Sed Strat Sample Questions SECTION I-V

Sed Strat Sample Questions SECTION I-V - Sedimentology and...

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Sedimentology and Stratigraphy Sample Questions SECTION I 1) A sandstone has the following characteristics. Composition 40% quartz; 30% K-spar; 27% rock fragments (fragments include: rhyolite(20%); quartz arenite(6%), and limestone(1%)); 2% accessory minerals (biotite, magnetite, and hornblende); 1% illite as matrix; 22% calcite as cement Fabric Rhombohedral packing; quartz grains have sutured boundaries Texture The mean grain-size is .75 mm with a standard deviation of 2.38 mm (1.25 phi) and a slight negative skew; quartz-grain roundness values have a bimodal distribution, with 50% of all quartz grains having an average roundness of 5.5 and the other 50% having an average roundness of 2.5; K- spar grains and rock fragments have an average roundness between 1 and 3 Other features K-spar, rock fragments, and accessory minerals are highly degraded (chemically broken down); the entire rock is stained a dark red color A) Classify this rock according to the McBride (1963) classification scheme. What is the mineralogic maturity of this sample? What is the textural maturity of this sample? B) Offer a possible historical interpretation for this rock. Be sure that your answer includes: discussion of rock types in the source area and geologic/tectonic setting of the source area (provenance), dominate modes of weathering in the source area, transport distance/processes, and diagenesis. Your discussion should offer a logical explanation for all of the descriptive features listed above, and all such explanations should be consistent with your overall historical interpretation. For each interpretive point, cite the features which support your argument. A point that is not supported is pointless! 2) Bedrock with the following composition undergoes weathering in southeast Missouri (Note: This is a modestly warm modestly humid temperate environment). 10% Basalt (20% olivine, 40% pyroxene, 30% Ca-feldspar, 10% amphibole); 70% Granite (30% quartz, 40% K-spar, 20% albite, 10% biotite); 20% Arkose (35% quartz, 35% K-spar, 10% albite, 10% basaltic rock fragments, 10% calcite cement) A) Identify the weathering processes which will act upon such bedrock in an environmental setting like that found in southeast Missouri. Indicate the processes which will be most important. Support your answer. B) List the above three rock types in order of increasing stability under Missouri weathering conditions. Support you answer. C) Identify the weathering products, and their relative proportions generated by weathering of the above rock sequence in the southern Missouri climate. Indicate general
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composition and relative proportions of specific residual/secondary minerals and detrital grains produced. Indicate the solutes produced by weathering. 3) A floodplain mud deposit 4 m thick in a dry region is composed of clay minerals
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This note was uploaded on 01/03/2011 for the course GEOL 3442 taught by Professor Staff during the Spring '08 term at UT Arlington.

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Sed Strat Sample Questions SECTION I-V - Sedimentology and...

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