Inland sea (geology) in the context of Cretaceous period

The Cretaceous (IPA: /krɪˈteɪʃəs/ krih-TAY-shəss) is a geologic period that lasted from about 143.1 to 66 Ma (million years ago). It is the third and final period of the Mesozoic Era, as well as the longest. At around 77.1 million years, it is the ninth and longest geological period of the entire Phanerozoic. The name is derived from the Latin creta, 'chalk', which is abundant in the latter half of the period. It is usually abbreviated K, for its German translation Kreide.

The Cretaceous was a period with a relatively warm climate, resulting in high eustatic sea levels that created numerous shallow inland seas. These oceans and seas were populated with now-extinct marine reptiles, ammonites, and rudists, while dinosaurs continued to dominate on land. The world was largely ice-free, although there is some evidence of brief periods of glaciation during the cooler first half, and forests extended to the poles.

Khor Al Adaid, (Arabic: خور العديد; also spelled Khawr Al Udayd and Khor Al-‘Udeid) is a settlement and inlet of the Persian Gulf in Al Wakrah Municipality in southeast Qatar, on the border with Saudi Arabia. Approximately 78 kilometres (48 mi) south of the capital Doha, it is also known to local English speakers as the "Inland Sea". It formerly accommodated a small town and served as the center of a long-running territorial dispute between Sheikh Jassim bin Mohammed Al Thani and Sheikh Zayed bin Khalifa Al Nahyan. At the present, it is designated as a major tourist destination for Qatar.

Khor Al Adaid was officially designated as a nature reserve by the Qatari government in 2007. Qatar has proposed the site's inclusion on the UNESCO World Heritage Site list, but as of 2025, it remains on UNESCO's Tentative List.

The Western Interior Seaway (also called the Cretaceous Seaway, the Niobraran Sea, the North American Inland Sea, or the Western Interior Sea) was a large inland sea that existed roughly over the present-day Great Plains of North America, splitting the continent into two landmasses, Laramidia to the west and Appalachia to the east. The ancient sea, which existed for 34 million years from the early Late Cretaceous (100 Ma) to the earliest Paleocene (66 Ma), connected the Gulf of Mexico (then a marginal sea of the Central American Seaway) to the Arctic Ocean. At its largest extent, the seaway was 2,500 ft (760 m) deep, 600 mi (970 km) wide and over 2,000 mi (3,200 km) long.