fodichniid trace of a deposit occur. Helmithopsis is regarded as the grazing trace of feeder, which can often be found in dysaerobic envi- a biofilm-feeding, shallow-tier mat-scratcher moving ronments (Ekdale et al. 1984; Gingras et al. 2011). below a thin veneer sediment (Seilacher 1990; Bua- The unit containing these trace fossils should be in- tois & Mángano 2012), so that this sedimentological terpreted to reflect a relatively short phase of very low- observation fits very well. Because sedimentological energy, marginal marine deposition under restricted, information from the host layers is very limited be- probably lagoonal conditions (Pemberton et al. 2001). cause of outcrop conditions, both assemblages can only be characterized relatively broadly as occurring Overall, the most remarkable features of the described in a shallow marine, biomat-bearing environment Cambrian ichnofossil assemblages are (1) their low which maybe was was possibly not very congenial for ichnodiversity, (2) the distinct predominance of ar- other animals. Although generally occurring in distal thropod and vermiform traces, and (3) the widespread Cruziana ichnofacies (Pamberton et al. 2001), for the trough cross-bedded and tabular cross-bedded depo- present example a more proximal tidal flat setting is sitional architecture of a tidally influenced, marginal conceivable. marine to probably freshwater-affected transitional host environment. 5) Skolithos assemblage The typically sporadic stratigraphic distribution of The ichnofossil content of this assemblage consists ex- these Egyptian ichnofossils (with the sole exception of clusively of densely packed Skolithos domichnia. The the Skolithos assemblage; see above) is characteristic host sediment is trough cross-bedded and distinctly of environments of episodic but rapid deposition (and coarser than for all other ichnofossil assemblages. erosion) and permanent spatiotemporal variability Characteristically, Skolithos is limited to layers of cen- in physicochemical conditions (Gingras et al. 2011). timetre-scale thickness resting on thick, trough cross- These aspects are typical of a wide range of environ- bedded sandstone dune and tabular cross-bedded sand- ments, e.g. prodeltaic and delta-front settings, shore- wave bodies (regular heterogeneous distribution sensu face and offshore settings, tide-dominated estuaries, Gingras et al. 2011). Internally, these sediments show flats, lagoonal and fluviatile settings. Freshwater input

eschweizerbart_xxx 146 O. Elicki et al. and fluctuating energy conditions, as in tide-domi- Acknowledgements nated estuaries or in some prodeltaic settings (Bann This investigation was only possible due to generous & Fielding 2004; Bann et al. 2004; MacIlroy 2004; financial support by the German Research Foundation to Buatois & Mángano 2012; Hofmann et al. 2012; O.E. (research projects EL 144/17-1 “Environmental analysis Knaust & Bromley 2012), commonly represent the and correlation of early post-Panafrican facies realms at the most important factors leading to reduced diversity northern edge of the Arabian-Nubian Shield” and EL144/17-2 “Palaeoecology, ichno- and micropalaeontology, and facies and sporadic, heterogeneous distribution of ichnofos- architectures of the Cambrian succession in the southern sils within these minimally burrowed environments. Wadi Araba (Jordan Rift Valley)”. Further thanks go to C. Some of the Egyptian ichnofossils (e.g., ?Bergau- Breitkreuz (Freiberg), H. Eliwa (Shibin el Kom), A.M.A. eria, R. burjensis, R. aegypticus, C. salomonis) clearly Marzouk (Tanta), A. Khalif (Cairo), and A. Leuschke indicate marine conditions. Nearly all the other rec- (Freiberg) for logistic help during fieldwork. G. Mángano (Saskatoon), F. Debrenne (Paris), G. Geyer (Würzburg) and ognized ichnofossils (e.g., Skolithos, Diplocraterion, P. Kruse (Second Valley) are gratefully acknowledged for Helminthopsis) suggest such conditions at least by their palaeontological advice. Many thanks to M. Magnus their occurrence in the Early Palaeozoic. The distinct (Freiberg) for taking photographs of the ichnofossils. S. impoverishment in ichnofossil diversity in most of Jensen (Badajos) and R. Mikuláš (Prague) helped with the observed assemblages can only be explained by critical reviews, P. Kruse (Second Valley) with important improvement of English language. ecological limitations. 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However, to synthesize the ichnological and sedimen- Andrawis, S.F., El Afify, F. & Abd El Hameed, A.T. (1983): tological information into a consistent depositional Lower Paleozoic trilobites from subsurface rocks of the model according to sequence stratigraphic aspects, Western Desert, Egypt. – Neues Jahrbuch für Geologie additional fieldwork including mapping of the strati- und Paläontologie, Monatshefte, 1983: 65-68. graphic succession and regional correlation, is needed. Bann, K.L. & Fielding, C.R. (2004): An integrated ichnological and sedimentological comparison of non-deltaic Nevertheless, the available ichnological data clear- shoreface and subaqueous delta deposits in Permian res- ly indicate (1) the early Middle Cambrian age of the ervoir units of Australia. – In: McIlroy, D. (Ed.): The Cruziana/Rusophycus-bearing siliciclastic rocks im- Application of Ichnology to Palaeoenvironmental and mediately overlying the erosional contact with the Stratigraphical Analysis. – Geological Society, London, basement, (2) the shallow to marginal marine char- Special Publications, 228: 273-310. Bann, K.L., Fielding, C.R., Mac Eachern, J.A. & Tye, S.C. acter of the depositional area, with various tide- and (2004): Differentiation of estuarine and offshore marine freshwater-influenced settings (deltaic, flats, lagoons, deposits using integrated ichnology and sedimentol- ?bays); and (3) the close palaeogeographic affinity of ogy: Permian Pebbley Beach Formation, Sydney Basin, northeastern Egypt with the Jordan Rift Valley area. Australia. – In: McIlroy, D. (Ed.): The Application of Ichnology to Palaeoenvironmental and Stratigraphical Analysis. – Geological Society, London, Special Publi- cations, 228: 179-211.

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