A short story of some ILD in Coprates Chasma



Frank Fueten, Laetitia Ledeit, Jessica Flahaut, Robert Stesky, Ernst Hauber

Located on the flank of the Tharsis region, Valles Marineris is a 4000 km long linked system of troughs. Coprates Chasma is one of the canyons of the Valles Marineris system, which is thought to have formed by faulting during extension. Located along the southern boundary of Coprates area is and area of interest because it contains several ILDs.

Location within VM

The southern boundary of the study area is formed by a plateau ridge with an elevation of approximately 3700m. Located approximately 25km north of the plateau ridge is a lower ridge of wall rocks, which decreases in elevation from approximately -700 m in the west to -3200 m in the east. Only at the western end is this ridge connected to the southern plateau by a series of wall-rock outcroppings. Wall-rock geometry has thus created a basin-like structure with maximum dimension of about 40 km by 25 km. The flat floor of this basin slopes from west to east, descending from an elevation of approximately -1300 m to -3000 m. At the eastern end, a gap in the northern wall rock ridge forms the geometry of an outlet to the basin into Coprates Chasma proper, which has elevations of approximately -5500m.

Location of 3 ILDs

Located near the southern wall are three prominent ILDs (here designated East, Central and West). Each is loosely confined between two wall rock spurs; none extend significantly beyond the extents of their confining spurs. In each deposit, the northern erosional edge displays well defined layering. Their presumed contact with the southern wall rock is covered by surficial deposits. Overall, layering in each deposit dips gently toward the north. The deposits are also associated with sulfates.

Large #D setting CTX

The deposit with the largest relief is the East IlD which is nestled between two wall rock ridges. The layers at the base of the deposit (yellow arrows) appear to follow the slope of the adjacent older wall rock (white arrows). This indicates to us that the deposit is older than the wall rock and that the material making up the deposit was laid down on pre-existing wall rock.

east ILD 3D

At the northern edge of the deposit, the thickness of the layered material is more than 600m (the blue lines represent elevation contours). We are able to measure the three dimensional orientations of the layers (white symbols) and find that they become shallower near the top of the deposit. This is what would be expected if a sedimentary deposit gradually fills a sloping floor. Near the base of the deposit layers will follow the slope of the substrate, as the sedimentary package gets thicker, the layers become more horizontal.

east ILD

In 3D the layering is clearly visible.

east ILD

This deposit as well as the two adjacent ones is currently the focus of a study that aims to understand their formation and subsequent history. Placing constraints on the geological history of deposits such as these will provide some insights into the history of Mars as a whole.