Topographic, spectral and thermal inertia analysis of interior layered deposits in Iani Chaos, Mars

E Sefton-Nash,D.C Catling,S.E Wood,P.M Grindrod,N.A Teanby

doi:10.1016/j.icarus.2012.06.036

Abstract

We present an analysis of Interior Layered Deposits (ILDs) in Iani Chaos using visible, infrared, hyperspectral and topographic datasets acquired by instruments aboard NASA’s Mars Global Surveyor, Mars Odyssey, Mars Reconnaissance Orbiter and ESA’s Mars Express spacecraft. We focus on four main regions where ILDs outcrop in Iani Chaos. Deposits span a ∼2km range of elevations and exhibit moderate to high albedos, layering at sub-decameter scales, thermal inertias of 300–800Jm−2K−1s−1/2 and a range of surface textures. Thermal inertia calculations use slope and azimuth corrections from High Resolution Stereo Camera (HRSC) topography. Spectral features in hyperspectral data acquired by NASA’s Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) suggest that gypsum (CaSO4·2H2O) and kieserite (MgSO4·H2O) are present in most deposits. We report absorptions typically exhibited by alunite (KAl3(SO4)2(OH)6) and jarosite KFe33+(OH)6(SO4)2 as well as a number of features that may be attributable to a wide range of mono- and polyhydrated sulphates and hydroxyl-sulphates bearing a number of cations, including Mg2+, Fe2+, Fe3+ and Ca2+. Spectral features similar to those of ammonium sulphates may also be present.Analysis of a HiRISE stereo DEM shows planar layering in some ILDs, favouring a sedimentary deposition origin. Stratigraphic mapping of hydration and sulphate spectral features in flat ILDs in central Iani Chaos suggest that specific elevation intervals in the stratigraphic column were subject to different levels of hydration, perhaps during episodes of water table elevation. This is consistent with formation models for ILDs and hydrological modelling. Geomorphic characteristics of deposits in northern and southern Iani Chaos suggest their relatively recent exhumation and significant erosion by aeolian processes. We conclude that any formation theory for ILDs in Iani Chaos should support mechanisms for different hydration states at different stratigraphic elevations and subsequent significant aeolian erosion, burial and re-exposure.

Highlights

The martian circum-Chryse outflow channel systems appear to be some of the most fluvially altered terrains on the planet
We address issues pertaining to the validity of detected absorptions, which may be affected when characteristic spectral features are altered by prolonged exposure to martian surface conditions (Cloutis et al, 2008; Dalton et al, 2011)
Through analysis of CRISM data in Iani Chaos we find diagnostic absorptions for gypsum and kieserite, several sets of features that could be indicative of alunite and jarosite and a range of weak absorptions possibly associated with the presence of polyhydrated sulphates

Summary

Introduction

The martian circum-Chryse outflow channel systems appear to be some of the most fluvially altered terrains on the planet. They are generally sourced by chaotic terrains, which comprise fractured regions, jumbled blocks, mesas separated by channels and low-elevation plains scattered with debris (Sharp, 1973). Areas of chaotic terrain towards the eastern end of the Valles Marineris system are thought to show a diverse, multi-episodic outflow history (Warner et al, 2009; Carr and Head, 2010). The cause of the outflow process (generally considered to be a large release of water causing subsidence, collapse and, the formation of chaotic terrain) is still poorly constrained.

Methods

Discussion

Conclusion