Contributions to Geology 32.1   

Marine ichnogenera within Torrejonian facies (Paleocene) of the Fort Union Formation, southeastern Montana

EDWARD S. BELT Department of Geology, Amherst College, Amherst, Massachusetts 01002; JOHN A. DIEMER Department of Geography and Earth Sciences, University of North Carolina, Charlotte, North Carolina 28223; EDWARD C. BEUTNER Department of Geology, Frankli

Pages
3-18

Keywords
Marine ichnogenera within Torrejonian facies (Paleocene) of the Fort Union Formation, southeastern Montana

Abstract
The trace fossils Ophiomorpha, Diplocraterion, Skolithos linearis, "Skolithos, " Thalassinoides, and Planolites have been identified in Paleocene strata near Ekalaka, Montana. These ichnogenera are confined to specific lithofacies within a new stratigraphic unit, the Ekalaka Member of the Fort Union Formation. The Ekalaka Member is of early to mid-Torrejonian age, is bounded by unconformities in the vicinity of the Miles City Arch, and varies in thickness from 20 to 70 m, thickening to the east, where the lower unconformity disappears. This new member has been mapped from the vicinity of Ekalaka to the South Dakota border, a distance of 50 km. The Ekalaka Member probably correlates with the massive D-Bed and E-Bed sandstones in the Cave Hills of northwestern South Dakota; both lithostratigraphic units lie below the U3 unconformity.

The six ichnogenera from the Ekalaka Member are all marine. However, the low numbers of individuals within each ichnogenus and the few numbers of individual ichnogenera suggest a brackish-water depositional environment. The most com-mon ichnogenus, "Skolithos" (defined as a short, thin, irregular tube with a vertical to subvertical sand wall), has been found in the same bed as Ophiomorpha and Skolithos linearis. Diplocraterion, Planolites, and Thalassinoides are also found in Ekalaka strata.

Ophiomorpha, Diplocraterion, and Skolithos linearis, although less common than "Skolithos," have been interpreted by previous workers to be euryhaline marine ichnogenera. Furthermore, the strata in which they occur show tidal reversed-ripple laminae on cross-beds and neap/spring tidal bundle laminae. Nevertheless, the attribution of marine influences on Ekalaka deposition can be more strongly argued on the basis of the same ichnogenera found in the Cave Hills sandstones, which at the same time contain marine sharks, skates, and rays.

Agonistic behavior in pachycephalosaurs (Ornithischia: Dinosauria): a new look at head-butting behavior

KENNETH CARPENTER Department of Earth Sciences, Denver Museum of Natural History, 2001Colorado Boulevard, Denver, Colorado 80205

Pages
19-25

Keywords
Agonistic behavior in pachycephalosaurs (Ornithischia: Dinosauria): a new look at head-butting behavior

Abstract
The hypothesis that pachycephalosaurid dinosaurs used their massive domed heads in agonistic head-to-head butting is reexamined. It is questionable whether such behavior was possible because of the small contact area of opposing heads. Instead, flank-butting is suggested based on analogy with extant African antelopes. Two types of flank-butting are recognized on the basis of dome structure. Type One is seen in Pachycephalosaurus, Prenocephale, and Stegoceras, all of which have tall, rounded frontoparietal domes. Such domes would maximize the mass of the head in flank-directed blows. Pain would be by the opponent without causing serious injury. Type Two is seen in Stygimoloch, in which squamosal horns are developed -along the posterior margins of the dome. These horns seem to be an adaptation for causing maximum pain locally during -flank-butting without causing serious injury. The horns probably were not sharp, but blunted.

Marine Upper Cretaceous rocks and their ammonite record along the northern flank of the Black Hills uplift, Montana, Wyoming, and South Dakota

WILLIAM A. COBBAN, U.S. Geological Survey, Mail Stop 913, Box 25046, Federal Center, Denver, Colorado 80225; NEAL L. LARSON, Black Hills Institute of Geological Research, Inc., Box 643, Hill City, South Dakota 57745

Pages
27-35

Keywords
Marine Upper Cretaceous rocks and their ammonite record along the northern flank of the Black Hills uplift, Montana, Wyoming, and South Dakota

Abstract
About 1,157 to 1,188 m (3,800-3,900 ft) of marine Upper Cretaceous rocks, chiefly shale, crop out around the northern flank of the Black Hills uplift. The formations are, from oldest to youngest: Mowry Shale, Belle Fourche Shale, Greenhorn Formation, Carlile Shale, Niobrara Formation, Pierre Shale, and Fox Hills Sandstone. Formally named members are applied to parts of the Greenhorn Formation and Pierre Shale, and all of the Carlile Shale. Ammonites are especially diverse and well preserved in calcareous concretions in the Belle Fourche Shale and Greenhorn Formation; 12 genera (19 species) are known from the Belle Fourche, and 16 genera ( 18 species) from the Greenhorn. The Carlile and Pierre shales contain well-preserved, but less diverse faunas. Only two ammonite genera are known from the Mowry Shale, and none is recorded from the Niobrara Formation and Fox Hills Sandstone.

Trace Fossils of the Fox Hills Formation, Bowman County, North Dakota

DANIEL J. DALY, Energy & Environmental Research Center, Grand Forks, North Dakota 58202-9018

Pages
37-50

Keywords
Trace Fossils of the Fox Hills Formation, Bowman County, North Dakota

Abstract
A limited suite of trace fossils dominates the fossil record of the marginal marine deposits of the Fox Hills Formation (Late Cretaceous, Maastrichtian) in outcrops at the south end of the Cedar Creek anticline in Bowman County, North Dakota. The 30-meter thick section contains feeding traces (Phycosiphon, Rhizocorallium) and two species of the burrow trace Ophiomorpha (O. borneensis, O. nodosa). Feeding traces dominate the silty sands of the lower shoreface deposits (Trail City and lower Timber Lake members). The species of Ophiomorpha dominate the very fine and fine hummocky bedded sands of the middle and upper Timber Lake Member. The delicate O. nodosa marks the relatively low-energy conditions of the lower shoreface, while upsection, the robust O. borneensis marks the relatively high-energy deposits of the middle and the upper shoreface. Ophiomorpha are rare in the medium-grained crossbedded channel facies of the upper Fox Hills Formation (Colgate Member).

A similar suite of trace fossils occurs in other outcrops of the Fox Hills Formation on the southwest rim of the Williston basin. The younger Fox Hills strata of the southeastern basin flank, including the type area of the formation, however, contain a varied assemblage of bivalves, oysters, and ammonites. Ophiomorpha, the only widely recognized trace fossil on the south-east flank, occurs with the bivalve Tancredia in sands of relatively high-energy barrier bar deposits.

A North Dakota Triceratops skull

F. D. HOLLAND, JR. Professor Emeritus, Department of Geology and Geological Engineering, University of North Dakota, Grand Forks, North Dakota 58203-8358

Pages
51-60

Keywords
A North Dakota Triceratops skull

Abstract
A dinosaur skull, from the upper Hell Creek Formation, Late Cretaceous in age, collected in 1964 in southwestern North Dakota is displayed on the University of North Dakota campus as Triceratops prorsus Marsh. This identification is reconsid-ered in light of work by Ostrom and Wellnhofer (1986) and Lehman (1990), who suggested that the range of morphological variation exhibited by latest Cretaceous ceratopsian skulls can be accommodated within one species of Triceratops, T. hor-ridus (Marsh), the type species. The skull is thought to be from a mature female, as indicated by forwardly inclined, wide-set, supraorbital horncores, characters chosen by Lehman as indicators of gender from an association of characters taken as sex--related. Dimensions of the skull are given. Based on detailed cladistic and morphometric analyses of many skulls, Forster (1996b) accepted two species of Triceratops as valid, T. horridus and T. prorsus. Consideration of her studies suggests that the skull is correctly identified. Reoccupation of the collecting site allowed its more accurate location, based upon newly avail-able topographic maps. Twenty-nine years after this skull was removed, little evidence of the access road or excavation remains at the site.

Mammals and mollusks across the Cretaceous-Tertiary boundary from Makoshika State Park and vicinity (Williston Basin), Montana

JOHN P. HUNTER Department of Anatomical Sciences, State University of New York at Stony Brook,Stony Brook, New York 11794-8081; present address: Department of Anatomy, New York College of Osteopathic Medicine, New York Institute of Technology, Old Westbur

Pages
61-114

Keywords
Mammals and mollusks across the Cretaceous-Tertiary boundary from Makoshika State Park and vicinity (Williston Basin), Montana

Abstract
Extensive outcrops in the badlands of Makoshika State Park near Glendive, Montana, and surrounding areas expose a continuous sequence of fossiliferous, fluviodeltaic sedimentary rock spanning both sides of the Cretaceous-Tertiary (K/T) boundary. This fortuitous circumstance has enabled us to document change in the composition of mammalian faunas during this time, to relate observed patterns to palynomorph and molluscan changes in composition, and to test hypotheses of faunal turnover at the K/T boundary. Of particular interest is the appearance and diversification of archaic ungulate mammals, since simultaneous dinosaur extinction along with ungulate radiation has been invoked in models of gradual faunal change at the K/T boundary. Fossil mammals have been recovered from six localities in and near Makoshika State Park. The known sam-ples represent three successive local faunas. Composition of the Muddy Tork Local Fauna from the Hell Creek Formation (Upper Cretaceous) resembles those of the Lancian North American Land Mammal "Age" (NALMA) from elsewhere in Montana and Wyoming. Composition of the Hiatt Local Fauna recovered from lower parts of the Ludlow Member of the Fort Union Formation (Paleocene) resembles faunas of the Puercan NALMA at northern latitudes. The diverse assemblage of archaic ungulates present in the Hiatt Local Fauna in conjunction with negative evidence (absence of the multituberculate Taeniolabis taoensis, the appearance of which marks the advent of the late Puercan) suggests that the Hiatt Local Fauna is no younger than middle Puercan (Pu2). The School Well Local Fauna (tentatively, Torrejonian NALMA) occurs higher in the Ludlow Member of the Fort Union Formation. Strata yielding typical Late Cretaceous mammals are separated stratigraphically from those yielding early Paleocene mammals by about 20 m. The K/T boundary in Makoshika State Park has been recog-nized in more detail on the basis of palynomorphs. Pollen studies have led to preliminary identification of a fern spike, noted elsewhere by others immediately above the K/T boundary. Lack of any type of Bug Creek vertebrate assemblage suggests that the controversial "Bugcreekian" biochron (Pu0) cannot be extrapolated to this area. Evolutionary radiation of archaic ungu-lates may not have begun until after dinosaur extinction.

Paleoenvironmental distribution of Paleocene palynomorph assemblages from brackish water deposits in the Ludlow, Slope, and Cannonball Formations, southwestern North Dakota

TIMOTHY J. KROEGER Department of Biology and Geology, Bemidji State University, Bemidji, MN 56601-2699
JOSEPH H. HARTMAN Energy & Environmental Research Center, University of North Dakota, Grand Forks, ND 58202-9018

Pages
115-129

Keywords
Paleocene, palynomorph, Ludlow Formation, Slope Formation, Cannonball Formation, North Dakota

Abstract
Two brackish water tongues of the Cannonball Formation (Fort Union Group) are exposed in badlands of the Little Missouri River in southwestern North Dakota. These brackish water deposits are intercalated with lignite-bearing, fluviolacustrine rocks of the Ludlow and Slope Formations (Fort Union Group) and, in total, represent a fluviodeltaic complex that prograded eastward into the Paleocene Cannonball Sea. The invertebrate fauna, lithology, and vertical lithologic sequences indicate that lacustrine, coal swamp, interdistributary bay or interlobe basin, and lake or bay fill depositional environments are represented by the brackish water deposits; the sub- and superjacent strata are of freshwater origin.

Cluster analysis and ordination statistical techniques demonstrate that paleoenvironment is a factor that exerted control on the taxonomic composition of palynomorph assemblages. In general, brackish water deposits are characterized by rare-to-abundant dinoflagellate cysts. Differences among assemblages within brackish water deposits appear to be related to salinity and the rate of clastic influx. Slightly brackish to fresh water deposits that received low clastic input are characterized by abundant freshwater algae, low diversity of dinoflagellate cysts, and few terrestrial palynomorphs. Brackish water deposits receiving high clastic input are characterized by abundant terrestrial palynomorphs and more diverse dinoflagellate assemblages. Lacustrine environments that had high clastic influx are dominated by terrestrial palynomorphs. Palynomorph assemblages recovered from coal swamp environments are variable, possibly reflecting localized plant communities. The rare presence of dinoflagellate cysts within the lignites suggests marine influence during peat deposition.