Read this: The Late Jurassic spans from 163 million to 145 million years ago. The Late Jurassic featured a massive extinction of sauropods and Ichthyosaurs due to the separation of Pangaea into Laurasia and Gondwana in an extinction known as the Jurassic-Cretaceous extinction. Sea levels rose, destroying fern prairies and creating shallows in its wake. Ichthyosaurs went extinct whereas sauropods, as a whole, did not die out in the Jurassic; in fact, some species, like the Titanosaurus, lived up to the K-T extinction. The increase in sea-levels opened up the Atlantic sea way which would continue to get larger over time. The divided world would give opportunity for the diversification of new dinosaurs.

The increase in sea levels closed up which sea?
What is the answer? (If it cannot be answered, return "unanswerable")
unanswerable