B4-Ex2 Sedimentary Rocks

Of the following processes, which is not an example of mechanical weathering?

Oxidation. Oxidation is a process whereby rocks are altered by a chemical change (reaction with oxygen in water or air).

Sand dunes are typically dominated by quartz grains and very little other mineral matter. Why does this selection occur?

Quartz is extremely resistant to all forms of chemical weathering. Quartz is not affected by hydrolysis, oxidation, or dissolution because it is an extremely resistant mineral.

Sort the following everyday examples of sedimentary processes into the bins labeled with the sedimentary processes they most closely represent. Drag the appropriate items into their respective bins.

Sediment Erosion/transport The dirt going down the drain after you give your dog a bath and drain the tub Dirt being blown off a patio Deposition of sediment Dust collecting on furniture Weathering of rock Tree roots extending into a rock layer and breaking it down Ice expanding in a crack in the road creating a pothole Compaction/lithification A dump truck dumps a load of gravel on your lawn. The dirt below it becomes more consolidated

Pre-existing rocks are broken down into smaller particles by which of the following processes?

frost wedging, unloading, and thermal expansion

The processes of chemical weathering results in the decomposition of minerals within rocks over time. Fill in the sentences below to explore the different chemical weathering processes. Match each key term to the appropriate sentence. Be sure to complete each sentence before submitting your answer. You don't need to use all words.

1. Chemical weathering alters the internal structure of rock materials. 2. Potassium feldspar weathers in the presence of water containing carbonic acid. 3. Iron weathers through the process of oxidation. 4. A greenhouse gas called carbon dioxide influences the rate of chemical weathering. Unlike mechanical weathering, which physically breaks rocks apart, chemical weathering changes the structure of minerals. The processes in chemical weathering typically involve water, which facilitates chemical reactions such as acid dissolution, oxidation, and reduction. Water can become slightly acidic as carbon dioxide from the atmosphere is taken up by water, forming carbonic acid.

The processes of mechanical weathering transform rocks exposed at the surface over time. In frost wedging, seasonal freezing of water causes expansion of cracks in rock. Salt crystal growth within fissures or cracks in rock similarly causes expansion and mechanical weathering. Sheeting occurs when large sheets of rock dome upward and peel off when overlying rocks are eroded away, decreasing pressure. Biological activity can also cause mechanical weathering of rocks when living things such as the roots of plants or bacteria cause rocks to break apart. Fill in the sentences below to explore the four different mechanical weathering processes. Match key terms to appropriate sentence. Be sure to complete each sentence before submitting your answer.

1. climate has a crucial influence on the rates of all types of mechanical weathering. 2. Salt crystal growth can contribute to crumbling roadways in areas where salt is spread to melt ice and snow in winter. 3. The fissures formed as a result of Sheeting in exfoliation domes can be further enlarged by Frost wedging in areas subjected to seasonal freeze-thaw cycles. 4. The break down of rock by moving fresh materials to the surface by burrowing animals is an example of mechanical weathering due to Biological activity. Together with chemical weathering, these processes help sculpt the land surface and generate new types of rocks, which are in equilibrium with Earth-surface environmental conditions.

There are four main types of mechanical weathering: frost wedging in which rocks are broken by water freezing within cracks, salt crystal growth in which rocks are broken by salt freezing within cracks, sheeting in which rocks dome upward and peel off, and biological activity in which living things such as tree roots break rocks apart. You will visually identify these types. Note that one of the images is not an example of mechanical weathering. Drag the appropriate labels to their respective targets.

1. frost wedging 2. salt crystal growth 3. sheeting 4. biological activity 5. not an example of mechanical weathering(Limestone cave is a weathering process not related to the physical breakdown of rock.)

Considering the following list, which is not an example of chemical weathering?

Exfoliation. Exfoliation is the breakdown of rocks by removal of overburden, a physical process.

In many older cemeteries, you can often find headstones made of slate. In viewing these headstones today, the lettering is as sharp and clear as the day it was cut. However, many marble headstone inscriptions are illegible. What property of slate allows it to survive the test of time?

Clay minerals in the slate make it extremely resistant to weathering. As silicate minerals undergo hydrolysis, clay minerals are formed, which lithify to make shale. Shale is then metamorphosed into slate. Clay minerals are extremely resistant to chemical weathering.

Working in the field, you find a rock that contains rounded fragments that are greater than 2 mm in diameter. What would you call this rock?

Conglomerate is a detrital sedimentary rock that is characterized by rounded fragments that are larger than 2 mm in diameter.

With the addition of water, the minerals in granite rocks chemically weather into other minerals, known as products. Test your knowledge of the by-product of each mineral as a result of chemical weathering by labeling the minerals below with their respective products.

Feldspar - Clay Quartz - No chem change Olivine - Limonite The minerals in granite rocks chemically weather into other minerals, known as products. Just as these minerals within granite, an intrusive igneous rock, crystallized from magma at different temperatures, they also have different resistance to chemical weathering. Minerals like quartz, which crystallize at low temperature, are less susceptible to chemical weathering than minerals like feldspar, which crystallize at high temperatures.

Which structure is common in sedimentary rock?

Fossils, cross-bedding, ripple marks, and mudcracks are all features found in sedimentary depositional environments.

The major determining factor for the chemical break down of rocks is their chemical composition. For example, granite and basalt are both igneous rocks with different chemical composition and structure and, therefore, different weathering rates. Rocks with minerals that crystallize late in Bowen's reaction series, like granite, are usually more resistant to chemical weathering than those with minerals that crystallize early, like basalt. Besides chemical composition, a secondary factor that affects the rate of weathering in such rocks is the amount of cracks/fractures present. Rank the rocks in order of the rate of chemical weathering they would experience, assuming they are all located in the same warm wet climate. Rank from slowest to fastest.

Granite, with very few or no cracks Granite, with abundant cracks Basalt with few to no cracks Basalt with abundant vesicles (holes)

Three types of chemical weathering processes are particularly important for transforming minerals within rocks into weathered products. These are hydrolysis, oxidation, and dissolution. Through hydrolysis reactions, minerals are weathered in the presence of water, often rainwater. Through oxidation reactions, iron-rich materials transform in the presence of oxygen in air. And through dissolution, minerals dissolve in water, making their chemical products ions within water. You will sort each example into its category of chemical weathering process.

Hydrolysis: granite to clay Oxidation:red color of rocks in national park yellow stained rocks Dissolution caves formed in limestone salty taste of ocean The processes involved with chemical weathering are responsible for most chemical weathering on Earth. When a process is applied to different types of minerals, different chemical products will form.

In what way does the amount of mechanical weathering that has taken place influence the rate at which chemical weathering occurs?

Mechanical weathering increases the surface area exposed to chemical weathering. The more surface area exposed to the atmosphere and hydrosphere, the more rapidly chemical weathering can occur (if conditions are right).

Read the following descriptions of several different environments. Based on the information given, sort each environment into the correct bin for an environment that would experience predominantly mechanical weathering or predominantly chemical weathering. Drag the appropriate items into their respective bins.

Mechanical weathering would predominate. A cold wet environment at high elevation, in which freezing and thawing is common. A cold dry environment experiencing uplift, in which material is being removed by erosion from an underlying pluton/intrusive igneous rock. Chemical weathering would predominate. A hot environment with many short but intense rainstorms. A hot humid climate with heavy precipitation that occurs all year. A warm wet environment with above average yearly rainfall and several stormy seasons each year.

For a detrital sedimentary rock that contains mudcracks, you could be confident that the environment in which it formed was _____.

alternately wet and dry. Alternating wet and dry conditions would be a prime environment for the formation of mudcracks.

The chemical weathering process known as dissolution is most effective in the breakdown of which of the following minerals?

calcite. Calcite is soluble in water and dissolves, especially if the water is slightly acidic.

The geologic laboratory where you work received a sample for analysis that is composed of calcite that includes many microscopic fossils of marine organisms and reacts with acid. What name would identify this rock?

chalk. Chalk is a biochemical sedimentary rock composed of calcite and contains many microscopic fossils of marine organisms.

Which two minerals are most common in detrital sedimentary rocks?

clay minerals and quartz. Clay minerals are the resistant by-product of chemical weathering and quartz is the most resistant common mineral in Earth's crust. They are common in detrital sedimentary rocks.

During hydrolysis, ions and clay minerals are produced by the decomposition of which of the following Earth materials?

feldspars. Exposure of feldspar to water causes it to break down by hydrolysis into clay minerals and ions.

In temperate and polar regions, the accumulation of talus slopes at the base of steep, rocky cliffs is most often attributed to which of the following processes?

frost wedging. Where steep, rocky slopes are subjected to many freeze-thaw cycles, talus slopes can accumulate at the base.

What property of detrital sedimentary rocks can be indicative of the energy of sediment transport?

grain size. Grain size in a detrital sedimentary rock typically indicates the amount of energy associated with the transport of the sediment. High-energy transport can move much larger grains than low-energy transport.

What is the most abundant chemical sedimentary rock in Earth's crust?

limestone

Look at the descriptions below of scenarios and determine whether the scenario inhibits weathering or enhances weathering. Drag the appropriate items to their respective bins.

limits weathering Rows of trees are planted on the border of a field to slow the wind and deflect it upward. Promotes weathering Humans remove trees and other vegetation in order to develop an area of land. LIchens, which secrete acids, are present on the surface of a rock. Animals burrow into the ground loosening the soil. Consistent grazing by a herd of cattle.

Which of the factors listed below does not influence the rate of chemical weathering?

mass of rock available. The original mass of rock available does not directly influence chemical weathering rates. Other factors, such as mineralogy, determine which chemical processes are most effective in weathering a mass of rock. The surface area available for reaction and the ambient conditions also affect how rapidly chemical processes are able to act upon the rock.

The chemical weathering process known as oxidation would be most effective in the breakdown of which of the following Earth materials?

pyroxenes. Minerals such as pyroxene that contain iron are very susceptible to oxidation.

Which is an example of a sedimentary rock composed of solid masses of intergrown crystals?

rock salt. Rock salt is a sedimentary rock that contains intergrown crystals of halite.

In your field area you find a quartz sandstone unit with cross-bedding in it that is on the order of 2 m high. In what environment would you deduce this rock formed?

sand dunes. Quartz sandstone with 2-meter-scale cross-bedding would be typical of sand dunes.

The production of tabular slabs of rocks caused by unloading of material overlying igneous bodies is known as _____.

sheeting. The production of large slabs of rock by unloading is referred to as sheeting.

The formation of sedimentary rock requires _____.

weathering and erosion of pre-existing rocks Weathering breaks down pre-existing rock into particles, while erosion moves the particles to a site of deposition. These processes begin the formation of sedimentary rock.

Which of the following agents is capable of moving sediment from the site of formation to the site of deposition?

wind, waves, running water, ice