Overview of the diagenetic features analyzed by ChemCam onboard Curiosity
Thursday, 17 December 2015
Poster Hall (Moscone South)
The Curiosity rover has encountered a variety of sedimentary rocks with significant variations in both texture and composition. Most of the sandstones and mudstones are interpreted as having been deposited in a fluvio-lacustrine environment, as analyzed in details in the waypoints named Yellowknife Bay, Kimberley and Pahrump. All of these sediments have been crossed by diagenetic features of different composition. Light-toned Ca-sulfate veins observed initially at Yellowknife Bay were observed along the traverse, and in high density at the Pahrump location. As they appear in all sediments and show straight fractures, they correspond to late-stage diagenetic features, due to fluid circulation, with fractures probably due to hydraulic stress at depth. In contrast to light-toned veins, earlier-stage diagenetic features have shown variable composition in the three areas. At Yellowknife Bay, raised ridges display enriched Mg proportion, probably linked to Mg-clay whereas outcrops at Kimberley display fracture fills enriched in Mn and Zn. Pahrump displays a large variety of diagenetic features distinct from these previous examples. Mg-enriched concretions contain S and abundant Ni. Mg enrichments have also been observed in resistant zones along fractures and in resistant layers. Locally concretions also display high Fe, S-bearing material interpreted as Fe-sulfate, probably jarosite. A special location named Garden City at the top of the Parhump sequence displays a complex area with light-toned veins surrounded by darker veins. The latter display strong Ca signatures correlated with F, interpreted as fluorite. No C or S emissions were observed that could alternatively explain the high Ca abundance by carbonates or sulfates. The dark tone of the F-bearing minerals may be due to the presence of Fe. These specific dark veins could derive from the leaching of F-apatite, a mineral that has been observed both in the sandstones and in some of the igneous clasts analyzed by ChemCam during the traverse. Altogether, these diagenetic features show that aqueous sediments were modified by a series of distinct diagenetic episodes, with strong local variability.