Contributions to Geology 30.2

Therian mammals of the Terlingua local fauna (Judithian), Aguja Formation, Big Bend of the Rio Grande, Texas

RICHARD L. CIFELLI Oklahoma Museum of Natural History and Department of Zoology, University of Oklahoma, Norman, OK 73019

Pages
117-136

Keywords
Therian mammals, Terlingua, Aguja Formation, Texas

Abstract
The Aguja Formation (Campanian) of southern Texas has yielded a diverse vertebrate assemblage which is of interest in that it represents a significant, southern range extension for local faunas of Judithian age. One tribosphenic therian, Paleomolops langstoni, new genus and species, cannot be confidently allied with either marsupials or eutherians. It is morphologically most similar to Iugomortiferum, from the early Campanian of Utah, but a special relationship is not supported by unambiguous synapomorphy. A possible second "tribothere" is represented by teeth not surely of the adult dentition. Five or more marsupials are present in the fauna. Of the four generically-identified taxa, one is described as a new species of Alphadon, A. perexiguus; two others are tentatively referred to the Judithian species A. halleyi and A. sahnii, respectively, and the last is most similar to Judithian Turgidodon lillegraveni. A eutherian is described as new and referred to the enigmatic genus Gallolestes, as G. agujaensis. Gallolestes is otherwise known only from the Campanian of Baja, California. Upper molars referred to G. agujaensis are of eutherian design and, assuming generic referral is correct, support placement of Gallolestes within the Eutheria. Although some of the therian taxa of the Terlingua local fauna are tentatively referred to Judithian species known from the central and northern Western Interior, at least half of the species represented are endemic. In addition, some taxa typical of Judithian and later faunas from the north are lacking; both the high degree of endemism and these apparent absences are presumably owing to biogeographic differentiation of the terrestrial biota during the Late Cretaceous of North America.

Geomorphic and structural features of the Alliance 1¡ x 2¡ Quadrangle, western Nebraska, discernible from synthetic-aperture radar imagery and digital shaded-relief maps

R. F. DIFFENDAL, JR. Conservation and Survey Division, IANR, University of Nebraska-Lincoln, Lincoln, Nebraska 68588-0517

Pages
137-148

Keywords
Alliance, Nebraska, geomorphology, structural features, synthetic-aperture, shaded-relief

Abstract
The digital shaded-relief map of the United States and the synthetic-aperture radar map of the Alliance Nebraska 1¡ x 2¡ area prepared by the U.S. Geological Survey (USGS) in the former case and for the USGS in the latter show oriented landforms and lineaments in northwest Nebraska. Parallel and subparallel hills and valleys developed on different geologic materials ranging from shales through sandstones to loess and eolian sand appear to be wind erosional features subsequently modified by running water. The long axes of these hills and valleys generally trend between N40¡W and N50¡W. Similar features also occur across major areas of the Great Plains from Montana southeast at least to Kansas. Most of the lineaments are in two sets, one trending northeast, the other northwest. There are some east-west and north-south trending lineaments in the western part of the quadrangle, some circular features in the northwest, and some chevronlike lineaments in the north-central part. Some lineaments appear to coincide wholly or in part with known faults in western Nebraska or with extensions of faults in east-central Wyoming into northwest Nebraska. All other lineaments are probably reflections of either jointing or, more likely, of faulting. Additional field work will be needed to verify which of these two, if either, is responsible for any particular lineament.

Time resolution at Carnegie Quarry (Morrison Formation: Dinosaur National Monument, Utah): implications for dinosaur paleoecology

ANTHONY R. FIORILLO Museum of Paleontology, University of California, Berkeley, California 94720

Pages
149-156

Keywords
Carnegie Quarry, Morrison Formation, paleoecology, Dinosaur National Monument

Abstract
Theoretical minimum and maximum time estimates for the formation of the Carnegie Quarry (Morrison Formation) in Dinosaur National Monument can be derived from the recognition of preburial bone weathering rates combined with a basic understanding of the stream-flow characteristics of a fluvial system. These time estimates suggest that the time of formation of the quarry assemblage was on the order of a few months to only a few years, thereby recording ecological time rather than evolutionary time.

Recognizing that ecological time is represented at Dinosaur Monument, the issue of coexistence of the dinosaur taxa within this ecosystem is confirmed from the preservational state of the various specimens. How did the different sauropod taxa coexist with respect to food resources? Preliminary work on the dental microwear patterns on the teeth of two of the most common sauropods, Camarasaurus and Diplodocus, suggests that some degree of partitioning of food resources took place by these animals within the Late Jurassic ecosystem, recorded by the Morrison Formation.

A sedimentary origin for the "microbreccia" associated with the Heart Mountain detachment fault

ANTONI K. TOKARSKI Polish Academy of Sciences, 31-002, Krakow, Poland
WILLIAM G. PIERCE U.S. Geological Survey, Menlo Park, California 94025
EWA PIEKARSKA Polish Academy of Sciences, 31-002, Krakow, Poland
WILLIS H. NELSON U.S. Geological Survey, Menlo

Pages
157-162

Keywords
microbreccia, Heart Mountain, volcanic, Wapiti Formation

Abstract
The volcanic rock in contact with the Heart Mountain fault has been interpreted by Hauge (1985; 1990) to be a microbreccia or cataclasite, an interpretation that is a basic tenet of the continuous allochthon model. However, thin sections of this rock show none of the distinctive features associated with cataclasites, such as grain fracture, grain angularity increase, grain size reduction, cataclasite foliation, feather fractures, Riedel shears, or angularity decrease in relation to the Wapiti Formation of which it is the basal unit. We interpret the widespread, very thin to absent, volcanic rock lying on the Bighorn Dolomite to be an airfall tuff, not microbreccia or cataclasite.