7. Compare the photomicrographs of sandstones in Figure 3.8 A and Figure 3.8 B.

Question

7. Compare the photomicrographs of sandstones in Figure 3.8 A and Figure 3.8 B. Which sandstone is more texturally mature? Which one is more compositionally mature?

8. Compare the photomicrographs of sandstones in Figure 3.8 A and Figure 3.8 C. Which sandstone is more texturally mature? Which one is more compositionally mature?

C. Thin section of felspathic arenite. Angular quarta (q) and feldspar (f) grains floating in calcite cement A. Thin section of subrounded quartz (q) grains embed- B. Thin section of fine-grained quartz arenite. Note ded in blue epoxy resin rounded quartz grains.

Explanation / Answer

The ratio of quartz to other components (feldspar and lithic fragments combined) is an index of compositional maturity. If a rock contains a low proportion of quartz and a higher proportion of softer, unstable elements, it an immature rock. If the sample contains a high proportion of resistant, stable quartz compared to the unstable elements it is a more mature rock.

In terms of textural maturity, a rock is immature when it contains angular, poorly sorted grains, and it is mature when it contains rounded, well-sorted grains

Using the above definitions

7) texturally mature :3.8B)

Compositionally mature : 3.8 B)

8) texturally mature : 3.8 A)

Compositionally mature : 3.8 A)

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