Eduqas GCSE Geology · 1.3

Sedimentary Rocks and their Fossil Content

50 revision questions with answers for 1.3 Sedimentary Rocks and their Fossil Content in Eduqas GCSE Geology (spec C480QS). Practise with flashcards, a topic quiz, a random quiz across the course, 5 crosswords, Five Degrees, Associations, or read every question and answer below. Not official Eduqas material.

All 50 questions and answers

Question 1
What is weathering?
Answer:
The breakdown or alteration of rock in place at or near Earth's surface.
Question 2
What is erosion?
Answer:
The removal of weathered material by agents such as water, wind or ice.
Question 3
How does deposition occur?
Answer:
Transported sediment settles or is laid down when the transporting agent can no longer carry it.
Question 4
What is lithification?
Answer:
The conversion of loose sediment into sedimentary rock, commonly through compaction and cementation.
Question 5
What is compaction?
Answer:
The squeezing of sediment under the weight of overlying material, reducing pore space.
Question 6
What is cementation?
Answer:
Minerals precipitate between grains and bind the grains together.
Question 7
How can the grain size of a sediment indicate transport energy?
Answer:
Coarser grains generally require stronger flow to transport than fine clay particles.
Question 8
What is sorting in sediment?
Answer:
The degree of similarity in grain sizes within a sediment sample.
Question 9
What is well-sorted sediment?
Answer:
Sediment whose grains are mostly of a similar size.
Question 10
What is poorly sorted sediment?
Answer:
Sediment containing a wide range of grain sizes.
Question 11
Why do transported pebbles often become more rounded?
Answer:
Repeated collisions and abrasion wear away sharp corners during transport.
Question 12
How is sphericity different from roundness?
Answer:
Sphericity describes how close a clast's overall shape is to a sphere; roundness describes its corners.
Question 13
Why is glacial till often poorly sorted?
Answer:
Ice can carry and deposit a wide range of particle sizes together.
Question 14
A sample has 2, 4 and 6 mm grains. Calculate the mean grain size.
Answer:
(2 + 4 + 6) / 3 = 4 mm.
Question 15
How do breccia and conglomerate differ?
Answer:
Breccia contains angular coarse clasts; conglomerate contains rounded coarse clasts.
Question 16
What grain size is used for coarse sedimentary clasts in the specification?
Answer:
Coarse clasts are larger than 2 mm.
Question 17
What grain size is used for fine sediment in the specification?
Answer:
Fine grains are smaller than 1/16 mm.
Question 18
Which rock is made mainly of sand-sized grains?
Answer:
Sandstone.
Question 19
Which listed rock is fine-grained and commonly laminated?
Answer:
Shale.
Question 20
How can limestone commonly be distinguished from quartz sandstone?
Answer:
Limestone containing calcite fizzes with dilute acid; quartz-cemented sandstone generally does not, though calcite cement can fizz.
Question 21
Name two evaporite minerals in the specification.
Answer:
Halite and gypsum.
Question 22
What is coal evidence of?
Answer:
Accumulation and burial of plant material, commonly in swampy terrestrial settings.
Question 23
A rock contains rounded pebbles set in finer material. Identify it.
Answer:
Conglomerate.
Question 24
A rock contains angular rock fragments over 2 mm. Identify it.
Answer:
Breccia.
Question 25
What environment can deposit well-sorted, cross-bedded sand?
Answer:
A wind-blown desert dune is one possibility; water currents can also create cross-bedding.
Question 26
What do ripples in sandstone show?
Answer:
A current or wave moved sediment; further evidence is needed to distinguish river and marine settings.
Question 27
What do desiccation cracks indicate?
Answer:
Wet sediment dried and shrank, showing exposure to the air at least periodically.
Question 28
What is graded bedding?
Answer:
A change in grain size through a bed, commonly coarse at the base grading to finer at the top.
Question 29
How can a graded bed form in deep water?
Answer:
A sediment-laden turbidity current slows; coarser particles settle before finer particles.
Question 30
What can a sequence of repeated graded beds suggest?
Answer:
Repeated sediment-laden flows, for example turbidity currents, deposited successive layers.
Question 31
What is cross-bedding?
Answer:
Inclined internal layers within a bed formed as ripples or dunes migrated.
Question 32
How can cross-bedding help reconstruct an ancient flow direction?
Answer:
The dip direction of foreset layers can indicate the direction sediment moved, subject to interpretation.
Question 33
Why can dark shale form in quiet water?
Answer:
Fine particles settle from suspension where water energy is low; dark colour can indicate organic-rich, oxygen-poor conditions.
Question 34
What conditions favour reef-building corals?
Answer:
Shallow, warm marine water.
Question 35
What do plant fossils in a sedimentary rock suggest?
Answer:
A terrestrial source and, where identified, evidence about the past climate.
Question 36
What is a trace fossil?
Answer:
Evidence of an organism's activity rather than its body, such as a footprint or burrow.
Question 37
What environment does a trilobite fossil indicate?
Answer:
A marine environment.
Question 38
What environment does an ammonite fossil indicate?
Answer:
A marine environment.
Question 39
How can footprint size and shape support a comparison of trackmakers?
Answer:
Different sizes or shapes may indicate different animals, but preservation and age can also affect appearance.
Question 40
How can rapid burial improve fossil preservation?
Answer:
It reduces exposure to scavengers and decay and protects remains within sediment.
Question 41
Why is the fossil record incomplete?
Answer:
Soft parts decay, many organisms are not buried, some fossils are destroyed, and many remain undiscovered.
Question 42
A fossil is 30 mm long in an image whose scale is 2x. What is its actual length?
Answer:
30 / 2 = 15 mm.
Question 43
What is porosity?
Answer:
The proportion of a rock's volume occupied by pore spaces.
Question 44
What is permeability?
Answer:
The ability of a rock to transmit fluid through connected spaces or fractures.
Question 45
Can a rock be porous but poorly permeable?
Answer:
Yes. Pores may be isolated or the connections between them may be very small.
Question 46
How does cementation commonly affect porosity?
Answer:
Mineral cement fills pore space, generally reducing porosity and often reducing permeability.
Question 47
Why might well-sorted sand have more connected pore space than clay-rich sand?
Answer:
A lack of fine particles leaves more open pathways between larger grains, although cementation also matters.
Question 48
What is a graphic log?
Answer:
A scaled vertical representation of a rock sequence showing features such as bed thickness and grain size.
Question 49
In a graphic log, why should bed thickness be plotted to a consistent scale?
Answer:
It preserves relative bed thicknesses so the sequence can be interpreted accurately.
Question 50
One bed is 2 m thick. At 1 cm representing 1 m, how thick should it be on a log?
Answer:
2 cm.

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Sedimentary Rocks and their Fossil Content

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