The index fossils are fossils of widely organisms that would live shortly in one period. They do help the geologist in matching the rock layers. In order to be a good index fossil it should be widely distributed.Hope this helps.
The process of compression always causes a profile to become thinner index fossils.
Explanation:
When a fossil is subjected to increasing pressure over years of development of layers of earthly material over it, it automatically undergoes compression and is shrunk down to become a thinner index fossil.
Once the fossil undergoes the process of compression, it becomes extremely hard to excavate it.
These unexcavated fossils later undergo the process of mineralization and get converted into certain minerals of usually untraceable origin.
