Chapter 8 Flashcards
A granitic rock contains inclusions (xenoliths) of basalt. What can you say about the relative ages of the granite and the basalt?
Xenoliths of basalt within a granite must be older than the granite according to the principle of inclusions.
Explain the differences between:
a disconformity and a paraconformity
a nonconformity and an angular unconformity
At both disconformities and paraconformities the beds above and below are parallel, but at a disconformity there is clear evidence of an erosion surface (the lower layers have been eroded).
A nonconformity is a boundary between sedimentary rocks above and non-sedimentary rocks below while an angular unconformity is a boundary between sedimentary rocks above and tilted and eroded and sedimentary layers below.
What are the features of a useful index fossil?
A useful index fossil must have survived for a relatively short period (e.g., around a million years), and also should have a wide distribution so that it can be used to correlate rocks from different regions.
We can’t use magnetic chronology to date anything younger than 780,000 years. Why not?
The last magnetic reversal was 780,000 years ago, so all rock formed since that time is normally magnetized and it isn’t possible to distinguish older rock from younger rock within that time period using magnetic data.
How did William Smith apply the principle of faunal succession to determine the relative ages of the sedimentary rocks of England and Wales?
William Smith was familiar with the different diagnostic fossils of the rocks of England and Wales and was able to use them to identify rocks of different ages.
What are the names of the last age (or stage) of the Cretaceous and the first age of the Paleogene?
The last age of the Cretaceous is the Maastrichtian (70.6 to 65.5 Ma) and the first age of the Paleogene is the Danian (65.5 to 61.7 Ma).
