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Six new foraminiferal zones have been established in the upper Mesozoic of the Scaramento Valley, California, as the result of detailed micropaleontological work in conjunction with several reconnaissance field mapping projects. The letter designations I, J-1, J-2, K, L, and M are proposed for these microfaunal zones. These designations are a downward continuation of the Upper Cretaceous zones of Goudkoff, who established the A through H Zones in 1945. The rocks on which this new zonation is based range in age from lower Early Cretaceous, Cenomanian stage, through Late Jurassic, Tithonian stage. Micropaleontological work is essential for mapping of this thick clastic sequence, because of the gross lithologic similarity and the lenticular, disconnected, and time-transgress ve nature of the coarse clastic marker beds. This study covers a 150 mile ± section along the regional strike of the outcrop along the western side of the Sacramento Valley, and also extends into the Redding area on the northeastern side of the valley.
Over 600 species, many of them new, and approximately 100 genera, including some new, were checklisted or recorded from more than 30 outcrop and well sections in the area. The new zones have been correlated approximately with the European stage classification. The I, J-1, and J-2 Zones range from Cenomanian to Aptian on the basis of both planktonic and benthonic Foraminifera; the K, L, and M Zones range from Barremian to Tithonian on the basis of cosmopolitan benthonic species. Correlations also were made between microfossil localities and northern California megafossil localities which have been equated with the European standard section.
Specific criteria for identification of the H Zone were not established by Goudkoff, but detailed study permits both identification and biofacies differentiation within it. The abundant and varied microfaunas of the "Middle" Cretaceous have made it possible to distinguish the I from the J Zones, separate the closely related J-1 and J-2, and divide the J-1 into three sub-Zones. The K, L, and M Zones are more difficult to differentiate, because of the absence of planktonics and the predominance of many similar Nodosariidae. The M Zone probably can be subdivided if more comprehensive work is done.
There is no faunal indication in the outcrop section of any unconformity between the Upper and Lower Cretaceous. Many species range through both Albian and Cenomanian sediments, without apparent interruption.
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