Synergistic Ground and Orbital Observations of Iron Oxides on Mt. Sharp and Vera Rubin Ridge.

A A Fraeman,M R Salvatore,R C Wiens,R V Morris,V K Fox,R E Arvidson,A R Vasavada,D F Wellington,B H N Horgan,J F Bell,P Pinet,S R Jacob,V Z Sun,M S Rice,J R Johnson

doi:10.1029/2019je006294

Abstract

Visible/short‐wave infrared spectral data from the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) show absorptions attributed to hematite at Vera Rubin ridge (VRR), a topographic feature on northwest Mt. Sharp. The goals of this study are to determine why absorptions caused by ferric iron are strongly visible from orbit at VRR and to improve interpretation of CRISM data throughout lower Mt. Sharp. These goals are achieved by analyzing coordinated CRISM and in situ spectral data along the Curiosity Mars rover's traverse. VRR bedrock within areas that have the deepest ferric absorptions in CRISM data also has the deepest ferric absorptions measured in situ. This suggests strong ferric absorptions are visible from orbit at VRR because of the unique spectral properties of VRR bedrock. Dust and mixing with basaltic sand additionally inhibit the ability to measure ferric absorptions in bedrock stratigraphically below VRR from orbit. There are two implications of these findings: (1) Ferric absorptions in CRISM data initially dismissed as noise could be real, and ferric phases are more widespread in lower Mt. Sharp than previously reported. (2) Patches with the deepest ferric absorptions in CRISM data are, like VRR, reflective of deeper absorptions in the bedrock. One model to explain this spectral variability is late‐stage diagenetic fluids that changed the grain size of ferric phases, deepening absorptions. Curiosity's experience highlights the strengths of using CRISM data for spectral absorptions and associated mineral detections and the caveats in using these data for geologic interpretations and strategic path planning tools.

Highlights

Vera Rubin ridge (VRR) is a topographic rise on the northwest flank of Mt
We calculated the spectral parameters that describe absorption features near 535 and 860 nm for all Chemistry and Camera (ChemCam) passive spectral targets acquired on sunlit bedrock surfaces and Mastcam Dust Removal Tool (DRT) surfaces in the Murray formation
Sharp. ChemCam passive spectra and Mastcam spectra associated with DRTed targets demonstrating the spectral variability of the Murray formation

Summary

Introduction

Vera Rubin ridge (VRR) is a topographic rise on the northwest flank of Mt. Sharp (formally named Aeolis Mons). Based on the putative CRISM hematite detection at VRR and lack of similar strong absorptions in strata immediately adjacent to the ridge, Fraeman et al (2013) hypothesized that VRR could be a unique hematite‐rich interval that marked a site of localized iron oxidation and potential past habitable environment. The MSL science team has defined two group‐level stratigraphic units within Mt. Sharp using a combination of orbital mapping and fine‐scale sedimentologic indicators documented by Curiosity's instruments. Sharp using a combination of orbital mapping and fine‐scale sedimentologic indicators documented by Curiosity's instruments These units are the Mt. Sharp group and the Siccar Point group (Banham et al, 2018; Fraeman et al, 2016; Grotzinger et al, 2015). The Sutton Island member is a heterolithic mudstone and sandstone

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