I want to know the answer to the following question:
Oxygen from what kind of fossil were used to date the Hirnantian faunal stage?
All the background I'm provided with is that "The ice age was probably not as long-lasting as once thought; study of oxygen isotopes in fossil brachiopods shows that it was probably no longer than 0.5 to 1.5 million years.". Is that enough to answer the question?
Answer: yes