Mars Sedimentary Geology: Key Concepts and Outstanding Questions

Abstract

Processes that operate at planetary surfaces have the
\npotential to record a history of planetary evolution in the
\nform of sedimentary rocks. This is important because our
\nexperience on Earth shows that sediments and sedimentary
\nrocks are the dominant archive of high-resolution proxies of
\npresent and past tectonic, climatic, and biological processes.
\nOur understanding of the evolution of Earth’s very ancient
\nclimate and paleobiological records derives from detailed
\nexamination of the mineralogical, textural, and geochemical
\nsignatures preserved in the sedimentary rock record.
\nSedimentary rocks were first recognized on Mars less than a decade ago (Malin and Edgett, 2000). Recent interpretations of data collected by the Mars Express and Mars Reconnaissance Orbiter spacecraft have confirmed the surprising abundance of these sedimentary rocks, the past role of water on the martian surface, and the similarity—in some cases—to sedimentary rocks formed on Earth. Thick sulfaterich deposits invite comparison to terrestrial evaporites (Grotzinger et al., 2005). In other cases, clay-rich strata are interpreted as the terminal deposits of source-to-sink systems with well-developed fluvial networks in the upper reaches of watersheds that date back to a much wetter period in Mars’ earliest history (Ehlmann et al., 2008; Metz et al., 2009). However, these Earth-like depositional systems contrast with other deposits that may be unique in the Solar System: for example, vast terrains as large as Earth’s continents covered by thick veneers of strata that may derive entirely from settling out of wind-transported dust (Bridges et al., 2010). Whatever their origin, it is now clear that the sedimentary rocks of Mars represent a new frontier for research. Mars science is in its golden era of exploration—the past decade of orbiter and landed missions has produced an extraordinary amount of new data relevant to the analysis of sediments and sedimentary rocks, and robust international programs exist for future missions. To help stimulate discussion of these data, the First International Conference on Mars Sedimentology and Stratigraphy was convened in El
\nPaso, Texas, in April 2010. The contents of this white paper
\nrepresent the most significant findings of the conference,
\nwith additional information provided by the coauthors, and
\nfocus on seven key questions for future investigation by the
\nsedimentary geology community.