Abstract
An abundant and diverse chrysomonad-cyst flora is present in the Marca Shale Member of the Moreno Formation of California. Associated with the siliceous cysts are diatoms, silicoflagellates, radiolarians, and, rarely, Foraminifera. Five preliminary biostratigraphic zones, based on variations in the kinds and quantities of cysts present, are recognized. Two new cyst-species, Archaeomonas microspinosa and Archaeomonas saturnoides, are described. The top sixty feet of the Marca Shale and the lower portion of the overlying Dos Palos Shale (Late Cretaceous-Paleocene) have yielded no siliceous microfossils, suggesting that siliceous microplankton productivity was a greatly reduced as that of the calcareous nannoplankton at the Cretaceous-Tertiary boundary.
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