Cathodoluminescence Images
for Compaction, Quartz Cementation & Porosity in Sandstone

Plane polarized light photomicrograph of a Bromide sandstone sample from Oklahoma illustrating the obscure nature of grain-cement relationships. Field of view shows quartz grains, quartz cement, and a small amount of intergranular porosity (dark blue epoxy has been partly discolored to brown by electron beam). Dust rims are present beween some grains and cement, but are insufficient to objectively define grain boundaries.(All bar scales are 200 micrometers long.)

Bromide sandstone from Oklahoma

Crossed polarized light photomicrograph of same field of view as A, illustrating that crossed polarization does not clarify grain-cement relationships.

CL micrograph of same field of view A and B, illustrating clear definition of grain-cement relationships, porosity(P), and additional details not revealed by transmitted light microscopy. Grain contacts can be distinguished as floating(F), tangential(T), long(L), and concavo-convex(C); no sutured contacts are present. Quartz overgrowths display distinct zonation, with an earlier zone of dull luminescence and a later zone of brighter luminescence(white arrow points to contact between zones). Some overgrowths nucleated on one grain are molded against rounded boundaries of other grains(white arrow), suggesting that some grains were better suited for authigenic quartz nucleation than others. Blue luminescing grain in lower part of micrograph contains a fracture healed by authigenic quartz(black arrowhead).

CL micrograph of Bromide sandstone sample from Oklahoma illustrating grain boundary extension fractures healed by authigenic quartz(black arrowheads). This field of view also shows a variety of grain contact geometries indicative of intergranular pressure solution, zoned quartz overgrowths(O), and porosity(P).

CL micrograph of Upper Cretaceous sandstone sample from the Green River basin illustrating plastic deformation of a ductile lithic fragment, a micritic limestone(bright orange luminescence labeled with a black M) squashed during mechanical compaction. Note distinction between the micritic lithic fragment and more coarsely crystalline calcite cement(black C). This field of view also shows pore filling kaolinite(bright blue luminescing mineral labeled K) and a siltstone lithic fragment(S). All other grains are quartz.

CL microgrph of Lower Cretaceous Mdduy Sandstone sample from the Powder River basin illustrating grain and cement truncation along a stylolite(S). Note truncation of both quartz grains and quartz cement(white arrows) along margin of stylolite. The stylolite is composed of authigenic illite(relatively non-luminescent, or black) that precipitated during stylolitization plus accumulations of relatively insoluble silicaate minerals, including feldspars(green)and remnants of quartz grains(red-brown). Pore filling kaolinite is bright blue and all grains are quartz. The relatively rough appearance of the microhraph is the result of insufficient polishing of the thin section.

CL micrograph of St. Peter Sandstone sample from the Illinois basin illustrating absence of grain contacts indicative of intergranular pressure solution, presence of dully luminescent quartz overgrowths(O), and presence of anhydrite cement(striped luminescence in pale blue and red-blue; labeled A) that clearly post-dates the quartz overgrowths. All grains are quartz.

CL micrograph of St. Peter Sandstone sample from same area and similar depth as sample shown in G. This field of view illustrates grain contact geometries indicative of intergranular pressure solution, an eaarly zone of dully luminescent quartz overgrowths(white arrows), a later zone of brighter luminescent quartz overgrowths, and remnant intergranular porosity(P).