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1. Paleothermometry of an enigmatic travertine deposit: Cottonwood Travertine, Stillwater Range, NV

   Jackson, A. (February 2023, Proceedings 48th Workshop on Geothermal Reservoir Engineering, Stanford University, Stanford, California.)

   ABSTRACT Hot and cold spring travertine deposits record integrated histories reflecting changing hydrologic conditions, informing our understanding of the driving forces behind factors impacting local hydrology. We present results from a geologic and geochemical investigation of Cottonwood Travertine, located in Dixie Valley, NV, where it is unclear if the paleospring system that deposited the travertine was driven by deeply sourced hydrothermal fluids, or high fluid flow driven by wetter paleoclimate conditions. The temperature of the spring water that precipitated the Cottonwood Travertine has implications for the relative importance of hydrothermal versus climatic processes influencing the formation and cessation of this enigmatic deposit. We identified four groups of samples based on geologic setting, sample textures, and stable and clumped isotopic analysis: 1) calcite cemented upper gravels, 2) a mound area at the upper bench of the deposit, 3) samples from the flanks and from vuggy veins and fault zone cements from the base of the deposit, and 4) fibrous sub-travertine veins. The calcite-cemented gravels yielded δ18OC values as low as -18.4‰ (VPDB) and apparent TΔ47 of 52°C. The top mound of the deposit returned calcite δ18OC values between -12.8‰ and -11.7‰ (VPDB) and clumped isotope temperatures (TD47) of 24 – 32°C. Higher d13C and d18Oc values at the mound site are interpreted to reflect off gassing of CO2 and disequilibrium conditions. δ18OC and TD47 values from the slopes and base of the deposit are between -15.9‰ and -14.5‰ (VPDB) and around 20°C, respectively. Structurally, texturally, and isotopically (δ18OC = -29.4‰ (VPDB); TΔ47 = 93°C), the fibrous sub-travertine veins are more consistent with the local Jurassic host rock and probably do not reflect recent hot spring conditions. Our analysis suggests that, despite the impressive volume, Cottonwood Travertine formed from springs that were not particularly hot, and the deposit instead reflects vigorous warm spring activity in a wetter climactic regime rather than fluid flow from an extinct higher temperature hydrothermal system. 

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2. Isotopic fractionation accompanying CO2 hydroxylation and carbonate precipitation from high pH waters at The Cedars, California, USA

   https://doi.org/doi.org/10.1016/j.gca.2021.01.003  

   Christensen, J. (January 2021, Geochimica)

   Teagle, Damon A (Ed.)

   The Cedars ultramafic block hosts alkaline springs (pH > 11) in which calcium carbonate forms upon uptake of atmospheric CO2 and at times via mixing with surface water. These processes lead to distinct carbonate morphologies with ‘‘floes” forming at the atmosphere-water interface, ‘‘snow” of fine particles accumulating at the bottom of pools and terraced constructions of travertine. Floe material is mainly composed of aragonite needles despite CaCO3 precipitation occurring in waters with low Mg/Ca (<0.01). Precipitation of aragonite is likely promoted by the high pH (11.5–12.0) of pool waters, in agreement with published experiments illustrating the effect of pH on calcium carbonate polymorph selection. The calcium carbonates exhibit an extreme range and approximately 1:1 covariation in d13C (
   9 to
   28‰ VPDB) and d18O (0 to
   20‰ VPDB) that is characteristic of travertine formed in high pH waters. The large isotopic fractionations have previously been attributed to kinetic isotope effects accompanying CO2 hydroxylation but the controls on the d13C-d18O endmembers and slope have not been fully resolved, limiting the use of travertine as a paleoenvironmental archive. The limited areal extent of the springs (0.5 km2) and the limited range of water sources and temperatures, combined with our sampling strategy, allow us to place tight constraints on the processes involved in generating the systematic C and O isotope variations. We develop an isotopic reaction–diffusion model and an isotopic box model for a CO2-fed solution that tracks the isotopic composition of each dissolved inorganic carbon (DIC) species and CaCO3. The box model includes four sources or sinks of DIC (atmospheric CO2, high pH spring water, fresh creek water, and CaCO3 precipitation). Model parameters are informed by new floe D44Ca data (
   0.75 ± 0.07‰), direct mineral growth rate measurements (4.8 to 8  10
   7 mol/m2/s) and by previously published elemental and isotopic data of local water and DIC sources. Model results suggest two processes control the extremes of the array: (1) the isotopically light end member is controlled by the isotopic composition of atmospheric CO2 and the kinetic isotope fractionation factor (KFF (‰) = (a
   1)  1000) accompanying CO2 hydroxylation, estimated here to be
   17.1 ± 0.8‰ (vs. CO2(aq)) for carbon and
   7.1 ± 1.1‰ (vs. ‘CO2(aq)+H2O’) for oxygen at 17.4 ± 1.0
   C. Combining our results with revised CO2 hydroxylation KFF values based on previous work suggests consistent KFF values of
   17.0 ± 0.3‰ (vs. CO2(aq)) for carbon and
   6.8 ± 0.8‰ for oxygen (vs. ‘CO2(aq)+H2O’) over the 17–28
   C temperature range. (2) The isotopically heavy endmember of calcium carbonates at The Cedars reflects the composition of isotopically equilibrated DIC from creek or surface water (mostly HCO- 3, pH = 7.8–8.7) that occasionally mixes with the high-pH spring water. The bulk carbonate d13C and d18O values of modern and ancient travertines therefore reflect the proportion of calcium carbonate formed by processes (1) and (2), with process (2) dominating the carbonate precipitation budget at The Cedars. These results show that recent advances in understanding kinetic isotope effects allow us to model complicated but common natural processes, and suggest ancient travertine may be used to retrieve past meteoric water d18O and atmospheric d13C values. There is evidence that older travertine at The Cedars recorded atmospheric d13C that predates large-scale combustion of fossil fuels. 

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3. Travertine records climate-induced transformations of the Yellowstone hydrothermal system from the late Pleistocene to the present

   https://doi.org/10.1130/B37317.1  

   Harrison, Lauren N.; Hurwitz, Shaul; Paces, James B.; Whitlock, Cathy; Peek, Sara; Licciardi, Joseph (February 2024, Geological Society of America Bulletin)

   Chemical changes in hot springs, as recorded by thermal waters and their deposits, provide a window into the evolution of the postglacial hydrothermal system of the Yellowstone Plateau Volcanic Field. Today, most hydrothermal travertine forms to the north and south of the ca. 631 ka Yellowstone caldera where groundwater flow through subsurface sedimentary rocks leads to calcite saturation at hot springs. In contrast, low-Ca rhyolites dominate the subsurface within the Yellowstone caldera, resulting in thermal waters that rarely deposit travertine. We investigated the timing and origin of five small travertine deposits in the Upper and Lower Geyser Basins to understand the conditions that allowed for travertine deposition. New 230Th-U dating, oxygen (δ18O), carbon (δ13C), and strontium (87Sr/86Sr) isotopic ratios, and elemental concentrations indicate that travertine deposits within the Yellowstone caldera formed during three main episodes that correspond broadly with known periods of wet climate: 13.9−13.6 ka, 12.2−9.5 ka, and 5.2−2.9 ka. Travertine deposition occurred in response to the influx of large volumes of cold meteoric water, which increased the rate of chemical weathering of surficial sediments and recharge into the hydrothermal system. The small volume of intracaldera travertine does not support a massive postglacial surge of CO2 within the Yellowstone caldera, nor was magmatic CO2 the catalyst for postglacial travertine deposition. 

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4. Record of Neotectonics and Deep Crustal Fluid Circulation Along the Santa Fe Fault Zone in Travertine Deposits of the Lucero Uplift, New Mexico, USA

   https://doi.org/10.1029/2020GC009454  

   Garcia, V. H.; Ma, L.; Ricketts, J. W.; Dosseto, A. (April 2021, Geochemistry, Geophysics, Geosystems)

   Abstract Travertine deposits preserve an invaluable record of both ancient and modern fluid flow. The goal of this study is to reconstruct spatial and temporal patterns in travertine deposition associated with tectonic and climatic controls along the Lucero Uplift in New Mexico, USA. Uranium‐series ages of travertine deposits in the Lucero Uplift range from 0.94 ± 0.01 to 592 ± 110 ka, indicating that travertine formation has been episodically active since at least ∼600 ka. We find minimal evidence to attribute glacial and interglacial cycles to travertine formation in the Lucero Uplift. δ¹³C values in travertine deposits range from 2‰ to 9‰ (Vienna Pee Dee Belemnite), δ¹⁸O values range from 21‰ to 25‰ (Vienna Standard Mean Ocean Water). Positive correlation between travertine δ¹³C and δ¹⁸O values indicate travertine formation is closely associated with various degrees of CO₂degassing.⁸⁷Sr/⁸⁶Sr values in travertine deposits range from 0.714 to 0.717 and (²³⁴U/²³⁸U)_ivalues exhibit a remarkably wide range from 3.6 to 9.3, indicative of fluid‐rock interaction during deep crustal circulation in more radiogenic basement rocks. Reconstructed δ¹³C, δ¹⁸O, and (²³⁴U/²³⁸U)_ivalues in the inferred deep fluid sources showed systematic variations with travertine formation ages, while⁸⁷Sr/⁸⁶Sr values remain relatively constant. Based on dating of undeformed travertine deposits, which overlie tilted Santa Fe Group units, and high (²³⁴U/²³⁸U)_iwe infer that the Santa Fe fault has not produced a ground‐rupturing earthquake within the last 490 ± 52 to 592 ± 110 ka (2σ). Our study suggest that travertine formation is driven by fluid flow facilitated by tectonic and mantle structures. 

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5. Global travertine deposition modulated by oscillations in climate

   https://doi.org/10.1002/jqs.3144  

   Ricketts, Jason W.; Ma, Lin; Wagler, Amy E.; Garcia, Victor H. (September 2019, Journal of Quaternary Science)

   ABSTRACT Travertine deposits are important records of past fluid flow in the Earth's crust, and document fluid migration through both tectonic activity and changes in climate. While many studies hint at possible relationships between travertine formation and global climate, none have investigated these connections on a global scale. Here we compile 1649 published travertine ages from six continents to test the hypothesis that global and/or regional changes in climate regulate travertine deposition. Peaks in bedded travertine ages occur with main frequencies that correspond to 100‐kyr changes in global climate, where most peaks occur during glacial terminations or interglacial periods, including a large peak that coincides with the Early Holocene climatic optimum. Time–series analysis also suggests a possible connection with 41‐kyr obliquity cycles. At regional scales, many peaks also correspond with local times of high precipitation or wet conditions. This can be attributed to higher groundwater recharge rates, providing the necessary water to form travertine. Many bedded travertine‐depositing systems may therefore be water‐limiting and sufficient CO₂may be present even during times of no travertine deposition. Exceptions to this conclusion are banded vein travertine deposits, which typically form during times of dry climate when water tables are low. Copyright © 2019 John Wiley & Sons, Ltd. 

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