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Transcript
CEE 437 Lecture 11 Sediments and Soils Thomas Doe What You Should Know Relationship of flow velocity to erosion, transport, and deposition Major depositional environments and their typical sediments Fluvial Alluvial Fan Deltaic Aeolian Beach and Lagoon Continental Shelf/Slope Waltham Sections 03 – Surface Processes: All 13 – Weathering and Soils: 14 – Floodplains and Alluvium – page 28 Emphasis on fluvial environments and their variability 17 – Coastal Processes agronomic and engineering soil definitions Physical vs chemical weathering Depth and climatic controls on weathering Limestones Sediment transport only 28 – Subsidence on Clays General familiarity, Expansive soils Be aware of where clays occur geologically Outline Why this is important Soil definition Flow Basics Features of depositional environments Depositional environments Continental Transitional Marine Soil and Sediment Definition (Waltham 13) Geologists and Agronomists Zone of weathered material, zoned from the surface with a significant component of organic material especially in the upper zones Engineers Weak material that can be excavated without ripping or blasting Granular materials appropriate for soil mechanics study Loosely covers sediments as well Energy Distribution in Channels Critical Drag Forces on Particles Settling, Suspensions, and Stokes Law Settling Velocity = 1/18 [((rs-rf) g D2)/m] Hjulström’s Diagram Sediment Sorting Also Waltham – Sediment Size Distributions Sedimentary Structure — Cross Bedding From Waltham Ripples, Dunes, Crossbeds Overview of Environments http://encyclopedia.vbxml.net/File:SedimentaryEnvironment.jpg Depositional Environments Synchroneity of deposition of different rock types Sedimentary facies Related to energy of environment A rock unit is not everywhere the same age: Bright Angel Shale (example channels and banks in fluvial systems) Energy related to topography, climate, and tectonic activity Some Challenging Environments (important slide) Fluvial Deposits from Suspensions (Lahars,Turbidites,Flood Deposits) Wide range of velocities Channels moving with time Difficult interpolations Very loose packed sands Highly unstable and liquefiable Lacustrine and Lagoonal High clay contents If under-consolidated, highly compressible Mexico City Venice Continental Environments Modified from Pamela, Gore, Georgia Perimeter College http://www.gpc.edu/~pgore/geology/historical_lab/environmentchart.htm Continental Environments Weathering and Mass Wasting Alluvial Fans Fluvial Environments Wide range of velocities Wide range of sediments Flow localized to channels which are moving over time Difficult to interpolate and extrapolate conditions using boreholes Fluvial and Lacustrine Environments Lacustrine Deltaic deposits at margins, finer materials in lake beds Settling area for fines and concentration of clays Alluvial-Lacustrine Example http://www.gnb.ca/0078/Minerals/pdf/McCully_Gas_Field_Project-e.pdf Clays Quick Clays Formerly glaciated areas (Scandinavia, Alaska, Canada, Russia Sudden and catastrophic loss of strength with liquefaction Chemical interactions as fresh water replaces marine? Mexico City Settlement Aeolian Deposits Transitional Environments Transitional Environments Modified from Pamela, Gore, Georgia Perimeter College http://www.gpc.edu/~pgore/geology/historical_lab/environmentchart.htm Deltaic Environments Variability based on proximity to source Stratigraphy effected by progradation Deltaic Development and Sedimentary Facies Marine Depositional Environments Modified from Pamela, Gore, Georgia Perimeter College http://www.gpc.edu/~pgore/geology/historical_lab/environmentchart.htm Marine Environments Continental Slope Environments Turbidites and turbidity currents Graded bedding poor sorting vertical zonation with fining upwards Turbidites and Turbidity Currents Turbidity Flow – Bouma Sequence Often soft sediment deformation
