Earliest Jurassic U-Pb ages from carbonate deposits in the Navajo Sandstone, southeastern Utah, USA

Judith Totman Parrish,E Troy Rasbury,Marjorie A Chan,Stephen T Hasiotis

doi:10.1130/g46338.1

Judith Totman Parrish, E Troy Rasbury + Show 2 more

Open Access

https://doi.org/10.1130/g46338.1

Copy DOI

Abstract

Abstract New uranium-lead (U-Pb) analyses of carbonate deposits in the Navajo Sandstone in southeastern Utah (USA) yielded dates of 200.5 ± 1.5 Ma (earliest Jurassic, Hettangian Age) and 195.0 ± 7.7 Ma (Early Jurassic, Sinemurian Age). These radioisotopic ages—the first reported from the Navajo erg and the oldest ages reported for this formation—are critical for understanding Colorado Plateau stratigraphy because they demonstrate that initial Navajo Sandstone deposition began just after the Triassic and that the base of the unit is strongly time-transgressive by at least 5.5 m.y.

Highlights

The Navajo Sandstone in southeastern Utah (United States) represents the largest erg in Earth history (e.g., Blakey et al, 1988), cropping out on much of the Colorado Plateau (Fig. 1)
The Navajo Sandstone contains carbonate deposits laid down in lakes and springs (Parrish et al, 2017) from which we report the first radioisotopic ages, acquired by U-Pb dating
The sampled limestone at Rocky Tops lies 65 m above the base of the Navajo Sandstone (Fig. DR1B), and at Horsethief Road, ∼90 m above the base of the Navajo Sandstone

Summary

Introduction

The Navajo Sandstone in southeastern Utah (United States) represents the largest erg in Earth history (e.g., Blakey et al, 1988), cropping out on much of the Colorado Plateau (Fig. 1). Poorly preserved, and/ or not age diagnostic. Determining the age of the Navajo Sandstone has, been challenging. The Navajo Sandstone contains carbonate deposits laid down in lakes and springs (Parrish et al, 2017) from which we report the first radioisotopic ages, acquired by U-Pb dating. The dates reported here set the stage for future work on the development of the Navajo erg and provide a framework for understanding mechanisms of the evolution of the basin in the Jurassic Period. PREVIOUS WORK ON THE AGE OF THE NAVAJO SANDSTONE

Methods

Results

Discussion

Conclusion