Depositional wedge tops: interaction between low basal friction external orogenic wedges and flexural foreland basins

Abstract

Growth structures develop mainly across depositional wedge tops where the top of the distal orogenic wedge lies below local base level within the £exural foreland basin. Documented examples indicate that optimum conditions for the development of a depositional wedge top occur when the dip of the upper surface of the outer orogenic wedge (a) is low (0^11), regardless of the taper angle (a1b), where b is the inclination of the base of the wedge. Low a angles are associated with the presence of low friction de¤ collements, usually salt.Therefore, depositional wedge tops develop most commonly on low basal friction wedges.In natural examples such as the northern Apennines, the South Central Pyrenees and the Zagros, it is shown that whereas a is consistently low, b can vary considerably (1^91), being principally controlled by £exure of the lower plate. In addition, the distribution of deformation in the wedge is complex.The applicability of the critical wedge model to low basal friction external orogenic zones is examined. Neither taper angles, nor the complex distribution of internal deformation nor the often associated forward slip of the whole wedge, can be satisfactorily explained by the established critical wedge model. As weak detachments such as salt cannot support any signi¢cant topography, it follows that low basal friction wedges cannot attain a critical state and, therefore, the critical wedge model cannot be satisfactorily applied to these external orogenic systems.This model, however, explains well the behaviour of external orogenic wedges with high basal friction. In the analysis of orogenic wedges, separate analysis of the angles a and b proves more useful than the critical taper angle a1b.

Structure and tectonic history of the foreland basins of southernmost South America

“…Data presented are integrated in a dynamical model describing the evolution of foreland basins (DeCelles and Giles, 1996;Ford, 2004) using a symptomatic approach in which sedimentary sources and depocenters migrate cratonward in response to the progressive advance of contractional deformation and tectonic load (DeCelles and Mitra, 1995;Londoño and Lorenzo, 2004). This analysis of the data allows us to challenge previous interpretations that considered the foredeep depocenter to be developed in a somewhat static location through time and helps clear up the apparent significant diachronicity in the evolution of the Austral basin when compared to the Malvinas and South Malvinas basins (e.g.…”

Anatomy of Anticlines, Piggy‐Back Basins and Growth Strata: A Case Study from the Limón Fold‐and‐Thrust Belt, Costa Rica

“…Turrini et al, 2001) and the impact of weak décollements has been discussed in the literature (e.g. Vergés et al, 1992;Costa & Vendeville, 2002;Ford, 2004). For the structural development of the Limón fold-and-thrust belt the lithology of pre-deformation strata is an important factor.…”

“…In contrast, high basal friction causes increasing underplating of weakly deformed thrusts and generates a steeper slope angle. Ford (2004) pointed out that wedges with low basal friction cannot attain a critical state and therefore the critical wedge model cannot be applied in such a case. In addition, the flexure of the lower plate influences the evolution of the wedge.…”

“…In addition, the flexure of the lower plate influences the evolution of the wedge. For the analysis of orogenic wedges a separate analysis of the slope angle α and the angle of the base of the wedge β will be more useful than the critical taper α + β (Ford, 2004).…”

“…Based on a depthconverted version of in-line d the surface has a slope angle α of 4°and the detachment angle β is 1.5°, implying a wedge taper of 5.5°. Following Ford (2004) natural wedges with low basal friction should have slope angles in the range of 0 -1°. Therefore, the slope angle of 4°observed for the offshore parts of the Limón fold-and-thrust belt points towards high basal friction.…”