About This Item
Share This Item
B. L. Clark and A. S. Campbell in 1942 published a pioneering biostratigraphic report on the radiolarian fauna from two shale units in the Mt. Diablo area. These shales, called by some authors the Sidney or Sidney Flat Shale and the Kellogg Shale, are about 11 mi apart and were considered to be two different units of the upper Eocene series. They noted that 63% of the Kellogg species are not present in the Sidney Flat and about 58% of the Sidney species are not present in the Kellogg. Sidney Flat was considered younger than the Kellogg by field evidence. Clark and Campbell's paper represented one of the first attempts to use radiolarians as a stratigraphic tool on land geology. The authors described many new species based on few and subtle differences in characters, but w th little knowledge of radiolarian morphological variation. Reevaluation of their taxonomy reveals that many characters are now considered nondiagnostic at the species level and that many of their species are synonymous. This result reduces the apparent biostratigraphic difference between the Kellogg and Sidney Flat Shales. Diatom, bethic, and planktonic foraminifers and silicoflagellates have shown that the Sidney Flat and Kellogg are very similar. The foraminifer data indicate that they are the same biostratigraphic unit. Diatoms suggest that the Sidney may be slightly younger. This study (1) reevaluates Clark and Campbell's radiolarian taxonomy, (2) reevaluates their stratigraphic and environmental significance, and (3) illustrates the importance of using characters that reflect evolu ionary change in biostratigraphy.
End_of_Article - Last_Page 425------------