Geo 120 1st EditionExam #2 Study GuideStudy Guide Exam 2Sedimentary Rocks1) Sedimentary rocks are made from the products of chemical and physical weathering, i.e. the break down of other rocks.2) Sedimentary rocks are classified according to what they are made of and what their texture is.3) Sedimentary rocks record information about the environment in which they are formed. So we can use them to reconstruct past environments and environmental change.Chemical Weathering:- -Dissolution (Dissolve) - -Oxidation (Oxygen breaks down)- -Biological - -Hydrolysis (Add Water)Physical Weathering: - -Fracturing - -Frost and mineral wedging- -Roots and other biologic activity Types of sedimentary rocks:Clastic: Composed of broken pieces or “Clasts” of older weathered/eroded rocks (Sediment of grains, fragmented rocks/minerals) (Shale-Siltstone-Sandstone-Conglomerate).Biochemical: Organic matter, fragments/shells of organisms of fossils, plant matter or charcoal.Chemical: Precipitated/formed out of liquid solution (like rock salt or rock gypsum, can be microcrystalline = Chert) Clastic:Clast Size: Boulders/cobbles/pebbles, Sand (Coarse, medium, fine), Silt and ClayClast Shape: Angular, Partially rounded, roundedRange of Clast Size: Poorly Sorted, moderately sorted, well sorted*Father from the source means rounder, smaller, better sorted, more energy to move it (i.e. steepness of slope = more steep can move bigger material) *Stronger current = larger pieces (Agent = Water, Wind, Ice)Methods of Transfer:Wind: Can only transport narrow size range (small and well rounded). - Iron oxides = must be from oxygen - Layered in several directions (Cross Bedding) Beach Environment: Sandstone (well sorted/well rounded)- Symmetrical ripples- Shale and Sandstone- Can have dinosaur tracks/plant fossilsWetland Environment (Lakes/swamps/wetlands):- Can have dinosaur tracks- Shale/sandstone and freshwater limestone- Fern Fossils- Colorful (red, yellow, purple)Rivers draining mountains: Poorly sorted – “Conglomerate breccia”- Mixed with sandstone- Layering- Angular clasts (quartz, potassium feldspar, mica)- Close to sourceDeep Ocean: Very-fine-grained (mass of clay that needs a calm environment to settle out- Shale (sand intermixed layers)- Shells, shark teeth, fish bones- Reconstructing changes in environments form sequence of rocks*Limestone- also common in clear/warm/shallow marine watersCross bedding: Groups of inclined layers, sloping layers-Tells us the depositional environment was water or wind (Ripple marks or dunes)Environmental Changes: When a beach moves in: Transgression = rise in sea levelLayers = 1. Limestone, 2. Mudstone, 3. SandstoneWhen a beach moves out: Regression = decrease in sea level Layers = 1. Sandstone, 2. Mudstone, 3. LimestoneMetamorphism and Deformation 1) When rocks are subjected to high heat and/or pressure they may become altered anddeformed.2) Rocks subjected to stress may deform brittlely or ductilely, depending on their depth in the crust and how rapidly the deformation happens.3) During metamorphism, the minerals in a rock can recrystallize into other minerals, migrate within the rock, and be deformed to become aligned in a preferred direction. Force: A push or pull, expressed as amount of acceleration experienced by a massStress: Force per area (increase by- increase force applied and/or decrease area applied to)*Stress = Force divided by areaBrittle Deformation: When a rock breaksDuctile Deformation: When a rock bends/folds “flows”Types of Stress: Confining Pressure: Same amount of stress from all directionsDifferential Stress: Different amounts of stress from different directions Deformation: Too much stress (greater than the strength of the rock) causing failure.*Strength of the Continental crust increases with depth then weakens3 Main Types of Stress: Compression: Convergent fault (Continental collision or subduction zone) Tension: Divergent fault (rifting, seafloor spreading) Shear: Transform faultsTypes of Rock Fractures: Shallow levels (Brittle)Normal Fault: Hanging wall slides under the footwallReverse Fault: Footwall slides under the hanging wall*Shallow depths = low temps (minerals may not be affected)Joint: Crack where rock pulled apartFault: Rocks have slipped past one anotherStrike-Slip Fault: Left or right lateral “Standing on one side where the other side is moving”Ductile Deformation causes: Folds, Synclines, Anticlines, Domes, and BasinsDeeper Levels-At deeper levels in the crust there is Compression, Stretching, Shearing (deformation)*Deeper depths/higher temps = may recrystallize/new crystalsFoliation: Result of Ductile Deformation- Anytime you get a plain or texture “mineral alignment”- Or flattened Pebbles- Or “Smearing” from shearingChemical Processes during Metamorphism:- Recrystallization- Pressure Solution- Remobilization (crystals lining up/grouping together)Physical Processes During Metamorphism:- Deformation of objects- Rotation- Shearing*What causes Physical or Chemical Processes: 2 typesContact: Contacts something hot (area around magma chamber)Regional: Large area like a burial, Subduction or circulation of hot fluidCleavage: In metamorphic rocks = fractures that are perpendicular to stressEarthquakes1) Earthquakes are the energy released during movement along faults.2) Energy released in earthquakes travels in seismic waves.3) Earthquakes can be located using the arrival times of seismic waves at different locations.4) The magnitude of an earthquake represents the amount of energy that is released.5) We can assess the risk of earthquakes a particular location by examining the tectonicsetting and the history of earthquakes for that location.P waves: Primary wave, compresses material, fastestS wave: Secondary body wave, shearsHorizontal surface wave: shears material Vertical surface wave: compresses material-these are called “ l-waves, they cause the ground to move back and fourthStress and earthquakes: 1. Before- stress increases, rock experiences elastic strain2. During- fault slips causing an earthquake 3. After- stress drops during quake followed by post-slip recovery of elastic strain; cycle starts again *”stick-slip behavior” because fault sticks and then slips Magnitude: (Richter scale) how much energy is released Intensity: How much shaking (severity) or strength or shaking How do we determine location?1) Earthquake recorded by seismic network2) Select earthquake records to find P and S waves