--> ABSTRACT: Paleomagnetic Dating of Depositional and Diagenetic Events in Upper Cambrian Rocks of Central Texas, by M. R. Farr, Wulf A. Gose, and G. L. Macpherson; #91030 (2010)

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Paleomagnetic Dating of Depositional and Diagenetic Events in Upper Cambrian Rocks of Central Texas

M. R. Farr, Wulf A. Gose, G. L. Macpherson

Hematite, magnetite, and goethite are present in samples from the Riley and Wilberns Formations in central Texas. Samples containing abundant goethite possess characteristic paleomagnetic directions that are Tertiary to recent in age. The goethite component is easily removed by thermal demagnetization temperatures greater than 150°C. A minority of samples from the Wilberns Formation contains magnetite as the dominant magnetic component. These samples display shallow easterly characteristic directions that we interpret as a true detrital remanent magnetization. Most samples from both units possess hematite as the dominant carrier of magnetic remanence. Samples in which hematite occurs as ooids and as a replacement for carbonate allochems possess shallow easterly decli ations similar to magnetite-dominant samples. This generation of hematite probably formed during or shortly after deposition. The paleopole for samples in which hematite occurs as a replacement for glauconite grains is similar to previously published Ordovician paleopoles. This indicated Ordovician age is corroborated by a previously published Late Ordovician radiometric age for glauconite from the Riley Formation. Samples in which hematite occurs as an infilling within fractures and pressure solution seams display characteristic paleomagnetic directions that indicate a late Paleozoic age. This age corresponds to tectonic activity along the Ouachita tectonic belt to the east. Such an age may reflect hematization from meteoric fluids during structural uplift of the area, or it might refle t precipitation during mixing of tectonically driven basin-derived fluid and meteoric fluid.

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