On the Depositional Response to Thrusting and Lithospheric Flexure: Examples from the Appalachian and Rocky Mountain Basins
- P. A. Allen and
- P. Homewood
Published Online: 5 MAY 2009
Copyright © 1986 The International Association of Sedimentologists
How to Cite
Tankard, A. J. (1986) On the Depositional Response to Thrusting and Lithospheric Flexure: Examples from the Appalachian and Rocky Mountain Basins, in Foreland Basins (eds P. A. Allen and P. Homewood), Blackwell Publishing Ltd., Oxford, UK. doi: 10.1002/9781444303810.ch20
- Published Online: 5 MAY 2009
- Published Print: 22 DEC 1986
Print ISBN: 9780632017324
Online ISBN: 9781444303810
- depositional response to thrusting and lithospheric flexure - Appalachian and Rocky Mountain basins;
- Appalachian and Cordilleran foreland basins of North America - regional isostatic adjustments of lithosphere to thrust-belt loading;
- tectonic framework;
- tectono-stratigraphy of Appalachian and Cordilleran basins;
- tectonic evolution of Appalachian and Cordilleran foreland basins;
- Appalachian foreland basin;
- Middle Ordovician transition from passive margin to convergent tectonics;
- Acadian-Alleghenian transition and tectonic implications
The Appalachian and Cordilleran foreland basins of North America resulted from regional isostatic adjustments of the lithosphere to thrust-belt loading. Flexural subsidence of these basins was accompanied by upwarping along their cratonward margins; subtle irregularities of the foreland lithosphere reflect variations in composition and inherited structural fabric. It is suggested that viscoelastic relaxation of plate bending stresses during tectonically quiescent interludes resulted in overdeepening of the shale-prone basins and upwarping along the basin margin arch systems.
On a large scale these basins evolved through three distinct phases as overthrust terranes migrated across older passive margins. Initially, exotic terranes were accreted on to the attenuated passive margin ramps, loading relatively thin lithosphere, and creating the deep Taconic (Appalachian) and Columbian (Cordilleran) foreland basins. The intermediate Acadian and mid-Cretaceous episodes were more passive in style, probably because the continental margin ramps impeded overthrusting for tens of millions of years. This was a period characterized by subtle adjustments and tectonic thickening of the overthrust loads, viscoelastic relaxation of the lithosphere, overdeepening of the shale-dominated basins, and upwarping of basin-margin arch systems. Marine environments were widespread. Eventually, tectonic overthickening resulted in topographic head sufficient to drive thin thrust sheets across the hingeline, loading thick, thermally mature, and rigid continental crust. The Alleghenian and Laramide basins oscillated between underfilled and overfilled conditions. Periodic abandonment of the depositional landscape is reflected in accumulation of thick and regionally persistent coal seams.
Many of the stratigraphic patterns predicted by viscoelastic models of the lithosphere are supported by field studies. Marine inundation (overdeepening) and dark shale deposition were most common during periods of relative orogenic quiescence. ‘Shelf’ sand-ridge and carbonate shoal deposition were controlled by actively rising basin margin arches during the quiescent episodes. Renewed overthrusting (Alleghenian and Laramide) introduced a flood of river-borne sediments, but the basement arches were no longer prominent.