Petrography of Silica Diagenesis in the Eagle Ford Formation, South Texas

Abstract

Mudrocks in the Eagle Ford Formation of South Texas are dominantly carls and argillaceous carls that represent mixtures of extrabasinal silicate detritus and intrabasinal carbonate grain assemblages containing both planktic and benthic carbonate allochems. There is also a significant component of biosiliceous debris in these mudrocks, much of which is extensively replaced. Close petrographic inspection of Eagle Ford lithologies reveals the local presence of sarls, dominated by massively calcitized radiolarian skeletons. Mobilization of silica by the replacement process is a likely cause of the precipitation of several forms of authigenic quartz, including microcrystalline allochem replacements, pore-filling quartz euhedra, and matrix-dispersed authigenic microquartz. Interestingly, little of this authigenic quartz is found associated with obvious radiolaria, suggesting considerable transport of the silica prior to precipitation. Cathodoluminescence imaging reveals that such authigenic quartz represents a large portion of the total quartz in the South Texas Eagle Ford Formation.

AAPG Datapages/Search and Discovery Article #90216 ©2015 AAPG Annual Convention and Exhibition, Denver, CO., May 31 - June 3, 2015