Quantitative Measurements of Brittle Deformation with Burial Compaction, Frio Formation, Gulf of Mexico Basin

By

MAKOWITZ, ASTRID, and MILLIKEN, KITTY L.

The University of Texas at Austin, Austin, TX

The Oligocene Frio Formation, Gulf of Mexico Basin, was used to test the relationship between brittle deformation and quartz cementation in the context of burial compaction. The sandstones of the Frio Formation represent an excellent case for this study because they are deposited on a passive margin setting and are presently at maximum burial depth, lacking any tectonic overprinting. Growth faulting allows initially uniform sediments to have experienced a wide range of burial depths and temperatures.

Brittle deformation is manifested as fracturing of grains during compaction. Fractures are subsequent filled with quartz cement. Fresh fracture surfaces provide a favorable nucleation site for quartz cement. Scanned cathodoluminescence imaging combined with backscattered electron imaging techniques were used, providing an unambiguous method for distinguishing detrital quartz from authigenic quartz.

Quantitative measurements of 17 samples were performed with depths ranging from 3,223 to 17,154 feet. The data show an exponential trend of increasing percentage of fractured quartz grains with increasing depth. Individually fractured grains become more fractured with depth. In general, a greater amount of quartz cement is associated with fractured grains compared to unfractured grains.

Results demonstrate the important role of mechanical compaction in diagenesis and its influences on the distribution of quartz cement. Understanding the association between deformation and cementation may enhance porosity and permeability prediction, with implications for reservoir quality prediction in the subsurface.