Overview of the composition of sedimentary rocks along the Curiosity rover traverse
Thursday, 18 December 2014: 10:50 AM
The Curiosity rover has encountered a variety of sedimentary rocks which overall have displayed significant variations in both texture and composition. Sandstones and mudstones, interpreted as having been deposited in a fluvio-lacustrine environment, were observed at Yellowknife Bay, a location identified from orbital images as of significant interest. The fluvial and lacustrine sediments at Yellowknife Bay have a basaltic composition, with main variations only related to diagenetic features including calcium sulfate veins and nodules, and raised ridges with enriched Mg proportion. Conglomerates, interpreted as fluvial in origin, were observed in the initial phase of the mission and later along the traverse from Yellowknife Bay to Mount Sharp. Conglomerates contain granules and clasts with a strong diversity in albedo and textures indicating multiple sources on the Gale crater rims. This includes identification of minerals such as feldspars. Assuming the conglomerates are a mechanically altered product of crustal rocks with relatively little aqueous alteration, the average composition of conglomerates can be considered as a proxy for the source rock composition. This average composition displays a more felsic composition than the Martian average crust as defined by meteorites and orbital data implying that the Gale crater rim is enriched in felsic rocks. More layered sandstones have been observed in the second terrestrial year of investigation in the outcrops named Cooperstown, Kylie and Kimberley, located unconformably over the conglomerates. They have compositions that are distinct from the Yellowknife Bay sandstones with especially enhanced K proportion. The three groups of sediments have been interpreted to be dominated by fluvial transport across Gale crater. They suggest distinct source rocks, and/or a distinct diagenetic history that needs to be considered in the broad context of Gale crater’s evolution.