ian series. A considerable .... few ostracodes, which M. J. Copeland (Geological. Survey of Canada ... Formation of Bolton (1972) (Copeland 1973), which.
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Schmidt (1980), and Schwarz and Fujiwara (1981) for between these units (see also Chandler and Schwarz parts of the Circum-Ungava Belt. The average direction 1980). for sites 1, 2, 4-6, and 8A giving sites equal weight corresponds well with the average obtained when giving BOSTOCK, H. 1970. Geological notes on Aquatuk River map area, Ontario, with emphasis on the Precambrian rocks. the specimens equal weight. Geological Survey of Canada, Paper 70-42, 57 p. Distributed blocking temperatures (TB) were obE. J. 1980. Tectonics of F. W., and SCHWARZ, served for specimens from sites 3 and 7. In general, TB's CHANDLER, the Richmond Gulf area, northern Quebec, a hypothesis. In are high and, as in many of the high coercivity AF Current research, part C. Geological Survey of Canada, results, an initial increase in intensity is observed due to Paper 80-lC, pp. 59-68. the removal of a downward viscous component during FUJIWARA, Y, and SCHWARZ, E. J. 1975. Paleomagnetism of heating to 200°C. Most specimens show very little the Circum-Ungava Proterozoic fold belt (I): Cape Smith change in direction, indicating a single component komatiitic basalts. Canadian Journal of Earth Sciences, 12, magnetization with TB > -200°C. An adequate number pp. 1785-1793. of end points for statistical purposes was obtained for SCHMIDT, P. W. 1980. Paleomagnetism of igneous rocks from the Belcher Islands, N.W.T., Canada. Canadian Journal of specimens from sites 2 , 5 , and 6 (Table 1). The average Earth Sciences, 17, pp. 807-822. direction for these sites calculated on either a site or a G. N. 1980. Preliminary paleoE. J., and FREDA, specimen basis shows a 7-8" higher negative inclination SCHWARZ, magnetic results for Sakami Formation red beds near La than that obtained from the AF experiments but this Grande 4. In Current research, part C. Geological Survey difference is probably not significant in view of the of Canada, Paper 80-lC, pp. 139-140. grouping statistics. The mean direction for the Sutton SCHWARZ, Y. 1981. Paleomagnetismof E. J., and FUJWARA, Lake diabase (Table 1) is comparable to those deterthe Circum-Ungava Belt 11: Proterozoic rocks of Richmond mined for the Eskimo volcanics of the Belcher Islands Gulf and Manitounuk Islands. In Proterozoic basins in (Schmidt 1980) and the Sakami Formation red beds of Canada. Edited by F. H . A. Campbell. Geological Survey the La Grande 4 outlier east of James Bay (Schwarz and of Canada, Special Paper, pp. 255-267. Freda 1980), indicating a time-stratigraphic relation
Conodonts and the position of the Ordovician-Silurian boundary at the eastern end of Anticosti Island, Quebec, Canada GODFREY S. NOWLAN Geological Survey of Canada, 601 Booth St., Ottawa, Ont., Canada KIA OE8 Received March 3, 1982 Accepted April 7, 1982
Conodonts have been recovered from a section spanning the Ordovician-Silurian boundary at the eastern end of Anticosti Island. They indicate that the systemic boundary lies slightly above or at the top of a pisolitic limestone bed. This placement of the boundary compares closely with that based on a previous interpretationof brachiopod faunas from the same section, and also with the position of the systemic boundary based on conodonts elsewhere on Anticosti Island. The conodonts are the first to be reported from the eastern end of Anticosti Island. Can. 1. Earth Sci., 19, 1332-1335 (1982)
Introduction Anticosti Island, in the Gulf of St. Lawrence (Fig. l), is renowned for its diversity and abundance of Late Ordovician and Early Silurian fossils. The stratigraphic sequence dips very gently to the southwest and comprises a thick, continuous sequence of mainly carbonate rocks. Deposition across the Ordovician-Silurian boundary is apparently continuous and the strata span a
period of time not represented over most of the rest of North America. For these reasons Anticosti Island is currently under review as a potential stratotype for the Ordovician-Silurian boundary and for the lowest Silurian series. A considerable amount of information has recently been published documenting the strata and faunas of the island and much of this is to be found in a volume produced for a field trip undertaken in 1981 by
0008-4077/82/061332-04$01 .OO/O 01982 National Research Council of Canada/Conseil national de recherches du Canada
FIG. 1. Map showing location of Anticosti Island and its main geographic features. Arrow in inset at right indicates the position of the section illustrated in Fig. 2. Formational boundary derived from Cocks and Copper (1981).
the International Union of Geological Sciences (IUGS) Subcommission on Silurian Stratigraphy and by the Ordovician-Silurian Boundary Working Group (LespCrance 1981). The papers in the volume enlarge upon the earlier work of Twenhofel(1928) and Bolton (1972), and provide much new information on the distributionof several faunal groups. Detailed analysis of the conodont biostratigraphy also has been recently published for the Upper Ordovician and lowest Silurian strata of Anticosti Island (Nowlan and Barnes 1981; McCracken and Barnes 1981). Most of the work published concerns the western, central, and east-central parts of the island. The western area around Port-Menier (Fig. 1) is readily accessible and much of the central and east-central areas as far as Salmon River (Fig. 1) are accessible by lumber roads. In contrast, the eastern end of the island is accessible at present only by boat or helicopter. The position of the Ordovician-Silurian boundary based on conodonts is well established for sections at Port-Menier and Salmon River (McCracken and Barnes 1981), but no conodont studies have been available from the eastern end of the island. Cocks and Copper (1981) recently published a report on the position of the Ordovician-Silurian boundary at the eastern end of Anticosti, based on the presence of brachiopods. They described and illustrated a section measured between the first point west of Fox Point, descending stratigraphically west towards Table Head (Fig. 1). The section illustrated is 22 m thick and spans the Ordovician-Silurian boundary. The lower 11 m (beds 1-10) comprises the uppermost part of the Ellis Bay Formation used in the sense of Petryk (1979,198I), who included the upper part of Bolton's (1972) Ellis Bay (most of member 6) in the overlying Becscie Formation.
The upper 11 m is ascribed to the Becscie Formation (Fig. 2). Cocks and Copper (1981) recovered a diverse faunal assemblage including Dalmanella testudinaria (Dalman), Eostropheodonta sp .,and Hirnantia sp . from the upper part of the Ellis Bay Formation (their bed 5 ) , to which they ascribed a Hirnantian (latest Ordovician) age. Bed 10 of Cocks and Copper (1981) is a pisolitic algal-coral limestone, which equates with the reefplatform bed of Petryk (1979, 1981). Elsewhere this bed is succeeded by the development of bioherms, but none is represented in this section. The lower part of the Becscie Formation (beds 11-14) yielded a brachiopod assemblage interpreted by Cocks and Copper (198 1) as a transgressive shallow to mid-shelf fauna of early Llandovery age, and hence they placed the OrdovicianSilurian boundary at the top of the reef-platform bed (pisolitic limestone of bed 10). Recently P. Copper (Laurentian University) supplied the author with several samples from this section. These have been processed for conodonts and the faunas recovered are discussed below.
Conodont faunas Twelve small samples (average weight 380 g) have been processed and nine of these yielded conodonts. The stratigraphic sequence and the localities are provided in Fig. 2. All of the barren samples are within the Ordovician part of the sequence, and of the almost 200 conodont specimens recovered only eight are from the Ordovician part of the sequence. The lowest sample (GSC loc. 98739; from bed 6) yielded only a single specimen assignable to Panderodus sp. Similarly only specimens of Panderodus were
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FIG.2. Diagrammaticrepresentationof sectionmeasuredby Cocks and Copper (198 1). For detailed section description see their Fig. 2. Bed numbers are shown to left of stratigraphic column, and sample numbers and levels to the right. " H shows level from which Hirnantian fauna was obtained. Triangle indicates barren sample. Star indicates lowest sample bearing diagnostic Silurian conodonts. mud. is anabbreviation of Rhuddanian, the lowest stage of the Llandovery. (Adapted from Cocks and Copper 1981, Fig. 2.)
recovered from the lower part of bed 9 (GSC loc. 98743). Specimens assignable to Oulodus rohneri Ethington and Furnish were recovered from the upper part of bed 7 (GSC loc. 98741) and also from bed 10 (GSC loc. 98745), the latter being the highest Ordovician unit according to Cocks and Copper (1981). Oulodus rohneri is a characteristic species known only from strata of Late Ordovician age. It was originally described from northern Manitoba (Ethington and Furnish 1959) and has recently been discussed in detail (Nowlan and Barnes 1981). A sample from the lowest 2-3 cm of bed 11 (GSC loc. 98746) directly above the reef-platform bed and therefore in the lowest part of the Silurian strata according to Cocks and Copper (1981) yielded two conodont speci-
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mens. They comprise one ambalodiform and one sagittodontiform element and are assigned to Icriodella sp. Specimens of the genus Icriodella occur in both Upper Ordovician and Lower Silurian strata. Species cannot be identified unless the platform (icriodelliform) element is present. Elsewhere on Anticosti Island, Icriodella is known only from Silurian strata (McCracken and Barnes 1981), but in Gasp6 Peninsula, 200km to the south, Icriodella has been recovered in strata of Late Ordovician age (Nowlan 1981). Thus the sample from the lowest part of the Becscie Formation may be either Ordovician or Silurian in age, but based on the local distribution of Icriodella it is more likely to be Silurian. A sample from the lowest metre of the Becscie Formation (GSC loc. 98747) yielded undiagnostic simple cone elements of Panderodus gracilis (Branson and Mehl) and Walliserodus curvatus (Branson, Mehl and Branson). The first conodonts of undoubted Silurian age occur in a sample from the upper metre of bed 11 (GSC loc. 98748), and include specimens of Ozarkodina oldhamensis (Rexroad) as well as simple cone conodonts assigned to Decoriconus costulatus (Rexroad), P . gracilis, and W . curvatus. Ozarkodina oldhamensis is known widely from strata of Early Silurian age and has recently been discussed in detail by McCracken and Barnes (1981), who noted its widespread distribution in the Oulodus? nathani Zone (earliest Silurian) of Anticosti Island. The sample from GSC loc. 98747 also yielded a few ostracodes, which M. J. Copeland (Geological Survey of Canada, Ottawa) kindly identified 8s Euprimitia gamachei Copeland and Schmidtella sp. The former species is restricted to member 6 of the Ellis Bay Formation of Bolton (1972) (Copeland 1973), which roughly equates with the lower part of the Becscie Formation as revised by Petryk (1979,1981) and as used herein. Euprimitia gamachei also occurs in GSC loc. 98749 (bed 13). Thus the ostracodes occur in this section at the same stratigraphic level as elsewhere on Anticosti Island, but the Ordovician-Silurian boundary based on ostracodes occurs higher than that proposed for conodonts (Copeland 1981, p. 188). Succeeding samples (GSC 98749, 98750) yielded diagnostic Silurian conodonts, including specimens of Ozarkodina hassi (Pollock, Rexroad and Nicoll) and 0 .oldhamensis. These samples also yielded specimens of Pseudooneotodus beckmanni (Bischoff and Sannemann). In the samples bearing diagnostic Silurian conodonts simple cone elements outnumber representatives of Ozarkodina by 10:1, with Panderodus being most numerous.
Summary The position of the Ordovician-Silurian boundary in this section can be said on the basis of conodonts to lie
within the lower part of unit 11. Despite the small size and wide spacing of the samples the boundary has been tied to a narrow interval and the conclusion is in agreement with the boundary based on brachiopods (Cocks and Copper 1981). Elsewhere on Anticosti Island the Ordovician-Silurian boundary based on conodonts is in interreef beds a few metres above the reef-platform bed (McCracken and Barnes 1981). With the absence of bioherms in this section at the eastern end of Anticosti Island the boundary appears to lie a little lower, possibly at the upper contact of hed 10, the reef-platform bed. Additional, larger samples from the critical interval are required to increase the precision of placement of the boundary. It is regrettable that no representatives of Gamacltig-
nathus McCracken, Nawlan and Barnes (McCracken er al. 1980) were recovered from the Ordovician part of the section because it is the key indicator of Fauna 13 (Gamachian). Similarly it is a pity that no elements of Oulodus? narhani McCracken and Barnes were recovered from the Silurian part of the section because that species is used to define the earliest Silurian zone on Anticosti Island (McCracken and Barnes 1981). Nevertheless the boundary can be identified and it is significant that it coincides with that suggested by the brachiopods.
Acknowledgments Dr. Paul Copper (Laurentian University) and Dr. C. R. Barnes (Memorial University of Newfoundland) kindly read a draft of this manuscript. The author is grateful to Dr. Copper for providing the samples. BOLTON,T. E. 1972. Geologic map and notes on the Ordovician and Silurian litho- and biostratigraphy, Antlcosti Island, QuCbec. Geological Survey of Canada, Paper 71-19. COCKS,L. R. M., and COPPER,P. 1981. The OrdovicianSilurian boundary at the eastern end of Anticosti Jsland. Canadian Journal of Eaah Sciences, I&,pp. 102% 1034. COPELAFJD, M. J. 1973. Ostracoda from the EUis Bay Formation (Ordovicim), Anticosti Island, Qutbec. Geological Survey of Canada. Paper 7243.
1981. Latest Ordovician and Silurian ostracode faunas from Anticosti Island, Qdbec. In Vol. LI: Stratigraphy and paleontology. Edited by P. J . LespCrance. Subcommission on Silurian Stratigraphy, Ordovician-Silurian Boundary Working Group, field meeting, Anticosti-Gasp6 (Que.), 1981, pp. 185-195. R. L., and FURNISH, W. M. 1959. Ordovician ETHINGTON, conodonts from northern Manitoba. Journal of Paleontology, 33, pp. 540-546. LESP~RANCE, P, J., editor. 1981. Vol. II: Stratigraphy and paleontology. Subcommission on SiIurian Sb-atigraphy, Ordovician-Silurian Boundary Working Group, field meeting,Anticosti-Gaspi (Quk.). 1981,321 p. MCCRACKEN, A. D., and BARNES,C. R. 1981. Conodont biostratigraphy and paleoecology of the Ellis Bay Formation, Anticosti Island, QuCbec, with special reference to Late Ordovician - Early Silurian chronostratigraphyand the systemic boundary. Geological Survey of Canada, Bulletin 329, pp. 50-134. MCCRACKEN, A. D., NOWLAN, G. S., and BARNES, C. R. 1980. Gamachignathus, a new multi-element conodont genus from the latest Ordovician, Anticosti Island, QuCbec. Geological Survey of Canada, Paper 80-l C, pp. 103-1 12. NOWLAN,G. S. 1981. Late Ordovician - Early Silurian conodont biostratigraphy of the Gaspt Peninsula-a preliminary report. In Vol. 11: Stratigraphy and paleontology. Edited by P. J . LespCrance. Subcommission on Silurian Stratigraphy, Ordovician-Silurian Boundary Working Group, field meeting, Anticosti-Gasp6 (QuC.), 1981, pp. 257-291. NOWLAN, G. S., and BARNES, C. R. 1981. Late Ordovician conodonts from the VaurCal Formation, Anticosti Island, QuCbec. Geological Survey of Canada, Bulletin 329, pp. 1-49. PETRYK, A. A. 1979. Stratigraphie revisCe de l'fle d7Anticosti. Ministkre de 1'Cnergie et des ressources, QuCbec (QuC.), DPV-711, pp. 1-24. 1981. Stratigraphy, sedimentology and paleogeography of the Upper Ordovician - Lower Silurian of Anticosti Island, QuCbec. In Vol. 11: Stratigraphy and paleontology. Edited by P. J . LespCrance. Subcommission on Silurian Stratigraphy, Ordovician-Silurian Boundary Working Group, field meeting, Anticosti-Gasp6 (QuC.), 1981, pp. 11-39. TWENHOFEL, W. H. 1928. Geology of Anticosti Island. Geological Survey of Canada, Memoir 154.
