402-pp18 - UNIVERSITY OF SOUTH ALABAMA GY 402: Sedimentary...

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Unformatted text preview: UNIVERSITY OF SOUTH ALABAMA GY 402: Sedimentary Petrology Lecture 18: Volcaniclastic Petrography Last Time Sandy Fluvial Siliciclastic Environments Meandering river dynamics Sedimentary facies The model (vertical sections) Meandering Rivers Are characterized by a distinct suite of facies and processes Oxbow lakes Levees Floodplains Cut banks Point bars Yazoo streams Cutoffs Meandering Rivers Water velocity is greatest where the channel is deepest resulting in a "corkscrew" flow pattern. http://www.geocities.com/sogodbay/Images/SDK/Inecar03.jpg Meandering River Facies The result is a classic fining upwards trend in point bars. From Walker, R.G., 1979. Facies Models. Meandering River Facies Apart from deposition in channels, rivers (meandering and braided alike) periodically flood resulting in sedimentation on flood plains Meandering River Facies Flood plain deposits are mostly laminated shales with plant fossils Sometimes paleosol horizons can be found Meandering River Model From Walker, R.G., 1979. Facies Models. Geoscience Canada Reprint Series 1, 211p. Today's Agenda Volcaniclastic Sedimentary Rocks Origin of volcaniclastic sedimentary rocks Classification of volcaniclastic sed. rocks Thin section petrography Volcaniclastic sedimentary rocks Volcaniclastic sedimentary rocks Volcaniclastic sedimentary rocks Air fall (tephra) Volcaniclastic sedimentary rocks Air fall coarse fine Volcaniclastic sedimentary rocks Pyroclastic surge deposits (Ignimbrite) Volcaniclastic sedimentary rocks Pyroclastic eruption (New Zealand 1980's) Volcaniclastic sedimentary rocks Volcaniclastic sedimentary rocks tephra ignimbrite tephra ignimbrite Volcaniclastic sedimentary rocks Volcaniclastic sedimentary rocks are sedimentary rocks... Volcaniclastic sedimentary rocks Parallel laminations Volcaniclastic sedimentary rocks are sedimentary rocks... Channel lag ... they follow sedimentary rules Volcaniclastic Petrography Carozzi, Source: Carozzi , A.V., 1993. Sedimentary Petrology. Prentice Hill, 263p. Carozzi, Source: Carozzi , A.V., 1993. Sedimentary Petrology. Prentice Hill, 263p. Volcaniclastic Petrography Lithic Tuff Carozzi, Source: Carozzi , A.V., 1993. Sedimentary Petrology. Prentice Hill, 263p. Volcaniclastic Petrography Crystal Tuff Carozzi, Source: Carozzi , A.V., 1993. Sedimentary Petrology. Prentice Hill, 263p. Volcaniclastic Petrography Vitric Tuff Vitric Tuff ppl porosity xn vitric fragments 5mm Vitric\Crystal Tuff quartz rock frag ppl vitric fragments xn 1.5mm Vitric\Crystal Tuff ppl xn 1.5 mm Vitric\Crystal Tuff ppl xn 3 mm Crystal Tuff ppl ppl xn 2mm 0.5 mm xn Vitric Tuff ppl Pumice fragments xn 1.5 mm Beware the red stain of calcium carbonate (see 2nd page of today's lab assignment) Flow Banded Tuff ppl xn zeolites?) 1.5 mm non-isotropic! (recrystallized to Upcoming Stuff Homework 1) Peer Review Exercise due now 2) Volcaniclastic thin section lab due Thursday Lab This Week Volcaniclastics lab Next Lecture: Deltas ...
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