Downloaded from http://sp.lyellcollection.org/ by guest on September 29, 2021 ITEMS (x) Kap Frankl~ granlte Devonian/Devonian Kejser Franz Joseph Fjord, East Greenland [73 ° 15' N, 22 ° Io' w]. Radiometric age K-Ar (/l/~ = 4"72 × IO-l°year-1; 2e = 0"583 × Io-X°year-1) KF-XtI, t80, I82 (biotite and muscovite): K = 7-87%, a°Ar* = I "37 × xo-4cma/g, 4°Ar*/4°K = [o'o255], age: 393m.y. Age: 393 4- 12m.y. (3% error in Haller& Kulp i962); 393 4- xom.y. (Kulp I96X ). Stratigraphical age. The granite intrudes the Vilddal Series (Middle Devonian) and is uncon- formably covered by the unfossiliferous Kap Franklin Series, which itself is followed by the Randb61 Series (Middle Devonian). The granite is one of a series of'late Caledonian' intrusive rocks of which a pegmatite elsewhere (HN-7b , not stratigraphically related), was dated as 394m.y.; (adopted age = 395 -4- xom.y.). The 'main Caledonian' orogeny, based on five scattered samples of metamorphic rocks, was given as 42o to 4oom.y. The end of the main orogeny from one sample was 4o5 4- xom.y. Refgt'~e$ BOTLER, H. I954. Die stratigraphische Gleiderung der mitteldevonischen Serien im Gebiet von Kap Franklin am Kejser Franz Joseph Fjord in Zentral-Ostgr6nland. Medd. GrBnland, xx6 (7), x-122. HALtmR, J. & KUTP, J. L. x962. Absolute age determinations in East Greenland. Medd. Grenland, xTx (x), x-77. KULP, J. L, x96 x. [W. B. Harland & A. G. Smith] Stratigraphical comment. The ages of the two limiting fossiliferous formations within the Givetian are indistinguishable on vertebrate evidence. The most recent statement of the faunas was by Jarvik (x96x). The pre-intrusion Vilddal Series is probably Givetian on the evidence of Gyro- ptychius cf. grgnlandicus. The post-intrusion RandbS1 Series is Lower Givefian on the evidence of Asterolepis cf. sKves6derberghi and Coccosteus el. halmodeus; whereas cf. Thursius macrolepidotus suggests a correlation with the Wick Flagstone Group of Scotland, which WestoU (195 I) regarded as high Eifelian. R~fgrgl~g$ JnaviK, E. I96I. Greenland Devonian vertebrates. In Geology of the Arctic. (ed. Raasch, G. O.) x, I97-2o 4. Toronto. WESTOTL, T. S. I95x. The vertebrate-bearing strata of Scotland. Int. geol. Congr. x8 (2), 5-2x. P. F. Friend This determination warrants further investigation, because if the structural relationships are as described and illustrated, it shows remarkably precise stratigraphical dating of a large intrusion and may throw some light on the rate of geological processes. W. B. Harland (2) Chattanooga Shale U. Devonian]U. Devonian Young's Bend area, Tennessee, U.S.A. 269 Downloaded from http://sp.lyellcollection.org/ by guest on September 29, 2021 /terns Radiometric age ~38U-2°6Pb (no constants given) on uraniferous shale. Depth Pb* Age (ft) U(ppm) Pb(ppm) 2°4Pb/2°~Pb ~°TPb/~°6Pb ~°sPb/~°6Pb (%) (m.y.) I75-12 1124-1 i924-6 u o.7684-o. I6 I'844-o'o4 13"2 45oa+7 o I76.95 9o.64-o.9 47.4+x-o o.o39o-t-o.ooo 5 o.6224-o.oo5 1.514-o-o2 28- 7 35oa+15 I8O'OO 68"34-o- 7 31.84-o.5 o'o375-t-o'ooo5 o'6o74-o'oo6 1"464-O'Ol 3 I"4 35°a4- I2 Age: 35oa4- Iom.y. (Cobb & Kulp I96o ). Stratigraphical age. The samples came from core Yn-9 from the upper black unit of the Gassaway member of the Chattanooga shale. Because the core was taken from only a few feet below the Devonian-Mississippian boundary, Cobb & Kulp (196o) assume that the adopted figure provides a firm minimum age for the Devonian-Mississippian boundary. Clark (I96 t) has challenged this conclusion, and by comparing the conodont content of the black shale unit with that of the standard conodont zonation of Europe, he suggests that the age of the unit ranges from upper- lower Upper Devonian to lower-middle Upper Devonian. The biostratigraphic age could be more precisely defined if the stratigraphical position of the core within the black shale unit were more accurately known. References BATES, T. F. & Sa'~HL, E. O. 1957. Mineralogy, petrography and radioactivity of representative samples of Chattanooga shale. Bull. geol. Soc. Amer. 68, i3o5-14. CHOW, T. J. & McKINNEY, C. R. 1958. Mass spectrometric determination of lead in manganese nodules. Analyt. Chem. 3 o, 1499-5o 3. Ct~RK, D. L. 196I. U-Pb age determinations and Upper Devonian stratigraphy. Bull. geol. Soc. Amer. 72, 163-6. -- & BEcmm, J. H. 196o. Upper Devonian correlations in western Utah and eastern Nevada. Bull. geol. Soc. Amer. 7 x, I67I-4 . COBB, J. C. & KULP, J. L. 196o. U-Pb age of the Chattanooga shale. Bull. geol. Soc. Amer. 7 x, 223-4. H.~ss, W. H. 1956. Age and correlation of the Chattanooga shale and the Maury formation. Prof. Pap. U.S. geol. Surv. 2116. Kvr.P, J. L. I96 I. [A. G. Smith] Radiometric comment. From a detailed mineralogical and petrographical study of the Chattanooga shale, Bates & Strahl (I 957) concluded that the uranium is authigenic and was precipitated from sea-water. According to Cobb & Kulp (196o) this effectively separates the uranium from any radiogenic lead previously associated with it. Any common lead could be detrital or precipitated. The greater part of any detrital lead would have been carried by feldspar. There is about 9% (Bates & Strahl 1957) in the shale, much of which is considered authigenic. Cobb & Kulp there- fore conclude that most of the common lead was precipitated from sea-water, and they estimate its isotopic composition from that inferred for oceanic lead in late Devonian time: 2°ePb/~°4Pb = I8"3; ~°TPb/2°4Pb = I5"7; ~°sPb/2°4Pb = 38"6. This composition is obtained by extrapolating backwards in time the isotopic composition of modern oceanic lead (Chow & McKinney 1958), assuming that the average U/Pb ratio in crustal rocks has not changed significantly since the late Devonian. The large uncertainties inherent in this procedure effectively eliminate con- sideration of 2asU-2°TPb ages. The two most probable types of alteration in the black shale--bulk lead loss and/or preferential loss of 2°6Pb--are believed to be negligible, and the ~3sU-2°6Pb ages are considered reliable minimum ages of the analysed samples. [A. G. Smith] 270 Downloaded from http://sp.lyellcollection.org/ by guest on September 29, 2021 /tems Stratigraphical comment. Clark & Becker (x96o) interpret the conodont assemblage as indicating their Zone C, which is correlated with the Upper Cheiloceras or Lower Platydymenia Stufe of Europe. These are the lowest two of four Stufe comprising the Famennien. P. F. Friend (3) Bentonltes ha Grnad Gr~ve Formation Devonian]Devonian Shiphead, Cape Gasp6, Quebec, Canada [480 46' N, 64 ° x4' W]. Radiometric age K-Ar (2p = 4"76 × Io-l°year-X; ire = o'589 × Io-l°year-1; *°K]K = o.oII8 at.%) '°K (ppm) '°Ar*#°K Age (m.y.) Biotite AK-I I3 (+325 mesh) 4"oI o.o245 3764-~6 AK-I38 (--325 mesh) 3"9o o'o253 388+27 Sanidine AK-136 (--270 to +325 mesh) 6.98 o'o251 3844-19 AK-I37 (--325 mesh) 5"43 o'o253 3874- I9 AK-X20 (--I20 to +270 mesh) 9" I8 0"0258 3944-20 Mean age: 3854-x5 [4-3]m.y. Stratigraphical age. The samples came from unmetamorphosed bentonites in the lowermost xoo ft of the Shiphead (total thickness 28oft), lowest member of the Grand Gr~ve Formation (9ooft thick). The last-named has been assigned to the Lower Coblenzian Substage of the Devonian System (=Oriskany Substage). Rgferel~e$ CUMMXNO, L. M. I959. Silurian and Lower Devonian formations in the eastern part of Gasp6 Peninsula, Quebec. Mem. geol. Surv. Can. 3o4 . SMITH, D. W. G., B.~DSO~RO, H., FOLINSBE~, R. E. & LIVSON, J. i96I. K/Ar age of Lower Devonian bentonites of Gasp6, Quebec, Canada. Bull. geol. Soc. Amer. 72, I7I-4. [A. G. Smith] Radiometric comment. Quartz-feldspar aggregates and mixed-layer clays were also dated, and gave 34---m.y. and 325 m.y. respectively. The authors have not included these in the mean age. A. G. Smith (4) Hecla Hoek mlca-schlsts Devonian/Ordovician Raudfjorden, Spitsbergen [79 ° 47' N, I2 ° E]. Radiometric age (I) K-Ar (2p = 4.72 × IO-l°year-1; ;te = 0-584 × Io-10year -1) K20 (%) 4°At (mm3/g) atm. 4°At (?) 4°Ar*/4°K Age (m.y.) Biotite n-829 6.07 o. 0899 3" 6 [o. 0252] 389± I4 ~--275 5 "65 o "0935 I4"8 [0"0249] 3844 - I3 ~-686 9"42 o. I576 5"6 [o'o278] 4254- 22 Mean age: 399 [+ 13] m.y. 271 Downloaded from http://sp.lyellcollection.org/ by guest on September 29, 2021 /tems (2) Rb-Sr (2 = x.47 × IO-11Year-x) Age (m.y.) Rb (ppm) Sr (ppm) STSr*(ppm) 8~Sr*/S~Rb 2 = z "39 2 = z "47 Biotite H-828 515 25" 8 o. 82 [o" oo562] [404] 382 4- 8 E-276B 54 x 7" z 0"86 [0"00561] [403] 379-4-6 ~-276B 542 7" 3 o" 86 [o" oo56o ] [4o2] 38o 4- 6 E-276B 54 x 8"8 O'85 [O'OO555] [398] 3754-6 Mean age: [4o2+x]m.y. (2 = x-39); [379 4- x]m.y. (2 = z'47 ). Adopted age using both methods: 383 4- xo m.y. (Hamilton, Harland & Miller I962). Stratigraphical age. The samples analysed came from schists correlated with the lower Hecla Hock rocks, unconformably overlain by unmetamorphosed Red Bay Conglomerates; 3oom above the unconformity there is a fish fauna.