Short Answer Questions. Answer Each Question. If the Question Asks for a Sketch Or Diagram

Name ______Geology 103

Midterm #1Spring 2017

Short answer questions. Answer each question. If the question asks for a sketch or diagram, be sure to include it. (5 points each).

1) What is the phi scale, and how does it work? (Give an equation!) What phi size is equivalent to 0.25 mm?

2) List at least 5 adjectives that you could use to describe sedimentary beds in the field, and draw a picture of each. Think about bed boundaries and beds in cross-section (internal features).

3) Describe the textural and compositional maturity of a medium-grained sandstone that is composed of 50% well-rounded chert grains (SRF), 30% subrounded quartz grains, and 10% each subrounded zircon and tourmaline grains. The sample is well sorted. Explain your answer.

4) What environment(s) of deposition might be indicated by each of these textures?

well sorted sediment-

polished grains-

frosted grains-

striated pavement (or striated grains)-

very poorly sorted sediment-

5) How would you distinguish between quartz and feldspar in a sand sample? Use properties that would be available with a dissecting microscope and simple tools (no thin section!).

Quartz Feldspar

6) What colors are common in shales, and what might these colors indicate about depositional environments, sediment sources, or composition of the shale?

7) Describe the particle motion, velocity patterns and erosive force of a fluid that is experiencing laminar flow. Where does this type of flow occur in nature (give examples)?

8) Describe the forces that combine to lift a sand grain from a streambed into suspension. Draw a picture to go with your answer.

9) What variables affect Stoke’s Law? Describe each variable, and whether it is directly or inversely related to settling velocity.

10) What conditions favor formation of oscillation ripples? Why can an oscillation ripple tell us the “up” direction of a sedimentary bed? Draw a picture to illustrate your answer.

11) What textural and compositional changes occur to sedimentary particles with increasing distance from the source area?

12) ) Reynolds numbers are calculated using the following formula: Re = UL/μ. List three natural conditions where changes in U, L or μ result in laminar flow conditions. Explain each.

13) Name four methods that geologists use to measure grain size. Describe each.

14) What geologic source areas contribute sediment to the lower American River?

15) Why is it easier to entrain a sand grain than a clay particle? Use the Hjulstrom diagram to support your answer. Which particle settles faster? (15 points)

16) Describe the progression of bedforms that would occur as medium sand experiences higher and higher current velocities. List each bedform, draw a simple picture and give a brief description of each bedform. (15 points)