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Samples containing pelagic Foraminifera were examined from five-widely spaced localities in the Upper Cretaceous Venado, Yolo, and Sites Formations on the western side of the Sacramento Valley, California.
The basal formation, the Venado, overlies the late Cenomanian "Antelope Shale," and is predominantly a sandstone unit with discontinuous beds of conglomerate and thin, dark-colored carbonaceous siltstone. Along Putah Creek, Yolo County, the Venado contains Globotruncana and Hedbergella, which suggest a Turonian age.
The overlying Yolo Formation is a dark-colored siltstone with some sandstone and shale beds. The siltstone and shale contain an abundant, well-preserved foraminiferal fauna, including Clavihedbergella, Globigerinelloides, and Heterohelix.
The Sites Formation is composed of thin, rhythmic sequences of siltstone and sandstone interbedded with thick sandstone beds. The finer clastics, in many places with a high mica and carbonaceous content, yielded the largest and most diversified planktonic assemblage. The genera Globotruncana, Rugoglobigerina, Hedbergella, and Schackoina are present.
The pelagic microfossils appear to correlate with the microfaunas from the Turonian of Europe and the Austin Group of the Gulf Coast. The Venado and Yolo Formations are correlated with Popenoe's Members II and III, and the Sites with Member IV of the Cretaceous strata in the Redding area, California. The planktonic assemblages fall within Goudkoff's H and G-2 zones.
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