Tertiary volcanics T1 14 P5 A 15 Tr1 Middle Jurassic J2 16 Tr2 Lower Jurassic J1

Question

Tertiary volcanics T1 14 P5 A 15 Tr1 Middle Jurassic J2 16 Tr2 Lower Jurassic J1 JI 16 Upper Triassic Tr2 10 Lower Triassic Tri T1 19 Tr1 Upper Permian P3 Middle Permian P2 13 19 P2 A Lower Permian P1 21 15 P1 Upper Pennsylvanian Pe2 14 Pe2 Lower Pennsylvanian Pe1 Scale 1:62,500 1 mi Cross section A A The above is a geologic map showing a cross section of the line A-A'. You're looking at the top or map view in the large image, and what is close to the side view in the cross-section. On the right is the key, or legend, which identifies ages of each rock by color and symbol (e.g. Pe1 is the name, and yellow- green the color). Use the above to answer the following questions 1) What are the oldest and youngest units on this map, according to the key? (Hint-geologic map keys always arrange units in a certain age order-think law of superposition) 2) Notice the map has dip and strike marked on the layers. Which unit on the map do most of the layers appear to be dipping towards? Where are the youngest layers on the map located? Where are the oldest? What geologic structure appears to be at unit J2 on the geologic map (excluding the faults and 3) 4) T1)? 5) What geologic structure appears to be in the lower right-hand corner of the map?

Explanation / Answer

1) As per the geology’s law of superposition, in an undisturbed succession of strata the older formation always lies below the younger formation. Using this analogy we can say that Lower Pennsylvanian formation i.e. Pe1 is the oldest while the Tertiary volcanics i.e. the T1 is the youngest.

2) If we’ll see the map we’ll find that apart from the lower right corner’s layer all the layers are dipping towards the formation J2.

3) The youngest layer that is T1 is located at the center and is shown by red colour while the oldest layer that is Pe1 is located at the right corner and is shown by parrot colour.

4) In order to know about the geologic structure that is present at unit J2, we have to look for the dip of beds lying right and left to J2. If we see the dips of bed lying right and left we’ll find out that all the beds are dipping towards J2 and hence J2 is forming a depression therefore the geologic structure at J2 would be a valley.

5) In order to know about the geologic structure that is present at on right corner we have to look for the dip of beds lying right and left to the right corner. If we see the dips of bed lying right and left we’ll find out that all the beds are dipping away from right corner and hence we can expect a high elevation point lying out there and therefore the geologic structure present at the right corners would be a mountain.

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