96-9 Megaquartz and Detrital Mica Pin Down the Origin of Lacustrine Dolostone and Gypsum Associated with the Moab, Utah Salt Wall

Session: Twenty-Seven Years of Advances in Understanding Salt-Sediment Interaction: A Legacy of Katherine A. Giles

Presenting Author:

Paola Salas Rivera

Authors:

Salas Rivera, Paola¹, Igomu, Charles², Tellez, Tricia A.³, Arribas, Antonio⁴, Labrado, Amanda L.⁵, Langford, Richard P.⁶, Gannaway Dalton, Cora Evelyn⁷, Brunner, Benjamin⁸

(1) Department of Earth, Environmental and Resource Sciences, The University of Texas at El Paso, El Paso, TX, USA, (2) Department of Earth, Environmental and Resource Sciences, The University of Texas at El Paso, el paso, Texas, USA, (3) Institute of Arctic and Alpine Research, University of Colorado Boulder, Boulder, Colorado, USA, (4) Department of Earth, Environmental and Resource Sciences, The University of Texas at El Paso, El Paso, Texas, USA, (5) Applied Physics Laboratory, University of Washington, Seattle, WA, USA, (6) Department of Earth, Environmental and Resource Sciences, The University of Texas at El Paso, El Paso, TX, USA, (7) Geosciences, Utah State University, PRICE, UT, USA, (8) Department of Earth, Environmental and Resource Sciences, The University of Texas at El Paso, El Paso, TX, USA,

Abstract:

At the Moab Valley salt wall, laminated dolostones interfinger with fluvial siliciclastic sediments of the Triassic Chinle Formation and are stacked atop gypsic caprock of the Pennsylvanian Paradox Formation. This stratigraphic relationship, along with distinct petrographic fabrics, suggests a Triassic lacustrine origin of primary dolostones at the diapir margin. Dissolution of samples yielded megaquartz and detrital mica grains from laminated, disturbed, and brecciated dolostone samples, as well as from some, but not all, gypsum samples collected near the dolostones. Megaquartz with boxwork fabric, interpreted as dolomite casts, is characteristic of sabkha environments. We propose that a hypersaline lake formed at the exposed Moab Valley salt wall under arid conditions. This is supported by the absence of macroscopic fossils and pollen, and is consistent with regional aridification trends in the Late Triassic. Whereas limestone was deposited in correlative lakes, i.e., the Owl Rock Member of the Chinle Formation, dolomite formation at the Moab Valley site was driven by elevated Mg:Ca ratios due to co-precipitation with gypsum. Detrital mica found in both dolostone and gypsum indicates some gypsum at the site may be Triassic, rather than exclusively Pennsylvanian in age. Dissolution of Mg-bearing minerals in the salt wall could have contributed to elevated Mg:Ca ratios and thus the local carbonate chemistry, differentiating it from other contemporaneous lacustrine carbonate systems. Our model for primary dolostone formation in a lacustrine setting at the Moab Valley salt wall may be applicable to other locations where dolostones are found proximal to passive diapirs.

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-4418

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