Date of Award


Document Type


Degree Name

Master of Science (MS)



First Advisor

A.M. Cvancara


In June and July, 1972, four stratigraphic sections were mea sured and described in Slope and Golden Valley Counties, southwestern North Dakota. Within the sections, the Cannonball and Ludlow Formations are recognized. The Cannonball consists of two tongues in the upper part of the Ludlow (perhaps equivalent to the Lebo Member), separated stratigraphically by about 30 roof Ludlow. The U tongue (upper tongue in the study area) is up to 11. 7 m thick. The L tongue (lower tongue. in the study area) is up to 3.8 m thick. The Cannonball is composed mostly of mudstones and the Ludlow consists of sandstones, mudstones, and lignite. The sections were sampled systematically for microfossils and macroinvertebrates, and 13 species in 12 genera ware identified. Both formations can be distinguished by their contained fossils. The fauna of the U tongue of the Cannonball consists of three bivalves (Corbicula berthoudi?, Corbula (Bicorbula) subtrigonalis., and Crassostrea glabra) and the trace fossil Ophiomorpha. The fauna of the L tongue of the Cannonball consists of two foraminiferids (Trochammina sp. and ?Haplophragmoides sp.) and three bivalves (Corbicula berthoudi?, Corbula (Bicorbula) subtrigonalis, and ?Ostrea sp .) The Ludlow biota consists of 3 gastropods (Viviparus sp., .Goniobasis cf. G. tenuicarinata, and ?Coniobasis sp.) 2 ostracods (Candona sp. and Ilyocypris sp.), and 1 charophyte (Sphaerochara sp.). No species are in common with the two formations and only two species are in common with the two Cannonball tongues (Corbicula berthoudi? and Corbula (Bicorbula) subtrigonalis). The ostracods and the charophyte in the Ludlow and the foraminiferids, ?Ostrea sp., and Ophiomorpha in the Cannonball tongues are here reported. The foraminiferids and Oohiomorpha have been reported from the marine Cannonball to the east of the study area, whereas sp. is newly reported for formation. The fauna of the tongues is characteristically brackish, but three species of the L tongue mina sp., ?Haplophragmoides sp. and ?Ostrea sp.) suggest conditions of slightly higher salinity than those in which the U tongue was deposited. The two tongues are interpreted to have been deposited on tidal flats and in lagoons in an interdeltaic region behind a barrier island.

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