Conodonts and associated graptolites from the late Early Devonian of east-central Alaska and western Yukon Territory. NORMAN M. SAVAGE. University of ...
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Fig. 2 is replaced by white o r any colour. This was confirmed quantitatively using the indirect experimental test of the preceding paragraph. In conclusion, I recommend that maps b e colour coded in spectral order, with red representing the highest values of the mapped data. (Nonspectral colours such as purple are to b e avoided.) Either black contours should separate the colours o r black dots (fine and sparse enough to be barely noticeable) should b e printed over the colours. (Alternatively, the observer can superimpose a transparent overlay of black dots.) Viewing through a large magnifying glass will then provide effortless perception of the map's implied third dimension. Psychologically, these recommendations are desirable even if a magnifying glass is not used, since the slight colour stereoscopy visible to unaided eyes in high illumination (Sundet 1976) should then be in spectral order.
Acknowledgments This study was assisted by a grant from the Natural Sciences and Engineering Research Council of Canada and was completed while the author was on sabbatical leave. I thank C. E. Hodych and E. R. W. Neale for reading earlier versions of this paper. ARVIDSON, R. E., BINDSCHADLER, D., BOWRING, S., EDDY,M., GUINESS,E., and LEFF, C. 1984. A Bouguer anomaly image for
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North America. Nature (London), 311, No. 5983, front cover. F. C. 1975. In Manual of remote sensing. Vol. 1. BILLINGSLEY, Edited by F. J. Janza. American Society of Photogrammetry, Falls Church, VA, p. 755. EINTHOVEN, W. 1893. On the production of shadow and perspective effects by difference of colour. Brain, 16, pp. 191-202. GRAY,D. E., editor. 1972. American Institute of Physics handbook. McGraw-Hill, New York, NY. H. VON 1910. Helmholtz's treatise on physiological HELMHOLTZ, optics. Vol. 3. Edited by J. P. C. Southall in 1926. Reprinted in 1962. Dover, New York, NY, p. 307. KAUFMAN, L. 1979. Perception. Oxford University Press, New York, NY, p. 211. KISHTO,B. N. 1965. The colour stereoscopic effect. Vision Research, 5, pp. 313-329. OKOSHI,T. 1976. Three-dimensional imaging techniques. Academic Press, New York, NY, p. 52. SUNDET, J. M. 1976. Two theories of colour stereoscopy-an experimental investigation. Vision Research, 16, pp. 469-472. VERHOEFF, F. H. 1928. An optical illusion due to chromatic aberration. American Joumal of Ophthalmology, 11, pp. 898 -900. Vos, J. J. 1960. Some new aspects of colour stereoscopy. Journal of the Optical Society of America, 50, pp. 785-790. R. T., WILLIAMS, H., and DANIELS, D. L. 1980. ZIETZ,I., HAWORTH, Magnetic anomaly map of the Appalachian orogen. Earth Sciences Department, Memorial University of Newfoundland, St. John's, ~ f l d . Map , No. 2a
Conodonts and associated graptolites from the late Early Devonian of east-central Alaska and western Yukon Territory NORMANM. SAVAGE University of Oregon, Eugene, OR 97403, U.S.A. ROBERTB. BLODGETT Oregon Slate University, Corvallis, OR 97331, U.S.A AND
HERMANN JAEGER Palaontologisches Museum, Invalidenstrasse 43, 1040 Berlin, D.D.R. Received May 3, 1985 Revision accepted July 9, 1985 Samples from two closely placed localities in western Yukon Territory have yielded late Early Devonian conodonts characteristic of areas farther to the north and east in Alaska and Yukon Territory and also characteristic of central and northern Siberia. Conodonts from a nearby locality in east-central Alaska indicate an age that makes the associated graptolites of considerable interest: they are among the youngest graptolites known in North America. Des Cchantillons provenant de deux localitts rapprochkes dans le Territoire du Yukon occidental ont foumi des conodontes d'Lge du DCvonien infkrieur caracttristiques des regions situkes plus au nord et a I'est en Alaska et dans le Territoire du Yukon et Cgalement caracteristiques du centre et du nord de la SibCrie. Les conodontes d'une localit6 tout proche dans le centre-est de 1'Alaska indiquent u n bge qui rend les graptolites associCs fort intkressants car ils sont parmi les plus jeunes graptolites connus en Amerique du Nord. [Traduit par le journal] Can. 1. Earth
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Late Early Devonian samples from localities 1 and 2 (Fig. la-c) in western Yukon Territory, 2.7 km east of the Alaska border, have yielded conodonts characteristic of areas farther north and east in Alaska and Yukon Territory and of central and northern Siberia. Locality 1 (65"02'55"N, 140°56'33"W) is 4.6-6.1 m above the base of a 38 m section of lime mudstone, wackstone, and crinoidal limestone of the Ogilvie Formation exposed on a ridge between tributaries of Harrington Creek and the Tatonduk River (Fig. Ic). The 4.6-6.1 m interval is located on the southwest side of a small hill on the ridge at an elevation of 1040 m. Samples from this locality have yielded 11 conodonts including nine specimens of Icriodus taimyricus Kuzmin, 1967 and one of Polygnathus dehiscens Philip and Jackson, 1967, indicating a late Pragian to early Zlichovian age within the P . dehiscens Zone. Locality 2 (65"02'57"N, 140°56'38"W) is 150 m northwest of locality 1 and consists of a small rubble exposure on the northwest side of the hill at an elevation of 1020 m (Fig. 1 c ) . It has yielded 12 conodonts including one specimen of Icriodus taimyricus and four of Pandorinellina exigua philipi (Klapper, 1969), also sugges1:ing the P . dihiscens Zone. Icriodus taimyricus was recorded from this zone in the Salmontrout Limestone of eastcentral Alaska (Lane 1974; Lane and Ormiston 1979) at a locality about 190 km farther north, near the confluence of the Salmon1:rout and Porcupine rivers, and is also known from the Michellle Formation, Yukon Territory, (Fihrzus 1971, P1. 78, figs.. 3-5) at a locality about 250 km east of our locality 1. The species is known is Asia from the type area of the Taymyr Peninsula (Kuzmin 1967), from the Zeravshan Range (Mashkova and Apekina 1980), and from Novaya Zemlya (Klapper and Johnson 1980). Locality 3 (65'01 ' 16"N, 14 1'1 2'46"W) is in east-central Alaska, 13.0 km southwest of localities 1 and 2 and 10.1 km west of the Yukon border on the north bank of the Tatonduk River (Fig. 1 a , b, d ) . Here graptolitic shales and interbeds of limestone debris of the limestone and shale member of the McCann Hill Chert dip to the west at about 60" in an exposure 23.0 m thick. We have recovered a total of 251 specimens of the conodorit Eognathodus sulcatus kindlei Lane and Ormiston, 1979, from the limestone interbeds at 4.3, 4.9, 5.6, 8.5, 8.7, 9.8, 10.1, 13.8, 16.6, 17.1, and 18.7 m, and five specimens of the conodont Polygnathus pireneae Boersma, 1974, at 18.7 m. This suggests the middle to late Pragian age E. kindlei Zone for the beds between 4.3 and 18.7 m above the section base. We have recovered graptolites from the 8.2, 11.5, 15.2, and 19.2 nn horizones. Our graptolites from 8.2 m include Monograptus yukonensis cf. fangensis Jaeger and Stein, 1969, those from 11.5 m include a form close to Monograptus craigensis Jaeger, 1970, those from 15.2 m include a possible new form approaching both Monograptus craigensis and Monograptus pacificus Jaeger, 1970, and those from 19.2 m include a possible new form resembling Monograptus telleri Lenz and Jackson, 1971. The Tatonduk River graptolites appear to be a little more advanced than the graptolites from the Port St. Nicholas section, southeastern Alaska, described by Jaeger (1970) and discussed by Churkin et al. (1970). In both areas the graptolites occur above limestone yielding Eognathodus sulcatus kindlei (Savage, Churkin, and Eberlein, 1977, PI. 2, figs. 19-22), but in the Tatonduk River section the uppermost graptolites occur above Polygnathus pireneae, a species that in the Salmontrout River sections appears in the upper part of the range of Eognathodus kindlei and extends well into the range of Polygnathus dehiscens. Lane and Orrniston (1979) have
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FIG. 1 . Map of east-central Alaska and western Yukon Territory with insets showing sample localities 1 , 2 , and 3.
used these occurrences to support the insertion of a P . pireneae Zone between the E. kindlei Zone and the P . dehiscens Zone in the Salmontrout River section. Our discovery of our highest level of graptolites above the appearance of P . pireneae is of considerable interest and indicates an horizon high in the Pragian. This may be the highest known occurrence of graptolites in North America, although a close contender is the occurrence of Monograptus yukonensis immediately below the limestone exposed at 987 ft (300.8 m) in section 1 at Royal Creek, Yukon Territory (Lenz 1967). In the Royal Creek section, the graptolites are above the last occurrence of Eognathodus kindlei but about 48 ft (14.6 m) below the first occurrence of Polygnathus dehiscens (Lenz 1967, p. 596; Klapper 1969, Table 1). The presence of E. kindlei Zone conodonts in the basal limestone and shale member of the McCann Hill Chert strongly suggests a mid-Pragian age for the base of this member, rather than the Emsian age indicated by earlier workers (Blodgett 1978; Clough and Blodgett 1984). Five Pa elements of Polygnathus pireneae (Pl. 1, figs. 2 1- 26) have been recovered from the 1 8.7 m horizon at locality 3. These are mature specimens, characterized by well developed lateral platform margins and a very high anterior edge to the blade, like that of the figured paratype of Boersma (1974, P1. 2, fig. 8). The nodes of the platform margins of some specimens may extend toward the carina as ridges (PI. 1, fig. 21), and the carina nodes may be fused along the anterior and middle part of its length (Pl. 1, fig. 26). The anterior part of the platform tapers to join the blade, which is about one third the length of the element and bears only three or four large denticles. The basal cavity extends the full length of the lower surface but has a pronounced and rounded expansion at about the midpoint (Pl. I, fig. 24).
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There are no small, immature specimens in the collection that would throw light on the possible conspecific relationship of Polygnathus boucoti Savage, 1977 to Polygnathuspireneae, discussed by Lane and Ormiston (1979) and Murphy and Matti (1982). The 14 specimens from northern California that Savage (1977) used to describe P . boucoti d o not include any with a platform, a high anterior margin to the blade, o r a midlength expansion to the basal cavity; nor are any specimens present in that collection that resemble the holotype of P . pireneae. Although it is possible that the ontogenetic development of P. pireneae ranges from platformless elements with relatively low anterior denticles, such as those described as P . boucoti, to elements with a full platform and a high anterior margin, such as those described herein, this ontogenetic range has yet to be demonstrated. BLODGET~, R. B. 1978. Biostratigraphy of the Ogilvie Formation and limestone and shale member of the McCann Hill Chert (Devonian), east-central Alaska and adjacent Yukon Territory. M.S. thesis, University of Alaska, Fairbanks, AK, 141 p. BOERSMA, I
