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107-20 Closed basin marginal paleo wetland sediments from the hyper-arid Salar de Atacama Basin, Chile

Session: Sedimentary Geology Division/SEPM Student Research Poster Competition: Dynamics of Stratigraphy and Sedimentation

Poster Booth No.: 163

Presenting Author:

Reagan Pennington

Authors:

Pennington, Reagan¹, Butler, Kristina², McCaffrey, Owen³, Ibarra, Daniel⁴, Munk, LeeAnn⁵, Boutt, David⁶

(1) Sustainable Earth Systems Science, University of Texas at Dallas, Richardson, TX, USA, (2) Sustainable Earth Systems Science, University of Texas at Dallas, Richardson, TX, USA, (3) Sustainable Earth Systems Science, University of Texas at Dallas, Richardson, TX, USA, (4) Department of Earth, Environmental and Planetary Sciences, Brown University, Providence, RI, USA, (5) Department of Geosciences, University of Alaska Fairbanks, Fairbanks, AK, USA; Geophysical Institute, University of Alaska Fairbanks, Fairbanks, AK, USA, (6) Department of Geosciences, University of Massachusetts Amherst, Amherst, MA, USA,

Abstract:

The Salar de Atacama (SdA), Chile is a hyper-arid closed basin that contains about 60% of the global lithium resources. Sediment cores from the marginal groundwater inflow area at SdA, the “Transition Zone”, are dominated by secondary carbonate phases, which confound reconstructions of past climate and hydrogeochemical conditions key to evaluating lithium brine generation. We evaluate a 120-meter sediment core from the margin of SdA using micropaleontology, sedimentary petrography and x-ray diffraction to generate a mineralogical, sedimentological, and paleo hydrogeochemical characterization. The sediment core records a ~1 Myr (ash zircon U-Pb ages 1.7 ± 0.03 and 2.27 ± 0.02 Ma) record of wetland sedimentation at the margin of the basin. We describe 6 sedimentary facies (diatomaceous mudstone, laminated carbonate mudstone, peloidal mudstone-wackestone, peloidal/oncoidal packstone-grainstone, volcanic ash, poorly sorted silty sandstone) corresponding to carbonate-dominated groundwater discharge (lagoon, spring, seeps) and alluvial fan depositional environments. These findings indicate Pleistocene hydrogeochemical conditions were less evolved along chemical divide pathways as compared to the present-day margin of SdA where gypsum and halite minerals are actively forming at groundwater inflow zones. We evaluated 9 diatomite intervals by scanning electron microscopy and found 33 diatom species that vary in preservation quality and diatom species variety with time indicating changes in hydrogeochemical conditions (e.g. water pH, salinity, CO₂ levels, air temperature). Pleistocene climate and hydrogeochemical conditions that differ from present day conditions have implications for SdA solute mass balance models and lithium brine formation timescales.

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

doi: 10.1130/abs/2025AM-9941

Closed basin marginal paleo wetland sediments from the hyper-arid Salar de Atacama Basin, Chile

Description

Session Format: Poster

Presentation Date: 10/20/2025

Presentation Room: HBGCC, Hall 1

Poster Booth No.: 163

Author Availability: 9:00–11:00 a.m.

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