Figure 2. Preliminary geologic map at LPSC (2015) Abstract #2942 1:1M scale (left) and correlation of Correlation of Map Units map units (COMU, right). White boxes show location of Figs. 3-6. PLATEAU AND Geologic Mapping and the SURFICIAL CRATER CRATER AND HIGHLAND MAJOR EVENTS DEPOSITS UNITS CHANNEL-FILL UNITS UNITS PERIOD Gradational History of Southern EPOCH Ad Margaritifer Terra on Mars 1:1M Scale Late Sharon A. Wilson1,2, John A. Grant1, Debra L. Buczkowski3 & Cathy M. Weitz4 1Smithsonian Institution, National Air and Space Museum, Center for Earth and Planetary Studies, Washington, DC ([email protected]), 2Department of 100 km Environmental Sciences, University of Virginia, Charlottesville, VA,3 JHU-APL, Fig. 6 4 Middle Mm Ac Laurel, MD Planetary Science Institute, Tucson, AZ 3

LEGEND AMAZONIAN Introduction Fig. 5 Ad Dune Unit Early Southern Margaritifer Terra on Mars preserves a long record of End of fan activity AHf AHs aqueous processes (Fig. 1). The Noachian-Hesperian age [1] Mm Mass Movement Unit Hale crater impact Uzboi-Holden flood Uzboi-Ladon-Morava (ULM) outflow system dominates the regional Late Layered materials (?) Holden crater impact drainage from Argyre to the northern plains [1-4]. Holden crater formed Hc Ac Crater 3 Unit 2 He in the mid to Late Hesperian [5] and blocked the northern end of Uzboi 3 Early

HESPERIAN Nc HNch Vallis, thereby creating an enclosed basin that flooded and formed a large 1 1 HNt Uzboi Vallis formed paleolake [6]. Alluvial fans in Holden and other craters were active as late Hc2 Crater 2 Unit as the Amazonian-Hesperian boundary [e.g., 7]. Finally, aqueous deposits Late Crater degradation related to the Hale impact may have modified Uzboi Vallis and its Nc1 Crater 1 Unit Nh tributaries [8] as late as the early-to-middle Amazonian [9]. Preliminary geologic mapping in Mars Transverse Mercator (MTM) AHf Fan Unit NOACHIAN Holden basin impact Nm map quadrangles -20037, -25037, -30037 and -30032 on Mars encompasses Middle Ladon basin impact Uzboi Vallis and terrain to the south, west and northwest of Holden AHs Smooth Unit crater (Fig. 1). This 1:1M scale geologic map broadens the regional framework by constraining the timing, duration and the relative He Etched Unit importance of aqueous to alternate geomorphic processes (Fig. 2). Description of Map Units HNch Channel Unit Acidalia Planitia 1 Plateau and Highland Materials (units Nm, Nh and HNt). The oldest material in the map area are remnant high-standing bedrock HNt Terra Unit promontories from the Ladon and Holden basin ring structures, Amazonis Chryse mapped as Early to mid-Noachian Mountainous unit (Nm) [10]. A large Planitia Nh Highland Unit outcrop of unit Nm occurs along the southern rim of Vinogradov Planitia crater near one intersection of the basin ring structures (Fig. 2). Arabia Nm Mountainous Unit The Highland unit (Nh) is likely late Noachian to early Hesperian Terra in age and occurs primarily in -30037 and -30032 (Figs. 1 and 2). Tharsis Margaritifer basin This unit is heavily cratered, differentially mantled, contains older Marg. valley networks, grabens, a few wrinkle ridges, and lacks evidence V. Marineris Terra of the phyllosilicate layer observed in the Terra unit (HNt) [11]. Unit Nh embays unit Nm and underlies all other units. Valles The Late Noachian to Marineris Ritchey Terra Early Hesperian Terra unit Noachis Morava Valles (HNt) is characterized by Sirenum Aonia Argyre Terra widespread, smooth to Terra rolling, cratered and variably dissected surfaces between 330E degraded impact craters [12]. 320E Fig. 3 340E In MTM -25037, unit HNt -15 Valles occurs beneath the continu- Marineris ous Holden ejecta (unit Hc2) and was modified by secondary craters related to -20037 Luba Ladon the impact. Unit HNt west of basin Uzboi Vallis consists of a laterally continuous ~10m Vinogradov thick Fe/Mg-smectite Figure 3. The Fe/Mg-smectite phyllosilicate-bearing layer phyllosilicate bearing layer (red -20 pixels) in Nirgal Vallis (see Fig. 2 for Gringauz Sigli located a few meters below Fig. 4 context). This layer is not seen east of

Valles the surface cap material and Uzboi Vallis. CRISM FRT 0000C875. Roddy M A R G A R I T I F E R stratigraphically above -25037 Eberswalde Al-phyllosilicates (Fig. 3) T E R R A [13-14]. Crater and Channel-Fill Units (units HNch, He, AHs and AHf). The Late Noachian to Early Hesperian Channel unit (NHch) are fluvially eroded surfaces related to the initial incision Holden ofChekalin Uzboi Vallis [12]. The floor of Nirgal Vallis is tentatively mapped as NHch but will likely change upon further investigation of its origin, age and relation to Uzboi. The floor of -25 basin Uzboi Vallis is mappedKasimov as Early to Late Hesperian Etched unit (He), characterized by erosionally resistant material exposed where aeolian deflation has selectively removed Holden light-toned layeredNoma material [12]. A similar etched unit exposing light-toned deposits occurs in crater Gringauz and possibly on the floor of the unnamed crater near 29°S, 326.6°E. Blunck The Late Hesperian to Early Amazonian Smooth unit (AHs) is a dark-toned deposit that is smooth at scales of 10s to 100s of m, typically bright in THEMIS day IR and has variable Ostrov thickness (Fig. 4). Channels and streamlined deposits are common close to HaleAHs crater south of the map area [9] (Fig. 1). Unit AHs occurs in pre-existing valleys, topographic -30037 -30032 depressions and craters and forms locally as lobes with distinct margins [9]. Some flow lobes are characterized by roughly parallel ridges oriented perpendicular to the presumed Surinda Valles direction of flow [8]. The deposit embays secondary cratersNh from Hale and thins with increasing distance from Hale [8]. We interpret these to be aqueous deposits that are related to and immediately post-date the formation of crater Hale. Uzboi Vallis The Late Hesperian to Early Amazonian Fan unit (AHf) are sloping or cone-shaped deposits that occur on the interior slopes of craters [12] (Figs. 5 and 6). Distributary Martynov paleo-channel networks are preserved in negative or (more commonly) positive relief. Cone-shaped deposits derived from deeply dissected impact crater walls coalesced into fans -30 Nirgal Vallis in craters Luba, Roddy (Fig. 5), Gringauz (Fig. 6) and Holden. Few boulders occur at HiRISE image resolution of ~1m and bright in THEMIS nighttime IR. We interpret AHf as alluvial deposits composed primarily of gravel and fines [e.g. 7, 15] emplaced by fluvial sediment transport with little to no evident contribution from debris flows. Zilair See J. A. Grant and S. A. Wilson Abstract 2538 Crater Units (units Nc1, Hc2 and Ac3). The Noachian Bond aged Crater 1 unit (Nc1) is characterized by rim remnants of heavily modified craters with little to no Elevation (m) N OBr iAgh tCer, cHra tIe rSed h ig h laTn d sE R R A (Unit Nh) preserved ejecta (e.g., craters Vinogradov, Roddy and Gringauz). The Late to Early Hesperian Crater 2 unit -4035 1545 Hale -35 (Hc2) are moderately degraded craters with relatively Figure 1. MOLA map with major place names showing global context continuous ejecta (e.g., craters Holden and Luba). Late Nh (above) of map quads (below). Map quads are located from 17.5°S-32.5°S, Hesperian to Late Amazonian Crater 3 Unit (Ac3) are 320°E-325°E and 27.5°S-32.5°S, 325°E -330°E (black boxes). Stars mark morphologically “fresh” craters with well-preserved craters hosting alluvial fans [e.g., 15-16]. Named craters include Luba, ejecta, little rim modification and (or) infilling. Roddy, Gringauz, Blunck and Martynov. MOLA over THEMIS day IR. [1] Grant, JA, 1987, NASA Tech. Memo. 89871, 1-268 [2] Grant, Surficial Deposits (units Mm and Ad). The Hesperian to Nh JA., TJ Parker, 2002, JGR, 107, doi:10.1029/2001JE001678 [3] AHs AHs Amazonian Mass Movement unit (Mm) is a single to References Parker, TJ, 1985, M.S. Thesis, Cal. State Univ. [4] Saunders SR, Bond 1979, USGS Map I-1144 [5] Irwin, RP, JA Grant, 2013, USGS Map I-3209 [6] Grant, J.A. et al., 2011, multi-lobed shaped deposit with distinct margins that Icarus, 212, doi:10.1016/j.icarus.2010.11. 024 [7] Grant, JA and SA Wilson (2011), GRL, 38, L08201, Figure 5. Unit AHf in Roddy (see Figure 6. Unit AHf in Gringauz occurs in craters Roddy and Blunck. This unit is doi:10.1029/2011GL046844. [8] Wilson SA et al., (2013), Abs. Ann. Mtg. Planet. Geol. Mappers, Fig. 2 for context). Fans are slightly terminate in scabby, light-toned Washington, DC. [9] Jones et al. (2011), Icarus, doi:10.1016/j.icarus.2010.10.014. [10] Shultz et al. concave, average 2O slope, ~40km deposit that may be a relict playa interpreted to be landslides possibly triggered by (1982), JGR, 87, 9803-9820. [11] Wilson SA et al., (2014), Abs. Ann. Mtg. Planet. Geol. Mappers, long [15]. Inverted channels on fan (see Fig. 2 for context). Fan nearby impacts. The Late Amazonian aged Dune unit Flagstaff, AZ. [12] Irwin, RP III and JA Grant (2013), USGS Map 3209 [13] Buczkowski, DL et al. CTX mosaic P21_009261_1472, P21_009050_1472, B22_018254_1472 (2010), LPSC, Abst. 1458 [14] Buczkowski, DL et al. (2013), LPSC, Abst. 2331 [15] Moore, JM and surface formed by differential surface has incised channels near (Ad) after [12] are concentrations of typically AD Moore (2005), JGR, 110, doi:10.1029/2005 JE002352. [16] Wilson et al. (2013), LPSC Abst. 2710. Figure 4. Hale deposits (AHs) in pre-existing topographic lows in the deflation, consistent with fine grains rim and inverted channels in the shed from the alcoves rather than distal fan that may have been dark-toned bedforms that are dark in THEMIS Noachian Highlands and Terra units (Nh and NHt) west of Bond (see the in situ breakdown of sediment. deposited into shallow water. nighttime IR data interpreted to be aeolian dunes. Smithsonian Institution, Fig. 2 for context). CTX mosaic over THEMIS daytime IR. North National Air and Space Museum CTX D03_028579_1572 and G19_02 CTX B18_016632_1 592 towards top. 5625_1582.