Geological analysis of Interior Layered Deposits occurring in chaotic terrains from Ganges Chasma to Iani Chaos on Mars

Abstract

In the chaotic terrains we investigate the structure of the Interior Layered Deposits (ILDs) regarding their elevation, stratigraphic position, thickness and geometry using HRSC- and high resolution MOC-data. ILDs appear at different elevations. The highest range of elevation is reached in Capri Eos Chasmata from at least -6000 m up to -2000 m, the lowest in Iani Chaos from -3800 m to -3000 m. The ILDs are variable in character. In Eos and Capri Chasmata, large complexes with planimetric forms and rugged surfaces are exposed, mostly superposed by thin smooth dust layers. The ILDs of Gangis Chasma and the ones in chaotic terrains sometimes show light and dark layering. Most of them are eroded into yardangs with rugged surfaces, steep slopes, slump structures, fractures, and fine layering in the lower parts changing into massive material in the upper parts. Debris fans exist on nearly every slope. In Aram and Aureum Chaos plate-like ILDs with smooth to coarse surfaces are detected, the layering seems to be horizontal to subhorizontal. In Aurorae Chaos some ILDs show fan-like morphologies with heavily fractured and rugged surfaces indicating flow directions from the north (in contrast to the indicated flow direction in Juventae Chasma). Flow-like structures are also observed in Iani Chaos were the ILDs embay mounds of chaotic terrain. The ILDs show a young erosional age (hardly cratered), superimpose the chaotic terrains and their elevation never exceeds the height of the surrounding level of the canyon rims. Debris fans and a lack of boulders at the base of the ILDs may point to loose to partly consolidated sedimentary rocks. The structure of the layering is analysed by using a DTM derived from HRSC stereo-data to get information about the internal layer geometry in order to discriminate between hypotheses concerning their origin.