Sediment petrography

All magnifications refer to a 13 inch (32 cm) wide screen set to 800 x 600 pixels.
Thin sections are standard epoxy-impregnated prepararations from air-dried sediment specimens.


 


Thin section of black organic-rich sediment, approx 9 times natural size. The cracks along the top of the image were made during mounting of the section. The brown streaks represent fragments of leaves. The round white object is a large quartz sand grain, while the brown object, lower right may be a leaf petiole. Additional sand grains, a chert grain, and gypsum are also present.


Detail from the small "hairpin" structure, at the center of the
right half of the image above, Approx. 225 x magnification.


More highly magnified, (720 x) details of the cellular structure become apparent. At standard thickness for petrographic thin sections, 30 microns, not all details are in focus simultaneously.


Dark gray sediment, 4 x natural size. The two light patches in the lower right corner are gypsum crystal agglomerations, visible in the image below.


Dark gray sediment, under polarized light, approx 80 times magnification. Large star-shaped object is an agglomeration of gypsum crystals. The large object, top center, and the vertical needle-like structure, upper left are also gypsum. These may have formed during the drying of the sediment specimen. Bright pink/orange/white grains are detrital carbonates, and blue gray grains are quartz and feldspar.

 

   
Laminated sediment,
approx. 9 x magnification.
    Boundary between coarse- and fine-grained
sediment., polarized light, approx. 80 x magnification.
Bright pink grains are detrital carbonates,
blue-gray grains are quartz and feldspar.


Thin section from the red indurated siltstone bed, approx. 9 x magnification.


Approx 360 x magnification of the siltstone above. The high-relief orange grains appear to be
siderite, FeCO3.


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