Question

In an undeformed and normal stratigraphic succession, a dolerite dyke was emplaced before deposition of sandstone B. The difference between the maximum ages (in Myr) of deposition of sandstone A and sandstone B is ............... 

Hint:

In stratigraphy, the principle of superposition helps determine the relative ages of rock layers. The maximum age of a layer is typically the age of the layer above it, unless other dating methods are used.

Answer 1

Correct Answer: 57

Step 1: Understanding the stratigraphy and relationships.
In a normal stratigraphic succession, the layers are deposited sequentially, and the oldest layers are at the bottom. According to the law of superposition, the dolerite dyke was emplaced before the deposition of sandstone B, which means the dolerite dyke is older than both sandstone A and B. - The age of the dolerite dyke is 75 Ma (million years ago). - The age of volcanic ash bed 1 is 132 Ma. - The age of volcanic ash bed 2 is 62 Ma.

Step 2: Analyzing the time difference.
- Sandstone A lies above the dolerite dyke and below volcanic ash bed 1. This means that the deposition of sandstone A occurred after the dolerite dyke was emplaced but before volcanic ash bed 1 was deposited. - Sandstone B lies below volcanic ash bed 2, meaning sandstone B was deposited before volcanic ash bed 2. The maximum age of deposition of sandstone A is the age of volcanic ash bed 1, which is 132 Ma, as this is the layer that it lies beneath. The maximum age of deposition of sandstone B is the age of volcanic ash bed 2, which is 62 Ma.

Step 3: Calculate the difference in ages.
The difference between the maximum ages of deposition of sandstone A and B is: \[ \text{Difference} = 132 \, \text{Ma} - 62 \, \text{Ma} = 70 \, \text{Ma} \] Thus, the difference between the maximum ages of deposition of sandstone A and sandstone B is 70 Ma.