Arkell.1956.Jurassic..

ARCTIC SLOPE 529
was refigured by Neumayr (1885, pp. 38, 141, pi. i, figs. 5-8) who assigned
it to Harpoceras. From the figures it appears to be a Toarcian Harpoceratid,
perhaps a Pseudolioceras (though evolute for the genus).
During 1954 Dr E. T. Tozer of the Geological Survey of Canada
measured sections on the island and collected ammonites which are being
studied by Dr H. Frebold at Ottawa. He has kindly sent me a copy of
his MS. preliminary report (Dec. 1954), from which he allows me to
quote the discovery of ammonite faunas belonging to three stages: Toarcian
(with Dactylioceras cf. commune and 'Harpoceras' m'clintocki), basal Lower
Bajocian (with Leioceras opalinum), and Lower Callovian (with Arctocephalites
(Cranocephalites) cf. vulgaris. There is also another Callovian
horizon with a new genus. According to Dr Tozer these beds are
followed by a non-marine series which is probably still Jurassic, and this is
overlain with local unconformity by a further marine sequence containing
Buchia spp.
The beds are unfolded and belong to an epicontinental series fringing
the Arctic Ocean (Fortier & others, 1954) (Plate 25).
THE ARCTIC SLOPE OF YUKON AND ALASKA
From the mouths of the Mackenzie River for about 700 miles westward,
to the entrance to Bering Straits, stretches the Arctic slope or coastal
plain. Bounded on the south by the Palaeozoic Brooks Range, it is a
low-lyingj bleak waste of permanently-frozen Mesozoic sediments, mainly
Cretaceous, intersected by frozen rivers and ending at a low coast which is
sometimes overridden by sea ice. (Fig. 85, p. 537.)
On the Firth River, 35 miles on the Canadian side of the international
boundary, strongly folded and semi-metamorphosed Jurassic rocks have
. yielded an ammonite assemblage of the Calloviense Zone, with six species
of Cadoceras and Pseudocadoceras, mainly of Russian and Franz Josef
Land species (Buckman in O'Neill, 1924, p. 14A). It is possible that
Jurassic rocks spread out under the delta of the Mackenzie River, where
'undifferentiated Mesozoics' are shown on the Canadian Survey map,
but the only evidence so far is of Trias and Lower Cretaceous.
On the Alaskan side of the boundary, in the Canning River district,
the Kingak Shale (1500 m. or more) has yielded a number of ammonite
faunas ranging from Upper Pliensbachian to Upper Oxfordian, and its
higher parts may include Kimeridgian and Portlandian, to judge by
species of Buchia (Martin, 1926, pp. 262-4; Inilay, 1952, pp. 982-3).
The exposed river sections have been supplemented by borings farther
west, in the Barrow area, which produced additional horizons down to
Lower Sinemurian. The faunas recorded by Imlay may be tabulated as
follows:—
LOWER PORTLANDIAN ? AND KIMERIDGIAN
Upper Kingak Shale with Buchia mosquensis, B. rugosa, B. bronni.
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