Spectroscopy of Carbonate Tufa and Travertine Deposits from the Western Great Basin

Eighth International Conference on Mars (2014) 1164.pdf

SPECTROSCOPY OF CARBONATE TUFA AND TRAVERTINE DEPOSITS FROM THE WESTERN GREAT BASIN. N. C. Pearson1 and W. M. Calvin1, 1University of Nevada Reno, Department of Geological Sciences and Engineering, 1664 N.Virginia St. Reno, NV 89557, email: [email protected]

Introduction: Past studies have found a range of slope with a broad weak absorption at 1.4μm. In the carbonates on Mars [1-3] including Fe, Mg and Ca as short wave infrared there are absorption at 1.9μm, the dominant cation. The exact nature of how these 2.3μm and 2.5μm. The 1.9μm absorption is broad deposits were formed is not well understood, and may and shows a variable center ranging from 1.9μm to vary by location on Mars. Among suggested 2.0μm, Figure 1. In the mid infrared there is a broad formation environments, alkali lakes and ancient deep absorption from 2.7μm to 3.7μm. An hydrothermal spring systems have been proposed overprinted doublet absorption occurs near 3.4μm, [3,4]. The Western Great Basin region of Nevada with minimum centers at 3.35μm and 3.47μm. Other includes terrestrial analogs for these types of martian major absorptions occur at 3.9μm 4.68μm and environments with abundant carbonates deposited as 5.56μm. shoreline or structurally controlled hydrothermal The absorptions centered on 1.4μm 1.9μm and spring deposits [5], providing a natural laboratory to 3.0μm are indicative of adsorbed water. The explore if spectral characteristics vary by formation absorptions at 2.3μm and 2.5μm were compared with environment. [10] and found to be consistent with calcium Three types of carbonate are examined in this carbonate. Figure 1 shows the USGS spectral library paper. The first, carbonate tufa columns, are calcite spectra compared with representative samples. deposited in and around ancient and retreating Absorptions in the mid-infrared at centered at 3.4μm, terminal lakes where warm calcium rich spring water 4.0μm, 4.7μm and 5.1μm absorptions match the mixes with carbonate rich lake water [6]. This mixing library calcite spectrum. generally only deposits calcium carbonate at colder A sample of Travertine, TF37 showed a large temperatures when ikaite, a hydrated calcite species, is shoulder to the 2.3μm band and shifted 1.9μm band thermodynamically stable, and later dehydrates to center relative to other spectra. It is likely that this calcite [7]. The second type, carbonate wave tufa, shoulder represents a 2.2μm Si-OH stretch absorption. may also a precipitate along shorelines as alkali water Figure 2 shows the spectra of TF37 compared with the 2+ degases CO2, increasing the activity of CO3 with USGS spectral library opal [11]. Band centers at wave action, coating shoreline materials and trapping 1.9μm and 2.2μm closely match the library spectrum. it in a carbonate matrix. This process generally forms Additionally a shoulder at 5μm also matches closely benches around alkali lakes, marking ancient with the opal spectrum. shorelines[6]. Finally, travertine deposits generally Conclusions: Spectra of carbonate tufa and

occur near hot springs, as dissolved CO2 degases from travertine show mainly calcium carbonate mineralogy geothermal water increasing the pH. This increase of based on the positions of 2.3μm and 2.5μm and pH exsolves carbonate minerals forming benches [8]. 3.4μm absorptions. Additional absorptions at 1.4μm Here we examine reflectance spectra of these 1.9μm and 3.0μm indicates that water is absorbed to deposits from across the Western Great Basin, from the samples. Variations in the 1.9μm band center and both modern and ancient lakes and springs. strength in samples suggests that there is varying Methods: Reflectance spectra of the tufa samples water content between samples. The addition of a were taken on an Analytical Spectral Devices, Field clear 2.2μm band and shift in the 1.9μm band center Spec Pro with a wavelength range of 0.35 to 2.5μm in one sample indicate a hydrated silica such as opal. using a diffuse spectralon panel as a white reference. References [1] Ehlmann et. al., Science, 322, Further reflectance spectra were collected from 1.66 to 2008 [2] Morris et. al. Science, 329, 2010 [3] Wray 6μm using a Thermo Fisher Nicolet 6700 FTIR et. al. LPSC, 42, 2011 [4]Allen and Oehler 2008 [5] spectrometer with DTGS detector with a bandpass Coolbaugh et. al. GRC Transactions, 33, 2009 resolution of 4cm-1. [6]Benson, Palaeogeogr. Palaeoclimatol. Palaeoecol., A continuum removal [9] was performed on 1994, 109 [7]Bischoff, J. et al., GCA, 55, 1743, 1991 selected bands to precisely locate the band center and [8]Ford and Pedley, Earth Science Reviews,Vol 41, the centers of selected absorptions graphed to view 1996. [9]Clark and Roush, JGR, 89, 1984 [10] Gaffey, variations in mineralogy. A list of all samples American Mineralogist, Vol71, 1986 [11] Clark et. Representative spectra are shown in Figure 1 al. USGS Data Series 231, 2007 Spectral Interpretation: These spectra showed a red slope in the visible that turned into a spectrally flat Eighth International Conference on Mars (2014) 1164.pdf

Collection Location Deposit Type Sample ID Diana's Punch Bowl, NV Travertine TF30 Bartine Hot Springs, NV Travertine TF31 Buffalo Valley, NV Travertine TF36 Kyle Hot Springs, NV Travertine TF37 Fales Hot Spring, NV Travertine TF38 Sou Hot Springs, NV Travertine TF34 Jersey Valley, NV Travertine TF35 Fales Hot Spring, NV Travertine TF39 Bonham Ranch, NV Tufa Column TF04C Winnemucca Lake, "Needle Rock", NV Tufa Column TF11 Winnemucca Lake Valley, NV Tufa Column TF14 Toulon, NV Tufa Column TF16 Desert Queen, NV Tufa Column TF20 Lee-Allen, NV Tufa Column TF26 Winnemucca Lake Valley, NV Tufa Column TF13 Honey Lake Valley, NV Tufa Column TF01A Figure 1: Representative tufa and travertine samples Bonham Ranch, NV Tufa Column TF04A compared to USGS spectral library spectra of Bonham Ranch, NV Tufa Column TF06 calcite(scaled for clarity) showing 2.33μm and 2.53μm Winnemucca Lake, absorptions indicative of calcium carbonate[10] bands "Needle Rock", NV Tufa Column TF10 centered at 3.4μm, 4.0μm, 4.7μm and 5.1μm are also Toulon, NV Tufa Column TF15 consistent with the calcite spectrum. Additionally water Desert Queen, NV Tufa Column TF17 absorptions in samples at 1.9μm and 3.0μm can be seen. Cinnabar Hill, NV Tufa Column TF23A Bradys Hot Springs, NV Tufa Column TF24A Lee-Allen, NV Tufa Column TF25 Pyramid Rock, NV Tufa Column TF40 Honey Lake Valley, CA Tufa Column TF01B Bonham Ranch, NV Tufa Column TF04B Desert Queen, NV Tufa Column TF18 Cinnabar Hill, NV Tufa Column TF23B Bradys Hot Springs, NV Tufa Column TF24B Wyemaha Valley, NV Tufa Column TF28 Astor Pass, NV Wave Tufa TF03 Winnemucca Lake, NV Wave Tufa TF12 Cinnabar Hill, NV Wave Tufa TF21 Carson Lake, NV Wave Tufa TF27 Table 1: Collection locations, types and sample ID of all samples studied

Figure 2: Spectra of sample TF37 compared with USGS library spectra of opal showing similarities at 1.9μm, 2.2μm, 3.0μm and 5.0μm.