Terrigenous Shelf Systems

Terrigenous shelves include both epeiric (epicontinental) platforms and continental shelves, with a mantle of land-derived sediments, as opposed to biogenic and chemical precipitates. Epeiric platforms are broad, shallowly inundated continental areas. Modem examples such as the North Sea, Hudson Bay, and Gulf of Carpentaria are small by comparison with many of their ancient counterparts. Continental shelves are submerged continental margins, dipping very gently from the outer edge of the shore zone to a depth, generally between 300 and 800 ft (100 and 250 m), at which there is an abrupt increase in slope. If the shelf break is not well defined, the shelf is arbitrarily confined to depths shallower than 200 m (650 ft) (Bates and Jackson, 1980). Present-day shelves have a complex depositional and erosional evolution which commenced in the Mesozoic (Swift, 1969).