Date of Award
Doctor of Philosophy (PhD)
F.D. Holland, Jr
The bivalve fauna of the Fox Hills Formation, Maestrichtian, of North Dakota was studied in an attempt to modernize the nomenclature of known bivalves, describe new forms, interpret the relationships of members of the formation, and establish the paleoecological setting in which the Fox Hills was deposited.
The Fox Hills Formation crops out in Logan, Emmons, Sioux, Morton, Burleigh, Kidder, Pierce, McHenry, Bottineau, and Bowman counties in North Dakota. It is best exposed along the Missouri River in south-central North Dakota. Traditionally, the formation has been subdivided into four members, all of which are exposed in the type area of the formation in north-central South Dakota. In North Dakota, however, the lowermost Trail City Member cannot be lithologically recognized and, therefore, only the Timber Lake, Bullhead, and Colgate members, in ascending order, have been recognized. Lithologically, the Timber Lake Member consists of medium- to fine-grained sandstone, which is either uncon solidated or loosely cemented. This unit becomes increasingly crossbedded toward the top. 'TIie Bullhead Member consists of a sequence of intercalated sandstone and shale which is essentially devoid of bivalves. The uppermost member, the Colgate, consists of light colored greywacke sandstone.
Forty-two species of bivalves were identified from the Fox Hills Formation in North Dakota and arranged in twenty-five genera. This number included three new species, Nucula enunonsensis, Modiolus siouxensis, and ?Astarte hollandi. Three other species which are characteristic of the Creta ceo~s of the Eastern Seaboard were identified for the first time from the Midcontinent.
Using ecological data derived by studying the ecology of recent bivalves of the same genera as those collected in the Fox Hills Formation and the sedimentologic data, it was concluded that the Fox Hills Formation in North Dakota represents the littoral and shallow subtidal margin of the retreating Cretaceous epicontinental seaway. Data from the bivalves indicated that, in general, water depth decreased from about 80 fathoms to O fathoms from the base of the formation to the top, an observation which is further stren gthened by sedimentologic evidence. These data in conjunction with those derived from the presence of a volcanic ash bed occurring in several parts of Emmons, Sioux, and Morton counties, which transcends the member boundaries, indicate that the members were being deposited penecontemporaneously across central North Dakota. At the time that the strand line, now represented by the Fox Hills-Hell Creek boundary, occupied the area of central Sioux County, the Pierre-Fox Hills bondary would have occupied an area in central Emmons County forty miles to the east. Deposition 0£ the Timber Lake Member was normal marine whereas that in the area of Bullhead deposition was apparently brackish, probably as a result of restriction caused by development of barriers in the area of the upper Timber Lake Member. The Colgate Member represents the strand line of the Fox Hills seaway.
Feldmann, Rodney M., "Bivalvia and paleoecology of the Fox Hills Formation (Upper Cretaceous) of North Dakota" (1967). Theses and Dissertations. 91.