Question

how old is the sedimentary rock in the picture below?
242 - 250 million years
269 - 279 my

242 my but < 279 my

260 my
30 my

242 my but < 269 my

250 my but < 279 my

Explanation:

Step1: Determine the age range of the igneous rock

The igneous rock has an age of \(274\pm5\) my. So the minimum age is \(274 - 5=269\) my and the maximum age is \(274 + 5 = 279\) my.

Step2: Determine the age range of the extrusive sill

The extrusive sill has an age of \(246\pm4\) my. So the minimum age is \(246- 4=242\) my and the maximum age is \(246 + 4=250\) my.

Step3: Apply the principle of cross - cutting relationships

The sedimentary rock is older than the extrusive sill (because the sill intrudes into the sedimentary rock in a way that the sedimentary rock must have been there first) and younger than the igneous rock (since there is an erosion surface separating them, but the sedimentary rock is above the igneous rock in the stratigraphic column, and considering the geological processes). So the age of the sedimentary rock is \(>242\) my (younger than the minimum age of the intruding sill's minimum age range) and \(<279\) my (older than the maximum age of the igneous rock's maximum age range)

Answer:

\(>242\) my but \(<279\) my