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A distillation test was made according to the oil-shale distillation method used by the Bureau of Mines for determining the yield of crude shale oil. The total time required for the distillation was one and one-half hours; rate of oil distillation, 0.5 cubic centimeter a minute.
Upon comparison with other crude oils that were obtained from typical oil shales by the Bureau of Mines distillation apparatus, using a similar distillation rate, the crude oil obtained from the sample of shale from Trout Creek may be described as high in gravity and low in setting point. In these respects it is more nearly like the crude oil obtained from the Kentucky oil shale.
The chemical composition of oil shales has not yet been sufficiently investi. gated to compare them with typical petroleums, such as paraffin-base petroleum, which is low in specific gravity and high in content of paraffin series hydrocarbons; or a naphthene-base petroleum, which is largely composed of naphthene series and other cyclic hydrocarbons; or a mixed-base petroleum, which is intermediate in gravity and composition between paraffin-base and naphthene-base petroleums. The high gravity of the crude oil obtained from the shale of Trout Creek favors its commercial use for the production of lubricating oils. The low setting point indicates the absence of commercial quantities of paraffin.
Oil shale is also known at other places in Alaska. A shale phenomenally high in its content of oil has recently been found in the valley of the Christian River, about 75 miles north of Fort Yukon. This shale contains 122 gallons of oil to the ton of rock and is therefore of higher grade than any oil shale so far found in the United States. Another bituminous deposit, first noted by Ensign (now Rear Admiral, retired) W. L. Howard in his traverse down the Etivluk River, northwestern Alaska, in 1886, has recently been revisited by P. S. Smith 81 This material has now been determined by David White, of the United States Geological Survey, as tasmanite. Similar material was also found by Smith on the Kivalina and Meade Rivers, in northwestern Alaska.
STRUCTURE AND THICKNESS
On account of the softness of this Upper Triassic shale and limestone the rocks of this formation crumble when exposed to the
80 Karrick, L. C., A convenient and reliable retort for assaying oil shales for oil yield: Bur. Mines Rept. 2229, 1921.
Smith, P. S., and Mertie, J. B., jr., Geology and geography of northwestern Alaska: U. S. Geol. Survey Bull. 815, p. 283, 1930.
atmosphere and are quickly eroded away. In addition the incompetency of these soft beds has rendered them particularly subject to deformation. The resulting poor exposures and accentuated folding make it difficult to obtain any satisfactory idea of the structure. The generalized section shown in Figure 6 conveys the writer's impression that these rocks are welded into a mass of small folds with a general northwesterly dip. A narrow covered zone separates the lowest of the Upper Triassic rocks from the uppermost Permian beds, but the two formations appear at least to agree in strike and dip. Little doubt can exist, however, that the contact between the two formations represents a great hiatus in sedimentation that corresponds geologically to Middle and Lower Triassic time and probably also to upper Permian time.
The top of the Upper Triassic sequence is not exposed, and therefore the total thickness of the formation can not be given. Martin, who examined these rocks in 1914, estimated that at least 400 feet of strata are exposed along the beach opposite the mouth of the Nation River. Blackwelder, in 1915, noted that the visible exposures indicated a thickness of 575 feet and possibly several times as much. The section given in Figure 6, though in part idealized, is plotted by the writer from the observed strike and dip and indicates that Martin's estimate is about correct, as nearly as may be judged from the available exposures.
AGE AND CORRELATION
Twenty fossil collections have been made from these Upper Triassic rocks, mostly from the Nation River locality. This fauna has been assembled by the writer in the table given below. T. W. Stanton, of the United States National Museum, has identified all this material.
82 Martin, G. C., Triassic rocks of Alaska: Geol. Soc. America Bull., vol 27, pp. 701-702, 1916. 68 Blackwelder, Eliot, unpublished notes.
Fossils from Upper Triassic rocks along Yukon River near mouth of Nation River
4054. Yukon River a quarter of a mile northeast of mouth of Nation River. Collector, E. M. Kindle.
8895. Yukon River, southwest bank about 1 mile above Nation River. From a 10-foot bed of dark noncrystalline limestone, which is probably not more than 50 feet above the crystalline Permian limestone. Collector, G. C. Martin.
8896, 8897, 8898, and 8899. Yukon River, southwest bank about 1 mile above Nation River. 8896 is about 31 feet stratigraphically above 8895. 8897 is about 10 feet stratigraphically above 8896. 8898 is from float along river bank between localities 8897 and 8899. 8899 is about 300 feet stratigraphically above 8897. Collector, G. C. Martin.
10266 and 10267. Trout Creek about 3 miles from confluence with Yukon River. Collector, G. C. Martin.
9382. Yukon River, southwest bank southwest of Nation River. Collector, Eliot Blackwelder.
9383. Yukon River, southwest bank about 2 miles above Nation. Collector, Eliot Blackwelder.
9384. Yukon River, southwest bank opposite Nation River. Collector, Eliot Blackwelder.
9385, 9387, and 9388. Hillside one-third of a mile northeast of mouth of Nation River. Collector, Eliot Blackwelder.
9321. Trout Creek about 3 miles from confluence with Yukon River. Collector, P. J. Hilliard, of Eagle, Alaska.
13423, 13425, 13426, and 13427. Yukon River, southwest bank 21⁄2 miles upstream from Nation. The relative positions of these four collections are given in the stratigraphic section on page 131. Collector, J. B. Mertie, jr.
13424. Southeast side of valley of Nation River near Yukon River. Collector, J. B. Mertie, jr.
The Triassic rocks of Alaska have been described in detail by Martin, and it is unnecessary to include here a faunal and lithologic correlation of the Upper Triassic rocks of the Yukon with the other Triassic rocks. Upper Triassic rocks are known at many localities in Alaska, of which Martin lists the Nizina Valley, Kotsina and Kuskulana Valleys, Cooper Pass, upper Susitna Valley, Kenai Peninsula, west coast of Cook Inlet, Iliamna Lake, Alaska Peninsula, Kodiak Island, Admiralty Island, Kupreanof Island, Gravina Island, Firth River, Canning River, Noatak Valley, Cape Lisburne, and Cape Thompson. To these should be added the numerous areas of Upper Triassic rocks recently discovered in northwestern Alaska, which, together with those at Cape Lisburne and on the Canning and Firth Rivers, in northeastern Alaska, indicate that a continuous Upper Triassic belt crosses northern Alaska from the Arctic Ocean to the international boundary. These Arctic Upper Triassic rocks differ lithologically, however, from those found along the Yukon in that they include a considerable amount of chert.
The rocks at the base of the Upper Triassic sequence at the Nation River contain certain genera of ammonites, such as Placites, Popanoceras, Trachyceras, Clionites, Monophyllites, and Nathorstites, which do not occur in the higher beds. These are accepted by Stanton as an integral part of the Upper Triassic fauna but are believed to represent a lower faunal horizon than the fossils found in the higher strata.
No Lower Triassic rocks have ever been found in Alaska; nor is the Middle Triassic represented, except possibly at one questionable locality at Brooks Mountain, in Seward Peninsula. In this connection, it should again be emphasized that the Tahkandit limestone, as well as the other Permian rocks in Alaska, represent only the lower part of the Permian sequence. Nevertheless, Upper Triassic rocks, wherever found in Alaska, appear to lie upon Permian, Pennsylvanian, or Mississippian rocks, without any angular discordance of bedding. It is believed that a gradual uplift of Alaska began in late Carboniferous time and culminated perhaps in the early Triassic, followed by submergence again in Upper Triassic time. The lack of any apparent angular unconformity between the Permian and Upper
4 Martin, G. C., Triassic rocks of Alaska: Geol. Soc. America Bull., vol. 27, 1916. Smith, P. S., and Mertie, J. B., fr., Geology and geography of northwestern Alaska: U. S. Geol. Survey Bull. 815, pp. 185-194, 1930.
Triassic rocks leads to the belief that this uplift was of the plateauforming type and was accompanied in Alaska by a minimum of warping and rock deformation; if any deformation took place it affected only the older, pre-Carboniferous rocks, which were more deeply buried. As this plateau-forming uplift in Carboniferous to Triassic time was not worldwide in extent, it follows that in areas adjacent to Alaska there must be a hinge zone, where this time interval will be found to be represented by deformed strata. Hence the postulate of an unconformity involving little or no rock deformation is intended to apply only to Alaska. It is believed that the deformation of the Carboniferous, Permian, and Triassic rocks, which resulted in the folding and faulting of these rocks, took place in one or more stages in post-Triassic time.
CRETACEOUS AND TERTIARY SYSTEMS
Jurassic rocks, though present in great thickness in southern Alaska and on the Alaska Peninsula, are unknown in the interior of Alaska and are very sparingly developed, if at all, in Arctic Alaska. The system next above the Upper Triassic in the Yukon region, therefore, is the Cretaceous. Two series of Cretaceous rocks have been differentiated in the upper Yukon Valley, of which the older is a well-developed Lower Cretaceous series. The younger is an Upper Cretaceous series, but as these rocks apparently grade upward lithologically into Eocene rocks in such a manner that it has not been possible to draw a line between the two series, they are herein mapped together and described under the heading Upper Cretaceous and Eocene series.
LOWER CRETACEOUS SERIES
The Lower Cretaceous rocks in this area occur mainly at two localities which will probably later be found to form parts of one continuous belt. Along the Yukon these rocks crop out about 10 miles below the Nation River and continue on both sides of the Yukon downstream to Coal Creek, thence thinning to a narrow band which continues northwestward to Woodchopper Creek and for some undetermined distance farther. (See pl. 11, B.) The other area is along the international boundary from the neighborhood of Sitdown Creek northward for at least 25 miles. This area, which was mapped by Cairnes, was not differentiated by him as Lower Cretaceous nor in fact as exclusively Cretaceous; his cartographic designation was "Cretaceous and Upper Carboniferous." The inclusion of "Upper