Geologic History of Margaritifer Basin, Mars: Evidence for a Prolonged Yet Episodic Hydrologic System

46th Lunar and Planetary Science Conference (2015) 1463.pdf

GEOLOGIC HISTORY OF MARGARITIFER BASIN, MARS: EVIDENCE FOR A PROLONGED YET EPISODIC HYDROLOGIC SYSTEM. M. R. Salvatore1, M. D. Kraft1,2, C. S. Edwards3, and P. R. Christensen1, 1School of Earth and Space Exploration, Arizona State University, 201 E. Orange Mall, Tempe, AZ, 85287-6305, [email protected]; 2Western Washington University, Bellingham, WA; 3U.S. Geological Survey, Flagstaff, AZ.

Introduction: Located within the “Tharsis trough tic in composition, with many areas exhibiting high abun- [1],” Margaritifer Basin is a critical component of the dances of olivine (> 20%). While the majority of Unit 2 is martian hydrologic system [2] (Fig. 1). This basin is lo- sparsely cratered and smooth, an olivine-enriched subunit cated at the terminus of the Uzboi-Ladon-Morava (ULM) is hummocky and polygonally fractured, exhibits a higher network of mesoscale outflow channels, which drains thermal inertia (315 J m-2 K-1 s-0.5, relative to < 300 J m-2 nearly 9% of the martian highlands [1-4]. Margaritifer K-1 s-0.5), and is stratigraphically below the smoother sub- and Iani Chaos separate the ULM system and Margariti- unit of Unit 2. This olivine-rich subunit is also found fer Basin from Ares and Mawrth Valles to the north, within Morava Vallis, where it is fluvially dissected. which eventually debouche into the northern lowlands. Unit 3 (-2210 m). Located only in western Margariti- Together, this network of valleys, basins, and chaos ter- fer Basin, Unit 3 is light-toned, heavily cratered, and ex- rain extend for more than 8,000 km [5]. hibits the highest thermal inertia measured throughout the The geologic history of Margaritifer Basin has not basin (> 350 J m-2 K-1 s-0.5). Many craters are infilled by been fully explored using recent orbitally derived da- material associated with Unit 3, suggesting that this mate- tasets. Therefore, we investigate the topographic, mor- rial was deposited on already cratered terrain. Fine-scale phological, and spectral character of the geologic units of layering is observed where the subsurface of Unit 3 is Margaritifer Basin using high-resolution datasets. We exposed by impact craters. CRISM data show strong 1.4 then reconstruct the geologic history of this basin based µm, 1.9 µm, and 2.3 µm absorption features, indicative of on observed stratigraphic relationships. Our results indi- the presence of Fe/Mg phyllosilicates. cate that Margaritifer Basin experienced fluvial, volcanic, Unit 4 (-2330 m). Unit 4 is only present along the and possible lacustrine activity throughout its history, floor of Morava Vallis. This unit has a thermal inertia with potentially long temporal gaps between many of comparable to Unit 2 (315 J m-2 K-1 s-0.5), yet lacks any these events. These results suggest that Margaritifer Basin diagnostic spectral signatures. The most diagnostic prop- experienced prolonged yet episodic hydrological activity. erty of Unit 4 is the complex network of polygonal frac- Methods: Mars Orbiter Laser Altimeter (MOLA [6]) tures, in addition to numerous long ridges that exhibit gridded and profile data were used for topographic anal- raised margins and extend for several kilometers. yses. Mars Orbiter Camera (MOC [7]), Context Camera Geologic History of Margaritifer Basin: Based on (CTX [8]), Thermal Emission Imaging System (THEMIS the properties and stratigraphic relationships of these geo- [9]), and High Resolution Imaging Science Experiment logic units, we are able to recreate the geologic history of (HiRISE [10]) visible imagery was used for surface and stratigraphic analyses. Compact Reconnaissance Imaging Spectrometer for Mars (CRISM [11]) data were used for visible/near-infrared spectral analyses, while THEMIS and Thermal Emission Spectrometer (TES [12]) data were used for thermal infrared compositional and ther- mophysical analyses [13]. Results: Four significant geologic units have been identified within Margaritifer Basin based on their unique geologic properties. Here we describe these units, ordered from highest to lowest mean elevation: Unit 1 (-1790 m). High-standing mountains within Margaritifer Basin are classified as Unit 1. These mountains stand up to one kilometer above the basin floor, and are spectrally, morphologically, and thermophysically similar to the surrounding plains of Margaritifer Terra. The mountains also exhibit fluvial dissection and muted landscapes, suggesting that they are ancient. Unit 2 (-2130 m). The majority of the flat-lying plains Figure 1. MOLA topography of Margaritifer Basin overlain on in Margaritifer Basin are grouped into Unit 2. CRISM, THEMIS daytime infrared imagery. A transect shown in Figure TES, and THEMIS analyses suggest that Unit 2 is basal- 2 is also identified. 46th Lunar and Planetary Science Conference (2015) 1463.pdf

Margaritifer Basin (Fig. 2). Fluvial and/or lacustrine sed- References: [1] Phillips R. et al. (2001), Science, 291, imentation (Unit 3) occurred in western Margaritifer Ba- 2587-2591. [2] Grant J. & Parker T. (2002), JGR, 107, sin, associated either with the initial activity in Morava 10.1029/2001JE001678. [3] Banerdt W. (2000), AGU Fall Vallis or with the more highly integrated fluvial networks Mtg., 81, P52C-04. [4] Irwin R. & Grant J. (2013), USGS Map, present throughout the nearby southern highlands (Fig. 3209. [5] Parker T. (1989), LPSC XX, 826-827. [6] Smith D. et 2b). Unit 4 either predates the emplacement of, or was al. (2001), JGR, 106, 23689-23722. [7] Malin M. & Edgett K. deposited contemporaneously with, Unit 3. Morava Vallis (2001), JGR, 23429-23570. [8] Malin M. et al. (2007), JGR, dissected Margaritifer Basin and continued to the north, 112, 10.1029/2006JE002808. [9] Christensen P. et al. (2004), eroding through several impact craters to the east of Mar- Space Sci. Rev., 110, 85-130. [10] McEwen A. et al. (2007), garitifer Chaos (Fig. 2b). Margaritifer Basin was then JGR, 112, 10.1029/2005JE002605. [11] Murchie S. et al. resurfaced by basaltic volcanism (Unit 2), which nearly or (2007), JGR, 112, 10.1029/2006JE002682. [12] Christensen P. completely obscured Morava Vallis (Fig. 2c). The wide- et al. (2001), JGR, 106, 23823-23871. [13] Fergason R. et al. spread formation of chaos terrain occurred following vol- (2006), JGR, 111, 10.1029/2006JE002735. [14] Goudge T. et canic resurfacing, exposing both light-toned sedimentary al. (2012), JGR, 117, 10.1029/2012JE004115. [15] Craddock layers and olivine-bearing basalts in the isolated mesas R. & Howard A. (2002), JGR, 107, 10.1029/2001JE001505. within the chaos terrain. The reactivation of Morava Val- [16] Andrews-Hanna J. et al. (2007), Nature, 446, 163-166. lis followed chaos formation, as the current extent of Mo- [17] Andrews-Hanna J. & Lewis K. (2011), JGR, 116, rava Vallis terminates at a small and isolated patch of 10.1029/2010JE003709. [18] Chapman M. & Tanaka K. chaos terrain located in the center of Margaritifer Basin. (2002), Icarus, 155, 324-339. [19] Warner N. et al. (2011), This later activation of Morava Vallis carved through JGR, 116, 10.1029/2010JE003787. basaltic materials associated with Unit 2 and, in places, exposed Unit 4 (Fig. 2d). Implications: The clear evidence for multiple episodes of fluvial activity within Morava Vallis that are temporally separated by basaltic volcanism suggests that the martian hydrologic system had been episodically ac- tive for a prolonged period of time. While the exact tim- ing of these events is not well constrained, evidence of lava-water interactions (e.g., lava deltas, littoral cones, rootless cones, tuyas) are absent [14]. This may suggest that water was absent from Margaritifer Basin before the volcanic resurfacing occurring, and that these volcanic surfaces had cooled and solidified prior to the reactivation of Morava Vallis. Alternatively, evidence of lava- water interactions may have been buried by subsequent volcanism. Therefore, it is impossible to determine the exact length of time separating these geological events. Episodic fluvial activity, however, suggests episodic recharge upstream from Morava Vallis. If the water was sourced from precipitation, this episodicity may be associated with global climatic or orbital cycles that recharged the atmospheric and/or subsurface water reservoirs [15- 17]. If the water was sourced from the subsurface, episodic melting of the cryosphere [18] or overpressurization of an aquifer [19] may have resulted in the observed geologic history. Although only two discrete episodes of fluvial activity can be confidently identified in Margaritifer Ba- sin, this study confirms that one single catastrophic event Figure 2. Hypothesized geologic history of Margaritifer Basin, did not form the mesoscale outflow channels located in from earliest (a) to latest (d). Grey, pink, blue, and maroon units the Tharsis trough. Recharge of surface and/or subsurface represent Unit 1, Unit 2, Unit 3, and Unit 4, respectively. (a) reservoirs must have occurred to produce the observed Margaritifer Basin prior to modification. (b) Sedimentary depo- morphologies and stratigraphy. Such episodic recharge sition within the basin, associated with fluvial and/or lacustrine and hydrological activity may, therefore, be representa- processes. (c) Volcanic resurfacing throughout the basin. (d) tive of the martian hydrological system as a whole. Reactivation of Morava Vallis following chaos formation.