Sedimentary Rock Formation

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What is the primary process by which sedimentary rocks are formed?

Metamorphism under high pressure
Deposition at the Earth's surface (correct)
Crystallization from a melt
Intrusion of magma

A clast is a term typically used for a particle within sediment, prior to it becoming part of a rock.

False (B)

Name the two main processes involved in the lithification of sediment into rock.

compaction and cementation

__________ is the term for post-depositional processes that alter sediment into sedimentary rock.

Diagenesis Signup and view all the answers

Match the following terms with their correct descriptions:

Sediment = Unconsolidated material deposited by water, ice, or wind Clast = A particle broken off from a pre-existing rock Diagenesis = Post-depositional processes that change sediment into rock Lithification = The process of converting loose sediments into solid rock Signup and view all the answers

Which of the following best describes the effect of matrix within a sandstone on pressure dissolution?

Decreases pressure dissolution by spreading the load and reducing pressure at grain contacts. (B) Signup and view all the answers

Pressure dissolution is more prevalent in texturally immature sandstones compared to texturally mature sandstones.

False (B) Signup and view all the answers

Insanely difficult: Assuming a sedimentary deposit begins with 45% porosity and, through compaction, reduces its volume by 20% while the solid grains experience negligible compression, what is the final approximate porosity percentage of the compacted sediment? (Assume initial total volume is 100 units)

Approximately 31% (C) Signup and view all the answers

What is the primary effect of small particles in a river's load on the surface they interact with?

Smoothing or polishing (D) Signup and view all the answers

Abrasion is most effective when a river carries very little solid load.

False (B) Signup and view all the answers

What happens to the size and shape of particles as they move downstream due to attrition?

Particles decrease in size and become more rounded. Signup and view all the answers

The upper reaches of a river tend to contain large, ______ sediment, whereas the downstream parts have fine, rounded particles.

angular Signup and view all the answers

What causes the corkscrew flow in meandering rivers?

The helical movement of surface water (D) Signup and view all the answers

The point of maximum erosion in a meander occurs exactly at the mid-point of the bend.

False (B) Signup and view all the answers

A river's abrasion effectiveness is most determined by which factor?

Sediment load (B) Signup and view all the answers

Insanely Difficult: Imagine a perfectly straight river channel is artificially forced into a meandering pattern. How would this alteration initially affect the river's overall slope (or gradient) and flow velocity according to the principles described?

The slope would lessen, and the flow velocity would decrease. Signup and view all the answers

Which of the following minerals is most resistant to chemical weathering?

Quartz (D) Signup and view all the answers

Minerals formed at high temperatures are generally more resistant to weathering than minerals formed at low temperatures.

False (B) Signup and view all the answers

What type of acid primarily attacks carbonate minerals during chemical weathering?

carbonic acid Signup and view all the answers

The chemical weathering process where shells of decomposed rock flake off in blocks is known as ___________ weathering.

spheroidal Signup and view all the answers

Which rock type is generally more resistant to weathering due to its non-porous nature?

Granite (B) Signup and view all the answers

In wet, tropical regions, what is the end product of feldspar decomposition after silica is leached away?

Laterite (C) Signup and view all the answers

Fine-grained rocks are generally less resistant to weathering than coarse-grained rocks.

False (B) Signup and view all the answers

Anorthite (CaAl$_2$Si$_2$O$_8$) is less stable than ______ (NaAlSi$_3$O$_8$).

albite Signup and view all the answers

What is the primary role of river systems in the context of sedimentary processes?

Transporting sediments from continental areas to the sea (A) Signup and view all the answers

The terms 'alluvial' and 'fluvial' are used interchangeably to describe only the river channel itself.

False (B) Signup and view all the answers

Name two types of alluvial environments based on river channel morphologies.

Meandering river channels and braided systems Signup and view all the answers

The area adjacent to a river channel that is typically flat and floods during high water levels is called the ______.

flood plain Signup and view all the answers

Which of the following is NOT a typical characteristic considered when interpreting environments of deposition?

Tectonic plate boundaries (A) Signup and view all the answers

Braided systems are more commonly found in desert environments than in glacial environments.

False (B) Signup and view all the answers

Insanely Difficult: Briefly explain how grain size within a sedimentary bed can be indicative of the energy of the depositional environment.

The grain size reflects the energy of the depositional environment. Higher energy environments, such as fast-flowing rivers, can transport larger and heavier particles (coarse grains). Lower energy environments, such as calm lakes, can only carry and deposit small, light particles (fine grains). Therefore, coarser grain sizes indicate higher energy, while finer grain sizes indicate lower energy. Signup and view all the answers

What is the name of the sediment deposit formed on the inside bend of a meander where the water flow is slower?

Point bar (C) Signup and view all the answers

Lateral erosion occurs on the inside of meander bends due to slower water flow.

False (B) Signup and view all the answers

What is the term for a meander that has been cut off from the main river channel and forms a crescent-shaped lake?

ox-bow lake Signup and view all the answers

Small ridges formed on the edge of a river channel due to sediment deposition during times of increased water level are called ______.

levées Signup and view all the answers

Match the process with its location in a meander bend:

Fastest water flow = Outside of the bend Sediment deposition = Inside of the bend Erosion = Outside of the bend Point bar formation = Inside of the bend Signup and view all the answers

Which of the following scenarios leads to the creation of a 'neck' of land that is easily breached, potentially forming a new river channel?

The rate of downstream migration of one meander is greater than another further downstream. (B) Signup and view all the answers

An oxbow lake is plugged with sediment and vegetation, this process is best described by what term?

Eutrophication (D) Signup and view all the answers

Describe the effect of increased water level on sediment transport and deposition in a river channel. Be specific about where the deposition occurs, and why?

Increased water levels result in water flowing over the channel, leading to a sudden reduction in flow velocity outside the channel, causing sediment, being carried, to be dropped, forming levées on the edge of the river channel. Signup and view all the answers

What is the primary factor causing small particles (less than 250 μm in diameter) to require disproportionately larger velocities to be lifted from a channel bed?

Cohesion of the particles towards each other. (A) Signup and view all the answers

Well-sorted sediments are typically deposited over a wide range of current velocities.

False (B) Signup and view all the answers

Name two characteristics, other than grain size, that should be examined to fully understand depositional conditions.

Grain shapes, surface textures Signup and view all the answers

A sudden decrease in current strength would most likely cause ______ sorted sediments to be deposited.

poorly Signup and view all the answers

Match each sedimentary environment with its typical sediment characteristics:

Alluvial Fans = Coarse, poorly-sorted gravel and sand Fluvial Environments = Coarse, rounded gravel and sand Signup and view all the answers

Which type of environment is characterized by fan-shaped deposits at the base of mountains, common in arid and semi-arid regions?

Alluvial fan (B) Signup and view all the answers

Fluvial environments exclusively consist of braided river systems.

False (B) Signup and view all the answers

Imagine a scenario where paleontologists discover well-preserved marine fossils in a sedimentary rock layer far inland. Which of the following is the MOST plausible interpretation regarding Earth's geological history, based on the principles described?

The area was once a shallow marine environment that has since been uplifted. (B) Signup and view all the answers

Sediment

Material deposited by water, ice, or wind; in geology, synonymous with 'grain'.

Clast

A particle broken off a pre-existing rock, often used within consolidated rock.

Clastic

Sedimentary rocks composed of particles broken off from pre-existing rocks (e.g., sandstone).

Diagenesis

The group of post-depositional processes that change sediment into sedimentary rock at low temperatures and pressures.