The holotype of the problematic structure "Astropolithon hindii" is described and interpreted as a deformed sand volcano, similar in morphology to many of the previously described sand volcanoes from the Cambro-Ordovician Meguma Group of Nova Scotia.

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			On red&#xE9;crit l'holotype de la structure problem at (que "Astropolithon hindii" et l'interpr&#xE8;te comme &#xE9;tant un volcan de sable d&#xE9;forme et semblable en morphologic &#xE0; plusieurs volcans de sable crits auparavant dans le Groupe de Meguma (Cambro-Ordovician de la Nouvelle-&#xC9;cosse).
		
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Pickerill, R. K.

English

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MARITIME SEDIMENTS AND ATLANTIC GEOLOGY 18 On the holotype of "Astropolithon hindii" R.K. PZckesuJUL, De.pcmtni£jvL o-fL Qe.oi.ogy, Urvlveju>i£y o/ New Biuru>uu.ck, TsiedesLLcton, N,B, £3B 5A3 The holotype of the problematic structure "Astropolithon hindii" is described and interpreted as a deformed sand volcano, similar in morphology to many of the previously described sand volcanoes from the Cambro-Ordovician Meguma Group of Nova Scotia. On redfecrit l'holotype de la structure problfematique "Astropolithon hindii" et l 'interprete comme fitant un volcan de sable dgforme et semblable en morphologie a plusieurs volcans de sable crits auparavant dans le Groupe de MSguma (Cambro-Ordovician de la Nouvelle-Ecosse). INTRODUCTION In 1979 Pickerill and Harris a t tempted to demonstra te that the problematic s t ruc-tures re fer red to by Dawson (1878, 1890) from the Cambro-Ordovician Meguma Group of Nova Scotia as Astropolithon hindii were physical ra ther than biogenic sedimentary structures. Pickerill and Harris (1979) envisaged these s t ructures as result-ing from fluidization along discrete flow paths of rapidly deposited turbiditic or liquefied sheet sandstones, the A. hindii specimens merely representing sand vol-canoes with a ra ther complex internal and external s t ructure . At that t ime the "holo-type" of Astropolithon hindii was unavail-able. Indeed, Hantzschel (1975) in the Treat ise of Invertebrate Paleontology s ta ted "... no type specimen from Canada located" (1975, p. 180). Since 1979, the "holotype" has now been located in the Redpath Museum, McGill University, N. 2.101 (Alison and Caroll 1972, p. 154). More importantly, however, the name Astropoli-thon has since and recently been resur-rec ted by Miller and Byers (1984) and in-terpre ted as a distinctive biogenic s t ruc-ture. The purpose of this note is therefore to describe the "holotype" of A. hindii and to fur ther comment on its physical, as distinct from biogenic origin. The "holotype" of A. hindii was collect-ed by Dawson (1878, 1890) from Waverley, 20 km to the north of Halifax, Nova Scotia (for location map see Pickerill and Harris 1979, p. 1030). Here, exposures are all within the Goldenville Formation of the Meguma Group. DESCRIPTION The "holotype" of Astropolithon hindii is an elongate ellipse-shaped structure, 10 MARITIME SEDIMENTS AND ATLANTIC GEOLOGY 20, 79-81 (1984) cm in length and 2.7 cm in maximum width. The ellipse-shape has been consider-ably accentuated by deformation, the long axis of the ellipse lying in the foliation plane (cf. Henderson 1983). On the upper surface of the ellipse are at least 15 straight riges radiating outward from a diffuse and poorly preserved, slightly de-pressed matrix-rich central zone of the fine-medium grained host sandstone. This central zone is a darker colour than much of the remainder of the ellipse as a result of the increased proportion of matrix. The ridges or radial septae are only present on the lower half (as viewed in Fig. la) and on one side of the specimen. They extend from the outer margin of the dif fuse cent -ral area to and then beyond the edge of the ellipse itself, gradually merging with and grading imperceptibly into the sur-rounding pale-green sandstone. The s teep f rac tured surface where the ridges extend beyond the ellipse is parallel to the main foliation of the specimen. The ridges ex-tend to a maximum of 15 mm down this f rac tured surface. They are relatively 'clean' , possessing very l i t t le matrix in comparison to the intervening grooves which possess a higher proportion of ma t -rix and, like the central zone, appear darker. DISCUSSIONS AND CONCLUSIONS The "holotype" of Astropolithon clearly exhibits similar if not identical charac te r -istics to specimens from Waverly previous-ly figured and described by Pickerill and Harris (1979). At Waverly the only ex-posures are horizontal ledge-like upper bedding plane surfaces. Most of these sur-faces are covered with randomly distri-buted, t runcated mounds, each possessing straight or slightly sinuous radial septae. 0711-1150/84/020079-03$!. 45/0 80 Fig. 1 - The "holotype" of Astropolithon hindii, (a) as viewed from above, (b) as viewed from the side, and (c) as viewed obliquely. Scales as follows: a = X 1.1, b = X 0.85, c = X 1.1 Invariably, the radial septae extend beyond the mounds represented sand volcanoes and interconnect with septae from adja- which possessed vertical radial septae cent mounds (cf. Pickerill and Harris 1979, which extended beyond the actual vol-fig. 2a). Like the "holotype" itself, the canoes as vertical dewatering sheet struc-ridges or septae possess a low matrix con- tures. The ridge and groove appearance tent in comparison to the intervening was simply a function of differential grooves and therefore appear as much weathering processes on matrix-rich cleaner structures in contrast to the (grooves) and matrix-poor elutriated darker grooves. Petrographic analysis of (ridges) structures. these structures reveals pronounced ef fec ts Although petrographic analysis of the of quartz diagenesis (pressure solution "holotype" is obviously impossible, the welding of quartz grains and quartz pre- specimen is remarkably similar to the cipitation) in the ridges in comparison to truncated sand volcanoes observed at the grooves. Based on such observations Waverley. There is no evidence to sug-Pickerill and Harris (1979) concluded that gest that the ridges and grooves are "radi-MARITIME SEDIMENTS AND ATLANTIC GEOLOGY 81 ating trails" (Dawson 1890) nor is there any evidence to suggest that the structure is biogenic in origin. Indeed, the curating staff of the Redpath Museum have label-led the specimen "probable bubble mark but not a plant", an interpretation more in accord with that presented herein. Thus the "holotype" of Astropolithon hindii is regarded as a truncated sand vol-cano similar to those described previously by Walter (1972) and Pickerill and Harris (1979). As such, the name Astropolithon must not be utilized for any biogenic sedi-mentary structure, as also noted by Pickerill (1984) in his discussion on the paper by Miller and Byers (1984). Speci-mens formally designated to Astropolithon and clearly of biogenic origin (e.g. Moreno et al. 1976, Crimes et al. 1977) should now be referred to Astropolichnus (Crimes and Anderson 1985). ACKNOWLEDGEMENTS I wish to thank Ingrid Birker for for-warding the specimen from the Redpath Museum, T.P. Crimes for access to unpub-lished information, A.G. Plint and J.M. Hurst for critically reading the original text and Joyce Ley who prepared the manuscript. ALISON, D. and CARROLL, R. 1972. Catalogue of type and figured fossils in the Redpath Museum, McGill University. Redpath Museum, McGill University, Mon-treal, 173p. CRIMES, T.P. and ANDERSON, M.M. 1985. Trace fossils from late Precambrian - early Cambrian strata of S.E. Newfoundland (Canada). Journal of Paleontology, 59, (in press). CRIMES, T.P., LEGG, I., MARCOS, A. and ARBOLEYA, M. 1977. ?Late Precambrian - low Lower Cambrian trace fossils from Spain. In Trace fossils 2. Edited by T.P. Crimes and J.C. Harper. Geological Journal Special Publication Number 9, Seel House Press, Liverpool, pp. 91-138. DAWSON, J.W. 1878. Supplement to the second edition of Acadian Geology. In Acadian Geology, The geolo-gical structure, organic remains and mineral resour-ces of Nova Scota, New Brunswick and Prince Edward Island (3rd dition), MacMillan, London 102p. DAWSON, J.W. 1890. On Burrows and Tracks of Inver-tebrate Animals in Palaeozoic Rocks, and other Markings. Quarterly Journal of the Geological Society of London, 46, pp. 595-618. HENDERSON, J.R. 1983. Analysis of fracture as a fac-tor controlling gold mineralization in Nova Scotia. In Current Research, Part B, Geological Survey of Canada, Paper 83-1B, pp. 13-21. MILLER, M.F. and BYERS, C.W. 1984. Abundant and diverse early Paleozoic infauna indicated by the stratigraphic record. Geology, 12, pp. 40-43. MORENO, F., VEGAS, R. and MARCOS, A. 1976. Sobre la edad de las series ordovicicas y Cambricas relac-ionadas con la discordancia "szardica" .en el anticlinal de Valdelacasa (Montes de Toledo, Espana). Breviora Geologica Asturica, 20, pp. 8-16. PICKERILL, R.K. 1984. Abundant and diverse early Paleozoic infauna indicated by the stratigraphic record - Comment. Geology, 12, (in press). PICKERILL, R.K. and HARRIS, I.M. 1979. A reinterpre-tation of Astropolithon hindii Dawson 1878. Journal of Sedimentary Petrology, 49, pp. 1029-1036. WALTER, M.R. 1972. Tectonically deformed sand vol-canoes in a Precmbrian greywacke, Northern Territory of Australia. Journal of the Geological Society of Australia, 18, pp. 395-399. Reviewers: A.G. Plint J.M. Hurst 

On the holotype of "Astropolithon hindii"

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On the holotype of "Astropolithon hindii"

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