COMPETITION BETWEEN FRACTURE GROWTH AND CEMENT PRECIPITATION IN NUGGET SANDSTONE: INFLUENCE ON VOLUME AND DISTRIBUTION OF FRACTURE POROSITY

Using petrography, fluid-inclusion analysis and high-resolution scanning electron microscope (SEM) -based cathodoluminescence mosaics we characterize fracture populations in Jurassic Nugget Formation sandstones, Utah. These outcrops are unusually well-preserved examples of fracture size distributions and internal textures—particularly fracture porosity structure—matching those found in cores from many deep basins. We report size scaling and fracture opening and sealing patterns that is a widespread structural association in core but that has not been described from outcrops, where other aspects of fracture patterns can be documented. Size scaling follows a power law that is similar to those measured in previous core studies. Evidence of coupled diagenesis and mechanics within growing and static fractures documents episodic fracture growth and later gradual, sometimes diverse, destruction of fracture porosity. Fracture porosity depends on growth processes that result in power-law fracture size distributions and on cement precipitation. Kinematic evidence in fractures shows these are linked processes. Results imply that fracture growth, fluid flow in deep basin fractures and fracture seismic response depends on diagenetic state.