Shahkarami et al.—Ediacaran–Cambrian ichnostratigraphy
Description.—Simple, small unbranched horizontal, sinusoidal trails. Trail width is 1.0–1.7mm; maximum preserved length is 36.5mm. Infill is massive. Preserved as positive hyporelief or negative epirelief.
Remarks.—Cochlichnus anguineus Hitchcock, 1858 is the type ichnospecies of Cochlichnus, and differs from the two other Cochlichnus ichnospecies,C. annulatus Orłowski, 1989, and C. antarcticus, Tasch, 1968, by lack of annulations or lateral markings and having the same filling as the host rock, respec- tively (Buatois and Mángano, 1993a; Keighley and Pickerill, 1997). Cochlichnus is a grazing trail (pascichnion) produced by many different invertebrates, including annelids and nematodes (Fillion and Pickerill, 1990; Lucas et al., 2010). It ranges from the Cambrian to Holocene (Mángano and Buatois, 2014), and occurs in a great variety of marine and non-marine environ- ments (Fillion and Pickerill, 1990).
Occurrence.—Lower and Upper Shale members. Ichnogenus Cruziana d’Orbigny, 1842
Remarks.—The ichnogenus Cruziana is mostly represented by a bilobate and elongated trail covered by transverse or herringbone- shaped ridges. Trailsmay be bounded by lateral outer zones with or without ridges (Häntzschel, 1975; Fillion and Pickerill, 1990). Cruziana comprises over 30 ichnospeciesmostly separated based onmorphologic features resulting fromthe leg morphology of the producer (Seilacher, 1970, 1992).Cruziana is best interpreted as related to combined locomotion and feeding strategy (pascichnia) (Seilacher, 2007). It iswidely accepted that the main producers of Cruziana in the marine Paleozoic were trilobites or trilobito- morphs (Seilacher, 1970, 1985, 1992; Hofmann et al., 2012). Cruziana ranges in age from early Cambrian to Holocene (Seilacher, 1970; Muñiz Guinea et al., 2015), and has been reported from a varied spectrum of paleoenvironments, ranging from typical shallow-water marine to freshwater settings (Bromley and Asgaard, 1979; Crimes, 1987).
Cruziana problematica Schindewolf, 1921 Figure 2.5
Materials.—Two slabs (P3311.13, P3313.10) containing two specimens.
Description.—Horizontal, gently winding, strongly convex, small, parallel-sided trails with transverse striation, and central groove dividing the trace longitudinally into two lobes. Width is 2.1–3.5mm; maximum preserved length is 44.5mm. Preserved as positive hyporelief.
Remarks.—Relatively small, simple Cruziana with transverse to nearly transverse scratch marks are traditionally included in Cruziana problematica (e.g., Schindewolf, 1921; Bromley and Asgaard, 1979; Fillion and Pickerill, 1990). Jensen (1997) regarded C. problematica as a junior synonym of Cruziana tenella (Linnarsson, 1871). However, C. problematica is widely reported and is considered the most stable ichnospecies (e.g., Mángano et al., 2002b). The specimens documented here are
1181
very similar to C. tenella described by Jensen (1997) from the Mickwitzia Sandstone, south-central Sweden and C. problematica described by Keighley and Pickerill (1996) from eastern Canada. The name C. problematica is preferred here over C. tenella for reasons of nomenclatural stability (Mángano et al., 2002b).
Occurrence.—Upper Shale Member.
Cruziana isp. Figure 2.3
Materials.—Five slabs (P3310.2, P3311.3, P3311.12, P3311.19, P3313.10) containing six specimens.
Description.—Small, horizontal, slightly oblique, unbranched, trails with bilobate lower surface, and poorly preserved scratch marks. Width is 2.3–5.2mm; maximum preserved length is 46.50mm. Preserved as positive hyporelief and negative epirelief.
Remarks.—Poor preservation does not allow determining the pattern of transverse striation, which therefore prevents ichnospecific assessment.
Occurrence.—Lower and Upper Shale members.
Ichnogenus Curvolithus Fritsch, 1908 Curvolithus isp. Figure 2.2
Materials.—Three slabs (P3311.19, P3317.2, P3319.1) con- taining four specimens.
Description.—Horizontal, straight to slightly oblique, unbran- ched trails with trilobate upper surface consisting of two outer narrow lobes (each 1.7–2.6mmwide) and one broad, flat central lobe (4.2–5.6mm wide). The marginal outer lobes are discontinuous along the structure. Width of the trace is 6.8–10.8mm; maximum preserved length is 89.0mm. Pre- served as positive epirelief and full relief.
Remarks.—Curvolithus comprises two ichnospecies: Curvolithus multiplex and Curvolithus simplex (Buatois et al., 1998b). Curvolithus multiplex has a smooth, trilobate upper surface and a convex, quadra-lobate lower surface; in contrast to C. multiplex, C. simplex does not have a quadra-lobate lower surface. The speci- mens documented here are assigned to Curvolithus isp. due to uncertainties in the number of lobes on the lower surface. Curvolithus has been interpreted as the locomotion trace (Repich- nia) of predators, including gastropods, flatworms, or nemerteans (Buatois et al., 1998b). Curvolithus ranges in age fromCambrian to Miocene and has been recorded from shallow-marine siliciclastic successions (Buatois et al., 1998b; Mángano and Buatois, 2014).
Occurrence.—Upper Shale Member.
Ichnogenus Didymaulichnus Young, 1972 Didymaulichnus miettensis Young, 1972 Figure 2.4
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