Section 2 Sedimentary Rocks

Abstract

Sedimentary rocks cover approximately 75% of the world’s surface comprising 20 Units and 13 Variants ordered in five Groups and three Subgroups. The Groups are: K – Carbonates are rocks formed of the carbonates of calcium, magnesium, and/or iron (Figs. 17 to 22). H – Saline and phosphatic rocks are composed of halite or any soluble salt – evaporites (Fig. 23). S – Detrital rocks also termed clastic are rocks which were derived from fragments of pre-existing rocks (Figs. 24 to 26). W – Interbedded sequences are beds lying between or alternating with others of different character (Figs. 27 to 29). D – Duricrusts are indurated horizontal layers of silica, alumina and iron oxide in varying proportions occurring as resistant caprocks or near the surface in semi-arid and tropical wet-dry climates.