English (United Kingdom)

https://curated-unify.zendy.io/wp-json/zendy-region/v1/featured_content/oa?rat=en

https://curated-unify.zendy.io/wp-json/zendy-region/v1/highlighted_journal/

Global: Zendy Plus annual

Presents the access of premium content as premium feature

Premium Content

Presents the keyphrase highlighting as premium feature

Keyphrase Highlighting

Presents the summarisation as premium feature

Summarisation

Insights

Presents the pdf analysis as premium feature

PDF Analysis

Presents the zaia usage as premium feature

ZAIA

Global: Zendy Plus monthly

Global: Zendy Tools annual

Global: Zendy Tools monthly

Global: Zendy Free Plan

Study of the ammonites in the earliest Cretaceous of California, Oregon, and Washington has made possible the recognition of 4 ammonite zones in beds of Valanginian age and 5 ammonite zones in beds of Hauterivian age. These zones provide general correlations with the Valanginian and Hauterivian stages in other parts of the world and detailed correlations along the Pacific coast. These correlations are strengthened by the associations of the Valanginian ammonites with the Valanginian pelecypod Bticliia crassicollis (Keyserling) and by the absence of earlier Cretaceous species of Buchia that occur from Washington northward to Alaska. On the basis of such associations, the oldest Cretaceous beds exposed in California and Oregon are considered to be not older than Valanginian and probably not older than middle Valanginian. Failure to find in California certain ammonite zones of late Valanginian to early Hauterivian age that are present in southwestern Oregon may be explained by nondeposition, slow deposition, unfavorable facies, inadequate collections, or some combination of these possibilities. The Valangiriian-Hauterivian ammonites found in the Pacific Coast States have a local aspect, owing to the presence of genera not yet found elsewhere, or only rarely elsewhere, and to the absence of genera that are common elsewhere. Provincial genera include Wellsia, Hannaites, Hollisites, and Hei*tleinites. Besides these genera Sliasticrioceras has been found elsewhere only in British Columbia and Japan, and Homolsomites, only in British Columbia and Greenland. The absence of such ammonites as Rogersites, YalanginUes, Distoloceras, and Leopoldia is in contrast to their abundance in the Mediterranean province, and Mexico. With these exceptions the Valanginian ammonites from the Pacific coast show affinities more strongly with ammonites in the Mediterranean province than with northern Eurasia, and the Hauterivian ammonites show affinities mostly with ammonites in northern Eurasia.

Ammonites of Early Cretaceous age (Valanginian and Hauterivian) from the Pacific Coast States