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50th Lunar and Planetary Science Conference 2019 (LPI Contrib. No. 2132) 2811.pdf

LANDSCAPE EVOLUTION COMPARISON BETWEEN , AND THE RIO CHAMA CANYON, NEW MEXICO, USA. J. M. Chesnutt1, K. W. Wegmann1, E. D. Szymanski2, P. K. Byrne1, and C. L. Kling1 1North Carolina State University, Department of Marine, Earth and Atmospheric Sciences, Raleigh, NC, United States, 2University of Michigan, Department of Earth and Environmental Sciences, Ann Arbor, MI, United States

Introduction and Background: Here we report on Rio Chama Canyon: The canyon of the Rio Chama initial findings of an Earth–Mars landscape evolution in north-central New Mexico is inset into the eastern- analog study of the Valles Marineris, Mars and Rio most portion of the Colorado Plateau as the river de- Chama Canyon, New Mexico. scends ~350 m off the plateau rim into the Rio Grande Rift. The Rio Chama has incised into the surrounding This research focuses on the escarpment–flank mass mesas. The dynamic landscape of the Rio Chama Can- wasting features and valley formation of both land- yon is an ideal area to study linkages between river in- forms. Notably, the northern wall of Valles Marineris cision, mass wasting and landscape evolution at the has retreated to approximately twice the extent as the physiographic transition from the Colorado Plateau to southern wall (Figure 1), and the southern wall of the the Rio Grande Rift. Similar linkages may have influ- Rio Chama canyon has eroded about three times the ex- enced the landscape evolution of Valles Marineris. tent of the northern wall (Figure 2). We explore the cause(s) of this differential erosion/formation. Methodology: Detailed field analysis and mapping of the Rio Chama Canyon was conducted in the summer of Valles Marineris: Valles Marineris is a 4,000 km- 2018 as part of a USGS-funded EdMap grant. Eight ter- long, 200 km-wide, and 11 km-deep trough that cuts race sites were sampled for radiocarbon and three sites along the Martian equator. There is no consensus on were sampled for optically stimulated luminescence how Valles Marineris originated. The dominant theories (OSL) geochronology to provide age controls on the late include trough formation through extensional tec- Quaternary incision history of the Rio Chama. Addi- tonism/geodynamic processes [1], progressive collapse tionally, four landslide and two slump block sites were into subsurface voids [2], vertical subsidence [3], vol- sampled for radiocarbon. By determining the age of canic rifting [4], or combinations of the above processes these terraces, landslides and slump blocks, we can chart the paleochannel of the Rio Chama and expose any [5]. Valles Marineris likely formed during the late Noa- spatial-temporal correlation to mass wasting phenom- chian to early period (~3.5 Gyr ago) and con- ena in the canyon. The analytical methodology for the tinued to evolve significantly through the Valles Marineris comparison utilizes available Mars im- (1.8 Gyr ago) [6]. agery and GIS techniques, primary via ArcMap™ and JMARS [10].

Figure 1. Valles Marineris MOLA Blended DEM Hillshade [7] . When measured against the medial axis of Valles - neris, the northern valley wall is more than twice the distance from that axis as the southern wall. Both walls contain nu- merous landslides [8]and the possible discovery mud volcanoes [9] hints that hydrologic process may have played an out- sized role in some aspect of Valles Marineris landscape evolution. 50th Lunar and Planetary Science Conference 2019 (LPI Contrib. No. 2132) 2811.pdf

Preliminary Results, Analysis, and Discussion: Our The north central wall of Valles Marineris contains the field mapping and analysis supported our hypothesis 800 km-long Candor and the 300 km-long that extensive tributary incision into the mesas compris- , whereas the -central wall contains ing the southern walls of the Rio Chama Canyon is the only the (350 km long). The northern likely mechanism driving wall retreat. Additionally, we chasmata also lie closer (200 km) to , found a regional ~10º southern dip which may contrib- the largest outflow channel on Mars, and thus it may ute to the extensive erosion of the southern valley wall. be that the proximity to an expansive ground water River terraces of the Rio Chama are also numer- source could have aided in the discordant erosion and ous, although initial results indicate that the path of the evolution between the north and south walls of this Rio Chama has not changed significantly through time system. The density of landslides, which is roughly since the late Pleistocene (c. 20 ka). A Rio Chama river equal on both the northern and southern flanks, alone terrace approximately ~200 m horizontally and ~20 m does not seem to explain why Valles Marineris (strath unconformity elevation) vertically from the cur- evolved discordantly. However, the volume of land- rent base level yielded a radiocarbon date of 19,996 ± 96 14C ypb. slides in the northern chasmata tend to be larger in size. Alternate explanations have been offered as to the plethora of landslides in Valles Marineris, namely impact-triggered slope failures [13], [14], [15] as well as a combination of weak material properties combined with high slope angles [16]. The role of water in molding the Rio Chama canyon is apparent, but the role hydrologic forces in the sculpting of Valles Marineris is contested [17], [18], [19]. If our GIS and imagery analysis of Valles Marineris uncovers any parallel hydrologically-driven geomorphological features similar to those we have documented in Rio Chama canyon, we may be able to discern causes of the discordant erosional patterns observed on either side of the medial valley axes at both study sites.

Figure 2. Lidar-derived hillshade of Rio Chama Canyon, New References: [1] Andrews-Hanna, J. C. (2012), JGR Mexico. When measured against the medial axis of the Can- Planets, 117, 6002. [2] Fueten, F. et al. (2017) JGR yon, the southern valley wall is more than three times the dis- Planets, 122, 11, 2223-2249. [3] McKenzie, D., and tance from the axis as the northern wall. As with Valles Mar- Nimmo F. (1999) Nature, 397, 231–233. [4] Mège, D. ineris, the area features numerous landslides. et al. (2003) JGR, 108, E5, 5044. [5] Lucchitta, B.K. et al. (1994), JGR Planets, 99, 3783-3798. [6] Anderson, Large-scale landslide activity on the walls of the Rio R.C. et al. (2001), JGR, 106, 20563-20585. [7] Fer- Chama Canyon represents the hillslope response to on- gason, R.L. et al. (2018) Astrogeology PDS Annex, going river incision and valley expansion. As accom- USGS. [8] Crosta, G.B. et al. (2018) ESS, 5, no. 4, 89- modation space is created by an upstream-propagating 119. [9] Kumar, P.S. et al. (2019) EPSL, 505, 51-64. wave of river incision, the adjacent and coupled [10] Christensen, P.R. et al. (2009) JMARS. [11] hillslope geomorphic system responds in kind via grav- Gallen, S.F. et al. (2011) ESPL, 36, 1254-1267. [12] ity-driven mass-wasting [11] that is also likely modu- Johnson, B.G. et al. (2017) ESPL, 42, 2223-2239. [13] lated by climate-driven variations in annual to decadal Tsige, M. et al. (2016), EMP, 118, 1, 15. [14] Crosta, amounts of precipitation [12]. Interestingly, in at least G.B. et al. (2018) ESS, 5, 4, 89-119. [15] Kumar, P.S. et four areas, Rio Chama Canyon walls have failed as co- al. (2019) EPSL, 505, 51-64. [16], [17] Bigot-Cormier, herent Jurassic Entrada Formation sandstone blocks. F., and Montgomery, D.R. (2007) EPSL, 260, 1–2, 179- One of these intact Entrada blocks is nearly 5 km from 186. [18] Soukhovitskaya, V., and Manga, M. (2006) the present valley wall, highlighting the dramatic valley Icarus, 180, 2, 348-352. [19] Watkins, J.A. et al. (2015), wall retreat on the southern flank of the Rio Chama Can- Geology (Boulder), 43, no. 2, 107-110.

yon. We wish to thank the USGS EdMap Program for fund- ing this research (Grant # G18AC00145) and the New Mexico Bureau of Geology and Mineral Resources for their assistance.