Picture Page 4: Silica Filled Cysts in the Chattanooga Shale

Silica filled cysts in the Chattanooga Shale (Late Devonian) are a potential source of "in situ" silt to sand-sized quartz grains (Schieber, J., 1996. Early diagenetic silica deposition in algal cysts and spores: A source of sand in black shales? Journal of Sedimentary Research, v. 66, p. 175-183). The following four pictures illustrate these grains. If you have seen shales with features resembling those shown below, send me a message ( schieber@uta.edu ). Photos are low resolution for faster loading. Click on the image to get a larger, high resolution picture.

Figure 4/1: Photomicrograph of Chattanooga black shale with abundant silica filled cysts (bright spots). Most cysts have been partially compressed. Scale bar is 0.1 mm long.
Figure 4/2: Photomicrograph (close-up) of partially compressed silica filled cyst. The quartz grain in the center is a single crystal, and is surrounded by the organic cyst wall (brownish membrane). The scale bar is 0.1 mm long.

Figure 4/3: Photomicrograph of spherical cyst in dolomitic shale bed. Shows the radial fibrous texture of chalcedony (crossed polarizers) that infills the cyst. The scale bar is 0.1 mm long.
Figure 4/4: Photomicrograph of a cyst quartz grain in a sandstone bed. The organic cyst wall has been removed during reworking, but the grain still shows an outer rim of fibrous chalcedony (marked R), and a central portion that is filled with megaquartz (marked M). The scale bar is 0.05 mm long.

 

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More Pictures on Sculpting of Muddy Bottoms, Erosion Surfaces and Ripples

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© Jürgen Schieber, UTA Department of Geology
Last updated: March 12, 2001.