Role of Contemporaneous Faulting During Basinal Subsidence

Abstract

Faulting contemporaneous with subsidence and deposition is known to characterize various depositional basins. For example, movement along major faults occurred during subsidence of the small but active Los Angeles, Hanna, and Ardmore basins and of large basins such as the Ouachita and Gulf Coast geosynclines. The data from these and other basins indicate that faulting is an important, if not the primary, mechanism of basinal subsidence. During subsidence of the basins studied, faulting proceeded independently of the depositional framework. Major fault movement occurred in the Los Angeles basin during the Mio-Pliocene as turbidites were deposited, in the Hanna basin during the Paleocene-Eocene as alluvial deposits formed, and in the Ardmore basin during the Pennsylvanian as shallow-marine and paralic sediments were deposited. During late Paleozoic time, contemporaneous faulting occurred in the Ouachita system as turbidites and, later, shallow-marine beds were deposited along its length. Subsidence of the Gulf Coast geosyncline is thought to have accompanied the same type of faulting which originates in the basement. There paralic and alluvial sediments overlie offshore or deep-water clay in the overall regressive se uence which formed during the Cenozoic. Another type of faulting, involving only the sedimentary basinal fill, occurred during subsidence of the Gulf Coast geosyncline. Salt and some thick shale units have been deformed by uniform flow which, in turn, apparently caused failure by faulting in the overlying paralic sediments. These sedimentary faults, which do not involve the basement directly, are thought to result from conditions analogous to those which give rise to the Recent mudlumps of the Mississippi delta or the slide-flows experienced in foundation engineering.