SAND GRAIN PROVENANCE CONTROLS STYLE AND AMOUNT OF QUARTZ CEMENT

SEM and cathodoluminescence (CL) were used to characterize hand-picked grain fractions from several fluvial sandstones for quartz cement stratigraphy and CL-based quartz provenance types. Quartz provenance appears to significantly influence the style and volume of quartz cement on a given grain. Three generations of overgrowths were documented by CL: (1) A dark, non-luminescent, thin (10-25 µm), and rough-textured layer of small coalescing crystals. Pore-filling kaolinite clearly pre-dates this first generation, as the non-luminescent quartz has grown around booklets and vermicules of the authigenic clay. This is particularly evident where kaolinite has been dislodged, leaving perfect casts of the clay crystals in quartz surfaces. (2) A moderately luminescent, thicker (20-125 µm), and better-developed layer with euhedral faces. It is volumetrically greater than the first generation and shows faint internal CL zoning. (3) A relatively brightly luminescent layer occurring in only trace amounts as scattered, isolated crystals on a few second-generation overgrowths. Hand-picked "clear" quartz grains are dominated by CL textures indicative of deeper plutonic crystallization, with lesser amounts of mechanically-tectonized metamorphic grains. The relatively strain-free plutonic grains have the thickest and best-developed quartz overgrowths. Dark, first-generation quartz cement is more uniform in thickness, and has smoother outer margins than on more-strained grain types. Lighter, second-generation overgrowths are much thicker, more uniform, and almost always show euhedral faces. "Frosted" and "cloudy-interior" grains are dominated by the higher-strain CL textures of intermediate-level plutonic grains, highly tectonized metamorphic grains, and internal quartz micro-veining common in stockworks on pluton margins. Dark, first-generation cement is less uniform in thickness and often shows ragged margins due to growth of multiple small crystals. Lighter, second-generation cement is not always present, and shows greater variability in thickness and grain coverage. Multiple crystal orientations and defects are likely not conducive to nucleation and growth of thick, uniform overgrowths; this may explain the difference in quartz cement development on strained versus unstrained grains.