Macropaleontology of the Gunn Member, Stony Mountain Formation (Upper Ordovician), Manitoba and North Dakota
Date of Award
Doctor of Philosophy (PhD)
F.D. Holland, Jr
The Gunn Member of the Stony Mountain Formation has long been known to contain an abundant and diverse fauna. This study was undertaken to identify and describe the macrofauna of the Gunn Member in the subsurface of North Dakota, previously neglected.
As a necessary first step, collections of fossils from outcrop were examined and identified. With the outcrop fauna serving as a reference collection, twenty cores from the North Dakota subsurface were examined, described, and their fossils sampled. Fossil and sediment samples were washed and sieved and the residues were picked for microscopic representatives of phyla usually considered to be macroscopic.
One hundred sixteen species-level taxa were identified from the Gunn Member. Thirty-five of these were found only in the subsurface, 40 only in outcrop, and 41 were found in both outcrop and the subsurface. There are 42 species of mollusks, 40 bryozoans, 15 brachiopods, ten corals, eight arthropods, and one stromatoporoid. A microscopic molluscan fauna was found in core from four wells in North Dakota. Five new genera and 19 new species were described; one species is a coral and the remaining new taxa are bryozoans.
Outcrop assemblages are dominated by brachiopods and solitary corals, subsurface assemblages by bryozoans and brachiopods. Most of the preserved fauna is inferred to have been of epifaunal suspension feeders. Most of the fauna seems to have little biostratigraphic utility, although a Richmondian age for the Gunn Member is confirmed by the presence of several Richmondian index fossils.
The sediments of the Gunn Member were deposited on a gentle northwest-sloping ramp. The decreasing thickness and decreasing proportion of terrigenous material toward the northwest indicates a southeastern source for the Gunn siliciclastics; the Transcontinental Arch is inferred to have been that source.
The term "Gunn Member" is used throughout this study to avoid confusion. However, it is suggested that the term "Stony Mountain Formation" might be restricted to what is now the Gunn and Penitentiary Members, and that the Gunton and Williams Members might be incorporated into an expanded Stonewall Formation.
Lobdell, Frederick K., "Macropaleontology of the Gunn Member, Stony Mountain Formation (Upper Ordovician), Manitoba and North Dakota" (1988). Theses and Dissertations. 177.