Physical Sciences and Mathematics Commons^™

Observations On The Paleoecology And Formation Of The “Upper Shell” Unit, Lee Creek Mine, H. Allen Curran, Patricia L. Parker

Geosciences: Faculty Publications

The "Upper Shell" unit at the Lee Creek Mine (Pliocene age, maximum thickness 3 m) is remarkable for its concentration of well-preserved mollusk shells in a sparse quartz sand matrix, and it is dominated by several species of bivalves, with many shells articulated. The unit can be subdivided into three bivalve assemblage zones characterized by associations of dominant species. Zone 1 is dominated by Mercenaria mercenaria, an infaunal, shallow- to medium-burrowing, siphonate clam. Zone 2 is characterized by an epifaunal bivalve assemblage that includes Glycymeris americana, Argopecten eboreus, Anomia simplex, and Ostrea meridionalis. Thin but highly concentrated …

Trace Fossils In Pleistocene Carbonate Rocks Of San Salvador, Bahamas, H. Allen Curran

Geosciences: Faculty Publications

Reprinted from: D.T. Gerace (ed.), Proceedings of 1st Symposium on Geology of Bahamas, CCFL, Bahamas Field Station, San Salvador, Bahamas

Diffusion Data For Clinopyroxenes From Homogenization And Self-Diffusion Experiment, John B. Brady, Robert H. Mccallister

Geosciences: Faculty Publications

Kinetic experiments involving the homogenization of fine-scale, coherent (001) pigeonite lamellae in a sub-calcic diopside have been used to constrain Ca-Mg interdiffusion coefficients for clinopyroxenes. At 1150°-1250°C and 25 kbar, "average" Ca-Mg effective binary interdiffusion coefficients are described by

Ď = (3.89 x l0^-7) exp(-360.87 kJ/RT) (m²/sec)

(Ď : (3.89 x l0^-3) exp(-86.25 kcal/RT) (cm²/sec))

with an uncertainty of a factor of 2. Because of the large thermodynamic effect on diffusion near a solvus, actual interdiffusion coefficients should vary by an order of magnitude or more with composition …

Interdiffusion Of K And Na In Alkali Feldspars: Homogenization Experiment, John B. Brady, Richard A. Yund

Geosciences: Faculty Publications

The rates of homogenization of coherent exsolution lamellaein cryptoperthites have been used to evaluate K-Na interdiffusion in alkali feldspars.An "average" interdiffusion coefficient (Ď) is between 2 and 4 x l0^-17 cm²/sec for a synthetic cryptoperthite at 600°C in the composition range Or₂₃-Or₅₃, and between 6 and 12 x 10^-16 cm²/sec for a natural cryptopertlite at 650°C in the composition range Or₀-Or₈₅. These values are for diffusion (801) at 1 atmosphere pressure. K-Na interdiffusion coefficients calculated from published K and Na self-diffusion coefficients and thermochemical solution data …

Intergranular Diffusion In Metamorphic Rocks, John B. Brady

Geosciences: Faculty Publications

Theoretical models of intergranular diffusion demonstrate that grain size and grain boundary width are the most important textural parameters influencing diffusion in metamorphic rocks. Taking diffusion in an aqueous solution as a limiting case for diffusion in the intergranular region of metamorphic rocks, it appears that the diffusivities of many species will be similar and relatively insensitive to variations in temperature and pressure over a wide range of metamorphic conditions. Observed variations in the mobility of chemical components during metamorphism may be related principally to variations in the ratio of the component density in the intergranular region to the component …