Lab 4

Question 1

Why are sedimentary rocks important

Answer 1

1. They cover 75% of the earth’s surface
2. They contain fossils
3. They contain almost all of our petrol, natural gas, and coal. Along with 85-90% of mineral products we use such as ores and building materials. They also serve as reservoirs for groundwater
4. Agents of sedimentary processes such as wind, glaciers, and rivers have major impacts on human communities worldwide

Question 2

What are the processes that lead to sedimentary rocks

Answer 2

Weathering, transport, deposition and lithification all combine to form sedimentary rocks

Question 3

What is weathering

Answer 3

Weathering is the change and or removal of material from previously existing rocks. Physical and Chemical

Question 4

what does physical weathering do

Answer 4

Physical weathering produces smaller particles from the source rock, in the form of discrete mineral particles (e.g. quartz grains) or simply smaller pieces of the source rock (“lithic fragments”)

Question 5

What does chemical weathering do

Answer 5

Chemical weathering produces dissolved substances such as Ca2+ and CO3 2-, and also new material such as clays and oxides which are the result of alteration of primary silicate minerals such as amphiboles, pyroxenes, and feldspars.

Question 6

What is Erosion

Answer 6

Erosion takes weathered materials and removes them from the source area. Not the same as weathering

Question 7

What is Transportation in regards to sedimentary rocks

Answer 7

Transportation by wind, glaciers, rivers, etc take particles and dissolved material away from its source region. Transportation may affect solid particles by rounding and sorting them

Question 8

What is deposition in regards to sedimentary rocks

Answer 8

Deposition causes particles to settle to the bottom of a depositional basin. This may occur by a decrease in current flow. An important aspect of studying sedimentary rocks is determining depositional environment

Question 9

What is lithification

Answer 9

lithification transforms the sediment into a cohesive, solid rock again through deep burial and chemical processes dependent in large part on circulating groundwater. Involves compaction and cementation

Question 10

What are the two lithification processes

Answer 10

Compaction presses particles together
Cementation glues particles together by precipitating mineral matter

Question 11

How are sands, clays, and calcium carbonate separated at an ocean or big lake

Answer 11

Once the river system reaches the shoreline solid particles quickly settle to the bottom in the nearshore zone. Less dense clay particles remain suspended and drift offshore into quieter water where they settle on the shelf. CaCO3 remains in solutions, where organisms like algae, mollusks, and corals extract it to build their skeletal structures. When they die, their skeletons settle out and form carbonate sediment on the outer shelf

Question 12

What are the two types of sedimentary rocks

Answer 12

Clastic rocks form from particles, or clasts, or pre-existing rocks (ex sandstone)
Chemical rocks form from precipitation of dissolved minerals (ex rock sold, reef limestone)

Question 13

What is texture for sedimentary rocks

Answer 13

Texture is the size, shape, and arrangement of the grains.
Factors that influence texture are grain size, rounding, sorting, and degree of compaction. All of these provide important clues to the nature of the transporting agent and depositional environment

Question 14

What is up with grain size in sedimentary rocks

Answer 14

The size of particles in clastic rocks is a good indicator of the energy of the depositional environment. Grains are classified as Coarse, Medium, or fine grained

Question 15

What are coarse grained sediments

Answer 15

Coarse grained are over 2mm in diameter, they are considered gravel size. Conglomerates are a type which are deposited in high-energy environments such as a mountain stream

Question 16

What are Medium grained sediments

Answer 16

Medium grained sediments are between 1/16 to 2 mm in diameter, called sand size. Sandstones are one type, which are deposited in environments of moderate current energy such as a beach, or river deltas

Question 17

What are Fine-grained sediments

Answer 17

Fine grained sediments are lower than 1/16 diameter, and are called either silt or clay size. Siltstones, shales, or mudstones are deposited in still water, such as frozen lakes, quiet lagoons, or the deep ocean.

Question 18

What is sediment rounding

Answer 18

rounding refers to the smoothness of the grains, which is a result of the amount of abrasion that the grains have undergone during transport. Sediments moved by ice or gravity are usually angular, whereas particles carried by wind or water are usually rounded

Question 19

What is sediment sorting

Answer 19

Sorting describes the relative abundance of different grain sizes in the rock.

Question 20

what does a well sorted rock mean

Answer 20

Well sorted means that most of the grains are within the same size category and suggests a uniform current or stable energy in the depositional environment

Question 21

what does a poorly sorted rock mean

Answer 21

Poorly sorted means that there are different grain sizes in the rock, occurs where the current fluctuates or in gravity deposits such as talus slopes of mudflow

Question 22

What does compaction of a sedimentary rock mean

Answer 22

Compaction occurs as sediments accumulate and are buried together. This process involves the loss of water and air as grains are squeezes more closely together, and the cementing or “gluing together” of these particles by the precipitation of silica or calcite cement from fluids circulating through the subsurface

Question 23

What are the two aspect of composing for clastic rocks

Answer 23

Particles and cement

Question 24

What are Particles in clastic rocks

Answer 24

Generally one or the more of the following
Mineral clasts
Lithic fragments
Biogenic clasts

Question 25

What are mineral clasts

Answer 25

a. Mineral clasts - Quartz, feldspars, and other silicate minerals such as mice and garnet, clay minerals, and iron oxides such magnetite and hematite (the present of iron oxides is often seen as reddish staining on quartz grins or as a fine-grained, brown, earthy matrix mixed in with the other mineral grains

Question 26

what are lithic fragments

Answer 26

Fragments of other rocks such as basalt or gneiss

Question 27

What are biogenic clasts

Answer 27

organic fragments such as fossils of plants and animals

Question 28

What is Cement in clastic rocks

Answer 28

The glue that holds particles together. Cementing material is precipitated around sediment grains after burial by circulating groundwater. The most common natural cements are calcite and quartz.

Question 29

How can you distinguish between the most common natural cements

Answer 29

The most common natural cements are calcite and quartz. Calcite cement can be identified using an acid tests Silica cement results in a hard rock from which individual grains are dislodged with difficulty

Question 30

What are two examples of gravel sized sedimentary rocks

Answer 30

Conglomerate: made from quartz, feldspars, rock fragments, and clay minerals that has rounded grains that are poorly sorted Breccia: made from lithic fragments, often basalt or chert, has angular grains, usually poorly sorted

Question 31

What are two examples of sand sized sedimentary rocks

Answer 31

Quartz sandstone is made from mostly quartz and has all types of rounding and sorting Lithic sandstone is made from dominating lithic fragments, may have abundant fine clays, silt. Usually poorly sorted

Question 32

What is the difference between silt and clay

Answer 32

Silt is between 1/256 mm to 1/16 mm in size Clay is anything smaller than 1/256 mm

Question 33

What are two examples of silt/clay sized sedimentary rocks

Answer 33

Silt stone is made from silt sized quartz grains that are very fine-grained, has a slight gritty feel, may show layering Mudstone or shale is made from clay, or organic particles, also minor amounts of carbon (black), reduced iron (green), or oxidized iron (red). Is fine grained, usually quite soft, may or may not show layering

Question 34

What is texture of chemical sedimentary rocks and the two types

Answer 34

The shoe and structure of particles and grains, but for chemical sedimentary rocks, we do not use terms such as rounding and sorting. Crystalline texture: Minerals precipitated from salt or fresh water (e.g. rock salt) consists of a network of interlocking crystals similar to the texture in some igneous rocks Skeletal texture: skeletal texture results from the presence of shells or other skeletal parts of organisms

Question 35

What is up with the composition of chemical sedimentary rocks

Answer 35

Grouped into sub-groups of chemical sedimentary rocks are based on their mineral composition. Grouped into Carbonates, Evaporites, Siliceous, and Organic

Question 36

What are Carbonates chemical rocks

Answer 36

Carbonates consist of 50% or more carbonate minerals (calcite and dolomite). When certain aquatic organisms die, their calcite shells or skeletons accumulate on the sea floor. During lithification, they become cemented by calcite from circulating groundwater. Carbonate rocks are often rich in fossils and may be termed "fossiliferous" or "bioplastic". Limestone is the most common chemical rock and is a Carbonate

Question 37

What are Evaporties chemical rocks

Answer 37

Evaporties are composed of minerals that precipitate out of seawater as a result of excessive evaporation. The most common evaporates minerals are halite (NaCl), sylvite (KCl), gypsum (CaSO4 * 2H2O), and anhydrite (CaSO4). The rocks that form are usually not pure forms of the mineral but are named for the dominant mineral, e.g. rock gypsum, rock salt, etc

Question 38

What are Siliceous chemical rocks

Answer 38

Siliceous rocks are composed mainly of microcrystalline quartz (SiO2); Chert is thought to be derived from the accumulation of silica in diatom-rich regions of the ocean. Other silica-rich rocks are jasper, chalcedony, diatomite, flint and opal

Question 39

What are Organic chemical rocks

Answer 39

Organic rocks (peat, coal, etc) form in environments where the rate of organic accumulation is very high, such as swamps, marshes, or stagnant lagoons.

Question 40

What are four carbonate rocks

Answer 40

Crystalline limestone has medium to coarse crystalline structure Coquina has shell fragments loosely cemented (skeletal structure) Fossiliferous limestone has abundant fossils (corals, shells, etc) in a calcite matrix (skeletal texture) Chalk is made from tiny shells of microscopic organisms, microcrystalline earthy lustre, usually white. All are made from CaCO3

Question 41

What is the main siliceous rock

Answer 41

Cehrt is microcrystalline, dense, has conchoidal fractures, and is hard (7). Made from SiO2

Question 42

What are two evaporite rocks

Answer 42

Rock gypsums is made from CaSO4 2H2O, fine to coarse crystalline Rock salt is made from Halite (NaCl) and is fine to coarse crystalline

Question 43

What are two organic rocks

Answer 43

Peat is made form plant remains and is fibrous with an earthy appearance Coal is black, made from carbon, has variable lustre and hardness

Question 44

What is a depositional environment

Answer 44

Depositional environment (or sedimentary environment) refers to the place where the sediment is deposited, and to the physical, chemical, and biological conditions of the place. Broken into continental, shoreline, and marine.

Question 45

What are 10 sedimentary environments

Answer 45

1. Alluvial fans 2. Fluvial (river) systems 3. Aeolian (desert) environments 4. Glaciers 5. deltas 6. Shoreline environments 7. a Reef 8. Shallow Marine environments 9. Deep ocean environments 10. Hypersaline seas or playa lakes

Question 46

What are Alluvial fans

Answer 46

convex, fan shaped stream deposits that accumulate near a mountain front, where there is a sudden decrease in slope. They contain poorly sorted, angular gravel and boulders and also fine grained sand and silt may be deposited near the margins of the fan. Rocks that form here include lithic sandstones, breccias, and conglomerates

Question 47

What are Fluvial (river) systems

Answer 47

river channels and their floodplains (nearly flat expanses across which rivers meander before reaching the sea). sediment is deposited in channels and on bars (conglomerate, sandstone) and on flood plains (finer siltstone and shale)

Question 48

What are Aeolian (desert) environments

Answer 48

areas where wind is an effective sorting agent that transports and deposits sand and silt (not gravel). Dunes form and their rock deposits are characterized by well-sorted, find quartz sandstones that exhibit cross-bedding. Intense oxidation of iron minerals may give ancient desert sands a reddish colour

Question 49

What are glaciers

Answer 49

glaciers transport but do not effectively sort material. Thus glacial deposits are unbedded and composed of unsorted accumulations of boulders, gravel, sand, and fine silt. Meltwater streams flowing out from glaciers will abrade and sort sediments, so bedded stream deposits can form

Question 50

What are deltas

Answer 50

Deltas form when flowing waters loses velocity upon entering a standing body of water. Deltaic environments are complex and dominated by thick deposits of sand, silt, and mud. Rock vary from conglomerates to muddy siltstones

Question 51

What are Shoreline environments

Answer 51

Occur when land meets the ocean. Includes beaches where medium to coarse grained, well sorted sand is well-washed by wave action (sandstone and conglomerate). Lagoons accumulate fine-grained sediments (mudstone) or evolve into swamps (coal). Tidal flats are also generally fine grained and can have evaporates form

Question 52

What are reefs

Answer 52

solid structures composed of the calcareous (calcite-rich) skeletons of marine organisms. The reef framework is typically built by corals and algae, but many other types of organisms contribute to the reef community. Together they produced fossiliferous limestone with skeletal texture. Burial and compaction of reef limestones and subsequent infiltration by groundwater will often change the appearance of the rock substantially - some fossils will disappear and recrystallization will produce a compact rock we call a crystalline limestone. This type of rock is wide spread on Vancouver Island and there are several outcrops in the Victoria area.

Question 53

What are Shallow marine environments

Answer 53

found along the continental margins, and in the past were even more extensive than today. Sediments deposited in shallow marine waters (<200m) form extensive layers of sandstone, shale, and limestone, which occur in a cyclic sequence as a result of shifting sea level.

Question 54

what are deep ocean environments

Answer 54

Those adjacent to the continents receive sediments from turbidity currents and are characterized by graded bedding (fining upward sediment). Include fine-grained shale, mudstone, and sandstone. Often produce an acid reaction due to calcite Those further offshore lack sediments from the continents and so sediments are dominated by the shells of tiny marine organisms. These can form chert and chalk depending on the shell composition of the organisms.

Question 55

What are Hypersaline seas or playa lakes

Answer 55

Sites where evaporite minerals precipitate out due to excessive evaporation of isolation from freely circulating ocean water. Extensive evaporite deposits have been found beneath the Mediterranean Sea and represent times when low sea levels isolated the basin from the open oceans.

Question 56

What are four hints to identify sedimentary rocks

Answer 56

1. Determine whether the rock has a clastic (granular) or a non clastic (crystalline or interlocking) texture. use a microscope or hand lens 2. If clastic, decide whether the grains are predominantly gravel, sand or clay sized. also not the abundance of matrix materials or cement 3. If crystalline (chemical) a vigorous acid reaction will tell you that you have a limestone. Could also indicate calcite cement in a sand stone so be careful 4. Use other senses, such as noting the difference between how a sandstone and a shale feels, or the earthy smell of a mudstone