Question 1

What is probably the single most important, original, depositional feature in all sedimentary rocks?

Accepted Answer

Bedding or stratification is considered the single most important and original depositional feature in all sedimentary rocks. It refers to the layering that occurs in sedimentary rocks as a result of the processes of sediment deposition over time. This feature provides critical information about the conditions under which the rock was formed.

Question 2

The aspect, thickness, and appearance of a rock unit, and reflecting its environmental conditions of origin, is collectively referred to as its__________ .

Accepted Answer

Facies refers to the aspect, thickness, and appearance of a rock unit, reflecting its environmental conditions of origin.

Question 3

A horizontally bedded succession of thick, well sorted sands, containing moderately dipping layers between the flatlying upper and lower surfaces of each bed are called _________.

Accepted Answer

Cross-beds are characteristic of sedimentary structures formed by the migration of dunes, deltas, or river channels, where the inclined layers (moderately dipping layers) are sandwiched between horizontal beds, indicating the direction of sediment transport and deposition.

Question 4

What kind of rock are most dripstones and stalactites in caves?

Accepted Answer

Dripstones and stalactites in caves are most commonly formed from limestone, as they are created by the deposition of calcium carbonate.

Question 5

Sedimentary rocks account for about what percentage of the Earth's outermost 10 kilometres of rock (first percentage). Also, what percentage of the Earth's continental area is covered by sedimentary rocks (second percentage)?

Accepted Answer

Sedimentary rocks account for about 5% of the Earth's outermost 10 kilometres of rock, but they cover about 75% of the Earth's continental area. This discrepancy is because sedimentary rocks are often found in layers at the Earth's surface.

Question 6

Which three elements are further concentrated in a residual brine after NaCl is crystallized?

Accepted Answer

Potassium and magnesium are typically more soluble than sodium chloride, so as NaCl is crystallized out of solution, these elements become more concentrated in the residual brine.

Question 7

Detrital sedimentary rocks are mainly classified (named) on what basis?

Accepted Answer

Detrital sedimentary rocks are primarily classified based on the grain sizes of the detrital particles, which include sand, silt, and clay, leading to the naming of rocks such as sandstone, siltstone, and claystone.

Question 8

What proportion of sedimentary rocks do the mudstones and shales comprise?

Accepted Answer

Mudstones and shales are the most common types of sedimentary rocks, making up approximately 50% of the sedimentary rock record. This is due to their formation from fine-grained sediments that are widely deposited in a variety of environments.

Question 9

Which of the following minerals are listed in order of increasing solubility in seawater (from least soluble to most soluble)?

Accepted Answer

Calcite (CaCO3) is less soluble than halite (NaCl), and halite is less soluble than sylvite (KCl). This order reflects their increasing solubility in seawater.

Question 10

What does the degree of rounding indicate in a sediment?

Accepted Answer

The degree of rounding in sediment indicates the distance travelled or the duration of time involved in sediment transport, as more rounded sediments have typically been transported over longer distances or for longer periods, leading to more abrasion and smoothing of edges.

Question 11

The dominant sediment of tidal flats would likely be________ .

Accepted Answer

Tidal flats are environments characterized by low energy where fine sediments like muds and silts can settle out of the water column. These areas often have some organic content due to the presence of microorganisms and plants.

Question 12

Laterally shifting depositional environments with time always produce_________ .

Accepted Answer

Laterally shifting depositional environments over time result in vertical facies successions. This is because as the environment changes (for example, from a river to a delta to a marine environment), different types of sediments are deposited on top of each other, creating a vertical sequence of different rock types or facies.

Question 13

What proportion of sedimentary rocks are "limestones"?

Accepted Answer

The answer of What proportion of sedimentary rocks are "limestones"?
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Question 14

Which sediment gets lithified to become mudstone?

Accepted Answer

Mudstone is formed from the lithification of clay and fine silt, which are the primary components of mud.

Question 15

Shales are usually described as weak because they are_______ .

Accepted Answer

Shales are considered weak because they are only compacted but not well cemented, which affects their strength and durability.

Question 16

Which type of sandstone contains abundant detrital feldspar grains?

Accepted Answer

Arkose sandstone is characterized by its high feldspar content, typically derived from the rapid erosion of granitic or metamorphic rocks, which contain abundant feldspar minerals. This distinguishes it from other types of sandstone, such as wacke, which is generally muddier, or orthoquartzite, which is very pure quartz sandstone with minimal other mineral content. Pegmatitic is not a type of sandstone but refers to a very coarse-grained igneous rock.

Question 17

Shales are distinguished from other mudrocks by their__________ .

Accepted Answer

Shales are distinguished from other mudrocks by their fissility, which refers to their ability to split into thin layers along bedding planes. This characteristic is due to the parallel orientation of clay minerals within the rock.

Question 18

What sedimentary rock type most commonly contains terrestrial plant fossils?

Accepted Answer

Dark organic rich shales are most commonly associated with the preservation of terrestrial plant fossils. These rocks are formed in low-oxygen environments where organic material can be preserved without extensive decay.

Question 19

Which type of sediment undergoes the most compaction as it lithifies to sedimentary rocks?

Accepted Answer

Marine mud undergoes the most compaction as it lithifies to sedimentary rocks because it is composed of very fine particles that can be densely packed together under pressure, significantly reducing its volume.

Question 20

A succession of beds containing small scale asymmetric ripples that alternate their orientations are likely to be_________ .

Accepted Answer

Asymmetric ripples that alternate their orientations are characteristic of environments where the current direction changes, such as in tidal areas. This results in current ripple marks.

Quiz 17: Glaciers and Glaciation