Paleomagnetic Dating of Liesegang Bands

Abstract

ABSTRACT Paleomagnetic analysis, in conjunction with petrographic studies, is used in this study to date the formation of hematite Liesegang bands in the Ordovician Upper Arbuckle Group in southern Oklahoma. The hematite bands form symmetrical patterns on both sides of calcite-filled fractures in dolomitic beds. The bands decrease in abundance and become more diffuse away from the fractures. Paleomagnetic specimens from distinctly banded dolomite near the fractures contain a relatively strong chemical remanent magnetization (CRM) with a southeasterly declination and shallow inclination. Samples farther from the fractures which are less distinctively banded or have no bands contain a weaker and less stable magnetization. Samples were collected from both flanks of the Arbuckle Anticline (late Pennsylvanian folding), and a fold test indicates that the CRM is postfolding. The pole position for the CRM corresponds to the Permian ( 280 Ma) part of the Apparent Polar Wander Path for stable North America. Petrographic evidence, stable demagnetization to above 600°C, and rock magnetic experiments indicate that the CRM resides i hematite. These results suggest that the Liesegang bands formed in the Early Permian, probably by precipitation of hematite from fluids that emanated from the fractures. The fluids also apparently caused dedolomitization and precipitation of calcite in intercrystalline pore spaces. Probable sources of the iron in the bands include these fluids, as well as iron released from dedolomitization and from oxidation of pyrite.