Grain Morphology

Grain Morphology

Domain of things that sedimentary are….1 A) Broad realm of the sedimentary…. Etymology: from the L. “sedimentum”, meaning “to settle out”, first used by C. Lyell (1830) in Principles of Geology to distinguish major genetic category of Earth’s rocks. Sedimentary components include: 1. particulates o clastic (derived from the greek “klastos”, meaning “broken”) . physically broken from bedrock o chemical precipitates . changes in a solution. a solution = solute + solvent o biogenic (from Gk. “bio”, meaning “life” and genic “ from Gk. “genesis" meaning “origin, creation" 2. fluids: (derived from the L. “fluidus” meaning “ to flow”), an inelastic material that permanently changes its shape in response to force, superductile o all four phases of matter may exhibit fluid behaviour: some solids (L. “solidus” meaning "firm, whole, entire" ice, glass), liquids (L. “to melt” or “flow”), gases (Gk. “khaos”), and plasmas (from Gk. “plasma, plassein” meaning “molded, spread thin”) o flow rate is quantified and qualified . viscosity (from L. “viscum” meaning “sticky substance”), defined as “resistance to flow” Earth’s Atmosphere, Hydrosphere, and Cryosphere all exhibit fluid movement (e.g. currents, convection) o Outer shells of density-stratified planet o Therefore, sedimentary environments include the parameters of the atmosphere, hydrosphere, and cryosphere, and their boundaries or interfaces with the lithosphere. o Temperature range from the (coldest temperature recorded on Earth, Vostok, Antarctica in 1983, -89 ºC (-129 ºF)) to about 150ºC (temperature of low grade deep burial metamorphism) Planets and other small solar system bodies (SSSBs) with significant atmospheres, cryospheres, or liquispheres also exhibit sedimentary processes o Examples include: Venus Mars Titan © WB Leatham, 2012 Domain of things that sedimentary are….2 Sedimentary Processes: Formation of Sediment: Breakdown of bedrock or other sediments, can have multiple geneses Weathering—breakdown of bedrock due to stationary exposure to surficial fluids 1. Disintegration (L. dis = “apart”, L. integratus = "make whole") Vulgar term = physical weathering, physical breakdown of rock Energy for disintegration from o Release of pressure trapped in crystallization, recrystallization, and diagenetic processes Plutonic magmatic crystallization Recrystallization due to burial metamorphism Deeply stratified sedimentary rocks . Process of Exfoliation Sheet structures o Gravitational Force (main component), synonymous with Mass- wasting) . Removal of underlying or lateral support . Stability = Gravitational Force/(bedrock or sediment strength) Slope and nature of lateral support (vectors of force) Strength of intergranular contacts o Composition dependency o Component morphology (shapes and surfaces) Changes in rock/sediment mass through permeation by intercomponent fluids o Permeabilty and porosity Friction o Shape factors o Surface factors o Fluid factors Types of movements (classified by direction and style of movement, and velocity) o Fall—movement is primarily through fluid, no surface parallel movement (fastest) o Topple—rotational fall around connected base (fast) o Roll, Tumble—material is transported along a slope, not induced by fluid flow . Origin usually a fall or topple o Slump—rotational movement producing curvilinear scarp © WB Leatham, 2012 Domain of things that sedimentary are….3 . Head scarp, basal scarp, often occurs in homogenous permeable materials . Upper surface often held intact or in blocks o Slide—movement is parallel to inherent structure of components or slope . stratigraphic control compositional differences attitude control . slope control . materials involved usually greatly broken through process . intergrades with flows in high- velocity systems e.g. Blackhawk/Silver Reef Slides, Gros Ventre Slide, Elm, and several others o Flow—material involved behaves as fluid, friction of material exceeds intergranular stability . Occurs at base of surface/fluid interface . Grainflow—elastic rebound of grains Lunar flows in craters, Martian flows, slipface of dunes, etc. Fluid/Sediment mixtures Fluid decreases grain friction Mudflow Debris flow Rock Flow . Avalanche May ride on cushion of fluid, decreasing friction, attaining speeds approaching free-fall velocity e.g. Blackhawk/Silver Reef Complex, Elm Switzerland Colorado Rocky Mountain High Snows o Build-up of weight in cornice, collapse, trapped air underneath breaks snowpack into granules separated by fluid © WB Leatham, 2012 Domain of things that sedimentary are….4 o o Phase change of H2O . Volumetric expansion begins about 3 ºC as energy is removed from system . Polarity of H2O aligns molecules along axis, spreading them apart, decreasing density, forms a hexagonal structure . Over 12 different structural phases of Ice exist, the one found at the Earth’s Surface is Ih (hexagonal ice) . Density of Ih is 0.917 g/cm3, change in volume is about +9% . Frost-wedging Requires numerous freeze-thaw cycles Liquid H2O flows into fracture, freezing widens fracture up to 9%, thawing allows liquid to penetrate more deeply into fracture, subsequent freezing widens fracture 9%, etc. Not important at high latitudes or equator (# of freeze thaw cycles insignificant) Temperate latitudes and high elevations Differential weathering on western slopes, and south-facing canyons in northern hemisphere o Haloclasty . salt crystallization in pore spaces of permeable or fractured rock saturated with saline fluids . evaporation on surface results in a rind enriched in salts . volumetric expansion caused by differential thermal retention of salt fractures rock. Up to 3% volumetric expansion. Often produces a reticulate pattern of differential weathering (honeycomb structure), arches and holes . Underside of boulders, coastal seacliffs, etc. Sodium sulfate, magnesium sulfate, calcium chloride o Volumetric expansion/contraction . Thermal Intensity = rate of temperature change*magnitude of temperature difference*differences in thermal conductivity o Max surface temps (four ft above ground in shade) = Death Valley 54 °C (134 ºF), recorded on 10 July 1913. Ground temperatures can exceed 90 ºCelsius (194 °Fahrenheit) in the deserts. © WB Leatham, 2012 Domain of things that sedimentary are….5 o Min surface temperatures = Vostok, Antarctica, −89 °C (-129 ºF) , recorded on 21 July 1983. o Total maximum temp range is only 143 ºC (263 ºF), but it is entirely theoretical. Daily temperature extremes (day-night) on order of 40 degrees F (x degrees C). Magnitude of daily change not great enough to induce rock fracture Thermal conduction of rock slow, insulative Thermal expansion/contraction in rock due to daily thermal cycles and/or weather changes not rapid enough Fire is only possible mechanism for inducing thermal fracturing of bedrock. Mineral Chemical Reactions—volumetric changes from reactions may induce intergranular/intercrystalline stress resulting in fracture e.g. feldspar to clay, Biotite to clay and ferrihydrite, gypsum to anhydrite, dehydration processes, etc. o Biotic weathering 2. Decomposition (L. compositus = “to put together,” from de = “away” and com = “together” and positus = “position”)—a chemical change in rock/sediment, usually induced by aqueous fluids and strong ions. Solution o Solvent + solute ↔ solution . polarity of water molecule . attachs itself to ionically charged edges of minerals . effective on weak ionic bonds, or on ions loosened through hydrolysis Hydrolysis (Gk. lysis = "a loosening, setting free, releasing, dissolution") . Addition of the hydronium ion to a mineral phase, loosened from acid . Acids donate hydronium . Strength measured by how easily hydrogen dissociates from acid pH (higher values indicate tightly bound H+) neutral is 7.0 natural H2O is slightly lower (between pH 5-6) because of presence of H2CO3 in solution . Products include both soluble and insolubles, and hydrated minerals . Types of natural acids H2O © WB Leatham, 2012 Domain of things that sedimentary are….6 o dissociates into H+ and HO- + - 2+ o Example: Mg2SiO4 + 4H + 4OH ⇌ 2Mg + - 4OH + H4SiO4 o Slow because of dissociation rate Carbonic acid (H2CO3) + - o H2O + CO2 ↔ H2CO3 ↔ H + HCO3 2+ o Example: Mg2SiO4 + 4(H2CO3) ⇌ 2Mg + - 4HCO3 + 4H4SiO4 o Example: 2KAlSi3O8 + 2H2CO3 + 9H2O ⇌ + - Al2Si2O5(OH)4 + 4H4SiO4 + 2K + 2HCO3 o Example CaCO Sulfuric acid (H2SO4) o Raw source is sulfur dioxide, SO2, volcanic emissions and combustion of sulfur in fossil fuels . SO2 + OH· → HOSO2 . HOSO2 + O2→ HO2· + SO3 . SO3 + H2O → H2SO4 o Replaces calcite with gypsum with subsequent rock degradation o Example: . CaCO3 + H2SO4 + H2O → CaSO4 2H2O + CO2 Humic substances o NOM typically endowed with acidic functional groups, mainly carboxylic acid, o Act as chelates on multivalent cations, e.g. Mg2+, Ca2+, and Fe2+. o Oxidation . Process of combining oxygen with a cation . Essentially “fixes” cations Bolide impact typically large scale, generally results in massive formation of sediment e.g. ejecta, mineral changes (coesite and stishovite), melted droplets (tektites), fragmented meteoritic material (rare-earth enriched) Erosion (L. erosionem from erodere "gnaw away," from ex- "away" + rodere "gnaw" (same stem as “rodent”). Plucking o Hydraulic—results from a low pressure area generated by aqueous fluid flow over the upper surface of a flattened object, similar to that of an airfoil, creating lift. Generally more efficient in sediments with flattened clasts and thin stratified weak units. © WB Leatham, 2012 Domain of things that sedimentary are….7 o Aeolian—results

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