201-9 Deep Chemical Weathering on Ancient Mars Landscapes Driven by Erosional and Climatic Patterns

Session: The G.K. Gilbert Award Session: Geology of Mars, Mercury, Asteroids, and Icy Satellites in Honor of Scott Murchie

Presenting Author:

Timothy Goudge

Authors:

Moore, Rhianna D¹, Goudge, Timothy A², Klidaras, Athanasios³, Horgan, Briony H N⁴, Broz, Adrian⁵, Wordsworth, Robin⁶, Farrand, William H⁷

(1) Department of Earth and Planetary Sciences, The University of Texas at Austin, Austin, TX, USA, (2) Department of Earth and Planetary Sciences, The University of Texas at Austin, Austin, TX, USA, (3) Department of Earth, Atmospheric, and Planetary Sciences, Purdue University, West Lafayette, IN, USA, (4) Department of Earth, Atmospheric, and Planetary Sciences, Purdue University, West Lafayette, IN, USA, (5) Department of Earth, Atmospheric, and Planetary Sciences, Purdue University, West Lafayette, IN, USA, (6) Department of Earth and Planetary Sciences, Harvard University, Cambridge, MA, USA; School of Engineering and Applied Sciences, Harvard University, Cambridge, MA, USA, (7) Space Science Institute, Boulder, CO, USA,

Abstract:

Past workers focused on characterizing the surface of Mars have used orbital spectrometers (such as CRISM) to identify thick sequences of clay mineral-bearing outcrops globally, which have Al-bearing clay minerals stratigraphically above Fe/Mg-bearing clay minerals. These clay sequences (CSs) are thought to have formed through top-down leaching early in Mars’s geological history (>3.7 Ga) under wetter, and potentially warmer, conditions than at present. Such weathering sequence deposits on Earth require specific landscape and climatic conditions to develop, including persistently wet climates, low relief/slope, and tectonically stable landscapes. However, it remains unclear how Mars’s local and global topography and past climate activity influenced surface weathering and CS formation, and what controlled the locations of observed CSs.

Here we present observations to address this knowledge gap by assessing the spatial and topographic properties of a globally distributed dataset of 112 CS locations, which we compare with the same properties of ‘typical’ early Mars terrain and other exposures of similar clay mineralogies. Contrary to expectations from weathering sequences on Earth, our results show that CSs tend to occur in regions of relatively high relief and slope, which we interpret as an observational bias – CSs are easiest to identify via CRISM in regions with significant vertically exposed outcrops with low dust cover. We also find that CSs tend to cluster around 20–30° N and S, which is suggestive of a climatic influence on CS development. Finally, we find that CSs tend to occur in regions with minimal valley network dissection and close to standing bodies of water, which we hypothesize were regions of early Mars where chemical weathering was favored over physical erosion, similar to where weathering sequences develop on Earth. We hypothesize that the development of thick CSs through enhanced chemical weathering on the tectonically stable surface of Mars may have led to an imbalanced weathering–climate feedback compared with Earth due to the lack of unweathered rock exposed through steady uplift. Our results also support the hypothesis that the sequestration of water and cations within clay minerals in the early martian crust may have inhibited hydrological activity, and potentially carbonate mineral formation, over time.

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

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