THE CURIOSITY ROVER IS EXPLORING A KEY SULFATE-BEARING ORBITAL FACIES
Résumé
Sulfate salts deposited in sedimentary basins are major geochemical markers of paleoclimate, source rocks, and dissolved gases and ions [1]. On Mars, prominent thick-layered sulfate-bearing deposits are observed at a number of late Noachian to late Hesperian locations (~3.5 Ga) [2]. Their apparent absence in older strata has led to the hypothesis that they represent the diminishing availability of liquid water on Mars [3]. In fact, a global survey of layered terrains provides a grouping of a few orbital facies, including the Laterally Continuous Sulfates (LCS) [4] a key facies of unknown origin within the Hesperian global hydrological change.
Until now, major sulfate-bearing strata documented by rover observations have been limited to the Burns fm. in Meridiani Planum, dominated by large aeolian cross-beds made of a sulfate-silicate assemblage with detrital grains, cements and later stage diagenetic features [5]. In Gale crater, the Curiosity rover is now set to explore the Layered Sulfate-bearing unit (LSu), which is a hundreds of meters thick package of LCS orbital facies within the Mt Sharp group (Fig. 1). The LSu has been mapped regionally from orbit and shows signatures of diverse poly- and monohydrated sulfate minerals and interfingering with clay-bearing strata [6].
The origin of sulfates in such strata remains unknown and the rover provides an opportunity to test formation models [7,8]. In particular, rover investigations can test whether processes are similar to the Burns fm., or distinct such as a form of primary evaporites, syndiagenetic or later stage diagenetic precipitations with different aqueous conditions.
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