Inland sea (geology)
An inland sea (also known as an epeiric sea or an epicontinental sea) is a shallow sea that covers central areas of continents during periods of high sea level that result in marine transgressions. In modern times, continents stand high, eustatic sea levels are low, and there are few inland seas, the largest being Hudson Bay. Modern examples might also include the recently (less than 10,000 years ago) reflooded Persian Gulf, and the South China Sea that presently covers the Sunda Shelf.
Modern inland seas
- The Baltic Sea is a brackish inland sea, arguably the largest body of brackish water in the world (other possibilities include the White Sea and Black Sea). The origin of the basin is not clear as there are differing views on the role of erosion and tectonics.
- Hudson Bay, including James Bay at its southern end, reaches within the North American continent from Baffin Island, Nunavut in the north to Quebec, Ontario and Manitoba in the south. The bay shares some similarities with the Gulf of Bothnia in Fennoscandia; it lies in the middle of a shield and it was the centre of an ice sheet during the Quaternary glaciations. However, the origin of both depressions is unrelated to glacier erosion.
- The Seto Inland Sea in Japan is not a true inland sea but rather a body of water separating Honshū, Shikoku, and Kyūshū, three of the four main islands of Japan.
Former epicontinental seas in Earth's history
At various times in the geologic past, inland seas have been greater in extent and more common than at present.
- During the Oligocene and Early Miocene large swathes of Patagonia were subject to a marine transgression. The transgression might have temporarily linked the Pacific and Atlantic oceans, as inferred from the findings of marine invertebrate fossils of both Atlantic and Pacific affinity in La Cascada Formation. Connection would have occurred through narrow epicontinental seaways that formed channels in a dissected topography.
- A vast inland sea, the Western Interior Seaway, extended from the Gulf of Mexico deep into present-day Canada during the Cretaceous.
- At the same time, much of the low plains of modern-day northern France and northern Germany were inundated by an inland sea, where the chalk was deposited that gave the Cretaceous Period its name.
- The Amazon, originally emptying into the Pacific, as South America rifted from Africa, found its exit blocked by the rise of the Andes about 15 million years ago. A great inland sea developed, at times draining north through what is now Venezuela before finding its present eastward outlet into the South Atlantic. Gradually this inland sea became a vast freshwater lake and wetlands where sediment flattened its profiles and the marine inhabitants adapted to life in freshwater. Over 20 species of stingray, most closely related to those found in the Pacific Ocean, can be found today in the freshwaters of the Amazon, which is also home to a freshwater dolphin. In 2005, fossilized remains of a giant crocodilian, estimated to have been 46 ft (14 m) in length, were discovered in the northern rainforest of Amazonian Peru.
- In Australia, the Eromanga Sea existed during the Cretaceous Period. It covered large swaths of the eastern half of the continent.
- Also in Australia the promise of an inland sea is often said to have been one of the prime motives of inland exploration during the 1820s and 1830s. Although this theory was championed by the explorer Charles Sturt, it enjoyed little support among the other explorers, most of whom were more inclined to believe in the existence of a Great River which discharged into the ocean in the north-west corner of the continent.
- The Lord Howe Rise that covers much of the sunken "continent" of Zealandia and the largely submerged Mascarene Plateau that includes the Granitic Group islands of the Seychelles could not be considered "inland"
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