HAMMES, URSULA, and DAVID A. BUDD, University of Colorado, Boulder, USA

ABSTRACT: Cathodoluminescence in Calcite Cements: New Insights on Activators, Sensitizers, and Quenchers Using Synchrotron X-Ray Fluorescence

A petrographic and geochemical study using cathodoluminescence and Synchrotron X-ray Fluorescence Microanalyses (SXRFMA) of low Mg-calcite cements in the Oligocene Suwannee Formation reveals that extremely low concentrations of transition elements are associated with luminescence in these cements. An early freshwater origin for the cements is indicated by an abundance of vadose features associated with many cements, and a precompaction origin of all cements. Cement distribution is also sporadic and related to intraformational exposure surfaces. Luminescence does not exhibit any regional trends, rather it too is associated with localized intraformational subaerial exposure surfaces.

The cements were analyzed for Mn, Fe, Pb, Zn, and Y. Measured concentrations of Mn, Fe, Pb, Zn, and Y are generally below 50, 80, 40, 20, and

40 ppm, respectively. Detection limits for these elements on the SXRF probe were 6, 4, 6, 2, and <1 ppm, respectively. The results are informative relative to minimum Mn concentrations to excite luminescence and the role of Pb, Zn, and Y as sensitizers in naturally occurring calcites.

Half of all luminescent cements have Mn/Fe ratios >2 whereas the other half and most non-luminescent cements are characterized by Mn/Fe ratios <2. Forcements with Mn/Fe ratios >2 the control on luminescence is the Mn content; it must exceed 15 ppm. For cements with Mn/Fe ratios <2, a sensitizer appears necessary. Pb seems to be that sensitizer in the Suwannee calcites, although the relationship is not strong. Zn and Y do not show any trends with luminescence.

AAPG Search and Discovery Article #90987©1993 AAPG Annual Convention, New Orleans, Louisiana, April 25-28, 1993.