Sample: |
Sample No. F-45 of MacKevett, 1961 -- USGS No. Mesozoic loc. 28540
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Locality: |
Field No. F-45 of MacKevett, 1961
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Description: |
Latitude 61o 32'18" ; Longitude 142o 41'48". Float ca 400' below Weyla ls. (description from transmittal sheet of D.L. Jones appended to Imlay E&R report of 11/9/61) [E.M. MacKevett, 1961. NW1/4SW1/4NE1/4 sec. 9, T. 4 S., R. 15 E., McCarthy (C-5) quadrangle. Wrangell Mountains, southern Alaska. Float collected about 400 ft (122 m) below top of upper member of McCarthy Formation. Early Pliensbachian. (from Imlay, 1981, p. 25)]; [Many localities in upper member of McCarthy Formation, in McCarthy C-4, C-5, and B-4, quadrangles, Wrangell Mountains, eastern Alaska (MacKevett, 1970a, b, 1971). Ammonites include Arietites (loc. 29870), Arnioceras (locs. 28535, 28536, 28538, 28688), Crucilobiceras (loc. 28537, 28540, 28671-73), and Microderoceras (loc. 14472). (description from Imlay and Detterman, 1973, p. 22)]; [USGS Mes. Cat.: Lower Jurassic. McCarthy C-5 Quadrangle. Orig. No. F45. Lat. 61 degs. 32 min. 18 sec.; Long. 142 degs. 41 min. 48 sec. About 400 ft. below Weyla ls. (float). Collector: E.M. MacKevett, 7/61] |
Location: |
Alaska Quadrangle: Mc Carthy C-5 Township&Range: T4S R15E Section: NW1/4SW1/4NE1/4 sec. 9 Lat.: 61o32'18 " Long.: 142o41'48 " |
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Reference
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Title: |
Report on Referred Fossils
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1961
(11/09)
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The Jurassic beds in the McCarthy area of the Chitina Valley represents at least the lower part of the Lower Jurassic, the Bathonian or basal part of the Callovian stages, and the upper Oxfordian and Kimmeridgian stages. The Lower Jurassic fossils are in general rather poorly preserved. Many of the identifications are querried and hence have little value in determining the exact age within the Lower Jurassic. Thus collections F-3A and F-45 contain ammonites resembling Wahneroceras which, if correctly identified, are good evidence for a Hettangian age. However, the specimens do not show certain critical features necessary for the identication of the genus. In contrast the Sinemurian stage of the Lower Jurassic is represented by Arnioceras (locs. F-4 and F-35) which in northwest Europe ranges through the lower and midle parts of the stage. The ammonites Crucilobiceras (Loc. F-1) and Microderoceras (Mes. loc. 14472) could be either uppermost Sinemurian or lower Pliensbachian. In addition the pelecypod "Entolium" semiplicatum (Hyatt) is probably indicative of a Sinemurian age as it occurs in abundance with ammonites of that age in eastern Oregon and locally in the Sierra Nevada (Sailors Canyon Formation). The Weyla-bearing limestone has furnished no fossils of age value other than Weyla itself, which genus is known only from the Lower Jurassic. I understand that Si Muller has examined the Weylas from the McCarthy area and identified some of them with a species that occurs in Nevada and Oregon in beds of late Pliensbachian to Toarcian age. Most of the collections from the Jurassic shale above the Weyla-bearing limestone contain species of Buchia of late Oxfordian and Kimmeridgian age. These include Buchia concentrica (Sowerby) (locs. F-17, F-19, F-34, F-50, 61-ABC-26, Mes. loc. 14495 and 14496), B. rugosa (Fischer) at many localities, and B. mosquensis (von Buch) at a few localities. Of these species, B. concentrica (Sowerby) is of late Oxfordian to early Kimmeridgian age (see Prof. Paper 314-G, p. 159, 165). Near the top of its range elsewhere in Alaska it is associated with B. rugosa (Fischer) and less commonly with B. mosquensis (von Buch), both of which range higher into beds of probably Portlandian age. The ammonite Prionodoceras (locs. 61-ABC-27, 61-ABC-36, 14495, 14496 and 14497) in the Boreal region is of late Oxfordian to early Kimmeridgian age and is commonly associated with Buchia concentrica (Sowerby). I suspect that it was collected lower than B. rugosa (Fischer), but I would be much interested in knowing your conclusions concerning the stratigraphic positions and ranges of these fossils in the McCarthy area. Three of the collections (locs. 61-60, F-28, 61-ABC19) from the shale above the Weyla-bearing limestone are of considerable interest because they contain genera of ammonites that have been found in the Cook Inlet area in the middle part of the Bowser member of the Tuxedni formation and in the lower part of the Chinitna formation. In my paper dealing with the Callovian ammonites from Alaska (Prof. Paper 249-B) I referred the ammonites in question to Procerites? (pl. 54) and Reineckeia (pl. 55). As your collections do not contain any of the ammonites, such as Cadoceras and Kepplerites, that are common in the Chinitna formation, I suspect that the collections represent older beds equivalent to some part of the Bowser member. In any case their age is either Bathonian, or early Callovian and they are distinctly older than the beds containing Buchia. We still lack descriptions of localities F-6, F-50 and 61-19. When these arrive, Mesozoic numbers will be assigned to the collections and a list sent to you. Also, sometime we would like to have a quadrangle map, or maps, showing the exact occurrences of the fossil localities. Any stratigraphic information that you can furnish relating to the localities to the tops or bottoms of formation, or to marker beds, will be nice to have in our record books. |
Report by: |
Ralph W. Imlay
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Referred by: |
David L. Jones
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E. M. MacKevett
, Jr.
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| Age: | Hettangian (Hettangian?) |
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Comment: | Cited in E&R report as being from "Lower Jurassic localities below the Weyla bearing limestone." Thus collections F-3A and F-45 contain ammonites resembling Wahneroceras which, if correctly identified, are good evidence for a Hettangian age. |
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Title: |
Jurassic Paleobiogeography of Alaska
,
1973
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ABSTRACT: Jurassic marginal seas occupied considerable areas in southern and northern Alaska and in the western part of the Kuskokwim region of southwestern Alaska. They appear to have been absent during late Callovian time, much restricted during Hettangian, Bathonian, early Oxfordian and late Tithonian time, and most extensive during Sinemurian, Bajocian, and late Oxfordian to middle Tithonian time. A large area in central Alaska was probably never covered. A southwestern prolongation of that area from the Talkeetna Mountains westward to the western end of the Alaska Penin- sula was the site of granitic intrusions during late Early Jurassic time and of extensive erosion during Middle and Late Jurassic time. Variations in the rate of uplift of the area of these granitic intrusive rocks may explain why marine transgressions and regressions were at different times in southern than in northern Alaska during the Bajocian and Bathonian. Connection of the northern and southern marginal seas occurred through Yukon Territory and eastern- most Alaska. The Jurassic ammonite succession in Alaska is similar to that in central and northern Europe and northern Asia. In Lower Jurassic beds, it is essentially identical. In Bajocian and in Oxfordian to lower Kimmeridgian beds, the ammonite succession in Alaska differs from that in the other areas mainly by the presence of some genera found only in areas bordering the Pacific Ocean and by the absence of a few genera common in central and northern Europe. In con- trast, the Bathonian rocks of Alaska contain ammonites, such as Arcticoceras, Arctocephalites, and Cranocephalites, that are widespread in the Arctic region but are unknown in central Europe. Comparisons with the Tithonian of Europe are not possible because ammonites of that age, other than Lytoceras and Phylloceras, are not yet known from Alaska. The Alaskan Jurassic ammonites of late Pliensbachian Age and of Bathonian to early Kimmeridgian Age belong mostly to the Boreal realm and have very little in common with Tethyan realm ammonites such as those found in areas bordering the Mediterranean Sea. |
Report by: |
Ralph W. Imlay
,
Robert L. Detterman
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| Age: | Sinemurian |
Formation: | McCarthy Formation (McCarthy Formation (upper member)) |
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Comment: | Age: Sinemurian upper member of McCarthy Formation Generalized location shown as locality 8 in figure 2 |
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