Pressure gradier differential stres Assigned Chapter Questions 3. To what extent
ID: 117069 • Letter: P
Question
Pressure gradier differential stres Assigned Chapter Questions 3. To what extent would a composite volcano (see chapter 4) be subject neme to the three principles described in this chapter? Virtue 4. Suppose a sequence of sedimentary rock layers was tilted into a how vertical position by tectonic forces. How might you determine (a) graph which end was originally up and (b) the relative ages of the layers? under 5. Note that in table 8.2, the epochs are given only for the Cenozoic Era www (as is commonly done in geology textbooks). Why are the epochs for Ft the Mesozoic and Paleozoic considered less important and not given? and o sectio 6. Why would you not be able to use the principle of superposition to determine the age of a sill (defined in chapter 3)? 7. Using information from box 8.4, calculate the age of a feldspar. At ww present, there are 1.2 million atoms of 40K. The amount of 40Ar in the Talk mineral indicates that originally, there were 1.9 million 4°K atoms in logic the rock. Use a half-life of 1.3 billion years. (Hint: The answer is 862 geolo inclu scient million years.) Exploring Web Resources Radio a very has be www.ucmp.berkeley.edu/exhibits/index.php Online exhibits at UCMP University of California Museum of Paleontol. gy virtual exhibit. Click on "Tour of Geologic Time." addres with tExplanation / Answer
4.a) To determine the youngest and the oldest layer, we need to find the orientation of the sedimentary structures in it, like the cross beddings. In a way up sequence, the cross beds shows that i) the lower slopes
of the subaqueous dunes are often gently curved
upwards; ii) as a new dune advances, it truncates
(cuts off) the top of the previous one.
So we can determine which is way up for the sedimentary sequence.
b) To determine the relative ages, we can find the
i)ages to which the fossil belongs and study their succession.
ii)Find the inclusions in the layers (if any). The layer containing the inclusion will be younger than the inclusions.
iii) Radiometric dating processes are also used to find the relative age.
6.
A sill is an igneous intrusion into older strata.
Suppose we consider about two pieces of bread instead of rock layers. According to the law of superposition: the top piece of bread was was laid down after the first piece of bread.
Now, if you wanted to turn these two pieces of bread into a sandwich, you'd have to lift up the top piece of bread, put all of your fillings inside (e.g. cheese, tomatoes), and then put the second piece of bread on top. The sandwich pieces will have to be laid down according to the law of superposition with the upper layers deposited after the lower layers.
But what if didn't want to lift up the top piece of bread? It would be hard to squeeze another piece of bread or cheese between the cracks, wouldn't it? But, what if you were going to put a liquid like mustard (i.e. hot magma!) between the cracks...that's much easier? You could actually deposit a layer of mustard or hot magma in this case between the layers that have already been deposited without moving them.
For this reason, when there is a sill between layers you don't know if it was deposited in order or if it flowed into the cracks between the layers at a later date.