FIRST INSIGHTS ON DEPOSITIONAL ENVIRONMENTS RECORDED IN THE "CLAY-SULFATE" TRANSITION AT GALE CRATER
Résumé
Gale crater preserves a 5-km-thick sequence of stratified rocks, the lower-most section of which exhibits orbital spectra signatures of clay miner-als transitioning up to sulfates over several hundred me-ters of stratigraphy [1,2]. Understanding the reason for this wet-to-dry change recorded in the mineralogical signature is one of the primary objectives for the Curi-osity rover. The rover is currently positioned at the base of the Layered Sulfate unit (LSu) exposed over a thou-sand meters of elevation, which is characterized from orbit by its general-layered texture and spectral signa-tures of monohydrated and polyhydrated Mg-sulfates [1–3]. Most of the LSu is composed of subparallel beds that vary in albedo, texture, and thickness [4]. The lower ~150 m interval of the LSu is topped by a distinctive layer referred to as the "marker bed" (Figure 1).
Here we reconcile orbital data with new in situ anal-yses using MastCam and the ChemCam instrument’s Remote Micro-Imager (RMI) to provide an updated documentation of the LSu stratal components at large outcrop scales and at the highest available resolution. We then propose provisional models for the deposi-tional systems and their evolution in the sulfate unit, hy-pothesized to reflect overall a history of the diminishing availability of liquid water on Mars.
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