Exercise 5.1. Unaltered and Re-formed Preservation (Sample Set 1)

What To Do

Download the printer-friendly worksheets in the format of your choice (available at the beginning of Lab 5).

Inspect the fossil specimens in Sample Set 1 (images available below), paying special attention to the features you are asked to examine. Answer questions (a)-(r) as you work through Sample Set 1.

Note: If the image slide-decks fail to load, click the sample title to open the slide deck in a new window.

If you are doing this lab in person, pay special attention to the handling directions for each sample.

Sample Set 1 & Questions

Unaltered Preservation

A. Sample 121-21: Insects in Amber

Sample 121-21 can be picked up but please treat it with care.

These insects got stuck in soft tree sap and over time, the tree sap has hardened to amber.


B. Sample FXA17E: Bone Cross-Section

Sample FXA17E can be picked up but please treat it with care.

Look first at the unpolished side of the sample. Observe the dense material on the outer edges of the sample that originally gave the bone its strength. Now find the porous parts.


Question a

a. What used to occupy the spaces in the porous parts of Sample FXA17E?


Look at the polished side (Slide 2 in the slide deck), and notice that the pore spaces are now filled. The two minerals most likely to be occupying these pore spaces are amorphous silica (solid silica deposited without forming a proper crystal structure) and calcite. Remember, no acid tests please. This sample has silica.

Notice that the outside of the bone is relatively smooth. Where tendons attach to bones the bone surface would be rougher and sometimes porous. These attachment points can be used to determine how muscles were arranged, how large the muscles were, and how an organism moved. This is how paleontologists and biologists have created computer models that can re-create how dinosaurs and other creatures move.


C. Sample 121-22: Fossilized Wood

Samples of 121-22 can be picked up but please treat them with care.

If you do not have access to Sample 121-22, examine the GIGAmacro image below to answer the questions.



Questions b-d

b. Both Sample 121-22 and the GIGAmacro petrified wood image above include the bark of the tree. Find the bark on the outside of the tree. Aside from being on the outside of the tree, how else can the bark be distinguished?

c. Find the layering within the fossil. What does the layering represent?

d. Compare the petrified wood to the images of non-fossilized trees in the slide deck below. (Click here to open the slide deck in a new window.) How well preserved is the petrified wood? Can you see any internal structures, cells, etc.? Can you easily identify it as wood? Explain your answer.


Imagine what happens to wood as it ages. It rots and crumbles, but these specimens are hard and have stayed more intact. Amorphous silica has replaced the organic tissue in the wood. Amorphous silica is what makes up chert; chert may form when a whole bed of microscopic silica-shelled organisms recrystallize into amorphous silica. We will see some of these silica-shelled organisms in Lab 8.

D. Sample L22: Pyrite Replacement of Shells

Sample L22 is very fragile. Please do not handle it or touch it.



Notice the gold-coloured material that glitters in L22. This is pyrite (FeS2), the sulphide mineral commonly known as “fool’s gold” for its gold-like appearance. The original calcite or aragonite carbonate shells of these organisms have dissolved and been replaced by pyrite. Pyrite forms in very oxygen-poor conditions.


Questions e-g

e. Give a full sedimentary description of this rock as you learned in Lab 1. NOTE: This rock fizzes vigorously in contact with acid, but do not conduct an acid test yourself.

f. Name one sedimentary environment where you might find a rock like this.

g. What common name would you give to these fossils, based on modern animals they resemble?


E. Sample GCS: Crinoids in Carbonate

Sample GCS can be picked up but please handle it with care.



Sample GCS is similar to a specimen presented in Lab 1.


Questions h-i

h. Determine which parts are rock and which parts are fossil. How did you distinguish between the two?

i. Both the rock and the fossils will fizz with acid. Describe and name this sedimentary rock.


Examine the pinkish fossil fragments. Notice that some are fine-grained. These are ones which are still composed of the fine-grained carbonate originally formed by this organism for its exoskeleton (the original material). Also look for larger pieces where you can see the bright clean faces of larger calcite crystals, which indicate that the fine-grained original material has recrystallized to larger calcite grains.


Question j

j. Based on the nature of the fossils in the pyrite sample (L22 previously) and this sample, which do you think was formed in a higher energy environment? Explain your answer.


F. Sample J1: Graptolites

Sample J1 is very fragile. Please do not handle it or touch it.

If you do not have access to Sample J1, examine the GIGAmacro images below to answer the questions. Note that the first image shows graptolite fossils that have been removed from the surrounding rock. Use these to help you pick out the graptolites in the second image.



Questions k-o

k. Is the rock of Sample J1 fissile? If you don’t have access to J1, answer this question by referring to the second GIGAmacro image. Note the edges of that sample.

l. Describe this sedimentary rock. (Indicate whether you are describing J1 or the second GIGAmacro image.)

m. What type of depositional environment did this rock likely form in? (Note the grain size.)

n. Use two or three common words to describe an individual fossil.

o. Is the preservation complete and unaltered? Explain your answer.


G. Sample F32: Assorted Plant Fossils

Sample F32 is very fragile. Please do not handle it or touch it.

A variety of plant types are preserved in this sample, including wood fragments.



Questions p-r

p. Name this clastic sedimentary rock. You may need to use a hand lens to observe the clast size, sorting and rounding. If you don’t have access to Sample F32, examine the last slide in the slide deck.

q. Is this considered high, moderate or low maturity for a clastic rock?

r. Explain how you might determine whether this sample formed in a terrestrial/aquatic/marine environment, and the energy (low, high) of that environment.




Laboratory Manual for Earth History Copyright © by kpanchuk. All Rights Reserved.

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