Red beds is a term referred to sediments or sedimentary rocks composed primarily of sandstone, siltstone, or shale that are predominantly red in color due to the presence of iron oxides. These sedimentary rocks are deposited in hot arid climates under oxidizing conditions. The red color in primary red beds derives from the dehydration of goethite to hematite, the former being unstable at high temperature and in absence of water. Red beds are common in the Proterozoic and Phanerozoic and mark particularly oxidizing periods such as during the Permian and Triassic. Their absence in sedimentary sequences older than 2.65 Ga is often interpreted as an evidence of a reduced atmosphere during the Archean.