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50th Lunar and Planetary Science Conference 2019 (LPI Contrib. No. 2132) 1929.pdf

ANALYSIS OF CLAY DEPOSITS IN AND AROUND LADON BASIN AND LADON VALLES. C. M. Weitz1, J. L. Bishop2, and J. A. Grant, 1Planetary Science Institute, 1700 E Fort , Tucson, AZ 85719, USA ([email protected]), 2SETI Institute, Carl Center, 189 Bernardo Ave., Mountain View, CA 94043, USA, 3Center for Earth and Planetary Studies, National Air and Space Museum, Smithsonian Institution, 6th at Independence SW, Washington, DC, 20560.

Introduction: We have identified, mapped, and We divide the deposits into three types: (1) Light- analyzed light-toned deposits, many of which are clay- toned layered deposits in the western uplands outside bearing, in and around Ladon basin and Ladon Valles Ladon basin; (2) Light-toned layered deposits in Ladon in Margaritifer Terra (Figure 1). The study region has Valles and southern Ladon basin; and (3) Light- to clays that likely formed from multiple aqueous proc- medium-toned deposits that lack fine-scale layering. esses, including fluvial, lacustrine, hydrothermal, and Type 1: Light-toned layered deposits in the in situ alteration. CRISM analysis of the light-toned western uplands outside Ladon basin: The light- deposits indicates the presence of Fe/Mg- toned layered sediments we have identified along the phyllosilicates. Light-toned layered outcrops in western uplands of Ladon basin are associated with and craters, near the mouth of Ladon valley networks that eroded and Early Hes- Valles, inside Ladon basin, and in several of the small perian geologic units and deposited these sediments upland basins west of Ladon are all characterized by within small basins, likely similar to the valley net- broadly similar morphology and expression [1-8], sug- works that deposited the delta in the larger Eberswalde gesting that their sedimentary depositional settings basin. Valleys sourcing many of these deposits head were perhaps similar. Some of the phyllosilicate- along an ancient ridge to the west forming one of the bearing sediments may be sourced from weathered eroded rings of the ancient Holden impact basin [9,10] upland rocks later transported into lower-lying areas that likely exposes rocks weathered during an early whereas others may be the result of alteration after the wetter period of the Noachian [11]. One deposit in- deposits were emplaced [4]. Although the origin of the cludes an inverted channel that lies in a shallow valley clays in the deposits could be from different processes, that may have been blocked by topography associated the clays almost certainly reflect past environments with Cardona crater ejecta. CRISM spectra from the characterized by prolonged chemical weathering in- deposit are consistent with nontronite-type clays as volving water. well as additional clay signatures that appear to be saponite, although the phyllosilicate signatures are weak in these deposits. Drainage from the ridge into Arda Valles and deposition of the layered sediments likely continued until outlets were established to the east, thereby enabling incision of the deposits and drainage onto the lower-lying floor of Ladon basin. Another smaller intersected a N-S trending Holden secondary , depositing sediments within the crater chain during the after the Holden impact [12]. Type 2: Light-toned layered deposits in Ladon Valles and southern Ladon basin: The utility of combined CRISM and HiRISE analyses is demon- strated using an example of the deposits located at the mouth of Ladon Valles (Fig. 2). Most CRISM spectra show features consistent with multiple types of OH- Figure 1. THEMIS mosaic showing the Ladon basin bearing materials, like Fe/Mg-rich smectites, and and Ladon Valles study region. Type 1 are light-toned HiRISE images indicate numerous beds with variable layered deposits along the western uplands (magenta). lithologies, including color and brightness variations. Type 2 are light-toned layered deposits within Ladon Spectra from several of the brightest upper beds in basin and Ladon Valles (yellow). Type 3 are light- to these deposits exhibit a 2.3 µm absorption but no hy- medium-toned units that do not show fine-scale layer- dration band at 1.9 µm (Fig. 2), which could reflect ing (blue). Inset is the topography of from dehydration from high temperatures that drove out the MOLA data in color with the location of Ladon basin water in the clays [13]. marked by the black square. 50th Lunar and Planetary Science Conference 2019 (LPI Contrib. No. 2132) 1929.pdf

Strike and dips for bedding planes within these de- water ponded inside the craters, as these craters all posits, calculated from HiRISE-derived DTMs, are have small valleys that intersect them. Unlike the Type shallow and between 1-4°. Although the general ap- 1 and Type 2 deposits, the absence of layering suggests pearance of the deposits suggests they are light-toned either limited deposition of sediments or alteration of in nature, HiRISE images reveal numerous bright pre-existing materials to explain the Type 3 deposits. beds interspersed with medium-toned and even darker References: Pondrelli, M., et al. (2005), J. Geophys. Res., beds, suggesting different source materials for the sed- 110, 2004JE002335; [2] Pondrelli, M. A. et al. (2008), Ica- iments over time. The brightest upper beds can be rus, 197, 429-451, doi:10.1016/j.icarus.2008.05.018. [3] Grant, J. A. et al. (2008), Geology, 36, 195-198, doi: traced over 65 km in distance from Ladon Valles into 10.1130/G24340A. [4] Milliken, R. E., and D. L. Bish southern Ladon basin, consistent with a lacustrine or (2010), Philosophical Magazine, 1478-6443, DOI: perhaps distal alluvial fan setting. 10.1080/14786430903575132. [5] Rice, M. S., et al. (2011), Type 3: Light- to medium-toned deposits that Geophys. Res. Letts., 38, doi:10.1029/2011GL048149. [6] lack fine-scale layering: Clays within Ladon basin can Rice, M.S., et al. (2013) MARS 8, 15-57, be associated with medium-toned fractured materials doi:10.1555/mars.2013.0002. [7] Weitz, C. M., and J. L. that exhibit few or no layering. The deposits in Ladon Bishop (2012), Lunar Planet. Sci. Conf., XXXXIII, Abstract 1243. [8] Weitz, C.M., et al. (2013) Lunar Planet. Sci. Conf. basin tend to be adjacent to fractures and could have 44th, Abstract 2081. [9] Schultz, P. H., et al. (1982), J. Geo- resulted from fluids emitted from the fractures [14]. phys. Res., 87, 9803-9820. [10] Grant, J. A. (1987), in Ad- Additional clays without layering are also found in vances in planetary geology, NASA Technical Memorandum older terrain exposed along the floor of Ladon Valles 89871, p. 1-268. [11] Bibring, J.-P., et al. (2006), Science (Fig. 2, l and m spectra) and could be mixed-layer 312, 400-404, DOI: 10.1126/science.1122659. [12] Irwin, smectite/chlorite produced by alteration from water R.P. and J. A. Grant (2013) Geologic Map of MTM -15027, - 20027, -25027, -25032 Quads, Margaritifer Terra region of that once flowed through Ladon Valles. Finally, light- Mars. [13] Morris, R.V., et al. (2010) LPSC 41, Abstract toned deposits are found in several impact craters 2156. [14] Thomas R.J. et al. (2017), J. Geophys. Res., along the western uplands of Ladon basin. These crater 122(3), doi:10.1002/2016JE005183. floor deposits could be altered materials from when

Figure 2. (a) HiRISE mosaic of clays in Ladon Valles. CRISM spectral parameters are overlain in color with indicating the presence of phyllosilicates (D2300). The clays are associated with light-toned layered deposits and also medium-toned altered material along the floor of Ladon Valles. Letters indicate the CRISM spectra with the same color (right), with color circles taken from image FRT0000B306 and colored squares taken from image FRT00008076. Spectra from the upper bright materials (b,c,d,e) exhibit a 2.3 µm absorption but no hydration band at 1.9 µm, which could reflect dehydration from high temperatures that drove out the water in the clays [15].