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Classification of Siliciclastic Sedimentary Rocks

Classification of Siliciclastic Sedimentary Rocks. Why bother with sedimentary classification?. Particle size classification = energy of deposition Grain type classification = origin of sediment The Problem: Sedimentary rocks come in more “flavors” than any other type of rock.

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Classification of Siliciclastic Sedimentary Rocks

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  1. Classification of Siliciclastic Sedimentary Rocks

  2. Why bother with sedimentary classification? Particle size classification = energy of deposition Grain type classification = origin of sediment The Problem: Sedimentary rocks come in more “flavors” than any other type of rock. How do you classify all of them? 1.5 mm FOV, PPL

  3. Sorting: Sorting is a measure of how similar grain sizes are within a sediment or rock and tells us about the relative strength of the current before it dropped (deposited) it cargo.

  4. Roundness: Angularity or roundness (antonym) is a measure of the distance of transportation (sort of)

  5. Conglomerates: Rock Fragments (not mineral grains) Generally larger than V.C.S. 2 types: Conglomerate vs. Breccia

  6. Concerning Sandstones: WACKE vs. ARENITE WACKES ARENITES HAVE HAVE >10% MATRIX <10% MATRIX (once you've decided "wacke" or "arenite", now you must describe mineralogy…) IS IT A "QUARTZ ARENITE" OR A "FELDSPATHIC WACKE" OR AN "ARKOSIC ARENITE"…

  7. Mudstones, Shales, etc. • >2/3 composition is silt = Siltstone • 2/3-1/3 composition silt = Mudstone • <1/3 composition is silt = Claystone • Laminated + brakes into sheets = Fissile Shale

  8. Diagensis = Diagnesis includes • (1) compaction = volume loss (mechanical squeezing) and is accompanied by dewatering (= water loss) (by chemical or physical means) • (2) changes in mineral composition (chemical process with heat and or fluids) • (3) cementation (physical) If a sediment eventually becomes a rock we say it is lithified.

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