Layered deposits of the eastern Valles Marineris and chaotic terrains on Mars

Kurzfassung

Light-toned and layered deposits (LDs) are present throughout the whole Valles Marineris and adjacent chaotic terrains. They are supposed to be of sedimentary [1,2,3] or volcanic origin [4]. Using high-resolution image and elevation data, we study their morphology, elevation, thickness, layer geometry, and consolidation in order to ascertain how they formed. LDs show differing morphologies. There are light-toned mounds with a flat top and steep slopes, flow-like structures where light-toned material flows around the chaotic-terrain material as well as terrace-like structures and razorblade-shaped morphologies that show massive cap rocks at their top and layering in lower parts. Often, there is a diffuse contact between LDs and chaotic terrain due to dust coverage. Many of the LDs exhibit yardangs, suggesting weakly consolidated and fine-grained material shaped by wind erosion. Wind activity is also indicated by dunes that occur in depressions (e.g., fractures) that are cut into the LD surfaces. Debris fans and a general lack of boulders at their base may indicate loose to partly consolidated sedimentary material. This is also confirmed by TES-derived thermal-inertia values of ~ 300 SI indicating rock materials [7]. Elevation data show that LDs are located in depressions at different elevations but far beneath the surrounding plateau rims (1000-4000 m in the chasmata, 200-1500 m in the chaotic terrains). LDs are superimposed on chaotic-terrain material and are therefore younger. Strike and dip measurements point towards sub-horizontal layering (in the range of lower than 10°) and NS- to NNE-SSW-strike for Iani Chaos. LD thicknesses vary in the range of 200-4000 m, assuming ILDs have horizontal to sub-horizontal stratification (Fig. 1.1, 1.2). When looking at higher-resolution MOC images, deposits show varying surfaces (rough, fractured, grooved, cap rock). Different surfaces textures may be due to differences in consolidation and/or wind erosion; the mineralogical composition is however comparable. LDs are closely connected to sulphate- [5] and hematite rich materials [6]. A topographic trend is observed as some LDs show surfaces that are restricted to chaotic terrains and other to chasmata. References: [1] Peterson, C. (1981), Proc. Lunar Planet. Sci. Conf., 11th, 1459-1471. [2] Nedell et al. (1987), Icarus, 70, 409-441. [3] Malin M. C., and K. S. Edgett (2000), Science, 290, 1927-1937. [4] Chapman M. G. (2002), Geol. Soc. Spec. Publ., 202, 273-303. [5] Gendrin A. et al. (2005), Science, 307, 587-1591. [6] Glotch T.D., and P.R. Christensen (2005), JGR, 110, doi:10.1029/2004JE002389. [7] Putzig et al. (2005), Icarus, 173, 325-341.