Isn't sandstone dated with index fossils ? If not, what dating method is used on this type of strata ?
The strata are dated by looking at the next oldest & youngest igneous rocks in the geologic column above & below the strata to be dated. Say we want to date "C", & it turns out that at the bottom of "B" & the top of "D" contained datable igneous rocks:
Strata A Strata B Igneous rock dates to 100 mya Strata C Strata D Igneous rock dates to 110 mya Strata E
Then "C" must be 100 to 110 mya. If around the world a particularly abundant fossil consistently dates in this age bracket & never anywhere else, then we can reasonably assume any strata containing that fossil is 100-110 mya.
Edited by mark24, : No reason given.
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