| Summary: | QE75 .P9 no. 647-B I 19.16:647-B 95 Series: Jurassic (Tithonian) and Cretaceous Buchia zones in northwestern California and southwestern Oregon; Geological Survey professional paper: 647-B.; Includes ill. and maps.; Includes bibliographical references. "Ammonites from the Buchia-bearing strata of northwestern California and southwestern Oregon represent the Tithonian stage at the top of the Jurassic and the Berriasian and Valanginian stages at the base of the Cretaceous. These ammonites are associated with various species of the pelecypod Buchia, which from oldest to youngest include B. piochii (Gabb) and B. aff. B. okcnsis (Pavlow) of Tithonian age, B. uncitoides (Pavlow) of Berriasian age, B. paciflea Jeletzky of early to middle Valanginian age, B. kcyscrlingi (Lahusen) of middle to early late Valanginian age, and Buchia crassicollis solida (Lahusen) of late Valanginian age. The ages cited are based primarily on the ammonites present but partly on the similarities of the Buchia succession Ito that in British Columbia and in the Arctic region. As the succession of the species of Buchia is similar to that in western Canada, the strata characterized by the species are herein considered assemblage zones in conformity with the usage in Canada" P. B1 [6].
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