Seven species of planktonic Foraminifera occur sporadically through 395 ft of the Cannonball Formation at Garrison Dam, North Dakota. Samples were obtained from a damsite core drilled by the U.S. Army Corps of Engineers. The species are: Globigerina edita Subbotina, Globorotalia pseudobulloides (Plummer), Globoconusa daubjergensis (Bronnimann), Subbotina triloculinoides (Plummer), Subbotina varianta (Subbotina), Chiloguembelina midwayensis (Cushman), and Chiloguembelina morsei (Kline).

This assemblage is indicative of the Globigerina edita Zone of Hollebrandt, 1965 (= Globorotalia pseudobulloides Zone of Bolli, 1966), and it generally is recognized as representing the lower parts of the Danian Stage (below the Globorotalia trinidadensis Zone). This precise correlation of the Cannonball with the lower Danian indicates a similar age for the nonmarine equivalents of the Cannonball (Ludlow and Tullock) on the west. The Ludlow in western North and South Dakota has been dated as Paleocene by plants, spores, and pollen. The Tullock has been dated previously as Paleocene on plant evidence and more recently as Puercan (early Paleocene) on the basis of mammals from eastern Montana. Therefore, the evidence presented here suggests that the Puercan is equivalent to the early Dan an.

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