Interpreting sandstone CL images, an introduction.

Images are color CL, showing fractures and microfractures in sandstones. Larger images are composites of 2 or more scans.

The Fall River Fm. from Wyoming. (245 Kb) One of the more dramatically fractured images I've ever taken. I'd rate it Ia+.

A partially-open fracture from the Flathead Fm. (856 Kb, FC6) Quartz grains are mostly red (some blue) Feldspars are dark blue and typically surrounded by a black rim of authigenic feldspar cement. Greenish-tinged dark areas are epoxy-filled fracture porosity. This sample is unusual for a quartz-cemented sandstone in that the quartz cement surrounding the detrital grains is bright red instead of the usual black to faint red.

A partially-open fracture from the Frontier Fm. (1.0 Mb, BH3-36) Depth in excess of 20,000'. Red is mostly detrital quartz and quartz cement. Greenish-tinged dark areas are epoxy-filled fracture porosity. Newer, better version.

A calcite-filled microfault from the Tensleep Fm. (308Kb, GV005C) Quartz is mostly red, calcite is dark blue cement. Some dark blue is feldspar surrounded by a black rim of authigenic feldspar cement. Greenish-tinged dark areas are epoxy-filled porosity.

The Palmerton Fm. from eastern Pennsylvania. (color, 443 Kb) 2 or more generations of microfracturing.

The Mt. Simon Fm. from northern Illinois. (color, 557 Kb) An intergranular quartz-filled microfracture cutting across several well-rounded quartz grains. The black, euhedral shapes in the center of the microfracture are crystals of barite.

The Frontier Fm. from Wyoming. (color, 261 Kb) One of the more colorful images of a sandstone that I've ever taken. Sample courtesy of Union Pacific Resources. A blue luminescent quartz grain is cut by fractures filled with red luminescent cement.

The Weber Fm. from northwest Colorado (gray-scale, 120 Kb, L15-5618C). A series of transgranular microfractures occur at a highly oblique angle to a macrofracture. The microfractures appear to predate the macrofracture.

The Weber Fm. from northwest Colorado (color, 92 Kb, L15-5618C). A concentrically-zoned quartz grain of probable igneous protolith with transcement microfractures.

Litharenites are challenging, at least when it comes to cathodoluminescence imaging. Some images from outcrops of the Frontier Fm. Samples courtesy of Jon Olson, UT-DoPGSE

Image 1 (Color, 699 Kb, J0-F-52.1) I'd bet that the blue-grey grain with the black cement rim in the left center part of the image is a feldspar with authigenic feldspar cement.

Image 2 (gray-scale, 264 Kb, J0-F-52.1) A fair amount of grain-crushing fractures, and a number of grains of peculiar luminescent characteristics.

Another litharenite

A v. coarse-grained poorly-sorted litharenite showing several styles/generations of microfracturing (color, 147 Kb) . The large black vertical fracture is open and probably related to sampling or preparation, but at least two quartz-lined fractures in other orientations cut both a grain and the surrounding cement. The blue grain is probably quartz. The complex grain in the upper right is probably a volcanic rock fragment. Sample courtesy of S. Dutton.

Single image close-ups of parts of a carbonate-cemented sandstone from the Tensleep Fm.

Image 1 (color, 252 Kb, GV005C) The dark blue grain in the right center of the photograph surrounded by the black rim is a feldspar with a rim of dark authigenic feldspar cement. Notice the transgranular fracture that cuts from the orangish quartz grain across cement and into the feldspar.

Image 2 (color, 252 Kb, GV005C)

A quartz grain from the Bone Springs Fm. of west Texas (color, 77 Kb). The blue grain shows internal zoning which suggests the grain originated either in an igneous rock or a fill in a fracture (either method could produce this zoning). The grain has three generations of authigenic cement. A truncated dark blue zone (which may be relict from a previous lithologic cycle), an orange zone, and an almost non-luminescent zone. Letters indicate the elements showing up in an EDS analyses of the "+".

A genuinely weird NaCl-cemented sandstone (color, 47Kb) from the Palo Duro Basin of the Texas Panhandle. The yellow-green luminescing cement is the halite. Blue grains at the top are k-spar with non-luminescent authigenic feldspar cement.
Sample courtesy of S. Hovorka UT-BEG.

A few miscellaneous sandstone images

Sandstone images that I'm not really sure if I can tell you where they are from, but since these are some of the best images I've ever gotten I'm going to show them anyway.

More sandstone images that I'm not really allowed to mention from whence they came.


A production of:
Robert M. Reed, Ph.D.
Bureau of Economic Geology
The University of Texas at Austin