Chapter 7

Front 1

· Sketch or describe the main sedimentaryenvironments on land, and describe some characteristics of each.

Back 1

Mountains are characterized by steep slones developed on bedrock. Because of their steepness, they tend to have flowing water with a high velocity. Because of the high velocity, there is abundant sediment flow in the form of angular rocks.

Mountains contain streams and rivers that typically have steep gradients. But after those streams leave the mountains and the gradient is much more gentle, that sediment can develop a braided appearance because a heavy amount of sediment has moved into an area where the velocity is much slower and there is a much lower sediment capacity. The adjective fluvial describes this process.

Dry climates contain large amounts of sand and fine particles which are moved around by wind. Sand dunes are formed as the sand moves back and forth.

In high mountains or at high latitudes (north and south pole) glaciers can form from frozen ice and erode the surrounding area of a moving glacier. As the glacier melts, the sediment is released towards the terminus (end) of the glacier.

Deltas are formed at the mouth of a river where the current has slowed down dramatically. Much of the eroded sediment is deposited here.

Very wet environments where soil is saturated with water can be called swamps, bogs, or ponds. Areas like this contain abundant water-dependent vegetation. The water also protects the underlying sediment from the atmosphere by limiting the amount of oxidation.

Lakes contain a range of environments from very quiet, deep water in the center, to more active water with wind-driven waves along the shoreline. Some lakes are always filled with water, but others dry completely when the water evaporates or when it seeps into underlying materials.

Flood plains are built by sand and mud as water overflows meandering rivers and causes the area around the river to be covered by water. The mud and sand are carried by the river and overflowed to the flood plain.

Front 2

· Sketch and describe the main sedimentary environmentsin oceanic and near-shore environments.

Back 2

Beaches are the primary sedimentary environment as they contain a lot of the accumulated sediment from the shore, consisting of sand, shells, and rounded gravel, cobbles, and boulders. If a shoreline has bedrock all the way to the ocean, there won't be much erosion and thus no sediment.

Lagoons are areas right off the coast that shelter the beach with shallow, calm, and warm water. They contain sand, mud, and stones derived from land, whereas the outer parts of the lagoon may have sand and other pieces from the reef.

Reefs are coral and marine creatures constructions that form in warm, clear, and shallow water that often parallel the coast, encircle islands, or form irregular mounds and platforms. Reefs generally protect the shoreline from the big waves from the deep ocean.

The deep seafloor mainly contains fine particles, wind-blown dust, and remains of single-celled organisms. It's a dark cold environment several kilometers down.

Sandy dunes near the coast are coastal dunes. These dunes commonly form where sand and finer sediment from the beach are blown or washed inland and reshaped by the wind. Depending on where the wind blows, the sand can move from the beach to the dune or vice versa.

Tidal flats are flooded areas of water near the coast that are filled with water during high-tide, and exposed to the air during low tide. They're using covered in mud, sand, and salt or evaporite minerals. Seawater and terrestrial waters evaporate under hot, and dry conditions forming minerals.

Submarine deltas are extensions of deltas below water than can extend for tens of kilometers. The muddy or sandy front of the delta may be unstable and could slide down the slope, sediment deeper into water.

Front 3

Describe the main processes of physical andchemical weathering.

Back 3

Physical weather occurs in the form of near-surface fracturing by processes breaking rocks into smaller pieces. Fractures also result while rocks are being uplifted to the surface and they are expanding after being progressively exposed to less pressure.

Frost and mineral wedging is another physical weathering that occurs when water freezes and expands in fractures. When the ice melts, the fracturd pieces can be dislodged from the bedrock. Crystals and other minerals that grow in thin fractures can also cause rocks to break apart in the same manner as frost.

Thermal expansion can occur due to rocks being exposed to to wildfires and the sun during the day. As rocks heat up, they can expand and fracture. This probably plays a minor role in weathering and it is highly debated today.

Biological activity can physically weather rocks through plants and animals. Plant roots can grow downward into fractures and pry rocks apart as the root diameter increases. Burrowing animals can transport rock and soil from depth and move it to the surface where it exposed to the elements, weathered, and eroded.

Chemically, the main chemical weathering occurs through dissolution, that is dissolved in water. Not to be confused with hydrolysis, which changes the rock chemically, but does not dissolve it. The dissolved material can be carried away in rivers, streams, or ground water, or be used locally by plants.

Oxidation is the process by which minerals, especially those containing iron, are unstable when exposed to earth;s atmosphere. These minerals combine to form with oxygen and are called oxides. Iron oxides compose the reddish-and yellowish material that forms when metal rusts.

Like previously stated, Hydrolosis is the process by which silicate materials react with water, particularly water that is somewhat acidic. Commonly, original materials are converted to clay minerals, and produces leftover dissolved material that is carried away by water.

Biological Reactions are things such as decaying plants producing acids that can attack rocks, or some bacteria consuming certain parts of rocks. These biological processes cause minerals to break down into their constituent elements.

Front 4

· Describe how the type of material and degree offracturing influence the type of sediment that results.

Back 4

The resulting sediment is influnced by the original rock and how that rock has been physically and chemically altered. Because some material are soluble in water and weak acids, they commonly weather to a pitted or grooved appearance like the weathered limestone. The water dissolves the soluble material and carries it away as dissolved ions which can later be precipitated in minerals. Quartz-rich rocks are much less soluble during weathering. Rocks that contain more than one kind of mineral can also weather differently and react differently. Pink and cream-colored feldspar in granite can chemically weather to clay or physically weather to sand grains. Fracturing allows my surface area to be weathered which means faster weathering and permission of water, air, and organisms to invade the rock causing other types of weathering.

Front 5

· Describe how rocks can be broken duringtransport.

Back 5

Rocks can be broken through abrasion from large boulders and cobbles breaking against other clasts or obstructions in streams and rivers. Because silt, sand, and larger clasts are sand-paper like, they can smooth out other rocks that obstruct them.

Front 6

· Sketch and describe how sediments are classifiedaccording to size, sorting, and shape of clasts.

Back 6

According to size, sediments are sorted from smallest to largest: mud - clay (less than 1/256th mm), silt (1/256th mm to 1/16th mm) sand - sand (1/16th to 2 mm) gravel - granule (2 to 4mm) pebble (4 to 64mm) cobble (64mm to 256 mm) boulder (256mm +). The sediments can be poorly, moderately sorted, or well sorted. Generally the farther they've traveled, the more time they've had to group together with similar rocks and thus become more well-sorted. The shape of clasts are angular, partially rounded, or rounded. This happens from smoothing of rocks as they travel. Rocks near origin are more angular than rocks that have been eroded thoroughly.

Front 7

· Describe how clast transport affects the size,shape, and sorting of clasts.

Back 7

The size of clasts decrease the farther it has traveled. The shape of clasts are more well-rounded the farther it has traveled. And clasts are more well-sorted the farther it has traveled.

Front 8

· Explain four factors that influence the type ofsediment that is transported.

Back 8

The steepness of slopes influences mountains which commonly have larger, angular clasts, that are poorly sorted. A river, beach, or other agent of transport can only move the sediment that is available. Wind can carry only sand and finer particles, but rivers, glaciers, mudflows, and other agents can pick up larger clasts. Sand dunes are formed from the fact that wind cannot bring any larger clasts other than well-sorted sand to the area. The strength of the current allows larger clasts to travel if the current is fast enough, but slower current will only allow for certain clasts to move.

Front 9

· Describe or diagram the classification of commonclastic sedimentary rocks.

Back 9

Conglomerate rocks consist of pebbles, cobbles or boulders, with a matrix of sand and other fine particles in between. Conglomerate rocks have rounded clasts. Breccia rocks consist of pebbles, cobbles, or boulders with a similar matrix, though the clasts are much more angular. Sandstone naturally consists of sand-sized clasts but has more defined layers than conflomerate or breccia rocks. Arkose sandstone are 25% sand-sized feldspar and typically contains coarse sand grains including pinkish or cream feldspar. Sandstone composed of mostly quartz grains is a quartz sandstone. In order for this to accumulate, the source must've already been quartz rich or weathering and transport destroyed grains of weaker minerals, like feldspar and mica minerals. Sandstones called graywacke contain minerals of quartz, feldspar, iron-oxide minerals, mica minerals, and small fragments of other rocks. Mud-sized clastic rocks include siltstone, containing silt (a gritty texture rock), and shale, a much smoother clay-based rock.

Front 10

· Describe what happens to clastic sediment as itbecomes buried and converted into rock.

Back 10

Clastic sediment begins to compact, but because they do not fit together tightly, they form pores that leave room for air and water. As the clastic sediment is buried, the weight from the overlying sediment forces the grains closer together and the pore space decreases as air and water are expelled. Since there still may be small pockets of pore space after compaction, there is an opportunity for certain mineral cements to form from dissolved materials precipitating and forming minerals that act as a natural cement.

Front 11

· Describe the natural cements that are common insedimentary rocks.

Back 11

The four main types of mineral cements that hold grains together are calcite, silica, clay minerals, and iron-oxides. Calcite (CaCO3) is a common cement, and while it holds grains together moderately well, it is easily redissolved, so a calcite-cemented sandstone may become friable (crumbly). Silica is a strong cement that can tightly bind grains and form a tough, resistant rock. Clay can cement together larger grains, including cement. They may have been deposited with the sediment or formed from the alteration of feldspar or volcanic ash. Iron oxide minerals, like hematite, precipitate from water as a natural cement between teh grains. Iron oxide minerals commonly give sediment deposited on land a reddish color, like the grand canyon.

Front 12

· Describe how some sedimentary rocks form through evaporation, precipitation, or other chemical reactions.

Back 12

If the water evaporatesin an ocean or lake while containing dissolved ions like sodium, calcium, andchloride, these substances can be left behind as salts or as carbonate mineralsif the water evaporates. These minerals are called evaporate minerals becausethey resulted from evaporated water. Precipitation on theother hand is the process by which dissolved minerals precipitate from waterlike in the case of iron formations that occurred millions of years ago intheory. Chemical reactions canalso occur like when the accumulation of calcium carbonate remains of animalssuch as coral clams form limestone, or when the accumulation of silica-richplankton cells compact and form chert.

Front 13

· Describe how limestone forms.

Back 13

Limestone forms from thecalcium carbonate remains of animals, or inorganically from the precipitationof water. Some limestone form from a combination of biological and inorganic.An example of the biological would be the calcium carbonate remains ofmicroscopic organisms forming chalk.

Front 14

· Describe how some sedimentary rocks form fromthe accumulation of plant materials.

Back 14

Peat forms through theaccumulation of plant material, usually in swamp environments. Peat is porousand retains much of the textual character of the original plant material. Ifits buried, compacted and heated, loses most of its water and oxygen, and isproperly heated and pressurized, coal can be formed.

Front 15

· Sketch or describe the types of layers thatsedimentary rocks contain, including how their thickness varies, what definesthe layers, and whether their boundaries are sharp or gradational.

Back 15

Sedimentary layers can bethick or thin. Thick layers that are part of a distinct rock unit and laterallytraceable are formations. The layers are referred to as beds or bedding thatcan be millimeters to meters thick. The layers can also be defined by the sizeof grains in each layer or different minerals in each layer. Some boundariesbetween layers are more defined than others, either by explicit colors or bytypes of mineral and rocks. Sharp and gradational boundaries are largely causedby geological factors such as erosion, changes in environment, etc.

Front 16

· Describe how layers, including graded beds andcross beds, form.

Back 16

Graded beds occur whenthe current of a river dramatically slows down and the coarser grains settlefirst followed by finer sediment. Cross beds are the accumulation of thin bedsof sand and silt on the down-current side of the dunes and ripples. Such bedsare at an angle to other beds in the same rock and so are called cross beds.Parallel beds are beds formed parallel to one another and are the predominantbedding.

Front 17

· Sketch or describe the characteristics of abreccia, and identify some environments in which this rock forms.

Back 17

Breccia rocks containpebbles, cobbles, and boulders of angular shapes surrounded by clay, silt, orsand. Breccia rocks tend to form close to their source from debris flows orrock slides, which aids to their angular shape. Because they don’t travel far,they don’t round out like their conglomerate counterparts. Glaciers can alsopick up loose clasts with fine dust and deposit the combination.

Front 18

· Sketch or describe the characteristics of aconglomerate, and identify some environments in which this rock forms.

Back 18

Conglomerates are similar in that they contain large clasts ofpebbles, cobbles, boulders. However, they are much more well-rounded orpartially rounded due to their distance from their source. Some of them haverelatively little matrix and can overlap clasts. Conglomerates can be poorlysorted often like their breccia counterparts. Conglomerates can form fromsediment deposited in or near a stream channel, where the clasts are rounded bya moderate amount of stream transport or through braided rivers with alluvialplains. Waves can churn and pound stones, causing stones to smash into eachother and round them out. High energy environments are required for theformation of conglomerate rocks.

Front 19

· Contrast breccia and conglomerate, and explainreasons why one rock type might form instead of the other.

Back 19

Breccia rocks are angularwhile conglomerates are rounder. Breccia rocks are more likely to form in ageological situation as a rock slide, whereas conglomerate rocks form over timethrough transportation and erosion. Though they retain a similar make-up, theirsource and destination dictate a lot of their characteristics.

Front 20

· Describe the characteristics of sandstones,including their expression in landscapes.

Back 20

Sandstones are mainlymade up of sand grains, though it can contain angular and well rounded. It canalso contain other larger grains so long as the majority of grains is sand.Most sandstone has layers differing in color, grain size, and shape. Theymostly form in parallel layers but can also for in cross beds. Very littlediversity in beds can make sandstone layers appear massive.

Front 21

· Describe the land environments in which sandstone forms, and how you might distinguish sandstone formed by sand dunesfrom those formed by rivers.

Back 21

Sand dunes containsandstone that is very well sorted, because the wind must be able to carrythose clast sizes easily. River sandstone will likely be inter-layered withsiltstone and other rock types, because floods and shifting positions haveoccurred near rivers. This changes the shape and color of the sandstonefeature.

Front 22

· Describe how sandstone forms along beaches, indeltas, and in offshore environments.

Back 22

Sandstone is common onbeaches because of the abundant sand content. Beaches contain shells, pebbles,and other blocks from nearby rock exposures, so the sandstone formations caninclude those, although the high energy of a beach may destroy shells beforethey can be preserved by the sandstone. Sand can be deposited by a delta into anear-shore marine area with other materials like shale. Sandstone can form nearbarrier islands offshore from the mainland.

Front 23

· Describe the main characteristics of shale andsiltstone, including which rock has the nest particles.

Back 23

Shale is primarily madeof clay, and breaks into one-direction cleavage. Shale has a very smoothtexture. It has the finest texture. Siltstone is made primarily from silt andso it is a little grittier than shale.

Front 24

· Describe the land environments in which shale,mudstone, and siltstone form.

Back 24

Shale primarily formsfrom chemically weathered minerals that form clay. After they accumulate as alayer of soil and are lithified, they usually form shale. Mudstone forms frommud at the bottom of lakes carried to the lakes by streams, rivers, wind, andby erosion of adjacent hillslopes. Lakes produce soft, thin-bedded rocks thatare dark if rich in organic material. Siltstone is formed from floodplains ofmeandering rivers that are carried away farther than coarser sediments and thesilt deposits when the water slows down. Wind can also transport and depositsilt over large areas. Windblown silt was especially abundant during periods ofglaciation, when moving ice sheets ground rock into powdery silt-sizedparticles.

Front 25

· Describe the environments near shorelines andfarther offshore in which shale and siltstone form.

Back 25

Shale can form fromsediment deposited in seas and ocean basins where fine particles are carried bywind and ocean currents. Deep-water shales are dark gray, due to a high organiccontent and relatively low oxidation on the seafloor. The calm water of alagoon is an efficient trap for mud and clay carried from land by streams,rivers, and wind. Lagoons commonly produce light gray or greenish shales, alongwith white sands derived from the disintegration of coral and shells. Mud flatsflooded at high tide can expose salt, gypsum, and other evaporate minerals whendry and evaporation has occurred.

Front 26

· Describe the characteristics of limestone and dolostone.

Back 26

Limestone is a carbonate(carbon and calcium) is mainly made upof calcite. It tends to have a “dissolved” appearance because it is moderatelydissolvable. Limestone frequently includes fossils of shells, corals, fish, andother marine organisms, like the fossil crinoids shown here. Limestones thatform in lakes may have fossils of nonmarine organisms, such as freshwater fish.Dolomite is the calcite converted to dolomite by the addition of magnesium. Dolomiteproduces the carbonate rock dolostone. Because dolostone contains magnesium, itis much more resistant and less soluble.

Front 27

· Describe the environments in which limestone,dolostone, and other deposits of calcium carbonate form.

Back 27

Most limestones form inmarine environments, but limestone can also be deposited around springs, inlakes, and as coatings and other features on the floors, roofs, and walls ofcaves. Limestone forms in lakes in hot, dry climates that experience largeamounts of evaporation. These limestones usually have creamy tan or browncolors. Travertine is a variety of limestone that’s porous and is precipitatedin cold springs, hot springs, lakes, and caves. Travertine is mostly layeredbecause different layers precipitate at different times, coating preexistingmaterials. Limestone in some lakes occurs as coatings of irregular masses ofwhite carbonate material. The carbonate can form pillars in exceptional caseslike the Mono Lake in eastern California.

Front 28

· Describe how carbonate rocks are expressed inthe landscape, including sinkholes and limestone pillars.

Back 28

Caves and sinkholes canform from abundant limestone dissolving, leaving caves that can collapse intosinkholes. Pillars can also be formed from uneven dissolution of in wetclimates where less fractured pillars were more difficult to dissolve. In dryclimates, limestone and dolostone are fairly erosion-resistant and will forgray cliffs and steep slopes composed of beds that may vary slightly inthickness and color.

Front 29

· Sketch or describe what happens during atransgression and during a regression, including which way sedimentary faciesshift.

Back 29

As the sea transgresses,beach sand is deposited over the bedrock base of the land. The base layer isburied with sand. As a reef as formed because of the distance between the shoreand the reef, a lagoon forms that is able to trap a mud layer above the layerof beach sediment. As the sea moves forward, the reef centralizes and limestonefrom the reef deposits onto the mud layer from the lagoon. With regression, thesedimentary environments shift toward the sea again. As the reef retreats backout toward the sea, the lagoon mud builds out over the limestone layer. Thelayer of mud is then covered by the sand being reworked in and out of the sea.

Front 30

· Sketch an example of a sequence of rocks formedduring a transgression and contrast it with a sequence formed during aregression.

Back 30

The bedrock is initiallycovered by sand, then mud from a lagoon, then limestone from the reef. Duringregression, that limestone is covered by mud from the lagoon, and then beachsandstone.

Front 31

· Describe the attributes that we observe insedimentary rocks and how each indicates something about the rock’s origin andenvironment.

Back 31

Color: Red sedimentaryrocks generally form on land where they can be oxidized (rusted) by theatmosphere whereas the dark gray sedimentary rocks form under water in low-oxygenconditions. Clast Size, Shape, Sorting: The size shape and sorting can tell ushow far a rock has travelled and how eroded its become. The thickness ofbedding implies bigger events, faster rate of deposition, or longer timesbetween environmental changes. Thin bedding implies smaller events or morerapidly changing conditions. The types of bedding can tell us the specificformations of bedding and the strength of the current and how it changed overtime. Mudcracks can tell us the history of mud in a location and the change inclimate. Fossils can tell us the temperature, elevation, rainfall, and otherenvironmental conditions.

Front 32

· Describe how sedimentary rocks help usunderstand modern and ancient environments, events, and life.

Back 32

Sedimentary rocks help us understand the record of pastenvironments, how the climate has changed, what ancient life was like and howthey might have evolved, assuming evolution is true. We can also see thesequence of past events and how they interacted with one another.