c8_continental_environments

c8_continental_environments - Part I Origin and Transport...

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Part I Origin and Transport of Sedimentary Materials MONDAY SEPTEMBER 21 EXAM 1 (CHAP. 1 AND 2) Part II Physical Properties of Sedimentary Rock WEDNESDAY OCTOBER 7 EXAM 2 (CHAP. 3 AND 4) Part III Composition, Classification, Diagenesis of Sedimentary Rocks MONDAY NOVEMBER 2 EXAM 2 (CHAP. 5,6 AND 7) Part IV Depositional Environments Part V Stratigraphy and Basin Analysis FRIDAY 3-5 pm DECEMBER 11 EXAM 2 (CHAP 8-12)
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C8 marginal marine environments
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Depositional environments • C8 continental environments • C9 marginal-marine environments • C10 siliciclastic marine environments • C11 carbonate and evaporite environments • C12 lithostratigraphy concepts
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C8 Continental environments • 4 kinds – Fluvial, desert, lacustrine and glacial • Similar sediments generated in more than one environment – E.g., eolian sediment found in deserts and glacial settings – E.g., fluvial sediments mainly in rivers of humid regions but also found in desert and glacial settings • Dominantly siliciclastic sediments – But also freshwater limestones and evaporites • Scarcity of fossils • Absence of marine fossils
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Fluvial systems Fluvial deposits = sediments generated by activities of rivers, streams and associated gravity flow processes • Two broad environmental settings that may overlap – Alluvial Fans – Rivers
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Alluvial fans: definition and depositional setting Alluvial fans = – convex up sediment cone @ confined channel mouth – Typically poorly sorted sediment – Abundant gravel detritus – Common at mountain-canyon base – In arid areas, AFs merge downslope with desert-floor internal drainage – In humid areas, AFs merge downslope with alluvial or delta plain and beach/tidal flat – Fan deltas = AFs built into lakes or ocean – Bajadas = coalescing AFs along a mountain front Debris-flow dominated AF canyon Mouth in Death Valley California
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Alluvial fans: Subdivision based on depositional process • Debris-flow dominated AFs – DFs may contain blocks and large boulders – Poorly sorted with muddy matrix – Steep with little vegetation – Mudflows and landslides may also common • Stream-flow dominated AFs – Sheet flow = broad unconfined sediment-laden runoff – Incised-channel flow = confined flow thru channels (usu. 1-4 m depth) – Sheet like deposits at fan margin – Gravel, sands, silts – Moderately well sorted
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Distinguishing characteristics • Cone or arcuate in plan view • downslope network of distributary channels • Concave upward in long profile • Greatest slope at fan apex • Convex upward on cross-fan profile • Downfan decrease in grain size and bed thickness • Downfan increase in sorting • Usually thickening and coarsening upward successions from active AF growth
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Ancient AF: Cannes de Roche Formation, Canada • Carboniferous Formation • Lower member = AF debris flow and stream flow deposits – Coarse red breccia = debris flow • Cherty limestones clast • Poorly sorted • Lacks stratification
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This note was uploaded on 02/20/2010 for the course GEOL 3032 taught by Professor Bouma,a during the Fall '08 term at LSU.

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c8_continental_environments - Part I Origin and Transport...

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