Ichnofossils and their significance in the Cambrian successions of the ...

Journal of Asian Earth Sciences 42 (2011) 1097–1116

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Ichnofossils and their significance in the Cambrian successions of the Parahio Valley in the Spiti Basin, Tethys Himalaya, India S.K. Parcha ⇑, Shivani Pandey Wadia Institute of Himalayan Geology, General Mahadeo Singh Road, Dehradun 248 001, India

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Article history: Received 9 February 2010 Received in revised form 12 January 2011 Accepted 22 April 2011 Available online 29 June 2011 Keywords: Spiti Lower Cambrian Ichnofossils Debsakhad Member

a b s t r a c t The Spiti Basin exposes well preserved Cambrian successions in the Tethys Himalaya. The present ichnofossil assemblage is reported from the Debsakhad Member of the Kunzum La Formation. The ichnofossils includes the ichnogenera Bergaueria, Chondrites, Cruziana, Didymaulichnus, Dimorphichnus, Diplichnites, Helminthorhaphe, Merostomichnites, ?Monocraterion, Monomorphichnus, Nereites, Palaeopascichnus, Palaeophycus, Phycodes, Planolites, Rusophycus, Skolithos, Scolicia, Treptichnus, etc. along with annelid worm, burrow and scratch marks. These ichnogenera can be assigned to cubichnial, repichnial, pascichnial to fodinichnial behaviors. The ichnofossils reported from this section provide evidence regarding the developmental patterns during the early phase of life. In absence of trilobites, the present assemblage of ichnofossils is very significant in assigning the age of the Debsakhad Member. The abundance of ichnofossils in sandstone, siltstone and in shale beds indicate that the ichnocenosis is dominated by a high behavioral diversity ranging from the suspension to deposit feeders. Three lithofacies were observed in this section, they show a vertical disposition, which further reflects general upward coarsening trend. Ichnofossils are mostly produced by arthropods along with crustacean, polychaetes and polyphyletic vermiforms. Due to the paucity of body fossil, as well as microbiota in the lowermost beds of the Debsakhad Member, the Precambrian–Cambrian boundary could not be demarcated. However, the presence of Treptichnus and Phycodes can be considered as a horizon marker for the beginning of Lower Cambrian in this section. Ó 2011 Elsevier Ltd. All rights reserved.

1. Introduction The Tethys Himalaya contains an extensive record of sediments ranging from Precambrian to Eocene. The Spiti Basin, a part of the Tethys Himalayan sedimentary sequence, is southwestern extension of the greater Tibetan Basin. It displays the largest marine and richly fossiliferous sedimentary succession. The Cambrian strata in the Spiti Basin are exposed in Pin Valley, Parahio Valley and in the Kunzum La – Takche sections. The present work deals with the Kunzum La Formation in the Parahio Valley. The formation is subdivided into two members namely Debsakhad and Parahio (Kumar et al., 1984). The Lower Cambrian succession of the Kunzum La Formation contains a variety of ichnofossils preserved in, siltstone, shale, sandstone and quartzite occurring at various startigraphic levels. In absence of body fossils, ichnofossils are useful for establishing the biostratigraphy and deciphering the paleoecology of the area.

⇑ Corresponding author. Tel.: +91 135 2525115; fax: +91 135 2625212. E-mail addresses: [email protected], [email protected] (Suraj Kumar Parcha). 1367-9120/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.jseaes.2011.04.028

Variety of ichnofossils has been recorded from the late Precambrian and early Paleozoic succession from Kashmir, Zanskar, Kinnaur, Kumaun region and from the Cambrian succession of the Lesser Himalaya. The presence of ichnofossils in the Lower Cambrian succession has a stratigraphic significance for demarcation of Precambrian–Cambrian boundary. The earlier record of ichnofossils from the Parahio Valley section is inadequate. The present ichnological study, therefore, is of a considerable stratigraphic importance for tracing out the biogenic record in the pre trilobitic-bearing Cambrian strata of the Spiti Basin. The Lower Cambrian succession of the Parahio Valley reveals a diverse group of ichnofossils. In the present study, 19 ichnogenera, an annelid worm and scratch marks are reported. The presence of ichnofauna reported from this section reflects the evolution of invertebrates. Besides this, a change in abundance and diversity of ichnofossils is observed throughout the succession. The diversity of the ichnofauna increases as we go higher in the section (Table 2). The location, lithological setup and distribution of ichnofauna reported from the Debsakhad and Parahio members of the Kunzum La Formation are illustrated in the Figs. 1 and 2. The present work is aimed to elucidate the ichnology and paleoecology of the Lower Cambrian of the Debsakhad Member exposed in Parahio Valley of the Spiti Basin.

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S.K. Parcha, S. Pandey / Journal of Asian Earth Sciences 42 (2011) 1097–1116

Fig. 1. Geological Map of the Spiti Basin of Himachal Pradesh.

2. Stratigraphy and geological setting The Spiti Basin lies in the Lahaul – Spiti district of Himachal Pradesh, northern India. The study area lies in the Parahio Valley, which is the subsidiary valley of the Pin Valley. This section is exposed near the confluence of the Khemangar and Debsakhad River. In this section the base of the Kunzum La Formation and its contact with the underlying Batal Formation is not exposed. In absence of body fossils, it does not allow any biostratigraphic detail of the boundary between these two units. The first geological work in the Spiti Basin was carried out by Stoliczkai (1865); he designated the Cambrian sequence as ‘‘Bhabeh Series’’. The Cambrian rocks of the Spiti region conformably overlie the Precambrian rocks of the Vaikrita System. The sequence between the Crystalline at the base and the Muth Quartzite above were designated by Griesbach (1891) as Haimanta System. Hayden (1904) carried out the geological studies of the Spiti region and

collected fauna from different levels. Later on Srikantia (1981) adopted the term Haimanta Group, which comprises of Batal, Kunzum La and Thango formations. The subsequent work on the geology of this region was carried out by Ranga Rao et al. (1982). They stated that the Haimanta Group cannot be subdivided on the regional basis, because the lithological units are not laterally continuous. Myrow et al. (2006) used the Parahio Formation instead of Kunzum La Formation. However, Bhargava (2008a,b) and in personal communication stated that the name Kunzum La Formation should retain, whose mapability has been proved from Spiti to Kinnaur in east and in Lahul–Zanskar in west. So in the present paper Kunzum La Formation is used and the classification proposed by Srikantia (1981) is adopted. The Spiti Basin contains the fossiliferous Cambrian successions, exposed in the Parahio Valley, Pin Valley, Kunzum La – Chandra Tal and in the Takche sections. Presence of fossiliferous rocks in the Cambrian successions of the Spiti region was first reported by


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Fig. 2. Lithostratigraphic column showing the distribution of Ichnofossils in the Parahio section.

Hayden (1904), whose collection was identified by Reed (1910). The ichnofossils in Spiti Basin were earlier recorded by Bhargava et al. (1982), Bhargava and Srikantia (1985), Bhargava and Bassi

(1988), Sudan et al. (2000), Parcha (1996, 1998a,b, 1999) and later on by Parcha et al. (2005). The Lower Cambrian succession of the Spiti Basin displays diverse assemblages of ichnofossils, occurring

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Fig. 3. Ichnofossils from the Debsakhad and Parahio members of the Kunzum La Formation. A, B, J and K. Skolithos isp. C. Merostomichnites isp. D and I. Nereites isp. E and F. Bergaueria isp. G, H and L. Dimorphichnus isp. M. Palaeopascichnus isp.

in various horizons within siltstones, sandstones and shale. So far there is no documentation of body fossils, except for a single occurrence of the Lower Cambrian trilobite Redlichia from a float. Thus

the ichnofossils play an important role for understanding the paleobiology of this part of the Spiti Basin. Sudan and Sharma (2001) reported ichnofossils from the Kunzum La section and


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Fig. 4. Ichnofossils from the Debsakhad and Parahio members of the Kunzum La Formation. A and I. Phycodes isp. B, F, Ga, H and J. Planolites isp. C. Scolicia isp. A. D. Diplichnites isp. A. E and Gb. Treptichnus isp. K. Scratch marks. L. Diplichnites isp. C. M. Diplichnites isp. B.

divided the ichnofossil bearing horizons into two levels TF1 and TF2. In the present studies these horizons are not distinguished; instead it was found that simple forms of ichnofossils occur at the

base of Kunzum La Formation and as we go higher in the succession the complexity of ichnofossils increases, following the evolutionary trend Table. 2.

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Fig. 5. Ichnofossils from the Debsakhad and Parahio members of the Kunzum La Formation. A, C, H and J. Monomorphichnus isp. A. B, E and Ka. Palaeophycus isp. A. D. Didymaulichnus isp. F. Monomorphichnus isp. C. G. Monomorphichnus isp. B. I. Helminthorhaphe isp. Kb. Cruziana isp. L. Palaeophycus isp. B.


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Fig. 6. Ichnofossils from the Debsakhad and Parahio members of the Kunzum La Formation. A. Rusophycus isp. A. B. Chondrites isp. C and D. Rusophycus isp. B. E. Burrow B. F. Rusophycus isp. C. G. ?Monocraterion isp. H. ?Annelid worm. I. Burrow A. Diameter of coin = 24 mm.

3. Mode of preservation The ichnofossils collected from the parahio section shows a variety of the ichnogenera as Bergaueria, Chondrites, Cruziana, Didymaulichnus, Dimorphichnus, Diplichnites, Helminthorhaphe,

Merostomichnites, ?Monocraterion, Monomorphichnus, Nereites, Palaeopascichnus, Palaeophycus, Phycodes, Planolites, Rusophycus, Skolithos, Scolicia, Treptichnus and trilobite scratch marks, etc. The ichnogenera so far reported from this region belong mostly to the traces of arthropods and other invertebrates. It is observed that

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the preservation of ichnofossils is mostly controlled by the characteristics of sedimentary matrix. Absence of trilobite body fossil in association with the ichnofossils has been observed in all the Himalayan successions, which seems to be a worldwide phenomenon. However, the trilobites predominantly occur in the beds overlying the beds bearing ichnofossils. The present ichnofossil assemblage contains resting and grazing traces together with tracks and trails on the bedding planes. They represent different behavior and biological functions such as feeding, dwelling and locomotion (Seilacher, 1953, 1964a,b). 4. Systematic ichnology Repository: nineteen ichnogenera along with annelid worm, scratch marks and burrows are described. The binominal system with alphabetical order has been followed to describe the ichnofossils. All the material is housed in the Repository section of the Wadia Institute of Himalayan Geology Museum, Dehradun, India under reference from WIHG/A/1590 to 1599 and WIHG/A/1900 to 1912. Ichnogenus: Bergaueria Prantl, 1945 Type Ichnospecies: Bergaueria perata Prantl, 1945 Bergaueria isp. (Fig. 3E and F) Repository Ref: In situ specimens and some field observations. Material: Specimens are preserved in sandstone, one as hyporelief and the other as epirelief. Description: Specimens are circular to sub-circular in outline, 4–10 mm in diameter and 3–4 mm deep. Fine and strong transverse constrictions are present on the surface. The specimen possesses slightly elevated protuberance. The uppermost part is unornamented; slightly elevated and the lower end of the specimen are gently rounded.

Remarks: The ichnogenera Bergaueria is regarded as the dwelling structure. The studied specimen shows some resemblance with B. perata Prantl (1945) particularly in the outer features, but differs from it in absence of shallow circular apical depression, which is prominent in the later. Due to the paucity of good material at present the ichnogeneric determination is possible only. The ichnospecies of Bergaueria have been widely reported from the Cambrian and Ordovician strata (Häntzschel, 1975) but is particularly common in the Lower Cambrian (McKee, 1945; Seilacher, 1956; Aria and McGugan, 1968; Schmitz, 1971; Young, 1972; Alpert, 1973; Arboleya, 1973; Crimes et al., 1977; Crimes and Anderson, 1985; Gámez Vintaned et al., 2006). Locality: This ichnotaxa is relatively rare and has been recorded from the middle part of the Debsakhad Member, in the Parahio section of the Kunzum La Formation.

Ichnogenus: Chondrites Sternberg, 1833 Type Ichnospecies: Fuciodes antiquus Brongniart, 1828 Chondrites isp. (Fig. 6B) Repository Ref: WIHG/A/1591 Material: The specimen is preserved in sandstone. Description: The specimen represents a regularly branched, unornamented radial pattern of burrows. On the bedding planes it shows a dendritic pattern. Burrows neither cross each other nor anastomies. The branching may reach up to

the second order. The specimen shows network of branches. The maximum length of the burrow 36 mm and width is 3 mm which remains constant throughout the length. The burrow fill material is same as the host rock.

Remarks: The specimen can be ascribed to ichnogenus Chondrites on the basis of ramifying tunnel structure. These burrows can be treated as feeding structure belongs to fodinichnia (Seilacher, 1955; Osgood, 1970). The present specimen shows some resemblance with the ichnogenus Chondrites described by Macdonald (1982) from Bay Formation, South Georgia, in the dendritic pattern, but due to the absence of third order branching it differs from it. Savrda and Bottjer (1989) stated that the Chondrites represent bioturbation produced by small organisms, located at shallow depth below the sediment–water interface. Seilacher (1990) stated that the trace maker of Chondrites may be able to live under anaerobic conditions as chemosymbiotic organism. According to Abbassi (2007) Chondrites can also live under dysaerobic and reducing conditions or even anaerobic environments. The present specimen differs with the ichnogenus Chondrites described from Rajasthan by Kumar and Pandey (2010) in the nature of dendritc pattern. Locality: This ichnotaxa is recorded from the lower horizon of Debsakhad Member in the Parahio section of the Kunzum La Formation. Ichnogenus: Cruziana dÓrbigny, 1842 Type ichnospecies: Cruziana rugosa dÓrbigny, 1842 Cruziana isp. (Fig. 5Kb) Repository Ref: In situ specimen Material: Several specimens are preserved on a block of siltstone on the bedding plane as hyporelief. Description: Bilobate straight to slightly curved furrows; lobes separated by a relatively shallow well defined median furrow. The specimens are 6–10 mm long and most of them are 1–3 mm wide. Some of them display, faint, transverse, thin v-markings. Surface of the lobes is smooth.

Remarks: Cruziana has been attributed as a crawling trace produced by trilobite activity, particularly in the Early Paleozoic (Osgood, 1970). Cruziana is mostly represented by a bilobate and elongated ridges covered by transverse or herringbone-shaped ridges. (Häntzschel, 1975; Pickerill et al., 1984; Fillion and Pickerill, 1990) stated that these are the crawling traces and may be marginated by lateral outer zones with or without ridges. This ichnogenus has been reported from a diverse range of paleoenvironment, ranging from characteristic shallow water marine to freshwater settings (Bromley and Asgaard, 1979; Seilacher, 1985; Crimes, 1987). The present specimen differs from the ichnogenera Cruziana isp. described by Seilacher (1970). The present form differs from Cruziana isp. described by Parcha (1998b) from the Lower Cambrian of Zanskar in the nature of claw markings. It equally differs with the Cruziana isp. described by Kumar and Pandey (2010) from Rajasthan. Due to the paucity of the material the present specimen could not be grouped to any known ichnospecies of the Cruziana. Locality: The specimen occurs in the middle part of the Debsakhad Member of the Kunzum La Formation.


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Ichnogenus: Didymaulichnus Young, 1972 Type Ichnospecies: Fraena lyelli Rouault, 1850 Didymaulichnus isp. (Fig. 5D) Repository Ref: In situ specimen Material: Specimen is preserved as hyporelief in siltstone. Description: Series of bilobed raised furrows, arranged in a straight to winding series. Each segment is 5–10 mm long and 2–2.8 mm wide. Median furrow deep separates the unornamented lobes. The two lobes are roughly parallel to each other.

area, Czech Republic. The ichnogenus Dimorphichnus is known from the Lower Cambrian succession of Wales (Crimes, 1970), Lesser Himalaya (Tiwari and Parcha, 2006), Zanskar (Parcha and Singh, 2010) and from Rajasthan (Kumar and Pandey, 2008, 2010). The present specimen differs from all known ichnospecies of Dimorphichnus. Locality: This ichnogenera occurs sporadically in the Debsakhad Member of the Kunzum La Formation, Spiti Basin.

Remarks: Didymaulichnus is regarded as a feeding structure. This ichnofossil possesses distinctive features in common with Didymaulichnus tirasensis Palij (1974). The illustrated material does not show any imbrications and overlapping of curved segments hence cannot be assigned to D. tirasensis. It differs with Didymaulichnus lyelli (Rouault, 1850) in absence of minor longitudinal undulations. The described ichnogenera also differs with the Didymaulichnus cf. tirasensis (Jensen and Mens, 2001) from the Lower Cambrian of Baltica, in the manner of narrow and deep lobes. Locality: The specimen occurs in the middle part of the Debsakhad Member of the Kunzum La Formation in the Parahio Valley, Spiti Basin.

Ichnogenus: Diplichnites Dawson, 1873 Type Ichnospecies: Diplichnite aenigma Dawson, 1873 Diplichnites isp. A (Fig. 4D) Repository Ref: WIHG/A/1598 Material: The specimen is preserved as hyporelief in sandstone. Description: Minute imprints composed of parallel rows of similar elongate to sub circular tracks. The individual imprint length varies from 2 to 3 mm. Distance between the two imprints is 1–3 mm and width is 0.8–1.2 mm; the two lines are 7–15 mm apart. The maximum length of the track is 70 mm. The paired imprints occur in a row to some distance and shift slightly towards the other side. Tracks are arranged differently depending on the direction of movement. These imprints suggest crawling activity of the arthropod on the soft sediments.

Ichnogenus: Dimorphichnus Seilacher, 1955 Type Ichnospecies: Dimorphichnus obliquus Seilacher, 1955 Dimorphichnus isp. (Fig. 3G, H and L) Repository Ref: WIHG/A/1590, 1902 and 1912 Material: Three specimens are preserved as convex hyporelief, one specimen preserved in sandstone and the others are in siltstone. Description: Asymmetrical trackways with two different types of impressions, long straight to slightly sigmoidal, short and comma shaped. Both the types of trackways are arranged in a series. The number of claw impressions in each set varies from 5 to 7. The width of individual claw marking varies from 1 to 3 mm and length from 2 to 8 mm. Distance between the two individual ridges in one row varies from 1.3 to 5 mm, and the distance between two parallel ridges varies from 7 to 40 mm. Total length of the specimens varies from 35 to 60 mm. One row of trackways is moderately bent, slightly curved at one side of the preserved section, passing to straight on the opposite side. Shifting of some markings suggest change in the movement of the animal on the substrate.

Remarks: The specimens described herein resemble with Dimorphichnus in the nature of the curved and sub parallel ridges. Ichnogenus Dimorphichnus is regarded as a grazing activity (Seilacher, 1955, 1985, 1990; Crimes, 1970; Fillion and Pickerill, 1990), resulting from trilobite movement by oscillatory currents (Osgood, 1970). The distinction between the Dimorphichnus and Monomorphichnus is complicated (Crimes, 1970). Though, various workers have given their opinion time to time regarding the status of these ichnogenera. The present specimens differ with the specimens described from the Pedroche Formation of the Spain in the manner of tightly blunt appearance of claw markings (Gámez Vintaned et al., 2006) and also with the species described by Mikuláš (2000) from the Barrandian

Remarks: Diplichnites is regarded as a crawling trace, mainly produced by trilobites. It has been recorded most commonly in the Cambrian rocks (Seilacher, 1955; Dzulynski and Zak, 1960; Radwanski and Roniewicz, 1963; Martinsson, 1965; Hecker and Zharkov, 1966; Crimes, 1970; Osgood, 1970; Häntzschel, 1975; Briggs et al., 1979, 1984; Mikuláš, 2000 and Mángano et al., 2005). The illustrated specimen differs with the ichnospecies described by Alpert (1976) from the Lower Cambrian rocks of White Innoy Mountains of California. Diplichnites is reported from the Upper Cambrian succession of northwestern Argentina by Mángano et al. (2005). In the East European platform Diplichnites first appears in the Lower Atdabanian (Urbanek and Rozanov, 1983; Crimes, 1987). The present specimens differ with the Diplichnites ichnospecies reported from the Tal Formation of Lesser Himalaya by Tiwari and Parcha (2006) and from Zanskar Himalaya by Parcha (1998b) and Parcha and Singh (2010). The present specimens differ with the Diplichnites ichnospecies described by Kumar and Pandey (2010) in the pattern of track, which consist of two parallel equally spaced rows of unequal fine ridges.

Diplichnites isp. B (Fig. 4M) Repository Ref: WIHG/A/1901 Material: Single specimen preserved as hypichinial casts in the sandstone. Description: Two parallel series of trackways, impression of track are well preserved and a series consisting of several tracks. The parallel series are separated by a distance of 9– 16 mm. Individual track length varies from 2 to 4 mm and the width is 1 to 2.2 mm. In one series the distance between the two claw markings is 1.5–2.2 mm.

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Remarks: The traces are less sigmoidal as compared to Diplichnites isp. A. Moreover, the pattern and nature of the claw markings also vary. It indicates the continuous movement of the organism. Due to the paucity of the material the present specimen was not grouped with any known ichnospecies of the Diplichnites.

Diplichnites isp. C (Fig. 4L) Repository Ref: WIHG/A/1595 Material: Single specimen preserved as convex hyporelief in sandstone. Description: Paired dissimilar and unequal rib shaped markings. Individual marking is about 3–5 mm long and 0.9–1.2 mm wide. The inner side of the depressions is broader, gradually taper towards outer side. The distance between the two markings is about 1–4 mm. The paired markings show the lateral displacement.

Remarks: The specimen apparently show resembles with the ichnogenera Diplichnites in the nature and pattern of markings. The illustrated specimen differs from all the above described forms, in presence of unequal size and in the nature of markings. Locality: The described forms of Diplichnites were reported from the different horizons in the Debsakhad Member of the Kunzum La Formation.

Ichnogenus: Helminthorhaphe Seilacher, 1977 Type ichnospecies: Helminthorhaphe japonica Tanaka, 1970 Helminthorhaphe isp. (Fig. 5I) Repository Ref: In situ specimen Material: Poorly preserved specimen present in siltstone, photographed in the field. Description: Tightly and regularly spaced parallel, convex meandering burrow system. The burrow width ranges from 3 to 5 mm. Each meander is separated by adjacent meanders by 0.5–2 mm. Individual meander is even occasionally curved, coiled and is 4 mm high from the base.

Remarks: The illustrated specimen shows close resemblance with the ichnogenus Helminthorhaphe in the nature and pattern of meandering burrow system and is regarded as a grazing trace. The variability of this ichnogenus has been clearly stated by Uchman (1995). The present specimen resembles with the ichnogenus Helminthoida in the absence of starter spiral, but differs with it in the pattern of tightly coiled, narrower lateral backfill zones (Seilacher, 2007). Locality: The specimen occurs in the upper part of the Debsakhad Member of the Kunzum La Formation, in the Parahio section.

Ichnogenus Merostomichnites Packard, 1900b Type ichnospecies: Merostomichnites beecheri Häntzschel, 1962 Merostomichnites isp (Fig. 3C) Repository Ref: In situ specimen Material: Specimen preserved as epirelief in sandstone. Description: Spindle or bow shaped row arranged obliquely. Individual impression varies in length from 12 to 15 mm and in width from 3 to 5 mm. The trace is preserved as epirelief.

Remarks: The specimen differs from ichnogenus Diplichnites Dawson (1873) and equally with Dimorphichnus Seilacher (1955) due to lack of median grove. The difference between the two ichnogenera were well described along with complete discussion on the use of Merostomichnites was given by Keighley and Pickerill (1998). The specimen equally differs with the Merostomichnites isp. described by Tiwari and Parcha (2006) in the pattern of parallel spindle shaped row. Due to the close resemblance with the ichnogenus Merostomichnites, which is a resting trace, the present specimen has been grouped under this ichnogenus. Locality: Single specimen was reported from the middle part of the Debsakhad Member of the Kunzum La Formation in the Parahio Valley.

Ichnogenus Monocraterion Torell, 1870 Type Ichnospecies: Monocraterion tentaculatum Hall, 1847 ?Monocraterion isp. (Fig. 6G) Repository Ref: In situ specimen Material: Single specimen preserved in fine grained sandstone bed. Description: A circular structure maximum 8 mm in diameter, cylindrical burrow funnel shaped at top. The diameter of the center of circle is 3 mm and is nearly 4 mm in depth. The center of burrow is deep and unornamented.

Remarks: The specimen though show close resemblance with the ichnogenus Monocraterion, but there is no prominent funnel, which is characteristic of the Monocraterion (Häntzschel, 1975). While studying the Lower Cambrian Pipe rocks of Scotland, Hallam and Sweet (1966) suggested that Monocraterion result for upward movement of an animal in its burrow. A considerable debate has taken place since then regarding its origin e.g. (Boyd, 1966; Goodwin and Anderson, 1974). The described forms differ from the Monocraterion described by Gámez Vintaned et al. (2006) in the nature of conical structure. The present specimen was grouped under the ichnogenus Monocraterion due to its close similarity with its characteristic features, but differs from all the known ichnospecies of this ichnogenus. Locality: The specimen occurs in the middle part of the Debsakhad Member of Kunzum La Formation.

Ichnogenus: Monomorphichnus Crimes, 1970 Type Ichnospecies: Monomorphichnus bilineatus Crimes, 1970 Monomorphichnus isp. A (Fig. 5A, C, H and J) Repository Ref: WIHG/A/1593, 1594, 1906 and 1908 Material: The specimens are preserved as positive relief in the sandstone; various other specimens are examined in the field. Description: Series of parallel straight to slightly curved ridges commonly impressed and regularly arranged. All specimens are preserved in a positive hyporelief. The ridges are forming sets, individual ridges varying in length from 2 to 32 mm and are 2 to 4 mm apart. The maximum number of ridges occurring on a set is 6–22. The maximum distance between the two sets of ridges is 2.8–7 mm.

Remarks: Monomorphichnus is defined by sets of elongate narrow ridges, which could have been made by sidewaysswimming of arthropods. Monomorphichnus is regarded as


swimming grazing traces (Crimes et al., 1977). Crimes (1987) stated that some traces of Monomorphichnus may have been produced by other arthpods. Seilacher (1985, 1990), regarded this ichnogenus synonymous to Dimorphichnus. Fillion and Pickerill (1990) provided a detailed discussion on the morphological characters of Dimorphichnus relating it to Monomorphichnus. Jensen (1997) stated that both ichnogenera may represent different behaviors of a same producer. The present specimens though resembles with the Monomorphichnus lineatus (Crimes et al., 1977) but lack in the sets of fine ridges, besides this the ridges in the present specimens are long. The specimen differs from Monomorphichnus bilinearis Crimes (1970) and equally with Monomorphichnus multilineatus Alpert (1976) in the pattern, shape and size of scratch marks. The specimen differs from the Monomorphichnus monolinearis (Shah and Sudan, 1983) from the Lower Cambrian succession of the Kashmir Himalaya in the nature and pattern of ridges. The specimen equally differs with the species Monomorphichnus sp. describe by Parcha (1998b) and Parcha and Singh (2010) from the Zanskar area of Ladakh Himalaya, in the manner of isolated ridges which repeated laterally and in shape of ridges. Locality: The specimens are preserved at different levels of Debsakhad and Parahio member of Kunzum La Formation.

Monomorphichnus isp. B (Fig. 5G) Repository Ref: In situ specimen Material: The specimen is preserved as positive relief in a block of sandstone. Description: Series of slightly curved ridges commonly impressed but regularly arranged. The ridges are not forming sets, ridges varying in length from 5 to 10 mm and are 5 to 8 mm apart.

Remarks: The present specimen resembles with the M. lineatus described by Crimes et al. (1977) but the ridges in the present specimens are long as compared to the specimen described above. The specimen differs with the M. monolinearis described from the Lower Cambrian succession of the Kashmir Himalaya by Shah and Sudan (1983) and also with the Monomorphichnus isp. from Rajasthan by Kumar and Pandey (2010), in the nature and pattern of ridges. Locality: The specimen occurs in the middle part of Debsakhad Member of Kunzum La Formation

Monomorphichnus isp. C (Fig. 5F) Repository Ref: WIHG/A/1900 Material: The specimen is preserved as hyporelief in a block of sandstone. Description: Straight to slightly curved regular ridges. The length of the individual ridge varies from 22 to 34 mm and the width varies from 3 to 5 mm. The two ridges are 10– 15 mm apart from each other.

Remarks: The illustrated specimen differs from the known species of Monomorphichnus and equally differs with the

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above described species of the Monomorphichnus in the pattern of ridges. In the present specimen no sets of ridges were observed. Locality: The specimen is preserved in the lower part of Debsakhad Member of Kunzum La Formation.

Ichnogenus Nereites Macleay, 1839 Type ichnospecies: Nereites cambriensis Macleay, 1839 Nereites isp. (Fig. 3D and I) Repository Ref: WIHG/A/1903 and an In situ specimen Material: Specimens are preserved as hyporelief in shale and sandstone. Description: Simple, irregularly meandering, horizontally oriented trail; consisting of two rows of sand infilled numerous irregular pellets typically on bedding plane. The width of the burrow is 2–5 mm and the total length is 35– 63 mm. The pellets are arranged in pairs, commonly parallel to the direction of the trail. The length of individual pellets is 2–6 mm. Pellets either isolate or adjacent but never overlap.

Remarks: Nereites is a feeding structure which, probably produced by worm like organism such as polychaetes. Chamberlain (1971) described the mode of formation of Nereites burrow. The described specimen differs from Nereites irregularis (Schafhautl, 1851) in absence of densely packed regular meanders, which are lacking in the present specimen. Uchman (1995) gave a detailed description about the preservational variation of Nereites. Aceñolaza and Aceñolaza (2006) described Nereites from the Puncoviscana Formation of northwesternArgentina and suggested that Nereites were the internal meandering trail which was interpreted as body fossil of an annelid worm. Locality: The specimens were reported from the upper part of Debsakhad Member and lower part of Parahio Member of the Kunzum La Formation.

Ichnogenus Palaeopascichnus Palij, 1976 Type Ichnospecies: Palaeopascichnus delicatus Palij, 1976 Palaeopascichnus isp. (Fig. 3M) Repository Ref: In situ specimen Material: The specimen is preserved as full relief in quartzite. Description: Closely positioned wide bars, bars are elongate and arranged in winding rows. The width of the segments varies from 3 to 6 mm and the length of segments varies from 8 to 13 mm. The two segments are aparted from each other from 7 to 22 mm. The total length of the specimen is 70 mm.

Remarks: The ichnogenus Palaeopascichnus is a feeding structure and has a wide distribution including Russia (Fedonkin, 1981), the Ukraine (Palij, 1976), South Australia (Glaessner, 1969; Jenkins, 1995), Poland (Paczesńa, 1986), and Newfoundland (Narbonne et al., 1987; Gehling et al., 2000). The illustrated specimen shows close similarity in the nature and pattern of the grooves with the specimen described by Jensen (2003). Locality: The specimen occurs in upper part of the Debsakhad Member of the Kunzum La Formation in the Parahio section.

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Ichnogenus Palaeophycus Hall, 1847 Type ichnospecies: Palaeophycus tubularis Hall, 1847 Palaeophycus isp. A (Fig. 5B, E and Ka) Repository Ref: WIHG/A/1904 and In situ specimen Material: The material comprises of three specimens preserved as full relief in siltstone. Description: Straight to gently curved bulbous burrow with distinct regularly spaced over imposed faint constrictions. Surface is covered with short ridges. The maximum observed length is 12–55 mm. The width of the burrow is 2–8 mm. Infilling material of the burrow is same as that of the host rock.

Remarks: The specimen shows close resemblance to Palaeophycus in the outer morphological characters. Palaeophycus is regarded as a dwelling structure. The present specimen differs with the Palaeophycus cf. alternatus Pemberton and Frey (1982) and Gámez Vintaned et al. (2006) in the nature of constrictions. The specimens equally differ with Palaeophycus sulcatus Miller and Dyer (1878) and Mikuláš (2000) in the nature and pattern of the burrow. The presence of transverse constrictions and the bulbous morphology avert identifying this ichnofossil with any known ichnospecies of the Palaeophycus. Pemberton and Frey (1982) and Keighley and Pickerill (1995) have given the detail discussion about the taxonomy of Palaeophycus. The differentiation of Palaeophycus from the morphologically similar ichnotaxa Planolites Nicholson (1873) was discussed in detailed by Osgood (1970), Pemberton and Frey (1982), Fillion (1989), Fillion and Pickerill (1990), Keighley and Pickerill (1995). It has now been generally accepted that the presence of lining in the Palaeophycus and an absence in the Planolites is the significant distinction between the two (Fürisch, 1974). Locality: The presently described specimens were reported from the lower and upper parts of the Debsakhad Member of the Kunzum La Formation

Palaeophycus isp. B (Fig. 5L) Repository Ref: In situ specimen Material: Specimen is preserved in sandstone as positive hyporelief. Description: Horizontally to slightly curved burrow, with branches not crossing each other. The length of the individual burrow is 26–53 mm and width varies from 3 to 6 mm. The length of burrow system is 85 mm. The infilling of the burrow is darker and the grains are finer than the surrounding host rock.

Remarks: The specimen differs with the Palaeophycus isp A. in absence of closely spaced bundled burrow and in the pattern of branching. Locality: The specimen was collected from the middle part of the Debsakhad Member of Kunzum La Formation.

Ichnogenus: Phycodes Richter, 1850 Type ichnospecies: Phycodes circinatum Richter, 1853 Phycodes isp. (Fig. 4A and I) Repository Ref: In situ specimens Material: Two specimens preserved as full relief in fine grained sandstone.

Description: Obliquely oriented slightly curved burrows depicting branch like manifestation. The branches do not cross each other. The maximum length of an individual burrow is 25–35 mm and width is 3–5 mm. The burrow system varies in length from 43 to 56 mm. The burrows are filled with the matrix of the host rock.

Remarks: The specimen though shows some comparison with the Phycodes palmatum reported from the Salt Range of Pakistan by Seilacher (1955) and with the specimen described Shah and Sudan (1983) from Kashmir and that with the specimen illustrated from Zanskar by Parcha (1998b) but the illustrated specimen differs with them in the absence of closely bundled burrow. Phycodes is interpreted as a feeding burrow made by frequent search by an animal into the sediment. Locality: The specimens were collected from the lower part of the Debsakhad Member of Kunzum La Formation.

Ichnogenus: Planolites Nicholson, 1873 Type ichnospecies: Planolites vulgaris Nicholson and Hinde, 1875 = (Palaeophycus beverleyensis) Billings, 1862 Planolites isp. (Fig. 4B, F, Ga, H and J) Repository Ref: WIHG/A/1596, 1904, 1907, and In situ specimens Material: Five specimens are preserved as hyporelief three in sandstone and two in siltstone. Description: Straight to slightly curved burrow, simple subcylindrical ornamented with closely to widely spaced straie. Length of the individual burrow ranges from 12 to 30 mm and the width from 3 to 11 mm; mostly the burrows are unbranched and horizontal in structure. The burrows are filled with the same material as that of host rock. In some specimens burrows are darker than the surrounding matrix.

Remarks: The ichnogenus Planolites is the most abundant ichnofossil in the Lower Cambrian of the Spiti Himalaya. Planolites is a feeding structure and is believed to have been formed by a worm like organism. Alpert (1975) have given a detailed analysis of the Planolites. The specimen differs with the Planolites balandus; Planolites serpenes Webby (1970) and with the Planolites reticularis Alpert (1975) in the diagnostic characters. The specimen somewhat resembles with Planolites corrugates Walcott (1889) in its outer features, but differs with it in the length and width ratio. The present form also differs with the Planolites describe by Parcha and Singh (2010) from Cambrian of Zanskar Valley. However, the specimen differs with all the known ichnospecies of the Planolites. Locality: The specimens are preserved at different levels in the Debsakhad Member of Kunzum La Formation.

Ichnogenus: Rusophycus Hall, 1852 Type ichnospecies: Fucoides biloba Vanuxem, 1842 Rusophycus isp. A (Fig. 6A) Repository Ref: WIHG/A/1592 Material: The material comprises of one block of sandstone. Description: Small, bilobate lobes; lobes are commonly parallel to sub parallel resembling coffee bean shape with faint claw markings gradually tapering from one end to


another. The lobes are 5–10 mm long and 3–5 mm wide. In the middle the lobes are 2.1–3.3 mm apart. Surface of the lobes are smooth.

Remarks: The lobate shape of this trace resembles closely to Rusophycus. It represents a resting excavation of trilobite origin (Seilacher, 1953, 1955; Crimes, 1970 and Young, 1972). Crimes (1970) opined that there could be no simple segregation into small and large forms, which can be an indication of growth in a population of same trilobite species. The presently described specimen resembles to some extent with Rusophycus cerecedensis Crimes et al. (1977) but differ with it in the pattern of claw markings. The illustrated specimen differs from the known ichnospecies of this ichnogenus from the Tethyan Himalayan region by Shah and Sudan (1983) from Kashmir and from Zanskar by Parcha (1998b).

Rusophycus isp. B (Fig. 6C and D) Repository Ref: WIHG/A/1597 Material: The specimens are preserved as hyporelief in siltstone. Description: Elongate, coffee bean shaped bilobate structures, with a central area depressed. Lobes are well organized in both side of depression and covered with scratch marks. The set of scratch marks, which are present are wider toward one end, narrowing back toward the other and makes a v-marking. The length of single scratch mark varies from 0.8 to 1.5 mm and the maximum length of the trace is 34 mm and the lobes are 10 to 14 mm in width.

Remarks: It is believed that these traces might have been produced while the trilobites were digging straight down into the muddy bottom. Due to this they might have left a set of scratch marks, which were wider toward one end, narrowing back toward the other and make markings. The present specimens shows close resemblance with the ichnogenus Rusophycus, but differs from all the known species reported from the Tethyan Himalayan regions in the shape and pattern of markings.

Rusophycus isp. C (Fig. 6F) Repository Ref: In situ specimen Material: Single block preserved as hyporelief in fine grained sandstone, contains various species of Rusophycus Description: Weakly bilobate, short coffee been like structure with a central furrow. Lobes are symmetrical, scratch marks poorly preserved. The lobes are closely spaced at one end and faintly making v-shape at the other end. The maximum length of each lobe is 8 mm and the maximum width of each lobe is 6 mm.

Remarks: The specimen differs in the nature and pattern of markings and equally in the length and width ratio with the Rusophycus isp. A. In the present described specimen the central ridges as well as markings are faint compare to other ichnospecies of this ichnogenus. Locality: The described forms of Rusophycus were reported from the middle part of Debsakhad Member of the Kunazum La Formation.

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Ichnogenus: Scolicia de Quatrefages, 1849 Type Ichnospecies: Scolicia prisca de Quatrefages, 1849 Scolica isp. (Fig. 4C) Repository Ref: In situ specimens Material: Specimens are preserved as hyporelief in sandstone. Description: Traces consist of meandering, looping, ridge exhibiting irregular circular habit with crossing pattern. The width of the burrow system ranges from 2 to 4 mm. The two lobes are separated from each other by 16 to 18 mm wide medium furrow. Ridges are always elevated above the bedding plane.

Remarks: The present described Scolicia differs with the _ ichnogenera Taphrhelminthopsis (Ksia˛zkiewicz, 1977) in the pattern of coiling meanders. The Scolicia may be identified as the crawling trails of echinoids. Locality: The specimen occurs in the upper part of the Debsakhad Member of the Kunzum La Formation in the Parahio section.

Ichnogenus: Skolithos Haldemann, 1840 Type Ichnospecies: Skolithos linearis Haldemann, 1840 Skolithos isp. (Fig. 3A, B, J and K) Repository Ref: WIHG/A/1909 and other In situ specimen Material: Four specimens are preserved as full relief three in sandstone and one in shale. Description: Smooth unbranched single, vertical to oblique, cylindrical burrows, walls unornamented. The diameter of the burrow ranges from 0.2 to 8 mm the diameter may vary slightly along the depth of the burrow, the inner circle of burrow is narrow and ranges from 0.2 to 0.4 mm. The burrows are widely spaced and have rounded outline.

Remarks: It is considered to be a dwelling burrow made by feeding vermiform organisms. In the present material no vertical section are available. The described specimens though show some similarity with S. linearis Haldemann (1840), but differ in some diagnostic characters. Alpert (1975) in his review of the ichnogenus Skolithos is identified as straight nature, vertical dispertion and distinct to indistinct burrow wall. It differs from ichnogenus Monocraterion Torell (1870); due to lack of prominent funnel shaped structure at the top of burrow. The present specimen differs from the Skolithos ichnogenera described by Parcha and Singh (2010) from Zanskar in morphological characters. Locality: The specimens are preserved at different levels in the Debsakhad Member and in the lower horizon of the Parahio Member of Kunzum La Formation.

Ichnogenus: Treptichnus Miller, 1889 Type Ichnospecies: Treptichnus bifurcus Miller, 1889 emended Schlirf, 2000 Treptichnus isp. (Fig. 4E and Gb) Repository Ref: In situ specimens Material: The material is preserved as hyporelief in two huge blocks of sandstone. Description: Slightly curved regularly alternating set of burrows. One set is connected with other at their lower parts. The individual burrows are from 21 to 46 mm in length and 5 to 8 mm in width. Burrows raise 2–6 mm (continued on next page)

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with the Treptichnus isp. described from Zanskar by Parcha and Singh (2010). Treptichnus have been reported from the various successions at the base of the Lower Cambrian. Locality: The present specimen occurs in the lower most part of the Debsakhad Member of the Kunzum La Formation in the Parahio Valley.

above the surface of rock sample. No internal structure or wall lining are visible.

Remarks: The material from Spiti locality has been compared to Treptichnus aequalternus (Schlirf, 2000) due to the regularity of the projections on either side of the main trace. Treptichnus has been interpreted as a feeding structure (Schlirf, 2000). Vannier et al. (2010) suggested that Treptichnus were produced by priapulid worms because the recent priapulid worms used the same locomotory mechanisms. The present form differs with the ichnogenera Treptichnus described by Jensen et al. (2000) from the Proterozoic of Nama Group, Namibia in the pattern of three lobed surface. The specimen equally differs

? Annelid Worm (Fig. 6H) Repository Ref: In situ specimen Material: Single specimen preserved in quartzite was photographed in the field. Description: The ichnofossil have anterior part, which is like a horseshoe shape with smooth, curved anterior margins and

Table 1 Presence of various ichnofossils reported in the Lower Cambrian successions of Indian Subcontinent. Ichnogenera

Astropolithon Aulichnites Bergaueria Bifungites Chondrites Cochlichnus Crossochorda Cruziana Cylindrichnus Didymaulichnus Dimorphichnus Diplichnites Gordia Gyrochorte Halopoa Helminthorhaphe Helminthopsis Isopodichnus Kupwaria Laevicyclus Lennea Lockeia Margaritchnus Merostomichnites Monocraterion Monomorphichnus Neonereites Nereites Palaeophycus Palaeopascichnus Plagiogmus Psammichnites Phycodes Planolites Protichnites Rhizocorallium Rosselia Rusophycus Scolicia Scoyenia Skolithos Taphrhelminthopsis Tasmanadia Teichichnus Treptichnus Zoophycos Scratch marks Worms and Burrows

Salt range, Pakistan (Seilacher, 1955)

+

+

+ +

Lesser Himalaya (Banerjee and Narain, 1976; Singh and Rai, 1983; Bhargava, 1984; Tiwari and Parcha, 2006)

Marwar Supergroup Kumar and Pandey, 2008, 2010)

Garhwal-Kumaun Basin (Tandon and Bhatia, 1978; Sudan and Sharma, 2000)

Kashmir Basin (Shah and Sudan, 1983 and Raina et al., 1983)

+ +

+

+ +

+ +

+ +

Zanskar Basin (Hughes and Droser, 1992; Parcha, 1998b; Parcha and Singh, 2010)

Spiti Basin (Bhargava et al., 1982; Sudan and Sharma, 2001; Parcha et al., 2005 and present work)

+ +

+

+ +

+

+ + +

+

+

+

+ +

+ +

+ + + +

+ +

+

+ + + +

+

+

+ + + + + + + + +

+ +

+ + + + + + +

+ +

+

+

+

+

+

+ + + + + + +

+

+

+ + +

+

+ +

+ +

+ + +

+ + +

+ + + +

+ + + + +

+

+ + + +

+

+ +

+ +

+

+ +

+

+

+ +

+ + + + +

+ +

+

+ + + +


have pointed posterolateral projection. On the anterior side a medial groove is present. Axial line is distinctly visible in the body. Series of broken segments were observed. The maximum width of the anterior side is 21 mm, whereas the posterior side width is 23 mm, and width of appendages is 7 mm. The total length of the specimen is 120 mm.

Remarks: Due to the general structure and the segmented body the present specimen is placed in the Annelida. In

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absence of traces of segmentation the present specime cannot be included in family Sprigginidae (Glaessner, 1958). The trunk of Spriggina flounderis (Glaessner, 1958) consisting of a very gently tapering series of segments, numbering up to 40, but due to poor preservation no clear segments were observed. Hence, it has been grouped with annelid worm in an open nomenclature. At present little information is available to understand the mode of life of this fossil and its relation to other annelids. It may also help to solve the problem of the origin of arthropod and its

Table 2 Distribution and behavioral pattern of ichnofossils in the Debsakhad and Parahio members of the Kunzum La Formation.

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relation to other arthropod ichnofossil, which indicates a pelagic adaptation. Locality: The specimen is preserved in the upper part of Debsakhad Member of the Kunzum La Formation.

Scratch marks (?) (Fig. 4K) Repository Ref: WIHG/A/1599 Material: The specimen is preserved in sandstone Description: The ridges are sigmoidal with a maximum width ranging from 3 to 5 mm and length 12 to 22 mm. Scratch marks are grazing traces might have been produced by trilobites and can be assigned as the isolated fragments of Monomorphichnus. Locality: Preserved in the lower part of Parahio Member of the Kunzum La Formation.

Burrow A (Fig. 6I) Repository Ref: In situ specimen Material: The specimen is preserved in sandstone. Description: Straight, simple, sub-cylindrical, unornamented with sharp outer margins. The length of the burrow is

33 mm and the width is 8 mm. The surface of the burrow is flat on the top and the edges are slightly curved. Burrows are considered as a feeding structure. Due to the paucity of the material the present specimen is grouped under open nomenclature.

Burrow B (Fig. 6E) Repository Ref: WIHG/A/1597 Material: The specimen is preserved in siltstone along with Rusophycus specimen Description: Specimen shows sub-circular structure and has variation in width. The minimum width is 8 mm and the maximum is 14 mm. The length of the burrow is 40 mm; the surface of the burrow is smooth along with faint ridges. On the rare side of this burrow some irregular striations have been observed, which are six in number. The specimen differs from Astropolichnus (Crimes and Anderson, 1985) with equal size of radial ridges separated by narrow grooves. Locality: The described burrows were reported from the different levels of Debsakhad and Parahio Member of the Kunzum La Formation.

Table 3 Stratigraphic range of ichnogenera occurring in the Debsakhad and Parahio members of the Kunzum La Formation.


5. Stratigraphic significance The diverse assemblage of ichnofossils is present in the Parahio section of the Spiti Valley. The Ichnofossils found in many successions spanning the Precambrian–Cambrian boundary, appear to be very useful for the global correlation of this section. The ichnofossil assemblage recovered from the Debsakhad and Parahio members of the Kunzum La Formation, is of much stratigraphic importance, due to the relationship of the morphospecies with the genetic body forms; and their rare association with body fossils. This discrete stratigraphic distribution of ichnofossil and body fossil will is important for deciphering the Neoproterozoic-Cambrian transition in absence of body fossils in this region. The ichnofossils collected from the Cambrian successions of the Spiti Basin are important in deciphering the age of pre-trilobite bearing beds. The distribution pattern shows that there is no record of body fossils from the basal part of Kunzum La Formation in the Parahio Valley, except a float of Redlichia from the Pin section by (Hayden, 1904 and Parcha, 1992). The ichnofossil assemblage present in the Lower Cambrian succession of the Spiti Basin occurs below the Pagetia bearing horizon (Parcha, 1999). The ichnofauna reported from this section shows that the simple forms evolve at the base of Debsakhad Member; whereas, complex forms starts appearing from its middle part and continues up to the base of Parahio Member. The distribution pattern indicates up-section increase in taxonomic and morphological diversity (Table 2). The proliferation of ichnofauna could be due to the extensive evolutionary changes, which have been reported from the well known section of Newfoundland by (Narbonne et al., 1987). The present assemblage of ichnofossil can be correlated with other contemporaneous horizons of Tethyan as well as Lesser Himalayan regions (Table 1). The ichnofossil assemblage indicates that the ichnocenosis is dominated by a high behavioral diversity ranging from suspension to deposit feeders. It reflects fodinichnia, pascichnia, repichnia, domichnia and cubichnia behavior pattern. Majority of the ichnofauna from the Lower Cambrian succession of Parahio section appears to be produced by trilobite or arthropods; whereas some of them might have been the trails of crustacean, priapulid worm, polychaetes and polyphyletic vermiforms. It is also observed that only few forms like Nereites, Skolithos, Monomorphichnus extend even in the Parahio Member (Middle Cambrian); whereas, some are confined to the Debsakhad Member (Lower Cambrian) (Table 3). The distribution of ichnofossils in the Lower Cambrian succession reflects the paleoecological conditions including the availability of oxygen and nutrient influx Parcha et al. (2005). Three ichnofacies (namely Cruziana, Skolithos and Nereites ichnofacies) described from the Lower Cambrian succession of Parahio Valley (Parcha et al., 2005) indicating behavioral diversity from suspension to deposit feeders, reveal anaerobic to aerobic trend in up section. The presence of Chondrite, Treptichnus, and Phycodes at the basal part of the Lower Cambrian indicates shallow to deep water environment with anaerobic condition. Moreover, the appearance of Chondrites indicates that the anaerobic environment of the ocean water impinges on slope, and upper bathyal zone not flushed by oxygen-rich current (Bromely and Ekdale, 1984). On other hand, the complex worms like Rusophycus, Cruziana, Monomorphichnus and Nereites indicate shelf to slope environment. The appearance of Skolithos in upper part of the Lower Cambrian and early part of the Middle Cambrian reflects well oxygenated high energy conditions. The environmental changes from an anaerobic to aerobic condition in the Debsakhad Member was distinctly marked by a faunal change from endobenthic, soft-bodied, deposit feeders to epibenthic grazers. The stratigraphic significance of Rusophycus and Cruziana is very well discussed by Seilacher (1970) and by Crimes (1970,

1113

1975). The occurrence of Rusophycus indicates Lower Cambrian age (Bergström, 1990). The stratigraphic significance of the Cruziana group of ichnofossil indicates different kind of trilobite burrowing and grazing trails has been widely discussed by various researchers (Crimes, 1970, 1975; Bergström, 1970; Alpert, 1977; Crimes et al., 1977; Bromley and Asgaard, 1979; Fortey and Seilacher, 1997; Jensen, 1997; Pollard, 1985; Seilacher, 1953, 1997, 2007). The Phycodes is known as a characteristic trace fossil of Lower Cambrian, and indicates deposition in intertidal transitional environment (Alpert, 1976; Kumar et al., 1977). The presence of Skolithos is considered as indicative of high energy depositional environment in which the organism occur, while Planolites does not have such significance due to its presence in the rocks of various facies. The ichnogenus Didymaulichnus have been reported from the Late Venidian to Early Cambrian (Palij et al., 1983; Fritz and Crimes, 1985; Fedonkin, 1988; Narbonne and Myrow, 1988); while the Diplichnites indicating the low energy environment, is widely known from the Cambrian (Crimes et al., 1977; Bromley and Asgaard, 1979). The bilateral tracks and trails with characteristic scratch marks observed in the Parahio Valley ichnofossil assemblage are well reported from above the basal Cambrian in Newfoundland (Narbonne et al., 1987). The Precambrian–Cambrian boundary in the Debsakhad Member of Kunzum La Formation could not be demarcated due to the paucity of body fossil, as well as microbiota in the lowermost beds. However, the presence of Treptichnus and Phycodes can be considered as a horizon marker for the beginning of Lower Cambrian. The possibility of relating the stratigraphic distribution of ichnofossils to significant body fossils will increase the objectivity of the correlation based on ichnofossils. In order to understand this problem, we need to access the relation between the ichnofossil and the organisms which are responsible for producing them, which, however, is yet to be established. Simultaneously, the total ranges and the stratigraphic distribution of the various morphotaxa need to be established in various facies as well as in different geographical provinces. Most of the ichnofossil do not occur in association with body fossils, but usually occur below the trilobite bearing horizons in Lower Cambrian. In Spiti Basin, the horizons that are rich in ichnofossils are devoid of body fossils; or the horizons where body fossils are common, the ichnofossils are quite rare. The presence of ichnofossils below the body fossil horizons of early Cambrian is noticeable in Zanskar, Kashmir, Kumaun and Garhwal as well as in the Spiti basin. The assemblage of ichnofossils reported from the Debsakhad and Parahio members of the Parahio section, has a significant stratigraphic importance as they provide evidence regarding the developmental patterns during the early phase of life on earth. These ichnofossils suggest that the availability of nutrients significantly increased their abundance as well as spatial distribution during Cambrian. Acknowledgements The authors are thankful to the Director, Wadia Institute of Himalayan Geology for their encouragement and for providing the necessary facilities. The authors are thankful to the anonymous reviewers for their insightful reviews. This work was carried out under the Project SR/S4/ES-62/2003 funded by the Department of Science and Technology, Government of India. References Abbassi, N., 2007. Shallow marine trace fossils from Upper Devonian sediments of the Kuh-E-Zard, Zefreh area, Central Iran. Iranian Journal of Science and Technology, Transaction A 31 (A1), 23–33.

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