Linked Mechanical and Chemical Processes in the Diagenesis of Sandstones

Kitty L. Milliken, Jackson School of Geosciences, The University of Texas at Austin, Austin, TX

Cathodoluminescence imaging has served to reveal previously unrecognized linkages between brittle processes and cementation in a wide variety of diagenetic settings. Because nucleation of quartz cement is highly localized on pre-existing quartz substrates, fracture processes enhance the potential for quartz cement emplacement by creating favorable surfaces. This phenomenon is observed in the context of burial compaction, in deformation bands, in quartz-rich fault gouges, and in tectonically-produced transgranular fractures. In each case the amount of quartz cementation is greater than the amount that would occur in the absence of fracturing. In turn, the quartz cementation imparts changes in the mechanical properties of sandstones. The conceptual framework that emerges from these observations is one in which mechanical and chemical properties of sandstones evolve in concert. Reservoir quality assessment in rocks that have experienced a protracted history of diagenesis requires approaches that explicitly acknowledge the genetic links between chemical and mechanical processes.