‘Plains-type folds’ are those folds formed in gently dipping sediments overlying a crystalline basement in cratonic areas of the world. They are the result of differential compaction of sediments over rigid basement fault blocks. Trends of the folds in the sedimentary section thus coincide with trends of basement features. Plains-type folds generally are (1) small in areal extent, (2) increase in closure downward, (3) without a corresponding depression, and (4) asymmetric and associated with faulting. The features were developed intermittently through time by differential compaction of the sediments over an inherent structural pattern of uplifted fault blocks in the basement. Plains-type folds were recognized early in the twentieth century in the Midcontinent (USA) as containing petroleum. They were the object of much speculation on their origin and development and were studied intensively in the 1920s and 1930s. Most of the studies were concentrated in Kansas and Oklahoma and revolved around the relation of the structures as mapped in the sediments to the configuration of the Precambrian crystalline basement, relation of structure and temperature, and the effect of sediment compaction over ‘buried hills.’
Crustal architecture beneath the southern Midcontinent (USA) and controls on Mesoproterozoic iron-oxide mineralization from 3D geophysical models