CONGLOMERATES IN GALE CRATER: PROVIDING INSIGHTS INTO THE HYDROLOGY OF ANCIENT RIVERS ON MARS

The Curiosity rover provided the first in situ evidence for past fluvial flows on Mars when it landed on fluvial conglomerates at Bradbury Landing, Gale crater. There, conglomerates occur as isolated blocks of cemented pebbles and sand with textures characteristic of fluvial deposits (e.g., rounded clasts, imbrication). By measuring grain size in these deposits and calculating their distributions, paleoflow properties were estimated. While these analyses are critical for constraining the paleohydrology and climate of early Mars, they only have been done for conglomerates at Bradbury Landing.

Our study builds upon previous work by performing grain size analyses of 12 conglomerates imaged by the ChemCam Remote Micro Imager (RMI) from sols 343−379 (-4500.84 to -4503.25 m in elevation). The RMI images were retrieved via the PDS Analyst’s Notebook and visualized using the ImageJ software. For each RMI, grains ≥2 mm were traced to calculate properties such as diameter and rounding. We also used a grid by point method to constrain the percentage of grains < 2mm. Matlab was used to calculate grain statistics, such as D50 (median), sorting, skewness, and kurtosis. For each rock, these metrics were placed into stratigraphic context by plotting them against elevation.

Preliminary results suggest that rocks in our study area have a D50 from 2.68−3.47 mm (very fine gravel), which is smaller than the D50 for Bradbury Landing rocks (4.5-8.5 mm). Maximum grain sizes range from 6.37−22.45 mm (fine to coarse gravel) and rocks are generally well to moderately well sorted. The consistency in D50 with elevation suggests that the typical energy of these ancient river flows in Gale was likely similar through time. Variations in grain size between elevations may suggest drier/colder (lower values) or wetter/warmer (higher values) periods in time. Thus, our results provide qualitative insights into the dynamics of past river flows on Mars and how they may have changed through time.