Shahkarami et al.—Ediacaran–Cambrian ichnostratigraphy
Książkiewicz, 1977; G. maeandria Jiang in Jiang, Luo, and Zhang, 1982; G. nodosa Pickerill and Peel, 1991; and G. indianaensis (Miller, 1889). Gordia marina can be easily differentiated from the other ichnospecies of Gordia because it lacks the annulations of G. nodosa, the angled turns of G. indianaensis, the apical arcuate bends of G. arcuata, and the guided meanders of G. maeandria (Fillion and Pickerill, 1990; Buatois et al., 1998a). Fillion and Pickerill (1990) questioned the validity of G. maeandria in that guided meander is not typical of Gordia. Gordia differs from Helminthopsis in its looped form, having overcrossing and never showing meanders (Pickerill and Peel, 1991). The ethology of Gordia and its pos- sible producers are not well constrained. Książkiewicz (1977) suggested that it might be a feeding burrow or trail produced by polychaetes. Yang (1984) considered it as a locomotion trace produced by worms or gastropods. Other authors (e.g., Aceño- laza and Buatois, 1993; McCann, 1993; Geyer and Uchman, 1995) have considered this ichnogenus as a pascichnia produced by worms or worm-like organisms. The ichnogenus Gordia ranges in age from Ediacaran to Holocene (Fillion and Pickerill 1990; Mángano and Buatois, 2014), and is known from non- marine, and shallow- to deep-marine deposits (Narbonne, 1984; Fillion and Pickerill, 1990; Norman, 1996). The ichnospecies Gordia arcuata has been documented in the Soltanieh Forma- tion by CiabeGhodsi (2007).
Occurrence.—Upper Shale Member.
Ichnogenus Helminthoidichnites Fitch, 1850 Helminthoidichnites tenuis Fitch, 1850 Figure 3.1
Materials.—Seven slabs (P3309.1, P3309.2, P3311.5, P3311.9, P3311.11, P3311.15, P3311.19) containing ten specimens.
Description.—Simple, unbranched, horiztontal, mostly straight to slightly bent, nonmeandering trails. Diameter is 0.9–1.9mm and may slightly vary along the course of individual trails. Maximum observed length is 83.8mm. Overlapping among different individuals is common, but there is no self over crossing. Trace fill is identical to the host rock. Preserved as positive hyporelief and negative epirelief.
Remarks.—Helminthoidichnites tenuis is interpreted as a graz- ing trace, most likely produced by vermiform animals (Buatois et al., 1998a). Helminthoidichnites comprises only one ichnos- pecies, H. tenuis, although the case may be made that a review of this ichnogenus may result in recognition of additional ich- nospecies. Helminthoidichnites differs from Gordia by lacking self-overcrossing and from Helminthopsis by having a non- meandering course (Hofmann and Patel, 1989; Buatois et al., 1998a). The ichnogenus ranges in age from Ediacaran to Holocene (Mángano and Buatois, 2014).
Occurrence.—Lower and Upper Shale members.
Ichnogenus Helminthopsis Heer, 1877 Helminthopsis tenuis Książkiewicz, 1968 Figure 3.3
1183
Materials.—Four slabs (P3309.1, P3309.2, P3311.17, P3311.18) containing eight specimens.
Description.—Horizontal, smooth, unbranched, unlined, irre- gular, high-amplitude meandering trails. Width is 1.0–1.8mm; maximum preserved length is 49.0mm. Preserved as positive hyporelief and negative epirelief.
Remarks.—There are three ichnospecies of Helminthopsis, separated based on their geometrical pattern (Wetzel and Bromley, 1996): H. abeli Książkiewicz, 1977; H. hieroglyphica Wetzel and Bromley, 1996; and H. tenuis Książkiewicz, 1968. Helminthopsis tenuis is distinguished from H. abeli and H. hieroglyphica by the lack of horseshoe-like turns and its high-amplitude winding (Wetzel and Bromley, 1996), and from Helminthoidichnites by its meandering course (Hofmann and Patel, 1989). Helminthopsis is thought to be a grazing trace (pascichnion) produced by deposit-feeding organisms in brackish to fully marine environments; polychaete annelids are regarded as potential tracemakers (Ksiazkiewicz, 1977). Helminthopsis ranges in age from Ediacaran to Holocene (Buatois et al., 1998a).
Occurrence.—Lower and Upper Shale members.
Ichnogenus Palaeophycus Hall, 1847 Palaeophycus tubularis Hall, 1847 Figure 3.4
Materials.—Seventeen slabs (P3311.1, P3311.4, P3311.7, P3311.10, P3311.12, P3311.14, P3311.19, P3311.20, P3312.1, P3313.1, P3313.3, P3313.9, P3313.10, P3314.1, P3315.1, P3316.1, P3318.1) containing thirty five specimens.
Description.—Horizontal, branched and unbranched, straight to slightly curved, unornamented, thinly lined cylindrical burrows. Burrow-fill is similar to the host rock. Width is 2.6–13.4mm; maximum preserved length is 172.5mm. Pre- served as positive hyporelief.
Remarks.—Palaeophycus is distinguished from Planolites primarily by the presence of wall linings and a burrow-fill identical to the host rock. Infills of Palaeophycus represent passive, gravity-induced sedimentation within open, lined bur- rows; collapse features show that some segments were incom- pletely filled by this process. The fillings, therefore, tend to be of the same composition as the surrounding matrix (Pemberton and Frey, 1982). Seven ichnospecies of Palaeophycus are currently accepted: P. tubularis Hall, 1847; P. heberti (Saporta, 1872); P. striatus Hall, 1852; P. sulcatus (Miller and Dyer, 1878); P. alternatus Pemberton and Frey, 1982; P. bolbitermilus Kim, Pickerill, and Wilson, 2000; and P. imbricatus (Torell, 1870). Palaeophycus tubularis is distinguished from the other Palaeophycus ichnospecies by its thin wall and the absence of striations (Pemberton and Frey, 1982). Palaeophycus is inter- preted as dwelling burrows (dominichnia) of suspension feeders or predators, such as polychaetes (Osgood, 1970; Pemberton and Frey, 1982), and ranges in age from Ediacaran to Holocene (Häntzschel, 1975). Palaeophycus is a facies-crossing
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