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The paradox of Lower Cretaceous gravels and the initiation of thrusting in the Sevier orogenic belt, United States Western Interior

Paul L. Heller and Chris Paola
The paradox of Lower Cretaceous gravels and the initiation of thrusting in the Sevier orogenic belt, United States Western Interior
Geological Society of America Bulletin (June 1989) 101 (6): 864-875

Abstract

Gravels of Early Cretaceous age that are widespread throughout much of the Western Interior are commonly assumed to have been deposited in a foreland basin adjacent to the Sevier thrust belt to the west. Synorogenic foreland conglomerates, however, are in most cases restricted to that part of the basin most proximal to the thrust system. In contrast, the Lower Cretaceous gravels of the Western Interior represent a widespread low-sinuosity stream system that deposited gravel more than 600 km from the closest possible site of thrusting. Although paleohydraulic calculations indicate that slopes on the order of only 1 m/km were needed to transport these gravels from the thrust belt, the results from flexural modeling indicate that even this slope could not have been sustained over great distances in a foreland basin adjacent to the Sevier belt. The gravel, therefore, reflects regional uplift to the west and may not be directly associated with thrusting.Several possible origins for widespread gravel deposition can be quantitatively tested. Of these, it is possible that the gravel resulted from thermal uplift that preceded thrusting, resulted from isostatic rebound that occurred after thrusting located much farther west had ceased, or was derived from the very earliest uplift of thrust sheets in the Sevier belt superimposed on regional doming. Our preferred model is that gravels were shed eastward from a regional thermal uplift associated with Jurassic-Cretaceous magmatism in the hinterland. Regardless of the origin, deposition of widespread gravel is associated with uplift to the west and not with regional subsidence associated with thrusting. Thus, the gravel is a harbinger of the onset of thrusting in the Sevier belt and appears to support models in which retroarc thrusting is associated with the development of the magmatic arc. On the basis of available stratigraphic evidence, the initiation of thrusting in the Sevier orogenic belt took place during or just prior to Aptian time and is recorded not by the widespread gravel deposits but rather by areally restricted gravels near the thrust front and fine-grained sediments over most of the foreland basin.


ISSN: 0016-7606
EISSN: 1943-2674
Coden: BUGMAF
Serial Title: Geological Society of America Bulletin
Serial Volume: 101
Serial Issue: 6
Title: The paradox of Lower Cretaceous gravels and the initiation of thrusting in the Sevier orogenic belt, United States Western Interior
Affiliation: Univ. Wyo., Dep. Geol. and Geophys., Laramie, WY, United States
Pages: 864-875
Published: 198906
Text Language: English
Publisher: Geological Society of America (GSA), Boulder, CO, United States
References: 104
Accession Number: 1989-048891
Categories: Structural geologySedimentary petrologyStratigraphy
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. 1 table, chart, sketch map
Secondary Affiliation: Univ. Minn. at Minneapolis, USA, United States
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2019, American Geosciences Institute.
Update Code: 1989
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