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Quiz%203%20comments - compositionally immature(2 A feldspar...

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Quiz 3 1. Sorting – good sorting improves porosity because there are not smaller framework grains to till among the coarser framework grains 2 pts Matrix – abundant matrix decreases porosity and low matrix increases porosity 2pts Grain shape – impact on porosity not well understood 2 pts Grain size (other than matrix) is not an aspect of textural maturity and does not impact porosity although it influences permeability 2. Feldspathic arenite is <10 to 15% matrix, <90% quartz; feldspar>lithics 1.5 pts Quartz arenite is < 10 to 15% matrix and > 90% quartz 1.5 pts To answer this you might focus on the matrix and suggest that a texturally immature sample should be a wacke not an arenite. I accepted that answer but point out that an arenite can have some matrix and thus, not be excluded as a texturally immature sample if the sorting is poor etc. The second approach is to focus on using textural maturity to predict compositional maturity. (1) A texturally immature sample suggests that the sample is also
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Unformatted text preview: compositionally immature. (2) A feldspar rich sample is compositionally immature, which is consistent with textural immaturity, therefore this is possible. (3) A quartz rich sample is compositionally mature, which is not consistent with the degree of transport typical of a texturally immature sample and the removal of unstable minerals or lithic fragments. 3. The most important information to be obtained from a rock fragment is the lithology of the source rock because the lithic fragment is a direct representation of source lithology. Lithic fragments can help determine compositional maturity; however, not all lithic fragments mean immaturity. Some lithic fragments (limestone fragments) are easily broken down but others (chert, quartzite) are very resistant. So, if you use lithic fragments to determine compositional maturity, you do need to determine the type of lithic fragment....
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This note was uploaded on 03/02/2010 for the course GEOL 3430 taught by Professor Kraus during the Spring '10 term at Colorado.

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