Planetary Geologic Mappers Meeting 2018 (LPI Contrib. No. 2066) 7030.pdf

ENIGMATIC SEDIMENTARY DEPOSITS WITHIN PARTIALLY EXHUMED IMPACT CRATERS IN THE AEOLIS DORSA REGION, : EVIDENCE OF PAST CRATER LAKES. S. E. Peel1 and D. M. Burr1, 1Department of Earth and Planetary Sciences, University of Tennessee, Knoxville ([email protected]).

Introduction: The Interpretation: paleo-fluvial deposits. (MFF) on Mars is an expansive sedimentary deposit of Concentric Ringed Unit (cr) – Layered with upper uncertain origin [e.g., 1-6, and citations therein] surface broken by concentric rings of irregularly to located west of and east of Crater. Within sinuously edged, pock-like depressions. Cliff-forming the westernmost extent of the MFF are a plethora of boundaries common. Interpretation: fine-grained sinuous ridges interpreted as inverted fluvial deposits deposits of lacustrine or aeolian origin. formed through the removal of previously overlying Crater Floor Unit (cf) – Largely smooth surface and adjacent material [e.g., 7-9]. These features are with many occurrences of linear and sinuous ridges spatially concentrated within the depression between and irregular high-standing features. Interpretation: the two high-standing plana (Aeolis and Zephyria Impact melt or fine-grained sedimentary deposits with Plana), a region called Aeolis Dorsa (Fig. 1). hydrothermally deposited minerals likely. As part of a larger mapping effort within this area High-standing Unit (h) – High-standing, semi- [10-11], we have mapped enigmatic sedimentary connected to disconnected mounds with serrated deposits found within partially exhumed impact craters appearance to edges. Upper surfaces often form (Fig. 1) using CTX [12] and HiRISE [13] images in amphitheater pattern of stepped rings. Interpretation: ArcGIS [14]. Here, we give brief descriptions (Fig. 2) lacustrine or aeolian deposits with fine layering and preliminary interpretations for these intracrater common. deposits, as well as possible correlative stratigraphy High-standing Ridged Terrain (hr) - High-standing (Fig. 3). with approximately uniform elevation throughout and cliff-forming boundaries. Upper surface has similarly striking ridges. Occurs over wide areas and as separate a ridges (mapped separately). Interpretation: delta Obock sedimentary fan and inverted fluvial features. Irregular Pocked Unit (ip) – Rough surface broken up by depressions of variable size. Irregular peaks and mesas that erode into large blocks with or without * cliff-forming edges common. Interpretation: fine- Neves * grained deposits of lacustrine or aeolian origin. Knobby Unit (k) – Preserved as approximately circular or elongate knobs, usually striking NW. Internal layering of coarse and fine materials common. Interpretation: cyclic origin likely, possibly within a lake. b Lineated Unit (l) – Arcuate to swirling lineations of Kalba light and dark materials. Alternates between protruding and recessive expressions over steep slopes. Interpretation: lacustrine or aeolian deposits with subsequent chemical alteration likely. Fig. 1: (a) Map area of [15] in MOLA topography Sinuous Unit (s) – Sinuous ridges that smoothly (area is ~500x500 km). Aeolis Dorsa is shown in transition or abruptly jump in elevation. Rarely occurs cooler colors. The five craters mapped in this project with branching planview. Interpretation: inverted are marked by arrows with their name (or * where no fluvial features. name was found) and numbered. (b) Image modified Sinuous Mesa Unit (sm) – High-standing with from [16] showing the MFF outlined in black and the irregular, discontinuous, and undulating surfaces. area of (a) outlined in white. Cuspate, cliff-forming edges common. Fine-grained material that erodes into blocks in some areas. Unit Descriptions and Interpretations: Interpretation: sediment transported and deposited by Branching Unit (b) – Fine-grained with surfaces wave action in standing water. Long troughs are that smoothly transition to different elevations over suggestive of ice-wedge marine scours. large areas, forming an overall branching appearance. Planetary

Fig. 2 (left column): Examples of each of the mapped intracrater units. The Geologic labels correspond with their descriptions and are used in Figure 3.

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Fig. 3: Possible correlative stratigraphy of the mapped intracrater units. The unit labels are those used in the unit descriptions and in Figure 2.

References: [1] Scott, D.H., Tanaka, K. L. (1986) USGS, IMAP 1802-A. [2] Greeley, R, Guest, J. (1987) USGS, IMAP 1802-B. [3] Watters et al. (2007) Science 318, 1125-1128. [4] Mandt et al. (2008) JGR Planets, 113, E12011. [5] Harrison et al. (2010) Icarus, 209, 405–415. [6] Kerber et al. (2011) Icarus 216, 212-220. [7] Burr, D. M. et al. (2012), JGR: Planets, 117.E3. [8] Lefort, A. et al. (2015), Geomorph. 240 121-136. [9] Jacobsen, R. E., Burr, D. M. (2015) LPSC 46, abs.1832. [10] Burr, D. M. et al. (2017) PGMM, abs.7010. [11] Burr, D. M. et al. (2016) PGMM, abs. 7013. [12] Malin, M.C. et al. (2007) JGR: Planets (1991-2012) 112(E5). [13] McEwen, A. S. et al. (2007) JGR: Planets, 112, E05S02. [14] ESRI (2011) ArcGIS Desktop: Release 10.1. Redlands, CA: Environmental Systems Research Institute. [15] Jacobsen, R. E., et al. (2018) this meeting, abs. 7014. [16] Kerber, L., Head, J. W. (2010) Icarus 206, 669-684.

7030 . pdf