Paper No. 11
Presentation Time: 11:00 AM
INCISION AND SALT DEFORMATION ALONG THE INCISING COLORADO RIVER AND ITS TRIBUTARIES NORTH OF MOAB, UTAH
Southeastern Utah’s famous salt-tectonic features, arising from deposits of the ancient Paradox Basin, are generally assumed to be reactivated by unloading attendant with incision of the Colorado River system. Yet, such Quaternary deformation is speculative in most cases and unquantified. We use luminescence-dated terrace deposits, longitudinal profile analysis, and terrain metrics to quantitatively assess recent salt deformation and regional incision upstream of Moab, Utah. Our chronostratigraphy of three correlative Colorado River terraces <70 ka in age reveals both highly localized collapse in the Cache Valley graben and ~15 m of broader subsidence across Professor Valley, perhaps related to diapirism. This deformation is superimposed upon the most rapid incision yet measured in the Colorado Plateau. High rates here are consistent with a bull’s-eye pattern of regional incision related to flexural rebound in the central plateau, yet also may reflect recent or transient increases in rate. Concavity and knickpoint distributions in tributary profiles indicate that salt tectonism produces distinct surficial expressions. For example, the Quaternary Onion Creek diapir is associated with knickpoints and low stream concavity extending downstream of the uplifting salt body, whereas in Castle Valley high concavity and major knickpoints are found only above the salt-cored graben, strongly suggesting active subsidence. Overall, measurements confirm active and varied salt tectonism concurrent with rapid erosional unloading, with signatures of subsidence and uplift potentially applicable to other study areas.