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

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

. 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

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.

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

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.

o Aeolian—results from atmospheric fluid flow, but because of viscosity and density of air, generally only affects small clasts (mainly silts and sands, some thin platy pebbles) . Generally only affects thinly or laminated bedded or micaceous foliated rocks, often loosened along laminations by weathering and exfoliation . Clay is generally too adherent to be easily plucked after deposition because of interlocking during settling and electrostatic cling. o Glacial—results from ice freezing to the bedrock, plastic gliding of the overlying ice picks up anything to which it is frozen as it slides from points of accumulation to points of ablation. Grain impact—probably most significant method for entraining clastics in fluid flow. o Force of impact and inherent momentum from grain collisions breaks and chips clasts from bedrock and sedimentary deposits, resulting in downcutting and erosion. Abrasion—grinding of surface from gliding, rolling, and sliding clasts. Differs from grain impact but cannot be separated naturally from it. Results from entrained clastics o Downcutting along flow lines o Generally smooths and may even polish surfaces dependent on entrained clast sizes o Typically generates a chain reaction, the more sediment is transported, the more sediment is generated until capacity is reached

Transportation (To move, or not to move….) Primary controls on fluid flow affecting sediment transport: 1. Viscosity—discussed in fluid flow o controls settling and entrainment 2. Density—discussed in fluid flow o controlled by salinity in aqueous conditions, can transport great amounts of dissolved substances in solution 3. Depth—discussed in fluid flow 4. Velocity—discussed in fluid flow o affects plucking, degree of grain impact, extent of abrasion o less energy required to keep an object moving than to entrain it o affects competency (maximum size of particles that can be moved by fluids) o Velocity decrease results in deposition, which may leave a fairly permanent deposit of material even if velocity increases slightly after it slows down because of the significant difference in energy required to erode sediment than to transport it. 5. All of the factors listed above affect how fluids behave, and even control whether flow lines are parallel (laminated flow) or turbulent (turbulent flow) 6. Capacity—essentially reached when fluid gets “saturated” with sediment o depth controlled by turbulence

o braided streams vs. alluvial streams

Deposition or Accumulation Results in stratification, a temporal indicator of previous events Results in a spatial distribution of various depositional environments, and varied sediments that indicate the complex nature of environments both past and present. Spatial relationships of deposits primary focus of stratigraphy and stratigraphic interpretation. Diagenesis (L. dia = “across, to stretch,” and genesis = “to form or originate”)—the processes which change sediment in place after deposition. May generate loss of information from sedimentary materials, e.g. through dissolution, coating of grain surfaces, biogenic etching, precipitation of new minerals around and through grains, etc. May provide information about subsequent aqueous environments, both above and below the sediment/water interface. Principle mechanisms for consolidating sediment include: 1. Compaction—changes grain orientation and packing of grains, resulting in greater grain to grain contacts, reformation of some surfaces in fairly elastic grains, etc. o Very common in mudrocks, compaction may decrease original thickness of strata by over 40%. 2. Cementation—precipitation of cements between grains in pore spaces through modification of aqueous chemistry. o Controlled by permeability and fluid flow (follows Darcy’s Law) o May be biogenically or taphonomically initiated, e.g. concretions (change in pH from decomposing proteinaceous compounds), stromatolites (change in pH from removal of CO2 or S from phototrophy or chemotrophy respectively), etc. o Usually results from interaction of sedimentary/biogenous materials and aqueous solutions below the sediment/water interface. o Siliceous cementation (increase in pH through organic decomposition in silica rich water (above 9 ppm). Examples include gels in Lake Magadi, silica gels on seafloor produced by dissolution/reprecipitation of silica from diatom, sponge, and radiolarian tests, spicules, and frustrules, increase in extrusive volcanism, producing great amounts of fairly soluble glass shards and tephra (e.g. Arkansas Novaculite) o Carbonate cementation—common in both clastic and carbonate rocks o Ferruginous cements—ferrihydrite, limonite, goethite, hematite