Alternating wet and dry depositional environments recorded in the stratigraphy of Mount Sharp at Gale crater, Mars

W Rapin,L.A Edgar,L Le Deit,B.L Ehlmann,G Dromart,N Mangold,O Gasnault,R.B Anderson,V Fox,S Le Mouélic,R.C Wiens,S Maurice,K Herkenhoff,J.L Dickson,D Rubin

doi:10.1130/g48519.1

Abstract

AbstractThe Curiosity rover is exploring Hesperian-aged stratigraphy in Gale crater, Mars, where a transition from clay-bearing units to a layered sulfate-bearing unit has been interpreted to represent a major environmental transition of unknown character. We present the first description of key facies in the sulfate-bearing unit, recently observed in the distance by the rover, and propose a model for changes in depositional environments. Our results indicate a transition from lacustrine mudstones into thick aeolian deposits, topped by a major deflation surface, above which strata show architectures likely diagnostic of a subaqueous environment. This model offers a reference example of a depositional sequence for layered sulfate-bearing strata, which have been identified from orbit in other locations globally. It differs from the idea of a monotonic Hesperian climate change into long-term aridity on Mars and instead implies a period characterized by multiple transitions between sustained drier and wetter climates.

Highlights

Gale crater on Mars, currently beingexplored by the Mars Science Laboratory (MSL) Curiosity rover, belongs to a family of impact craters referred to as “overfilled” (Grotzinger and Milliken, 2012; Bennett and Bell, 2016) with kilometer-thick exposures of layered fill approaching or even exceeding the crater rim elevation
Orbital High Resolution Imaging Science Experiment (HiRISE, aboard Mars Reconnaissance Orbiter) images showed that the layered sulfate-bearing unit (LSu) is composed of subparallel strata that vary in albedo, surface texture, and thickness from decameter to meter scale (Stack et al, 2013)
We report the first ground-based rover observations of bedding structures, textures, and stratigraphic architectures throughout the LSu using the Remote Micro-Imager (RMI) of the ChemCam instrument (Le Mouélic et al, 2015), the first ground-based images resolving bedding structures throughout the LSu

Summary

Introduction

Gale crater on Mars, currently beingexplored by the Mars Science Laboratory (MSL) Curiosity rover, belongs to a family of impact craters referred to as “overfilled” (Grotzinger and Milliken, 2012; Bennett and Bell, 2016) with kilometer-thick exposures of layered fill approaching or even exceeding the crater rim elevation. The rover has analyzed the claybearing lacustrine deposits of the Murray formation at the base of Mount Sharp, and is currently just below the thicker interval referred to as the layered sulfate-bearing unit (LSu) (Fraeman et al, 2016; Fig. 1). Orbital High Resolution Imaging Science Experiment (HiRISE, aboard Mars Reconnaissance Orbiter) images showed that the LSu is composed of subparallel strata that vary in albedo, surface texture, and thickness from decameter to meter scale (Stack et al, 2013).

Results

Conclusion