Structural analysis of interior layered deposits in Northern Coprates Chasma, Mars

Interior layered deposits within an embayment on the northern wall of Coprates Chasma in the Valles Marineris, Mars, are studied using HRSC, CTX, HiRISE and CRISM data. The layered material outcrops in three separate locations. The largest layered deposit within the embayment, a free standing central mound, has an approximate stratigraphic thickness of 2 km. Dip directions change along the central axis of this mound, which is also a zone of deformation. The surface texture of layers within this mound displays polygonal structures at HiRISE scale. By contrast, the western layered deposit abuts directly against the chasm wall and appears to have a relatively uneroded depositional surface approximately 600 m below the current top elevation of the central mound. A basement ridge, exposed by a landslide scar near the eastern portion of the area, is covered with layered material and shows downward displacement. We suggest that the entire embayment originated as a small ancestral basin. The displaced basement ridge is evidence of the early basin collapse. The central mound was most likely deposited on a wall rock spur. Deposition did not fill the basin evenly. The detection of hydrated sulfates attests to alteration or deposition by liquid water. Following an erosion event, which coincided with or postdated Valles Marineris formation, thin mesa-forming materials covered most of the area.