| Gai-As Formation | |
|---|---|
| Stratigraphic range: Kungurian-Wordian ~ | |
| Type | Geological formation |
| Unit of | "Ecca" Group |
| Sub-units | Upper, lower |
| Underlies | Etjo Sandstone or Doros Formation |
| Overlies | Huab Formation |
| Thickness | 70 m (230 ft) |
| Lithology | |
| Primary | Sandstone, siltstone, mudstone |
| Other | Tuff, chert, halite |
| Location | |
| Location | Damaraland |
| Coordinates | 20°48′S 14°06′E / 20.8°S 14.1°E |
| Approximate paleocoordinates | 49°06′S 22°36′W / 49.1°S 22.6°W |
| Region | Kunene & Erongo Regions |
| Country |  Namibia |
| Extent | Huab Basin |
| Type section | |
| Named for | Gai-As |
| Named by | Horsthemke 1992 (original) Stanistreet & Stollhofen 1999 (redefined) |
| Location | Gai-As |
 Geologic map of Namibia with the Gai-As Formation partly cropping out in the northwestern area (orange) | |
The Gai-As Formation is an Early to Middle Permian (Kungurian to Wordian) geologic formation correlated with the Ecca Group and designated "Ecca" Group, because it does not belong to the Karoo, in the southwestern Kunene Region and northern Erongo Region of northwestern Namibia. The Gai-As Formation represents the second-oldest sedimentary unit of the Huab Basin, overlying the Huab Formation. The formation was deposited in a fluvial to lacustrine setting.
The Gai-As Formation is correlated with a series of formations in the Pelotas and Paraná Basins in southeastern Brazil, deposited in a larger basinal area, 150 million years before the break-up of Pangea. The abundance of Glossopteris and Mesosaurus fossils in the underlying Huab Formation are characteristic of the Gondwanan correlation across present-day South America, Africa, Antarctica and Australia. The Gai-As Formation has provided fossil bivalves and an indeterminate stereospondylid.