Teacher’s Guide Diatoms: Life in Glass Houses

Diatomite at Lompoc, California. Johns-Manville Corporation (1964) mines some of the large diatomite deposits laid down in Santa Barbara County in the middle to upper Miocene (5-25 million y.a). Many of the current coastal regions, including those now occupied by Los Angeles and San Francisco, were then under the sea. The Lompoc area was probably an archipelago or series of shallow bays and between 3-400 species of fossil diatoms have been recorded here. Rarely, fossils of sea-birds, fish, porpoises and other animals have also been uncovered in the diatomite. The deposits at Lompoc are very rare in being unusually well preserved in their original form; more commonly, such deposits are profoundly altered by geophysical factors into a variety of dense siliceous rocks.