Hydrogen Variability in the Murray Formation, Gale Crater, Mars

Area of Science:

• Planetary Science
• Astrogeology
• Geochemistry

Background:

• The Mars Science Laboratory (MSL) Curiosity rover is investigating the Murray formation in Gale crater, a ~350m thick sequence of sedimentary rocks.
• These strata represent ancient fluvial deltaic and lake deposits, offering insights into Mars's past aqueous environments.
• Understanding hydrogen content in bedrock is crucial for reconstructing water history.

Purpose of the Study:

• To analyze hydrogen (H) content in Murray formation bedrock using millimeter-scale ChemCam laser-induced breakdown spectroscopy (LIBS) data.
• To correlate hydrogen abundance with specific geological units and chemical compositions.
• To infer the history of water-rock interactions within Gale crater.

Main Methods:

• Analysis of over 4,500 bedrock points in the Murray formation using ChemCam LIBS.
• Utilized recent laboratory calibrations for H measurements.
• Compared LIBS H measurements with data from Dynamic Albedo of Neutrons (DAN) and Sample Analysis at Mars (SAM) instruments.

Main Results:

• Murray formation bedrock shows an interquartile range of 2.3-3.1 wt.% H2O, consistent with other MSL instruments.
• Specific stratigraphic intervals exhibit significantly higher H targets (6-18 wt.% H2O), associated with opal, hydrated sulfates (Mg, Ca), Mn-rich units, and iron oxyhydroxides.
• Higher hydrogen concentrations correlate with Fe, Ca, Mg, Si, and Mn, and are also observed in coarser-grained rocks, independent of chemical variations.

Conclusions:

• Variability in rock hydrogen content signifies a complex history of water-rock interaction in Gale crater.
• Evidence suggests changes in lake water chemistry during Murray formation deposition.
• Multiple subsequent groundwater episodes likely influenced the observed hydrogen distribution.