31 Stratigraphic Studies in the Colorado Plateau

This session features stratigraphic studies that resolve the geological history of modern and ancient sediment routing systems, and their processes, within the Colorado Plateau using data from field, analytical, experimental and/or numerical modeling investigations.

Tuesday, 19 May 2026
1:30 PM - 4:00 PM
Alvarado C

Bridging the Divide: Toward a Unified Chronostratigraphic Framework for Early Cretaceous Strata in the Abajo Mountains Region, Southeast Utah

Paper number: 31-6
Program: Technical Sessions
Time: 3:02 PM – 3:22 PM

Authors

Abstract

The Cedar Mountain and Burro Canyon Formations are stratigraphically equivalent, laterally continuous components of an extensive fluvial system that routed sediment from the Sevier Mountains and Mogollon Highlands through the Cordilleran foreland basin during Early Cretaceous time. This stratigraphic package, including its presumed counterpart in New Mexico, the Jackpile Sandstone, displays a substantial west-to-east thickness change across its ~500 km-wide depositional belt— from 250+ meters along the Sevier thrust front to 50 meters or less across the forebulge crest near the Utah-Colorado boundary. In southeast Utah, these strata lie between the Late Jurassic Morrison Formation and the mid-Cretaceous Naturita (Dakota) Formation with unconformable lower and upper contacts. Establishing the nature and longevity of depositional hiatuses at these contacts is critical for documenting tectono-climatic trends during the waning stages of isolated foreland basin deposition prior to transgression of the Western Interior Seaway. Without a reliable chronostratigraphic framework, authoritative chronicling of paleoenvironmental changes has eluded researchers— complicating factors include poor outcrop exposure, scarce volcanic ash horizons, sedimentary facies heterogeneity with multiple localized internal unconformities, and disproportionately distributed biostratigraphic data.

To improve the chronostratigraphic framework and paleoclimate interpretations of these strata, we conducted systematic petrographic, geochemical, and geochronological work on eighteen rock core and forty-six outcrop samples from type-section locations near Naturita and Slick Rock (Colorado), three roadcut exposures of Jurassic-through-Cretaceous strata near Blanding (Utah), and two U.S. Environmental Protection Agency groundwater monitoring wells near White Mesa (Utah). Paleosols & pedogenic nodules within fine-grained facies were targeted specifically. Preliminary bulk clay analyses reveal variable kaolinite enrichment— an indicator of intense chemical weathering under hot, humid tropical conditions—through the section: the Morrison Formation (Brushy Basin Member) yielded roughly equal proportions of illite (~50%) and kaolinite (~50%); the Burro Canyon Formation (Yellow Cat Member) contained the greatest concentration of kaolinite (up to 100%); and the Burro Canyon Formation (main body) consisted mostly of illite and smectite. None of the results yet provide reliable stratigraphic breakouts. Two kaolinite-rich samples have been high-graded for clay oxygen and hydrogen isotope analysis for paleothermometry, and new paleontological surveys in Bug Basin (Utah) are underway to trace stratal ages and unconformities across surface exposures.

Geological Society of America Abstracts with Programs. Vol. 58, No. 4

doi: 10.1130/abs/2026RM-410725

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