52nd Lunar and Planetary Science Conference 2021 (LPI Contrib. No. 2548) 1502.pdf

DIAGENESIS IN THE GLEN TORRIDON REGION OF GALE CRATER, MARS USING VNIR SPECTRAL DATA FROM THE CURIOSITY ROVER. A. Rudolph1, B. Horgan1, J. R. Johnson2, J. F. Bell III3, K. Bennett4, V. Fox5, S. Jacob3, S. Maurice6, E. Rampe7, M. Rice8, C. Seeger5, R. Wiens9, 1Purdue University (rudolph4@pur- due.edu), 2JHU/Applied Physics Lab, 3Arizona State University, 4USGS Astrogeology Science Center, 5California Institute of Technology, 6L’Institut de Recherche en Astrophysique et Planétologie, 7Johnson Space Center, 8Western Washington University, 9Los Alamos National Laboratory.

Introduction: The Curiosity rover on the Mars Sci- calibrated using a target on the rover [4,10]. Reflectance ence Laboratory mission (MSL) is currently exploring spectra for left and right camera images of manually de- the Glen Torridon (GT) region of Gale crater, Mars (Fig. fined Regions of Interest (ROI) were averaged and 1) [1]. This region exhibits the largest abundance of scaled based on the wavelength value of 1013 nm. phyllosilicates to date (>30 wt.%) along Curiosity’s ChemCam collects single point passive reflectance traverse [2]. Phyllosilicate formation requires water- spectra between 400-840 nm to support laser-induced rock interactions, and their sheet-like structure can help breakdown spectroscopy (LIBS) [11,12]. The spectra preserve biosignatures in the sedimentary record [e.g., were calibrated as described in [13]. This data provides 3]. While the presence of clay minerals in GT is con- better resolution of the shape and position of absorp- firmed, their origin is unclear, as well as what makes GT tions in this range and the red/blue slope, which together unique to allow the amount of clay minerals observed can be used to constrain Fe2+/3+ mineralogy [e.g., 13] (i.e., location, past environments, composition and mor- Here we investigate spectral variability within GT phology of primary materials, localized diagenesis). using VNIR spectral data acquired between sols 2302 - In this study, we characterize the spectral diversity 2911 and search for trends within morphologic mem- of GT using Mastcam multispectral images and Chem- bers: the GT Jura member, the Knockfarril Hill member Cam passive hyperspectral reflectance data to constrain (KHm), and the Glasgow member (GGm) [1]. The GT the composition and distribution of phyllosilicates and Jura is characterized by thinly laminated mudstones, a other Fe-bearing minerals in GT. We are particularly in- purple/gray/red hue, and sometimes a specular surface. terested in their relationship to key depositional facies The KHm is characterized by fractured bedrock with in- to test hypotheses for their formation environment (e.g., terstratified mudstones and sandstones and is often ob- detrital deposition, in situ sub-aerial weathering, authi- served as a capping unit on buttes. The GGm is charac- genic lacustrine deposition) and the timing of their for- terized by light-toned, highly fractured, and finely lam- mation (e.g., early or late diagenesis). inated bedrock. From orbit, transitions between mem- bers are noted visually by an increase in fracturing over- all, and a lighter-tone in the GGm specifically. Results: Mastcam spectral classes. GT exhibits sig- nificant variability in Mastcam spectra, indicated by the variable color of bedrock and drill tailings (Fig. 3). We identified five spectral classes within GT. The first spec- tral class (Fig. 2) exhibits a strong red slope at shorter wavelengths and a weak or flat absorption at ~900+ nm. This class could be consistent with several phases, but ferric smectites are plausible based on their strong or- bital detections and CheMin detection of >30 wt.% phyllosilicates in regions it is observed [2,14]. This class is observed only in GT Jura and KHm (Figs. 1,2). The second spectral class (Fig. 2) exhibits a strong Figure 1: HiRISE color mosaic of GT and surroundings. red slope at shorter wavelengths and a weak absorption Stars represent drill sites and colored dots represent spectral centered at 860 nm. This is consistent with fine-grained classes, for clarity shown here at drill sites only. Preliminary red crystalline hematite and could be due to small stratigraphic member boundaries are denoted by color lines. amounts of hematite (e.g., <2-3 wt.%) [15]. Weak hem- Curiosity’s traverse is denoted by the solid gray line. atite signatures are observed on the margins of GT in Methods: Mastcam has 12 narrow- and wide-band orbital data [16], and CheMin analyses show minor filters in the visible to near-infrared (VNIR; 445-1013 hematite (<3 wt.%) in almost all GT drill samples [2]. nm) spread across two cameras at different focal lengths This class is observed in all GT members (Figs. 1,2). (100 and 34 mm) [4]. This spectral range is ideal for The third spectral class (Fig. 2) exhibits a flattening or tracking variations in Fe-bearing materials from absorp- weak absorption centered at ~700 nm and is observed tions due to Fe2+/3+ charge transfer [5,6] and crystal field with both weak and strong red slopes. This absorption effects in Fe-bearing silicates [7-9]. Images are can be present in Fe2+/3+-smectites, microplaty hematite, 52nd Lunar and Planetary Science Conference 2021 (LPI Contrib. No. 2548) 1502.pdf

Figure 2: Each plot shows representative Mastcam spectral classes observed in morphologic members. Numbers to the right of each spectrum correspond with their spectral class. goethite, and lepidochrosite [17]. This spectral class is

observed across all GT members (Figs. 1,2). Figure 3: ChemCam passive reflectance drill tailings spectra The fourth spectral class (Fig. 2) exhibits a very grouped by morphologic members. Bottom right shows Mast- weak red slope and a reflectance peak between 640-750 cam enhanced color composites (638 nm/551 nm/493 nm) of nm with a small negative slope through the end of the drill holes (AB = Aberlady, KM = Kilmarie, GE1 = Glen Etive Mastcam wavelength range. This overall flattening of 1, GE2 = Glen Etive 2, HU = Hutton, GG = Glasgow). this class is consistent with a lack of Fe-minerals and/or We hypothesize that weak clay and patchy hematite very spectrally flat Fe-bearing materials (e.g., coarse- signatures in GT may be consistent with an interplay be- grained gray hematite or magnetite) [17]. This class is tween early alteration and subsequent diagenetic pro- observed only at the Glasgow drill site (Figs. 1,2). cesses. The ubiquity of clay minerals in GT Jura and The fifth spectral class (Fig. 2) exhibits flat spectra KHm suggests that they formed in the early surface en- at short wavelengths (low red/blue ratio), absorptions at vironment or during early diagenetic processes prior to 530, ~700, and 860 nm, and a downturn to longer wave- lithification. Because they are observed in both mud- lengths. This is consistent with a lack of fine-grained red stones and sandstones, this suggests that they are not de- hematite, but the 860 nm absorption may indicate the trital, and instead may have formed through a more presence of coarse-grained hematite [17]. This spectral ubiquitous process like surface weathering. In contrast, class is observed only in Hutton drill tailings (Figs. 1,2). patchy hematite could have formed due to subsequent ChemCam analyses. ChemCam spectra (Fig. 3) ob- diagenesis, where clay minerals might have inhibited served in drill tailings at drill sites within GT exhibit fluid flow, leading to patchy diagenetic alteration. similar patterns to Mastcam data (Fig. 2). GT Jura and Similar patchy clay and hematite spectral signatures KHm spectra exhibit an absorption at 535 nm, flattening in Sutton Island below Vera Rubin Ridge (VRR) have around 650 nm, and a reflectance peak between 759 - been attributed to similar weathering and diagenetic 800 nm, with greater 770/535 nm slopes in GT Jura rel- processes [21]. In contrast, the lack of clay spectral sig- ative to KHm (Fig. 3). This is consistent with spectral natures on VRR [17] may be due to either (1) a lack of classes 1-3. Absorption bands centered at 650 nm have phyllosilicate formation in VRR, or (2) more intense been observed elsewhere in GT [18] but drill tailings an- late diagenetic alteration of VRR. [e.g.,17,22]. alyzed here only exhibit flattening. GGm spectra exhib- References: [1] Fox V. et al. (2019) LPSC L, #2826. [2] its flattening in Hutton and a 535 nm absorption with Thorpe M. et al. (2020) LPSC 51, #1524. [3] Orofino V. et a. reflectance peak at 689 nm in Glasgow (Fig. 3) [19]. (2010) Icarus, 208. [4] Wellington D. et al. (2017) Am. Min., 102. [5] Morris R. et al. (1985) JGR., 90. [6] Sherman D. M. This is consistent with spectral classes 4 and 5. (1990) ACS Symp. Series, Chp. 15. [7] Adams J. (1968) Sci- Discussion: Spectral class 1 (and possibly 3) are con- ence, 159. [8] Cloutis E. & Gaffey M. (1991) Earth, Moon, sistent with the Fe/Mg-smectites detected in GT by Che- Plan., 53. [9] Horgan B. et al. (2014) Icarus, 234. [10] Bell III Min [2,20] and in orbital spectra [14]. However, these J. et al. (2017) E&SS., 4. [11] Wiens R. et al. (2012) Space Sci. signatures are best observed in small patches, and weak Rev. 170. [12] Maurice S. et al. (2012) Space Sci. Rev., 170. red crystalline hematite signatures spectrally dominate [13] Johnson J. et al. (2015) Icarus, 249. [14] Fraeman A. et bedrock outcrops, consistent with hematite detected by al. (2016) JGR, 121. [15] Morris R. et al. (1989) JGR, 94. [16] CheMin [2,15]. We hypothesize that clay minerals are Horgan B. et al. (2015) LPSC 46, 2943. [17] Horgan B. et al. uniform throughout GT Jura and KHm, but that abun- (2020) JGR, 125. [18] Johnson J. et al. (2019) AGU #489891. [19] Johnson J. et al. (2020) AGU #680708. [20] Bristow T. F. dance, crystallinity, and/or grain size of spectrally dom- et al. (2019) 9th Mars, #6390. [21] Haber J. et al. (2020) LPSC inant hematite is spatially variable. 51, #2112. [22] Rampe E. et al. (2020) JGR, 125.