Geology 103
Review Questions, Test #1
The following questions are similar to the essay or short answer questions that will appear on
your first midterm exam. This is NOT intended to be an exhaustive study guide. These
examples will help you study some of the major points that we have covered in lecture, but you
should also read the assigned reading and study your notes.
1) What is roundness? What field terms could a geologist use to describe roundness? How does
roundness differ from sphericity?
2) Describe a laboratory method that could be used to measure grain size distribution. What
statistical methods would you use to report and analyze grain size distribution in sediments?
3) Name four methods that geologists use to measure grain size. Describe each.
4) What is the phi scale? What phi number would we assign to a grain that is 1/256 mm?
5) How do geologists describe sorting in the field? Give examples of depositional environments
that might be represented by the extremes in sorting.
6) What is the difference between textural maturity and compositional maturity? Give an
example of each.
7) Describe the general relationship between grain size and composition in clastic sedimentary
rocks. Predict what a shale might be made of.
8) What environments might be indicated by each of these textures: well sorted sediment,
polished sediment, frosted grains, very poorly sorted sediment.
9) What descriptive terms or modifiers could you add to a shale or siltstone name?
10) What is the difference between laminae and beds?
11) What is dynamic viscosity? How is it measured?
12) What is kinematic viscosity? How is it used?
13) What two physical properties are used to define the characteristics of a fluid? In your
discussion, you should mention the following points: What Greek symbol is used to define the
property? How does the property change with an increase in temperature? How do changes in
the property affect the ability of a fluid to transport or erode sediment?
14) Reynolds numbers are calculated using the following formula: Re = UL/μ. Define the
variables in this formula, discuss the difference between laminar and turbulent flow (as defined
by the Reynolds number) and list three natural conditions where changes in U, L or μ result in
laminar flow conditions.
15) Describe the forces that act on a grain during entrainment. How are particle size and current
velocity related to the ability of a fluid to erode and transport a grain?
16) What is the difference between bed load, suspended load and wash load?
17) What variables or physical parameters are involved when a grain settles through a fluid?
How would an increase in each of the variables from this group affect the settling velocity of a
grain?
18) How would you distinguish between quartz, orthoclase, plagioclase and microcline in a sand
sample?
19) Describe how compositional and textural maturity would change during weathering and
transport of a sediment that was derived from a granitic source area.
20) Describe the major types of lithic clasts that occur in sedimentary rocks. What would each
look like in a hand specimen? (Assume that you have access to a good hand lens or dissecting
microscope).
21) A sand sample contains quartz, feldspar, mica and plutonic rock fragments. All particles are
subangular to angular, and the sample is poorly to moderately sorted. What interpretations can
you make about this sample? Discuss distance to the source, composition of the source rock and
energy of the system.
22) What adjectives are used to describe the configuration of bedding surfaces? Draw a simple
sketch to illustrate each type of bedding.
23) Discuss the sequence of bedforms that develop in a medium sand sample as current velocity
increases. Show the boundary between the upper and lower flow regimes. Use simple sketches
of the bedforms to illustrate your discussion.
24) What is the difference between the upper and lower flow regime? How are these defined
mathematically?
25) Describe the differences between planar tabular cross stratification and trough crossstratification. Draw a simple block diagram of each bed form, and show the internal structures.
26) Describe flaser, wavy and lenticular bedding. What flow conditions lead to their formation?
27) Name the parts of a ripple. How do ripples form, and what grain sizes have ripples?
28) Describe the difference between an oscillation ripple and a current ripple. What current
conditions are responsible for the formation of each type of ripple, and what depositional
environments might produce these conditions?
29) What is a sand crystal? How do they form?
30) How do hopper crystals form?
31) How do flute casts form?
32) How do concretions form?
33) What is convolute lamination? How does it form?
34) What conditions might lead to the formation of massive bedding, Dude?
35) Describe the difference between an oscillation ripple and a current ripple. What current
conditions are responsible for the formation of each type of ripple, and what depositional
environments might produce these conditions?