The Green River lakes
Vast lakes in Wyoming and Utah lay down finely banded shale holding millions of fish, insects, birds and bats.
- When
- —
- Duration
- 5 million years
- Known to
- ± 500 thousand years
- Era
- Eocene, Cenozoic
Three large intermontane lakes fill basins between the rising Rocky Mountain ranges and persist for several million years. Their bottom waters are still and oxygen-poor, so anything sinking is buried undisturbed in paper-thin annual laminations. The result is one of the richest fossil deposits on Earth: complete fish by the million, insects with wing venation intact, birds with feathers, early bats, horses and a crocodile fauna. The same shales hold an enormous — and commercially unrealised — reserve of kerogen oil shale.