192-3 Zebra Limestone: A striped Chameleon

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

Poster Booth No.: 152

Presenting Author:

Kathleen Olivas

Authors:

Olivas, Kathleen K¹, Navarrette, Rebecca², Arribas, Antonio³, Bernasconi, Stefano M⁴, Labrado, Amanda L⁵, Langford, Rip⁶, Gannaway Dalton, Evey⁷, Brunner, Benjamin⁸

(1) Departments of Earth, Environmental and Resource sciences, University of Texas at El Paso, El Paso, Texas, USA, (2) Department of Earth, Enviormental and Resources science, University of Texas at El Paso, El Paso, Texas, USA, (3) University of Texas at El Paso, El Paso, USA, (4) Geological Institute, ETH Zurich, Zurich, Switzerland, (5) Applied Physics Laboratory, University of Washington, Seattle, Washington, USA, (6) Univeristy of Texas at El Paso, El Paso, Texas, USA, (7) Geoscience, Utah state University, Price, Utah, USA, (8) Departments of Earth, Environmental and Resource Science, University of Texas at El Paso, El Paso, Texas, USA,

Abstract:

Zebra rocks are characterized by alternating, millimeter to centimeter thick, light and dark colored bands of crystals. They are often associated with carbonate-hosted lead-zinc ore deposits (Mississippi Valley type, MVT) and found in hydrothermal dolomite-hosted hydrocarbon reservoirs.  Outcrops of Zebra limestone (>90% calcite) have been discovered in the Paradox Basin in southwestern Colorado at the Gypsum Valley salt wall. Understanding their formation can give insights into episodic fluid flow at salt diapir margins and the processes driving Zebra rock development.  At Gypsum Valley, we observe a range of fabrics within the Zebra limestones, from regular banding to chaotic distributions of bands and vugs with sedimentary infill and a subsequent cementation of cavities with dolomite. Curiously, there are two distinct and seemingly inverse banding patterns within the outcropping Zebra limestones. In the literature, dark Zebra rock bands are formed by finely crystalline dolomite, whereas light bands are formed by coarse crystalline dolomite. Our findings for the regular-banded Zebra limestones at Gypsum Valley indicate that they exhibit a different mineralogy and an inverse color banding pattern, with coarse crystalline dark calcite bands and finely crystalline light calcite bands. However, we also find Zebras bands more consistent with the literature, where finer crystalline bands are dark and coarser crystalline bands are light.  What differentiates the these from the regular banded Zebra limestones is that the latter display much coarser crystals approaching 1 cm in size.  Integrating field observations, structural, petrographic, and geochemical analyses we conclude that Zebra limestones at Gypsum Valley formed through the replacement of either petroliferous, microcrystalline lime- and/or dolostone that was originally part of the layered evaporite sequence of the Pennsylvanian Paradox Formation and has since been incorporated into the caprock of the Gypsum Valley salt wall. We hypothesize that the reversible conversion of anhydrite to gypsum in the cap of the diapir resulted in cycles of localized compression and extension in the overlaying lithologies and acted as a driver for Zebra rock formation.

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

doi: 10.1130/abs/2025AM-4819

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