Environmental controls on silica sinter formation revealed by radiocarbon dating

Radiocarbon Dating of Silica Sinter and Postglacial Hydrothermal Activity in the El Tatio Geyser Field

“…Late Pleistocene ages (~10 to 27 ka CalBP) appear distributed in different areas of the field, suggesting widespread hydrothermal activity during that period (Figure 1). In the north and active part of the field, the new radiocarbon ages are consistent with previously determined Holocene ages (Slagter et al, 2019) but document a longer depositional period of 17.7 ± 0.04 ka CalBP. There is a gap of 10 ka between the beginning of the hydrothermal activity in the north and the south of the field, which may either record a gap in hydrothermal activity between both areas or insufficient sampling.…”

“…To account for this variability, we crushed different parts of each sample and processed replicates in separate vials of about 100 g, ending up with 70 aliquots. Following established methods for extracting organic carbon from the sinter (e.g., Howald et al, 2014; Lowenstern et al, 2016; Slagter et al, 2019), we first submerged the samples in 1 M hydrochloric acid (HCl) for 24 hr to eliminate the nonorganic carbonates. Next, we immersed the samples in concentrated (48%) hydrofluoric acid (HF) at a controlled temperature of ~70°C for 48 hr to dissolve silicate minerals.…”

“…(a) Apparent ages in modern samples according to depositional temperature (linear trend). (b) Ages of modern samples showing increase with δ 13 C. Red triangles correspond to fresh bacterial mats, blue diamond to a modern partially silicified marsh, and gray diamond to a distal apron collected by Slagter et al (2019). (c) δ 13 C versus radiocarbon age for all sinter according to the depositional environment.…”

“…Based on the current rates of silica precipitation and the thickness of the sinter deposits in El Tatio, Nicolau et al (2014) inferred that deposition would likely have begun at ~4 ka. However, radiocarbon ages of sinter deposits from the active hydrothermal area yielded ages up to 10.8 ka BP (Slagter et al, 2019). Holocene sinters overlie older sinter platforms that extend beyond the active hydrothermal area, suggesting an even earlier inception of hydrothermal activity (Figure 1 and supporting information Figures S1 and S2).…”

“…For samples with duplicates, we calculated the weighted mean (Table S1). Samples labeled ET belong to this study, while samples with asterisks are from Slagter et al (2019).…”