we ca revealed-not even in the Grand Canyon. And at any one point in find eviden
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we ca revealed-not even in the Grand Canyon. And at any one point in find evidence of all of the environments listed above-plus the deep marine an oceanic island settings. To work out a history for the entire planet, we first the records of local areas and combine them into regional and largerscale This requires just about all of the skills you've learned during this course. interpreting ancient environments and processes from the rocks they produ deciphering the sequence of events and how long ago they occurred. Exer introduces you to the kind of reasoning used in combining information from different areas into a regional picture stories from two EXERCISE 17.8 Lithologic Correlation Name: Course: Section Date: Five years ago, geologists determined the relative ages of rocks in two parts of the midcontinent, but the sequences were not the same (see the figure on the facing page). Unfortunately, similar rocks appear at several places in each section, making it difficult to know exactly which limestone, for example, in the western section correlates with a particular limestone in the east It is better to compare sequences of units based on similar sequences of depositional environments rather than similarities in e rock units Suggest correlations between layers of the two sequences by connecting the tops and bottoms of layers in the western section to those you believe are their matching layers in the eastern section. As in the real world, there may be more than one hypothesis, so explain your choice(s) and how you might further test them Do you think the environments indicated by the sedimentary rocks are the same in both the east and the west? Was deposition continuous (conformable) in both areas? Explain why or why not. (continued) O CHAPTER 17INTERPRETING GEOLOGIC HISTORYExplanation / Answer
a) it is possible to have a matching sequence in both section. because the formation of rocks.
b) yes , the depostiona is conformable. as you can see the depositon is occurred without any pause or any igneous intrusion. we can say that the deposition is limited to the sedimentary formation.till the 17th layer, the depostiond is same but after that the environmental variation occurs and deposition changes. if you observed, the western section is showing limestone dominance after 17th layer, and in Eastern section the conglomerate is dominance. both these rocks have very different formation process like limestone form in marine shallow water zone but conglomerate form in fluvial or stream environment or because of marine strong currents. now from the environment of deposition we can deduce the area of deposition as follows,
the limestone dominant in western part is indicating that area is marine and shallow also it shows marine organisms.
conglomerate shows that the strong water current in the ocean transported thet large size sediments from ocean to land.
c) according to the additional information provided, it is saying that in limestone we got trilobites hence it is now easy to correlate. now layer 14 is having the limestone containing the trilobites which is correlated with layer B and then go on upward one by one. sometime you will find that One layer is present at left lithology but not in another, well it is local condition prevails over there thats why sometime shale is formed at one place but not at another.
d) the index fossils indicate the specific age of that layer and also it helps to correlate the lithology from all over the world. for example the gondwanaland, the presence of dinasaur in that time are covered in that age of rock.( this is example which don't have any relation to the above asked question.)
marine organisms are best fossils which are easily recognisable and easy to interpret it.
In the above question, both section shows one identical
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