T224 The Geology and Environmental Impacts of Lithium Resources in North America and other Globally Significant Deposits I

Wednesday, 12 October 2022
8:00 AM - 12:00 PM
603

~200 KYR PALEOCLIMATE RECORD FROM SALAR DE ATACAMA BASIN-MARGIN CARBONATES: IMPLICATIONS FOR LITHIUM ACCUMULATION IN THE WORLD’S LARGEST PRODUCING LITHIUM BRINE DEPOSIT

Paper number: T224-4
Program: Technical Sessions
Time: 8:40 AM – 8:55 AM

Authors

Abstract

Basin-flanking carbonates record climatic conditions during halite and lithium brine accumulation in the world’s largest producing lithium brine resource, the Salar de Atacama (SdA) basin, Chile. Previous work has shown that Li accumulation in SdA balances over a ~2 Myr timescale based on present-day magnitude of solute fluxes. Published stratigraphic reconstructions from deep cores in the SdA halite nucleus suggest there may have been wetter/drier periods during the Pleistocene-present. Conceivably, such changes in the basin’s climate history would impact Li mass balance timescales. We present 𝛿18O, 𝛿13C, and ∆47 carbonate isotope compositions spanning ~200 ka of deposition at the basin margin of the Salar de Atacama, Chile. To determine age and depositional context to our sample suite, we correlate 12 drill cores along ~5-7 km transects starting in the sulfate-carbonate dominated transition zone and ending in the halite nucleus using 8 U-Th carbonate ages (~27-312 ka) and 2 40Ar/39Ar sanidine ages (~3-5.5 Ma). These were used to develop a preliminary age-depth model to estimate sedimentation rates and approximate sample ages. Depositional settings across these transects during ~5.5 Ma-present include lagoonal carbonates and muds, ephemeral saline lakes/ponds, saline pans and mudflats, with rare sheet sands and perennial lakes, and interbedded ash fall tuffs and ignimbrites. SdA basin mid-Pleistocene to present day lagoonal, ephemeral pond, and mudflat carbonates give generally high isotopic values and cool formation water temperatures: 𝛿13C values range from -3 to 12‰ (VPDB), 𝛿18O ranges from -8 to 12‰ (VPDB), and preliminary ∆47 values from 0.633-0.680‰ (I-CDES) indicate formation temperatures of 0 to 12°C. As expected for evaporation-dominated closed basin settings, carbonates show positive covariation (R2 = 0.4) between 𝛿18O and 𝛿13C. We observe similar degree of variation in the isotopic values of the modern carbonate samples (-8 to 7‰ 𝛿18O, -3 to 12‰ 𝛿13C) as compared to the Pleistocene subsurface samples (-5 to 12‰ 𝛿18O, 1 to 12‰ 𝛿13C), suggesting evaporative conditions and formation water composition and temperature may have been similar throughout the middle-late Pleistocene as it is today.

Geological Society of America Abstracts with Programs. Vol. 54, No. 6

doi: 10.1130/abs/2022AM-381688

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