The phrase "ancient seaway" is correct and usable in written English.
It can be used when referring to a historical body of water that existed in the past, often in geological or paleontological contexts.
Example: "The ancient seaway that once connected the Atlantic and Pacific Oceans played a crucial role in the distribution of marine life."
Alternatives: "prehistoric waterway" or "historic marine passage".
Reef organisms flourished in the ancient seaway, laying the foundations for today's pan-tropical coral reef communities.
This ancient seaway was later to extend farther westward to Gibraltar as rifting between Laurasia and Gondwana began in the Late Triassic.
No geological evidence for a mid-peninsular seaway ∼1 Ma exists [24], but geological evidence (albeit controversial) suggests the existence of a more ancient seaway.
Our comparative analyses of biogeographic patterns amongst Rhizophora taxa worldwide support the hypothesis that ancient dispersals along the Tethys Seaway and subsequent vicariant events that divided the IWP and AEP lineages resulted in the major disjunctions.
The seaway divided North America into two halves: an eastern portion dominated by the already ancient Appalachian Mountains and a western part composed primarily of the still growing Sevier Mountains; formed from shallow thrust faulting caused by the Sevier orogeny.
The ancient depositional environment of the region around what is now Bryce Canyon National Park varied from the warm shallow sea (called the Cretaceous Seaway) in which the Dakota Sandstone and the Tropic Shale were deposited to the cool streams and lakes that contributed sediment to the colorful Claron Formation that dominates the park's amphitheaters.
The St . Lawrence Riverand Seaway.
The seaway became operational in April 1959.
Others, like Seaway Trail Scenic Byway, were unfamiliar.
The architecture and morphodynamics of modern and ancient tidal straits and in particular the deposits of strait-margin zones, have been significantly understudied compared to other marginal marine settings, even though many reservoirs in the North Sea and the Norwegian Continental Shelf are developed in narrow grabens or seaways.
