Paleomagnetic Dating of Dedolomitization in Cambrian-Ordovician Arbuckle Group Limestones and Pennsylvanian Collings Ranch Conglomerate, Southern Oklahoma

Kevin E. Nick, R. Douglas Elmore

Paleomagnetic and petrographic techniques have been used to date dedolomitization in stratigraphic and tectonic dolomites exposed in the Arbuckle Mountains, southern Oklahoma. We examined red dedolomites and their dolomite precursors from the Cambrian-Ordovician Arbuckle Group and dolomite clasts in the Pennsylvanian Collings Ranch Conglomerate. Authigenic hematite is associated with the dedolomite and precipitated as a result of the dedolomitization process. Dedolomite is associated with paleokarst and fractures, burrows, Liesegang bands, and red rims on conglomerate clasts.

Magnetic directions from these dedolomitized rocks range from Dec = 145° to 154° and Inc = 2° to 9°, with ks greater than 50 and ^agr95s less than 5. The directions are constrained by fold tests to be post-structural (Late Pennsylvanian to Early Permian) and in the Collings Ranch to post-depositional. These directions correspond to a reversed Pennsylvanian pole position and the magnetizations are interpreted as chemical remanent magnetizations (CRM) acquired when hematite precipitated during dedolomitization. In contrast to the dedolomitized rocks, unaltered dolomite contains a Cambrian-Ordovician magnetization in magnetite (Dec = 105°, Inc = 4°, k = 27, ^agr95 = 10°) that could be primary. The acquisition of the CRM is temporally related to uplift i this region and dedolomitization presumably resulted from exposure to meteoric waters. The results emphasize the importance of a regional, Late Pennsylvanian dedolomitizing and remagnetizing diagenetic event that affected some early Paleozoic magnetic directions and dolomite.

AAPG Search and Discovery Article #91030©1988 AAPG Annual Convention, Houston, Texas, 20-23 March 1988.