Name Section EXERCISE 5 Date Constructing a Columnar Section from a Geologic Cro
ID: 290789 • Letter: N
Question
Name Section EXERCISE 5 Date Constructing a Columnar Section from a Geologic Cross Section Figure 2.12 is a schematic geologic cross section based on the mapping of different outcrops from several locali- ties in a geographic area covering about 10 square miles. Formations shown by the same color and symbols are the same age. Study the cross section and complete the work called for in questions I and 2 1. Construct a columnar section from this cross adjacent geologic cross section. Igneous rock masses of the same age should be listed on the same line. Remember that the oldest unit is listed at the bottom. 2. Reexamine figure 2.12. In this simplified geologic section using the numbered lines at the right of figure 2.12 to record your interpretation. Indicate the name of a rock formation (e.g., shale, granite, alluvium) or an unconformity in its appropriate position in the section as determined from the cross section, no evidence of metamorphic activity has been shown. Recall the earlier discussion of types of metamorphism, metamorphie grade, and the classification of metamorphic rocks. Had metamorphic rocks been included, indicate what types you would expect to find, and why (see pages 45-46) 10 Alluvium Surface Alluvium Baslt8 Arkose Sandstone4 Granile Geologic Cross Section Columnar Section re 2.12Explanation / Answer
The column representing the age of the rocks in increasing order is -
1. Limestone
2. Granite
3.Shale
4.Sandstone
5.Granite cross cutting dykes
6.Unconfirmity
7.Conglomerate
8.Arkose
9.Basalt
10.Aluvium
This listing is mainly made by the help of the laws of stratigraphy given by Steno where he applied the law of hortizontality which states that the rock layer deposited below another layer would have an older age as compared to the rock deposited above. He also stated the law of cross cutting relationships where the body cutting across a specific strata (like the granite and basalt dykes given in this example) is always younger than the the strata which it cuts across.
An unconfirmity is usually said to be a surface of erosion and weathering. In this example, the surface of erosion is said to be between the sandstone and conglomerate where we generally get an angular relationship between the inclination of the beds. This is said to be a typical example of angular unconfirmity.
2. We can see here that the metamorphism ( even if it is bought into action ) can be subjected by introducing the increasing temperature from the dykes. This can be an example of contact metamorphic regime where the changes in mineralogy might be due to the presence of excessive heat produced by the incoming dykes.
Related Questions
Navigate
Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.