Abstract

Dissolution is the main process responsible for modifying detrital feldspar assemblages in the Oligocene Frio Formation of South Texas, accounting for up to 80% of feldspar modification in completely altered assemblages. This finding is supported through two independent calculations, one based on an estimate of initial feldspar content of the sandstones, the other on estimated initial composition of the feldspars themselves. Volumetric loss of detrital feldspar on the observed scale over such a short time span has major implications for provenance interpretations and for understanding the basin-wide mass balance of several major diagenetic components. The wide variation of feldspar content and composition at any given depth (temperature) attests to the premier significance of fluid composition and flux in driving the reactions that bring about dissolution of feldspars in these rocks.

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