Late Miocene and Early Pliocene Siliceous Microfossils from the Upper Monterey and Lower Sisquoc Formations, Sweeny Road, Santa Barbara County, California


  • W.H. Akers
  • R.E. Marolt Chevron Oil Field Research Company, La Habra, California
  • R.J. Navarette Chevron Oil Field Research Company, La Habra, California


Radiolaria, diatoms, and silicoflagellates are identified and illustrated from the late Miocene and Early Pliocene beds of the Monterey and Sisquoc Formations that are exposed along Sweeny Road, near Lompoc, California.  The greatest number of species recovered belong to the Bacilariophyceae (diatoms).  Radiolaria are second in species abundance and silicoflagelates third.   Radiolaria were found to outnumber diatoms in rocks affected by diagenesis or dissolution.  In some intervals, diatoms and silicoflagelates were rare or absent, and only three or four species of Radiolaria, predominantly SPUMELLARIA Ehrenberg 1875, were found.  In general, the rocks that were least subjected to diagenesis or dissolution yielded the highest species diversity and the most specimens of all three groups of siliceous microfossils.