Source‐to‐Sink Terrestrial Analogs for the Paleoenvironment of Gale Crater, Mars

Abstract

Preserved in the sedimentary rock record of Mars is an ancient (>3 Ga) history of fluvial activity that persisted long enough to create landforms and layered sequences that suggest both subaerial and subaqueous deposition (Malin & Edgett, 2000, 2003). Geomorphological features observed from orbit provide evidence for extensive fluviolacustrine processes, as evidenced by channelized flow features and delta-like distributary fans (Hynek et al., 2010; Milton, 1973; Sharp & Malin, 1975). On the ground, sedimentological observations by the Curiosity rover include conglomerates, sandstones, and mudstones interpreted to have fluviolacustrine origins (e.g., Grotzinger et al., 2014, 2015). Geochemical and mineralogical investigations of these fluviolacustrine sedimentary rocks have revealed sediment interaction with surface and ground waters in

Intense subaerial weathering of eolian sediments in Gale crater, Mars

“…These clay mineral–bearing sandstones could alternatively represent chemically weathered eolian deposits after their emplacement in a subaerial environment. The chemical index of alteration (CIA) [CIA = 100 * Al 2 O 3 /(Al 2 O 3 + CaO + Na 2 O + K 2 O)] is discussed and applied to be a first-order estimate for weathering intensity on Mars ( 18 – 22 ). Quantitative mineralogical abundances are used to exclude the Ca, Na, and K contributed by salts ( 21 , 23 ) when x-ray diffraction (XRD) data are available.…”

“…is discussed and applied to be a first-order estimate for weathering intensity on Mars (18)(19)(20)(21)(22). Quantitative mineralogical abundances are used to exclude the Ca, Na, and K contributed by salts (21,23) when x-ray diffraction (XRD) data are available.…”

Sedimentological and Geochemical Perspectives on a Marginal Lake Environment Recorded in the Hartmann's Valley and Karasburg Members of the Murray Formation, Gale Crater, Mars

“…While secondary Ca‐sulfates are common throughout Gale crater stratigraphy (e.g., Kronyak et al., 2019; Sun et al., 2019), some studies (McLennan et al., 2014; Siebach et al., 2017) do not remove Ca associated with sulfate and interpret geochemical trends with this consideration. Other studies filter out geochemical targets based on identification of diagenetic features in images (Mangold et al., 2019) or choose representative end‐members to evaluate weathering extent (Thorpe et al., 2020). When no correction is made, the value of CaO* is equal to the measured wt% of CaO (Equation ): $$$\mathrm{U}\mathrm{n}\mathrm{c}\mathrm{o}\mathrm{r}\mathrm{r}\mathrm{e}\mathrm{c}\mathrm{t}\mathrm{e}\mathrm{d}:\,{\mathrm{C}\mathrm{a}\mathrm{O}}^{\ast }={\mathrm{C}\mathrm{a}\mathrm{O}}_{(\mathrm{T})}$$$ …”

“…In each ternary diagram, weathering, sorting, and diagenesis in terrestrial settings generally follow predicted geochemical pathways (e.g., Babechuk et al., 2014; Fedo et al., 1995; Fedo et al., 2015; Nesbitt & Young, 1984). Although geochemical trends within sedimentary systems on Mars reveal compositional differences compared with terrestrial systems (Thorpe et al., 2020), predicted pathways nevertheless form the basis from which to evaluate sediment on Mars. Typical pathways emanate from a starting point, the unaltered source (triangle a , Figures 3a–3c), which may be a composite of several source rock compositions (e.g., different lava flows).…”

“…Linear trends produced from chemical weathering of source bedrock (arrow 1, Figure 3a; Nesbitt & Wilson, 1992; Thorpe et al., 2020) can be used as a means to indirectly estimate the original source composition. In the A‐CN‐K ternary diagram, the lowermost point along the chemical weathering path plots at low values of CIA (the vertical axis of the ternary diagram) and typically represents a measured unaltered source rock composition (triangle a , Figure 3a).…”