Clastic Sedimentology And Petrography-quiz 1

Sorting is the correct answer because it refers to the process of separating sediments based on their particle size due to variations in current velocity. When the current velocity decreases, larger and heavier particles settle first, while smaller and lighter particles remain suspended for longer periods. This results in the segregation or sorting of sediments based on their size, with coarser particles being deposited closer to the source and finer particles being transported further away.

The correct answer is "Conglomerate, sandstone, siltstone." This is because conglomerate is made up of large particles, sandstone is made up of smaller particles, and siltstone is made up of even smaller particles. Therefore, the order goes from largest to smallest particle size.

The angularity of the edges and corners of grains in a sedimentary rock is referred to as rounding. Rounding refers to the process by which the sharp edges and corners of grains become smoother and more rounded over time due to erosion and transport. This can occur through processes such as abrasion and attrition, where the grains collide with each other or with other materials, causing them to wear down and become rounded. The degree of rounding can provide valuable information about the history and transportation of the sedimentary rock.

The given statement is true because it states that sandstones and conglomerates make up 20-25% of the sedimentary rocks in the stratigraphic record, while mudrocks account for 60% of the total. This implies that sandstones, conglomerates, and mudrocks are the dominant types of sedimentary rocks in the stratigraphic record, with mudrocks being the most prevalent.

When discoid clasts, which are flat and round-shaped rocks, are transported by water, they tend to align themselves in a specific orientation. This alignment causes the clasts to stack up on top of each other, forming a structure called imbrication. Therefore, the statement that discoid clasts can stack up in imbrication when moved in a flow of water is true.

Siltstones are coarser grained than claystones.

Clastic sedimentary rocks are composed of minerals and rock fragments derived from pre-existing material. This means that these rocks are made up of both individual mineral grains and larger pieces of rocks that have been broken down and transported by natural processes. The minerals in clastic sedimentary rocks can vary depending on the source material, but common minerals found in these rocks include quartz, feldspar, and clay minerals. The presence of minerals and rock fragments in clastic sedimentary rocks is evidence of their origin from pre-existing materials.

In turbulent flows in an upper flow regime, the velocity of the fluid is high enough to cause the formation of antidunes. Antidunes are formed when the sediment on the bed of the flow is transported and deposited in a way that creates a series of upstream-facing, steep slopes. These slopes then cause the water to flow faster over them, leading to the formation of waves that move upstream against the flow direction. Therefore, in turbulent flows in an upper flow regime, the formation of antidunes is expected.

The statement is false because clasts over 4mm in diameter are actually divided into granules, pebbles, cobbles, and pebbles, not boulders.

Gravels (including pebbles) are pieces of older rock material that are larger than 2 mm in size. This means that any rock material smaller than 2 mm would not be classified as gravel.

The given answer "flute cast" suggests that the symbol represents or is associated with a flute cast. The term "flute cast" refers to the process of creating a mold or cast for a flute, which is a musical instrument. Therefore, the symbol in question may be a visual representation or a symbol used to represent the flute cast or the process of creating a flute mold.

Load casts are a type of sedimentary structure that are formed when a denser layer of sediment is deposited on top of a less dense layer. The weight of the overlying sediment causes the lower layer to deform and create elongated, lens-shaped structures. These structures are commonly found in sandstone and are indicative of the movement and deformation of sediment layers due to the force of gravity.

If the Froude Number in an open channel flow is greater than 1, it indicates that the flow is super-critical. In super-critical flow, the flow velocity is greater than the wave velocity, causing the water surface to be relatively flat and the flow to be rapid. This type of flow is characterized by a high energy level and is typically observed in steep or rapidly varying channels.

The statement is false because the correct answer is that only 45% of feldspar needs to be present for the rock to be called a feldspathic arenite, arkosic arenite, or arkose.

The correct answer is "A rock formed from the cementation of transported grains." Clastic rocks are formed from the accumulation and cementation of fragments or grains that have been transported and deposited by water, wind, or ice. These fragments can be made of various minerals, such as quartz, feldspar, or clay, and they are bound together by a cementing material, such as calcite or silica. The process of cementation involves the filling of spaces between the grains with the cementing material, which solidifies and holds the rock together.