Chapter 5 Answers

Review Question Answers:

1. Sand grains range in size from 1/16 mm to 2 mm.

2. Conglomerate cannot be deposited by a slow-flowing river because clasts larger than 2 mm are not transported by slow-moving water.

3. Sediments are buried beneath other sediments where, because of the increased pressure, they become compacted and water is forced out from between the grains. With additional burial they are warmed to the point where cementing minerals can form between the grains (less than 200˚C).

4. Lithic arenite has less than 15% silt- and clay-sized particles, while a lithic wacke has more than 15%. Both have more than 10% rock fragments and more rock fragments than feldspar.

5. Feldspathic arenite has more than 10% feldspar and more feldspar than rock fragments. Quartz arenite has less than 10% feldspar and less than 10% rock fragments. Both have less than 15% silt and clay.

6. Source area lithology: rock that contains quartz (such as granite or sandstone). Strong weathering is required to remove feldspar, and long fluvial transportation to round the grains.

7. The carbon within carbonate deposits such as limestone ultimately comes from the atmosphere.

8. Most of Earth’s banded iron formations formed during the initial oxygenation of the atmosphere between 2.4 and 1.8 Ga because iron that had been soluble in the anoxic oceans became insoluble in the oxidized oceans.

9. Terrestrial depositional environments: rivers, lakes, deltas, deserts, glaciers. Marine depositional environments: continental shelves, continental slopes, deep ocean.

10. A foreland basin forms in the vicinity of a large range of mountains where the weight of the mountains depresses the crust on either side. A forearc basin lies between a subduction zone and the related volcanic arc.

11. (a) Bedding forms where there is an interruption or change in the depositional process, or a change in the composition of the material being deposited. (b) Cross-bedding forms in fluvial or aeolian environments where sand-sized sediments are being moved and ripples or dunes are present. (c) Graded bedding forms when transport energy decreases, depositing finer and finer particles. (d) Mud cracks form where fine-grained sediments (silt or clay) are allowed to dry.

12. Reverse-graded bedding forms during gravity flows, such as debris flows.

13. A formation is a series of beds that is distinct from other beds above and below it, and is thick enough to be shown on the geological maps that are widely used within the area in question.

14. The Nanaimo Group was actively mined for coal for many decades. During that time the names were given to members and individual beds that were important to the coal miners.