GEOL Test 3 Cheat Sheet

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Geology

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Oct 30, 2023

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GEOL Test 3 Cheat Sheet Lesson 3.1 Clastic: Made from sediment clasts (fragments) of older rocks (Ex. Conglomerate, Sandstone, Shale) Chemical: Form from precipitation of new minerals from water (Ex. Limestone, Chert) (Ex. Evaporating lakes precipitate salts) Mechanical Weathering (break rocks into smaller pieces) 1. Frost wedging (Water expanding in cracks resulting in rocks breaking into smaller pieces) 2. Salt wedging 3. Jointing due to decompression (cracks... after erosion removed overburden, rocks expand, cool, and crack, to form joints) 4. Biological agents (plants and animals) 5. Abrasion (sand blasting, glaciers, water+sediment) Erosion (movement of sediment) occurs by wind, water, gravity or ice Roundness—increases with distance traveled - Well-rounded: long transport distances - Angular: slight transport Sorting—the uniformity of grain size - Well-sorted: uniform grain size - Poorly-sorted: variety of grain sizes - Larger grains require more energy to transport o Ex. Faster streams have more energy and can transport larger grains

Conglomerate(A): big grains, > 2 mm across Sandstone(B): grains are smaller than in a conglomerate, but you can still see them with your naked eye or with a magnifying glass Siltstone(C): grains are too small to see, but the rock feels distinctly gritty when you chew it Mudstone or shale(D): grains are so small that the rock feels smooth when you chew it Lesson 3.2 Chemical sedimentary rocks are made of minerals precipitated from ions dissolved in solution , • Form… • In environments where ion concentration, dissolved gasses, temperatures, or pressures are changing , which causes minerals to crystallize . • From shells of underwater organisms which extract chemical components from the water and use them to build shells • plant and animal remains that are transformed through burial and heat, and end up as coal, oil, and methane • Chemical weathering creates the dissolved materials in water that ultimately form these rocks Chemical Weathering: change in chemical composition (WATER is KEY) - Dissolution: some minerals dissolve easily in water, other dissolve easily in acid - Oxidation: rusting - Hydrolysis: water will react with feldspar to make clay minerals What controls the rate of weathering? 1. Environment (warm, wet environments fastest) 2. Surface area (more surface area = more weathering) 3. Mineral type (some minerals are less stable at surface conditions) Types of chemical sed rocks: - Limestone o Biological (biochemical): from the accumulation of the shells of living creatures  Chalk = Made from the carbonate skeletons of microscopic planktonic algae (coccolithophores) o Abiological (chemical): precipitation of CaCO3 without the aid of critters  Travertine = Limestone that forms at hot springs o Caves occur where groundwater has dissolved away pre-existing Limestone. This same rock can also be formed later in the cave by abiologic processes. - Dolostone

o Over time, Mg-rich fluids underground can add magnesium to existing layers of limestone. This converts the mineral calcite (CaCO3) in limestone to the mineral dolomite (CaMg(CO3)2), creating a rocks called dolostone - - Chert (biologic or abiologic) o Made of Microcrystalline quartz (SiO2) o Like limestones, the silica in cherts can be of biological (plankton) or abiological origin - Evaporites: Created from evaporated sea or lake water. o Halite (rock salt) o Gypsum - Coal o Organic carbon o Made from the buried remains of plants or algae Two naturally occurring acids: 1. Sulfuric Acid (Acid rain) = H2O + SO2 a. Dissolves silicate rock. 2. Carbonic Acid = H2O + CO2 a. forms in sea water when carbon dioxide reacts with water and dissolves (chemically weathers) the shells of many sea creatures b. Dissolves carbonate minerals Which of these two rock types do you think is more easily broken down by chemical weathering? Chert or Limestone ? Lesson 3.3 • Bed = single layer with recognizable top and bottom • Bedding plane = the boundary between two beds • Strata = Several beds together • Bedding/stratification = the overall arrangement of sediment into a sequence of beds 1. Ripples marks (water) o Internal cross-bedding (paleocurrent direction) o Think of the sand at the beach when the tides change 2. Dunes (air) o Internal cross-bedding (paleocurrent direction) 3. Imbrication (water) 4. Graded bedding (water) o Forms in turbidity current = underwater sediment avalanche o What depositional environment would be a likely place for graded bedding to form? Deep water.

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• Mudcracks • Sole marks • Scour marks (scours made by turbulent water – tells direction of water flow • Flute Casts = scour holes filled by overlying layer – seen on underside of a bed • Tool marks (scratches made by debris dragging across bed surface – can tell direction of water flow) • Trace fossils : sediment disturbed by organisms in some way • Ex. Bird footprints, worm tracks, worm burrows, dinosaur footprints

Lesson 3.4 Continental: - Dune field ( wind ) (beach and desert environments) o You come across an outcrop and observe 2-3 m thick cross-bedded sandstone beds. The sandstone is very well sorted and very well rounded. You look, but don't find any fossils... if they are there, they must be scarce - Playa Lake (occasionally in desert environments after heavy rains or snowmelt, water evaporates quickly leaving behind evaporates … gypsum / halite) o You come across an outcrop of thin beds alternating between mudstone that contains mudcracks, gypsum and rock salt (halite). You look around but cannot find any fossils. - Streams (erode transport and deposit more land material than any other process in the continental environment) (channel deposits tend to be medium to coarser-grained and the floodplain deposits are usually finer-grained sediment) - Glaciers (important source of deposition and erosion) (erode and transport huge volumes of sediment of all sizes) o You come across an outcrop of very poorly sorted sediment, with grain sizes ranging from clay all the way to refrigerator-sized boulders. There are no sedimentary structures, layering, or fossils within this deposit. Marine - Shallow marine (made up of the continental shelf, which is a gently sloping submerged surface extending from the shoreline toward the deep-ocean basin) (grain size routinely decreases with distance from shore; sediment sorting also tends to be rather good. Shallow water, nearshore sediments form thick sand blankets with abundant ripple marks. As depth increases and water movement decreases, average grain size decreases, and sand, silt, and clay occur interbedded) - Deep Marine (all the floors of the deep ocean) (chalk and chert) o You come across an outcrop and observe layers of chert and shale. The beds are thin, and have no other notable sedimentary structures. You don't see any large fossils, but after you take it back to the lab and study it under the microscope, you see it is full of micro-fossils of planktonic algae. - In hot regions where the sea is located in a restricted basin, evaporation can trigger the precipitation of evaporites (gypsum, halite). - Reef (Coral reefs are associated with warm, shallow marine environments) (rigid framework of carbonate rock (limestone), which is also a major source of sediment of various grain sizes) Transitional - Beach (Shorelines lie between the continental and marine environments) (Sand and gravel are dominant) - Tidal Flat (Muds occur in tidal flat and estuary environments, often covered with sheets of water for part of the day and exposed to air as the tides rise and fall. Near the shore the waves and currents distribute the sand creating depositional features such as spits, bars, and barrier islands)

- Delta (Occur when rivers meet the sea and slow down abruptly causing them to drop their sediment load) - Swamp You come across an outcrop that consists of moderately sorted and very well rounded conglomerate. The conglomerate bed is not laterally extensive - it is about 1 meter thick and only about 10 m wide, where it thins and pinches out. To the sides of the conglomerate bed, there is shale that is rich in terrestrial plants and contains mudcracks. At the base of the conglomerate bed you observe scour marks in the underlying layer. (RIVER CHANNEL) How to interpret a rocks depositional history? 1. Color (land vs. water) a. A red or brown sedimentary rock formed by deposition on land. i. Any iron in the sediment was exposed to air and was oxidized, turning the sediment, and therefore the rock, red. b. A gray sedimentary rock formed by deposition in water (e.g. ocean or lake) i. the sediment is not exposed to air, and iron in the sediment cannot be oxidized. 2. Grain size, sorting, and rounding (Indicative of the type of current which deposited the sediment) a. Maximum sizes of sediments moved by glaciers are bigger than those moved by water, which tend to be bigger than those moved by wind. b. Large clasts breakdown as they tumble, so large clasts are often a sign that the deposit is not too far from its source. c. Water and wind can sort sediments much better than ice or gravity d. The longer sediment has been buffeted by the waves, wind, or currents the rounder it gets. 3. Sedimentary structures (Can indicate paleoenvironment in many different ways) a. cross-beds, mudcracks, ripplemarks, etc 4. Fossils a. Assume the rock was formed in the same environment where that creature lived

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Lesson 3.5 Magma composition described by silica content - Felsic (light in color / viscous) o From fel dspar + si lica o High silica (SiO 2 ) content o ex.: granite - Mafic (dark in color / fluidal) o From ma gnesium + f err ic (=iron-rich) o Low silica content o Ex: basalt Cooling rate  Big crystals = slow cooling  Tiny crystals = fast cooling  No crystals = SUPER fast cooling Pegmatite(intrusive): Crystals are extremely large! Too big to even explain by the slowest cooling. Melts that form pegmatites are rich in water – this helps crystals grow large

Porphyrytic(extrusive) = some large isolated crystals surrounded by a groundmass of tiny crystals (2- stage cooling) - Magma cools slowly in the magma chamber for a little while  forming the big crystals – we call these phenocrysts - Then it erupts and the rest of it cools very fast  forming the small crystals in the groundmass Aphanitic(felsic) = fine grained - Fast-cooling - Ex. Rhyolite Phaneritic(felsic) = coarse grained - Slow cooling - Ex. Granite Intrusive bodies 1. Dike = sheet-like shape, cuts across rock layers 2. Sill = sheet-like shape, parallel to rock layers 3. Pluton = frozen magma chamber (Batholith) Lesson 3.6 There are three primary types of Lava flows 1. Pahoehoe (Surface of basalt flow is warm) 2. A’a (Surface of basalt flow is cold and freezes—it breaks up as magma inside continues to flow) 3. Pillow lavas (Result of underwater eruption) Lava Flow shape and runout distance – (depends on viscosity of lava) 1. Basalt lava – Very hot, mafic, and low viscosity . a. Basalt flows are often thin and fluid. 2. Andesite lava flow – intermediate silica, intermediate viscosity a. Forms thick, blocky flows 3. Rhyolite lava flow – felsic, lower temp, very high viscosity a. Lava flows look like mounded domes Bubbles that are frozen in lava are called vesicles Bubbles drive explosivity in eruptions and create pyroclasts 1. Steam and gas separate into bubbles as lava rises (due to decrease in pressure) 2. Bubbles grow as they rise 3. Magma becomes frothy 4. Bubbles begin to inter-connect and burst, forcing magma apart

Pyroclasts are classified into three size ranges 1. Ash (size of sand or smaller) 2. Lapilli (size of pebbles) 3. Block/Bombs (size of cobbles-boulders) In explosive eruptions, pyroclastic debris causes considerable hazards to people in the form of ash falls, and deadly, hot pyroclastic flows. Pyroclasts are generated when bubbles growing in the erupting lava explode What causes bubbles (aka. vesicles) to form in a magma/lava? reduction in pressure as it rises to the surface Lesson 3.7 Types of volcanoes 1. Shield a. Erupts effusive, low viscosity (mafic) lava b. Gentle slopes, broad feature c. Olympus Mons, Mars (largest volcano in solar system) d. Mafic e. Long-lived f. Lava flows g. DRAW 2. Cinder Cone a. Eruptions spatter mafic lava (pyroclasts) that falls to earth and builds up a steep cone b. Paracutin, Mexico / Mt. Etna, Italy / Arizona c. Mafic d. Single eruption e. Pyroclastic and flows f. DRAW 3. Stratovolcano a. Alternating layers made by both effusive and explosive eruptions b. A stratovolcano consists of alternating layers of ash and lava. c. Felsic and mafic d. Long-lived e. Both pyroclastic and lava flows f. DRAW 4. Caldera a. Crater Lake / Long Valley Caldera, CA b. Felsic and mafic c. Long-lived d. Mostly pyroclastic e. DRAW

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Craters vs. calderas Craters: depression on top of volcano is there because former top of volcano exploded away Caldera: depression on top of volcano is because magma was removed from within, causing the top to collapse inwards Lesson 3.8 5 ways to create magmas of variable compositions: 1. Melting different source rocks (e.g. crust vs. mantle) 2. Magma mixing = when magmas of two different compositions mingle with each other in the chamber 3. Assimilation = Rocks that form wall of magma chamber melt & get mixed into magma 4. PARTIAL MELTING (When we melt a rock, we never melt ALL of the rock before that new molten material is squeezed up and away) ( different minerals melt at different temperatures ) a. High silica (felsic) minerals i. Melt at lower temperatures (i.e. as you start to heat the rock, they will melt first) b. Low silica (mafic) minerals i. Melt at higher temperatures (i.e. as you heat the rock, they melt later) c. Partial (initial) melts are more felsic than parent rock i. partial melt of a more mafic rock will produce a more felsic magma 5. FRACTIONAL CRYSTALIZATION a. Crystals sink