FORELAND BASINS

FORELAND BASIN Occurs at the subduction zones and it is formed due to the collision between two continental plates. Two basins are to be formed: Primary basin develops on the subduction plate due to thrust loading. Secondary Basin is formed on the overriding plate due to back thrusting.

FORELAND MECHANISM Thinning of the subducting plates Deposition of the condensed section (May be repeated due to stops and jumps in thinning and subduction rates) Downgoing plate of the continental sediments is thrusted and sheared which leads to an inverted sequence Due to crust shortening, Isostatic pushes down on the basin as adjustments

Sequences Continental basement Margin Sediments (In Situ as well as thrusted) Oceanic Crust Accreted Sediments Uplifted oceanic crust Island arc rocks Condensed Section Flysch Molasse

Flysch & Molasse Flysch: Thick, thinly bedded, graded, poorly fossilferous marine sediments with large percentage of turbidities (typically marls, muds, and sandy shale). They are mainly deep –water sed deposited at the early stage of the basin development. Molasse: Shallow water sediments (partially marine and partially none marine (deltaic). They are thick ungraded cross-bedded sand stone, shale, and mud sediments.

Foreland Examples Most of giant oil fields in the world are located in the foreland basins such as: Arabian Gulf Central Appalachian Basin Alps Foreland Basin North Slope of Alaska South Flanks of Himalayas East Flanks of Andes