| Studies of recently acquired collections of Jurassic fossils from the east shore of Puale Bay, Alaska Peninsula demonstrates the presence of at least 1300 feet of Bajocian beds in that area. Of these, about 900 feet underlie the massive conglomerate that was mapped as the base of the Shelikof Formation by Capps (1922, USGS Bull. 739, p.90). At least 400 feet of Bajocian beds overlie the massive conglomerate. These conclusions are based on fossil collections made by the Richfield Oil Company in 1962 and borrowed from Stanford University at the suggestion of Norm Silberling. The fossil evidence for these conclusions is cited below under the descriptions of localities which for the Puale Bay area are listed stratigraphically from youngest to oldest. Estimates of the stratigraphic positions in feet of the Richfield Oil Company collections are calculated on the assumption that the strike is N. 40 deg. E. and the dip is 25 deg. N.W. Also, some notes supplied by Norm Silberling (see enclosed copy) provide data concerning the relative stratigraphic positions of some collections. All stratigraphic data should be rechecked. Bajocian fossils have been found at two localities above the massive conglomerate. One of these occurs in siltstone at Puale Bay about 400 feet above the massive conglomerate (ROC 1472) and contains fragments of sonninid ammonites resembling the small whorls of Sonninia and Witchellia. These genera occur at Wide Bay in the Parabigotites-bearing beds in the upper part of the Kialagvik Formation. They occur north of Cook Inlet in the upper part of the Red Glacier Formation. The presence of sonninid ammonites at ROC loc. 1472 is evidence, therefore, for an early middle Bajocian age probably corresponding in time to the Otoites sauzei zone of Europe. Also, the fact that the Callovian ammonites Cadoceras, Stenocadoceras, and Pseudocadoceras have been found at Puale Bay only several hundred feet higher in the siltstone (Mesozoic loc. 3106) is good evidence that the boundary between the Bajocian and Callovian lies in a siltstone sequence as it does at Wide Bay. Perhaps the boundary between the Bajocian and Callovian beds can be recognized by the abrupt appearance of white to yellowish brown ashy or bentonitic beds such as characterize the basal part of the Shelikof Formation near Wide Bay. The other Bajocian locality above the massive conglomerate occurs about half a mile south of the head of Alinchak Bay in pebbly sandstone (Mesozoic loc. 12390) which rests on siltstone about 400 feet thick that rests in turn on the massive conglomerate. The fossils present include 5 specimens of Inoceramus lucifer Eichwald and many other pelecypods identical with species in the Kialagvik Formation at Wide Bay. They also include a single specimen of Inoceramus ambiguous Eichwald obtained as float at the base of a sandstone cliff. This specimen indicates the presence of beds of middle Bajocian age younger than the highest part of the Kialagvik Formation at Wide Bay and at least as young as the Fitz Creek Siltstone north of Cook Inlet. Bajocian fossils have been found also at Puale Bay throughout hundreds of feet of a siltstone sequence underlying the massive conglomerate mapped as the base of the Shelikof Formation. The evidence consists of Inoceramus lucifer Eichwald. (Mesozoic loc. 21235) about 200 feet below the conglomerate, of Tmetoceras (ROC locs. 1370 and 1366) from 800-840 feet below the conglomerate, of Pseudolioceras whiteavesi (White) (ROC locs. 1356 and 1351) from 900 to 950 feet below the conglomerate, and immature specimens of Erycitoides (Kialagvikes) with Tmetoceras (ROC 1370). The lowest occurrence of Pseudolioceras whiteavesi is 320-370 feet above a middle Toarcian ammonite Haugia (Mesozoic loc. 19804) which was collected only 30 feet above the base of the siltstone sequence. In summation, near Puale Bay early Bajocian ammonites have been found from 800-950 feet below the massive conglomerate and early middle Bajocian ammonites about 400 feet above the conglomerate. Inoceramus lucifer of Bajocian age, not younger than the Otoites sauzei zone, has been found about 200 feet below the conglomerate at Puale Bay and more than 400 feet above the conglomerate near Alinchak Bay. The presence of Inoceramus ambiguus near Alinchak Bay shows that beds younger than the Otoites sauzei zone are present. Overall this evidence confirms the conclusions of W. S. Smith (1926, USGS Bull. 783, p. 67, 71) concerning the Bajocian age of some beds above the massive conglomerate. The Lower Jurassic fossil collections made by the Richfield Oil Company have not furnished any new stratigraphic data. The occurrence of a Callovian ammonite (ROC 3000) from near Alinchak Bay will be useful in drawing a boundary between Bajocian and Callovian beds. On the basis of this new evidence, I recommend that the Survey map in detail the area between Puale and Alinchak Bay at least as far west as the base of the Shelikof Formation. The entire section should be measured in detail from the Permian, or Triassic to the Callovian, should be collected carefully for megafossils, and all soft siltstone units should be sampled for microfossils. Evidently the soft siltstones above the tuffaceous sandstones of Sinemurian age do contain ammonites that are not obvious on weathered surfaces. Failure to find any ammonites of upper Sinemurian, Pliensbachian and early Toarcian ages needs investigating in order to determine whether their absence is due to faulting or to nondepostion. |