Research Note Acanthodian scales and worm tubes from the Kapp Kjeldsen Division of the Lower Devonian Wood Bay Formation, Spitsbergen ROBERT R. ILYES Ilyes, R. R. 1995: Acanthodian scales and worm tubes from the Kapp Kjeldsen Division of the Lower Devonian Wood Bay Formation, Spitsbergen. Polar Research 14(1), 89-92. Results of a thin section study of bonebeds from the Kapp Kjeldsen Division are presented and discussed. The material for this study was collected in the talus on the south-eastern side of Bockfjorden, northern Spitsbergen. The stratigraphical position of the Kapp Kjeldsen Division within the Devonian strata of Spitsbergen is shown in Table 1 . The thin sections for this study were not made to standard thickness, but are slightly thicker for better resolution of the vertebrate material. Each thin section was individually polished. The photos are made with crossed nichols. Robert R . llyes, Norsk Polarinstitutt, P . O . Box 5072 Majorstua, N-0301 Oslo, Norway. ‘J*p&AR,~s,“ Acanthodian scales Fossils of acanthodians are quite common in the Devonian strata of Spitsbergen, and occur from the Red Bay Group to the Mimerdalen Formation (Blieck et al. 1987). 0rvig (1967) described the The presence of at least three new genera indi- cate that the acanthodian fauna of the Kapp Kjeldsen Division is more diverse than previously considered. Invertebrates and plants first acanthodians’ from -the Kapp Kjeldsen Division, Xylacanthus grandis and “Onchus” ouerathensis based on macrofossils of jaw- elements and fin spines. Scales from this unit were first reported by Ilyes (1990). The scales are all of the “Acanthodes” hist- ologic-type of Moy-Thomas & Miles (1971). Such scales have a thick base of acellular bone with non-vascular canals, and a crown of true dentine. The scale shown in Fig. 1A is assigned to the genus Cheiracanthus Agassiz, 1835, on the basis of external morphology and internal structure of the crown. The scale in Fig. 1B has a morphology suggesting that it is a scale from the genus Ptych- odichtyon Gross, 1973. The overall morphology of the scale in Fig. 2C suggests that it can be assigned either to the genus Cheiracanthus or Ptychodichtyon. The scale in Fig. 1D has ageneral morphology indicating that it belongs to the genus Acanthodes Agassiz, 1833. Scales from the younger Grey Hoek Formation with a mor- phology very similar t o this form have previously been described as Acanthodes? sp. (Valiukevicius 1979, 1985). Worm tubes of the genus Spirorbis Daudin, 1800, have been found in thin sections together with the acanthodian scales (Fig. 2A and B). Fossil worm tubes are very rare in the Devonian strata of Spitsbergen, and have previously only been described from the Red Bay Group (Friend 1961). As they are useful in discussions regarding paleo- environment, their presence in the Kapp Kjeldsen Division is significant. None of the three specimens of Spirorbis found were attached t o substratum; this indicates that they have been transported post mortem. The specimens appear, however, not to be damaged, suggesting that they must have lived near the area of deposition (Ilyes 1990). Ostracods and charophytes are well repre- sented in the bonebeds (Fig. 2C-I). Valves from both large leperditiid and small, smooth non- leperditiid ostracods are present. However, the large and thick valves of the leperditiid ostracods dominate totally in a number of individuals. The leperditiid ostracods are represented only by dis- 90 Robert R . Ilyes articulated valves, while some of the valves of the non-leperditiid ostracods are articulated. Articu- lated valves indicate short or no post rnortem transport. represented by female reproductive organs, the oogonia. Their overall morphology suggests that they belong to the genus Trochiliscus, and some of the plant macrofossils found in the studied In the thin sections the charophytes are only material from the Kapp Kjeldsen Division Fig J Vcrtical thin sections through acanthodian scales. ( A ) Genus Cheiracanthus, 83 x . (B) Genus Ptychodichfyon, 85 X . (C) Genus Prvchodichyon or Cheiracanthus. 85 X . (D) Genus Acanrhodes?. 83 X . Fix 2 T h i n sections of invertebrates and plants. ( A ) Spirorbis. 40 x . ( B ) Spirorbls, 45 x . (C) “Bonebed”, 25 x . (D) Valve of a Ieperditiid ostracod. 40 X . ( E ) Unidentified smooth. small ostracod with both valves in situ. 63 X . (F) Charophyte oogonia (Trochrlrscw 5p.’?), 1 0 0 ~ . ( G ) Charophyte oogonia (Trochilircus sp.?). 63 X . ( H ) Unidentified fossil (invertebrate?), 63 X . ( I ) Charophyte oogonia (Trochilrscus sp.’?), 63 x . ( J ) Plant macrofossils, “Hostirndla”. Acanthodian scales and worm tubes 91 92 Robert R . I l w Table 1. Stratigraphy of the Devonian strata of Spitsbergen (after Blieck et al. 1987) Mimerdal Formation Wijde Bay Formation Grey Hoek Formation (Eifelian) Wood Bay Formation ( Pragian-Emsian) Stjsrdalen Division KeltiefjeUet Division Kapp Kjeldsen Division Sigurdfjellet Division Red Bay Group (Fig. 2J) might consist of charophyte plant bodies. The plant material is, however, of the “Hosfi- mel1a”-type which lacks characters for proper identification. The paleoenvironment of the Kapp Kjeldsen Division is not well understood at the present time. The Kapp Kjeldsen Division is a faunal division based on agnathe and vertebrates which incorporate different lithologies. ranging from fine-grained red and green micaceous sandstones to coarser pebble conglomerates. This indicates different depositional environments. It has pre- viously been interpreted as a pure freshwater deposit with no marine influence (Friend 1965; Friend & Moody-Stuart 1972). The association of leperditiid ostracods, charophyte oogonia, and worm tubesof the genus Spirorbis in the bonebeds indicate, however, that at least parts of the Kapp Kjeldsen Division have been deposited in brack- ish water (D. Vachard per. commun.). The co- occurrence of different freshwater and brackish environments in the Kapp Kjeldsen Division may be an indication of deposition in the lowland near the paleocoast where freshwater and brackish environments intertwined in at least parts of the depositional area (Ilyes 1990). Acknowledgements. - 1 wish to thank J . Valiukevicius from the Lithuanian Geological Research Institute. Vilnius, for help with idcntification of the acanthodian scales. 1 also wish to thank D . Vachard, Universite des Sciences et Techniques de Lille- Randre- Artois, France, for help with the microfacies analysis. References Blieck, A . , Goujet, D., & Janvier. P. 1987: The Vertebrate Stratigraphy of the Lower Devonian (Red Bay Group and Wood Bay Formation) of Spitsbergen. Modern Geol. 1 1 , 197-217. Friend. P. F. 1961: The Devonian Stratigraphy of North and Central Vest-Spitsbergen, Proc. Yorks. Geol. SOC. 33, 77- 118. Friend. P. F 1965: Fluviatile sedimentary structures in the Wood Bay senes (Devonian) of Spitsbergen. Sedimentology j, 39-68. Friend. P. F. & Moody-Stuart, M. 1972: Sedimentation i n the Wood Bay Formation (Devonian) of Spitsbergen: Regional analysis of a late orogenic basin Norsk Polorinsr. Skr. 157. 1-77. llyes. R . R . 1990: Agnathan and Gnathostome fish from the Kapp Kjeldsen Division, the Wood Bay Fm. (Lower Devonian), Spitshergen (in Norwegian). Unpubl. Cand. Scienl. thesis, Universily of Oslo. 161 pp. Moy-Thomas. I. A . & Miles, R. S . 1971: Palaeozoic Fishes. Chapmann and Hall. London. 259 pp. 0 ~ g . T. 1967: Some new acanthodian material from the Lower Devonian of Europe. 1. L i n n . SOC. ( Z o o l . ) 4 7 ( 3 / 1 ) , 131-153. Valiukevicius, J . J. 1979: Acanthodian scales from the Eifelian of Spitsbergen. Poleoniol. 1. 13(4), 482492. Valiukevicius, I . I. 1985: Akantody Narovskogo gorizonta glavnogo devonskogo polja (Acanthodians from the Narva Regional Stage of the main Devonian field). Mokslas, Vilnius. 143 pp. (in Russian).