How do shallow estuary water create unique habitats for organism living here and why

Estuaries harbor unique plant and animal communities because their waters are brackish—a mixture of fresh water draining from the land and salty seawater. Estuaries are some of the most productive ecosystems in the world. ... Estuarine habitats are typically found where rivers meet the sea.

i think the miocene epoch spans the time from 23 million to 12 million years ago.

true, i don't really know what you're asking but from the info you provided im guessing the answer is true.