Dinoflagellates and acritarchs are abundant in the upper Moreno Formation (Late Cretaceous-Paleocene) in Escarpado Canyon, California, the type area for the members of the Moreno Formation. Samples of the Marca Shale and the overlying Dos Palos Shale Members were studied from a subsurface cored section. The age of these units is well established by use of criteria independent of palynology, such as ammonites and foraminifers. The Cretaceous-Tertiary boundary usually has been placed somewhat arbitrarily at the contact of the Marca and Dos Palos Shales, but by the use of palynological evidence is placed in the Dos Palos Shale about 20 feet above the top of the Marca Shale. The phytoplankton assemblages exhibit marked changes at this level and further changes are evident hig er up in the Dos Palos Shale.

The Maestrichtian is characterized by Gymnodinium nelsonense Cookson, Deflandrea cretacea Cookson, and a distinctive new species of Hystrichosphaera. The Danian is characterized by new species of Areoligera, Hystrichosphaeridium, Cannosphaeropsis, Deflandrea, and Palmnickia. A new species of Palaeostomocystis, and Membranosphaera maestrichtica Samoilovitch are abundant in the Danian but occur rarely in the Maestrichtian. Forms restricted to the lower Danian of the Dos Palos Shale include Peridinium and a new genus of Deflandreaceae. Forms restricted to the upper part of the Dos Palos Shale include Cordosphaeridium inodes Klumpp, Deflandrea speciosa Alberti, and Glyphanodinium facetum Drugg. Pollen and spores are present also in large numbers in the upper Moreno Formation. With a few e ceptions, they are generally inferior to the phytoplankton for purposes of age-dating and zonation. There is good reason to believe that the phytoplankton eventually will prove to be as useful as planktonic foraminifers for correlation purposes.

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