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SEDIMENTARY ROCKS

SEDIMENTARY ROCKS. MUDROCKS. SEDIMENTARY ROCKS. Mudrocks:. 2/3 of all sedimentary rocks, but poorly understood: not very resistant too damn fine-grained clays change composition. SEDIMENTARY ROCKS. Mudrocks:. Color: gray to black – free carbon, reducing environment

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SEDIMENTARY ROCKS

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  1. SEDIMENTARY ROCKS MUDROCKS

  2. SEDIMENTARY ROCKS Mudrocks: • 2/3 of all sedimentary rocks, but poorly understood: • not very resistant • too damn fine-grained • clays change composition

  3. SEDIMENTARY ROCKS Mudrocks: Color: gray to black– free carbon, reducing environment red– ferric oxide brown- ferric hydroxides green– unstained, color of clay minerals

  4. SEDIMENTARY ROCKS Mudrocks: Texture: grain size and sorting by nibble method roundness and shape by assumption: qtz always angular, clays tabular

  5. SEDIMENTARY ROCKS Mudrocks: Structure: fissility – property of breaking along thinly spaced planes parallel to bedding flocculation? compaction? lamination – layer within, parallel to bed lamina < 1 cm; bed > 1 cm

  6. SEDIMENTARY ROCKS Mudrocks: • Composition: • first approach by nibble method • petrographic scope – resolution .5 – 1 µm; • sodium bisulfate fusion – qtz vs K-spar • X – Ray diffraction • SEM & microprobe

  7. SEDIMENTARY ROCKS Mudrocks: • Composition: • Clays • montmorillonite – Na, Ca clay, most abundant in young rocks • illite – K – clay found in older rx; 4km, 100°C • kaolinite – 3rd in abundance; hot, wet climates

  8. SEDIMENTARY ROCKS Mudrocks: • Composition: • B.Quartz • 30% of average mudrock • mostly silt • always angular • detrital vs. secondary?

  9. SEDIMENTARY ROCKS Mudrocks: • Composition: • C. Feldspar • about 5% of average mudrock • not much known • surprising to exist in such small size • secondary?

  10. SEDIMENTARY ROCKS Mudrocks: • Composition: • D. Others • carbonate – calcite common cement, dolomite common in older rx • pyrite • hematite • organic matter

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