Jurassic Utah-Idaho Trough

The Utah-Idaho Trough consists of Jurassic sedimentary rocks that are exposed in a deep elongate basin located in Utah and Idaho (see map, below). These sedimentary rocks attain a thickness of more than 2000 meters in west-central Utah and thin eastward into the western part of the Colorado Plateau. Christian Bjerrum, a graduate student at the University of Copenhagen in Denmark, spent a year studying and doing field work for his Masters thesis here at NAU. In a recent collaborative project, Christian and I analyzed abundant data for Middle Jurassic strata in the western Colorado Plateau, which were previously known to be related to development of the Utah-Idaho trough.

The main elements of this project included: (1) detailed compilations of regional stratigraphic data; (2) stratigraphic correlations based on biostratigraphy and scant geochronologic data; (3) qualitative stratigraphic analyses in light of recent models for dynamic stratigraphy; (4) quantitative subsidence analysis using standard decompaction techniques; (5) numerical flexural modeling; and (6) talking and e-mailing with colleagues who kindly told us what they thought and why. We concluded that Clark Burchfiel and Terry Jordan were right all along: the Middle Jurassic Utah-Idaho trough was a retroarc foreland basin that experienced flexural subsidence in response to crustal loading in a large Jurassic fold-thrust belt to the west.

There are a couple of folks out there who disagree with our model. A competing hypothesis, recently proposed by Tim Lawton, attributes subsidence in the Utah-Idaho trough to something called "dynamic subsidence". This is the name of a new model developed by Mike Gurnis (Cal Tech) in which regional basin subsidence is caused by the geodynamic effects of initial and early subduction of an oceanic slab beneath the continent. The dynamic subsidence model is appealing, but we have some reasons to favor good old flexural subsidence produced by something you can see and touch, a mountain belt. Our paper, which was recently published in Tectonics, provides the numerical models, tectonic reconstructions, and boring discussions in which we develop our thinking on this problem.

[Utah-Id Trough]

This is a map of the U.S. western interior, showing the Utah-Idaho trough, some related tectonic elements, and stratigraphic transects analysed in our recent study.

One paper and one abstract on the Utah-Idaho Trough:

Bjerrum, C.J. and R.J. Dorsey (1995) Tectonic controls on deposition of Middle Jurassic strata in a retroarc foreland basin, Utah-Idaho Trough, western interior, USA. Tectonics, vol. 14, p. 962-978.

Bjerrum, C.J., Dorsey, R.J., and Becker, U. (1993) Onset of foreland-basin subsidence in the Middle Jurassic Utah-Idaho Trough, E Nevada and W Utah: Geological Society America Abstr. with Progr., vol. 25, p. 10.

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