Clastic Sedimentology And Petrography-quiz 1- Jan 2018

Explanation
At high wind velocities, silt- and clay-sized particles are not carried as bed load. Bed load refers to the particles that are transported along the bottom of a river or stream. However, silt- and clay-sized particles are so small and light that they can be easily lifted and carried by wind, forming suspended dust clouds. Therefore, the statement is false.

Explanation
The statement explains that grain roundness is a characteristic that can be easily observed in hand specimens using a hand lens or in thin-sections of aeolian sandstone under a microscope. This implies that it is possible to visually identify the roundness of grains in these samples, supporting the statement's truthfulness.

Explanation
A lagoon is not the marine-influenced portion of a drowned valley. It is actually a shallow body of water separated from a larger body of water by a barrier such as a sandbar, coral reef, or barrier island. Lagoons can be found along coastlines and are often characterized by calm, clear waters.

Explanation
The given statement is false because sediment supply to the estuary is not solely from river sources. It can also come from other sources such as coastal erosion, windblown sediment, and human activities. Additionally, the processes that transport and deposit sediment in the estuary are not only a combination of river and wave and/or tidal processes, but also include other factors such as currents and storm events. Therefore, the statement is incorrect.

Explanation
The explanation for the given correct answer is that the statement is incorrect. The difference between an estuary and a delta is that a delta is formed by the deposition of sediment at the mouth of a river, causing it to extend outward into a body of water such as a lake or sea. On the other hand, an estuary is a partially enclosed coastal body of water where freshwater from rivers and streams meets and mixes with saltwater from the ocean. In an estuary, sedimentation occurs in the drowned valley, not in the form of a retrograde inward extension like a delta.

Explanation
An estuary developed in an area with a large tidal range and weak wave energy will not typically have three divisions. The presence of a large tidal range and weak wave energy would result in a single division estuary, where the tidal currents dominate and prevent the formation of distinct divisions. Therefore, the statement is false.

Explanation
The Bay head delta refers to a specific type of delta that forms at the head of a bay or estuary. In this type of delta, the dominant processes are related to the river or fluvial system that feeds into the bay. Fluvial processes include the transportation and deposition of sediment by rivers, such as erosion, sedimentation, and channel formation. Therefore, it is correct to say that the Bay head delta is the zone where fluvial processes are dominant.

Explanation
An estuary is actually a partially enclosed coastal body of water where freshwater from rivers and streams meets and mixes with saltwater from the ocean. It is not separated from the deeper sea by any barrier beach, sandbank, coral reef, or similar feature. Therefore, the correct answer is False.

Explanation
The Bernoulli effect is a phenomenon that occurs when there is a difference in fluid velocity between two points in a tube. As the fluid flows through a narrower section of the tube, its velocity increases and the pressure decreases. This can be observed in various situations, such as the lift generated by an airplane wing or the flow of blood in our circulatory system. Therefore, the given statement that the Bernoulli effect can be explained by considering the flow of a fluid in a tube that is narrower at one end than the other is true.

Explanation
In cross-section, wave ripples are generally symmetrical in profile, meaning that the shape of the ripple is the same on both sides. Additionally, within each ripple, the laminae (layers) dip in both directions and overlap. This means that the layers of sediment within the ripple are inclined in opposite directions, and they also partially cover each other. Therefore, the statement is true.

Explanation
Wave ripples are formed in shallow water because the waves interact with the bottom sediment, causing the particles to move and form ripples. On the other hand, current ripples can form in any depth of water because they are caused by the movement of water itself, regardless of the depth or subaqueous environment. Therefore, the statement is true, as wave ripples are indeed formed only in relatively shallow water in the absence of strong currents, while current ripples can form in any depth.

Explanation
This statement is true because lavas, which are molten rocks, are typically found near the site of the volcanic eruption. They flow out of the volcano and solidify close to the eruption site. On the other hand, volcanic ash, which consists of small rock fragments, dust, and gases, can be carried by wind and spread over long distances. It can travel tens, hundreds, or even thousands of kilometers away from the eruption site, depending on the strength and direction of the wind.

Explanation
Basaltic magmas tend to form volcanoes that produce large volumes of lava, but small amounts of volcanic ash. This is because basaltic magmas have low viscosity and flow easily, allowing them to spread out and cover large areas as lava flows. However, they do not typically produce explosive eruptions that generate significant amounts of volcanic ash.

Explanation
Volcanoes with more silicic magma are indeed more explosive because the high viscosity of silicic magma traps gases, leading to increased pressure and explosive eruptions. The high silica content also causes the magma to solidify more quickly, resulting in the formation of large amounts of particulate matter that is ejected from the volcano during eruptions. This can lead to the creation of volcanic ash clouds and pyroclastic flows, which pose significant hazards to surrounding areas. Therefore, the statement is true.

Explanation
Calcium carbonate (CaCO3) is indeed the principal compound found in limestones. Limestone is a sedimentary rock that is primarily composed of calcium carbonate, along with other minerals and organic matter. This compound is responsible for the characteristic properties of limestone, such as its hardness and ability to effervesce when in contact with acids. Therefore, the statement is true.

Explanation
Calcite and aragonite are both forms of calcium carbonate and have the same chemical composition. The only difference between them is their crystal structure. Calcite has a trigonal crystal structure, while aragonite has an orthorhombic crystal structure. Therefore, the statement that there is a chemical difference between calcite and aragonite is false.

Explanation
Cherts are indeed fine-grained siliceous sedimentary rocks composed of silt-sized interlocking quartz crystals and chalcedony, which is made up of radiating fibers. This statement accurately describes the composition and characteristics of cherts, making the answer "True" correct.

Explanation
The statement is incorrect because sediments and sedimentary rocks with a high proportion of organic matter are actually termed as carbonaceous rocks, not carbonates. Carbonates, on the other hand, are sedimentary rocks that contain carbonate minerals such as calcite or dolomite.

Explanation
The given statement is false. Fusain is not bright or shiny black coal. It is a type of coal that is dull and lacks luster. Additionally, fusain does not break cubically and is not composed mostly of woody tissue.

Explanation
Volcaniclastic sediments are indeed the products of volcanic eruptions or the breakdown of volcanic rocks. During volcanic eruptions, various materials such as ash, pumice, and volcanic bombs are ejected into the air and can eventually settle as sediment. Additionally, over time, volcanic rocks can weather and break down into smaller particles, contributing to the formation of volcaniclastic sediments. Therefore, it is true that volcaniclastic sediments are the result of volcanic activity or the breakdown of volcanic rocks.

Explanation
If all the clasts in a conglomerate are of the same material, it is considered to be monomict, not polymict. Polymict conglomerates contain clasts of different materials. Therefore, the statement is false.

Explanation
The explanation for the given answer "False" is that silt is not defined as the finest grade of clastic sedimentary particles less than 4 microns in diameter. Silt is actually defined as particles between the sizes of sand and clay, with a diameter ranging from 0.0625 to 0.004 mm. Therefore, the statement is incorrect.

Explanation
The statement is false because when clay- and silt-sized particles are mixed in unknown proportions as the main constituents in unconsolidated sediment, the material formed is not shale. Shale is formed when fine-grained sedimentary rocks, primarily composed of clay minerals, are compacted and hardened over time. In this case, the material described is simply an unconsolidated sediment mixture of clay- and silt-sized particles, which has not undergone the processes necessary to become shale.

Explanation
The given statement is false because feldspar is actually the most common mineral seen in granite, not in silt deposits. Silt deposits are typically composed of fine particles of clay, silt, and sand, whereas feldspar is a common mineral found in igneous rocks like granite. Therefore, feldspar is not the most common mineral seen in silt deposits.

Explanation
Montmorillonite minerals have a unique layered structure that allows them to absorb water molecules in between the layers. This property is known as swelling. The water molecules are attracted to the negatively charged surfaces of the mineral, resulting in the expansion of the layers and the absorption of water. Therefore, the statement that Montmorillonite minerals cannot absorb water within their structure is false.

Explanation
A well sorted deposit contains clast sizes that are similar in size, rather than a wide range of sizes.

Explanation
The explanation for the given correct answer is that the fabric of a rock refers to its internal arrangement or structure. If a rock has a tendency to break in a specific direction or if it shows a strong alignment of elongate clasts (rock fragments), it indicates that the rock has a distinct fabric. Therefore, the statement "If a rock has a tendency to break in a certain direction, or shows a strong alignment of elongate clasts, this is described as the fabric of the rock" is true.

Explanation
The given statement is false. Cement is not a fine-grained material occurring between the sand grains. Cement is actually a binder material that is used to bind together other materials, such as sand and gravel, to form concrete. It is a powdery substance that hardens when mixed with water, and it is commonly used in construction projects.