Geochemical Trends in the Burns Formation Layered Sulfate Deposits at Meridiani Planum, Mars, and Implications for Their Origin

Abstract The layered deposits that comprise the Burns formation at Meridiani Planum have a chemical composition that closely resembles Martian basalts with addition of an oxidized sulfur component. Alternative scenarios proposed to explain this composition differ over whether the sulfur component was added by itself ( sulfur only ) or was accompanied by transport of other elements, primarily Mg, Fe, and Ca ( sulfur‐plus‐cations ). Analysis of trends in elemental abundance relative to SO 3 and TiO 2 indicates that many elements, including Si, Al, K, Na, P, Cr, and Ti, were essentially immobile during the addition of the sulfur component and throughout all subsequent diagenetic processes. Conversely, the divalent cations (Fe, Mg, Ca, Mn, and Zn) were mobilized during diagenesis. This mobilization obscures any trends in composition that were established prior to diagenesis, making it difficult to determine whether these elements were transported into the materials along with sulfur or not. Mass balance models indicate that the current compositions can plausibly be accounted for by either sulfur‐only or sulfur‐plus‐cations scenarios. However, the sulfur‐plus‐cations scenario requires that the bedrocks had a much more complex geochemical history in order to arrive at their present chemical composition, including highly variable compositions prior to diagenetic alteration and extensive mobilization of elements during diagenesis. Conversely, sulfur‐only scenarios are consistent with the evidence for immobility of many elements and require only limited mobilization of cations during diagenesis. Overall, sulfur‐only scenarios provide a much simpler and more straightforward means of accounting for the chemical composition of the Burns formation than scenarios that involve cation mobility.