Chemical weathering over hundreds of millions of years of greenhouse conditions on Mars

Abstract

Chemical weathering profiles on Mars which consist of an upper Al clay-rich, Fe-poor layer and lower Fe/Mg clay-rich layer are believed to have formed due to precipitation-driven top down leaching process in an ancient, reducing greenhouse climate. Here we use remote sensing imagery and spectroscopy coupled with topographic data and crater chronology to explore the geological characteristics, stratigraphy and relative age of >200 weathering profiles across the southern highlands of Mars. We find that nearly all exposures show a similar, single stratigraphic relationship of Al/Si materials over Fe/Mg clays rather than multiple, interbedded mineralogical transitions. This suggests either one single climate warming event or, perhaps more likely, chemical resetting of weathering horizons during multiple events. While the time required to form a typical martian weathering profile may have been only ∼106−107 years, the profiles occur in deposits dating from the Early Noachian into the Hesperian and suggest that chemical weathering may have occurred over a large range of geologic time, with a peak around 3.7–3.8 billion years ago.

Eocene (50-55 Ma) greenhouse climate recorded in nonmarine rocks of San Diego, CA, USA

“…The absorptions at 1.41 µm are indicative of the first kaolinite overtone whereas the 1.9 µm band is from a combination tone of Al-OH bending and H-O-H stretching in H2O (Goudge et al, 2015) or from the presence of another hydrated phase. A shoulder exists at 2.16 as a doublet with the 2.20 µm band, which is caused by a combination tone of the OH stretch (Bishop et al, 2008) and is diagnostic of kaolinite (e.g., Ye and Michalski, 2022). A band near 2.39 µm could also be consistent with OH stretching and bending combinations in a Fe 3+ phyllosilicate, possibly due to the isomorphic substitution of Al or Fe for Si in the tetrahedral layers, or from cation bonding between tetrahedral and octahedral layers (Bishop et al, 2008).…”