Clastic Sedimentology And Petrography-quiz & Test II

When a river meanders, it forms curves in its course. Over time, these curves can become more pronounced and the river may cut through the narrow neck of land between two curves, creating a shortcut. This process is known as an oxbow lake formation. The abandoned meander loop is then isolated from the main river channel and becomes a separate body of water called an oxbow lake. Therefore, the statement "The abandoned meander loop becomes isolated as an oxbow lake" is true.

Antidunes are formed in supercritical flow conditions, where the Froude number is greater than 1.0 or the flow velocity exceeds the wave velocity. This is also known as the upper flow regime. In this regime, the flow is fast and unstable, causing the formation of sand dunes that move upstream against the flow direction. Therefore, the statement "Antidunes occur in supercritical flow, meaning that the Froude number is greater than 1.0 or the flow velocity exceeds the wave velocity; this is also known as upper flow regime" is true.

Draas, or dryland riverine systems, typically consist of dunes on both the stoss (upwind) and lee (downwind) sides. However, in some cases, a single slip face can form on certain lee slopes. This means that the statement "Draas are usually made up of dunes on the stoss and lee sides, but a single slip face may develop on some lee slopes" is true.

The thalweg refers to the line in a channel or watercourse that represents the deepest part. It is the path that water would naturally take if it were flowing freely. This line is important for navigation and determining the lowest point in the channel. Therefore, the statement that the line of the deepest part of the channel is called the thalweg is true.

Meanders are sinuous curves or bends that form in a river or stream. They are created by the erosive action of the water on the outer bank of the river bend, which is closest to the thalweg (the deepest part of the channel). As the water flows faster on the outer bank, it exerts more force and erodes the bank, causing the river to meander. Therefore, the statement that meanders develop by the erosion of the bank closest to the thalweg is true.

The explanation for the given correct answer is that the height and energy of waves are indeed determined by the strength of the wind and the fetch. The wind strength affects the size of the waves, with stronger winds creating larger waves. The fetch, which is the distance over which the wind blows, also plays a role in wave height. A longer fetch allows waves to build up more energy and therefore become larger. Therefore, it is true that the height and energy of waves are determined by the strength of the wind and the fetch.

The statement accurately describes aeolian sedimentary processes as those involving the transportation and deposition of material by the wind. This means that wind can pick up loose particles such as sand or dust and move them to another location where they are deposited. This process is responsible for the formation of sand dunes and the redistribution of sediments in arid and coastal regions. Therefore, the correct answer is true.

Longitudinal bars are sedimentary features that form parallel to the flow direction in a channel. They are elongate in shape and align with the axis of the channel. This means that they are oriented in the same direction as the flow of water. Therefore, the statement "Longitudinal bars are elongate along the axis of the channel" is true.

The statement is true because a bayhead delta refers to a type of delta formed at the head of a bay or estuary. In this zone, the dominant processes are related to river or fluvial activity. Fluvial processes involve the transportation and deposition of sediment by rivers, which can contribute to the formation and shaping of a delta. Therefore, the given statement accurately describes the nature of a bayhead delta.

The explanation for the given correct answer is that delta form and facies are indeed influenced by various factors such as the size and discharge of the rivers, the energy associated with waves, tidal currents and longshore drift, the grain size of the sediment supplied, and the depth of the water. These factors play a crucial role in shaping the morphology and sediment composition of deltas, leading to different delta forms and facies.

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 when a river deposits sediment and builds up land at its mouth, causing the land to extend outward into a body of water. On the other hand, an estuary is a partially enclosed body of water where freshwater from a river 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 movement as stated in the question. Therefore, the correct answer is False.

Quartz arenites are sandstones that are composed predominantly of quartz grains. Wind-deposited sands, both in modern and ancient times, are often composed of quartz grains due to their durability and resistance to weathering. Therefore, it is true that most modern and ancient wind-deposited sands are quartz arenites.

The statement is true because in cross-section, wave ripples are indeed generally symmetrical in profile. This means that the shape of the ripples is the same on both sides. Additionally, laminae within each ripple dip in both directions, meaning that they slope downwards in opposite directions. Furthermore, the laminae overlap each other, indicating that they are stacked on top of one another. Therefore, all the characteristics mentioned in the statement are accurate, making the answer true.

The Bernoulli effect states that as the flow of a fluid (such as air or water) passes through a tube that is narrower at one end than the other, the speed of the fluid increases while the pressure decreases. This can be observed in various phenomena, such as the lift generated by an airplane wing or the flow of blood in blood vessels. Therefore, the given statement is true as it accurately describes the explanation of the Bernoulli effect.

The statement suggests that grain roundness can be observed either with a hand lens or under a microscope in the case of an aeolian sandstone. This implies that grain roundness is a visible characteristic that can be easily identified in these types of specimens. Therefore, the answer is true.

When the wind direction is onshore, it means that the wind is blowing from the sea towards the land. In this scenario, wind-blown carbonate sands, which are composed of carbonate minerals derived from marine sources, can accumulate and build up dune bedforms. This is because the wind carries the carbonate sands from the beach or shallow water areas onto the land, where they can be deposited and shaped by the wind into dunes. Therefore, the statement "If the wind direction is onshore, wind-blown carbonate sands can accumulate and build up dune bedforms" is true.

In a gravelly braided river, the bar deposits typically contain cross-stratified granules, pebbles, or occasionally cobbles in a single set. This means that the sediments within the bar deposits are arranged in distinct layers or beds, with each layer showing a consistent pattern of sediment size and orientation. This is a characteristic feature of braided rivers, which have multiple channels that constantly shift and braid, leading to the formation of these distinctive bar deposits. Therefore, the statement is true.

The statement is true because it states that a lake is a body of water that is 2 hectares or more in area. This means that any body of water that meets this criteria can be considered a lake.

Wave ripples and current ripples are different types of sedimentary structures that form in water environments. Wave ripples are formed in shallow water where waves interact with the sediment on the bottom. They are typically symmetrical and have a gentle slope. On the other hand, current ripples can form in any depth of water and are caused by the movement of water currents. They are often asymmetrical and have a steeper slope. Therefore, the statement is true because wave ripples only form in relatively shallow water in the absence of strong currents, while current ripples can form in any depth and any subaqueous environment.

An erg is a type of desert landscape characterized by extensive sand dunes. These dunes are formed by the action of wind, known as aeolian processes, which transport and deposit sand particles in a particular area. Therefore, the statement that an erg is an area where sand has accumulated as a result of aeolian processes is true.

A submarine fan is a deposit of sediment on the sea floor that is formed by mass-flow processes. These processes can create a fan-shaped body of sediment, but they can also result in more elongate or lobate shapes. Therefore, it is true that submarine fans can have various geometries, including fan-shaped and elongate/lobate shapes.

The statement is suggesting that the deposition of coarse detritus occurs at the edge of the alluvial fan. This is true because alluvial fans are formed by the deposition of sediment carried by a river or stream as it flows out of a mountainous area and onto a flatter plain. The sediment consists of various sizes of particles, with the coarsest particles being deposited at the outer edges of the fan. Therefore, the statement is correct.

The statement is true because the overbank area or floodplain is indeed the area of land that only receives water when the river is in flood, apart from rain. This means that during normal conditions, the floodplain remains dry, but it gets inundated with water when the river overflows its banks.

Aeolian ripples are formed by wind erosion and deposition in sandy environments. The variable wavelengths of these ripples can be attributed to the varying wind speeds and sediment sizes. In areas with stronger winds, the ripples tend to have larger wavelengths, while in areas with weaker winds, the wavelengths are smaller. This variability in wavelengths can range from a few centimeters to several meters, making the statement "Aeolian ripples have extremely variable wavelengths ranging from a few centimeters to several meters" true.

Plane beds form in coarser sands at relatively low flow velocities. This means that when the flow velocity is low, the sand particles are able to settle and arrange themselves in a flat, horizontal layer known as a plane bed. This is more likely to occur in coarser sands because the larger particles have a higher settling velocity and are less easily transported by the flow. In contrast, finer sands are more easily transported by the flow even at lower velocities, leading to the formation of dunes or ripples instead of a plane bed. Therefore, the statement is true.

An estuary is not separated from the deeper sea by a shallow or exposed barrier beach, sandbank, coral reef, or similar feature. Instead, it is a partially enclosed coastal body of water where freshwater from rivers and streams mixes with saltwater from the ocean. Estuaries are typically found where rivers meet the sea and are characterized by fluctuating salinity levels and a unique ecosystem that supports a diverse range of plant and animal species.

At high wind velocities, silt- and clay-sized particles are not carried as bed load. Bed load refers to the larger and coarser particles that are transported by flowing water or wind by rolling, sliding, or bouncing along the streambed or ground surface. Silt- and clay-sized particles, on the other hand, are much smaller and lighter, and they are typically carried as suspended load in the air or water. Therefore, the statement is false.

A braided river is a type of river that has multiple channels that split and rejoin, creating a braided pattern. Mid-channel bars are deposits of sediment that form in the middle of the river channel. These bars are typically submerged or covered by water during bank-full flow, which is when the river reaches its maximum capacity and water spills over onto the floodplain. Therefore, the statement that a braided river contains mid-channel bars that are covered at bank-full flow is true.

The statement in the question is discussing the maximum size of quartz grains that can be moved by strong winds over land areas, which is around a half a millimeter in diameter. It states that at these wind velocities, the upper limit on grain size is medium sand. Therefore, the statement is true.

Lakes in regions with large seasonal variations can indeed have annual laminations, known as varves. During the summer, when there is anoxia (lack of oxygen), clay rich in organics can settle at the bottom of the lake. In contrast, during winter storms, silt can be deposited. These alternating layers of clay and silt form distinct annual bands, providing a record of the lake's history. Therefore, the statement "True" is an accurate explanation of the given information.

The statement is false because a lagoon is not a marine-influenced portion of a drowned valley. A lagoon is actually a shallow body of water separated from a larger body of water, such as a sea or ocean, by a barrier such as a sandbar or barrier island. It is typically found along coastlines and can be either saltwater or freshwater.

False. Rivers with a high proportion of sediment carried by suspension along the channel floor are actually referred to as suspended load rivers, not bedload rivers. Bedload rivers, on the other hand, primarily transport sediment by rolling, sliding, or bouncing along the river bed.

Aeolian carbonate deposits are more stable features than dunes made of quartz sand. This is because carbonate deposits, which are formed from the precipitation of calcium carbonate, tend to be more cohesive and resistant to erosion compared to quartz sand dunes. Additionally, carbonate deposits have a higher density and are more cemented, making them less susceptible to wind erosion and movement. Therefore, the statement that Aeolian carbonate deposits are less stable features than dunes made of quartz sand is false.

The 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 sediment resuspension.

Wave ripples can form in any cohesive sediment, but they are not principally seen in coarse silts and sand of all grades. They are commonly observed in fine-grained sands and silts, where the cohesive nature of the sediment allows for the formation and preservation of ripples. Therefore, the statement that wave ripples can form in any cohesive sediment and are principally seen in coarse silts and sand of all grades is false.

Current ripples are actually formed by low energy flow velocities over a hydrodynamically smooth bed. When the flow velocity is low, the sediment particles settle and form ripples on the bed. These ripples are typically small and have a symmetrical shape. In contrast, high energy flow velocities can cause the sediment particles to be transported and deposited in a different manner, such as forming dunes or bars. Therefore, the correct answer is false.

The statement suggests that in the transfer zone, streams actively remove bedrock from the valley floor and valley sides through downslope movement of material into the stream bed. However, this statement is false. In the transfer zone, streams are not actively down cutting or removing bedrock. Instead, they are usually depositing sediment and filling the valley with alluvium.

An estuary developed in an area with a large tidal range and weak wave energy will typically have three divisions. This statement is false. Estuaries are typically classified based on their geomorphology and the dominant processes shaping them, rather than tidal range and wave energy. The number of divisions in an estuary can vary depending on various factors such as the shape of the coastline, sediment deposition, and river flow. Therefore, it cannot be generalized that estuaries in such areas will always have three divisions.

Antidune cross-bedding refers to the stratification of sediment that dips upstream, not downstream. Therefore, the statement that antidune cross-bedding would be stratification dipping downstream is incorrect.

The statement is false because the deposits of a meander bend actually have a characteristic profile of coarser material at the base, becoming progressively finer-grained up the inner bank. This is due to the process of sedimentation, where the heavier, coarser particles settle first and the finer particles are carried further by the flowing water before settling.

If avulsion is frequent, it means that the river channels are constantly changing their course. In this case, there would be less time for lateral migration to occur, as the channels are constantly shifting. Therefore, the architecture would not be characterized by broad channel deposits, but rather by a more chaotic and unpredictable pattern of deposition. Hence, the statement is false.

The statement is false because turbidite deposits are not formed by the remobilization of sediment from the edge of the shelf or the top of the slope. Turbidite deposits are actually formed by underwater landslides or turbidity currents that carry sediment down the slope and deposit it on the basin plain.

The statement is false because arid areas receive less than 250mm yr-1 precipitation, not less than 500mm yr-1.

A braided river is a type of river that consists of multiple, interconnected channels that are separated by areas of gravel or sandbars, rather than floodplain. This creates a complex network of channels that constantly shift and change course. Therefore, the given statement that a braided river consists of multiple channels separated by floodplain is incorrect.

Barchan dunes do not form where there is an abundant supply of sand. In fact, they form in areas where there is a limited supply of sand. Barchan dunes are crescent-shaped dunes that are formed by wind erosion and deposition. They typically occur in desert regions with moderate sand availability and consistent wind direction. In areas with abundant sand, other types of dunes such as linear or star dunes are more likely to form. Therefore, the statement that barchan dunes form where there is an abundant supply of sand is false.