Evolution of major sedimentary mounds on Mars: Buildup via anticompensational stacking modulated by climate change

Abstract

We present a new database of >300 layer orientations from sedimentary mounds on Mars (Mount Sharp/Aeolis Mons, plus Nia, Juventae, Ophir, Ceti, Melas, Coprates, and Ganges Mensae). Together, these mounds make up ~ ½ of the total volume of canyon/crater-hosted sedimentary mounds on Mars. The layer orientations, together with draped landslides, and draping of rocks over differentially eroded paleodomes, indicate that for the stratigraphically uppermost ~1 km, the mounds formed by the accretion of draping strata in a mound shape. The layer-orientation data further suggest that layers lower down in the stratigraphy also formed by the accretion of draping strata in a mound shape. The data are consistent with terrain-influenced wind erosion but inconsistent with tilting by flexure, differential compaction over basement, or viscoelastic rebound. We use a simple model of landscape evolution to show how the erosion and deposition of mound strata can be modulated by shifts in obliquity. The model is driven by multi-Gyr calculations of Mars' chaotic obliquity and a parameterization of terrain-influenced wind erosion that is derived from mesoscale modeling. The model predicts that Mars mound stratigraphy emerges from a drape-and-scrape cycle. Our results suggest that mound-spanning unconformities with kilometers of relief emerge as the result of chaotic obliquity shifts. Our results support the interpretation that Mars' rocks record intermittent liquid-water runoff during a ≫ 108 yr interval of sedimentary rock emplacement.