Triple oxygen isotopes, aridity and uplift: a case study from the Atacama
Abstract
Oxygen isotope records are widely used to reconstruct histories of climate, topography and uplift, but their sensitivity to multiple variables often results in competing views of their interpretation. Carbonate clumped isotope paleothermometry aids interpretation of these data by providing constraints on both uplift and burial histories and the δ18O values of waters from which carbonate forms. However, even with these constraints, it can be difficult to draw definitive conclusions about climate and paleoelevation because the relationship between δ18O values of formation waters and local precipitation (e.g. influence of evaporation) is unknown. Recent work on triple oxygen isotopes (18O-17O-16O) in waters and carbonates demonstrate their sensitivity to evaporation and potential for evaluating the effects of evaporation on δ18O records. The Atacama Desert, one of the driest places in the world, is a perfect place to explore the utility of Δ17O because δ18O records are extensively used to infer its climate and uplift history but their interpretation is widely debated. Here we present triple oxygen (Δ17O) and clumped (Δ47) isotope data from nine palustrine, groundwater and soil carbonate samples from the Atacama (Barrancas Blancas region and Calama Basin) that span the last 24 Ma. Δ47 temperatures range from 8 to 49 ˚C, with the warmest temperatures from the oldest samples. Reconstructed water δ18O values range from -4 to +1 ‰ and do not show significant trends with time but overlap with or are more positive than δ18O values of Atacama meteoric waters today. Carbonate Δ17O values (-167 to -141 per meg, reference λ = 0.528, VSMOW-SLAP) do not exhibit any temporal trends. Reconstructed water Δ17O values (-59 to -12 per meg) are lower than those for the majority of global meteoric waters today and indicate that highly evaporative conditions may have existed in the Atacama for the last 24 Ma, even amidst significant uplift. This result is in contrast to interpretations based on δ18O carbonate records alone. We will need additional Δ17O data from samples with greater temporal and spatial resolution to truly evaluate the history of aridity in the Atacama, but our initial results demonstrate the promise of combining δ18O, Δ47, and Δ17O data for understanding the influence of temperature and evaporation on δ18O records.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFM.T52B..06L
- Keywords:
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- 8125 Evolution of the Earth;
- TECTONOPHYSICS;
- 8169 Sedimentary basin processes;
- TECTONOPHYSICS;
- 8175 Tectonics and landscape evolution;
- TECTONOPHYSICS;
- 8177 Tectonics and climatic interactions;
- TECTONOPHYSICS