Contributions to Geology 5.2

Iron content of fossil bones of Tertiary age in Wyoming correlated with climatic change

R. S. HOUSTON Department of Geology, University of Wyoming, Laramie, Wyoming
HEINRICH TOOTS Department of Geology and Geography, C. W. Post College, Greenvale, NY
JAMES C. KELLEY Department of Oceanography, University of Washington, Seattle, Washington

Pages
1-18

Keywords
Miocene, iron, fossil, Tertiary, Wyoming, climate

Abstract
The iron content of Tertiary bones from Wyoming varies with age, the older bones generally having a higher iron content. The changes in iron content are not strictly proportional to age, there being step-like changes. Thus time has to be rejected as the controlling factor. Instead climatic changes operating through soil-forming processes are proposed as the main cause of the variations in iron content. Other factors may have a modifying effect.

A study of Tertiary bones interred under conditions of warm humid climate supports the interpretation of climatic control as does the regional pattern of iron content in bones of the Upper Miocene of North America.

Elastic strain energy and mineral recrystallization: a commentary on rock deformation

GEORGE W. DEVORE Department of Geology, Florida State University, Tallahassee, Florida

Pages
19-43

Keywords
deformation, recrystallization, strain, mineral, elastic, model, orientation

Abstract
A model is developed that accounts for mineral recrystallization under directed stress that results in a minimum Gibbs and a maximum Helmholtz free energy for the equilibrium orientation. Maximum and minimum elastic compliances have been computed and listed for minerals of which elastic data are available for compressive and shear strains. The relation between maximum compliance, crystallographic direction and the tectonic A, B and C directions are generalized into eight groups. Correlations between calculated orientations, and the observed perferred orientations are established for hornblende, mica, quartz, tourmaline, olivine and perhaps dolomite if the minerals recrystallized in response to a shear strain that acted parallel to tectonic B in the tectonic A-B plane. Shear strain parallel to tectonic A is responsible for determining the fabric of the rock but apparently is a relatively unimportant strain in determining the final mineral recrystallization. Usually, only half of the possible shear equilibria orientations are present in the rock. This is explained by an assumption of nonuniform application of shear strain to the rock along the tectonic C direction. It is suggested that uniform strain in a crystal is a requirement for equilibrium and that grain size and orientation are influenced by the uniform strain requirement. The possibility that strain energy and thermodynamic equilibrium throughout a stressed system be used quantitatively to describe relative strain differences in different parts of the deformed system is indicated.