Reference Detail of

Report on Referred Fossils
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Stratigraphic range: Late Jurassic & Late Cretaceous
Kinds of fossils: Mollusks
Quadrangle or area: Russian Mission, Kuskokwim area
Shipment No.: A-58-12
Referred by: Hoare, Joseph M.
Report prepared by: Imlay, Ralph W.
Date: 12/19/1958


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Brief statement of problem and remarks (from collector):
Problem is to date a large belt of interbedded volcanic and sedimentary rocks. The rocks previously been mapped as Paleozoic (PP 192). Between 1946 and 1948, I got 4 collections of fossils from this belt. Three of those collections (21033, 21029, 21481) were identified as being of Cretaceous age. One collection (#20714) is Upper Jurassic. The Jurassic fossils come from rocks which would well underlie or be in fault contact with the Cretaceous volcanics and I mapped the Jurassic rocks as a window surrounded by Cretaceous rocks. This summer (1958) R.A. Jennings of Amerada Petroleum Co., found fossils at 4 other places in the belt of volcanic rocks. One collection (F-1) consists of Inoceramus which appear identical to Inoceramus previously reported to be of Upper Cretaceous age. Dave Jones has looked at this new collection and says he thinks that the fossils are Jurassic age. They resemble Inoceramus which Grantz says are Jurassic. If they are Jurassic, then most of the volcanic rocks are probably Lower Cretaceous--like the volcanic rocks found by Patton in the Koyukuk Basin.
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58AMER-F1 , Russian Mission , Collection was made from a graywacke unit which either lies upon or is interbedded with the surrounding volcanic rocks which have been assinged an Upper Cretaceous age on the basis of other fossils age determination. Location determined on Russian Mission Quadrangle, 1:250,000, 1950; 12.7 miles S 59 W from confluence of Buckstock and Aniak Rivers and 6.8 miles N 55 E of Mt. Hamilton. On crest of low ridge that lies approximately two miles east of and parallel to Discovery Creek. Fossils occur in fine-grained, platy graywacke which dips 30 degrees north. Graywacke with thin interbeds of dark-gray siltstone crops out for three miles to the north and one mile to the south. Collected August 27, 1958 by R.A. Jennings and L.H. Roth of Amerada Pet. Co. (description from transmittal sheet)
Inoceramus
58AMER-F2 , Unknown
Buchia rugosa (Fischer)
Buchia mosquensis (Von Buch)
58AMER-F3 , Russian Mission , Collection was from a thin siltstone bed interbedded with volcanic rock that has been assigned an Upper Cretaceous age. Location determined on Russian Mission Quadrangle, 1:250,000, 1950; 3500' S 59 E from confluence of Tuluksak River and California Creek and 12.3 miles S 32 W from Mt. Hamilton. On side of hill about 2000 feet east ("west" originally written here, crossed out by J.M. Hoare) of Tuluksak River and 1000 feet above it. Fossils are in medium-gray siltstone which occurs within section of quartzite and argillite. these sediments are interbedded with volcanic rocks and dip southwestward about 50 degrees. Collected September 5, 1958 by R.A. Jennings and L.H. Roth of Amerada Petroleum Corpoation (description from transmittal sheet)
small, hump-shaped Inoceramus similar to ....
Inoceramus corpulentus McLearn, .....
or to immature forms of Inoceramus yabei Nagao and Matsumoto ......
and also to Inoceramus uwajimensis Yehara
58AMER-F4 , Russian Mission , Collection made from quartzitic sandstone interbedded with volcanics assigned an Upper Cretaceous age. Location determined on Russian Mission Quadrangle, 1:250,000, 1950; 4,000 feet due south from confluence of California Creek and the Tuluksak River and 12.9 miles S 33 W from Mt. Hamilton. In old road cut along west side of Tuluksak River. Fossils occur in bluish or greenish-gray sandstone which dips 55 degrees to the southwest. The rocks are very sparsely fossiliferous. The outcrops is about 200 yards in length and is bounded on either side by volcanic rocks. Collected September 5, 1958 by R.A. Jennings and L.H. Roth of Amerada Petroleum Corporation. (description from transmittal form)
larger specimens of Inoceramus having the same general characteristics as those at 58AMER-F3