Salty Residues on Mars Mark Changing Geochemical Environments

Ninth International Conference on Mars 2019 (LPI Contrib. No. 2089) 6148.pdf

SALTY RESIDUES ON MARS MARK CHANGING GEOCHEMICAL ENVIRONMENTS. J. L. Bishop1, C. M. Weitz2, J. Flahaut3, C. Gross4, A. M. Saranathan5, J. M. Danielsen1,2, G. S. Usabal1,6, J. K. Miura1,6, Y. Itoh5, and M. Parente5, 1SETI Institute & NASA-Ames (Mountain View, CA; [email protected]), 2Planetary Science Institute (Tucson, AZ), 3CRPG-CNRS (Vandœuvre-lès-Nancy, France), 4Free University of Berlin (Berlin, Germany), 5Uni- versity of Massachusetts at Amherst (Amherst, MA), 6Brown University (Providence, RI).

Introduction: Remote characterization of unique We are also using CRISM images prepared with a salty outcrops on Mars using CRISM, HiRISE and new algorithm developed by Itoh and Parente [10] for HRSC imagery indicate geochemical transitions from simultaneous atmospheric correction and denoising. Im- sedimentary phyllosilicate beds to evaporative, acidic, ages calibrated using this new method remove most of or hydrothermal environments. We have identified the residual of the atmospheric correction from the vol- these salty residues using a spectral “doublet” feature cano scan method, as well as spurious noise that masks near 2.21-2.23 and 2.26-2.28 µm at multiple locations surface spectral signatures in the 1.0-2.6 µm spectral including Mawrth Vallis, Noctis Labyrinthus, Melas range. Spectra of selected “doublet” units at Mawrth Chasma, and Ius Chasma. This study builds on previous Vallis were analyzed from images calibrated with both analyses [1-8] to characterize the band centers and rela- methods to ensure consistency (Fig. 2). tive band depths of the “doublet” signatures in the de- posits that were difficult to resolve in the past, using new image calibration [9,10] and processing techniques [11]. All occurrences of these “doublet” materials are associated with phyllosilicates and sulfates, and indicate changes in pH, salt levels, and/or water/rock ratio.

Figure 2. Selected CRISM spectra illustrating variations in “doublet” type units for 5 sites across the Mawrth Vallis region (yellow, Fig. 1), compared with the more common Al-rich smectite (blue, Fig. 1) and Fe-rich smectite (red, Fig. 1) spectra (data from multiple CRISM images). We are processing images identified by our team having this “doublet” feature with a new feature extract- Figure 1. View of multiple mineral horizons at Mawrth Vallis. ing algorithm [11] based on Generative Adversarial a) HRSC oblique view, 5x vertical, featuring phyllosilicate- Networks (GANs). This method is highly effective at and sulfate-bearing outcrops in CRISM false-color data with allophane (green), Al-clays (blue),“doublet” unit (yellow), identifying locations of the “doublet” unit and mapping and nontronite in (red), b) CRISM false-color data overlain subtle differences in the “doublet” materials using hy- on HiRISE for region in yellow box in (a). perspectral factors in the feature extraction rather than Methods and Data: Recently developed MTRDR just one band, ratio, or slope in the spectrum (Figs. 3-4). images [9] were evaluated that contain joined spectra Results: The “doublet” units spanning the Mawrth across the 0.4-3.9 µm range and improved spectral qual- Vallis, Noctis Labyrinthus, Melas Chasma, and Ius ity due to enhanced flat field and other corrections. Chasma sites exhibit features characteristic of jarosite in Spectral parameters [12] were used to map individual some cases [1,2] with bands near 1.85 and 2.27 µm [13] mineral units in complex outcrops in CRISM scenes and (Fig 2: spectra 1, 5). More typically, these units are char- overlay these on CTX imagery and HRSC DTMs using acteristic of jarosite or gypsum mixtures with phyllo- ArcGIS [4] as in Fig. 1. silicates or opal [8]. In the Mawrth Vallis region some Ninth International Conference on Mars 2019 (LPI Contrib. No. 2089) 6148.pdf

“doublet” materials (100-500 m across) surround tiny between the Al-smectite and Fe-smectite strata could be jarosite outcrops (50-100 m across) [14], suggesting that due to evaporative processes, similar to these environ- these are related and that jarosite is present at variable ments. Acid leaching of volcanic ash at Kilauea, HI [17] amounts in these sites, but only observed where it is and LaSolfatara, Italy [18] has produced mixtures of more abundant. Observations of the shape of the “dou- nontronite, jarosite, gypsum, and opal. This scenario blet” units at Mawrth Vallis vary widely (Fig. 2), con- may better explain the “doublet” units observed at Noc- sistent with multiple types of materials. tis Labyrinthus and Melas Chasma. The extensive “doublet” units observed at Ius Chasma are attributed to a more regional process and could be due to alteration of ash in shallow salty ponds or acidic water from melting snow/ice over sulfate rocks. The presence of different, overlapping “doublet” units is consistent with a change over time in the pH, salt levels, or water/rock ratio.

Figure 4. Unratioed, continuum removed (CR) CRISM spectra of 4 “doublet” type sites from the Ius Chasma region compared with the more common Al-rich, Fe-rich and Mg-rich Figure 3. View of Ius Chasma “doublet” units. a) CRISM smectite spectra. Spectra 2 and 3 illustrate typical “doublet” false color images over CTX on HRSC DTM. b) 3D view of type material, while spectrum 1 likely contains opal and spec- CRISM FRT0000A202 over MOLA highlighting the “dou- trum 4 may be a mixture of montmorillonite and nontronite. blet” materials in pale blue/white and smectites in green, 10x. c) map of 2 distinct “doublet” phases using feature learning Acknowledgements: We are grateful to funding [11]. Small occurrences of other hydrated phases (blue, red) from the NAI, MDAP, and PDART for this work. observed beneath or intermixed with “doublet” unit. References: [1] Roach L.H. et al. (2010) Icarus 206, At Ius Chasma, the “doublet” type unit occurs across 253-268. [2] Weitz C.M. et al. (2011) Geology 39, 899-902. 35 km of light-toned material at Geryon Montes [6] and [3] Weitz C.M. et al. (2015) Icarus 251, 291-314. [4] Bishop is associated with smectites and other hydrated materi- J.L. et al. (2016) LPSC 47, #1332. [5] Flahaut J. et al. (2014) 8th Mars, #1411. [6] Wetiz C.M. et al. (2019) 9th Mars, this als. The “doublet” type units at Noctis Labyrinthus and volume. [7] Kaplan H.H. et al. (2016) Icarus 275, 45-64. [8] Melas Chasma occur in smaller outcrops and are asso- Danielsen J.M. et al. (2019) LPSC 50, #3017. [9] Seelos F P. ciated with phyllosilicates and sulfates [2-3]. et al. (2016) LPSC 47, #1783. [10] Itoh Y. & Parente M. Implications: Comparison of these “doublet” out- (2019) LPSC 49, # 2025. [11] Saranathan A.M. & Parente M. crops with terrestrial analog sites enables identification (2019) LPSC 50, #2698. [12] Viviano-Beck C.E et al. (2014) of alteration environments producing such features. JGR 119, 2014JE004627. [13] Bishop J.L. & Murad E. (2005) Amer. Miner. 90, 1100-1107. [14] Usabal G.S. et al. (2019) Shallow salty lakes in Western Australia contain mix- LPSC 50, #2234. [15] Benison K.C. & Bowen B.B. (2006) Ic- tures of phyllosilicates, opal, gypsum, and jarosite [15], arus 183, 225-229. [16] Flahaut J. et al. (2017) Icarus 282, similar to Chilean salars [16]. The highly variable “dou- 152-173. [17] Bishop J.L. et al. (2015) AGU Fall mtg, Abs. blet” type signatures at Mawrth Vallis, interspersed #62066. [18] Flahaut J. et al. (2019) Amer. Miner., in review.