Precipitation Driven Pedogenic Weathering of Volcaniclastics on Early Mars

Abstract

Compositional stratigraphy, generally composed of Al rich clay minerals overlying Fe/Mg rich clay minerals, is observed in many locations on Mars. Here we describe the occurrence of such mineralogical stratigraphy in settings where the protoliths are almost certainly pyroclastic materials. One such example includes altered rocks high on the summit and flanks of explosive volcanoes in Thaumasia Planum. These clay bearing deposits are most consistent with precipitation driven weathering of ash deposits. Considering explosive volcanism was pervasive in the Noachian, the early sedimentary record of Mars in some locations is likely dominated by glassy, fragmented, porous, chemically reactive materials with highly specific surface area. These pyroclastic deposits were potentially a critical geological component linking clay minerals to elements of Mars' climate, weathering, and sedimentary puzzle.